Fastest Piston Engined Aircraft of WW2?

drgondog · Sep 5, 2022

Macandy - The aroma of bovine fecal matter is in the air.

Nagasaki and Hiroshima and cessation of Invasion plans for Japan were the reason the P-51H contract was truncated from 2500 to 550.

The AAF wisely saw the jet - in the FJ-1/F-86 from NAA, P-80/F-80 from Lockheed and F-84 from Republic were sounder from performanc growth stand point than any Piston Engine Fighter and purchased accordingly. That said, the P-82/F-82 purchases continued into post war years to augment the P-51H and replace the P-61 as primary Night Air Defense primary fighter.

NAA contracts for XP-86 and USN FJ-1 began in May and June 1945 respecively

The P-51H and then P-82/F-82 were dedicated to Air Defense post WWII because of the Performance combined with Range. Not the P-47N, Not the P-38. The transition from AAF to National Guard units tasked to Air Defense were made on both coasts primarily, post WWII. Certainly not because the P-51H was a failure. During the post war 1940s the P-82 was the Only Log Range Escort capable of escorting B-29s, then B-36s, from England to Moscow.

The P-51H was stressed to 7.5 G for limit loading at max internal gross weight - nearly a full G above the P-51B/D at the same Gross Weight at take off (6.66) for 9600 pounds GW.

The maintainability of the P-51H, was particularly easy with respect to the engine maintenance and removal due to the unique combined purpose of the outer side panel dual engine mount/cowl design. It was the only model with Proven net Thrust Meredith exhaust system due to the improved lower cowl design.

Last but not least - the P-51H performance compared to P-51B/D at WEP was approximately 40mph faster (FTH to FTH), with much better climb rates and superior manueverability in all respects save equality in turn.

Shortround6 · Sep 5, 2022

wuzak said:
Hmm, max power of the V-1650-7 in the P-51D was 1,900hp+ using PN150 fuel. About 1,700 with PN130 fuel.

Pretty much correct.
The V-1650-7 in the P-51D was good for 1720hp at 18 1/4lbs boost in low gear (6200ft no RAM) which is NOT where the plane did 440mph. The extra 20hp is no big deal. The boost used is important as is the altitude. things that our contrary poster is leaving out.
In high gear the V-1650-7 was good for 1505hp at 18 1/4lbs at 19,300ft (no RAM). Both of these were using 100/130 fuel.

The V-1650-9 engine in the P-51H used the same supercharger gears as the V-1650-3 used in the P-51B. It had other changes that allowed to stand up to the power better. It was rated at 1930hp (close enough) at 10,100ft using 25lbs of boost (needs the 150 fuel or 115/145) and 1630hp at 23,500ft using 25lbs of boost.

The -9 engine was fitted for water injection and perhaps it could use 25lbs of boost using 100/130 fuel and the water injection.

RR might have gotten over 2270hp out of a Merlin on a test stand but that required either more than 25lbs of boost, low attitude operation and lower supercharger gears or over revving the engine or a combination.

In any case the 487mph speed (??? or anything over 450mph depending on airplane and racks fitted ) of the P-51H was not done using anything much over 1700hp.

In fact under test a P-51H did 450mph at 30,500ft using 67in (18 1/4lbs) about 1330hp according to the chart. 100/130 fuel and no water injection.

ThomasP · Sep 5, 2022

Thank you for the info on 262 losses.

GrauGeist · Sep 5, 2022

Macandy said:
There are plenty of other examples of late war piston engined fighters that required 50% or more power and the extra fragility to gain only an incremental gain in speed while even the first jets low powered were leaving them trailing helplessly in the slipstreams.

So why even bother putting any effort into upgrading prewar fighters at all, then?

Look at all that time and money wasted on trying to improve piston powered aircraft when they could have just waited ten years for reliable jets to become available.

Howard Gibson · Sep 5, 2022

Macandy said:
Ah yes, the decidedly unsuccessful P-51H, (quickly cancelled at wars end), a super stripped down ultra lightweight airframe fitted with a 2,270 hp Merlin to gain just 40MPH of performance over the much more durable P-51D that only required 1,315 hp while doing much the same job.
As we can see, the P-51D had a long post war service, because it rather proved the point, the extra bit of performance the P-51H provided with such great effort, was simply not worth the squeeze - and the huge extra maintenance headaches of running what was effectively a race plane.

