Post by volkerboehme on Oct 19, 2008 15:50:09 GMT -5
As has already been explained, most piston propliners still used for public transport, including cargo operations, have engines no more powerful than the R-2800-CB16/17 that suffer little penalty from use of 100/130 Octane. Crucially the R-2800 will tolerate use of high blower when 100/130 Octane is in use. The R-2800 was designed so long ago that even the final variants were designed around the assumption that most commercial users would not have access to what was then 'military grade' 115/145 octane fuel in most locations. Those who had access could quickly reconfigure the R-2800-CB16 engine as a CB17 so that it could produce extra power when using 115/145 Octane. My 'CB16' flight dynamics have the correct air file curves for 100/130 Octane whilst my 'CB17' flight dynamics have the correct curves for 115/145 Octane. I supply CB16 versus CB17 flight dynamics and matched handling notes for both the DC6B v DC6A and for the CV34 v CV44.
No CV24, M202 or M404 owners ever configured their R-2800 engines as CB17s to make use of 145 Octane and to the contrary many soon removed the high blowers from their CB16s turning them into R-2800-CB3s.
I have not, and do not intend to replicate dual capability for the R-3350 or R-4360 powered propliners. Too few remain in public transport service for reasons mentioned by others and which I will now attempt to illustrate in greater detail below. I will use this opportunity to address the issue of other 'restricted power' propliner cases and the wider history of the need to 'make do' with low octane fuels.
Aircraft and engine certification is highly specific to individual variants so when you say;
<<For example, the R-3350 are today limited to 52" MAP>>
That may be true for a particular variant of that engine, in a particular variant of a particular aeroplane, and as a condition of employment for a particular employee, in association with an aeroplane relegated to a particular non public transport role, but it is sure to be false as a generic statement.
Let's consider two specific cases, both relating to R-3350 public transport certification. Consider the DC-7 and the DC-7B.
Regardless of the sub variant of R-3350-DA engine employed use of anything less than 145 Octane AVGAS is simply not authorised in the DC-7. Nobody ever applied for such certification, potentially just because nobody was willing to pay for the trials. However the DC-7 may be powered by the R-3350-DA2 engine and that may be significant.
To the contrary the DC-7B does have a schedule for 130 Octane, but the DC-7B must be powered by the R-3350-DA4 or later EA series engines. Somebody (presumably Wright) paid for (only) those late production engines to be certificated for use with 130 Octane. I surmise that Wright had already done company trials which caused them not to apply for the R-3350-DA2 and therefore caused Douglas not to apply for the DC-7 to have authority to use 130 Octane.
For the DC-7B which can lawfully be powered only by R-3350-DA4 or later series engines;
Using 145 Octane TOGA rating at sea level is 3250bhp at 2900 RPM at 56.5 MAP
Using 130 Octane TOGA rating at sea level is 2880bhp at 2900 RPM at 51.0 MAP
The TOGA application limit falls from 120 seconds to 90 seconds (from throttle up). Much more importantly use of R-3350 high blower is forbidden when using less than 115/145 Octane. All the high blower ratings are lost. The high altitude envelope is lost and cruising velocity is consequently greatly restricted. Max gross is reduced to 117,900lbs or less and METO power is also reduced.
So what are the implications for MSFS users who seek realism?
The issues are in reality just the usual ones. No one can extract realism from flight dynamics, however good or bad, without handling notes which mandate the inputs that must be made during each phase of the flight, and the limits that must be observed. The issue is not primarily one of flight dynamics. If we reduce weight to 117,900lbs and apply 51 inches instead of 56.5 for take off we will obtain a 'somewhat realistic' simulation of revised max gross 130 octane take off in a DC-7B using my existing FD. However to have identical realism for both fuels we need to swap between FD created to be equally realistic with either fuel which is what I have provided for the DC6B/A and CV34/44 as CB16/17 specific releases.
However.......
a) In my standard DC7B FD blower switching is automated (our virtual FE decides when it is appropriate). We must restrict our operating altitude; or procure alternative FD with manual blower switching and take care not to switch to HI gear.
b) MSFS is limited by an air file design that is 20 years old. The air file requires authoring of very simplistic 'segmented curves'. Between the numerically restricted vertices of the segmented curves errors maximise because the straight line no longer approximates the true curve. The 'art' of FD authoring is deciding where 'realism' will maximise and where it will minimise; using simplified handling notes to direct the process, both during authoring of the air file, and then during subsequent use of the air file.
