Post WW II fighters, Ki-84 Hei vs TA-152H vs F8F-2

Ronny

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These fighters are from the end of WW II period,
But they arrive too late to have any impact in the war. However, if they can arrive at the start of WW II
which one is the best as air superiority fighter?
Best here defined as they are most likely to win in air combat when face the others two
Ki-84 Hei
22249C17-2E79-48AC-98FE-03950864C7CD.jpeg

F8F-2 Bear cat
374434DA-8654-4DC3-9593-522EFFEA40AA.jpeg

TA-152H
869FDF2C-355A-4719-900B-9B5443DB48E1.jpeg
 
I think perhaps this topic belongs in alternative history/speculation.
 
Grumman F8F Bearcat was designed to be a fleet defense interceptor. Try to think of Bearcat as a pre-shrunk Hellcat, built around the same engine, but optimized for rapid climb. The USN hoped that Bearcats could intercept kamakazi well befor ethey got close enough to damage capital ships.
Meanwhile, Kurt Tank designed the Ta 152 as a high-altitude interceptor. Its extended wings and super-charged engine were deigned to still climb well above 30,000 feet where WALLIED heavy bombers cruised on their way to bombarding targets within Germany.
 
Grumman F8F Bearcat was designed to be a fleet defense interceptor. Try to think of Bearcat as a pre-shrunk Hellcat, built around the same engine, but optimized for rapid climb. The USN hoped that Bearcats could intercept kamakazi well befor ethey got close enough to damage capital ships.
Meanwhile, Kurt Tank designed the Ta 152 as a high-altitude interceptor. Its extended wings and super-charged engine were deigned to still climb well above 30,000 feet where WALLIED heavy bombers cruised on their way to bombarding targets within Germany.
I know that, but F8F-2 is introduced much later than Ta-152H so maybe the high altitude capability has been improved
 
Grumman F8F Bearcat was designed to be a fleet defense interceptor. Try to think of Bearcat as a pre-shrunk Hellcat, built around the same engine, but optimized for rapid climb. The USN hoped that Bearcats could intercept kamakazi well befor ethey got close enough to damage capital ships.
Meanwhile, Kurt Tank designed the Ta 152 as a high-altitude interceptor. Its extended wings and super-charged engine were deigned to still climb well above 30,000 feet where WALLIED heavy bombers cruised on their way to bombarding targets within Germany.
I know that, but F8F-2 is introduced much later than Ta-152H so maybe the high altitude capability has been improved
Two different missions/scenarios. Protection of the fleet/carriers which is a relatively small footprint whereas the Ta152H needed to cover more ground or at least range further to intercept the bomber stream before it got to the Fatherland or the target. Size is always an issue on the carrier as well which drove some of the design requirements. Bearcat was designed to address targets at medium/low altitudes, the Ta-152H at higher altitudes where the bobmers were to be found. If they had flown against each other, the only time they likely would have met was when the Bearcat was intercepting it taking off or landing, much like Mustangs did with Me262s. As for the Ki-84, F6Fs held their own against them over Japan in the final months of the war but that can also be due to the experience of the Hellcat pilots and their superior numbers. The Ki-84 is my favorite of the late war Japanese fighters with the Ki-100 a close second..

Enjoy the Day! Mark
 
Regarding top speed:
At 35,000 ft:

P-51H reached 482.5 mph = 776 km/h
F4U-5 reached 395 knots = 731 km/h
Ta-152H reached 715 km/h
F8F-2 reached 360 knots = 666 km/h
At 25,000 ft:
P-51H reached 487.5 mph = 784 km/h
F4U-5 reached 407 knots = 753 km/h
Ta-152H reached 700 km/h
F8F-2 reached 383 knots = 709 km/h
At 15,000 ft:
P-51H reached 465 mph = 748 km/h
F4U-5 reached 390 knots = 722 km/h
Ta-152H reached 655 km/h
F8F-2 reached 373 knots = 690 km/h
At 5,000 ft:
P-51H reached 445 mph = 716 km/h
F4U-5 reached 364 knots = 674 km/h
Ta-152H reached 607 km/h
F8F-2 reached 353 knots = 653 km/h
Apparently, Ta-152H is nothing specially unless at extremely high altitude, and P-51H is so extremely fast, it even faster than F8F-2 and F4U-5 at low altitude
F8F-2 chart
F8F-2 chart.jpg

P-51H charts
P-51H speed HG.jpg

Ta-152 charts
Ta-152 chart.jpg

F4U-5 chart
F4U-5 chart.jpg
 
Hi Ronny,

Regarding top speed:
At 25,000 ft:
P-51H reached 487.5 mph = 784 km/h
F4U-5 reached 407 knots = 753 km/h
Ta-152H reached 700 km/h
F8F-2 reached 383 knots = 709 km/h

It's worth noting that the P-51H when tested at Wright Field in 1946 only achieved a top speed of (if my conversion is correct) 726 km/h at its high gear full throttle height of 6460 m, using 90" Hg @ 3000 rpm (on a V-1650-9 running full war emergency boost without requiring water injection):


I haven't quite figured out the V-1650-9's history and timeline yet to understand why they would use special high octane fuel for testing when the aircraft was actually supposed to use water injection, though I noticed Calum Douglas' book does have an interesting graph showing the engine's rather complicated family history :)

On a related note, the F8F-2 manuals I have seen indicate that the water injection system was not yet installed at the (fairly late) date the manuals were issued, and I'm not certain they were ever retro-fitted.

Regards,

Henning (HoHun)
 
Hi Ronny,

Regarding top speed:
At 25,000 ft:
P-51H reached 487.5 mph = 784 km/h
F4U-5 reached 407 knots = 753 km/h
Ta-152H reached 700 km/h
F8F-2 reached 383 knots = 709 km/h

It's worth noting that the P-51H when tested at Wright Field in 1946 only achieved a top speed of (if my conversion is correct) 726 km/h at its high gear full throttle height of 6460 m, using 90" Hg @ 3000 rpm (on a V-1650-9 running full war emergency boost without requiring water injection):


I haven't quite figured out the V-1650-9's history and timeline yet to understand why they would use special high octane fuel for testing when the aircraft was actually supposed to use water injection, though I noticed Calum Douglas' book does have an interesting graph showing the engine's rather complicated family history :)

On a related note, the F8F-2 manuals I have seen indicate that the water injection system was not yet installed at the (fairly late) date the manuals were issued, and I'm not certain they were ever retro-fitted.