There are plenty of other examples of late war piston engined fighters that required 50% or more power and the extra fragility to gain only an incremental gain in speed while even the first jets low powered were leaving them trailing helplessly in the slipstreams.

The speeds quoted for the lightweight Mustangs are based on 150 octane fuel and water injection. With the same fuel and stuff injected into the intakes, the lightweight Mustangs would be slightly faster, and they would be significantly more manoeuverable and faster climbing than a P-51D.

My general impression is that late war USAAF aircraft used 150 octane gas in testing anyway, and US Navy stuff didn't. The Goodyear F2G Corsair's top speed of 431mph does not sound impressive until you remember this, and note the 16,500ft altitude it was flying at.

Thumpalumpacus · Sep 5, 2022

The P-51H didn't fail; the war ended and that was that. The decision to cancel the remaining contract was not due to the airplane, but the circumstances.

GrauGeist · Sep 5, 2022

No jets postwar (1st gen) were reliable and they lacked range.

This is why the predominant aircraft in Korea were piston powered.

The F8F, P-51H and others were developed wartime with no real idea when the war would end (best estimates were 1946 or early 1947 at the latest).

The Japanese were still developing improved aircraft, their late war types (while not in great numbers) were formidible and a cause for concern for Allied leaders, especially since the Japanese were keeping their more advanced types in reserve on the home islands for the coming Allied invasion.

eljefe · Sep 5, 2022

I'm not sure this really fits with the intent of this thread, but I can't help but wonder how fast the Do-335 would have gone if they had avgas of comparable quality (octane) to that available to the Allies (with engine development based on that higher octane to match).

GrauGeist · Sep 5, 2022

One factor against the Do335, was it's weight - German engines performed well with the lower octane, but trying to move something that weighed in the neighborhood of 10 tons any faster than it already did, was going to take more than just high octane fuel.

Shortround6 · Sep 6, 2022

eljefe said:
I'm not sure this really fits with the intent of this thread, but I can't help but wonder how fast the Do-335 would have gone if they had avgas of comparable quality (octane) to that available to the Allies (with engine development based on that higher octane to match).

Well, pour 100/130 octane fuel or higher into the the fuel tanks. tweak the boost settings and watch (from behind cover) as the DB 603 engines throw large parts far and wide from the airframe or test stand.

A RR Griffon was 36.7 liters, a DB 603 was 44 liters.
However a single stage Griffon was about 1790lbs and a DB 603 was about 2000lbs and the 603 was a bit heavier (larger supercharger compared to the 603 A,B,C,D.
two stage Griffon was around 2075lbs.

There was no magic metallurgy. If you want 1800-1900hp out of a 2000lb engine you had several paths you take, One path used higher octane fuel and higher pressure in the cylinders and the weight of the construction that would stand up to the higher pressure/stress levels. Another path use lower octane fuel and lower pressure in the larger cylinders that allowed for larger but lighter cylinders (for their size) and engine construction.
You want to use the higher octane allied fuel and the higher pressures in the cylinders that fuel will allow you need to increase the weight of the engine parts to standup to the loads/stresses.
The Jumo 213 used a 3rd path. it stayed at the 35 liter displacement of the Jumo 211 but they increase the engine rpm to make more power. And at comparable power to the Griffon and DB 603 it would up weighing a bit over 2000lbs. If you increase the RPM by 10% you increase the loads on the pistons, con rods and crankshaft by 21%. A Jumo 213A ran 25% faster than Jumo 211J.

The Germans designed engines that would give them the power to weight ratio that they wanted (everybody wanted higher power to weight ratios) with the fuels they could get or planned to get. RR designed engines that would give them similar power to weight ratios using the fuel/s they could get.
There were a few points of difference but the Germans were not going to get a large boost in power using the higher octane (higher pressure in the cylinders) without either breaking the engines or adding a fair amount of weight (and larger radiators).

Macandy · Sep 6, 2022

Thumpalumpacus said:
The P-51H didn't fail; the war ended and that was that. The decision to cancel the remaining contract was not due to the airplane, but the circumstances.

