Hi again,
FSAviator has some comments about the upcoming "technology demonstrator":
Anyone interested in this topic should download and read all of the following pdf provided by the American Society of Mechanical Engineers.
files.asme.org/ASMEORG/Communities/History/Landmarks/5572.pdf I draw your attention to the correct usage of 'controllable pitch' throughout, correctly differentiating c/p screws from automated variable pitch (v/p) propellers of the Ratier type used in the D.H.88 Comet. The following is abbreviated from the full text above. The added emphasis is mine.
QUOTE
In 1930, Hamilton Standard introduced to the aviation world the first practical controllable pitch propeller. ....To achieve maximum takeoff power,the pilot shifted a lever in the cockpit. Oil pressure from the engine actuated a piston, attached to the propeller, which twisted the blades to low pitch. The propeller revolved rapidly, taking small bites of air and maximizing thrust.
When the aircraft reached sufficient cruising altitude, the pilot repositioned the lever in the cockpit, which automatically pulled the blades into high pitch *via centrifugal force on two counterweights attached to the hub* and blades..... (during 1935)... Hamilton Standard, in collaboration with the Woodward Governor Company, added the constant speed governor to the propeller........Higher engine power.. (later)... required larger propellers with greater pitch change capability. Faster aircraft required a wider range of pitch change, and more maneuverable aircraft demanded faster rates of pitch change to hold constant RPM.
Controllable propellers up to that point used internal hydraulic pressure acting on a piston to move blades toward low pitch. *Counterweights, mentioned previously, were attached to the root of the blades to provide the force to change blades to high pitch*.
The Hydromatic Solution.
All these challenges led Hamilton Standard engineers to an entirely new design solution, which evolved into the Hydromatic propeller. To meet the need for higher actuation forces, engineers designed a system with a larger piston that could be actuated in both directions by hydraulic pressure.
The piston was located in a large dome in front of the propeller, and larger oil pumps and longer cams were developed. With a longer cam, the travel path of the pitch change cam slot could be increased, which permitted a wider range of pitch change. ......Perhaps the most important design change was the addition of a flat portion to the slot which, together with an independent oil supply, provided the feathering feature....The Hydromatic propeller was offered to the airlines in 1937, and was quickly adopted by 21 foreign and domestic commercial carriers. Prominent among the many aircraft equipped with Hamilton Standard Hydromatics were Douglas DC-2s and DC-3s; Boeing 247s, Stratoliners and Clippers; Sikorsky Flying Boats; Martin Clippers; and Lockheed 12s, 14s and Lodestars.
Between 1937 and 1939, the airline safety record improved dramatically, and Hydromatic propellers, with their quick feathering feature, were recognized for helping to make this achievement possible.
UNQUOTE
In reality of course aircraft like the DC2, B247, and M130 had to be retrofitted with fifth generation Hydromatic c/s aircrews and controls which only became available during 1937, long after they had been delivered. Early B247s had been delivered with first generation fixed pitch (f/p) screws, or second generation ground adjustable pitch (a/p) screws. Later models such as the B247D had fourth generation counter weighted c/p screws. None had fifth generation constant speed screws at delivery, and none could have feathering Hydromatic screws until 1937. Of course it wasn't just the US designed aeroplanes mentioned above that were retrofitted as Hamilton Standard patent technology advanced.
From 1935 screws (patented anywhere) which had a constant speed (governor) unit, (a CSU), continually micro varying pitch, to target constant RPM, did not need mass balance counterweights to suddenly flip-flop them from a very low pitch to another much higher pitch. The reverse motion was always hydraulic.
The 'Boys Big book of Wonderplanes' whatever its actual title is a very unreliable source concerning these issues for four reasons.
1) The propulsion technology fitted to even a single airframe varied as time passed.
2) The nuances of adjustable versus variable versus controllable (pitch), each specifying a different and more advanced technology are usually discarded by translators of original sources. So whenever we use a source that is not in the native language of the place of *aircraft* design the information concerning the propulsion system is often false.
3) Many such sources are written by 'aircraft enthusiasts' or 'journalists' who have never understood that five different propulsion systems need to be carefully differentiated.
