The Savoia-Marchetti SM-73

[volkerboehme]

Hi all,

I decided to post the reference files of this plane here on the forum. While this plane has no relation to California, it is suggested for FsAviators training missions using GPS/Navigator simulation.

The pack includes several files, I will post each as a separate post, spread out across several posts if necessary.

Best regards,
Volker

[volkerboehme]

Although the current release relates only to the Savoia S.73 airliner it will be followed in due course by a release featuring the S.73 airliners’ twin brother the S.M.81 heavy bomber. Their development and deployment history is so closely related that this text explains the history of both types.

It would be a shame to treat the Savoia Marchetti S.73 and its twin brother the S.M.81 bomber as just another two FS aircraft. They are worth studying in some detail. There is much that can be learned. These vintage era aircraft can only be appreciated and understood if they are operated in the locations where they were based in real life and in context; so let's begin with the historical context.

As the nineteenth century progressed to the twentieth the Turkish (Ottoman) Empire was in steep decline. All the European Empires wanted to grab a slice. France seized Tunisia, Algeria and half of Morocco. Spain grabbed the other half. Italy seized Libya carrying out the first ever air combat operations with aeroplanes in the process.

Britain seized Egypt, the Sudan, Eritrea and most of Somalia, but France moved quickly to seize the only deep water port in Somalia known as Djibouti. Britain and France built the Suez Canal linking the Mediterranean to the Red Sea and the Indian Ocean. Surrounded by all this mostly British occupied territory lay the Coptic Christian nation of Ethiopia which had never been a Turkish Islamic province. Italy attempted to invade Ethiopia in 1896 but was defeated. Ethiopia was flourishing, as the demand for ivory grew and grew. By the end of 1912 the Imperial European powers had seized all of north and east Africa, save for Ethiopia. Some of these new colonies had valuable resources and some had none. Most had dreadful communications links and a hardly explored hinterland.

Then in 1914 along came the First World War. Britain was desperate to bribe Italy to declare war on the Central Powers, which were Germany, Austro-Hungary and Turkey. In 1915 Italy agreed to join the allies in return for the gift of Somaliland and Eritrea which the British regarded as more trouble to govern and subdue than they were worth. Ethiopia was suddenly surrounded by two Italian armies of occupation on its eastern and southern borders. Italy soon set about converting the small Eritrean port of Massawa into a major naval base from which the Italian Navy could blockade the southern approaches to the Suez Canal which ran through British occupied Egypt. All was fair in love and imperialist wars still to come.

The post war treaties would give most of the Turkish offshore Islands, (the Dodecanese), including the most important (Rhodes), to the Italian Empire as part of the victors’ spoils of war. Italian naval bases, and soon major air bases, were slowly but steadily surrounding the Suez Canal which lay at the heart of the British Empire.

When the Italian Fascist party under Mussolini came to power in 1923 British relations with Italy suffered further decline. However the British were keen to begin airline services to Alexandria in Egypt which in reality was the hub of the British Empire. This would require Imperial Airways to procure landing rights in Italy and would require the appeasement of Mussolini. However the British had no intention of allowing any Italian airline to serve Britain and no Italian airline was allowed to serve Britain until 1938.

Italy grudgingly allowed Imperial Airways to set up a flying boat base near Brindisi on the heel of Italy, but refused overflying rights so that the Imperial Airways service to Alexandria from London terminated in Paris where Imperial Airways passengers had to board the overnight express train right across Europe to Brindisi. This impasse stood for many years with neither side prepared to make further concessions.

Then in the mid 1930s Mussolini decided that it was time to expand the Italian Empire again. The Italian Army invaded Ethiopia again, this time from both ends whilst the Regia Aeronautica conducted a chemical warfare campaign from the skies. Italy soon controlled a large slice of the very lucrative ivory trade.

The larger the Italian Empire became the more Italy desired Imperial Air Routes the length and breadth of their growing Empire. It was what all the European Empires desired, but Italy had no way to reach its growing Empire in the Horn of Africa by air without landing rights in both Egypt and Sudan, both of which were under British military occupation.

It was finally time for some determined Imperial horse trading. Italy agreed to allow Imperial Airways to overfly Italy, but would grant no new landing rights to Britain and in return Britain would allow a single 'chosen instrument' of the Italian Government landing rights in Egypt and the Sudan. Italy remained without landing or overflying rights of the British Isles, but was granted the right to manufacture under licence certain British aero engines and superchargers for military use.

Both Imperial governments set about subsidising and procuring aircraft to fly the new services that the newly agreed landing and overflying rights permitted. Both Imperial governments would ensure that the airliners procured could be turned into combat aircraft with no trouble at all. This was standard Imperial practice. Like Britain, Italy had many barely solvent small airlines. They would now be forced by the Italian government to merge into the equivalent of Imperial Airways. Thus Ala Littoria was born as the chosen instrument to serve the Italian Empire across the sea

The aeroplane the British taxpayer procured for their chosen instrument, (Imperial Airways), to fly the new London - Marseilles - Brindisi service was the Avro Anson. From February 1936 the Anson equipped nine anti-submarine squadrons of RAF Coastal Command and Ansons were soon flying with the air forces of Australia, Ireland, Finland, Estonia, Greece and Turkey. Those supplied to the last two air forces were perfectly placed to bomb Brindisi or Rhodes and any Italian shipping or submarines.

Savoia Marchetti, like Avro, spent the early 1930s manufacturing trimoters with high wings, either under licence from Fokker, or as near pirate copies of Fokker designs. These aircraft had their wings above the fuselage because all these aircraft belonged to the Pioneer era of aviation. They were navigated solely by visual reference to the surface and low wings blocked the view of the terrain, line features and land marks being used for navigation.

On all continents the switch to low wing monoplanes was conditioned by progression from the pioneer era of aviation to the vintage or classic era in which navigation was conducted primarily by radio direction finding, whether point source over the continental United States, or wide source RDF = GPS everywhere else.

Unlike the Avro Ansons used by Imperial Airways all Savoia S.73s had multi stage flaps to further improve low speed safety and to improve visibility ahead at low IAS on the approach. This was also true of its twin brother the S.M.81 bomber transport which entered service with the Regia Aeronautica in May 1935. These had production priority over the S.73 which began to appear in Ala Littoria livery about October 1935. These had however been preceded by five S.73s for SABENA earlier in 1935, but we will get back to the Belgian S.73s later.

Thirty-six S.M.81 bombers deployed to Asmara, the capital of Eritrea, in December 1935 and immediately joined the tail end of the bombing campaign against Ethiopia.

One obstacle remained to be solved. Ala Littoria needed landing rights in French Somaliland (Djibouti) and for a while it seemed that the invasion of Ethiopia might delay this, but France like Britain wanted to profit from Italian militarism. France did not want Britain to tie up all the military production licensing deals. Landing rights in Djibouti were quickly forthcoming.

The Imperial route which Ala Littoria had been created to service was originally intended to start in Paris, proceed via Rome, and terminate in Mogadiscio, (now called Mogadishu), the capital of Italian Somaliland. A new 24 passenger, four engined airliner, the Savoia Marchetti S.74 had been ordered for the high density flagship stopping service between Paris and Rome.

The original intention was that the long Trans Mediterranean legs of the Ala Littoria Linea Imperiale south of Rome would be flown by the Cant Z.506 seaplane airliner powered by the same Wright Cyclone F52 engines as the Ala Littoria S.73s, but the Z.506 development project had run into various problems and deliveries were delayed. Consequently it was decided that the Ala Littoria S.73s that were originally intended to be based in Benghazi on the coast of Libya would instead be based initially in Mogadiscio, and would open up the southern end of the Imperial route first.

The delay to S.73 production, arising from the priority given to the S.M.81 bomber variant, allowed the larger and superior S.74 to initiate Rome - Paris services even before the S.73 began to operate air services from Mogadiscio. The prior existence of the superior four engined S.74 meant that the S.73 was never needed on the Ala Littoria service north of Rome.

I believe the original November 1935 service was;

Mogadiscio - Djibouti - Assab - Massawa - Asmara

Within weeks a branch line was opened to the newly conquered capital of Ethiopia;

Asmara - Addis Ababa

Soon afterwards the original service was extended through British occupied Sudan and Egypt to Libya;

Asmara - Khartoum - Wadi Halfar - Cairo - Benghazi

As it became clear that delays to the Cant Z.506 would be substantial it was decided that the S.73 service would fly all the way to Rome until they arrived;

Benghazi - Catania - Rome

This situation lasted for about the first five months of 1936. Around May 1936 the Cant Trimotor Seaplanes finally took over the Trans Mediterranean legs as planned, leaving the Ala Littoria S.73s operating only from Benghazi to Mogadiscio plus the long climb up the branch line to Addis Ababa.

Those who fly the S.73 where they usually fly every other aircraft in FS9 will never understand it. Flying the Cyclone engined 'flagship' version of the S.73 over the 'Linea Imperiale' attempting take off and climb out from Addis Ababa en route to Asmara is the only way to understand it, and is why it needed the best American engines available for export in 1935.

Now that brings us to a wider point which will lead into later military use of the S.73 and S.M.81, but also relates directly to wider issues of flight dynamics in MSFS. It is time to confront the random numbers and nationalistic bias published in the many different books about aircraft which are collectively only worthy of the title, 'The Boys Big Book of Wonderplanes'.

Pick up any of the many 'Boys Book of Wonderplanes' that deal with the S.73 or S.M.81 and we will almost certainly be confronted with the information that it had 550/760hp engines. These data are either randomly chosen numbers from the certification schedule or more likely they are intended to denigrate Italian aviation in the 1930s.

A Wright R-1820-F52 Cyclone is the same engine whether it powers a DC-2, an S.73 or a Cant Z.506. Read the 'Boys Book of Wonderplanes' by an American or British author about an American aeroplane that used this engine and we will be assured that it was a wonder engine of the day producing 875hp. Read about the same engine in an Italian aeroplane and suddenly it is a puny, worthless 550/760hp engine. Those Italians sure were useless at aviation. Look how they screwed up truly great American aero engines!

Well of course they didn't!

But the trouble is that most MSFS flight dynamics authors take these data at face value and replicate it in air files. Of course what is really happening is that all the authors of all the many 'Boys Book of Wonderplanes' since WW2 just plagiarise the last one all the way back to an original journalistic source written just before, or just after, WW2 when it was compulsory to denigrate Italian militarism in all its aspects. Freeware web pages just plagiarise the payware plagiarism.

Of course Italy isn't the only nation subjected to this nonsense, but the S.73 and S.M.81 provide an ideal opportunity to grasp what those apparently random quoted numbers 550/760hp in the ‘Boys Book of Wonderplanes’ are all about when the Wright R-1820-F52 Cyclone is well known to produce 875hp for take off.

Use of TOGA power was only allowed if the tank selected for take off contained military grade high lead 87 octane AVGAS. Under all other circumstances take off was conducted using only METO power. This is why there were 8 fuel tanks for 3 engines. Military grade AVGAS was only available to Ala Littoria in a very few places along the Imperial route, which were both under Regia Aeronautica control, and easy to supply by ship. The military grade fuel was carefully safeguarded in its own tanks and never adulterated with airline grade 76 Octane in the other tanks.

Once power was retarded from TOGA the flight engineer switched tanks to one containing only airline grade fuel for climb and cruise. The tanks containing military grade fuel were used as little as possible to ensure that some would remain available for subsequent take offs and approaches at the airfields down the Linea Imperiale which were not controlled by the Regia Aeronautica.

Tanks containing military grade fuel were selected when downwind to land so that go around power would be available on final if required. If it became necessary to top up a tank normally containing military grade fuel with airline grade fuel all subsequent take offs and go arounds had to be flown using only Rated power until the tanks were drained and refilled with military grade fuel at a major Italian military base.

Quoting TOGA power for American aircraft, but only Rated power and/or max cruise power for non American aircraft with the exact same engine is intended to denigrate and confuse. Replicating that denigration and confusion within MSFS just propagates misinformation by new means and helps nobody to understand anything.

Now let’s get back to November 1935 when the 3 x 875hp Savoia Marchetti S.73 first entered revenue service. Italy wasn't a backward insignificant nation struggling to get to grips with modern aviation in 1935. The Regia Aeronautica was flying more combat missions than every other air force on the planet put together. The Regia Aeronautica also had more military transport aircraft than every other air force bar that of the Soviet Union and it was the Regia Aeronautica that was pioneering the air mobile combat operations that would soon be copied everywhere.

That is the context for operating the S.73 to and from places like Addis Ababa, where no one else attempted scheduled air services in 1935. That short, tough, heavily braced landing gear may cause a lot of drag, but it is essential to the task. The efficient, but fragile flaps are essential to the task. The large, multi discipline, crew is essential to the task. Tasking the S.73 to do something trivial in FS9 in a different infrastructure, at low altitude, on long flat runways, using point source navigation aids, is pointless. It will just seem mundane and backward.

Armchair generals discuss strategy and tactics. Real generals plan logistics.

Ala Littoria did not receive the Cyclone powered S.73 until adequate supplies of military grade 87 Octane AVGAS were available in Mogadiscio, Massawa, Asmara and Benghazi. Of course military grade AVGAS was in place in Egypt, Sudan and possibly French Somaliland for use by the relevant Imperial Air Force, but Ala Littoria could not buy military grade fuel at British and French run military airfields, even though they had landing rights on those airfields.

Thus there were places that Ala Littoria could load only airline grade 76 octane fuel, which potentially precluded use of TOGA power.

From the invention of the poorly named Octane rating system by Ricardo in the early twenties, to 1945 and beyond, what differentiated nations was their ability to source military grade AVGAS and ship it to all the places they might need to use it. Only a few superpowers had an oil industry which could create it and only a few favoured client nations were allowed to purchase it from them.

Belgium was a minor Imperial Power. It had few bargaining chips at the Imperial table. The Belgian Empire had no access to military grade AVGAS. Consequently SABENA had no such access and could not order first rate American engines to power its aircraft. It could only order second rate engines that would run on 76 Octane airline grade AVGAS which could be bought on the open market. SABENA could order and deploy the S.73 before Ala Littoria because SABENA did not need to wait for military grade AVGAS to be in place anywhere. Belgium wasn’t able to buy any anywhere.