Nope, the juice wasn't worth the squeeze, jets were faster and had limitless potential to get much faster. They all got the chop, the current and planned piston engined fighters, with the exception of the F4U which still had utility as a ground pounder.

The P-51H was a fragile race plane, so fragile, the USAF wouldn't send it to Korea and send the marginally slower, but much tougher P-51D instead.

Macandy · Sep 6, 2022

Howard Gibson said:
The speeds quoted for the lightweight Mustangs are based on 150 octane fuel and water injection. With the same fuel and stuff injected into the intakes, the lightweight Mustangs would be slightly faster, and they would be significantly more manoeuverable and faster climbing than a P-51D.

My general impression is that late war USAAF aircraft used 150 octane gas in testing anyway, and US Navy stuff didn't. The Goodyear F2G Corsair's top speed of 431mph does not sound impressive until you remember this, and note the 16,500ft altitude it was flying at.

Using ever conceivable racing plane trick, Dago Red, the fastest Mustang ever needed 3,800 hp to achieve 520 mph - a marginal improvement over the P-51H

P-51D - 1,315 hp - 440 mph
P-51H - 2,270 hp - 490 mph
Dago Red - 3,800 hp - 520 mph

Prop planes had hit a brick wall and you were doubling the installed hp for every increment of performance up till the tips crapped out and the prop couldn't give any more thrust

wuzak · Sep 6, 2022

Macandy said:
Using ever conceivable racing plane trick, Dago Red, the fastest Mustang ever needed 3,800 hp to achieve 520 mph - a marginal improvement over the P-51H

P-51D - 1,315 hp - 440 mph
P-51H - 2,270 hp - 490 mph
Dago Red - 3,800 hp - 520 mph

Prop planes had hit a brick wall and you were doubling the installed hp for every increment of performance up till the tips crapped out and the prop couldn't give any more thrust

P-51D

P-51D Performance

(5)	Maximum Speed – War Emergency Power (3000 RPM. – 67" Hg. M.P.)

	At Sea Level	368 MPH
	At Low Blower A.C.A.*	414 MPH/11,300 ft.
	At High Blower A.C.A.*	440 MPH/24,500 ft.

(6)	Maximum Speed – Military Rating (3000 RPM – 61" Hg. M.P.)

	At Sea Level	355 MPH
	At Low Blower A.C.A.*	412 MPH/13,300 ft.
	At High Blower A.C.A.*	435 MPH/26,200 ft.

P-51H

P-51H Performance

(5)	Maximum Speed – Combat Rating (3000 R.P.M. – 90" Hg. M.P. – W.I.)

	In High Blower at A.C.A.*	471 m.p.h./22,700 ft.
	In Low Blower at A.C.A.*	449 m.p.h./9000 ft.
	In Low Blower at Sea Level	413 m.p.h.

(6)	Maximum Speed – Combat Rating (3000 R.P.M. – 80" Hg. M.P. – W.I.)

	In High Blower at A.C.A.*	466 m.p.h./25,700 ft.
	In Low Blower at A.C.A.*	447 m.p.h./12,700 ft.
	In Low Blower at Sea Level	395 m.p.h.

(7)	Maximum Speed – War Emergency Rating (3000 R.P.M. – 67" Hg. M.P.)

	In High Blower at A.C.A.*	447 m.p.h./29,800 ft.
	In Low Blower at A.C.A.*	433 m.p.h./17,800 ft.
	In Low Blower at Sea Level	360 m.p.h.

(8)	Maximum Speed – Combat Rating (3000 R.P.M. – 61" Hg. M.P.)

	In High Blower at A.C.A.*	441 m.p.h./32,000 ft.
	In Low Blower at A.C.A.*	431 m.p.h./20,400 ft.
	In Low Blower at Sea Level	342 m.p.h.

Note that the P-51H has maximum performance of 447mph at 29,800ft on 67" Hg MAP against the P-51D's 440mph at 24,500ft, also at 67" Hg MAP.

Piloted by Steve Hinton, this heavily modified WWII era P-51 managed to shatter the piston-powered aircraft speed world record. Although to clock an official top speed, that velocity had to be held over 3 kilometers. Following such official speed records, Voodoo sustained 531 MPH over the 3 KM but managed to record a blistering 554 MPH top speed during a low fly-by.

https://www.hotcars.com/the-15-fastest-propeller-driven-airplanes-of-all-time/

But that is at a lower altitude than the max speeds of the P-51D and P-51H. Lower than the altitudes for max speed in low blower as well.

