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Big Piston Aero Engine using today's technology


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#1 Wuzak

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Posted 13 April 2013 - 01:08

This question was asked on a WW2 aircraft forum:

If a WWII fighter engine were produced with today's technology, what would we get?
It's easy to forget that the technology that produced the great aero-engines of WWII is seventy years in the past. On a power to capacity ratio the motorcycle in my carport makes a Rolls Royce Griffin look puny. So, forget the jet engine ever happened- if we designed an engine of the same dimensions as those used in the Spitfire, 109 or Thunderbolt with today's technology, how much power could we get? What would be the limiting factors? Where the hell is Lord Lucan? Answer these questions and eternal fame will be yours.


My suggestion would be that the engines would have oversquare dimensions, and use a larger number of smaller cylinders.

The Rolls-Royce Griffon was a 36.7l (6" bore x 6.6" stroke. 2239ci) V-12. Its ultimate versions produced around 2500hp at 2750rpm with +25psi boost.

In 1945 a Rolls-Royce engineer, Stewart Tresilian, proposed an alternative 2500hp engine. It would be an X-16 with bore of 3.9" and of stroke of 3.3", for a capcity of 10.3l (630ci). The engine would be supplied by the Griffon supercharger. The max rpm would be 7250. The length was less than half the Griffon's, so less than 40" (1016mm) in length. The engine would be about the diameter of the supercharger housing. This means a maximum of about 30" (762mm), probably a few inches less. For comaprison the Griffon was 30.3" wide x 46" tall.

I would think that a modern piston aero engine would go along similar lines, with improvements in stressing ana materials the weight would be reduced and the engine made more compact. Modern ignition and fuel systems would raise the engine's efficiency and power, as would modern compressor technology.

I know that there are 630ci V8s that can make 2500hp, but under the aero engine type tests of WW2 they certainly wouldn't get rated that highly. The British test, for example, lasted for 114 hours. The US test required that an engine run for 7.5 hours at maximum power (war emergency power) in 5 minute bursts for it to rated at that power level.

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#2 bigleagueslider

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Posted 13 April 2013 - 02:12

Given the condition of "similar dimensions" posed in the original question, there are a couple things to consider about how much power a modern recip engine design could produce. Obviously, we could use modern engineering tools to produce component and system designs with lower weights, greater strengths, higher efficiency, etc. A modern valvetrain would give much better flows, modern combustion chamber design would give much better combustion, and modern compressor design would greatly improve supercharger performance. Of course the biggest improvement would come from using modern electronic fuel and ignition systems.

The only thing that would favor the WWII engines would be the fuels they used. The gasoline used in WWII aircraft had significant amounts of anti-knock additives like TEL, which would not be acceptable today. TEL was a very effective compound for suppressing detonation.

#3 Wuzak

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Posted 13 April 2013 - 04:57

Thanks slider, I hadn't even considered fuels.

I think, though, modern combustion chambers, materials, etc, would allow higher compression ratios and/or boost despite the lower octane fuel ratings.

The best fuels used in WW2 had a performance number of 150. What are modern aviation fuels rated to?

#4 bigleagueslider

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Posted 13 April 2013 - 05:47

The best fuels used in WW2 had a performance number of 150. What are modern aviation fuels rated to?


Wuzak- There are some fuels that have very high knock resistance, such as methanol, hydrogen, natural gas, etc. While they may not have been practical to use in WWII piston engines, it is possible to use them with modern fuel injection systems. Another thing to remember is that modern closed-loop engine fuel and ignition systems have the ability to adjust fuel mixtures and ignition timing if any knock or lean combustion is detected, while the WWII engines did not have such ability.

I could imagine a modern version of the R-R Griffon V-12 producing around 5,000hp.

#5 Wuzak

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Posted 13 April 2013 - 05:49

I could imagine a modern version of the R-R Griffon V-12 producing around 5,000hp.


Reliably?

#6 bigleagueslider

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Posted 13 April 2013 - 06:02

Reliably?

Sure. The Griffon was a big engine. If a modern 1.5L production turbo auto engine can make 200hp on pump gas, why wouldn't it be believable for a Griffon to make 5,000hp using special fuel?

#7 Bob Riebe

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Posted 13 April 2013 - 06:28

Thanks slider, I hadn't even considered fuels.

I think, though, modern combustion chambers, materials, etc, would allow higher compression ratios and/or boost despite the lower octane fuel ratings.