Regards,

Henning (HoHun)
That because the P-51H in that test carry bomb rack and rockets rack, which slow it down and the aircraft also heavier than other test since it carry full fuel
Capture.JPG

In NA-117 test, gross weight 7302lb, the top speed is 481mph
p-51h-na117.jpg


In NA-126 test, Report No. NA-8284, gross weight 8000lb the top speed is 491mph.
p-51h-altperf-91444.jpg
 
Hi Ronny

That because the P-51H in that test carry bomb rack and rockets rack, which slow it down and the aircraft also heavier than other test since it carry full fuel

From my experience in analysing WW2 aircraft performance, empty bomb racks and rocket launcher stubs don't make enough of a difference in total drag to explain the performance difference. Weight also hasn't much of an influence on top speed at full throttle height since that's a situation dominated by parasite drag.

I don't believe the graph you're showing is actual tested performance, as it's attributed to report NA-8284, which in the revision NA-8284-A clearly states is based on calculations (with some flight test results thrown in, admittedly :):


"Revised performance calculations for the subject airplane have been prepared on the basis of wind tunnel data, estimated engine performance, and correlations with the results of flight tests. These calculations were necessary to provide complete performance data for airplane equipped with an engine incorporating a carburetor for fuel metering instead of the speed density pump originally anticipated in preparing report NA-8284 dates September 25, 1944. This report presents the results of the revised calculations together with a discussion of the data and methods used."

This test ...


... notes that the P-51H achieved 724 km/h at 9370 m (with bomb racks, but no rocket stubs) using only dry war emergency power (67" Hg @ 3000 rpm):

"High speed and climb performance were good and results obtained compare very closely to the manufacturer’s guarantee."

If the full 90" Hg had been available (which due to technical difficulties weren't), the tested P-51H would indeed have been markedly faster, but only at altitudes below the full throttle height for 67" Hg. Above, it was limited by the capability of the supercharger to generate boost pressure, and while that would have been slightly improved by the charge cooling effect of the injected water-alcohol mixture, that effect would have been quite small. (A British report expected a 4% power increase from MW50 on German engines above full throttle height, and that would translated into something like a 1% speed increase.)

Regards,

Henning (HoHun)
 
Hi Ronny
That because the P-51H in that test carry bomb rack and rockets rack, which slow it down and the aircraft also heavier than other test since it carry full fuel
From my experience in analysing WW2 aircraft performance, empty bomb racks and rocket launcher stubs don't make enough of a difference in total drag to explain the performance difference. Weight also hasn't much of an influence on top speed at full throttle height since that's a situation dominated by parasite drag.
The rack will reduce top speed by around 12 mph or around 19 km/h ,as shown on P-51B test. P-51H fly faster and overall a less draggy aircraft, so the effect of the rack on overall speed of the aircraft would be greater compared to P-51B
and even though weight is no longer the dominate influence at high speed, i doubt that it wouldn't make a few percentage different
P-51B.JPG


I don't believe the graph you're showing is actual tested performance, as it's attributed to report NA-8284, which in the revision NA-8284-A clearly states is based on calculations (with some flight test results thrown in, admittedly :):


"Revised performance calculations for the subject airplane have been prepared on the basis of wind tunnel data, estimated engine performance, and correlations with the results of flight tests. These calculations were necessary to provide complete performance data for airplane equipped with an engine incorporating a carburetor for fuel metering instead of the speed density pump originally anticipated in preparing report NA-8284 dates September 25, 1944. This report presents the results of the revised calculations together with a discussion of the data and methods used."
Well, while they certainly didn't fly all point in the envelope to get that chart, they certainly did the flight test to draw the chart, whether the flight test included the top speed test is up to debate


This test ...


... notes that the P-51H achieved 724 km/h at 9370 m (with bomb racks, but no rocket stubs) using only dry war emergency power (67" Hg @ 3000 rpm):

"High speed and climb performance were good and results obtained compare very closely to the manufacturer’s guarantee."

If the full 90" Hg had been available (which due to technical difficulties weren't), the tested P-51H would indeed have been markedly faster, but only at altitudes below the full throttle height for 67" Hg. Above, it was limited by the capability of the supercharger to generate boost pressure, and while that would have been slightly improved by the charge cooling effect of the injected water-alcohol mixture, that effect would have been quite small. (A British report expected a 4% power increase from MW50 on German engines above full throttle height, and that would translated into something like a 1% speed increase.)

Regards,

Henning (HoHun)
In that test,
the flight test crew was unable to obtain preliminary performance at the war emergency rating using water injection (90 “Hg and 3000 RPM) due to the engine surge and general malfunctioning of the water injection system and Simmons manifold pressure regulator
There is quite a big different in speed between 67" Hg and 90" Hg
2222.JPG
 
Last edited:
Hi Ronny,

The rack will reduce top speed by around 12 mph or around 19 km/h ,as shown on P-51B test. P-51H fly faster and overall a less draggy aircraft, so the effect of the rack on overall speed of the aircraft would be greater compared to P-51B
and even though weight is no longer the dominate influence at high speed, i doubt that it wouldn't make a few percentage different

Thanks for the data points! The P-51B with the razorback actually is cleaner than the P-51D too, so I'm not sure how the P-51H compares, even if it might be cleaner than the P-51D as well.

Well, while they certainly didn't fly all point in the envelope to get that chart, they certainly did the flight test to draw the chart, whether the flight test included the top speed test is up to debate

The top speed test is hard to replace as airframe and engine are subject to some non-linear influences up there. But you're right, they unfortunately were a bit vague on the nature of the tests.

In that test,
the flight test crew was unable to obtain preliminary performance at the war emergency rating using water injection (90 “Hg and 3000 RPM) due to the engine surge and general malfunctioning of the water injection system and Simmons manifold pressure regulator
There is quite a big different in speed between 67" Hg and 90" Hg

Yes, and that makes these graphs a bit suspect. To get from 460 mph to 482 mph (roughly reading the chart) at the same altitude, you need very roughly (482/460)^3 = 15% more power. At the same rpm and the same boost pressure, how is that extra power going to be generated?

One explanation might be that the graph was prepared for an increase in rpm figured in for war emergency power.

You can see the same kind of difference between the 46" Hg and the 67/70" Hg graphs as between the 67/70" Hg and the 80/90" Hg graphs. I'm pretty sure the 46" Hg graph is for a reduced rpm, for example 2700 rpm. By extrapolation, the 80/90" Hg would appear to be based on an engine speed increased beyond the 3000 rpm used with the 67"/70" Hg settings - maybe 3200 rpm, for example.

