If you could go back to WW-2 with the knowledge you have now in engine design...what would you improve? No jets...
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Shortround6
Major General
I am sure a modern system (or even not so modern) could do a better job of controlling the spark. The question becomes at what cost? and how much improvement is needed if you don't change the operating range of the engine by very much? If the engine, once in the air, operates over a 2 to one speed ratio (1500rpm to 3,000rpm for instance) how important is variable ignition timing? Some engines did a get a crude form of ignition advance (useful for cruising?) and others were able to retard the timing for starting only. Many aircraft had trouble with ignition systems at altitude and had to resort to pressurizing the ignition system to prevent cross firing. I believe the Wright R-3350 in the B-29s resorted to a low tension ignition with coils for each plug? I could be wrong on that.
Look up the Chrysler 300 saga of the late 50s when they tried to use "electronic" fuel injection supplied by an aircraft company (Bendix) which turned into a fiasco, however well Bendix fuel management systems may have worked in an aircraft. reliability at car prices wasn't there.
I would note than many American engines (and a few British ?) used "pressure" carburetors which weren't really carburetors at all but single point throttle body fuel injectors. Not as good as multi point fuel injectors but better than some carburetors.
I have no idea how good or bad some of these carburetors were. But again, trying to compare a supercharged aircraft engine to a car ignores a few differences. The fuel, after going through the supercharger was better atomized than most cars with carburetors, In fact many early engines (late 20s) called the spinning impeller between the carb/s and the inlet pipes a "mixing fan" as it didn't provide much, if any boost and in a few engines ran at crankshaft speed, but then with 70 octane or under fuel you weren't gong to use much boost anyway.
P & W on the C series R-2800 didn't use a fixed jet to inject the fuel under pressure into the airstream but feed a "slinger ring" that went around the inlet of the supercharger with multiple openings that got a better fuel distribution than the fixed jet.
I would also note that RR got over 1800hp out a Merlin on a test stand in 1938 when they were working on the "Speed Spitfire" for a record attempt (not on gasoline) and I believe they managed 1600hp or better for 10 hours. It was this experience that helped convince them that the Merlin was capable of a lot of development without needing a lot of redesign.
RR also figured (in 1940 or just before) that give suitable fuels the potential power at sea level if the throttle could be fully opened of some of their engines were 1500hp (55.5hp per liter) at 2600rpm for the Melrin II and X. For the the Peregrine they were figuring 1365hp (64.6hp per liter) and 0.81hp per pound at 2850rpm. Both engines ran higher rpm in service but the throttles were not fully opened anywhere near sea level. This numbers were published in 1940, what was going on in secret?
I have no doubt that using modern knowledge and materials improvements could be made, It is just that the aircraft engines of the day were in a whole different catagory than even most race car engines of the day so the difference between modern car engines and those aircraft engines might not be anywhere near the difference that exists between modern car engines and racing car engines of the day.
Look up the Chrysler 300 saga of the late 50s when they tried to use "electronic" fuel injection supplied by an aircraft company (Bendix) which turned into a fiasco, however well Bendix fuel management systems may have worked in an aircraft. reliability at car prices wasn't there.
I would note than many American engines (and a few British ?) used "pressure" carburetors which weren't really carburetors at all but single point throttle body fuel injectors. Not as good as multi point fuel injectors but better than some carburetors.
I have no idea how good or bad some of these carburetors were. But again, trying to compare a supercharged aircraft engine to a car ignores a few differences. The fuel, after going through the supercharger was better atomized than most cars with carburetors, In fact many early engines (late 20s) called the spinning impeller between the carb/s and the inlet pipes a "mixing fan" as it didn't provide much, if any boost and in a few engines ran at crankshaft speed, but then with 70 octane or under fuel you weren't gong to use much boost anyway.
P & W on the C series R-2800 didn't use a fixed jet to inject the fuel under pressure into the airstream but feed a "slinger ring" that went around the inlet of the supercharger with multiple openings that got a better fuel distribution than the fixed jet.