The best fuels used in WW2 had a performance number of 150. What are modern aviation fuels rated to?

Today's low lead 100/130 aviation fuel has far more lead than the old leaded automobile gasoline.

The high performance aviation gasoline used at Reno, is far more complex than the low lead used for general aviation and has maximum rating of 127/160.

As I am sure you are aware power delivery in aircraft is totally different that that for automobiles. Steady state power settings are used.
The throttle changes power setting, the propeller changes rpm.

The carburettors used on the highest performance aircraft engines of WWII are often considered for all practical purposes a mechanical version of todays electronic fuel systems.

A large unstressed engine is far more desirable than a small highly stressed one.

They have tried exotic fuel at Reno and have found it is simply not worth the effort.
Current engines are well over three thousand horsepower with the Merlins (3,500-3,800) and the larger radials and the Griffon have the advantage in hp that comes with greater displacement. Around 4,000 hp plus or minus.

This site, which at times has posters that work on Reno engines may be able to answer some of your questions. http://www.aafo.com/hangartalk/

Edited by Bob Riebe, 13 April 2013 - 06:37.


#8 Wuzak

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Posted 13 April 2013 - 07:27

100/130 would be much the same as the bulk of the fuel used by the Allies in WW2.

I don't think that comparing the power outputs of Reno racers is valid. Certainly a 3500-3800hp Reno Merlin doesn't go through the same certifying process as a 2200hp Merlin 130.

Thanks for the link Bob.

#9 bigleagueslider

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Posted 13 April 2013 - 07:41

The high performance aviation gasoline used at Reno, is far more complex than the low lead used for general aviation and has maximum rating of 127/160.

As I am sure you are aware power delivery in aircraft is totally different that that for automobiles. Steady state power settings are used.
The throttle changes power setting, the propeller changes rpm.

The carburettors used on the highest performance aircraft engines of WWII are often considered for all practical purposes a mechanical version of todays electronic fuel systems.

A large unstressed engine is far more desirable than a small highly stressed one.

They have tried exotic fuel at Reno and have found it is simply not worth the effort.
Current engines are well over three thousand horsepower with the Merlins (3,500-3,800) and the larger radials and the Griffon have the advantage in hp that comes with greater displacement. Around 4,000 hp plus or minus.


Bob Riebe- With a highly boosted SI engine, the fuel properties are of more concern than simple octane ratings. Factors such as fuel latent heat can also have a big impact on performance. In this regard, methanol looks very good.

As for the carburettors used on WWII piston engines, they are far inferior to any modern electronic DI fuel system. A modern electronic DI fuel system has the ability to deliver the precise amount of fuel to each cylinder at every cycle. This means that the engine is able to operate at the absolute limit of performance. This is not possible with a carburettor fuel system.

#10 MatsNorway

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Posted 13 April 2013 - 08:03

Surely they would favour a fuel with high energy density?

Edited by MatsNorway, 13 April 2013 - 08:08.


#11 Wuzak

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Posted 13 April 2013 - 13:10

Bob Riebe- With a highly boosted SI engine, the fuel properties are of more concern than simple octane ratings. Factors such as fuel latent heat can also have a big impact on performance. In this regard, methanol looks very good.

As for the carburettors used on WWII piston engines, they are far inferior to any modern electronic DI fuel system. A modern electronic DI fuel system has the ability to deliver the precise amount of fuel to each cylinder at every cycle. This means that the engine is able to operate at the absolute limit of performance. This is not possible with a carburettor fuel system.



Isn't the latent heat issue more beneficial for engines like the Merlin and Griffon, where the fuel is mixed with the air before the supercharger, than for direct injection engines?

#12 PJGD

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Posted 13 April 2013 - 14:31

I think that I may have posted this in the past, but this trade press report gives an indication of where things were going with post war aero engines. In the case of the Centaurus, an improvement in rating of ~10% was achieved with DI in an essentially like-for-like engine specification, but direct in-cylinder injection also enabled higher boost pressures due to improved cylinder cooling from increased overlap without fear of impaired fuel consumption resulting from blow-through. This was expected to give ~26% increase in rating.

PJGD

#13 ray b

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Posted 13 April 2013 - 15:15

the unlimited hydro's used those motors [griffons] with gas +NOX before the turbines came in to the sport ruining the sounds of the big boats
I bet they made more then 5000 hp in that form

#14 desmo

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Posted 13 April 2013 - 17:47

For aviation isn't fuel efficiency everything for an engine/powertrain? Fuel is heavy.