You can see how at the same rpm, the 67" Hg and the 90" Hg curves could be expected to coincede at altitude, as in this graph:


What do you think of this? It's a fresh thought I haven't cross-checked, so I might well be wrong even if it looks plausible at first sight :)

Regards,

Henning (HoHun)
 
The Republic P-72 should have been quite the performer. The estimate was for a speed of 504 mph at 25,000 feet with a R-4360-19 engine producing 3,650 hp. Production models were supposed to use the P-47N wing however which had a slightly greater span and would decrease that top speed slightly.

Two USN aircraft worth mentioning are the Grumman F7F and the Boeing XF8B. The F7F might be cheating by using two engines however.
 
Hi again,

To get from 460 mph to 482 mph (roughly reading the chart) at the same altitude, you need very roughly (482/460)^3 = 15% more power. At the same rpm and the same boost pressure, how is that extra power going to be generated?

One explanation might be that the graph was prepared for an increase in rpm figured in for war emergency power.

OK, I just found this graph:


This indicates clearly that my hypothesis regarding War Emergency Power being attained at an engine speed greater than 3000 rpm is not correct.

You can see that the static power (red graph) at 30000 ft is ...

3000 rpm, 90" Hg, water injection: 1450 HP
3000 rpm, 80" Hg, water injection: 1450 HP
3000 rpm, 70" Hg, no water injection: 1220 HP
3000 rpm, 61" Hg, no water injection: 1220 HP

And at 13000 ft ...

3000 rpm, 90" Hg, water injection: 1880 HP
3000 rpm, 80" Hg, water injection: 1880 HP
3000 rpm, 70" Hg, no water injection: 1620 HP

So the assumption apparently is that the addition of water injection at unchanged boost pressure increases horse power by 230 HP in high supercharger gear, and by 260 HP in lower supercharger gear.

As this is a gain in the region of 16 - 19% of brake horse power at the respective altitudes, this seems to be far more than the 4% expected under the same condition by the British estimate I mentioned earlier.

What's more, the power curves in the booklet are not identical to the one used for the revised edition of the NAA report, which due to the substitution of the Bendix speed density pump with a carburetter have a reduced full throttle height.

Original curve with the Bendix speed density pump:


Revised curve with carburettor:


The report (referred to as NA-8284-A, I believe) states:

"These calculations were necessary to provide complete performance data for airplane equipped with an engine incorporating a carburetor for fuel metering instead of the speed density pump originally anticipated in preparing report NA-8284 dates September 25, 1944. "

This leads to the following conclusion:

- The coloured "booklet" figures were prepared on the basis of an estimate of engine power for the expected production configuration, which is shown in p-51h-booklet-pg10.jpg, which is basically identical to that in p-51-powercurve.jpg.
- Engine power had to be revised a bit towards lower altitudes due to the (expected) introduction of a carburettor, and that power curve is depicted in p-51h-na-8284-pg12.jpg.
- The revision of the power curve means that the coloured "booklet" performance figures are purely theoretical as they represent an interim state of planning that was invalidated by the course of engine development.
- The calculated performance resulting from the revision is depicted in this graph: http://www.wwiiaircraftperformance.org/mustang/p-51h-na-8284-pg5.jpg

I hope that helps to sort out the various and partially controdicting charts! :)

Regards,

Henning (HoHun)
 
Hi again,

To get from 460 mph to 482 mph (roughly reading the chart) at the same altitude, you need very roughly (482/460)^3 = 15% more power. At the same rpm and the same boost pressure, how is that extra power going to be generated?

One explanation might be that the graph was prepared for an increase in rpm figured in for war emergency power.

OK, I just found this graph:


This indicates clearly that my hypothesis regarding War Emergency Power being attained at an engine speed greater than 3000 rpm is not correct.

You can see that the static power (red graph) at 30000 ft is ...

3000 rpm, 90" Hg, water injection: 1450 HP
3000 rpm, 80" Hg, water injection: 1450 HP
3000 rpm, 70" Hg, no water injection: 1220 HP
3000 rpm, 61" Hg, no water injection: 1220 HP

And at 13000 ft ...

3000 rpm, 90" Hg, water injection: 1880 HP
3000 rpm, 80" Hg, water injection: 1880 HP
3000 rpm, 70" Hg, no water injection: 1620 HP

So the assumption apparently is that the addition of water injection at unchanged boost pressure increases horse power by 230 HP in high supercharger gear, and by 260 HP in lower supercharger gear.

As this is a gain in the region of 16 - 19% of brake horse power at the respective altitudes, this seems to be far more than the 4% expected under the same condition by the British estimate I mentioned earlier.

What's more, the power curves in the booklet are not identical to the one used for the revised edition of the NAA report, which due to the substitution of the Bendix speed density pump with a carburetter have a reduced full throttle height.

Original curve with the Bendix speed density pump:


Revised curve with carburettor:


The report (referred to as NA-8284-A, I believe) states:

"These calculations were necessary to provide complete performance data for airplane equipped with an engine incorporating a carburetor for fuel metering instead of the speed density pump originally anticipated in preparing report NA-8284 dates September 25, 1944. "

This leads to the following conclusion:

- The coloured "booklet" figures were prepared on the basis of an estimate of engine power for the expected production configuration, which is shown in p-51h-booklet-pg10.jpg, which is basically identical to that in p-51-powercurve.jpg.
- Engine power had to be revised a bit towards lower altitudes due to the (expected) introduction of a carburettor, and that power curve is depicted in p-51h-na-8284-pg12.jpg.
- The revision of the power curve means that the coloured "booklet" performance figures are purely theoretical as they represent an interim state of planning that was invalidated by the course of engine development.
- The calculated performance resulting from the revision is depicted in this graph: http://www.wwiiaircraftperformance.org/mustang/p-51h-na-8284-pg5.jpg

I hope that helps to sort out the various and partially controdicting charts! :)

Regards,

Henning (HoHun)
I think i found where the 495 mph top speed came from
Capture.JPG
 
Last edited:
Hi Ronny,

I think i found where the 495 mph top speed came from
View attachment 667900

Good find! :)

The second XP-51G was shipped to the United Kingdom in February 1945. This plane was also named Mustang V, and bore the RAF serial number FR410. It is widely reported to have achieved a speed of 495 mph during tests at the A&AEE at Boscombe Down in February 1945, although NAA claimed only 472 mph for the other G at the same altitude.

