Shortround6
Major General
Thank you
What was the most efficiently-built aircraft engine in World War II?
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ThomasP
Senior Master Sergeant
To be fair the Cheetah X was only rated for 375 BHP at TO and a max of 355 BHP at 7,500 ft rated altitude.
On the other hand, based only on power output and TBO, the Cheetah X (355 BHP & 1200 hrs TBO) is 5.68x more efficient than the Jumo 004 (3000 BHP & 25 hrs TBO).
On the other hand, based only on power output and TBO, the Cheetah X (355 BHP & 1200 hrs TBO) is 5.68x more efficient than the Jumo 004 (3000 BHP & 25 hrs TBO).
Unfortunately, HP doesn't move airplanes, thrust does. So what is the thrust put out by that Cheetah @ 10k ft, or 20k or 30k vs the Jumo. Then factor in the thrust to weight ratio for both powerplants. For extra fun factor in the fuel weight as well but remember the cost of leaded high octane avgas vs jet fuel.To be fair the Cheetah X was only rated for 375 BHP at TO and a max of 355 BHP at 7,500 ft rated altitude.
On the other hand, based only on power output and TBO, the Cheetah X (355 BHP & 1200 hrs TBO) is 5.68x more efficient than the Jumo 004 (3000 BHP & 25 hrs TBO).
If all you consider is the outright cost of the engine, then the 2-strokes powering drones were the best engines of the war.
If you consider all factors that favour one engine to be paramount then that engine is favourite to be judged as the best. The war started in Europe in September 1939, being there in 1939 must be an important consideration, in my opinion.
But the question is what was the most efficiently built aircraft engine of the war.
If all you care about is ease of production then it must be some low HP 2-stroke because those are the simplest and cheapest engines used on aircraft during the war. But thats probably not what the OP had in mind, is it?
So work out some metric for evaluating the relative performance of different engines used on manned aircraft. Then work out a metric of comparing the production costs, like manhours + raw materials. Now evaluate the relative performance against the relative costs. If you want to factor in availability then that is a different factor, like adding in fuel consumption or high-altitude perf or even accessory/armament issues.
Shortround6
Major General
trying to fit the needed 12 or so engines on a single seat fighter was a bit of problem.
And building 10-12 five cylinder engines instead of one 12-14 cylinder engine doesn't really seem cheaper.
Great, but starting in 1939 for European engines and 1941 for engines from USA and Russia and add in a metric for minimum airframes in service and minimum engine life. An engine with a service life of 25 to 50 hours is experimental, you cannot run an air force with it.
ThomasP
Senior Master Sergeant
Hey blueskies,
The Jumo 004 put out ~1980 lbf static thrust at sea level. The 3000 BHP I listed for the Jumo 004 is the effective HP at ~560 mph at altitude. It is not exact as the efficiency of the Jumo 004 varied quite a bit at different speeds and pressure/density altitudes, but it is probably within 10%.
If we use the BHP divided by the weight of the engines, the value for the Cheetah X is ~.5 BHP/lb (355 BHP & 700 lbs) and that of the Jumo 004 is ~1.9 BHP/lb (3000 BHP & 1600 lbs). That makes the Jumo 004 about 3.8x as efficient as the Cheetah X in terms of HP/lb.
So if we divide the 5.68 value by 4 we get the Cheetah X coming out on top by a factor of 1.49.
If we throw in the man-hours labor per engine I think the Jummo 004 would come out ahead by a small margin, but if we use the total manufacturing costs including tooling and engine materials I suspect the Cheetah X would increase its lead. Unfortunately I do not have any info on the actual man-hours needed or the wholesale cost for the Cheetah X.
The Jumo 004 put out ~1980 lbf static thrust at sea level. The 3000 BHP I listed for the Jumo 004 is the effective HP at ~560 mph at altitude. It is not exact as the efficiency of the Jumo 004 varied quite a bit at different speeds and pressure/density altitudes, but it is probably within 10%.
If we use the BHP divided by the weight of the engines, the value for the Cheetah X is ~.5 BHP/lb (355 BHP & 700 lbs) and that of the Jumo 004 is ~1.9 BHP/lb (3000 BHP & 1600 lbs). That makes the Jumo 004 about 3.8x as efficient as the Cheetah X in terms of HP/lb.
So if we divide the 5.68 value by 4 we get the Cheetah X coming out on top by a factor of 1.49.
If we throw in the man-hours labor per engine I think the Jummo 004 would come out ahead by a small margin, but if we use the total manufacturing costs including tooling and engine materials I suspect the Cheetah X would increase its lead. Unfortunately I do not have any info on the actual man-hours needed or the wholesale cost for the Cheetah X.