SABENA chose the Gnome Rhone Mistral engine which required only 76 Octane airline grade fuel to develop its lesser TOGA power.

But aviation journalism and publishing was then, and is now, dominated by authors whose first language is English, and whose publishers have the narrow minded nationalistic prejudices to match. They are just as biased against French developed technology, or Belgian deployed technology, as they are against Italian deployed technology. Consequently almost every copy of the many different 'Boys Book of Wonderplanes' will misinform us that the Gnome Rhone Mistral installed in SABENA S.73s was a 600hp engine. This is once again nothing more than anglophone nationalistic bias. The Gnome et Rhone GR9Kfr Mistral installed in the SABENA S.73s was TOGA rated at 770hp at 720 metres.

600hp is only the Rated power of this engine. Once again a European continental product is deliberately denigrated in the many different English language 'Boys Book of Wonderplanes' to make British or American engines seem vastly superior by comparison. From the perspective of MSFS fight dynamics development the many different 'Boys Book of Wonderplanes' must not be trusted and of course their deliberately false content is plagiarised all over the internet, often translated into continental European languages, making us less suspicious of nationalistic bias which is nevertheless present in large measure.

The Belgian Empire lay in the Congo Basin of central Africa thousands of miles south of Belgium. The Belgian Congo which the SABENA S.73s were procured to serve then included the three modern African nations of Zaire, Rwanda and Burundi.

However when SABENA took delivery of their first five S.73s from February 1935 they were at first judged too good to be used on the Belgian Imperial route. They were therefore initially used to displace less capable Fokker F.VII/3m Trimotors that were immediately redeployed to inaugurate the Belgian Imperial route, also from February 1935.

So for most of 1935 the routes being flown by the first five SABENA 3 x 770hp Mistral powered S.73s were;

Brussels - (Lille) - Ostende - London

Brussels - (Lille) - Paris

Brussels - Hamburg - Copenhagen - Malmo

OO-AGL was the second SABENA S.73 and it flew all three routes during 1935. Most of these stages were compatible with carrying a full load of 18 passengers

SABENA were delighted with the S.73 and sought a licence to produce it in Belgium which was duly granted by Savoia Marchetti. SABCA delivered seven more to SABENA before the end of 1937 but all of these were powered by the much more powerful GR14K Mistral Major engine. These had only eight or ten seats and were used on the Imperial route to the Congo from October 1936.

The flying time from Brussels to Elizabethville (now called Lubumbashi) fell to 44 hours when the S.73 replaced the Fokkers. Of course there were still three night stops in hotels along the way and four days of hard flying 11 hours per day instead of six such gruelling days and five night stops in a Fokker Trimotor.

After the S.73 took over the Imperial route to Elizabethville the Fokkers which had been flying it were based in Stanleyville (now called Kisangani) to provide extensive Imperial regional services, but especially the seven stop route right across the Congo basin to Leopoldville, (now called Kinshasa), in the far west. Brazzaville the capital of the French Congo lay just across the river on the other bank. But for colonialism and the aftermath of colonialism Kinshasa and Brazzaville would be a single city with a major river running through it. They are still in different countries.

The original five S.73s including OO-AGL seem to have had the number of seats aboard reduced to ten and later joined the Belgian Congo service as demand increased, but continued to fly the European services above as well.

Of course Belgium needed overflying and landing rights across the French Empire to reach the Belgian Congo, but this was no problem since Air France’s colonial subsidiary Air Afrique required overflying and landing rights in the Belgian Congo to reach French Madagascar. Belgium had the necessary bargaining chips at the Imperial table.

As far as I can tell the Belgian Imperial S.73 service routed;

Brussels - Marseilles - Oran - Bechar - Reggane - Gao - Niamey - Fort Lamy - Bangui - Bumba - Stanleyville - Kigali - Bujumbura - Elizabethville.

Nowadays Stanleyville is called Kisangani and Elizabethville is called Lubumbashi. On the entire Belgian Imperial route only Elizabethville (Lubumbashi) lies within the modern state of Zaire. Kigali has become the capital of Rwanda and Bujumbura has become the capital of Burundi. All points prior to Kigali lay within the French Empire and none have changed their names after independence from France.

By this time Air France already had a subsidiary holding company known as Air Afrique which managed a variety of French colonial airlines operating in Africa. The pre existing Air Afrique interline service, (which was effectively code and ticket sharing with SABENA), obviously started in Paris and then continued beyond Elizabethville, via a further five stops, through the British and Portuguese Empires, to Tananarive the capital of French Madagascar. This route required eight consecutive days of long hard flying.

It was Air Afrique’s subsidiary Compagnie Transafricain d’Aviation which inaugurated the first Trans Saharan service to the Congo River basin in September 1934 using Bloch 120 Trimotors. I believe they routed;

Paris - Marseilles - Algiers - Bou Saada - Ghardaia - Tessalit - Gao - Niamey - Fort Lamy - Bangui - Bumba - Stanleyville - Kigali - Bujumbura - Elizabethville and onward through Ndola in Northern Rhodesia (now called Zambia) and four further stops to Tananarive.

Of course it suited the French to force SABENA to route via Oran where there were fewer passengers than in Algiers and of course the S.73 service from Brussels to Paris fed the alternative and shorter Air Afrique service to the Belgian Empire. Imperialism was a dirty game.

It is not possible to understand the nature of 1930s airline flying, or the Savoia Marchetti S.73 in particular, without simulating operations to and from places like Elizabethville (now Lubumbashi) in real weather, (real temperatures), using realistic flight dynamics and realistic RDF = GPS radio navigation procedures.

Many airliners and military aircraft designed and produced in Europe were not in the least intended for use in Europe. They were designed to operate in the hinterland of the European Empires which have become ‘the third world’. They were bush planes intended to operate from some of the worst, hottest, highest, roughest, bush country on the planet. The S.73 was no exception.

SABENA could not participate on the collaborative route to the Congo basin until they increased capacity by taking delivery of the S.73 from February 1935. Once the S.73 took over the Imperial Route from October 1936 it was obvious that it was very superior to the ‘competing’ Bloch 120. Air Afrique operated the French Imperial service to Madagascar, through the Belgian Congo, in its own name and livery from September 1937 using the Bloch 120 until France and Belgium were both invaded by Germany in May 1940 suddenly terminating all such services.

Which brings us neatly to military usage of the S.73, and its twin brother the S.M.81 bomber, all of which were subsequently converted to military transports, which then hardly differed from the original S.73.

Thus far I have gone out of my way to demonstrate how English language sources, whether first published in Britain or the United States, deliberately diminish the status of Italian Aviation. We must now come to terms with the opposite situation. The Italian fascist state censored the Italian media and required them to convey various ideas about the status of Italian aviation to exaggerate the extent to which Italian aviation relied only upon Italian products. That propaganda is also widely repeated within the many different ‘Boys Book of Wonderplanes’ and then plagiarised all over the web.

This part of our story must also begin before the First World War and then move to Bristol in England, and then to Paris, before returning to Italy.

The Radial engine was invented by the Italian engineer Anzani before the First World War. It was soon eclipsed by the literally revolutionary Rotary engine invented by the French Seguin brothers. They set up a company called Gnome to manufacture their rotary engines which were soon widely copied via licences or just piracy.

One competitor who copied the Seguin’s Rotary engine was Le Rhone. Anzani responded by inventing the two row radial, but he never really solved the problems of cooling the rear row of cylinders and he soon discontinued production of two row radials. By 1918 the British engineer Bentley had created a rotary engine that produced 242hp continuously at sea level. The gyroscopic forces of these revolving engines were now so great, and so difficult to control, that no more powerful rotary engine could even be contemplated.

The Holy Grail pursued by the international aero engine industry was the *reliable* two row radial, but first the world needed a better single row radial to replace the reliable single row pre WW1 Anzani.

This was soon invented by the British engineer Fedden who led the new aero engine design team, which included 31 other engineers, at Bristol. He called his new 9 cylinder radial the Jupiter. It was soon being produced under licence in seventeen nations and powered over 260 different types of aircraft in the 1920s and 1930s.

This was an interesting development since Bristol had managed to design only one good aeroplane, the Bristol Fighter, and had no reputation or prior experience of aero engine development and manufacture at all! Over in Paris Gnome and Le Rhone had plenty of both but no product to manufacture. The first step was for Gnome to make a takeover bid for Le Rhone creating Gnome et Rhone and then for Gnome et Rhone to enter into a secretive ‘arrangement’ with Bristol.

That 'arrangement' would be one of the most controversial in aviation history. Much of it was always secret. Bristol regarded it as a technology transfer and licensing deal whilst Gnome et Rhone regarded it as a Euro collaborative project akin to the modern Airbus concern in which they would have equal rights going forward. Three Bristol engineers moved to Gnome et Rhone in Paris where parallel development of the Jupiter soon proceeded.

Meanwhile Fedden and his team in Bristol created two new engines that used shortened Jupiter cylinders. The first with only seven shortened cylinders for use in commercial aircraft they called the Titan. The one with nine shortened cylinders for use in fighters they called the Mercury. The shortened cylinders of the Mercury reduced its frontal area and profile drag, but it had to run at higher rpm, or employ a more powerful supercharger, to match the power of the Jupiter.

Further development of the original Jupiter engine slowly became neglected with all new improvements being incorporated into the Mercury. These were then suddenly incorporated into the Jupiter, at which point it became the Pegasus. All four engines in this family had many parts and maintenance procedures in common. Over in Paris the engineers from Bristol, Gnome, and Le Rhone put their heads together and soon began to make many minor improvements to this Jupiter family without altering the basic design.

Also in France the Farman brothers now invented and patented a superior airscrew reduction gear mechanism. Gnome et Rhone licensed it from Farman, but at first Bristol did not.

Based on their version of the ‘arrangement’ that Bristol had entered into Gnome et Rhone now began to manufacture the slightly modified Mercury with Farman patent airscrew drive as the Gnome et Rhone GR9 Mistral and ceased paying royalties to Bristol even though over 90% of the parts were manufactured from Bristol drawings. Gnome et Rhone then began manufacture of the 7 cylinder Bristol Titan with the same modifications applied using the brand name GR7 Titan, again claiming that it was a different engine and refusing to pay royalties to Bristol.

However the real goal in both Bristol and Paris was still the Holy Grail, which was a reliable two row radial. In 1928 the three teams of engineers in Paris cracked it and what might logically have been called the Twin Titan was actually branded the GR14 Mistral Major. Gnome et Rhone now claimed that this engine was exclusively theirs and that Bristol had no right to build it. This caused the final breakdown in the ‘arrangement’. The three engineers from Bristol returned to Bristol where in due course they all joined the board and helped Bristol to bring assorted law suits against Gnome et Rhone for hardware piracy. However Bristol failed to put the world beating Mistral Major into production in England, suggesting that they gave some credence to the claims made by Gnome et Rhone concerning the nature of the secret ‘arrangement’.

After studying the Mistral Major for four years Pratt & Whitney would create a competing two row 14 cylinder radial that did not infringe either Bristol or Gnome et Rhone patents. The Twin Wasp dates from 1932, but in some ways it remained inferior to the 9 cylinder Wright Cyclone until the end of the 1930s.

It is impossible to understand the S.73 airliner and its twin brother the S.M.81 bomber transport without first understanding the above and I will now explain why.

The S.73 and the S.M.81 shared a single prototype which the many ‘Boys Book of Wonderplanes’ will inform us was powered by Piaggio P.X Stella engines. In a sense this is true, but the information that was withheld by the Italian censor is that the Piaggio P.X is nothing more than the Gnome Rhone GR9 Mistral manufactured under licence.

That common prototype, and the next four aircraft from the S.73/S.M.81 production line, then pass to SABENA. From then onwards SABENA sourced more powerful replacement GR9Kfr Mistral engines and spares from Gnome et Rhone in Paris.

You will recall that in early 1935 SABENA wanted Mistral engines because they were designed to run on airline grade 76 Octane AVGAS. Now it is time to grasp that in early 1935 the Regia Aeronautica had exactly the same requirement. Italy had not yet procured adequate stocks of military grade AVGAS from the few superpowers which could sell it to them, or withhold it. In addition Italy was at war in Ethiopia and needed to base modern heavy bombers inland from the coast of Africa in places where it was not possible to supply both adequate stocks of military grade fuel and airline grade fuel.

The S.M.81 bombers destined for service in Italian East Africa would all be powered by Mistral/Mercury engines, built by Piaggio, requiring only airline grade AVGAS. We must now think of those initial production S.M.81s as the S.M.81-I.

When the first S.M.81-I rolled off the Savoia production line Savoia had not yet begun licensed production of the Hamilton Standard 'Hydromatic' two pitch airscrew. When they did it would of course be refered to as a Savoia two pitch airscrew. The Piaggio P.X Stella (actually Mistral) engines in the earliest S.M.81-Is would have to drive four blade fixed pitch screws. The engine that powered them would however benefit from a much more powerful Bristol Mercury supercharger than the Gnome Rhone Mistral supercharger fitted to the more powerful GR9Kfr in the SABENA S.73s.

The TOGA rating of the Piaggio P.X/R.C.35 Stella = Mistral with a late model Mercury supercharger was 650hp at 3500 metres. Italian built engines are easy to decode, R = airscrew reduction gear, C = Compressed and 35 = 3500 metres rated altitude. This Piaggio version of the Mistral/Mercury engine was highly optimised for use from the Eritrean highlands, over the Ethiopian highlands and it would only ever be based in Eritrea and Ethiopia.

Apart from Asmara and Addis Ababa the Piaggio engined S.M.81s were also based at;

Macalle (now called Mekele)

Gura (now called Gura’e), but we should use Axum in FS9.

Assab

Scenele (now called Chinile) but we must use Dire Dawa in FS9.