#15 MatsNorway

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Posted 13 April 2013 - 17:49

For aviation isn't fuel efficiency everything for an engine/powertrain? Fuel is heavy.


My point.

#16 Bob Riebe

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Posted 13 April 2013 - 18:02

Nitrous is used at Reno.
By exotic fuels I was referring liquid, non-pressure tank, fuels such as alcohol, nitro-methane etc.

ADI- anti-detonation injection- is also used which is an alcohol-water mix.

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Addendum:
Bendix-Stromberg who built the carbs used in WWII did go on, before the end of the war to build an injection system which was used on turbo-compound engines.
From this the injection systems currently used on many civilian aircraft came to be.

The carb used was a pressure carb quite different from an automobile carb.

Edited by Bob Riebe, 13 April 2013 - 18:16.


#17 rory57

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Posted 13 April 2013 - 19:59

Mats: energy density of fuel is definately top priority for long range aircraft where fuel load is a big part of take-off weight. Todays jet fuel has more energy per unit mass than either Diesel or petrol fuels for just that reason.

For fighter aircraft of the WW2 type, fuel load was a small part of the take-off weight but engine weight / power was the main design driver.
At that time fuel was seen to limit the max power from a given petrol engine (due to detonation) and there was serious interest in Diesels because they were not so limited.
Uneven mixture distribution was a problem for all carburretted / single - point injection engines, much development effort was expended, many pistons melted, inlet manifolds exploded etc. Todays fuel injection technology could fix all of that.

I am sure that such an engine would be turbocharged rather than supercharged now that we know so much about turbines and compressors. However, we now know so much about turbines and compressors that we leave out all of the now unneccessary reciprocating gubbins - and leave ourselves with the gas turbine. Have a look at this, as much power as a late-model Rolls-Royce Merlin and you could carry it home on the back seat. http://www.pwc.ca/en/engines/pt6c

Edited by rory57, 13 April 2013 - 20:00.


#18 Tony Matthews

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Posted 13 April 2013 - 20:11

...you could carry it home on the back seat. http://www.pwc.ca/en/engines/pt6c

I can't see any weights, but 2' dia x 5' long ain't big!

#19 MatsNorway

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Posted 13 April 2013 - 22:34

Ive allways dreamt of having a turbine in the trunk kinda like that Flåklypa car that inspired Christian von Koniengsegg (impossible name that last one)

You can see the turbine exit here.
https://www.youtube....G0AYUNOZY#t=27s

Edited by MatsNorway, 13 April 2013 - 22:35.


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#20 Bob Riebe

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Posted 13 April 2013 - 22:48

I am sure that such an engine would be turbocharged rather than supercharged now that we know so much about turbines and compressors. However, we now know so much about turbines and compressors that we leave out all of the now unneccessary reciprocating gubbins - and leave ourselves with the gas turbine. Have a look at this, as much power as a late-model Rolls-Royce Merlin and you could carry it home on the back seat. http://www.pwc.ca/en/engines/pt6c

Heat is the problem with exhaust driven blowers.


That turbine is not near the power of a Merlin but it is still fascinating.


#21 Wuzak

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Posted 14 April 2013 - 00:32

That turbine is not near the power of a Merlin but it is still fascinating.


PT6C-67A - 1940hp.


#22 Bob Riebe

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Posted 14 April 2013 - 05:21

PT6C-67A - 1940hp.

My screw-up I was thinking of the Wright 3350.

#23 Wuzak

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Posted 14 April 2013 - 05:58

My screw-up I was thinking of the Wright 3350.


Wright R-3350 - 2200hp, 2670lb, 55.78" diameter x 76.2" long.

Later engines could get up to 2800hp, and up to 3500hp in turbo compound form. You could stick a pair of PT6C-67s in the space required for an R-3350 and have room to spare. And it would still be lighter.

I can't find a weight for the PT6C-67, but the PT6A is around 300lbs, depending on version.

#24 Wuzak

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Posted 14 April 2013 - 06:03

How about a Pratt & Whitney PW150?

44.7" diameter, 95.4" long, 1521lb - 5000hp+, 0.43slb/hp/hr sfc.

https://engineering....rops/pw100.html

Edited by Wuzak, 14 April 2013 - 06:03.