Shortround6 · Sep 6, 2022

Macandy said:
P-51D - 1,315 hp - 440 mph
P-51H - 2,270 hp - 490 mph
Dago Red - 3,800 hp - 520 mph

Since you are not providing the altitude at which those speeds were achieved, a critical piece of of information, the information is worthless.

Dago Red's speed record was set over Mojave and at under 5,000ft. (air Field was 2801 ft ) Actual altitude density due to temperature was higher.

A P-51D needed 1650hp to go 395mph at 5,000ft on a "standard day" (59 degrees F at sea level).
The P-51D needed a bit over 1400hp to do 442mph at 26,000ft.

Speeds without altitude are worthless.

Shortround6 · Sep 6, 2022

wuzak said:
But that is at a lower altitude than the max speeds of the P-51D and P-51H. Lower than the altitudes for max speed in low blower as well.

Reports say that the Record over Mojave was done at 110in Hg. M.P.
It was also done at 3800 rpm which allows the supercharger to be turning at 26.66% faster than at 3000rpm which can really change the pressure.
Assuming that the supercharger gears and the impeller were stock.

Macandy · Sep 6, 2022

drgondog said:
Macandy - The aroma of bovine fecal matter is in the air.

Nagasaki and Hiroshima and cessation of Invasion plans for Japan were the reason the P-51H contract was truncated from 2500 to 550.

The AAF wisely saw the jet - in the FJ-1/F-86 from NAA, P-80/F-80 from Lockheed and F-84 from Republic were sounder from performanc growth stand point than any Piston Engine Fighter and purchased accordingly. That said, the P-82/F-82 purchases continued into post war years to augment the P-51H and replace the P-61 as primary Night Air Defense primary fighter.

NAA contracts for XP-86 and USN FJ-1 began in May and June 1945 respecively

The P-51H and then P-82/F-82 were dedicated to Air Defense post WWII because of the Performance combined with Range. Not the P-47N, Not the P-38. The transition from AAF to National Guard units tasked to Air Defense were made on both coasts primarily, post WWII. Certainly not because the P-51H was a failure. During the post war 1940s the P-82 was the Only Log Range Escort capable of escorting B-29s, then B-36s, from England to Moscow.

The P-51H was stressed to 7.5 G for limit loading at max internal gross weight - nearly a full G above the P-51B/D at the same Gross Weight at take off (6.66) for 9600 pounds GW.

The maintainability of the P-51H, was particularly easy with respect to the engine maintenance and removal due to the unique combined purpose of the outer side panel dual engine mount/cowl design. It was the only model with Proven net Thrust Meredith exhaust system due to the improved lower cowl design.

Last but not least - the P-51H performance compared to P-51B/D at WEP was approximately 40mph faster (FTH to FTH), with much better climb rates and superior manueverability in all respects save equality in turn.

Nope, the USAF had ordered jet fighters by the thousands by wars end and was planning a mass transition to jets in 1945/46.

The P-51H order of 2,000 was a bit part player to tide units over until they got their jets - it was the Mustangs last hurrah - the USAF had ordered 5,000 P-80's in the first tranche, and was going to order a further 5,000
Lets just put that P-51H order into perspective - the USAF cancelled orders for 5,092 B-29 heavy bombers on VJ Day

Jets were the future, no amount of tinkering could change the fact, the piston engine couldn't drive a fighter any faster than @ 500mph, and propellor efficiency started to drop off dramatically after 450mph needing insanely increasing amounts our power just to gain a few MPH.

Meanwhile, the much more efficient jet engine, was rule of thumb translating 1,000lb of thrust into @ 1,000 hp equivalent.
So a P-80 had nearly '5,000hp' in a cleaner airframe than a P-51 - and was not much heavier.

wuzak · Sep 6, 2022

Also, from the previous documents:

P-51D

(11)	Time to Climb to 20,000 ft.

	At War Emergency Power	6.4 min.
	At Military Power	7.0 min.
	At Normal Power	10.7 min.