4) Legally a 'variable pitch' prop is any prop whose pitch the pilot or FE cannot hold constant at will. Some authors therefore describe fifth generation constant speed props as v/p which is legally true, but very confusing.
Consequently, at a simplistic level we, (but especially FS developers), must determine which technology was present at what date, by inspection of photographs of known date, in aeroplanes of known ownership. Deciding what date, and which airline or air force, is going to be simulated is always a key choice during both FS development and subsequent FS use.
Any screw with counter weights around the hub, one for each blade, is a c/p screw.
www.flickr.com/photos/21736736@N08/2100648750 The Bristol Blenheim had 'de Havilland' c/p screws.
www.wwiivehicles.com/unitedkingdom/aircraft/bomber/bristol-blenheim.asp Although less reliable the flat (undomed) nose of the central hydraulic piston is an indicator that the screw is only c/p. This may. or may not, be correctly replicated in 3 view drawings, and they may, or may not, cite a specific owner and a date, and that attribution may, or may not, be true. Note that wwwiivehicles.com is incorrect when it states that the depicted 'de Havilland' screws are v/p. Their pitch can be controlled by the pilot and they are therefore c/p.
www.military-aircraft.org.uk/ww2-fighter-planes/bristol-beaufighter-ww2-fighter.htm The longer domed hydraulic cylinders, and absence of counterweights illustrate that the Bristol Beaufighter by contrast had 'de Havilland' c/s screws. While a 'flat nosed' hydraulic cylinder is probably not quite a certain identification of Hamilton Standard c/p technology, the converse probably is true. If the cylinder is long and domed the technology is c/s.
www.yorkshire-aircraft.co.uk/aircraft/yorkshire/york42/r2764.html The ex Jersey Airways de Havilland Flamingo above had c/s technology from prewar airline delivery.
By viewing a series of photos we can usually tell whether the screw fitted by a particular owner, at a particular date, was c/p. However the problem that FS developers (and historians) face is that between maintenance sessions it may be covered by a prop spinner to reduce co-efficient of profile drag.
commons.wikimedia.org/wiki/File:Bristol_Blenheim_Mk.IV_(BL-200)_K-SIM_11.jpg This is not a new topic here at Calclassic.com. After Jens released his M130 China Clipper I provided a 'Calclassic realism update' to illuminate and demonstrate the difference between the original deliveries in 1935 with c/p screws and the situation after Hydromatic constant speed screws became available for retrofitting in 1937.
The M130 was the first ever series production aeroplane to have c/s Hydromatic screws, but only by retrofitting in 1937. Because MSFS has no support for c/p screws the August 2008 Calclassic M-130 realism update uses v/p screws in the 1935 model. The flip flop from fine to coarse pitch is invoked by our virtual FE at 100 KIAS, but in MSFS we have no way to change back to fine pitch even though the real FE did. I therefore had to write air file code which delivers the correct thrust in the wrong screw pitch during the 1935-37 approach phase. After 1937 with fifth generation Hydromatic screws we can control engine RPM. Being able to set engine RPM independently from fuel flow = power was a huge advance in engines which must not be run 'undersquare' (MAP < rpm/100). This was the generation of piston engines in which the values of MAP and RPM were highly relevant to that need.
In principle Tom's new gauge allows me to provide a better realism update for the 1935 model M-130 which was cruise climbed less efficiently, at constant screw pitch, in lieu of constant engine RPM, but the 'water viscosity bug' in MSFS is so huge that all hydroplanes need 'fake' thrust code to 'work around' that bug anyway, else they will not taxi on water. For that reason I do not contemplate production of a c/p update for the 1935 model M130.
I do not currently contemplate updating the Alfa Romeo A.R.126 (Bristol Pegasus) flight dynamics for the S.M.73 to deliver realistic screw management, but I will bear that possibility in mind for the future. My flight dynamics for the Gnome Rhone Mistral Major powered variety of the Savoia Marchetti S.M.81, designed specifically for use in Africa, including the Eritrean and Ethiopian highlands, available from elsewhere, like the 1935 model M130 use MSFS v/p support to replicate operation of c/p screws. Again during approach my code has to supply real thrust at false screw pitch. All other S.M.81s had only first generation f/p, or second generation a/p, screws.