I would also note that RR got over 1800hp out a Merlin on a test stand in 1938 when they were working on the "Speed Spitfire" for a record attempt (not on gasoline) and I believe they managed 1600hp or better for 10 hours. It was this experience that helped convince them that the Merlin was capable of a lot of development without needing a lot of redesign.
RR also figured (in 1940 or just before) that give suitable fuels the potential power at sea level if the throttle could be fully opened of some of their engines were 1500hp (55.5hp per liter) at 2600rpm for the Melrin II and X. For the the Peregrine they were figuring 1365hp (64.6hp per liter) and 0.81hp per pound at 2850rpm. Both engines ran higher rpm in service but the throttles were not fully opened anywhere near sea level. This numbers were published in 1940, what was going on in secret?
I have no doubt that using modern knowledge and materials improvements could be made, It is just that the aircraft engines of the day were in a whole different catagory than even most race car engines of the day so the difference between modern car engines and those aircraft engines might not be anywhere near the difference that exists between modern car engines and racing car engines of the day.
The T34 and the converted "hot rod" Apache in our Navy flying club both had Bendix mechanical pressure carbs, and they worked a treat. Bulletproof maintenance wise, economical on fuel, and seemingly immune to carb ice. Carb ice? In Key West, FL? Huh? You betcha! That's one of the little surprises that climate has for unsuspecting northcountry pilots who bring their planes down for a little fun in the sun. Continental powered 182s were the most frequent victims, along with the occasional older float carb Bonanza. Lycoming engines seemed to be less susceptible.
Cheers,
Wes
chipieal
Airman
I will admit to not much practical knowledge in this area. However, the Chrysler aircraft engine developed late in WW II had 4 vales per cylinder with Hemi heads. I just read an article that stated they installed one of these in a P - 47 designated (P-47M) At sea level that huge Jug hit 504 MPH. I never have found any figures at altitude but it must have been impressive. This is only 20 MPH slower than The Dornier Arrow with two engines. Maybe if everyone did not jump into turbojets which at that time had only two advantages (speed and quiet) this magnificent engine could have been developed instead of shelved.
Shortround6
Major General
Whoever wrote that article has managed to confuse a number of different P-47 prototypes and has no concept of altitude.
See; http://www.wwiiaircraftperformance.org/p-47/comp-p47dmn.jpg
for the performance of a P-47M which was a production aircraft using the R-2800 C series engine. With 2800hp it hit 367mph at sea level.
The version that is claimed to have hit 504mph was the XP-47J.
But it sure wasn't done at sea level.
The Chrysler engine was installed in the XP-47H
Some accounts claim it had trouble hitting 420mph as the engine did NOT deliver the rated power.
Most accounts also say 2 valves per cylinder.
This does not stop Chrysler fanboy sites from claiming all sorts of things. Like this was the first Hemi head engine. it was the first Chrysler Hemi head but the hemi head dates to 1913 and the Peugeot grand Prix car (at least that is what most engine histories say).
See; http://www.wwiiaircraftperformance.org/p-47/comp-p47dmn.jpg
for the performance of a P-47M which was a production aircraft using the R-2800 C series engine. With 2800hp it hit 367mph at sea level.
The version that is claimed to have hit 504mph was the XP-47J.
But it sure wasn't done at sea level.
The Chrysler engine was installed in the XP-47H
Some accounts claim it had trouble hitting 420mph as the engine did NOT deliver the rated power.
Most accounts also say 2 valves per cylinder.
This does not stop Chrysler fanboy sites from claiming all sorts of things. Like this was the first Hemi head engine. it was the first Chrysler Hemi head but the hemi head dates to 1913 and the Peugeot grand Prix car (at least that is what most engine histories say).
swampyankee
Chief Master Sergeant
- 4,002
- Jun 25, 2013
The Chrysler IV-16 was also ridiculously long -- 45 inches longer than the Griffon.
wuzak
Captain
The Chrysler IV-2220 had 2 valves per cylinder, as did the Continental IV-1430 and Lycoming O-1230/H-2470. These were all based, at least loosely, on the Army "hyper" cylinder design.