#25 Kelpiecross

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Posted 14 April 2013 - 12:55

How about a Pratt & Whitney PW150?

44.7" diameter, 95.4" long, 1521lb - 5000hp+, 0.43slb/hp/hr sfc.

https://engineering....rops/pw100.html


What about an RR RB162 - 5250 lbs thrust, weight 280 lbs. I think this equates to about 5000+ HP.

Edited by Kelpiecross, 14 April 2013 - 13:12.


#26 Magoo

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Posted 14 April 2013 - 14:19

The best fuels used in WW2 had a performance number of 150. What are modern aviation fuels rated to?


Modern unleaded and low-lead automotive racing gasoline will grade higher than that in performance number with lower sensitivity than WWII-era fuels. PN is a fairly archaic system.

Fuel is not really much of an issue as I see it. The energy density of gasoline pretty much is what it is (alcohol blends excluded) with maybe four percent possible variation, which could possibly be an issue... depending on how far we are war-gaming this pipe dream. Transatlantic piston-engine bombers?

Anyway, what you and PJGD and others said. GDI + turbocompunding = considerable gains in output and efficiency.

#27 mariner

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Posted 14 April 2013 - 15:01

For combat aircraft there were (are?) two conflicting engine requirements. For fighters pure power is everything, consumption is important but secondary as it will never be large part of the all up weight.

For bombers etc. fuel efficiency is everything because the fuel load trades off against bomb load so a bit of extra engine weight via complexity is OK if it improves BMEP.

The B -36 thread is old now but when you look at the range and very high ceiling of that huge plane I think you can se where post WW2 piston design went

#28 Bob Riebe

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Posted 14 April 2013 - 20:25

The sad fact, in a way is, once turbine engines hit the scene development of piston engines pretty much stopped.
Items in the pipeline were finished as need be but all future efforts went into turbine engines.

the XF-12 Rainbow was probably the ultimate piston engine aircraft.
If I remember correctly they feathered all four props and flew it just on the turbo-compound exhaust in one test.

Pistons, at least radial pstone engines have one great advantage over any turbine, or water-cooled piston engine. The ability to suffer great damage and still get the aircraft home.
That is the reason the Air Force really wanted P-47s in Korea but internal Air Force stupidity had crippled the P-47 supply to the point there were not enough aircraft of spare parts for the number needed.

The rating of WWII military gasoline was 115/145 but right after the war, highlighted by developments for the Cleveland air races aviation gasoline went through some major development.
The aviation gasoline rating as Magoo said is an odd outdated system but is still used because they can.

Had turbines not killed piston engine development, the Rolls-Royce Crecy, had it been developed or what it could have led to, would given the turbines serious competition

It makes me wonder with the new COIN aircraft being adapted with their turbine engines, they suffer the same, or worse,. short comings of water cooled piston engines from battle damage yet do not come near the performance of the SPAD in 'Nam.



#29 twotempi

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Posted 14 April 2013 - 20:45

Look up "Rolls Royce Crecy" which was a V12 direct injection TWO-STROKE !!.

They say that half the thrust was contributed by the noise.

The advent of turbines put an end to development.

#30 Wuzak

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Posted 14 April 2013 - 21:20

the XF-12 Rainbow was probably the ultimate piston engine aircraft.
If I remember correctly they feathered all four props and flew it just on the turbo-compound exhaust in one test.


That would be incorrect. To feather the throttle you would need to stop its rotation, and this the engine's.

Also, the Rainbow wasn't fitted with turbocompound engines. Only one turbo-compound R-4360 engine flew - a test engine in a B-50. The engine was R-4360 VDT (Variable discharge turbine, the turbine speed governed by the exhaust outlet flow), and it needed constant manual adjustment to be controlled. The VDT was planned for future versions of the XF-12.


#31 Wuzak

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Posted 14 April 2013 - 22:45

I had a quick look at World's Fastest Four-Engine Piston-Powered Aircraft and found the claim that the exhaust thrust of the R-4360s in the XF-12 was equivalent to 250hp, though it doesn't mention at what speed. This is on 3500hp engines.

This is much the same as a 2 stage Merlin with ejector exhausts. The Crecy would give 865ehp! The Merlin with turbine installation (an estimated turbo-compound version) would have around 95ehp exhaust, the Crecy around 265. These are engines around 38% of the capacity of the R-4360.