(12)	Service Ceiling

	At 3000 RPM	36,900 ft.
	At 2700 RPM	35,500 ft.

P-51H

(15)	Time to Climb to 20,000 ft.

	With Combat Power (90") Hg. M.P.	4.58 min.
	With Combat Power (80") Hg. M.P.	4.81 min.
	With War Emergency Power	6.37 min.
	With Military Power	7.03 min.
	With Normal Power	11.35 min.

(16)	Service Ceiling

	At 3000 R.P.M.	40,100 ft.
	At 2700 R.P.M.	37,100 ft.

Shortround6 · Sep 6, 2022

OK lets put the P-51H order into perspective.

Macandy said:
The P-51H order of 2,000 was a bit part player to tide units over until they got their jets - it was the Mustangs last hurrah - the USAF had ordered 5,000 P-80's in the first tranche, and was going to order a further 5,000
Lets just put that P-51H order into perspective

Out of those 10,000 planes they built 1715, and it took them until 1950 to do it.

drgondog · Sep 6, 2022

Macandy said:
Nope, the USAF had ordered jet fighters by the thousands by wars end and was planning a mass transition to jets in 1945/46.

The P-51H order of 2,000 was a bit part player to tide units over until they got their jets - it was the Mustangs last hurrah - the USAF had ordered 5,000 P-80's in the first tranche, and was going to order a further 5,000
Lets just put that P-51H order into perspective - the USAF cancelled orders for 5,092 B-29 heavy bombers on VJ Day

Jets were the future, no amount of tinkering could change the fact, the piston engine couldn't drive a fighter any faster than @ 500mph, and propellor efficiency started to drop off dramatically after 450mph needing insanely increasing amounts our power just to gain a few MPH.

Meanwhile, the much more efficient jet engine, was rule of thumb translating 1,000lb of thrust into @ 1,000 hp equivalent.
So a P-80 had nearly '5,000hp' in a cleaner airframe than a P-51 - and was not much heavier.

Troll? or Ignorant?

The P-80 at VJ Day was less capable, performance wise than the Me 262. The AAF transitioning to becoming a separate service as USAF had the prime mission of a Strategic/Global reach Air Force with reach and destructive power unattainable by USN. The B-29 was the centerpiece and escorted missions with nuclear strike emphasis was the primary reason for being a separate command. At VJ Day, the US Army and USN and USMC all had tactical assets under their command much more capable for CAS than P-80.

The P-80 had no role in LR Strategic missions. At its development level on VJ Day and for several years afterwards, it was primarily a short range (comparably) interceptor and an intermediate range candidate for CAS. However it was less suited for tactical operations when compared to P-47 or P-38 or P-51 (D or H). Ditto FJ-1 and F-86 and F-84.

There was zero option to discard the P-51D/H just because the top speeds were well under the P-80 for max continuous power. Both had equal bomber killing firepower to the P-80. Both were capable of converting to 20mm. There were no threats for the post war years that dictated point interception superior performance at any location in continental US over a P-51H. IIRC the ceiling for the P-51H was considerably higher than the P-80 - and the tactical radius was far greater - making it far more capable as an escort fghter than the P-80.

Wuzak and Shortround nailed your lack of understanding of variable altitude and boost settings for performance comparisons. Please note that the speed runs for Voodoo for closed course runs, achieved 550ph - approximately 80mph over P-51D at 67" at 5000 ft and faster than VJ Day P-80.

Shortround6 · Sep 6, 2022

I would also note that the early jets sucked up fuel at a tremendous rate. They were experimenting with towing a P-80 behind B-29s for "escort" duty with not only the P-80 being towed out with a dead engine and starting the engine once the tow was disconnected but the P-80 was expected to hook back on once the group had exited the danger area for the flight back. While a few test tows the P-80 went ok the first attempt to actually hook on in flight didn't go well and once hooked on the pilot had extreme difficulty unhooking and the attachment would up pointed backwards blocking the pilots view. He was able to land the P-80 but that ended the experiment.

Piston powered planes were going to be needed to escort piston powered bombers for several years after the war and in fact it was possible to escort the early jet bombers like the B-45.
The B-45 could fly faster than the P-51 but it's cruising speed was within the speed range of the P-51 if max range was not needed.

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