Once Savoia began series manufacture of the Hamilton Standard two pitch screw it was fitted to the Piaggio manufactured Mistral to create what we should think of as the S.M.81-II. Maybe the first thirty or forty S.M.81s had four blade fixed pitch screws and were S.M.81-Is. The rest were S.M.81-IIs with three blade variable pitch (v/p) screws. Both types served only at the East African bases indicated above.

Now remember that that there was no point manufacturing S.73s with Cyclone engines until the Italian Empire had adequate stocks of military grade 87 Octane, (supplied one way or another by the Soviet Union), all round the coast of its African colonies. Once that was true, and adequate supplies of military grade AVGAS were also present at a few locations in Italy, the Regia Aeronautica could order into production a variety of S.M.81 with superior engines that used 87 Octane AVGAS to generate TOGA power. We should call this the S.M.81-III.

So it came to pass that Alfa Romeo now obtained a licence from Bristol to build the Bristol Pegasus under licence as the Alfa Romeo 125 and 126. These Alfa Romeo engines had many of their parts in common with the Piaggio P.X because both were varieties of Bristol Jupiter. The only significant difference was in the length of the cylinders and the manifold pressure to which they could be boosted by a supercharger. High compression requires high octane AVGAS however the high compression arises.

The Pegasus engined S.M.81-IIIs all had Savoia two pitch screws. Unusually they were intended for use in Europe not Africa, but as we shall see the S.M.81-III soon wound up flying combat missions from Africa against Europe anyway.

The licence obtained from Bristol, (in return for Imperial Airways gaining the right to overfly Italy), included the right for Alfa Romeo to produce the very latest two speed Bristol Mercury supercharger. This was very advanced technology compared to the Gnome Rhone superchargers being built under licence by Piaggio intended for use in military aircraft using airline grade 76 Octane fuel, or even the General Electric superchargers on the Cyclone engines being imported from the United States for use in the Cants and Savoias of Ala Littoria which required military grade fuel.

In England Bristol were not yet using powerful Mercury two speed superchargers with Pegasus engines. It was this combination pioneered by Alfa Romeo in 1936 for the S.M.81-III that would cause Bristol to eventually do the same, but not until 1938. The Anglophone authors of the many different examples of the ‘Boys Book of Wonderplanes’, will quickly misinform us that the Italians could screw up British engines too. They will often report the Alfa 126/R.C.10 as a 680hp engine!

The Alfa Romeo 126/R.C.10 was actually TOGA rated 850hp and actually for odd reasons at 1150 metres rather than 1000.

Of course by now there was a better engine even than the Bristol Pegasus. The Holy Grail of aero engine design had been discovered in Paris in the form of the GR14 Mistral Major, yet another variety of the same Bristol Jupiter engine.

So naturally it came to pass that Issota Fraschini sought and obtained a licence from Gnome et Rhone to manufacture the GR14K Mistral Major in Italy to power what we should think of as the S.M.81-IV. This version was intended for use only from Tripoli, Benghazi, and El Adem, (just south of Tobruk), all in Libya.

El Adem is now called Gamel Abd El Nasser (by Microsoft).

The S.M.81-IV was far more powerful than the other varieties of S.73 and S.M.81. This allowed it to fly at higher weights, carry more fuel, and bomb more distant targets with the same bomb load. It could also sustain longer maritime patrols. S.M.81-IVs, originally with engines purchased from Gnome et Rhone deployed to their combat bases in Libya from December 1936 onwards. As Libya was overrun by the British Army in 1943 these aircraft retreated to Lampedusa, then Pantalleria, and finally to Palermo and Catania. None seem to have survived the allied invasion of Sicily.

Of course the Anglophone ‘Boys Book of Wonderplanes’ will quickly misinform us that the clueless Italians could screw up French engines too. When the magnificent GR14K, the Holy Grail of aero engines, was deployed by Italy it is often reported as a 650hp engine.

In reality the Isotta Fraschini 140/R.C.40 Mistral Major was TOGA rated at 860hp!

It had many parts in common with the Piaggio and the Alfa Romeo and like them it drove a Savoia (Hamilton Standard) two pitch screw, via a Farman reduction gear box. It would have been utterly stupid of the Regia Aeronautica to deploy four varieties of S.M.81s with three entirely different engines at the same time, and so the Anglophone ‘Boys Book of Wonderplanes’ reports that they did just that. Of course they didn’t. Just as the Bristol Mercury engines of the Blenheim are closely related to the Bristol Pegasus engines of the Hampden and Wellington, so the Piaggio, Alfa Romeo and Issotta Fraschini engines are closely related, have common maintenance procedures, and many parts in common.

Of course both the British Government and the French Government cried crocodile tears over the plight of the poor Ethiopians, and not long after more crocodile tears over the plight of the poor Spanish, but they signed the end user certificates for the licensing agreements for military use eagerly enough and added the royalties paid by the fascists to the Imperial National Product of Britain and France.

Imperialism was a dirty game.

... Continued in next post ...

[volkerboehme]

In 1936 the Spanish Fascist Party under the leadership of General Franco lost the Spanish general election. They immediately staged a coup, but at first they were weak because most of the Spanish Army was in Africa imposing the will of Spain upon its colonies. Once the Spanish Civil War was underway Franco was soon receiving covert and overt aid from Mussolini. Similar aid to rid Europe of the ‘Asiatic Bolshevik Insurgency’ would later be provided by Hitler who had become Chancellor of Germany in 1933.

In July 1936 a squadron of Regia Aeronautica S.M.81-III bombers with Alfa Romeo engines set off from their base in Cagliari for Nador in Spanish Morocco where most of the Spanish Army was based. Three crashed or made forced landings en route. On arrival the squadron commander realised that Spain had no access to military grade 87 Octane AVGAS. It was a bad start, but for two million pounds sterling, (equivalent to eight million 1936 US dollars), paid in cash, Franco had acquired nine examples of the only heavy bomber in the world produced outside the Soviet Union. What’s more it could operate from African bush strips.

All bar half a dozen S.M.81-IIs supplied as transports, used during the Spanish Civil War, required military grade 87 octane fuel. Mussolini was consequently ‘obliged’ to supply limited quantities of military grade AVGAS to Franco. The first Italian military AVGAS tanker didn’t dock in Spanish Morocco until August and combat operations could not begin until it did.

Meanwhile the Italian aircrew who had managed to reach Spanish Morocco resigned from the Regia Aeronautica and joined the Spanish Foreign Legion, which now operated the nine surviving S.M.81s. Their first task was to escort the Armada which carried the Spanish Army from Africa to Spain, but soon after they were bombing Spain from their new base in Africa. Italy suddenly found itself with many new logistic problems in the Spanish Empire. Of course in reality this was the beginning of the Second World War, but English speaking authors, politicians and historians, impose different nationalistic definitions to match the parochial experience of their own linguistic population.

After also operating from Melilla and Tetouan in Spanish Morocco the now Spanish S.81s moved to Seville and eventually to airfields nearer the front line, but Seville remained the maintenance base. Once losses up on the front line airfields mounted Spnaish S.M.81s were progressively based in Palma (Majorca) bombing the Spanish east coast cities that were under democratic government control.

By mid November 1936 Soviet fighter opposition over Spain forced the S.M.81s to abandon daylight attacks for a while and switch to night bombing. At this point the Spanish decided to call the S.M.81 ‘the Bat’ which in Spanish is ‘Pipistrello’. This Spanish name was later also adopted by Italian aircrew, but was never official, and it isn’t even Italian.

About sixty five S.M.81-IIIs flew combat missions with the Spanish Nationalist Air Forces during the civil war, but by 1940 all forty survivors had been converted to transports. By then twenty were based in Vilanubla maintaining military communications across mainland Spain. The other twenty were based in Palma (Majorca), maintaining communication between the Balearic Islands and between Palma and Madrid via all the relevant mainland east coast airfields all of which were in fascist hands after the civil war.

In August 1937 Franco had created a new fascist airline which he called Iberia. At first he welcomed investment and technical help from both Lufthansa and Ala Littoria. Soon two ex Ala Littoria S.73s were among the earliest equipment of Iberia. I have no certain knowledge of the routes which they flew for Iberia, but I believe they were based in Seville and since they were highly optimised for operation from African bush strips it seems likely that they served Spanish Africa, though other aircraft including ex Lufthansa Junkers Ju52/3ms would also have flown African services for Iberia.

I believe Iberia routed to Rabat from Seville and then onward to Casablanca, Marrakech, and Sidi Ifni. Then onwards again to the Spanish Canary Islands, (especially Tenerife and Gran Canaria), which lay west of Sidi Ifni, or further down the coast into the Spanish Sahara terminating at Villa Cisneros, (now called Dakhla).

Avio Linee Italiane, a Fiat subsidiary, and the only Italian airline to survive the creation of Ala Littoria as the 'chosen instrument' of the state, purchased powerful Alfa Romeo engined S.73s, including I-SAUL, for use on its network in 1937. Their trunk route appears to have been Turin - Milan - Venice, though they had other internal services and a Milan - Munich - Berlin international service. Milan - Paris was added after delivery of the S.73s. However it fell to Ala Littoria to serve Eastern Europe. Consequently Ala Littoria now acquired half a dozen 'economy models' of the S.73 with low powered Piaggio engines to fly the two routes Rome - Venice - Trieste - Klagenfurt - Bratislava - Prague and Rome - Venice - Trieste - Belgrade - Bucharest.

Despite its huge size, from late 1940, the S.M.81 was adopted by the Regia Aeronautica as an instrument rating trainer and was used to teach IFR procedures that were a new concept in the Regia Aeronautica. Very oddly the Scuola Volo Senza Visibilita was in the Alps at Porta Littoria (now called La Thuile, but Turin must be used within FS9). Instrument training in such difficult terrain and weather was certainly an ‘interesting’ choice. These S.M.81 trainers had no armament and closely resembled the S.73.

During 1936-37 Piaggio engined S.M.81-IIs undertook pre-deployment training from Bresso, Vicenza, Naples, Bologna, Catania and Cagliari before moving to their combat bases in Italian East Africa where the main servicing facility for Piaggio engines was located, (at Harar Medar). All bar a handful of these Piaggio engined S.M.81s were lost as British Dominion forces overran Italian East Africa in 1940-41.

I believe several squadrons of S.M.81s, with different engines, formed at Vicenza in turn before deploying to Africa. This may have been true of the other locations above. Oddly it seems that the only S.M.81 Stormo fully dedicated to maritime patrol and anti submarine warfare was based in or near Bologna for an extended period before deploying to Tirana and Valona (now called Vlora) in Albania.

Nevertheless understanding this complicated family of Savoia aircraft requires us to grasp that they were African bush planes of the 1930s, not European airliners and heavy bombers of the 1940s. They should not be compared with the aircraft of the 1940s, or aircraft designed to operate from nice cool, long, flat, grass airports, let alone airports with hard runways. They must be understood within the context of their real timeline and the hostile African highland and jungle bush environment they were designed to match.

During the 1930s a heavy bomber was defined as one that could lift a 2,000Kg bomb load (4400lbs). The first such bomber was the Tupolev TB-3 deployed by the Soviet Union from mid 1932.

The second nation to deploy heavy bombers was Italy who deployed the Savoia S.M.81 in the spring of 1935. By December 1935 the S.M.81-I and S.M.81-II were flying intensive combat operations over some of the worst terrain imaginable from some of the worst airfields imaginable. A few weeks after the Regia Aeronautica deployed the S.M.81-I the RAF deployed the truly awful Fairey Hendon I monoplane night bomber. The S.M.81 was 50% faster than the Hendon and carried almost three times the bomb load. The awful Hendon was barely a medium bomber.

The third nation to deploy heavy bombers was Spain, but of course these were S.M.81s transferred from the Regia Aeronautica from 1936 onwards. The fourth nation to deploy heavy bombers was France who deployed the Farman 222 in the Spring of 1937. These were augmented by the LeO 451 from the end of 1938.

The fifth nation to deploy heavy bombers was Germany, but not until February 1938. The maximum bombload of the Heinkel He 111E-1 was also 2,000Kg. It was the first Heinkel able to carry a heavy bomb load. The sixth nation to deploy heavy bombers was Britain who did not manage to deploy the Wellington I (max bomb load 4500lbs) until October 1938. By then the S.M.81 heavy bombers of the Regia Aeronautica were being augmented by the superior Cant Z.1007 Alcione.

Only those six nations possessed heavy bombers before the 1940s.

The seventh nation to deploy heavy bombers was the United States which did not deploy its first heavy bomber, the B-17B, until April 1940, five years behind Italy. Its maximum bomb load was 4800lbs, just 400lbs more than the S.M.81. By then Italy had deployed almost six hundred heavy bombers and they had flown many thousands of combat sorties. It is pointless to compare the S.M.81 to aircraft of a different decade. Aircraft from later decades are always superior.

When Germany invaded Belgium in May 1940 seven SABENA S.73 airliners made their way to London where they were quickly requisitioned and operated by 24 Sqn and 271 Sqn RAF, alongside their normal equipment, probably both based at Hendon in north London during May and June 1940. Hendon now houses the RAF museum, but is no longer an airfield. It can be replicated in FS9 using nearby Elstree (EGTR) which is about the right size for a 1940 RAF transport base. OO-AGL passed to 271 Sqn.

At first the RAF used their Mistral powered S.73s to supply the RAF squadrons supporting the British Expeditionary Force in Northern France and Belgium with operations into all relevant continental airfields, but following the collapse of French morale on their southern flank the BEF were soon retreating to Dunkerque.

The RAF S.73s now flew round the clock evacuating the RAF personnel and equipment they had just supplied. OO-AGS was shot down over Belgium whilst serving with 271 Sqn RAF in June 1940. I believe the six survivors then all passed to 271 Sqn and moved to that squadron’s main base which was Doncaster.

From there 271 Sqn provided the airlift capability for RAF Fighter Command during station relocation which was a common event just before the Battle of Britain which was about to begin. However the probability that RAF operated S.73s would be lost to ‘friendly fire’ once the Battle of Britain got underway was so great that they were placed in reserve and in practice were never needed again. 271 Sqn’s main equipment throughout this period had been the Handley Page Sparrow.