A 4 valve cylinder head was doable for a single row radial. Bristol and its licensees built many Jupiters, Pegasuses, and derived engines. It was much more difficult to come up with a practical arrangement for a double row radial with 4 valve cylinder heads. AFAIK, there were some efforts in Italy and Japan, but none of these were very successful.
Also, the P-47 never achieved anything close to 504 mph with the Chrysler engine. Both the engine and its installation needed much more work.
I would suggest that most countries had too many engine development programs and that many of these were ill conceived.
A few examples:
Hispano-Suiza attempted to develop their 14AA air cooled engines based on Wright technology in the late 1930s. The resulting engines were mediocre at best and their development took much needed resources away from the development of their 12Y and 12Z engines.
Similarly, Isotta-Fraschini took out a license for the GR 14 and failed to accomplish much.
The US had the Hyper engine development program. There were also development programs for monstrous engines, perhaps the largest being the Studebaker XH-9350.
I'm not sure how Napier managed to stay in the aero engine business. The Dagger should have finished them off. The Sabre did, eventually, reach a reasonably useful state, but it would have been better to focus on the Bristol Centaurus for high power requirements.
The Germans certainly had their share of engine development programs which went nowhere.
A few examples:
Hispano-Suiza attempted to develop their 14AA air cooled engines based on Wright technology in the late 1930s. The resulting engines were mediocre at best and their development took much needed resources away from the development of their 12Y and 12Z engines.
Similarly, Isotta-Fraschini took out a license for the GR 14 and failed to accomplish much.
The US had the Hyper engine development program. There were also development programs for monstrous engines, perhaps the largest being the Studebaker XH-9350.
I'm not sure how Napier managed to stay in the aero engine business. The Dagger should have finished them off. The Sabre did, eventually, reach a reasonably useful state, but it would have been better to focus on the Bristol Centaurus for high power requirements.
The Germans certainly had their share of engine development programs which went nowhere.
Ain't 20/20 hindsight wonderful? Now if your chrystal ball were clear enough to recognize "ill conceived" while it's still only an idea, what a wonderful world that would be!
thunderbird
Airman
- 74
- Jul 8, 2009
Reverse engineer the Hooker developed two-stage, intercooled mechanical supercharger from the Merlin/Packard merlins for the Allison V-1710. Reverse engineer the German fuel injection systems and single power lever systems for The V-1710 and P&W R-2800. Put the P-47 turbocharged R-2800 into both the F6F and F4U corsairs (with the German fuel injection technology and single power lever). Develop a short path turbocharged and intercooled system with fuel injection and single power lever for the P-38's V-1710. Less interdivisional Argument, less "not invented here" bullshit and more pooling of resources and more cooperation. Doesn't take any modern secrets to produce dramatically improved engines.
The question of ignition timing is i and the conflicts caused by
For higher octane fuels, more timing is needed due to slower flame speed
For large combustion chambers, more ignition timing is needed
For forced induction, less timing is needed because of faster flame speed
For emission controls, less timing is used to reduce smog compounds
For richer fuel mixtures, more timing is needed due to slower flame speed
Yes sir, I am aware of then engines using an early form of throttle body injection to direct the fuel into the
I would point out that fuel injection was available during WWII in GDI form on the R-3350-57
Speed-density carburetors were in use and could easily be considered the fore-runner of the mechanical fuel control. If memory serves me correctly they boosted engine output efficiency to the point where ADI became a requirement to derive the max WEP.
BTW, I disagree that engines were not operated at WOT at sea level. (Take off,and low speed? agree 100%)
Shortround6
Major General
Not with the manufacturer's recommendation or approval.
An Allison with the 8.81 Supercharger gears could make just about 70in of MAP at sea level with no ram effect. take-off was usually at 44in. of MAP, hardly wide open.