During FS development of an aircraft with a/p screws the FD author chooses which value in the a/p range will be used constantly in MSFS. In real life the a/p screw would be adjusted by the FE on the ground to be coarser in thin air departing high altitude runways in the Ethiopian highlands so that it could 'bite' the same mass of air as a finer screw departing Rome.
Tom's new fourth generation 'c/p gauge' thus also (potentially) solves the problem of realistic simulation of second generation a/p screws which were even more widespread than fourth generation c/p screws. The handling notes, (but more likely an included tutorial), could indicate the % position of the lever for runways of given altitude density. Before engine start, we could select the correct (ground only) adjustable pitch for the weather and location, using cockpit levers or push rods, (usually on a pop up window providing just the a/p = c/p gauge), in lieu of our FE standing on a ladder and using the relevant tool on the hub collars.
During the 1930s many expensive aeroplanes misrepresented in MSFS as having f/p screws really had a/p screws. In real combat situations a/p screws were rotated according to the load to be lifted for a specific mission. Full fine if very heavy versus the runway length available, else much coarser to increase cruise TAS on that mission, which is the same thing as increasing range (combat radius) with the given bomb load, or supply load, or paratroops.
Thus the two settings, full fine and full coarse, which are all we need to replicate two position c/p screws from the 1930s, are not the only way we will use Tom's new gauge in FS9 in the future. Screw designers outside the US soon created three pitch c/p screws with settings for take off, climb and cruise. When we simulate relevant aircraft we will need to set specified % values away from the max and min, which are not necessarily 'mid'. Soviet Bloc c/p screws, manufactured well into the modern era, have many such settings, as did some earlier German c/p screws. The way c/p screws were used in US aviation in the 1930s is not the only simulation problem 'potentially resolved' by such a gauge.
However there is a danger everybody will miss the point. The new gauge will not convert c/s air files into c/p air files, or a/p air files. The new gauge only enables the possibility of creating realistic new air files for second generation a/p, and fourth generation c/p screw propulsion, along with the handling notes which explain when to set what lever / push rod %. Standard operating procedures differed from nation to nation using identical technology. Tom's new gauge could set a specified 'lever %' using an existing c/s air file, but both RPM and thrust would be false versus current IAS windmilling the same motoring screw in the absence of the constant speed unit. The FD author has to provide different air file code that models what happens in the absence of a csu. The flight (screw) dynamics are different, (the air file must be different) with, and without, a csu in the power train.
There is much more to this than just adding one gauge to an existing panel.cfg, but Tom and I are working towards a 'technology demonstrator' for use in FS9 so that the skills involved, and the problems fourth generation (U.S patent) c/p screws caused, compared to (French patent) third generation v/p screws, can be studied and overcome during simulation. Without understanding the problems fourth generation c/p screws invoke it is not possible to understand why fifth generation c/s screws are so superior, to both third generation v/p screws, and fourth generation c/p screws.
To keep things simple the first 'Calclassic technology demonstrator release will allow simulation only of Hamilton Standard two pitch c/p screws. Tom and I 'may' follow that up with a 'multi-pitch technology demonstrator', but that may come much later, or not at all. After the release of the 'technology demonstrator' it is up to other developers to study what is involved and make use of the new opportunity in future releases. I imagine relatively few existing FD will be updated, however inaccurate using the wrong type of propulsion makes them.
Now turning to potential misunderstandings and other historical issues already raised in this thread......
Volker has described the (French) Ratier patent v/p screw in the D.H.88 Comet. Puzzlingly he said,
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Here's the line from the aircraft.cfg:
fixed_pitch_beta_auto_cruise= 35,130 //For AutoCruise, angle and airspeed at which to switch from default pitch
Seems like at some point, the prop automatically switches to 'AutoCruise', even though I have not identified the trigger.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
As Microsoft's REM states the trigger is pilot flying allowing / promoting profile = windmill drag on the operating plate to reach 130 KIAS. The fine pitch lock is withdrawn and the screw flips to 35 degrees pitch, for high velocity cruising during the race to Australia. It cannot be reset without using the bicycle pump again on the ground between flights, which is why it is a variable pitch (v/p) prop and not a controllable pitch (c/p) prop. Once the D.H.88 pilot allows profile = windmill drag to increase beyond the trigger IAS he is stuck with coarse pitch, and very low engine RPM, even if he needs to go around.