Boscombe Down tests normally are quite thorough, so that's promising. The test of FR.410 doesn't seem to be on Mike William's site though, and if Joe Bougher writes "widely reported", that probably is a phrase he chose because he wasn't able to verify the claim.

Mike has one test on his site that is relevant to the P-51H, though it's for a Mustang III airframe with a RM 14SM Merlin 100 engine:


Note that the full throttle heights are lower than for the projected data even in the revised report.

This matches this test:

http://www.wwiiaircraftperformance.org/mustang/p-51h-64182.html

C. Critical Altitude.

The critical altitudes for normal rated power climb (46" Hg., MP and 2700 rpm) are 17,400 ft. for low blower and 30,700 ft. for high blower. The critical altitudes for war emergency power climb (90" Hg., H2O and 3000 rpm) are 16,000 ft. for high blower and by extrapolation, approximately 2200 ft. for low blower.

According to my estimate, the static full throttle heights (without ram effect) would be as follows:

- High Gear: 19,500 ft, Low Gear: 4,000 ft ... original draft, Bendix pressure pump
- High Gear: 17,000 ft, Low Gear: 3,500 ft ... revised draft, carburetor
- High Gear: 14,900 ft, Low Gear: 900 ft ... actual testing by USAAF (I calculated these static values from the climb speed values given in the report)

The British test (with ram effect at climb speed) is not directly comparable as the values are for +25 lbs/sqin boost (= 80" Hg) :

- High Gear: 13,000 ft, Low Gear: 1,600 ft

High gear full throttle height is even lower than in the USAAF tests, so maybe that engine was not representative for production status either. Still some things left to be figured out! ;-)

Regards,

Henning (HoHun)
 
Hi agin,


I just found this article explaining the pump and its history:


The article is a bit confusing, as it states, on one hand:
Successfully tested on a Merlin 66, the speed-density fuel metering system then became standard equipment on all following engine models.

But also on the other hand:

A decision was made to use the Speed Density equipped V-1650-11 in the P-51L airplane, and it was necessary to provide Water Injection (ADI) for high power detonation control. The second-generation models incorporating this feature were the SD-400C2 and SD-400D25. A new "Water Regulator" was developed and integrated with the Speed Density Fuel Control.

Engineering and development delayed the production of an initial batch of 70 SD-400C2 units intended for the first batch of 50 P-51L airplanes that was scheduled for completion by September 1945. In June 1945, the decision was made to defer production of this first batch of production aircraft, engines and fuel controls until January 1946.

Development of the SD-400C2 fuel control was not completed prior to the end of hostilities in August 1945, which resulted in the immediate termination of production contracts for the V-1650-11 and the P-51L. Development work did continue on the V-1650-11 until October 1945. Following the third unsuccessful attempt to run a 50-hour preliminary flight-rating test, the program was terminated.

So I suppose this does not imply that the V-1650-9 wasn't planned for, at least, temporarily, a speed density unit. Also "the program was terminated" seems a bit ambiguous as it's not clear if that's the fuel control development program for the V-1650 in general, or the V-1650-11 in particular (or maybe the P-51L in particular).

Regards,

Henning (HoHun)
 
Hi Ronny,

I think i found where the 495 mph top speed came from
View attachment 667900

Good find! :)

The second XP-51G was shipped to the United Kingdom in February 1945. This plane was also named Mustang V, and bore the RAF serial number FR410. It is widely reported to have achieved a speed of 495 mph during tests at the A&AEE at Boscombe Down in February 1945, although NAA claimed only 472 mph for the other G at the same altitude.

Boscombe Down tests normally are quite thorough, so that's promising. The test of FR.410 doesn't seem to be on Mike William's site though, and if Joe Bougher writes "widely reported", that probably is a phrase he chose because he wasn't able to verify the claim.

Mike has one test on his site that is relevant to the P-51H, though it's for a Mustang III airframe with a RM 14SM Merlin 100 engine:


Note that the full throttle heights are lower than for the projected data even in the revised report.

This matches this test:

http://www.wwiiaircraftperformance.org/mustang/p-51h-64182.html

C. Critical Altitude.

The critical altitudes for normal rated power climb (46" Hg., MP and 2700 rpm) are 17,400 ft. for low blower and 30,700 ft. for high blower. The critical altitudes for war emergency power climb (90" Hg., H2O and 3000 rpm) are 16,000 ft. for high blower and by extrapolation, approximately 2200 ft. for low blower.

According to my estimate, the static full throttle heights (without ram effect) would be as follows:

- High Gear: 19,500 ft, Low Gear: 4,000 ft ... original draft, Bendix pressure pump
- High Gear: 17,000 ft, Low Gear: 3,500 ft ... revised draft, carburetor
- High Gear: 14,900 ft, Low Gear: 900 ft ... actual testing by USAAF (I calculated these static values from the climb speed values given in the report)

The British test (with ram effect at climb speed) is not directly comparable as the values are for +25 lbs/sqin boost (= 80" Hg) :

- High Gear: 13,000 ft, Low Gear: 1,600 ft

High gear full throttle height is even lower than in the USAAF tests, so maybe that engine was not representative for production status either. Still some things left to be figured out! ;-)

Regards,

Henning (HoHun)
Could the reason that make the P-51H in British test faster than in American test due to the 150 grade fuel?
 
Hi again,

To get from 460 mph to 482 mph (roughly reading the chart) at the same altitude, you need very roughly (482/460)^3 = 15% more power. At the same rpm and the same boost pressure, how is that extra power going to be generated?

One explanation might be that the graph was prepared for an increase in rpm figured in for war emergency power.

OK, I just found this graph:


This indicates clearly that my hypothesis regarding War Emergency Power being attained at an engine speed greater than 3000 rpm is not correct.

You can see that the static power (red graph) at 30000 ft is ...

3000 rpm, 90" Hg, water injection: 1450 HP
3000 rpm, 80" Hg, water injection: 1450 HP
3000 rpm, 70" Hg, no water injection: 1220 HP
3000 rpm, 61" Hg, no water injection: 1220 HP

And at 13000 ft ...

3000 rpm, 90" Hg, water injection: 1880 HP
3000 rpm, 80" Hg, water injection: 1880 HP
3000 rpm, 70" Hg, no water injection: 1620 HP

So the assumption apparently is that the addition of water injection at unchanged boost pressure increases horse power by 230 HP in high supercharger gear, and by 260 HP in lower supercharger gear.