In fact nearly every engine that was rated for WEP was using the extra supercharger capacity that existed because the engine was throttled back below it's FTH or critical altitude.
Take-off power was rarely (for later engines) done at WOT.
This is true for British and American engines, Other countries may differ.
In some cases for American engines you may see something like 1200hp at 48in for take-off at 2700rpm which can be held to 3,000ft. Which means the plane was allowed to use 48in at 2700rpm at an airfield 3000ft above sea level. At a sea level airport the plane was NOT allowed to use higher than 48in (officially) even though the supercharger would supply a bit more than 48in at sea level.
I agree that engines were specifically limited by the OEM.
However, I believe that we can both agree the copper wire was routinely broke at sea level during combat. (With a subsequent plug change or engine pull.)
(BTW, a few companies put ball-flags on their engine indicators/monitors now and record the exceedance so the knuckle daggers can bust the glorious pilots that go over limit and fail to tell us.)
Compression ignition two stroke radial with expansion chambers, turbo compounded. I think that expansion chambers on two strokes had significant possibilities in time travel fantasy land. Relatively low tech, yet produce more power. Other ideas would be to promote early adoption of things that worked, such as ADI, more carefully designed superchargers and drives. Ensuring that the cooling systems of liquid cooled engines were based on the Meredith effect, that the Bf109 had space for an intercooler, that the Luftwaffe worked on the motor cannon earlier so that it was actually reliable by 1939, etc. Some of these are bordering on exiting the OP's "engine design"...
If you're going to go compression ignition, why not use the blown two stroke approach GM was developing about that time? In the '60s I drove busses powered with V6 and V8 versions of that. They spun at propeller speeds, produced gobs of torque, and were significantly lighter than comparable four strokes, despite the heavy Rootes blower on top, and didn't have the one-way lubrication system most two strokes had. They were good for three overhauls at 500K mile intervals and sold used at two million miles. I think a radial air cooled version of that with a centrifugal blower in the nose case in place of the unnecessary planetary reduction gear would have promise in Fantasyland. What say?
Cheers,
Wes
The 2-stage supercharged R-2800 powered the XF4U-1 on 29th May 1940. With historical development, that's about the only engine USA might need for a fighter in their part of ww2. Even without German-engineered bits & pieces.
Fellow Vermonter,
With our mutual interest in parsimonious fuel consumption and cost reduction, the use of compression ignition is the way backward in this time travel fantasy.
The use of exhaust valves in the head was an aspect of the Detroit Diesel engine I would prefer to avoid to reduce the height of the engine, the weight, and the cost.
One of the great advantages of the exhaust port is the reduction in engine diameter. I figure a stroke to diameter ratio of 1:6.5 or 1:7 which is about a 15% reduction in diameter and a 28% reduction in area of an equivalent poppet valve engine. In terms of installed in an airframe it offers even greater potential reduction vis a vis the poppet valve engine.
Instead, using exhaust ports with the time transported "power valves" that adjust the height of the exhaust port depending on rpm could be attempted. It may be necessary to liquid cool the exhaust ports. The expansion chambers have the potential to vastly increase the specific power even using 3 cylinders/expansion chamber. With the cool exhaust, the exhaust turbine is going to have a longer, happier, lighter and cheaper life. With at least 12 cylinders and up to 24, the turbine drive to the crankshaft should be engineerable pre-computer. In a pursuit plane, the turbo would be in the aft fuselage with a drive quill to the engine, multi stage supercharger and inter/intracoolers. The compression ratio would be lowered as much as possible (hopefully to 12:1) to allow lower weight, less drive line resonance. Boost would increase the power and the working compression ratio to stabilize ignition. Glow plugs would assist during start up.
I thought that 2 strokes would have lower rpm as well, but the Junkers opposed piston ran at 3000 rpm, so perhaps keeping the rpm high and continuing the use of a propeller speed reduction unit (PSRU).
My first thought is I would not place the superchargers in the nose case. The standard location behind the engine seems more durable and easier to plumb the intercoolers.