Consequently application of 56.5 MAP at 2900 RPM at SL in ISA will deliver very close to 3250bhp, but applying 51 MAP @ 2900 RPM will approximate 2880bhp much less closely. 51 MAP @ 2900 RPM will not co-incide with a vertex in my DC-7B R-3350-DA4 air file code because my code assumes 145 Octane.
The upper power curves for 145 and 130 octane are different and they are as different as writing two different sets of FD for two different engines. To have equal realism, when simulating 130 octane, DC7B FD specific to that case would need to be produced, with each air file vertex at the appropriate conjunction of MAP and RPM for 130 octane accompanied by handling notes directing the user to apply those specific real world conjunctions. Creating 130 octane FD and handling notes from 145 octane FD and handling notes requires about 50% of the time taken to produce the original 145 octane FD and handling notes. It is not just the take off case that differs.
For instance in the DC-7B;
Using 145 Octane METO rating at sea level is 2700bhp at 2600 RPM at 49.0 MAP
Using 130 Octane METO rating at sea level is 2380bhp at 2600 RPM at 41.5 MAP
Although I do not intend to produce 'reduced power' flight dynamics and handling notes for R-3350 or R-4360 powered aircraft I have already done so for all other 'relevant' engines. The situation for those is as follows.
Partly in order to illustrate that this issue is not a 'modern' issue my Goose handling notes address the issue of variable octane, because for 'bush planes' variable fuel quality away from 'airports' and anywhere in the 'underdeveloped world' has been an issue since the 1930s.
My Goose handling notes specify;
<<This aircraft may be operated using all or part 80 Octane AVGAS but during LOW OCTANE operation MAP must NEVER EXCEED 33.5 inches and RPM must NEVER EXCEED 2200 until fuel tanks have been drained and pure 87 Octane or better loaded. Do NOT use full fine screws for 80 Octane departure.>>
I included those low octane R-985 handling notes for the Goose because in the absence of high gear blowers it is that simple. TOGA time limit does not vary, METO does not vary, gross weight is not reduced, but take off run is extended. I doubt that my singular Goose FD for use with either octane fuel replicate the penalty of using 80 Octane fuel with any precision, (and certainly won't from over viscous MS water), but the issues can be confronted and the need to moderate both MAP and RPM realistically in relation to many older engines may be experienced.
Some of my propliner FD address 'relegation with age' and the change of role issue.
For instance the Canadair C-4 Argonaut handling notes specify;
***********************************
BOAC (launch customer) normal cruise:
BOOST = 5
RPM = 2350
Check RADIATORS < 100C
Plan 1800 PPH
Note: yields 256 KTAS at FL250
****************************
BMA (second hand user) normal cruise:
BOOST = 2.5
RPM = 2200
Check RADIATORS < 100C
Plan 1400 PPH
Note: yields 230 KTAS at FL250
****************************
Long haul scheduled flying in the 1950s and and medium haul inclusive tour work in the 1960s required different cost controls to maximise profit. Both airlines needed to use HI blower, but for different reasons. BOAC needed to market the high cruising velocity of the Argonaut to attract premium fare passengers, but were happy with low utilisation. BMA needed a single crew to make two rotations per day from the UK to the Mediterranean resorts. That required cruising velocities obtainable only in thin high air in order to deliver the necessary low fare seat miles per day from just one rostered crew. So both airlines used 145 octane fuel and employed similar techniques before and after cruise at high level, but by the 1960s inclusive tour propliners cruised no faster than was necessary to deliver the desired daily rotations within the daily crew hours limitations which were then subject only to union agreements and not to UK government regulation.
The 'restricted power' operating cases are fairly well catered for, but only if I deemed the 'restricted power' case to have had sufficient significance and usage in the real world to justify the extra work involved in creating two sets of flight dynamics and/or handling notes. Use of R-3350 and R-4360 engines with 130 octane fuel is, and always has been, abnormal, but for the R-2800 using 130 octane was always the norm in commercial service with 145 octane the norm in military service, so I created both sets of FD and both sets of handling notes for relevant versions of the R-2800. Older engines like the R-2000 derived no benefit from using 145 octane. For the Argonaut and the Goose I created only one set of FD and handling notes, but placed air file segmented curve vertices to deliver 'realistic' output at both relevant conjunctions, because that was possible for the R-985 and the Merlin.
Engines like the R-1830 used in the M130 and R-2600 used in the B314 have similar issues to the R-985, but PAA, BOAC and the USN were always supplied with the highest grade fuels and those boats never had to make do with low octane fuel, however that was defined at the time.