However a third generation (French) v/p screw only ever revs engines down. Consequently a v/p screw can never cause sudden engine over speed and a v/p screw can never cause sudden undersquare running by sudden elevation of RPM > MAP multiplied by 100. A third generation v/p screw never allows the pilot to select FINE PITCH causing either of those engine failure modes.
The arrival of fourth generation c/p screws gave humans access to new gross engine mismanagement possibilities and some aircraft designers soon believed that c/p screws might cause more accidents than they prevented. The whole issue of (avoiding) undersquare running dates from the invention and widespread deployment of the c/p screw in the mid 1930s, not the arrival of the c/s screw in 1937.
Because the August 2008 Calclassic realism update for the original 1935 model M130 had to use v/p technology to misrepresent c/p technology we must not allow our profile drag to reach 100 KIAS until we are ready to initiate enduring cruise climb. From the Calclassic 1935 model aircraft.cfg
[propeller]
propeller_type=1
propeller_blades=3
gear_reduction_ratio=1.5
propeller_diameter=11.1
propeller_moi=40
fixed_pitch_beta=15
fixed_pitch_beta_auto_cruise= 20,100 <<<<<<<<<<<<<<<
As we reach 100 KIAS our virtual FE moves all four virtual prop control levers from 15 (virtual) degrees to 20 (virtual) degrees screw pitch. Those pitches are not real. The data inside the air file 'labeled' as relating to those pitches is 'realistic data' for the two real world pitches. The engine is revved down hard using the real criterion used by the real FE.
What is missing from MSFS is the ability to rev them up hard again for the approach. From now on, with a c/p gauge on a pop up window using new 'matched' c/p air files, (but not for the M130 or other hydroplanes), we will be able to decide when to rev up hard. Only when we can watch engine RPM 'rev up hard' *at constant throttle and MAP* inside MSFS will we be able to understand why c/p screw technology unfortunately made undersquare running of vulnerable types of engine possible for the first time. That issue drives how we must sequence variable geometry targets and IAS targets as we prepare to 'rev up hard' having carefully set MAP to a value that will still be oversquare, even after we 'rev up hard'.
FS9 added support for third generation v/p screws, but fourth generation c/p screws, for which MSFS and CFS have no support, dominated aviation from about 1935 to the middle of WW2. Expensive c/s Hydromatic screws, that could also 'feather' airscrews to extremely coarse pitch after engine failure, remained relatively rare. That was especially true in single engine aeroplanes. Additionally all the real designers of fifth generation c/s screws struggled to create c/s screws which could control RPM accurately over a very large range of pitches to encompass both low windmill drag = IAS during take off, and huge windmill drag = IAS on the screw in 'high speed' combat. Yet no version of CFS has support for the ubiquitous c/p propulsion system that dominated the first half of WW2.
Early c/s screws had fragile CSUs, or had CSUs that only worked within part of the range of pitch motion of the screw fitted. Consequently combat aircraft, and some others, delivered 1937 - 1943, had a lever to revert them to c/p mode for particular types of high stress combat manoeuvre, and as a back up in case of csu failure. To access extreme and available screw pitches, c/s mode had to be rejected, and c/p mode had to be invoked. Once a combat aeroplane had 'c/p mode reversion' it tended to be retained even after c/s screws were 'reliable' and could control the whole pitch range. So for instance most, and maybe all, versions of the Curtiss P-40 with Allison engines had c/p reversion and pilots who were used to c/p screws seem to have used the reversion mode much more than we might expect. Tom's gauge will eventually be adapted to allow 'c/p mode reversion' from c/s mode, but new relevant air file content will again be needed.
Eventually Curtiss developed an electronic c/s hub. The ramifications of Hamilton Standard hydraulic patent versus Curtiss electric patent issues were addressed in some detail within last year's B367/B377 Calclassic realism update and included history / tutorial / handling notes. Hamilton Standard screws still struggled to control very large screws, (which had high moments of inertia), across a wide velocity (TAS) and screw pitch range, with fatal results, but Curtiss electronic c/s screws had other issues which that Calclassic B367 and B377 realism updates, history, tutorial and handling notes addressed and allowed us to understand.