As this is a gain in the region of 16 - 19% of brake horse power at the respective altitudes, this seems to be far more than the 4% expected under the same condition by the British estimate I mentioned earlier.

What's more, the power curves in the booklet are not identical to the one used for the revised edition of the NAA report, which due to the substitution of the Bendix speed density pump with a carburetter have a reduced full throttle height.

Original curve with the Bendix speed density pump:


Revised curve with carburettor:


The report (referred to as NA-8284-A, I believe) states:

"These calculations were necessary to provide complete performance data for airplane equipped with an engine incorporating a carburetor for fuel metering instead of the speed density pump originally anticipated in preparing report NA-8284 dates September 25, 1944. "

This leads to the following conclusion:

- The coloured "booklet" figures were prepared on the basis of an estimate of engine power for the expected production configuration, which is shown in p-51h-booklet-pg10.jpg, which is basically identical to that in p-51-powercurve.jpg.
- Engine power had to be revised a bit towards lower altitudes due to the (expected) introduction of a carburettor, and that power curve is depicted in p-51h-na-8284-pg12.jpg.
- The revision of the power curve means that the coloured "booklet" performance figures are purely theoretical as they represent an interim state of planning that was invalidated by the course of engine development.
- The calculated performance resulting from the revision is depicted in this graph: http://www.wwiiaircraftperformance.org/mustang/p-51h-na-8284-pg5.jpg

I hope that helps to sort out the various and partially controdicting charts! :)

Regards,

Henning (HoHun)
From a late F-51H manual:
so P/F-51H in US service only use 100/130 octance fuel and therefore limited to 80Hg MP and 410 knots top speed?
0.png
1.JPG
2.JPG
 
Hi Ronny,

Mike has one test on his site that is relevant to the P-51H, though it's for a Mustang III airframe with a RM 14SM Merlin 100 engine:


Note that the full throttle heights are lower than for the projected data even in the revised report.

This matches this test:

http://www.wwiiaircraftperformance.org/mustang/p-51h-64182.html
Could the reason that make the P-51H in British test faster than in American test due to the 150 grade fuel?

Are you referring to the tests linked in the quotes in this post? The Mustang III is not actually a P-51H, but a P-51B/C airframe, and the tested example had merely received a Rolls-Royce-built engine that matched the specification of the V-1650-9 of the P-51H.

The Mustang III was using +25 lbs/sqin boost in the test, which is 80.8" Hg - in other words, less than the P-51H in the US test, which was using 90" Hg. The test report notes:

AN-F-33 fuel was used throughout the tests, making it possible to obtain up to 90 inches of mercury manifold pressure with water injection.

This document clarifies that AN-F-33 fuel was 115/145 octane fuel: http://www.wwiiaircraftperformance.org/mustang/Grade_115-145_Fuel_17May45.pdf

So the US test used a higher boost pressure plus water injection, while the British used 150 octane fuel and a lower boost pressure with no water injection.

Accordingly, the available power in the US test would have been quite a bit higher than in the British test. However, the British aircraft climbed better than the US aircraft, and though it was a bit lighter, I'd have expected a lower-powered aircraft not to climb as well as it apparently did. (I didn't actually calculate anything, so I might be wrong about this.)

One difference we haven't talked about yet is that the both aircraft were using different propellers:

P-51H: 11' – 1" diameter four-bladed Aero Products propeller H-20-162-29M5, design No. 86892
Mustang III: 11’2” diameter, 4 metal blades, Hamilton hydromatic, Mark 24D-50-65

Generally speaking, the slightly smaller diameter of the Mustang III's propeller should give it a disadvantage regarding top speed as the tip Mach number would be slightly greater, and the propeller slightly less efficient as a result. At the same time, the bigger propeller should be slightly more efficient in the climb than the P-51's smaller one. However, as the propeller blades probably were different in shape as well, other factors might outweigh these general considerations.

Regards,

Henning (HoHun)
 
Hi Ronny,

From a late F-51H manual:
so P/F-51H in US service only use 100/130 octance fuel and therefore limited to 80Hg MP and 410 knots top speed?

It looks like it. Note that this document ...


... mentions that conversion of the P-51H from AN-F-33 to AN-F-28 fuel (as your document indicates was used later) required modifications that were "major in nature" and expected to take six months. Of course, it might be possible that after this initial work was done, switching over was relatively simple ... maybe the manual covers this? Is there another page showing the limits for AN-F-33 fuel, perhaps?

With regard to the 410 knots top speed, I'm not sure what to think of that yet. Doesn't sound too bad, does it?

Regards,

Henning (HoHun)
 
Hi again,

With regard to the 410 knots top speed, I'm not sure what to think of that yet. Doesn't sound too bad, does it?

Well, I checked the small print on the Standard Aircraft Characteristics Sheet, and it says:

22 March 1949 version:

"Performance data are flight test values and are based on AMC Tests and North American Report No.-8284-A dated 1 November 1945."

That's the material posted on Mike Williams' site, so there is nothing this SAC sheet adds over these.

19 May 1950 version:

"Engine ratings shown on page 3 are engine manufacturer's guaranteed ratings. Power values used in performance calculations are as follows:"

On page 3, take off, military (61" Hg, by the engine chart posted by Ronnie above) and normal powers are listed, but not the war emergency powers - this implies that the WEP powers weren't guaranteed.

What's more, the engine ratings listed in both the 1949 and the 1950 SAC sheets are identical, and show the following full throttle heights with ram effect at top speed:

Max (wet) high blower: 1790 BHP @ 3000 rpm at 22700 ft
Max (wet) low blower: 2220 BHP @ 3000 rpm at 9000 ft

If you correlate the 2220 BHP data point to this curve ...


... this is a match for the speed of ca. 450 mph from the SAC speed chart.

This leads to the conclusion that the SAC chart is calculated for 90" Hg, based on the initial engine data from 1945.

When the F-51H was operated at 80" Hg, it obviously would not have achieved exactly the performance as depicted in the SAC data sheets, but a bit less. So the 410 KTAS top speed at "wet" emergency power would not have been obtained, but something closer to 396 KTAS (by the simple P~v^3 approximation). However, at 80" Hg the full throttle height would be a bit higher, so chances are the drop in boost would still have allowed a top speed at best altitude in excess of 400 KTAS.

Regards,

Henning (HoHun)
 
Are you referring to the tests linked in the quotes in this post? The Mustang III is not actually a P-51H, but a P-51B/C airframe, and the tested example had merely received a Rolls-Royce-built engine that matched the specification of the V-1650-9 of the P-51H.