The wider picture is that 145 Octane was an oil superpower resource. Ditto for lower octane fuel timeframe by timeframe in aviation history. Only nations which were granted a favourable trading status were granted the right to buy 'military grade fuel' from an oil superpower. The need to make do with 'low' octane fuel is not modern, but for most of aviation history the reasons were different. Nations that were not abiding by restrictions imposed by an oil superpower on their internal and external political and trading behaviour often had to make do with aeroplanes and engines that could cope with 'low octane' fuel and they had to make do with the resulting restricted performance and consequences. Whether those aeroplanes were for combat or transport use.
Producing 'realistic' FD and handling notes for combat simulation is a nightmare. The following, although off topic here, may help to illustrate the complexity and how quickly things may change from a real world and MSFS user perspective.
The octane rating of fuel supply in the logistics chain has been a huge issue throughout the history of the piston aero engine. In the late 1930s France made the mistake of assuming that if it was allowed to import the latest American combat aircraft with engines that required high octane fuel to deliver TOGA and WEP the United States government would automatically allow US oil companies to supply it. They did not. The 'Boys Book of Wonderplanes' will tell us that the Curtiss P-36s of the French Air Force employed during the Battle of France had '1200hp engines' superior to the '1100hp engines' in the Bf-109E, but of course they did not. France could only produce 87 Octane fuel in its refineries and could not run the latest R-1820 Cyclone or R-1830 Twin Wasp engines at more than 1050hp (their METO rating). To produce TOGA or WEP both required 100 Octane and the US government withheld it.
RAF units based in France, for the defence of France in June 1940, were supplied by France, regardless of engine type and prior command structure. They all received only 87 Octane. A Hurricane I running on 87 Octane was limited to only its rated power of 1030hp (no WEP available), much less than a Bf-109E. After evacuation to RAF Biggin Hill and filled with UK or US refined 100 Octane the same engine could be overboosted to about 1225hp (WEP), much more than a Bf-109E, during the subsequent Battle of Britain.
For the poor old RAF Lysander pilot the situation was reversed. In the French Army logistics chain in the morning he received 87 Octane and could deploy 890hp WEP for five minutes, but on evacuation to RAF Gatwick, suddenly back in the British Army logistics chain he could obtain only 83 Octane in the afternoon and lost the ability to generate WEP and was restricted to TOGA power and only for TOGA duration. If realism is desired a move of less than 100 miles in a day involving a change of fuel supply invokes different MSFS flight dynamics, but especially requires different handling notes. Biggin Hill and Gatwick are a few minutes flying time apart, but it is the fuel available that matters and that may have little to do with the date of the simulation. The octane rating of fuel available is mostly about logistics and is highly relevant to simulation realism, (or any wider historical comparative evaluation of aircraft capability), at any date.
FSAviator.
No CV24, M202 or M404 owners ever configured their R-2800 engines as CB17s to make use of 145 Octane and to the contrary many soon removed the high blowers from their CB16s turning them into R-2800-CB3s.
I have not, and do not intend to replicate dual capability for the R-3350 or R-4360 powered propliners. Too few remain in public transport service for reasons mentioned by others and which I will now attempt to illustrate in greater detail below. I will use this opportunity to address the issue of other 'restricted power' propliner cases and the wider history of the need to 'make do' with low octane fuels.
Aircraft and engine certification is highly specific to individual variants so when you say;
<<For example, the R-3350 are today limited to 52" MAP>>
That may be true for a particular variant of that engine, in a particular variant of a particular aeroplane, and as a condition of employment for a particular employee, in association with an aeroplane relegated to a particular non public transport role, but it is sure to be false as a generic statement.
Let's consider two specific cases, both relating to R-3350 public transport certification. Consider the DC-7 and the DC-7B.
Regardless of the sub variant of R-3350-DA engine employed use of anything less than 145 Octane AVGAS is simply not authorised in the DC-7. Nobody ever applied for such certification, potentially just because nobody was willing to pay for the trials. However the DC-7 may be powered by the R-3350-DA2 engine and that may be significant.
To the contrary the DC-7B does have a schedule for 130 Octane, but the DC-7B must be powered by the R-3350-DA4 or later EA series engines. Somebody (presumably Wright) paid for (only) those late production engines to be certificated for use with 130 Octane. I surmise that Wright had already done company trials which caused them not to apply for the R-3350-DA2 and therefore caused Douglas not to apply for the DC-7 to have authority to use 130 Octane.