Italy bided its time until French morale collapsed and then declared war on both Britain and France in June 1940. Imperialism was a dirty game. To cut a very long and very interesting story short Britain responded by moving forces into Kenya and then moving north invaded Italian Somaliland, Ethiopia and Eritrea in turn. Regia Aeronautica bombing attacks against Egypt from Eritrea, Libya and Rhodes began. This obviously terminated the Ala Littoria ‘Linea Imperiale’.

A little over a month after the RAF had requisitioned seven SABENA S.73s the Regia Aeronautica requisitioned thirteen belonging to Ala Littoria. I-ASTI is likely to have been one of them. Serving with 605 and 606 Sqns of the Regia Aeronautica these now supplied the Italian Army in Libya via Benghazi and later Tripoli. Italian forces in Eritrea, Ethiopia and Somalia could no longer be reached by air on a regular basis.

By the summer of 1941 more and more S.M.81 bombers were being converted to transports and joining the S.73s in air supply duties. Some of the S.73s and a larger number of S.M.81s were used in paratroop training. Special forces combat operations were conducted by S.M.81 transports based in Tripoli. Others became glider tugs and were used to train glider crews in Italy, probably at Viterbo.

The S.M.81 bomber-transport always had a troop transport capability, but cabin space was occupied by defensive gun positions limiting the transport capability in the delivery configuration. As the primary role of the S.M.81 progressed from bombing to air mobile warfare the defensive armament was removed step by step, to free up valuable cabin space, until the S.M.81 looked more and more like its twin brother the S.73 airliner.

The two S.M.81s allocated to Mussolini and the King of Italy at the end of 1936 were also based near Rome, though the wartime airfield no longer exists, so we should probably use Viterbo in FS9 to simulate S.M.81 armed VIP transport missions.

By late 1942 almost all of the surviving S.M.81s had been converted to military transports, many disarmed and quite difficult to tell apart from a true S.73 airliner. S.73s and S.M.81s now served alongside one another in the same transport units. Disarmed S.M.81 ambulances increasingly evacuated Italian wounded from Libya to Lecce and as the Italian Army retreated further and further westwards, eventually from Tunis to Palermo or Viterbo.

During 1942 the 18 Stormi Transporti, based in Libya, flew 4,105 sorties totalling 10,860 flying hours carrying 28,613 troops and over two thousand tons of cargo. A transport Stormi typically had 24 aircraft so that’s roughly one 2.66 hour sortie every other day per aircraft. We can see that the standard passenger load was still only seven or eight troops. By 1942 military grade AVGAS was in short supply in Libya.

From March 1941 the Italian Army became more and more reliant on the Deutsche Afrika Korps and the Luftwaffe for offensive operations in North Africa. Italy gradually owed more and more favours to Germany. So in the summer of 1941 Italian forces deployed to the Eastern Front to fight the Soviet Army.

The Regia Aeronautica deployed S.M.81s to Bucharest and Stalino, (now called Donets’k), in January 1942. A few of the requisitioned Ala Littoria S.73s and S.M.81 transports now maintained a military air bridge;

Lecce - Tirana - Bucharest - Odessa - Donets’k

These aircraft may have been based in Bucharest which as we shall see later was also the southern terminus of the Lufthansa S.73 service from Prague at that time.

In February 1943 one of the two squadrons at Stalino fell back to Odessa and the other returned to Lecce. Odessa was abandoned in April 1943. Most surviving S.M.81s now assembled in Palermo, first to evacuate the Italian Army from Tunis and then for the airlift to Lampedusa and Pantellaria. These were the last intensive air mobile operations by the S.M.81 in Regia Aeronautica service.

By the time that Italy surrendered to the allies in September 1943 only a handful of either type were in good enough condition to later serve with the allied Italian co-belligerent air force. As far as I can tell they were still based mostly at Lecce. One S.M.81 transport was captured intact at Benghazi and then served with 112 Sqn RAF while they were based at Benghazi in 1942-1943.

On the Mediterranean front apart from Lecce the main Regia Aeronautica S.M.81 *bomber* bases in Europe had been Bologna, Viterbo, Rhodes, (in the Dodecanese Islands), plus Tirana and Valona, (now called Vlora), both of which are in Albania. S.M.81s also flew high endurance maritime patrol and anti submarine patrol missions 1936-1942. Until mid 1943 less than a quarter of Regia Aeronautica S.M.81 bomber or transport aircraft were based in Italy and by then only remnants remained.

Regia Aeronautica S.M.81s in northern Italy, all transports not bombers by then, were seized by the Luftwaffe when Italy surrendered and thereafter operated in Luftwaffe markings with the Italian flag under the cockpit. They were based at Bergamo. In January 1944 these moved briefly to Germany, but were then used to supply the retreating German armies. I believe they were mostly based in Warsaw, Prague and Vienna in the early stages of the retreat before finally moving to Goslar south east of Hannover. We should use Drutte (EDVS) instead in FS9 to represent a late WW2 Luftwaffe transport base. These must have been the last S.M.81s to fly combat missions.

When simulating the operation of these transport aircraft in FS9 remember that they are STOL bush planes. In Europe they belong on airfields the size of Elstree and Drutte. Better still use them from modern high altitude African bush strips to understand their aerodynamics and their power dynamics. Some SABENA S.73s were captured by Vichy French forces in the French African colonies in 1940, but oddly they seem to have made no use of them, perhaps they were handed over to Italy.

Italy had attempted to sell the S.M.81 to the air forces of Austria, China, Germany, Uruguay and Venezuela during the 1930s, but apart from Germany none had any hope of acquiring military grade AVGAS from the then oil superpowers, (Britain, France, Holland, USA, USSR).

They could only have purchased the Mistral powered S.M.81-II and although many nations desired heavy bomber capability the S.M.81-II was too lacking in performance compared to the latest airliners with American engines, such as I-ASTI, to attract any export orders. Germany decided to persevere with development of the He 111 until it could match the capability of the S.M.81, three years later.

We should remember at this point that the Ju52/3m was only a medium bomber with half the maximum bomb load of the S.M.81 and with pathetically weak defences. Although the S.M.79 medium bomber had an earlier designation it was in fact a later aircraft, also able to carry only half the bomb load of the S.M.81. The S.M.81 underwent torpedo bomber trials but the smaller S.M.79 was superior in that role and so operational S.M.81s were never converted to carry torpedoes.

The bombs were loaded vertically into the bomb bay, nose down. They tumbled badly after release. All of the bomb load was internal, which was particularly impressive in the mid 1930s. The S.M.81 could actually achieve the design cruise velocities in the supplied handling notes, with a full bomb load, provided the turrets were retracted. Heavy bombers that carried half, or all, of their bombs externally could not achieve their claimed cruising velocities in practice.

Any S.M.81 could carry 4 x 500Kg bombs, but use of bombs larger than 100Kg seems to have been rare. In practice the bomb bay had only sixteen tail lugs for 100Kg bombs. However when attacking ‘built environment’ targets including dockside warehouses or hangars the balance of 2000Kg could be loaded as incendiaries and small anti personnel bombs, potentially with clockwork delay fuses to disrupt fire fighting. The S.M.81 could not deploy sea mines. This was a deficiency by later standards, but in 1935 no bomber could deploy sea mines.

The defensive armament was truly impressive. Both turrets really were hydraulic powered turrets, not just gun cupolas trained slowly and with difficulty by the muscles of the gunner. Both turrets had excellent fields of fire compared to the poor gun mountings in bombers like the Heinkel 111 and both had twin guns. The S.M.81 could also carry a single WW1 surplus Lewis gun on a Scarf Ring between the beam hatches. Some early examples may have had two Lewis guns on pintle mounts. The retractable ventral turret design was hardly bettered in the 1940s and when extended it created much less drag than equivalent installations of the 1930s.

The defensive positions were only extended and manned if a Savoia came under fighter attack. Four hydraulic fast training machine guns with an almost uninterrupted field of fire remained an impressive defensive capability for many years after 1935 and certainly put much later German bombers to shame. Later the twin 7.7mm guns in the original dorsal turret were sometimes replaced by a single 12.7mm in a new Lancia turret more than doubling the firepower of the dorsal turret.

During 1937 one other airline had purchased the S.73. That was CSA (Ceskoslovenska Statni Aerolinie) who operated five S.73s from 1937 to about 1943. Just as the Bristol Pegasus was built under licence in Italy by Alfa Romeo so it was built under licence in Czechoslovakia by Walter. However since Czeckoslovakia like Belgium had no access to military grade AVGAS Walter manufactured the Pegasus II.M2 which ran on airline grade fuel. It was TOGA rated 620hp at 600 metres.

Thus the CSA S.73s were the least powerful variety of this interesting family of airliners and military transports by a large margin. However they did not need to cope with the hot and high bush strips of Africa. Rated power of the Walter Pegasus engines was 580hp, only 20hp less than the GR9Kfr Mistral used by SABENA and the climb and cruise ratings would each have been down by about 20hp (=< 5%) compared to the SABENA aircraft.

Whilst these things do not really convert in a truly linear fashion simply subtracting 0.33 Ata from each Mistral power setting (bar TOGA) specified in the supplied SABENA handling notes will replicate operation of the Pegasus II.M2 by CSA in Eastern Europe well enough. When simulating CSA procedures climb should be conducted at 0.867 Ata, econ cruise at 0.6 Ata, and so on. Performance and mission profiles will self adjust.

A CSA take off must be simulated with the engines throttled to 0.95 Ata against the brakes, before brake release, to replicate the lower TOGA power of the Walter manufactured Pegasus II.M2 compared to the GR9Kfr in the SABENA version whose air file we should use.

Now we must remember that the major Czechoslovak airline before WW2 was CLS. They held the really lucrative route licences. CSA was only allowed the route licences that CLS did not want extending to the less lucrative east. I believe the five CSA S.73s flew the following two services;

Prague - Vienna - Zagreb - Bucharest

and

Prague - Warsaw - Moscow

Most of these stages allowed (far) fewer than 18 passengers.

The assets and aircraft of CSA were seized by the German government and handed over to Lufthansa after the invasion of Czechoslovakia, but they continued to fly the same two routes.

So by the end of 1945 all the S.73s had gone and the only significant remaining operator of the S.M.81 military transport was the Spanish Air Force. By then it is likely that their aircraft had been re-engined with the Alfa Romeo 126/R.C.34 Pegasus. All had been relegated to transport duties six years earlier. They didn’t last much longer.

The place names given in this text are those used by Microsoft in FS9 in their world/goto menu. If a named location has several airfields in the 21st century the smallest should be used to replicate the 1930s. In addition we should take off and land either side of any modern hard runway to allow the higher friction of the surrounding surface to be experienced correctly.

I have supplied on screen and separate printable handling notes elsewhere in this package.

Finally a quick comparison of the four types of S.73 supplied in this package.

Early 1935 - SABENA launch customer model - 3 x 770hp Mistral medium superchargers - quite good all round, but best at nothing. Low profit margins. Quite good for use in both Europe and Africa.

Late 1935 - Ala Littoria Flagship model - 3 x 875hp modest superchargers, but only with military fuel. The fastest variant. However with airline grade fuel less powerful than the earlier SABENA aircraft and a waste of money if used without access to military fuel. Highly optimised for the Italian colonies in Africa at any price.

1936 - Ala Littoria economy model - 3 x 650hp Piaggio very powerful superchargers. Not capable of using very short runways, very slow at low levels, but quite fast at high levels. Offered the best profit margin. Optimised for Europe. The easiest to fly within its engine and aerodynamic limits.

1937 - ALI - 3 x 850hp Alfa Romeo very weak superchargers - almost as good as the Cyclone variant for STOL performance despite using airline grade fuel, but only from low altitude runways. Capable of cruising fast, but not economical, and poor performance from high altitude runways. Optimised for Europe.

In common with most aircraft of this era there was no airscrew de-icing and no airframe de-icing of any kind. When simulating the operation of these aircraft in FS9 remember that the flaps installed on airliners and heavy bombers in this timeframe were very fragile. This is not an all metal wonder from Boeing or Douglas. The wing is just bits of dead fir trees stuck together with the sticky bits from a dead horse. We must treat it carefully or it will fall apart. It will start to fall apart of its own accord after about ten years anyway without any abuse from us.


FSAviator 12/2007.

[volkerboehme]

Savoia Marchetti S.73 detailed handling hints - all four versions.

It is important to understand that this release has four different versions of the S.73 included, each with different engines, and one with different landing gear, not just many different liveries. Each version has different engines, different performance, and different handling is required. The differences are explained in the different on screen handling notes for each version. This text applies to all four versions unless specified.

The S.73 entered airline service in February 1935. It had fairly primitive engine cowls which predate NACA cowls with cowl flaps. Each engine type had different cowls, but in each case the cowls were designed to ensure that each engine type was unlikely to suffer from overheating in flight, even in the African temperatures for which most versions were designed. Consequently the need to monitor and control operating temperatures is minimal compared to later aircraft in which engine drag was much reduced by NACA cowls, but which then required constant attention to cowl flap management to ensure adequate cooling.

On the other hand these engines are prone to shock cooling at high altitude if Ata is reduced too quickly. From top of descent power reductions must be in steps of 0.1 Ata at intervals of one minute.

This aircraft has the same two pitch Savoia screws mounted on all the different varieties of engine, but FS9 has no means to simulate variable pitch screws; it can only simulate fixed pitch or constant speed screws. Consequently pitch switching will be undertaken by the virtual flight engineer. There are no engine rpm controls in this aircraft. Engine rpm are controlled by variation of throttle, by variation of IAS, and by variation of altitude. For almost the entire flight the screws are in their course pitch. The screws brake the engines when in course pitch.

It is not possible to obtain maximum power at low engine rpm. Because the drag on the screws is very high in thick air at low altitude it takes substantial supercharge to achieve rated rpm at low altitude. At high altitude no supercharge is required to achieve rated rpm because the air is thin and the drag on the screws is minimised.