The Mustang III was using +25 lbs/sqin boost in the test, which is 80.8" Hg - in other words, less than the P-51H in the US test, which was using 90" Hg. The test report notes:

AN-F-33 fuel was used throughout the tests, making it possible to obtain up to 90 inches of mercury manifold pressure with water injection.

This document clarifies that AN-F-33 fuel was 115/145 octane fuel: http://www.wwiiaircraftperformance.org/mustang/Grade_115-145_Fuel_17May45.pdf

So the US test used a higher boost pressure plus water injection, while the British used 150 octane fuel and a lower boost pressure with no water injection.

Accordingly, the available power in the US test would have been quite a bit higher than in the British test. However, the British aircraft climbed better than the US aircraft, and though it was a bit lighter, I'd have expected a lower-powered aircraft not to climb as well as it apparently did. (I didn't actually calculate anything, so I might be wrong about this.)

One difference we haven't talked about yet is that the both aircraft were using different propellers:

P-51H: 11' – 1" diameter four-bladed Aero Products propeller H-20-162-29M5, design No. 86892
Mustang III: 11’2” diameter, 4 metal blades, Hamilton hydromatic, Mark 24D-50-65

Generally speaking, the slightly smaller diameter of the Mustang III's propeller should give it a disadvantage regarding top speed as the tip Mach number would be slightly greater, and the propeller slightly less efficient as a result. At the same time, the bigger propeller should be slightly more efficient in the climb than the P-51's smaller one. However, as the propeller blades probably were different in shape as well, other factors might outweigh these general considerations.

Regards,

Henning (HoHun)
What do you think about XP-51G test?

7253EC46-2019-4081-AF20-523714A3993D.png
2560726D-DAF8-4026-BE20-4E311886218C.png
 
Hi again,

With regard to the 410 knots top speed, I'm not sure what to think of that yet. Doesn't sound too bad, does it?

Well, I checked the small print on the Standard Aircraft Characteristics Sheet, and it says:

22 March 1949 version:

"Performance data are flight test values and are based on AMC Tests and North American Report No.-8284-A dated 1 November 1945."

That's the material posted on Mike Williams' site, so there is nothing this SAC sheet adds over these.

19 May 1950 version:

"Engine ratings shown on page 3 are engine manufacturer's guaranteed ratings. Power values used in performance calculations are as follows:"

On page 3, take off, military (61" Hg, by the engine chart posted by Ronnie above) and normal powers are listed, but not the war emergency powers - this implies that the WEP powers weren't guaranteed.

What's more, the engine ratings listed in both the 1949 and the 1950 SAC sheets are identical, and show the following full throttle heights with ram effect at top speed:

Max (wet) high blower: 1790 BHP @ 3000 rpm at 22700 ft
Max (wet) low blower: 2220 BHP @ 3000 rpm at 9000 ft

If you correlate the 2220 BHP data point to this curve ...


... this is a match for the speed of ca. 450 mph from the SAC speed chart.

This leads to the conclusion that the SAC chart is calculated for 90" Hg, based on the initial engine data from 1945.

When the F-51H was operated at 80" Hg, it obviously would not have achieved exactly the performance as depicted in the SAC data sheets, but a bit less. So the 410 KTAS top speed at "wet" emergency power would not have been obtained, but something closer to 396 KTAS (by the simple P~v^3 approximation). However, at 80" Hg the full throttle height would be a bit higher, so chances are the drop in boost would still have allowed a top speed at best altitude in excess of 400 KTAS.

Regards,

Henning (HoHun)
On a separate note, do you have the chart for F4U-5 where the performance is not just estimated?, iam trying to figure out which one of them is faster, the P-51H with 150 octane fuel or the F4U-5.

F4U-5 chart.jpg
 
Hi Ronny,

What do you think about XP-51G test?

View attachment 669216

I'm not sure. The book listed as source on the placard in your photograph is "Mustang Designer", and it doesn't have the kind of technical detail that would allow one to make a detailed cross-check.

I have this book somewhere, but I can't find it at the moment, so I have to go by memory for now ... keep in mind that this can go terribly wrong. What I seem to remember is that Schmued described talking to one of the executives, and being impressed that this executive didn't want to round up the 496 mph reported by Schmued to 500 mph, which in the context of the error margins involved in Schmued's view could have been justified. Schmued also remarked something like "The wartime aero industry was a highly competitive environment", and reading between the lines, I think by relating this story in the way he did, he was implicitly expressing doubts about the performance figures reported by other companies.

Back to the placard, it's worth noting that this mentions "2200 HP @ 120 inches manifold pressure". If that's accurately describing the high supercharger gear power (since at low gear, the engine would do much more than 2200 HP), that might explain why the XP-51G was so fast, as this was considerably more power than the F-51H had available (1790 BHP @ 3000 rpm at 22700 ft, according to the SAC sheets).

At the same time, that would also tell us that this speed was probably never achieved in actual flight testing, as at the time the XP-51G flew, as far as we can tell there was no V-1650-9 available that would run at 120" Hg. However, I'm not entirely sure we can rely on the information on the placard with great confidence, so please take that with a healthy dose of salt.

Regards,

Henning (HoHun)
 
Regarding top speed:
At 35,000 ft:

P-51H reached 482.5 mph = 776 km/h
F4U-5 reached 395 knots = 731 km/h
Ta-152H reached 715 km/h
F8F-2 reached 360 knots = 666 km/h
At 25,000 ft:
P-51H reached 487.5 mph = 784 km/h
F4U-5 reached 407 knots = 753 km/h
Ta-152H reached 700 km/h
F8F-2 reached 383 knots = 709 km/h
At 15,000 ft:
P-51H reached 465 mph = 748 km/h
F4U-5 reached 390 knots = 722 km/h
Ta-152H reached 655 km/h
F8F-2 reached 373 knots = 690 km/h
At 5,000 ft:
P-51H reached 445 mph = 716 km/h
F4U-5 reached 364 knots = 674 km/h
Ta-152H reached 607 km/h
F8F-2 reached 353 knots = 653 km/h
Apparently, Ta-152H is nothing specially unless at extremely high altitude, and P-51H is so extremely fast, it even faster than F8F-2 and F4U-5 at low altitude
F8F-2 chart
View attachment 666668

P-51H charts
View attachment 666669

Ta-152 charts
View attachment 666670

F4U-5 chart
View attachment 666671

I appreciate its what you`ve got, but these estimated charts are sometimes wildly different to real service aircraft performance.