The Rolls Royce Merlin I engine, designed to power the Fairey Battle I, delivered from early 1937, could drive only very primitive one piece wooden fixed pitch screws. However de Havilland had obtained a license to manufacture fourth generation Hamilton Standard c/p screws back in 1935, and they procured a license to also manufacture fifth generation c/s screws during 1938. Like Hamilton Standard, de Havilland always fitted metal blades in both types of screw. Delivery of Spitfire Is with 'de Havilland' two position c/p screws, driven by Merlin II engines, began during the late spring of 1939. 'de Havilland' c/p screws were fitted to the 78th Spitfire I onwards.
However in the UK Rotol (later Dowty) also procured a license to manufacture Hamilton Standard c/s hubs, but fitted with wooden blades. Delivery of Spitfire Is with Merlin III engines driving Rotol c/s screws began in November 1939. Deliveries of Spitfire Is with 'de Havilland' c/s screws had already been underway for several weeks. During the competitive trials in November 1939 the wooden Rotol blades made the Spitfire I up to 2% slower at very low level, but had little impact at typical combat levels. Rotol wooden blade c/s screws can be identified by their very rounded (slightly over size) spinner. When all were running on airline grade 87 Octane AVGAS either c/s screw achieved an advantage of 730 ft/min VSI versus the two pitch c/p Spitfire I at sea level.
Although the forthcoming 'Calclassic c/p technology demonstrator' will have little in common with a Spitfire it will explicitly allow us to simulate and understand why c/s technology can add 730 ft/min to VSI with no change to the available power from the engine. It does *not* explicitly relate to more efficient traction as some histories suggest. It relates to the way in which full coarse pitch reduces engine RPM, which reduces turbine RPM, which reduces available MAP from a single speed gear driven supercharger.
Consequently all two pitch (Merlin II) Spitfires were retrofitted with Merlin III engines driving de Havilland c/s screws from June 1940 onwards. Thus the RAF flew two position c/p screw Spitfire Is for over a year. The last operational c/p Spitfire I was converted to c/s propulsion in August 1940 and the last Hurricane I not until September or October 1940. The RR Merlin II had c/p controls to operate a 'de Havilland' c/p screw, but could still mount an f/p screw, and the RR Merlin III had cockpit controls for a 'de Havilland' c/p screw and either (DH metal or Rotol wooden) type of c/s screw.
Fairey Battles (unofficially) bore the mark number of their Merlin, which (almost) denoted the type of screw technology fitted.
ww2today.com/air-reconnaissance-over-the-western-front The flat nosed hydraulic cylinder and the counter weights in the photo above indicate that the photographed aeroplane is a Battle II or Battle III with a Merlin II or Merlin III engine driving a 'de Havilland' c/p screw. The openly declared squadron number within the livery dates the photo to August 1939 or earlier. The short video on the same page shows more Battle IIs or IIIs with c/p screws in France after August 1939. Their 1939 Hurricane I escort still has a Merlin II engine driving a primitive two blade wooden f/p screw, but the British Expeditionary Force in France flew Hurricanes with all four types of 'British' airscrew propulsion before evacuation to the UK in June 1940.
By contrast to the Battle, the mark numbers of Spitfires and Hurricanes tell us nothing about the engine or screw technology. The interim and transient Merlin II could drive a 'de Havilland' c/p screw, but had nothing to do with the Spitfire IIs and Hurricane IIs that both made their combat debut during the Battle of Britain. They both had much more powerful later model (XII or XX) Merlin engines with (usually Rotol wooden blade) c/s screws from time of manufacture.
Thus Hurricane Is with c/p screws attached to Merlin II or Merlin III engines were in use from about May 1939 to October 1940. The Air Marshalls of the RAF had earlier insisted that c/p technology was only needed in multi engine bombers and single engine dive bombers. They all had 'de Havilland', c/p screws from early 1937 onwards. Thus the Blackburn Skua 'fighter - dive bomber' had 'modern' U.S. propulsion technology in the form of a 'de Havilland' c/p screw a year before any Spitfire, but even the Fleet Air Arm, (part of the RAF until May 1939), only started to introduce c/p screws in the Blackburn Skua a year after PAA were removing them as outdated from their M-130 China Clippers.