Aircraft with v/p screws have very poor performance when operated at low altitude or low IAS, because the screws brake the engine to inefficient rpm. These aircraft are only efficient when operated at or above design cruise altitude. This is an engine variable (see variant on screen handling notes). For instance the Piaggio engined 'economy model' of the S.73 will sustain a cruising velocity of 155 KTAS using economical power at 5000 metres but only 130 KTAS at 1000 metres. A five hour flight becomes a six hour flight if we cruise at the wrong altitude.

The Alfa Romeo engines were military engines running on inferior airline grade fuel. They will rev freely to RPM which may cause an engine failure with airline grade fuel. RPM must be restrained. Throttle settings that are safe for climb at low IAS are not safe for cruising at higher IAS. See Alfa Romeo handling notes.

The Cyclone engines 'required' military grade fuel. This limited where they could be operated efficiently. See History.txt. Procedures for operating the Cyclone with airline grade fuel are however supplied in the variant handling notes.

The complex fuel management system of the S.73 is not part of this simulation package. It was operated by the flight engineer.

Once No.2 engine is running we must ensure that the generator attached to the central engine is turned ON, using the electrical panel at bottom left, else many systems will soon fail as the battery is exhausted. During engine failure training we must not fail engine 2 unless we wish to invoke electrical failures to complicate the emergency.

Navigation is explained in a separate text; however we must remember that where these aircraft flew there were no airways, no en route ATC, and no assigned cruising levels whose direction depended on aircraft course. Outside the United States airlines still made up their own rules and their own procedures whilst en route.

Some variants have copious supplies of oxygen for the passengers as well as the crew. They are designed to operate at higher altitudes than most airliners of the 1930s, which is one reason that they have more engines. Other variants are limited to only 30 minutes above 3000 or 4000 metres. See variant on screen handling notes.

Design cruise altitude was targeted in all directions subject to icing. The S.73 has only carb heat and pitot heat, no other de-icing. Since it was heavily optimised for use over Africa this was not a major problem, but if you venture north of Libya in a Savoia S.73 beware. Ice kills.

Each set of on screen handling notes explains the power to be applied during each phase of the flight. Max cruise is used only to battle headwinds. Econ cruise is employed with tailwinds or to maximise profit with nil wind, otherwise design cruise is appropriate in these aircraft subject to what follows.

During descent engine rpm must be retrained to the correct value for the engine type as stated in the on screen handling notes. Rate of descent must also be restrained to keep profile drag below 310 KmIAS in all variants. Due to the fixed gear this should not be a material problem. However several variants have enough power to rip their own tail off, in cruising flight, in only moderate turbulence, at low level, so when flying the high powered variants throttle must be moderated to avoid 310 KmIAS for safety reasons, and may need to be moderated further still, depending on current weight, to preclude nose down pitch cruising for economic reasons. FS9 flight dynamics can contain a great deal of realism, but it is always the user who must extract the encoded realism by application of acquired skill.

The correct cruising level is the one which, allows use of design cruise power, without invoking nose down pitch, or invoking IAS > Vno = 310 KmIAS, or exceeding max rpm for the engine in question, without invoking icing. Thus the correct cruising level varies with both weather and weight. The captaincy skill required to locate the correct cruising level only comes with experience. Target cruising velocities stated in the variant handling notes are for guidance. The aircraft should be operated in accordance with all the above restrictions which may result in higher or lower cruising velocity in given weather at a given weight. PPH will vary with altitude. The figures stated in the variant handling notes should be used for flight planning regardless.

To achieve a mandatory rate 1 turn, during holding and approach procedures, the turn needle must obscure the mark about half way towards S or D according to direction of turn. The gauge far right which looks as though it might be a turn gauge for the co-pilot is actually the rudder trim indicator.

The flaps have 'blow shut' protection. They will not *travel* with excessive profile drag (IAS) applied. Once locked they will withstand higher drag, but we should avoid applying it anyway. The three flap stages are indicated with lights. The lights below are engine overheat lights which should rarely trouble us if we use the on screen handling notes correctly. The 'engine sub panel' which will appear bottom centre of the Cockpit View gives us access to some of the flight engineer's gauges including fuel contents remaining. He will take care of any cross feeding necessary and will safeguard any high lead military fuel (See Cyclone aircraft.cfg).

At this date very few aircraft had flaps. The flaps on the S.73 are 'adequate', but it can develop a high nose angle on approach. Achieving Vref is vital for short landings, but at Vref the S.73 is already almost in the landing attitude. Power must be applied throughout the final approach to control VSI and hold the glidepath.

If we flare with any vigour we risk tail strike. A little extra power to reduce VSI, or very gentle use of elevator, after nailing Vref, followed by a mainwheel only landing is closer to what is required. Retard throttles only after touchdown on the mainwheels at minimal negative VSI. Get the yoke full aft and flap retracting before braking.

Arriving over the fence at less than Vref will place the aircraft so nose up that visual contact with the touchdown zone may be lost and a tail first landing is very likely with unfortunate results. If we cannot nail Vref then we should arrive a little faster, never a little slower.

These are all STOL bush planes. They are highly compatible with short, rough, and hot bush strips across the deserts and jungles of Africa. Those designed to operate from high strips have the necessary engines for the job. Most will outperform a Beaver in STOL capability at low altitude. Some easily outperform a Beaver at high altitude. Use them from short bush runways or you will not understand why they have such a strong fixed undercarriage. However the drum brakes are weak and will also fade. Follow the on screen handling notes correctly or braking will be poor and nose over may become a threat.

The S.73 is more or less 'self righting' due to its high pendulum stability, but it reacts slowly due to the high inertia of those offset masses. The flying controls are manual with no power assistance. You will be handling a ten ton truck manually with only thin air for traction.

Taxi slowly. Use differential braking in lieu of differential power. Some limited tailwheel steering has been made available. The tailwheel does not lock. If you follow the handling notes it won't be on the ground long enough to matter. View ahead is very poor due to the central engine and cowl. Follow the edge of taxiways and runways looking left and down from the VC. Line up on a runway using the same method. Taxi slowly enough to retain control in an aircraft whose ground handling characteristics were poor by modern standards.

One line reminders for all the above are in the variant on screen handling notes. Handling notes are not a checklist. Handling notes state targets that must be achieved and sustained, the power to be employed whilst seeking the target, as well as limits which must be avoided. They set out the order in which handling targets must be achieved. They explain when to switch handling target, and when to change aircraft configuration. WHAT to achieve and WHEN to alter the handling target, whether it is an input target or an output target, not just a sequence of switch flicking regardless of whether we have achieved our current operating targets.

Use of the pilot's goniometer and the Lorenz (Standard) Beam Receiver are explained in full within the accompanying document 'Navigating the S.73.txt'. They are both fully functional, in all modes, within FS9 and allow the user to explore the transitional years in which the vintage phase of aviation was slowly giving way to the classic phase of aviation history outside the United States. The clock has a stopwatch function for the second hand to assist in 4D navigation.

Italian aircraft of this period had a gyro comparison compass and loosely associated 'autopilot' systems which were very similar to those in use in Germany. Some of these have been explained correctly in other FS9 releases and some have been 'faked'. Nothing you encounter here is fake and that requires the user to understand how to use the five different compasses correctly.

The magnetic compass is top centre. Directly underneath is a gyro repeater compass. Now locate the gyro comparison compass between the altimeter and the artificial horizon. It has two rotating drums, one above the other. The lower drum is controlled with the left hand knob. It must be set equal to the magnetic compass as frequently as may be necessary so that it displays current magnetic heading. This lower drum also drives the gyro repeater compass under the magnetic compass. They are in fact slaved to one another so that the co-pilot can adjust the main comparison compass lower drum which is in front of the captain using the control under the repeater compass.

The upper drum of the gyro comparison compass (in front of the captain) is set with the right hand knob. It must be set to the assigned heading. The document 'Navigating the S.73.txt' explains in detail how we discover (or calculate) our assigned heading to set on this upper compass drum.

The internal gyroscopes of the captain's comparison compass then compare the two headings and drive the heading deviation compass situated above the comparison compass. Every time our assigned heading changes (perhaps only every ten or thirty minutes whilst en route, (see 'Navigating the S.73.txt'), we must make fine adjustments of the difficult to read 'gyro comparison compass', but in between we use the easy to read and interpret 'heading deviation compass' above to operate the aircraft, whether en route or during an approach.

None of that has anything to do with whether the aircraft even has an autopilot (AP) or whether the AP fitted will cope with what we are trying to achieve by way of 4D navigation. None of those instruments is an AP or even part of an AP.

These aircraft do have an automatic pilot (AP) of sorts. The 'Corretore Autodirezionale' is a primitive device of limited capability. It can hold assigned headings and little more. To do this it senses the gyroscopes of the captain's gyro comparison compass and if the actual heading deviates even a little from assigned heading it uses the rudder to maintain course with many 'very little and often changes'. It can be used to make *small* heading changes, by slight variation of the assigned heading on the upper drum of the captain's comparison compass, but since it has no control over pitch status changes of pitch may be induced as the rudder attempts to roll the aircraft to a new assigned heading.

The 'Corretore Autodirezionale' master switch is bottom right of the captain's panel. The normal procedure is that we first set the magnetic heading on either lower drum, (main or repeater), then the assigned heading on the upper drum of the captain's gyro comparison compass, then we manually achieve zero deviation on the deviation compass above, then (maybe) we turn on the 'Corretore Autodirezionale' if the assigned heading is expected to endure long enough to make using the AP worthwhile.

The 'AP' has no control over pitch. The aircraft can be pitched with elevator or power whilst the AP is engaged. In real life it could be rolled with aileron against the rudder inputs of the AP, but FS9 will not allow that. There is an AP connected warning light above the deviation compass.

Be warned this system has been misrepresented in some other FS9 releases and you may need to relearn its usage before operating the S.73. Now would be a good time to read the longer and more detailed 'Navigating the S.73.txt'.

FSAviator 12/07

[volkerboehme]

This part of the Savoia Marchetti S.73 package explains how to navigate the S.73 realistically. It is extracted from a prospective addition to the Propliner Tutorial available from Calclassic.com. Many other parts of the original Propliner Tutorial also apply to the S.73.


THE FOUR PHASES OF AVIATION HISTORY

Aviation history is about much more than aeroplanes because the things achieved by aeroplanes and those who fly them depend on a complex external infrastructure that is often ignored. What each phase of aviation has in common in every country, whenever it arrives, is nearly identical public sector aviation infrastructure, (civilian or military), regardless of aircraft diversity or airline ownership and control.

The pioneer phase of aviation in each nation, or sector of aviation, was characterised by irregularity of service and high death rates due to inadequate public sector infrastructure. Aircraft were operated by pilots who had no formal training or qualifications in wireless operation or aerial navigation. They compared a road map to the scenery as it went by and often became fatally lost. Being a qualified pilot is not the same thing as being a qualified navigator.

The vintage phase of aviation that followed, (everywhere except the Continental United States = CONUS), was characterised by large flight deck crews including a qualified wireless telegrapher and a qualified navigator. They used global positioning systems (GPS) to navigate without reference to the scenery. Using GPS they flew direct from departure to destination. Those vintage era GPS techniques were never adopted over the CONUS which moved directly to the third and classic phase of aircraft navigation. On the other hand the European powers, and their associated world wide empires, progressed much sooner to the vintage phase of aircraft navigation.

How we should conduct a realistic propliner, maritime patrol, or bomber simulation within FS9 depends on;

1) crew complement

2) the avionics being simulated

3) location

4) date


By the time that the Savoia Marchetti S.73 entered service with SABENA in February 1935, followed by Ala Littoria in November 1935, most European empires, including the Belgian and Italian empires, had already entered the vintage phase of aircraft navigation. Airlines no longer relied on seeing any scenery to maintain an airline schedule, and no longer relied on primitive post medieval navigation devices such as sextants. They used GPS.

GPS does not require orbiting satellites to generate the necessary electronic signals. That is just a characteristic of the latest system. Earlier systems were terrestrial.


THE VINTAGE PHASE - GLOBAL POSITIONING SYSTEMS

The vintage phase of aviation dawned with the arrival of highly trained and qualified wireless operators (wireless telegraphers), and highly trained and qualified navigators who joined the flight deck crew, and sometimes displaced pilots as captain of the aircraft.

When we use any flight simulator we must always act as both pilot flying and aircraft captain. Performing other crew roles is optional. This tutorial provides a framework for piloting and captaining aircraft in the vintage phase of aviation. If you wish to role play telegrapher or navigator you will need to obtain a different tutorial.

Both Wireless Telegraphy (W/T = Morse) and Radio Telephony (R/T = Voice) pre date the powered aeroplane. Aircraft use of electronic global positioning for navigation dates from the Zeppelins of the Imperial German Navy. A Wireless Telegrapher or Radio Operator asked an operator on the surface to manually direction find (D/F) the aircraft's transmissions in the High Frequency H/F waveband. The ground operator used a large rotating Adcock array. The bearings supplied back to the qualified WTO or RO were then plotted on a chart by a qualified navigator. Ideally three bearings from different D/F operators in sequence were used to triangulate present (actually recent) position. Just as in a surface ship the airship navigator then instructed the helmsman what heading to steer based on where the vessel was believed to have been a few minutes earlier.

By 1935 many airliners including the Savoia Marchetti S.73 had combined gyroscopic compasses and course deviation monitors. In some airliners including the S.73 these were already combined within a wing levelling autopilot which drove the rudder trim tab when activated. It is important to understand however that the assigned heading was always bugged whether or not the wing leveller was going to be used. The heading assigned by the navigator was dialled into the assigned heading monitor on the upper scale of the captain's gyro compass. The actual heading revolved below. As pilot flying we must always keep them superimposed, but after dialling current and assigned heading into the comparison compass we actually do that using the heading deviation compass above.

Today in the 21st century pilot flying is assigned headings by qualified radar controllers looking at a radar plan position indicator (RPPI). In the vintage era he was instead assigned headings by a navigator looking at a GPS display which he was updating manually. It makes no difference at all to us as pilot flying in FS9, or to us as the aircraft captain in FS9, who mandates the assigned heading, or whether they are aboard the aircraft. Actually it makes no difference in real life either.