For example the 152 data comes from a lengthy report, with dozens of different charts, with a whole raft of different specifications,
one shows the 152 top speed with jumo213E to be 750km/h for example, because it is based on speed with C3 fuel. Your chart shows performance on B4 (87 octane). All the other aircraft performance is (I think) based on 100/130 or 110/145 or even 100/150 PN. So you need to decide whats pertinent to your question, two of those fuels do not exist at the start of the war...

The very small German text on the chart says "ignoring compressiblity effects, surfaces smoothed over and varnished, without
external electrical gear, with landing gear doors"

Do you have similar lists of assumptions for the others ? Or know what the calculation methods were, sometimes these charts
had a LOT of mathematics put into them (I suspect the 152 charts are actually not too bad), but in other cases (genally, not referring to these), they sometimes were in a rush and just took some existing curves and did a bit of "yea I reckon a bit more HERE... and a bit less THERE..."

I would not personally try to answer your question using this set of charts. However I will make one comment, you state which one would be best at the START of the war, well I can tell you that the US plane performance will be dramatically impacted by having to be derated to use fuels from 1940-ish. Interestingly, the 152 speeds on B4 would have been possible on fuel from even the mid-1930`s. So thats an "alternative history" consideration to ponder (I dont know enough about the Japanese engine to pass similar comment)
 
Last edited:
Hi Calum,

Or know what the calculation methods were, sometimes these charts
had a LOT of mathematics put into them (I suspect the 152 charts are actually not too bad), but in other cases (genally, not referring to these), they sometimes were in a rush and just took some existing curves and did a bit of "yea I reckon a bit more HERE... and a bit less THERE..."

Over on flugzeugforum.de, Peter Achs posted some excerpts from a BMW document showing that at least that company was taking a lot of the more complicated interactions between aerodynamics and engine performance into account.

However, I've had good success matching many WW2 era estimates, and (frequently, but not always) tests, with a somewhat simpler approach, which I've described here (in German) ... :


Now that I look at it, my calculation for the Me 109E with GM-1 injection might give the explanation for the speed advantage increase with altitude on which you commented in the first video you made with Chris of Military Aviation History. That's not a function of some non-linearity in engine power, but simply the result of the un-augmented aircraft's speed dropping off quite sharply near the aircraft's ceiling.

The graph for the Typhoon shows that I can't always match test results, but it also shows that the test results in themselves are not consistent, because the two tested aircraft showed climb rates differing by 3 m/s in high blower and by 5 m/s in low blower despite supposedly using the same engine settings and, consequently, powers.

The graph for the Cessna C172 is just for illustration ... I match the manual values perfectly, but really shouldn't, because I'm assuming a constant speed propeller where the reference values are for a fixed-pitch propeller, which really has a different characteristics. I suppose the guys at Cessna used a similar mathematical approach as I did to arrive at their aircraft manual values by means of calculation! Which sort of confirms your initial point.

Regards,

Henning (HoHun)
 
Hi Ronny,

What do you think about XP-51G test?

View attachment 669216

I'm not sure. The book listed as source on the placard in your photograph is "Mustang Designer", and it doesn't have the kind of technical detail that would allow one to make a detailed cross-check.

I have this book somewhere, but I can't find it at the moment, so I have to go by memory for now ... keep in mind that this can go terribly wrong. What I seem to remember is that Schmued described talking to one of the executives, and being impressed that this executive didn't want to round up the 496 mph reported by Schmued to 500 mph, which in the context of the error margins involved in Schmued's view could have been justified. Schmued also remarked something like "The wartime aero industry was a highly competitive environment", and reading between the lines, I think by relating this story in the way he did, he was implicitly expressing doubts about the performance figures reported by other companies.

Back to the placard, it's worth noting that this mentions "2200 HP @ 120 inches manifold pressure". If that's accurately describing the high supercharger gear power (since at low gear, the engine would do much more than 2200 HP), that might explain why the XP-51G was so fast, as this was considerably more power than the F-51H had available (1790 BHP @ 3000 rpm at 22700 ft, according to the SAC sheets).

At the same time, that would also tell us that this speed was probably never achieved in actual flight testing, as at the time the XP-51G flew, as far as we can tell there was no V-1650-9 available that would run at 120" Hg. However, I'm not entirely sure we can rely on the information on the placard with great confidence, so please take that with a healthy dose of salt.

Regards,

Henning (HoHun)
How about the F4U-5 , do you have any data?
 
Regarding top speed:
At 35,000 ft:

P-51H reached 482.5 mph = 776 km/h
F4U-5 reached 395 knots = 731 km/h
Ta-152H reached 715 km/h
F8F-2 reached 360 knots = 666 km/h
At 25,000 ft:
P-51H reached 487.5 mph = 784 km/h
F4U-5 reached 407 knots = 753 km/h
Ta-152H reached 700 km/h
F8F-2 reached 383 knots = 709 km/h
At 15,000 ft:
P-51H reached 465 mph = 748 km/h
F4U-5 reached 390 knots = 722 km/h
Ta-152H reached 655 km/h
F8F-2 reached 373 knots = 690 km/h
At 5,000 ft:
P-51H reached 445 mph = 716 km/h
F4U-5 reached 364 knots = 674 km/h
Ta-152H reached 607 km/h
F8F-2 reached 353 knots = 653 km/h
Apparently, Ta-152H is nothing specially unless at extremely high altitude, and P-51H is so extremely fast, it even faster than F8F-2 and F4U-5 at low altitude
F8F-2 chart
View attachment 666668

P-51H charts
View attachment 666669

Ta-152 charts
View attachment 666670

F4U-5 chart
View attachment 666671

I appreciate its what you`ve got, but these estimated charts are sometimes wildly different to real service aircraft performance.

For example the 152 data comes from a lengthy report, with dozens of different charts, with a whole raft of different specifications,
one shows the 152 top speed with jumo213E to be 750km/h for example, because it is based on speed with C3 fuel. Your chart shows performance on B4 (87 octane). All the other aircraft performance is (I think) based on 100/130 or 110/145 or even 100/150 PN. So you need to decide whats pertinent to your question, two of those fuels do not exist at the start of the war...

The very small German text on the chart says "ignoring compressiblity effects, surfaces smoothed over and varnished, without
external electrical gear, with landing gear doors"

Do you have similar lists of assumptions for the others ? Or know what the calculation methods were, sometimes these charts
had a LOT of mathematics put into them (I suspect the 152 charts are actually not too bad), but in other cases (genally, not referring to these), they sometimes were in a rush and just took some existing curves and did a bit of "yea I reckon a bit more HERE... and a bit less THERE..."