For the DC-7B which can lawfully be powered only by R-3350-DA4 or later series engines;
Using 145 Octane TOGA rating at sea level is 3250bhp at 2900 RPM at 56.5 MAP
Using 130 Octane TOGA rating at sea level is 2880bhp at 2900 RPM at 51.0 MAP
The TOGA application limit falls from 120 seconds to 90 seconds (from throttle up). Much more importantly use of R-3350 high blower is forbidden when using less than 115/145 Octane. All the high blower ratings are lost. The high altitude envelope is lost and cruising velocity is consequently greatly restricted. Max gross is reduced to 117,900lbs or less and METO power is also reduced.
So what are the implications for MSFS users who seek realism?
The issues are in reality just the usual ones. No one can extract realism from flight dynamics, however good or bad, without handling notes which mandate the inputs that must be made during each phase of the flight, and the limits that must be observed. The issue is not primarily one of flight dynamics. If we reduce weight to 117,900lbs and apply 51 inches instead of 56.5 for take off we will obtain a 'somewhat realistic' simulation of revised max gross 130 octane take off in a DC-7B using my existing FD. However to have identical realism for both fuels we need to swap between FD created to be equally realistic with either fuel which is what I have provided for the DC6B/A and CV34/44 as CB16/17 specific releases.
However.......
a) In my standard DC7B FD blower switching is automated (our virtual FE decides when it is appropriate). We must restrict our operating altitude; or procure alternative FD with manual blower switching and take care not to switch to HI gear.
b) MSFS is limited by an air file design that is 20 years old. The air file requires authoring of very simplistic 'segmented curves'. Between the numerically restricted vertices of the segmented curves errors maximise because the straight line no longer approximates the true curve. The 'art' of FD authoring is deciding where 'realism' will maximise and where it will minimise; using simplified handling notes to direct the process, both during authoring of the air file, and then during subsequent use of the air file.
Consequently application of 56.5 MAP at 2900 RPM at SL in ISA will deliver very close to 3250bhp, but applying 51 MAP @ 2900 RPM will approximate 2880bhp much less closely. 51 MAP @ 2900 RPM will not co-incide with a vertex in my DC-7B R-3350-DA4 air file code because my code assumes 145 Octane.
The upper power curves for 145 and 130 octane are different and they are as different as writing two different sets of FD for two different engines. To have equal realism, when simulating 130 octane, DC7B FD specific to that case would need to be produced, with each air file vertex at the appropriate conjunction of MAP and RPM for 130 octane accompanied by handling notes directing the user to apply those specific real world conjunctions. Creating 130 octane FD and handling notes from 145 octane FD and handling notes requires about 50% of the time taken to produce the original 145 octane FD and handling notes. It is not just the take off case that differs.
For instance in the DC-7B;
Using 145 Octane METO rating at sea level is 2700bhp at 2600 RPM at 49.0 MAP
Using 130 Octane METO rating at sea level is 2380bhp at 2600 RPM at 41.5 MAP
Although I do not intend to produce 'reduced power' flight dynamics and handling notes for R-3350 or R-4360 powered aircraft I have already done so for all other 'relevant' engines. The situation for those is as follows.
Partly in order to illustrate that this issue is not a 'modern' issue my Goose handling notes address the issue of variable octane, because for 'bush planes' variable fuel quality away from 'airports' and anywhere in the 'underdeveloped world' has been an issue since the 1930s.
My Goose handling notes specify;
<<This aircraft may be operated using all or part 80 Octane AVGAS but during LOW OCTANE operation MAP must NEVER EXCEED 33.5 inches and RPM must NEVER EXCEED 2200 until fuel tanks have been drained and pure 87 Octane or better loaded. Do NOT use full fine screws for 80 Octane departure.>>
I included those low octane R-985 handling notes for the Goose because in the absence of high gear blowers it is that simple. TOGA time limit does not vary, METO does not vary, gross weight is not reduced, but take off run is extended. I doubt that my singular Goose FD for use with either octane fuel replicate the penalty of using 80 Octane fuel with any precision, (and certainly won't from over viscous MS water), but the issues can be confronted and the need to moderate both MAP and RPM realistically in relation to many older engines may be experienced.
Some of my propliner FD address 'relegation with age' and the change of role issue.