Today a GPS can update the aircraft plot in less than a second. In 1915 or 1935 it took a few minutes to use GPS signals to update the GPS plot in an ocean liner, a battleship, or an aircraft with the relevant crew complement and H/F wireless transceiver.

Using GPS to simulate the pioneer phase of aviation symbolised by the FS9 default single crew Ford 4-AT-E Trimotor is cheating and is pointless. Using GPS to simulate the vintage phase of aviation which followed is entirely realistic. Most FS9 users fail to differentiate between the two phases and therefore fail to deploy GPS correctly during propliner, (and military or naval), simulation of the vintage phase of aviation.

Remember the pioneer and vintage eras of aviation, overlapped in different places, and in military v naval v commercial aviation infrastructure at the same time.


THE NEED FOR Radio Direction Finding (RDF)

Nobody believed that aeroplanes could achieve scheduled operation using sextants for astronavigation. Attempts usually ended in death, but even when hampered by the critically low endurance of aeroplanes a qualified navigator could get lucky a few times with a sextant and live to tell the tale.

Think about how useful a sextant is when the entire flight has to be conducted in or below cloud, or in limited visibility. Sextants only work well enough to be useful in vessels that can afford to have little idea where they are for days on end. That sometimes included airships, but not aeroplanes. Of course sextants were installed in some aeroplanes. They were just useless weight much of the time in any aircraft that had to maintain a schedule.

Sextants were much used by military and naval aviators, because their command structure could just postpone missions for days on end until the weather was good enough to navigate using post medieval means of navigation. Under combat conditions radio silence may be necessary. Post medieval means of navigation were sometimes all that were available during 20th Century combat missions, or during training for combat in radio silence, but airlines were not constrained to radio silence, except in a very few places during WW2.

Radio Direction Finding = RDF, (in the HF band = HFDF pronounced Huff Duff), began to replace sextants for oceanic navigation world wide from 1909. The RMS Titanic was being navigated by RDF when she struck an iceberg in 1912. Aircraft were simply no different. By 1912 few vessels in the developed world attempted scheduled ocean crossings without both a qualified wireless operator and a qualified navigator aboard. It soon occurred to the Imperial powers that the Sahara, the Arabian Deserts and the equatorial jungles of Africa were just another kind of ocean. Then the Imperial powers decided to treat the entire planet as an ocean whose mountains were just another kind of reef. The entire planet could be navigated using GPS, not just the oceans, and it was.

By 1929 RDF was possible using HF stations 1200 miles away, *in any direction*. HFDF provided wide source infrastructure to vessels in transit, whether on the sea or in the air. When using wide source infrastructure, however the GPS signal is delivered and decoded, the vessel does not navigate from GPS transmitter to GPS transmitter. It receives their signals anywhere and everywhere. They are wide source, not point source. Consequently the vessel attempts to navigate directly from point of departure to its destination without zigzagging across the planet from one radio beacon to another.


AIRCREW COMPLEMENT CONSEQUENCE

Across the British Empire RDF was a viable global positioning system (GPS) before WW1 never mind WW2.

Aircraft with significant useful loads had large crews, whether military or commercial, precisely because they used the form of GPS known as RDF to navigate. That is why a Boeing Clipper, or a Savoia S.73 could not have a DC3 flight deck complement of just two pilots, who only knew how to find and follow a series of radio beams from one point source beacon to the next.


FLIGHT BY U.S. AIRCRAFT OUTSIDE THE CONTINENTAL UNITED STATES

The USN deployed RDF from 1918 onwards, but they did not share it with anyone else, (unless for one off propaganda purposes). The early US airlines had neither point source navigation infrastructure, nor wide source navigation infrastructure. Their fatality rate was dreadful. Over the CONUS the federally imposed detailed procedures that gave rise to the third and classic phase of navigation were introduced from 1932. Outside the CONUS all US aviation slowly caught up with the USN, the European powers, and everybody else, by introducing RDF.

When using FS9 we must never forget that for aircraft with large useful loads, everywhere except over the CONUS, GPS in the form of Marconi + Adcock RDF was the primary commercial, military and naval navigation system in use from WW1 onwards. During and after WW2 it was gradually replaced by LORAN, GEE, Decca Navigator and OMEGA, but from our perspective of both pilot flying and the aircraft captain each is just a slightly longer ranged, or faster decoding, or slightly more accurate GPS. Somebody else in the aeroplane operated each of them to create the GPS plot.

How the GPS signals were decoded at a particular date is not the point. The point is that with a large enough crew of specialists the captain of a Savoia S.73, and pilot flying if a different individual, both had access to GPS in 1935 whilst the instrument rated crew of a DC-2 flying over the CONUS in 1935 navigating along the audio beams generated by point source radio ranges did not.

The Savoia S.73 did not use point source radio navigation in the en route phase. It used wide source radio navigation (GPS). Just because two aircraft existed at the same time on different continents does not mean that their operation and navigation was similar. They were not. The tiny crew complement of land based US airliners required very expensive point source public sector infrastructure. Each of the hundreds of Radio Ranges required a power supply from a nearby power plant. By the 1930s that was possible within the CONUS, but it was totally impossible in the middle of the Sahara desert, or the middle of the vast African rain forests. Everywhere outside the CONUS wide source infrastructure was already in use and vessels in transit, whether on the surface or in the air, had the necessary crew complement to use it to create their GPS plot.



REGULATORY CONSEQUENCES

RDF provided a wide source infrastructure. Unlike Radio Ranges and the hardly different VHF Omni Ranges (VORs) that replaced them it was not associated with federal regulations, airways, en route air traffic control, or mandated procedures.

Everywhere except over the CONUS Huff Duff was widely available allowing multi crew aircraft to navigate above cloud without visual reference to the surface, and just as easily within cloud, or below cloud, without visual reference to heavenly bodies for astro navigation, on a scheduled basis, even in really bad weather.

Every government except that of the United States wanted wide source navigation systems (GPS) to be the basis of post WW2 international aerial navigation, despite their short comings, since they had to be maintained for use by all kinds of marine vessels anyway. The shortcomings of all the early GPS systems were complex radio encoding requiring a dedicated wireless operator whilst manual plotting of the position decoded also required a qualified navigator. Not much problem in a ship, but for the US domestic airlines, already accustomed to two crew IFR operation using point source radio beams over the CONUS, a huge commercial problem in an airliner.

The US view prevailed and GPS is still fighting for acceptance as a primary aerial navigation system despite automatic real time decoding and plotting. Both real time decoding and plotting have been available in British GPS moving map systems such as Decca Navigator since the early 1950s.



SIMULATION OF RDF GPS IN FS9

In theory the FS9 GPS code could be made to behave exactly like a human navigator waiting for decodes from a human WTO before plotting the symbol on the map with suitable inaccuracy and delay, but this is not really necessary.

The rules for conducting a GPS navigated flight using Marconi + Adcock technology during the vintage phase of aviation history only requires self disciplined use of the default FS9 GPS.

1) The aircraft, (whether civil, military or naval), must have at least a qualified WTO and a qualified Navigator.

2) The GPS window must be 'popped up' only at substantial intervals during cruise; perhaps every 10th minute for a short haul flight, or every 30th minute for a long haul flight.

3) Once every such position update interval, a course correction not exceeding five degrees, and always rounded to five degrees, is made after using the GPS to establish whether the flight is currently left or right of flight plan track due to wind drift and any other cumulative navigation errors, (that we have perpetrated).

What we will be simulating using intermittent course changes and headings, which will be wrong by up to four degrees 80% of the time, is the error that arose from the manual plotting delay and the bearing errors inherent in using HFDF as the contemporary GPS system at extended range.


CREW RESOURCE IS THE KEY

Multi crew aircraft outside the CONUS knew roughly where they were all of the time, in any weather, using RDF as a slow to update and slightly inaccurate GPS. Aircraft like the Ford 4-AT-E Trimotor with inadequate crew resource could still only fly the pioneer way by visual reference to the scenery.

Classic era airliners like the Boeing 247, DC-2 or DC-3 had two pilots, neither of whom was a trained navigator, and neither of whom was a trained telegrapher. They used point source navigation and followed audio beams, zig-zagging from beacon to beacon. That classic phase method of navigation did not exist outside the CONUS.

So during the vintage phase of aviation, everywhere except over the CONUS, (which never had a vintage phase), a flight in an aircraft with adequate crew resource for GPS navigation begins with a visual departure flown by visual reference to the surface until clear of all potential obstructions. This is followed by a climb to design cruising level, whether or not design cruising level is in cloud, below cloud, or above cloud, directly on track to destination. Then every ten to thirty minutes, FS9 GPS is used to adjust heading left or right five degrees in units of five degrees until the flight reaches a position where it is deemed to be safe to descend again near to destination.

Of course any aircraft may need to climb above design cruising level to clear a mountain range, or descend below design cruising level to clear ice, in the absence of de-icing equipment. In 1935 very few aircraft had any de-icing equipment beyond carb heat and pitot heat. Equally some stages may be so short that it is not possible to reach design cruising level.

Note especially that no RDF signal is needed from destination, or anywhere en route to destination. The GPS stations in the 1930s were up to 1200 miles away from both the aircraft and its destination.


LIMITATION OF UTILITY OF RDF

The slowly updating and somewhat inaccurate GPS used by the navigator of the Titanic in 1912 was not adequate to enter a harbour blindly in fog without reference to the local scenery. Nor was it good enough to allow an aircraft navigator to find a particular runway without visual reference to the local scenery. However, the GPS of 1912 was good enough to navigate from somewhere close to Ireland to somewhere close to New York, whether by a ship, or by aircraft. With sufficient training and skill, both undersea motionless reefs, and continental mountains, marked on a (GPS) chart could be avoided. Moving icebergs could not.

Just because the GPS systems used from 1909 to the 1990s were too poor to be used as approach aids, or could not be used to avoid collision with other moving objects, does not mean that they could not be used, or were not used, for en route navigation. Of course they were. Unless radio silence was required for combat operations GPS was the primary means of en route navigation in any vessel with a qualified crew complement and save for the CONUS continental land masses were just treated as another kind of ocean with bigger rocks and reefs projecting above their surface.

Most FS9 users never quite grasp this. Sextants are occasionally useful in aircraft with enough power to climb above all cloud, but vintage airliners needed to maintain a schedule. On many days, and on many legs, a sextant would have been as useful as a chocolate coffee pot.

Now notice that the Savoia S.73 does not have an astrodome. One or usually both of the pilots is also a qualified navigator. They are both qualified to use a sextant, but there is nowhere for either of them to stand and use a sextant. There was no sextant. The S.73 was navigated using GPS, not astro-navigation. Now think about all the other airliners and aircrew flying schedules, whatever the weather, who could not rely on post medieval navigation techniques and who had no reason at all to maintain radio silence. Most of the airliners they were flying also had no astrodome and no sextant. When flying boats were used as airliners they often did, but they also tended to lack the power required to climb above cloud to take astro shots, so they too were heavily reliant on GPS.

In the real Savoia Marchetti S.73 pilot not flying (PNF) was the navigator. He maintained the GPS plot on his lap. Every ten minutes he worked out whether the airliner was left or right of flight plan track and if necessary assigned a different heading to pilot flying (PF). In many vintage airliners the comparison gyro compass was placed where PNF could update the assigned heading for PF. In the S.73 he used the slaved repeater gyro compass under the magnetic compass.

FS9 users may have come to think of the comparison gyro compass as part of a vintage era autopilot, and it may be, but that is not its primary use. The assigned heading is always bugged, (usually by PNF), and equality maintained by PF. In FS9 we must play both roles. Only every ten or thirty minutes we must pop up the GPS window and determine whether we are converging with flight plan track. If not we bug a heading five degrees more convergent with flight plan track and then we fly it. Whether or not we intend to use an autopilot to maintain the assigned heading. An AP is a luxury in any vintage airliner. A gyro comparison compass is not.

We never bug a heading that is not divisible by five and we never attempt to navigate direct to anywhere many miles ahead. We always bug and then fly a heading that converges with our flight plan track. Unless of course our current bugged heading is holding flight plan track exactly in the current crosswind. If we are using real weather, that happy co-incidence will never last for long.


LOCAL INFRASTRUCTURE CONSTRAINT

O.K. let's consider the rules of conduct for flight simulation of a SABENA Savoia Marchetti S.73 flying the London to Oostende schedule in the winter of 1939. On this flight we can use Belgian and British commercial aviation infrastructure which includes GPS widesource signals, but not point source Radio Range signals of the kind that were in use in the United States. It will be cloudy and raining a lot of the time. We do not wait for clear blue sky because we do not need to climb above cloud to take sun shots. We have nowhere to stand to take sun shots with a sextant anyway. We do not wait for high visibility at low level because we do not intend to navigate en route by reference to the scenery.

We could use ancient pioneer era, flight by visual reference to the scenery, navigation techniques to locate Oostende, but our track mileage will be less if we use GPS to proceed in a straight line, and SABENA are not paying the other three aircrew in our virtual cockpit for nothing. We will also enjoy a much faster cruising velocity up at 4000 metres in nice thin, low drag, air.

If we have not installed a third party scenery of Croydon we will use nearby Redhill (EGKR) in FS9 instead. We must climb out over the local terrain to somewhere safe, by reference to the scenery, potentially using a map, before climbing into or above cloud. Climbing out of Croydon or nearby Redhill that will be no problem, but in Africa which was the natural home of the Savoia S.73 it may be a significant problem due to high mountain ranges.

Once in the cruise at an altitude of four thousand metres, potentially above, or quite often within cloud, cruising fast at high TAS in nice thin air, the goal is to transition from the en route phase to the arrival phase using GPS to decide when it is safe and appropriate to descend. This is a short haul schedule, so we pop up the FS9 GPS window only once every ten minutes and make course changes of no more than five degrees in units of rounded five degrees until on one of those updates we decide it is time to descend. This is the key captaincy decision when navigating using GPS in the vintage phase of aviation. It is the descent through cloud that may kill us all.

At this point the Classic phase techniques already in use in the United States and the Vintage phase techniques in use everywhere else merge and become identical. The means of terminal guidance was becoming universal. Non Directional Beacons, (transmitting in the Medium Frequency M/F band), were becoming common. However Automatic Direction Finding (ADF) was still a rarity.