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Shortround6
Major General
only if you include the hand crank for the Cheetah
You are making a very big mistake in comparing HP of a jet engine to HP of a piston engine. Thrust is what makes aircraft go, not HP. You need to compare that instead.
Thrust for a piston engine is (HP x Prop Efficiency x 326)/KTAS. A suitable peak prop efficiency for the WW2 era is ~0.88 - but keep in mind that it will depend on speed and altitude. Props lose efficiency with alt while jet engines generally gain.
Also keep in mind that prop weight should be taken into account for this sort of comparison;
Using an estimated prop weight of 110lbs for a total engine+prop weight of 810, I get this thrust to weight for a Cheetah X assuming a constant prop efficiency of 88% (note that the prop efficiency will never be 88% across the whole speed range)
Compared to the Jumo
When converted to SI
Regardless the Cheetah was thoroughly obsolescent as a combat type when WW2 started. It'd be much better to compare a wartime engine...
ThomasP
Senior Master Sergeant
Hey blueskies,
Do you realize that pretty much everything you just said (except for adding the prop weight & efficiency to the Cheetah data) was what I said?
At 500 KTAS (you used 575 mph while I used 560 mph) the thrust/weight you calculated for the Cheetah is .25 and for the Jumo 004 is 1.04, which gives a ratio of 4:1 in favor of the Jumo 004 (I came up with 3.8:1 in favor of the Jumo 004). I am pretty sure I understand the difference between thrust (force) and effective HP (power).
In reality, I do not think you could get a WWII era propeller to handle the tip speeds at 575 mph. So I limited the Cheetah driven airplane to ~475 mph, which is where the difference in our thrust/weight (or effective HP/weight) ratios came in.
Do you realize that pretty much everything you just said (except for adding the prop weight & efficiency to the Cheetah data) was what I said?
At 500 KTAS (you used 575 mph while I used 560 mph) the thrust/weight you calculated for the Cheetah is .25 and for the Jumo 004 is 1.04, which gives a ratio of 4:1 in favor of the Jumo 004 (I came up with 3.8:1 in favor of the Jumo 004). I am pretty sure I understand the difference between thrust (force) and effective HP (power).
In reality, I do not think you could get a WWII era propeller to handle the tip speeds at 575 mph. So I limited the Cheetah driven airplane to ~475 mph, which is where the difference in our thrust/weight (or effective HP/weight) ratios came in.
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ThomasP
Senior Master Sergeant
Also, the OP says nothing about what type of engine (ie fighter, bomber, transport, piston, axial jet, centrifugal jet, diesel, early-war, late-war, etc).
Yes, but by the time jet engines were entering service in non-experimental fashion, what was the average lifetime of a Luftwaffe piston fighter before it was shot down or strafed/bombed on the ground? Wouldn't surprise me if it was less than 25 hours?
ISTR that the TBO of the Napier Sabre was 25 hours well into 1943.
Luckily the RAF still had lots of other planes.special ed
1st Sergeant
- 4,857
- May 13, 2018
Various Lycoming, Franklin, Continental opposed engines of 40, 65 HP.
Note that today, GE has predicted that barring damage from outside sources, airliners could be scrapped after service life without removing the engines.
To digress into automotive, the original mid-50s small block Chevy V8 was optimized for low cost production, and only cost about $60 to produce: materials + labor.
Racers brag about what a successful engine it was, pointing out the multitude of wins ... however ... they often overlook the cost of aftermarket parts needed to make it live under racing conditions, including:
new and better sealing timing covers, valve covers and oil pan;
better forged or billet crank and rods;
girdle and cross drilled main bearing caps;
completely new valve actuators;
higher quality valves and seats;
different cam drive and flywheel systems;
and then the manifold scheme and matching was always a nightmare.
And that doesn't even begin to address the weaknesses of bean-counter influence on accessory design and compromises.
To digress into automotive, the original mid-50s small block Chevy V8 was optimized for low cost production, and only cost about $60 to produce: materials + labor.
Racers brag about what a successful engine it was, pointing out the multitude of wins ... however ... they often overlook the cost of aftermarket parts needed to make it live under racing conditions, including:
new and better sealing timing covers, valve covers and oil pan;
better forged or billet crank and rods;
girdle and cross drilled main bearing caps;
completely new valve actuators;
higher quality valves and seats;
different cam drive and flywheel systems;
and then the manifold scheme and matching was always a nightmare.
And that doesn't even begin to address the weaknesses of bean-counter influence on accessory design and compromises.
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