The licensing of Hamilton Standard airscrew technology by Isotta Fraschini, Fiat and Alfa Romeo is documented in my various 'Italian aircraft' tutorials within relevant releases available elsewhere. Supply of the latest US propulsion technology to Mitsubishi and Nakajima was essential to increasing the strike range of IJN aircraft, all of which had the latest propulsion courtesy of Hamilton Standard by the end of 1937, aiding IJN ability to strike deep into China and all along the Chinese coast from their JNAS in Formosa, (now called Taiwan). Four years later that US technology transfer would be used by the IJN to enable long range strike against a much wider range of targets.
Germany failed to develop worthwhile radial engines and so BMW obtained a license to build the P&W Hornet under license, carefully rebranded for domestic consumption as the 'BMW 132'. The Hornet soon powered most Ju 52/3ms. 'BMW' Hornets drove only a/p screws, hence the poor cruising velocity and therefore poor range of the Ju52/3m.
upload.wikimedia.org/wikipedia/commons/7/7d/Ju_52_Motoren.jpg The standard Ju52/3m blades can be rotated and restrained to the chosen pitch only on the ground. They are individual metal blades inserted into a hub collar, but the hub has no counter weights and the projecting prop shaft cover is not a hydraulic cylinder.
www.airliners.net/photo/Lufthansa-(Berlin-Stiftung)/Junkers-Ju-52-3mg8e/1361488/L/ Aircraft on the airshow circuit today have usually been re-engined, and in this case we can clearly see that Hamilton Standard three blade c/p screws have been retrofitted to different engines during the modern era.
Again it comes down to owner and date. If BMW could not deliver efficient propulsion during the 1930s export customers sometimes specified a power train from elsewhere for their Junkers Ju52/3ms, or soon retrofitted one. British Airways' Ju52/3ms all had BMW 132 engines with a/p screws when delivered in 1937, but during the Battle of Britain they were re-engined with Pratt & Whitney Wasps driving c/s screws for service with BOAC in Africa. All Ju52/3m deliveries to Argentina originally, or eventually, had the same power train, again with engines, screws and spares sourced from the USA, not Germany. AB Transport in Sweden flew the Ju 52/3m-1 variant, which had P&W S1E-G Hornets with c/s screws from delivery in 1938, but Sweden had to source the power train from the USA. Italian airlines like Ala Littoria also rejected BMW technology and fitted Piaggio engines with Hamilton Standard c/p screws manufactured in Italy to their Ju52/3ms. Similarly SAA in South Africa and DETA in Portuguese Africa did not have to make do with the screw technology inflicted by BMW on Lufthansa, but DDL in Denmark and e.g Det Norske in Norway, did.
Unlike Italy, Japan and the UK, Germany does not seem to have licensed Hamilton Standard c/p or c/s technology. They (soon) developed their own superior c/p screws so that many / most German c/p screws could be 'many pitch'. Germany also developed indigenous c/s technology.
Most of the problems historians (and FS developers) face in understanding which airframes, had which propulsion technology, at which date, stems from nationalism, via careful rebranding of identical US technology as 'de Havilland' or 'Rotol' or 'Fiat' or 'Alfa Romeo' or 'Mitsubishi' or 'Nakajima' when they are all just Hamilton Standard hydraulic hub screws being built under a royalty license.
Hamilton Standard screws were also built in huge numbers in the USSR for use with the Wright Cyclone and the Hispano Suiza V-12, also built there in huge numbers under royalty licences. However the Soviet Union went on to develop its own c/p screws, (or maybe copied German technology after 1945), and 'many pitch' c/p screws were mass produced in the Soviet Bloc for use in single engined public transport aircraft well into the modern era of aviation history. The counter weights are different, but in combination with the short hydraulic cylinder we can tell that these are both classic / modern era 'Soviet' c/p screws.
www.flickr.com/photos/flyingaxel/2830711885/sizes/l/in/photostream/ www.flickr.com/photos/aerofossile2012/5140939508/ Tom and I hope to make a fourth generation 'two pitch' c/p screw 'technology demonstrator' available 'soon'.
FSAviator.