Sometimes only the middle third of a short haul flight undertaken in the vintage phase of aviation outside the CONUS will be conducted using GPS, but San Francisco to Honolulu would be RDF = GPS more than 95% of the way. In real life the way an aircraft is operated has nothing to do with the aircraft type or its date of manufacture. It depends on the current technology phase of the local aviation infrastructure. That is what we must seek to replicate and simulate within FS9.

By 1939 the R.A.F. already had fourth generation modern phase infrastructure within Britain, but British commercial aviation which spanned an empire was stranded in the vintage phase. This constrained the operation of commercial aviation over and near Britain whether the airline was British, Belgian, Dutch, Danish or German.


PLANNING TOP OF DESCENT (TOD)

In the vintage era of aviation there were no mandatory arrival and approach procedures published by a federal agency via an arrival and approach plate. The key flight planning decision was always voluntary placement of top of descent (TOD) to terminate the limit of the GPS component of the vintage phase flight outside the CONUS. We must descend through cloud somewhere that does not risk collision with terrain in the descent. We must plan and then vertically limit the descent accordingly.

There were no federally mandated procedures outside the CONUS, so they were employer (airline) mandated instead. In general the present day federally mandated procedure is just an amalgam of the prior employer mandated procedures many of which date back to the thirties. They are the same thing really, so if a current NDB arrival and approach procedure is available for download, it should be downloaded and followed. Even if it appears that a modern STAR has no relevance to vintage airliner operation in the 1930s it probably does. The current approach plate is always relevant. It tells us what our minimum descent altitude must be in FS9 since we must avoid masts present in FS9 whether or not they were present in the thirties, forties or fifties.

The rules for planning top of descent are therefore those explained in the original Propliner Tutorial available from Calclassic.com even though it addressed only flight in the Classic phase of aviation history.

In FS9 we will use GPS to navigate the Savoia S.73 as explained above until it is time to descend. Then we will switch to terminal guidance which is identical to terminal guidance in the classic phase already in use over the CONUS.


THE ARRIVAL PHASE

Part 3 of the Propliner Tutorial explains in detail how to fly arrivals and non precision approaches in propliners, whether they are vintage or classic era propliners. Whether over the CONUS or anywhere else that vintage/classic phase arrival and approach guidance infrastructure was, and still is, in place today.

Oostende (EBOS) still has all of its vintage and classic era terminal guidance navigation infrastructure present within FS9. Three NDBs, and two Lorenz Beams. All the vintage era infrastructure we could possibly need in a Savoia S.73 or any other vintage/classic propliner.


GONIOMETERS

However what vintage airliners lacked was ADF to home those NDBs. Vintage era propliners had Goniometers instead.

The standard American Goniometer is called a U.S. Army Aviation Section Signal Corps Receiver (USAASSCR), or just Signal Corps Receiver (SCR) for short. It is of course a default gauge in both of the default FS9 Lockheed Vegas. It is mounted to the left of the Altimeter in their VCs, immediately above their all important gyro comparison compass. In the Savoia S.73 the European pattern goniometer is underneath the Air Speed Indicator. It works just like the FS9 default goniometer, but I have a nasty suspicion that most FS9 users have never bothered to learn how to use a goniometer. Shame on you! Now you have another chance, and the tutorial that Microsoft could not be bothered to supply.

An ADF is also called a radio compass. It has a 360 degree compass within a circular gauge. An automated system points the ADF needle at the NDB which we tuned using the avionics panel. The Goniometer is not automatic. It uses the circular MFDF loop on top of the aeroplane, in this case on top of the Savoia S.73. We tune it the same way as an ADF though, and to the same frequency.

The MFDF loop is there mostly for use by our virtual telegrapher during the en route phase. It is mounted on a periscope stand and operated just like a periscope. The telegrapher turns the periscope until the signal minimises. Then he notes the bearing from the base of the periscope stand just like a submarine captain taking a bearing on a ship to the beam. Over the second and third world where NDBs are very few and far between our virtual telegrapher must employ the Huff Duff techniques described earlier instead.

The telegrapher may swing the loop aerial manually during the en route phase. However just before top of descent he locks the MF loop facing forward and the telegrapher tunes the NDB that is the initial approach fix (IAF) for destination. Then he informs pilot flying that the blind flying panel goniometer is tuned. We must tune the goniometer to the NDB, by popping up the avionics window in FS9.


BEACON (NDB) APPROACH

The goniometer has no automation. The MF loop has no automation. Pilot flying (we) now turn(s) the whole aeroplane manually until the NDB which is the IAF for our approach is on the nose, using the obscured arc goniometer (SCR) to determine when it is dead ahead. Now we home to the IAF, keeping the needle centred just as though we had a radio compass (ADF) even though we only have a goniometer and a locked MF loop.

We can fly any vintage era, classic era, or current era NDB arrival, holding, or approach procedure using a goniometer. ADF is a ‘modern’ luxury that is not required to fly modern era approaches.

Why not repeat the exercises in Part 3 of the Propliner Tutorial using the Savoia S.73 and its goniometer. Don’t try the goniometer approach to Moosehead Lake aquadrome though. That one is strictly for the Calclassic updated Grumman Goose!

I am not going to repeat everything in Part 3 of the Propliner Tutorial here. You can download it from the Tutorials section at Calclassic.com. The only difference when flying a Savoia S.73 instead of a Goose or a Convair 440 is that we use a goniometer instead of an ADF to fly the holding pattern, the arrival, and the approach.


LORENZ BEAM APPROACH

These days everybody calls Lorenz Beams, Localizers. Around 1939 the British used to call them Standard Beams, because they wanted to pretend they were not reliant upon a German technology. However a Lorenz Beam Approach (LBA), A Standard Beam Approach (SBA), and a Localizer (LOC) approach are all the same thing. LBA gauges use a vertical LOC needle to find and then follow a Lorenz Beam (Approach) to a runway threshold.

Others like the Standard Beam Approach (SBA) gauge in the DZN L-049A Constellation for FS9 use a pair of lights to indicate left right guidance to find and then follow the Lorenz Beam (LOC). The use of a needle makes the gauge an LBA gauge following the German pattern and the use of lights makes the gauge an SBA gauge following the American and British pattern. The Savoia S.73 has a German pattern LBA gauge to the right of the Goniometer.

Unlike an NDB, Lorenz Beams promote straight in approaches to specific runways and allow much lower minima because they are precision approaches providing terminal track guidance inside the Final Approach Fix (FAF).

A Lorenz Beam Approach can be attempted without flying a holding pattern for inbound track guidance first.

Berlin and New York had Lorenz Beam Approaches in 1936. The rest of the commercial and military world soon followed. Today Oostende has a Lorenz Beam at each end of its instrument runway.


STANDARD BEACON APPROACH

The Standard Beacon Approach must not be confused with the Standard Beam Approach even though they have the same abbreviation!

The Standard Beacon Approach combines one or more NDBs with a Lorenz Beam to provide easier interception of the Lorenz Beam (LOC) via one NDB and potentially distance to go data from a second NDB closer to the runway threshold.

All three Oostende NDBs (on different frequencies!) are conveniently located under the two Oostende Lorenz Beams.

Oostende (EBOS) offers Standard Beacon Approaches to both ends of its instrument runway and because it is adjacent to the coast Oostende is a great place to practice NDB approaches with a goniometer, and Standard Beacon approaches with the Goniometer and the Lorenz Beam Receiver together in the SABENA Savoia S.73 OO-AGL.

We should practice with good visibility and only moderate cloud cover at first, but eventually with two miles visibility, and 8/8 cloud at 700 feet, until we can maintain the London - Oostende SABENA S.73 schedule whatever the weather.


APPROACH PLATE AVAILABLE FOR DOWNLOAD?

I have provided copies of relevant, but out of date, EBOS plates originally uploaded by IVAO, so that everyone who downloads OO-AGL can fly the real procedures for EBOS. Don’t use them in real life. IVAO are a good source of other plates. As it happens the current EBOS plates are also a free download from Eurocontrol, but some aviation regulators do not provide free downloads of their current flight safety procedures. If no approach plate is available fro download we must deduce the arrival and approach procedure for our destination using an FS9 flight planner.

Study the supplied EBOS plates. They relate to an airfield whose elevation is to all intents and purposes sea level. At another airfield the procedures will usually be much the same. However the courses will be the runway courses of that other airfield’s runways and the altitudes to be flown will be displaced upwards by the elevation of the other airfield.

What we are required to do at a different airfield is the same thing at different altitudes and on different headings. The concept should be easy enough to transfer to Addis Ababa when flying I-ASTI, but the inbound course will be 253 and 2000 feet QNH must become 2000 plus 7624 feet = 9624 feet = 2934 metres and so on, because the elevation of HAAB is 7624 feet, not a few feet above sea level.

Before flying any approach in FS9 it is anyway a good idea to write it out in text form so that it is the ATC clearance for the approach. It makes the approach easier to understand and we can read it to ourselves as the approach proceeds.



ATC APPROACH CLEARANCE TO RWY 08 at Oostende:


After studying the plate supplied we would write;

Tune ONO. Descend to cross the RWY 08 Initial Approach Fix ONO at 3000 QNH = 920 metres.

After ONO fly course 103 and descend 2000 (QNH) = 650 metres

When level 650M QNH turn left to cross ONO on course 258

Tune DD. Track to DD.

After DD fly course 283 and descend 1400 QNH = 430 metres

When level 430M QNH turn left to cross DD on course 079

Descend 500 QNH = 170 metres before DD

If runway (lights) not seen over DD at 170M QNH go missed

Missed = climb track 079 to 2000 QNH = 650 metres

Tune ONO. Track to ONO. Enter ONO holding pattern 650M QNH

Repeat procedure or divert.


This will be flown using the Goniometer tuned first to the ONO on 399.5 Kcs and then to the DD on 352.5 Kcs.

No DME is involved in this vintage phase Beacon Approach procedure. By the 21st century, in the modern phase of aviation, a VOR+DME has been established at KOK to deliver a DME cross check. We simply ignore that modern development when flying the vintage phase approach.

I hear people saying they wish more vintage and classic era approaches were available for download. Hundreds of vintage and classic era approaches are still in use around the world and available for free download.

This particular plate was uploaded to an FS site by IVAO, but it is copyright AIS Belgium and was made available by them as a public safety and training resource. Many such plates are available as free downloads direct from the relevant federal authority. Why not use FS9 to learn to fly real propliner procedures instead of just making them up? The nice thing about the real ones is that they actually work and are compatible with real(istic) flight dynamics.

Why not fly the procedure above in FS9 in steadily worsening weather which you control with the user menu until you can land the SABENA S.73 OO-AGL at EBOS in a fully realistic way with the visibility down to only 2 miles and 8/8 cloud at 700 feet.

Save a flight with a start position to the west of Oostende descending through 1000 metres QNH and then practice, practice, practice the approach above in ever worsening weather. When the visibility is poor we may be too high to execute a straight in approach to RWY 08. No problem. We are then required to fly a tight left hand visual circuit at 500 QNH = 170 metres and then land on 08 from that visual circuit.

Now notice that if the wind requires the landing runway to be some runway other than 08 we can still fly this approach to 08 and then join the visual circuit for the landing runway. In a propliner the runway we make an approach to is often not the one we are cleared to land on. We must often ‘circle to land’.

Look carefully at the bottom of the real plate and you will see that propliners intending to circle to land must arrest their descent at higher altitudes according to their size. Vintage propliners with multiple engines can all be treated as class B, or single engine as Class A. In the Savoia S.73 (Class B) if the landing runway is not 08 we will arrest our descent at 660 feet QNH = 200M, cross DD maintaining 200M QNH and then circle to land at 200 metres. Whether the landing runway is 26 or 32 or 14.

Circling to land on 32 or 14 after approaching 08 presents a nice skill challenge in OO-AGL. In 1939 many runways at international airports on major routes were only that size. We should also practice nil wind (worst case) departures from RWY 14 at EBOS. If we never attempt to use runways of that size in vintage propliners we will never understand what vintage propliners are all about. The Savoia S.73 is a huge bushplane whose airfield performance is as good as a Beaver. It is a giant bushplane. It was optimised for use from African bush strips, not modern international airports.

Note that EBOS still has no co-located DME associated with its Lorenz beams even today. The DME needle on the LBA receiver will indicate zero whilst we fly the Goniometer approach and if we do not tune the Lorenz Beam, whilst we conduct Goniometer approach training, the LOC needle will give no guidance either. We don’t really need it. The Beacon Approach to EBOS QFU 08 explained fully above will always get us down, if we have acquired the necessary skill.


LBA + DME TRAINING

To conduct LOC+DME training we must continue down the SABENA route to Lille (LFQQ) south of Oostende where the Lorenz Beam has a co-located DME that will deliver height required data if we tune QFE on our altimeter by subtracting the elevation of Lille, which is 157 feet = 48 metres, from the prior display which is QNH.


HEIGHT not ALTITUDE (QFE not QNH)

In both the vintage and classic eras of aviation approaches were flown with the Altimeter set to QFE so that they displayed height above destination runway, and not set to QNH to display altitude above sea level.

The use of QNH to fly approaches, with an altimeter displaying altitude, is a concept from the modern phase of aviation history. Consequently it is the default within FS9, but when flying either a an Lorenz Beam Approach (LBA with no NDB under the beam) or a Standard Beacon Approach (SBA with an NDB under the beam) we must always reset the altimeter from QNH to QFE by subtracting the elevation of the instrument runway from the default altimeter QNH setting.


SETTING QFE in FS9

To set QFE we need to know the altitude of the destination runway. We should always know that anyway during flight simulation, but it was even more important before the modern era. If we have downloaded the real approach plate, (always the best option), it will tell us. It can also be discovered using a flight planning tool. Super Flight Planner is about the best freeware tool, but FS9 has a default flight planner that will allow us to discover the altitude of our destination runway. To set QFE we simply mouse the Kollsman knob on the Altimeter to subtract runway elevation from current altitude. We should work it out on the back of an envelope or if necessary with the Windows calculator first.