For instance the Canadair C-4 Argonaut handling notes specify;
***********************************
BOAC (launch customer) normal cruise:
BOOST = 5
RPM = 2350
Check RADIATORS < 100C
Plan 1800 PPH
Note: yields 256 KTAS at FL250
****************************
BMA (second hand user) normal cruise:
BOOST = 2.5
RPM = 2200
Check RADIATORS < 100C
Plan 1400 PPH
Note: yields 230 KTAS at FL250
****************************
Long haul scheduled flying in the 1950s and and medium haul inclusive tour work in the 1960s required different cost controls to maximise profit. Both airlines needed to use HI blower, but for different reasons. BOAC needed to market the high cruising velocity of the Argonaut to attract premium fare passengers, but were happy with low utilisation. BMA needed a single crew to make two rotations per day from the UK to the Mediterranean resorts. That required cruising velocities obtainable only in thin high air in order to deliver the necessary low fare seat miles per day from just one rostered crew. So both airlines used 145 octane fuel and employed similar techniques before and after cruise at high level, but by the 1960s inclusive tour propliners cruised no faster than was necessary to deliver the desired daily rotations within the daily crew hours limitations which were then subject only to union agreements and not to UK government regulation.
The 'restricted power' operating cases are fairly well catered for, but only if I deemed the 'restricted power' case to have had sufficient significance and usage in the real world to justify the extra work involved in creating two sets of flight dynamics and/or handling notes. Use of R-3350 and R-4360 engines with 130 octane fuel is, and always has been, abnormal, but for the R-2800 using 130 octane was always the norm in commercial service with 145 octane the norm in military service, so I created both sets of FD and both sets of handling notes for relevant versions of the R-2800. Older engines like the R-2000 derived no benefit from using 145 octane. For the Argonaut and the Goose I created only one set of FD and handling notes, but placed air file segmented curve vertices to deliver 'realistic' output at both relevant conjunctions, because that was possible for the R-985 and the Merlin.
Engines like the R-1830 used in the M130 and R-2600 used in the B314 have similar issues to the R-985, but PAA, BOAC and the USN were always supplied with the highest grade fuels and those boats never had to make do with low octane fuel, however that was defined at the time.
The wider picture is that 145 Octane was an oil superpower resource. Ditto for lower octane fuel timeframe by timeframe in aviation history. Only nations which were granted a favourable trading status were granted the right to buy 'military grade fuel' from an oil superpower. The need to make do with 'low' octane fuel is not modern, but for most of aviation history the reasons were different. Nations that were not abiding by restrictions imposed by an oil superpower on their internal and external political and trading behaviour often had to make do with aeroplanes and engines that could cope with 'low octane' fuel and they had to make do with the resulting restricted performance and consequences. Whether those aeroplanes were for combat or transport use.
Producing 'realistic' FD and handling notes for combat simulation is a nightmare. The following, although off topic here, may help to illustrate the complexity and how quickly things may change from a real world and MSFS user perspective.
The octane rating of fuel supply in the logistics chain has been a huge issue throughout the history of the piston aero engine. In the late 1930s France made the mistake of assuming that if it was allowed to import the latest American combat aircraft with engines that required high octane fuel to deliver TOGA and WEP the United States government would automatically allow US oil companies to supply it. They did not. The 'Boys Book of Wonderplanes' will tell us that the Curtiss P-36s of the French Air Force employed during the Battle of France had '1200hp engines' superior to the '1100hp engines' in the Bf-109E, but of course they did not. France could only produce 87 Octane fuel in its refineries and could not run the latest R-1820 Cyclone or R-1830 Twin Wasp engines at more than 1050hp (their METO rating). To produce TOGA or WEP both required 100 Octane and the US government withheld it.
RAF units based in France, for the defence of France in June 1940, were supplied by France, regardless of engine type and prior command structure. They all received only 87 Octane. A Hurricane I running on 87 Octane was limited to only its rated power of 1030hp (no WEP available), much less than a Bf-109E. After evacuation to RAF Biggin Hill and filled with UK or US refined 100 Octane the same engine could be overboosted to about 1225hp (WEP), much more than a Bf-109E, during the subsequent Battle of Britain.
For the poor old RAF Lysander pilot the situation was reversed. In the French Army logistics chain in the morning he received 87 Octane and could deploy 890hp WEP for five minutes, but on evacuation to RAF Gatwick, suddenly back in the British Army logistics chain he could obtain only 83 Octane in the afternoon and lost the ability to generate WEP and was restricted to TOGA power and only for TOGA duration. If realism is desired a move of less than 100 miles in a day involving a change of fuel supply invokes different MSFS flight dynamics, but especially requires different handling notes. Biggin Hill and Gatwick are a few minutes flying time apart, but it is the fuel available that matters and that may have little to do with the date of the simulation. The octane rating of fuel available is mostly about logistics and is highly relevant to simulation realism, (or any wider historical comparative evaluation of aircraft capability), at any date.
FSAviator.