#32 Bob Riebe

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Posted 14 April 2013 - 23:27

That would be incorrect. To feather the throttle you would need to stop its rotation, and this the engine's.

Also, the Rainbow wasn't fitted with turbocompound engines. Only one turbo-compound R-4360 engine flew - a test engine in a B-50. The engine was R-4360 VDT (Variable discharge turbine, the turbine speed governed by the exhaust outlet flow), and it needed constant manual adjustment to be controlled. The VDT was planned for future versions of the XF-12.

In an adjustable prop., they can be adjust to zero thrust.


Feathering
On some variable-pitch propellers, the blades can be rotated parallel to the airflow to reduce drag.
Depending on design, the pilot may have to push a button to override the high-pitch stops and complete the feathering process, or the feathering process may be totally automatic.


I am sure they did this on all four engines of the Rainbow and did not lose atltitude.

#33 Lee Nicolle

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Posted 15 April 2013 - 00:03

While I do not have a great understanding of propellers and thrust I would be very surprised if the air racers who are at low altitudes could not make double the power of military planes from WW2. Modern engineering with pistons, conrods, cylinder head flow, valve timing plus modern fuel injection and supercharging methods yet alone modern fuels mean the engines should be able to be turned a lot harder with minimum hours reliability. Even in WW2 if they wanted to race only they could have upped the power considerably, BUT could not have engines constantly in service because of lack of reliability. Not much good having fighter planes with 15 or 20 hour engine overhauls required!
Just as a matter of interest do they use German,,, or Japanese aero engines from the period too? I suspect the German engines would have been very good also. Even maybe the Japanese ones.

#34 Wuzak

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Posted 15 April 2013 - 00:22

While I do not have a great understanding of propellers and thrust I would be very surprised if the air racers who are at low altitudes could not make double the power of military planes from WW2. Modern engineering with pistons, conrods, cylinder head flow, valve timing plus modern fuel injection and supercharging methods yet alone modern fuels mean the engines should be able to be turned a lot harder with minimum hours reliability. Even in WW2 if they wanted to race only they could have upped the power considerably, BUT could not have engines constantly in service because of lack of reliability. Not much good having fighter planes with 15 or 20 hour engine overhauls required!
Just as a matter of interest do they use German,,, or Japanese aero engines from the period too? I suspect the German engines would have been very good also. Even maybe the Japanese ones.


Yes, they run Merlins at around 1.5-2 times the rated wartime power.

Not too many German engines available for use in air racing. Even less Japanese engines.

#35 Wuzak

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Posted 15 April 2013 - 00:31

In an adjustable prop., they can be adjust to zero thrust.


Feathering
On some variable-pitch propellers, the blades can be rotated parallel to the airflow to reduce drag.
Depending on design, the pilot may have to push a button to override the high-pitch stops and complete the feathering process, or the feathering process may be totally automatic.


I am sure they did this on all four engines of the Rainbow and did not lose atltitude.



Feathering was used to protect failed engines. If the prop can't be feathered it will windmill and cause extra drag, possibly causing loss of speed and/or altitude.

I am not sure why you would set a perfectly fin engine to zero thrust on the prop. It would be quite wasteful and inefficient.

http://napoleon130.t...;target=tlx_new
http://napoleon130.t....com/id697.html

Note that the feathering uses is a slightly different process to normal pitch adjustment.

Edited by Wuzak, 15 April 2013 - 00:33.


#36 Wuzak

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Posted 15 April 2013 - 00:36

How much more compact could a modern version of the Griffon be?

For example - 6" bore, 6.9" bore spacing. COuld teh bore spacing be tightened significantly with modern materials/design?

#37 johnny yuma

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Posted 15 April 2013 - 02:53

[quote name='Wuzak' date='Apr 13 2013, 13:10' post='6223283']
Isn't the latent heat issue more beneficial for engines like the Merlin and Griffon, where the fuel is mixed with the air before the supercharger, than for direct injection engines?

As far as I can speed read so far,the Merlin carby philosophy, promoted by Hooker,the air/fuel guru at the time,was carburettor feed facilitated a 25 degree C cooling of the inlet mixture BEFORE it hit the Supercharger as 100% of the fuel had vaporised,making volumetric efficiency of a cooler (denser) charge superior to direct injection.A recent study suggests this might more realistically have been 66%.However this was better than 0% for engines like the Messerschmitt Me109 using direct injection.The last 2 versions of the replacement for the earlier Messerschmitt engine near war's end used Methanol/Water injection to a bigger engine with nitrous injection at high altitude and boost. By 1943 pressurised carburettors were used in the Merlins to overcome the deficiencies of float bowls in a sudden steep dive,but the pressure was only 5 psi. Both used intercoolers between the Supercharger/s and the manifolds ,as well.