Ideally we will always download the real and current approach plate for our FS9 destination. That will tell us the real elevation to use of course, but not all AF2 authors use the data they should use when creating an AF2.bgl. That includes Microsoft.

Oostende is at an elevation of only 15 feet above sea level. We wind the altimeter down by 15 feet or 5 metres to set QFE instead of QNH. Our altimeter now displays height not altitude.

We do this just before we cross the Final Approach Fix of the approach, or just before intercepting the Lorenz Beam, whichever is the sooner. That is the moment when we lose interest in our vertical displacement from the sea (our altitude) and gain interest in our vertical displacement from the instrument runway (our height).

When flying I-ASTI into Addis Ababa (HAAB) in the winter of 1939 we must instead subtract 7624 feet (2324 metres) from the current reading on our altimeter to obtain a QFE height reference since that is the elevation of the instrument runway at HAAB within FS9.



REAL PROCEDURES

The reason that QNH is the international default today is mostly the invention of the Radar Altimeter. In the modern commercial and military cockpit the RADALT can display current height whilst the Altimeter continues to display current altitude.

When a vintage era cockpit has two altimeters, only pilot flying (PF) sets his altimeter to QFE to display height. Pilot not flying (PNF) retains QNH. That is the procedure in the Savoia S.73 cockpit.

Remember on the approach plate the elevations of mountains and masts are all altitudes (QNH). During final approach from the FAF or along the LOC PF loses his altitude frame of reference to concentrate on height. PNF continues to monitor altitude.


USING an LBA gauge

Take a hard look at the Lorenz Beam Receiver to the right of the Goniometer in the S.73 panel. It looks like an ILS receiver, but if you try to use it as one it will kill you.

The vertical needle is a LOC needle and it is used just like a LOC needle, but the horizontal needle is NOT a glideslope needle. It is a DME needle. It shows distance from the threshold of the instrument runway PROVIDED of course that the Lorenz Beam (LOC) in question has co-located DME in real life and therefore in FS9.

It is used as a DME needle in any approach that requires LOC co-located DME. However it has a second and primary usage which is why we always fly an LBA or SBA approach using QFE.

The horizontal needle of an LBA gauge is the HEIGHT REQUIRED needle.

There are five check marks. These are at 8, 6, 4, 2 and 0 nautical miles DME.

However the Lorenz Instrument Landing System is European and metric. When a LOC/DME approach is flown using a metric altimeter set to QFE these LBA check marks must be crossed at 800, 600, 400 and 200 metres QFE.

The whole point of using QFE to fly the Beam approach is that these required height values never change for any runway, anywhere. They are identical at Oostende and at Addis Ababa, because by setting QFE we see displacement from the runway (our height).

As we descend along and track the Lorenz Beam (LOC) using the vertical needle for track guidance we as Pilot Flying make sure our altimeter set to QFE never reads less than 800, 600, 400, 200 at each check mark as we descend along the Beam. Anywhere and to every runway. *But we must set QFE on the PF altimeter first.*

In the days before radar altimeters this was how height had to be monitored and how descent on the beam was monitored.

When we reach the penultimate check mark at 2 DME we should be at a height of 200 metres, anywhere and everywhere, and in accordance with (most) vintage era beam approach minima we must start a missed approach if we cannot see the instrument runway (lights) at that moment. The missed approach procedure is on every approach plate.

In 1939 we would not set off from London to Oostende, or from Oostende to Lille if the cloud base was below 200 metres or the visibility was less than 2 miles at destination. In FS9 we always check this before take off using freeware FSMETAR to obtain the destination actual (weather) that FS9 is using to generate cloud and visibility at EBOS or LFQQ. If we allow real weather to update during the flight, or allow user defined weather, or weather themes, a non zero rate of change, it may deteriorate of course.

These procedures are specific to the LBA receiver in the Savoia S.73 package of which this file is a part. These procedures do not apply to all gauges with the same bitmap. They may have different code content. They may not be metric either.

Users of FS9 must be realistic concerning their own ability. Every FS9 user should teach themselves to fly NDB approaches (Beacon Approaches) using the Propliner Tutorial from calclassic.com. Every FS9 user should teach themselves to fly Lorenz Beam Approaches, Lorenz Beam + DME approaches and Standard Beacon Approaches using this tutorial in conjunction with the original Propliner Tutorial Part 3, but each user of FS will at any stage of their self training have a skill level less than a real 1939 airline pilot, (unless they are a real instrument rated pilot of course), and every user should use these tutorials to determine what their own level of skill and training currently is.

We must all determine what *our* cloud base and visibility minima are and observe them until more and more self training allows us to reach higher standards of skill, until we too can hand fly an approach in 2 miles visibility and with a 700 foot cloud base at EBOS, or LFQQ or anywhere else in FS9.

Happily the lumbering Savoia S.73, with realistic flight dynamics, carefully encoded gauges, and correctly encoded FS9 scenery projection, makes an ideal instrument rating trainer. Unlikely as it may seem the huge lumbering bomber equivalent (S.M.81) of the S.73 airliner was used as an instrument rating trainer by the Regia Aeronautica.

There is so much more to do with well designed FS9 freeware releases than use them as radio control models for thirty minutes before losing interest and demanding another passing visual novelty. Used wisely and well the Savoia S.73 can deliver hundreds of hours of self training and skill enhancement within FS9.

This tutorial is an addition to Part 3 of the Propliner Tutorial, not a replacement. Much that is relevant to flying the Savoia S.73 realistically is not repeated here.



AFTER WW2.

En route to EBOS we use GPS to ensure that we descend through cloud early and over the sea. On the other hand if simulating a British South American Airways (BSAA) Avro Lancastrian schedule from Buenos Aires to Santiago in 1947 aboard the ‘Star Dust’, unlike the real captain, we must ensure that the navigator and telegrapher use GPS to instead ensure that we descend plenty late enough to have crossed the Andes before initiating descent.

What most commentators on these issues fail to comprehend is that the headwind encountered is irrelevant and the cloud base is equally irrelevant. Flight by visual reference to the surface scenery is irrelevant. The flight must be conducted using RDF based GPS else we are all doomed to die on a glacier on the wrong side of the Andes. The telegrapher in Santiago can D/F our normal H/F wireless traffic (COM not NAV) signal and tell us when we are due north of Santiago, and until then we must not descend. Above all we must never pretend that sextants and 'dead reckoning' can be used to navigate aeroplanes safely during scheduled operations. By 1947 thousands of aircrew had already died trying, and even in the U.K. it was almost time to end the pretence. The 'Star Dust' disaster would just hasten the end of that long standing pretence.

However in 1947 there existed many (British) aircrew who had been so extensively indoctrinated in maintaining radio silence during combat missions that they neglected to obtain the necessary RDF bearings to create the GPS plot when they became airline aircrew after WW2. BSAA propliner, after BSAA propliner, manned almost entirely by ex RAF Bomber Command aircrew, became lost with fatal consequences. None of these losses was mysterious. The aircrew did not obtain the necessary RDF bearings to create the necessary, but not always mandatory, GPS plot.

This was the era of make it up as you go along aerial navigation. No mandatory flight planning procedures, often no worthwhile flight plan at all. The crew just glanced at the GPS plot and decided what to do next. The flight meandered backwards and forwards across the flight plan track turning five degrees right and five degrees left depending on which way the mid course line was. Only TOD was ever really planned and checked at all, and some captains and some navigators just guessed, (dead reckoned), that too. They soon reckoned wrongly and were soon dead.

We should always plan TOD carefully. During vintage phase navigation TOD has nothing to do with the runway location. It has everything to do with where the initial approach fix (IAF) is and the bearing from which we must approach the IAF to remain clear of mountains.

If when simulating operation of a BSAA Lancastrian setting off from the Azores to Bermuda in the late 1940s, we use dead reckoning, or better still a sextant, then we can personally simulate starting the Bermuda Triangle myth because we have no chance of finding Bermuda in bad visibility. It could not be located without RDF in the late 1940s any more than Howlett Island could be found by a Lockheed Electra with no trained or qualified telegrapher aboard a decade earlier. A highly qualified navigator had never been enough to keep anyone aboard alive. In the vintage phase of aircraft navigation GPS required a qualified telegrapher too. The Savoia S.73 always had one. He was there for a reason.

There has never been the slightest mystery why BSAA Star Dust or Earhart and Noonan disappeared 'without a trace'.

The 'trace' in question is the line on the ground or ship based D/F operator’s oscilloscope that shows the bearing of the transmitting vessel. He tells the on board telegrapher what that bearing is using Morse code. The WTO decodes it and tells the navigator. The navigator updates the GPS plot and nobody dies. If the vessel had no trained WTO everybody died sooner or later. If the qualified WTO, (who was rarely the captain of the vessel), was never ordered by the navigator or the captain to obtain a radio bearing everybody died sooner or later.

In the vintage phase of aviation history the key to survival was a large crew complement, professionally trained and qualified in diverse but essential skills, and above all who were sufficiently well trained and indoctrinated in the use of RDF based GPS. Those with the wrong training and the wrong indoctrination had ‘the right stuff’ for combat flying in radio silence, but ‘the wrong stuff’ for airline flying in safety.

British airlines like BSAA were still stranded in the pre Zeppelin era of aviation history, even in the late 1940s. BOAC were reliant on wide source infrastructure and still not subject to adequate safety regulation of the type that had been introduced over the CONUS from 1932. Both British airlines still had the fatal accident record to match. Aircraft have such short endurance that they are much more vulnerable to navigation error than ships.


TIME TO RECAP.

The S.73 was carefully designed to utilise vintage phase en route navigation techniques and, as soon as they were available, location by location, also classic phase terminal guidance techniques such as Beacon approaches and Beam Approaches. The departure was always flown visually, just as it had been in the pioneer era. On some flights, if the weather permitted, the crew could just follow a coastline in the en route phase, but there was no coastline, river, or railway for SABENA aircrew to follow crossing the Sahara or the vast equatorial rain forests of the Belgian Empire where SABENA Savoia S.73s did most of their flying.

Do not confuse the wide source GPS signals used by the WTO and navigator in the S.73 with the point source radio beams used by the two pilots of a DC-2 to navigate over the Continental United States (CONUS) in the same timeframe.

The S.73 did not zig zag from one beacon to another beacon. It used radio signals from a Global Positioning System whose radio source was up to 1200 miles away in any direction. The navigator who was Pilot Not Flying, (PNF), used that GPS plot to give vectors to Pilot flying, often reaching across to set the revised assigned heading on the gyroscopic comparison compass or the repeater compass. He vectored pilot flying just like a radar controller who looks at where a blip is on a radar screen and roughly estimates the heading required to get to somewhere else on the same radar map. There is no beacon and no beam pointing to that waypoint.

In the 1930s point source navigation (Radio Ranges) existed only over the CONUS and along some parts of the Lufthansa network. Because low frequency (L/F) band Radio Ranges were also blind bombing beams, and were much used for blind bombing by the Luftwaffe 1939-45 there was a great deal of reluctance to install them after WW2. However under pressure from the United States, most of Europe nevertheless adopted point source Radio Ranges in the late forties, only to replace them as quickly as possible with VHF Omni Ranges (VORs) from the mid fifties. In the second and third world the vintage phase navigation techniques lasted much longer.

With only two crew the DC-2 and DC-3 were poorly suited to European aviation infrastructure in the vintage phase of aviation history, but ideally suited to the classic phase that arrived in the late forties. They needed long range point source beacons creating beams for pilots, who were not navigators, to follow. Those long range radio beams only existed within the CONUS and certain parts of the Lufthansa route structure prior to the late forties. Airlines like KLM and Aeroflot purchased DC-3s before WW2. They were fast, but they were a poor choice. Aeroflot and the Soviet Air Force soon redesigned the DC-3 to have a dedicated telegrapher so that Soviet GPS could be employed, thus creating the Lisunov Li-2.

When the Li-2s and later multi crew Soviet propliners were pensioned off by the Soviet Union in the sixties and seventies they were still optimal for use in many third world nations which still relied on vintage phase wide source navigation. In some parts of the third world the vintage phase lasted into the 1990s. Vintage phase navigation is not about dates. It is about infrastructure and development in different nations at different times.

No precision is required or involved when navigating the Savoia S.73 and analogous aircraft, during the en route phase within FS9 during vintage phase en route navigation. Once every ten minutes we pop up the GPS window and turn five degrees right, or five degrees left, depending on which side of the desired track we seem to be. That is all. Nothing more. Nothing less.

The key captaincy decision is Top of Descent. We must descend through cloud somewhere safe. This may be well before the coast, or well after the mountain range. It just depends on the current leg and the nature of the obstacles that may kill us on that leg.

Of course GPS is still available in a Savoia S.73 below cloud and at low level because it has the huge crew complement of specialised air crew needed to make use of vintage phase GPS. HF signals can be received at low level. MF signals used to drive the needle of a Goniometer or an ADF may suddenly disappear if we descend below the curvature of the earth or pass behind the shadow of a mountain. They bend. They wander. They are inaccurate. It is only safe to use Goniometers or ADF at short range.

The thing to remember is that vintage era HF band GPS was very long range, but slow to update. We should look at the GPS picture only once every ten minutes, then roughly adjust our heading based on what we see, then close the GPS until we are due another update in tem minutes time. After using GPS to descend safely through cloud, on a safe bearing, towards the IAF, we transition to using classic era terminal guidance with the Goniometer and at major airports the LBA receiver, which may or may not be able to provide DME as well as LOC data. Like everything else in aviation that depends on the local infrastructure outside the aeroplane.

We use the panel clock to time our GPS updates. Updating late is OK, but allowing ourselves to update at intervals of less than 10 minutes, or allowing continuous display of the GPS is cheating. Vintage phase GPS did not have that continuous and instant update capability.

FSAviator 12/07

[volkerboehme]

The SM-73 never flew in California and is therefore not available from the CalClassic download section.

You can download the planes from AVSIM here:

library.avsim.net/download.php?DLID=114075

Upgrade to version 2.1:
library.avsim.net/download.php?DLID=128835

Best regards,
Volker