Edited by johnny yuma, 15 April 2013 - 02:55.


#38 Wuzak

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Posted 15 April 2013 - 03:37

Both used intercoolers between the Supercharger/s and the manifolds ,as well.


Merlins and Griffons did (2 stage engines). Daimler-Benz's didn't. Junkers did on some (Jumo 213).


#39 Bob Riebe

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Posted 15 April 2013 - 04:33

Feathering was used to protect failed engines. If the prop can't be feathered it will windmill and cause extra drag, possibly causing loss of speed and/or altitude.

I am not sure why you would set a perfectly fin engine to zero thrust on the prop. It would be quite wasteful and inefficient.

http://napoleon130.t...;target=tlx_new
http://napoleon130.t....com/id697.html

Note that the feathering uses is a slightly different process to normal pitch adjustment.

I know what it is for.
I doubt there were many instances of engines being feathered, although a four engine aircraft with two engines feathered and idling would consume less fuel.
Feathering would be far superior an idea to an air restart.

As I said it was an experiment on an experimental aircraft.
I read this a long time ago.


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#40 Bob Riebe

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Posted 15 April 2013 - 04:59

While I do not have a great understanding of propellers and thrust I would be very surprised if the air racers who are at low altitudes could not make double the power of military planes from WW2. Modern engineering with pistons, conrods, cylinder head flow, valve timing plus modern fuel injection and supercharging methods yet alone modern fuels mean the engines should be able to be turned a lot harder with minimum hours reliability. Even in WW2 if they wanted to race only they could have upped the power considerably, BUT could not have engines constantly in service because of lack of reliability. Not much good having fighter planes with 15 or 20 hour engine overhauls required!
Just as a matter of interest do they use German,,, or Japanese aero engines from the period too? I suspect the German engines would have been very good also. Even maybe the Japanese ones.

While hp is something they strive for, even with the competition engines durability is number one, two and three on the list of items of greatest concern.

Hot rod ideas for more horse power simply to not transfer to aircraft engines as the power delivery is totally different.
There is an airplane in the sport class running a NASCAR (components) engine and the hp level is hundreds less than one set up for NASCAR.

Engine failure can easily be fatal.

There is no money in air racing, so there is no money to make improved engines.
The Allison is actually a stronger engine than the Merlin but to take it to the performance level of the Merlin costs money that no one has any reason to spend.
On another site, there was an gentleman who works for the company that builds current Allison engines for use. He says that versions existed that could go heads up with the Merlin but to build test and make them reliable costs money no one wants to spend.
The sleeve-valve engines the British used are even more expensive to work on which is why the Furies all have poppet-valve engines installed.

The big radials have people that build improved cases and heads but that is a long way from an entire engine, and just those parts are very expensive.

To build an engine for Reno is far easier than for commercial use than for commercial use as they have to jump through a myriad of hoops to be certified and that is extremely expensive.

In the rumor mill is that one of the rebuilt Focke-Wulfs may possibly be raced at Reno but that is just rumor mill stuff.


#41 Wuzak

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Posted 15 April 2013 - 05:03

While hp is something they strive for, even with the competition engines durability is number one, two and three on the list of items of greatest concern.

Hot rod ideas for more horse power simply to not transfer to aircraft engines as the power delivery is totally different.
There is an airplane in the sport class running a NASCAR (components) engine and the hp level is hundreds less than one set up for NASCAR.

Engine failure can easily be fatal.

There is no money in air racing, so there is no money to make improved engines.
The Allison is actually a stronger engine than the Merlin but to take it to the performance level of the Merlin costs money that no one has any reason to spend.
On another site, there was an gentleman who works for the company that builds current Allison engines for use. He says that versions existed that could go heads up with the Merlin but to build test and make them reliable costs money no one wants to spend.
The sleeve-valve engines the British used are even more expensive to work on which is why the Furies all have poppet-valve engines installed.

The big radials have people that build improved cases and heads but that is a long way from an entire engine, and just those parts are very expensive.

To build an engine for Reno is far easier than for commercial use than for commercial use as they have to jump through a myriad of hoops to be certified and that is extremely expensive.

In the rumor mill is that one of the rebuilt Focke-Wulfs may possibly be raced at Reno but that is just rumor mill stuff.


One of these?

http://www.flugwerk....hp?GID=19&SID=4

#42 Wuzak

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Posted 15 April 2013 - 05:21

There is no money in air racing, so there is no money to make improved engines.
The Allison is actually a stronger engine than the Merlin but to take it to the performance level of the Merlin costs money that no one has any reason to spend.
On another site, there was an gentleman who works for the company that builds current Allison engines for use. He says that versions existed that could go heads up with the Merlin but to build test and make them reliable costs money no one wants to spend.


The Allison does, indeed, have some features which make it potentially better than the Merlin. The head design, for one is more modern. The method for sealing barrels to heads is probably better. The rods are stronger - and many of the Reno Merlins run Allison G6 rods.

Where the Allison fell behind in WW2 was the supercharger development. Rolls-Royce offered single speed-single stage, two speed-single stage and two speed-two stage Merlins during WW2, but Allison only had single speed single stage engines for much of the war, with two stage engines coming out in quantity very late in the war. I think for Reno you would want the two stage engine, but probably want to lock the auxiliary stage to a set speed (it was hydraulically driven). Then the problem becomes length - the 2 stage Allison is longer than the Merlin.


The sleeve-valve engines the British used are even more expensive to work on which is why the Furies all have poppet-valve engines installed.


By sleeve-valve you are really talking about Sea Furies that have ditched their Centauruses. Don't think their are any Sabres still flying.

But if you could have a Sabre the power potential would be great. Post war tests of the Sabre went as high as 4000-5000hp, reliably.



#43 gruntguru

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Posted 15 April 2013 - 05:44

Here's my wild guess.

Designing a new engine to replace a late WW2 aero engine - say the Merlin, to fit in the same envelope and weigh the same or less and pass the same certification tests. All power to be taken from the piston engine crankshaft (No compounding allowed or we might as well go straight to a gas turbine)

1. Using the original bore and stroke: The new engine would benefit from pent-roof chambers, DI, turbocharging, modern materials etc. Result would be a 20% increase in rpm and 100-200% power increase ie 4,000 - 6,000 hp for a Merlin replacement.

2. Bore and stroke free: Lots more pistons and cylinders. This would permit higher rpm and higher boost. The power is limited mainly by limits to cost/complexity. At reasonable cost/complexity levels - say 24 cyl, 110mm bore and stroke - result would be a 70% increase in rpm and 200-450% power increase ie 6,000 - 11,000 hp for a Merlin replacement.

Although the new engine would fit within the same envelope as the original Merlin, the extra heat loads would require larger radiators and intercoolers. The increase would not be proportional to the power increase - thermal efficiency would be significantly better, plus DI would permit greater scavenging of waste heat to the exhaust as mentioned in an earlier post.

#44 gruntguru

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Posted 15 April 2013 - 05:50

. . . the Merlin carby philosophy, promoted by Hooker,the air/fuel guru at the time . .

The carb-supercharger layout was determined long before Hooker got involved.

#45 Wuzak

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Posted 15 April 2013 - 06:24

Here's my wild guess.

Designing a new engine to replace a late WW2 aero engine - say the Merlin, to fit in the same envelope and weigh the same or less and pass the same certification tests. All power to be taken from the piston engine crankshaft (No compounding allowed or we might as well go straight to a gas turbine)

1. Using the original bore and stroke: The new engine would benefit from pent-roof chambers, DI, turbocharging, modern materials etc. Result would be a 20% increase in rpm and 100-200% power increase ie 4,000 - 6,000 hp for a Merlin replacement.

2. Bore and stroke free: Lots more pistons and cylinders. This would permit higher rpm and higher boost. The power is limited mainly by limits to cost/complexity. At reasonable cost/complexity levels - say 24 cyl, 110mm bore and stroke - result would be a 70% increase in rpm and 200-450% power increase ie 6,000 - 11,000 hp for a Merlin replacement.

Although the new engine would fit within the same envelope as the original Merlin, the extra heat loads would require larger radiators and intercoolers. The increase would not be proportional to the power increase - thermal efficiency would be significantly better, plus DI would permit greater scavenging of waste heat to the exhaust as mentioned in an earlier post.


What about option 3 - design for teh same power level - say 2500hp (ie Griffon class)?

#46 Wuzak

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Posted 15 April 2013 - 06:28

The carb-supercharger layout was determined long before Hooker got involved.


Indeed, the Merlin arrangement was around since '34, and Hooker joined in '38. And teh Merlin arrangement was basically similar to the Kestrel from the late 1920s.

#47 gruntguru

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Posted 15 April 2013 - 07:14

What about option 3 - design for teh same power level - say 2500hp (ie Griffon class)?

I am sure that pent-roof + turbo + DI + materials technology would allow you to chop at least one row (4 cylinders) off the Tresilian X-16 (same bore and stroke) and still make the 2,500 hp target.

#48 GreenMachine

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Posted 15 April 2013 - 07:37

I know what it is for.
I doubt there were many instances of engines being feathered, although a four engine aircraft with two engines feathered and idling would consume less fuel.
Feathering would be far superior an idea to an air restart.

As I said it was an experiment on an experimental aircraft.
I read this a long time ago.


Let's be clear. Feathering a (piston) engine means stopping the engine. It is an emergency procedure, when an engine is damaged or has run out of fuel. The process normally involves turning off the fuel, switching the ignition off, and feathering the prop. The last because, even though the engine is now officially dead, the airflow acting on the propellor blades will exert tremendous pressure to turn them. This leads to increased drag (the last thing you need when you have just lost an engine), and will probably lead to more damage to the engine if the reason for the failure is mechanical, rather than say running out of fuel. So feathering the propellor blades means they turn perpendicular to the airflow and the drag of the stationary blade is minimised. And it was a regular ocurrence in the piston engined world.

You do not idle an engine with a feathered airscrew. As far as I know no operational piston engine had a clutch mechanism to allow the engine and propellor to be disconnected.

This may not apply to the turboprop word though. The Double Mamba in the Gannet allowed one of the paired engines to be shut down in flight and decoupled from the transmission, and I have a feeling the Bregruet Atlantique MR aircraft was intended to patrol on only one of its two (uncoupled) engines, the other I believe being shut down (not idled) once it reached its patrol area.

I don't know, but I hypothesise that jets may idle an engine in similar circumstances, if the fuel cost of idling is less than the fuel cost of the extra thrust to overcome the drag arising from a shut down engine.

#49 Lee Nicolle

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Posted 15 April 2013 - 07:41

While hp is something they strive for, even with the competition engines durability is number one, two and three on the list of items of greatest concern.

Hot rod ideas for more horse power simply to not transfer to aircraft engines as the power delivery is totally different.
There is an airplane in the sport class running a NASCAR (components) engine and the hp level is hundreds less than one set up for NASCAR.

Engine failure can easily be fatal.

There is no money in air racing, so there is no money to make improved engines.
The Allison is actually a stronger engine than the Merlin but to take it to the performance level of the Merlin costs money that no one has any reason to spend.
On another site, there was an gentleman who works for the company that builds current Allison engines for use. He says that versions existed that could go heads up with the Merlin but to build test and make them reliable costs money no one wants to spend.
The sleeve-valve engines the British used are even more expensive to work on which is why the Furies all have poppet-valve engines installed.

The big radials have people that build improved cases and heads but that is a long way from an entire engine, and just those parts are very expensive.

To build an engine for Reno is far easier than for commercial use than for commercial use as they have to jump through a myriad of hoops to be certified and that is extremely expensive.

In the rumor mill is that one of the rebuilt Focke-Wulfs may possibly be raced at Reno but that is just rumor mill stuff.

Hot rod ideas are quite valid. Using 60-70y/o reciprocating parts in these engines would be committing suicide. And the little I have read they do. Durability is obviously no 1 but it does not need to be durable for 100s of hours, just dozens. At low altitude. So I doubt that many people would be using original 40s rods, pistons, valves, springs etc. They are consumables and can all be made a lot better these days. Coupled with better oils and fuels far more reliable power and at least a few more RPM, which generally makes power

#50 Wuzak

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Posted 15 April 2013 - 07:44

I am sure that pent-roof + turbo + DI + materials technology would allow you to chop at least one row (4 cylinders) off the Tresilian X-16 (same bore and stroke) and still make the 2,500 hp target.


So, a 7.5l X-12?

The Bugatti Veyron engine is 8l and 1000hp. How much more could be freed up for aviation use (fewer emissions and noise laws)? How much would then be lost when it gets type tested (to be rated?