I would not personally try to answer your question using this set of charts. However I will make one comment, you state which one would be best at the START of the war, well I can tell you that the US plane performance will be dramatically impacted by having to be derated to use fuels from 1940-ish. Interestingly, the 152 speeds on B4 would have been possible on fuel from even the mid-1930`s. So thats an "alternative history" consideration to ponder (I dont know enough about the Japanese engine to pass similar comment)
Thank you, that a very good point which i overlooked
 
Hi Ronny,

How about the F4U-5 , do you have any data?

I had a look at the engine description, as the combat power graph has an unusual shape. The R-2800 variant in question appears to have some quite complex features, but unfortunately I don't have any books covering it, or the F4U-5.

Regards,

Henning
 
Hi Ronny,

What do you think about XP-51G test?

First off, I had a look at the XP-51F, and apparently, it was powered at least initially with the older V-1650-3 engine, which makes sense as it was roughly the same as a V-1650-9 which couldn't run high levels of boost.

Here's a chart of estimated performance for the XP-51F with that engine, showing a top speed of 461 mph @ 29000 ft.


Here's another esimate based on flight tests with a P-51B, showing that the V-1650-3 was indeed basically the same as the RM14SM, only with higher levels of boost. I'm not sure why intercooling percentage is higher - that might be based on the assumption that the redesigned radiator of the later P-51 variants is more effective.


XP-51F performance with the V-1650-3 is estimated as 459 mph @ 26750 ft here, not quite the same as the estimate above.

Top speed with the RM14SM is 462 mph @ 19500 ft. What surprises me is that the speed at the same power is about 10 mph with the RM14SM than with the old V-1650-3. Maybe it's the new propeller that introduces this speed loss, as it probably needed to be changed to transfer 1900 HP instead of just 1500 HP in a climb at sea level, and that might mean it's not as well suited for high speeds at high altitudes as the older one - but I honestly don't know.

Then here's calculated performance for the XP-51G ... the engine is not stated, but with +25 lbs/sqin boost (81" Hg), it will be a RM14SM/V-1650-9, I guess. It shows 495 mph @ 22750 ft.


The higher climb rate probably indicates that this engine runs at a higher boost than the one used for the XP-51F estimates above. However, its full throttle height is 3250 ft than the one with the RM14SM before. As we know from the P-51H report that the V-1650-9 power estimates had to be adjusted to lower full throttle heights, maybe this is the result of a period of optimism that was dashed again by technical factors later.

Then here's the another performance estimate chart for the XP-51G:


This notes the use of a 4-bladed Aeroproducts propeller of 11 ft 0 in diameter, which is smaller than the propeller used on the earlier production Mustangs (by 2 in) and on the P-51H (by 1 in). Combat boost is noted as +20 lbs/sqin (70.6" Hg), speed as 492.5 mph @ 25200 ft.

So full throttle height is up compared to the other one for this type, which is consistent with the lower boost used here. It's interesting that the propeller reduction gearing here is stated as 0.42:1, which is a departure from the earlier Packard-built Merlins which had a 0.479:1 reduction ratio as far as I know, which is less suited for high speeds at high altitude than the lower ratio of the British engines (but probably better suited to climb at low and medium altitude). Of course, the propeller model plays a role as well!

So far, all these charts shows estimated performance, not actually tested performance, so I'm not sure what to think of them as the development of the performance estimates for the later P-51H shows that a lot of the assumptions on engine power were,by necessity, preliminary, and final performance really depended on what the production engine could actually deliver at service ratings.

Regards,

Henning (HoHun)
 
Hi Ronny,

What do you think about XP-51G test?

First off, I had a look at the XP-51F, and apparently, it was powered at least initially with the older V-1650-3 engine, which makes sense as it was roughly the same as a V-1650-9 which couldn't run high levels of boost.

Here's a chart of estimated performance for the XP-51F with that engine, showing a top speed of 461 mph @ 29000 ft.


Here's another esimate based on flight tests with a P-51B, showing that the V-1650-3 was indeed basically the same as the RM14SM, only with higher levels of boost. I'm not sure why intercooling percentage is higher - that might be based on the assumption that the redesigned radiator of the later P-51 variants is more effective.


XP-51F performance with the V-1650-3 is estimated as 459 mph @ 26750 ft here, not quite the same as the estimate above.

Top speed with the RM14SM is 462 mph @ 19500 ft. What surprises me is that the speed at the same power is about 10 mph with the RM14SM than with the old V-1650-3. Maybe it's the new propeller that introduces this speed loss, as it probably needed to be changed to transfer 1900 HP instead of just 1500 HP in a climb at sea level, and that might mean it's not as well suited for high speeds at high altitudes as the older one - but I honestly don't know.

Then here's calculated performance for the XP-51G ... the engine is not stated, but with +25 lbs/sqin boost (81" Hg), it will be a RM14SM/V-1650-9, I guess. It shows 495 mph @ 22750 ft.


The higher climb rate probably indicates that this engine runs at a higher boost than the one used for the XP-51F estimates above. However, its full throttle height is 3250 ft than the one with the RM14SM before. As we know from the P-51H report that the V-1650-9 power estimates had to be adjusted to lower full throttle heights, maybe this is the result of a period of optimism that was dashed again by technical factors later.

Then here's the another performance estimate chart for the XP-51G:


This notes the use of a 4-bladed Aeroproducts propeller of 11 ft 0 in diameter, which is smaller than the propeller used on the earlier production Mustangs (by 2 in) and on the P-51H (by 1 in). Combat boost is noted as +20 lbs/sqin (70.6" Hg), speed as 492.5 mph @ 25200 ft.

So full throttle height is up compared to the other one for this type, which is consistent with the lower boost used here. It's interesting that the propeller reduction gearing here is stated as 0.42:1, which is a departure from the earlier Packard-built Merlins which had a 0.479:1 reduction ratio as far as I know, which is less suited for high speeds at high altitude than the lower ratio of the British engines (but probably better suited to climb at low and medium altitude). Of course, the propeller model plays a role as well!

So far, all these charts shows estimated performance, not actually tested performance, so I'm not sure what to think of them as the development of the performance estimates for the later P-51H shows that a lot of the assumptions on engine power were,by necessity, preliminary, and final performance really depended on what the production engine could actually deliver at service ratings.

Regards,

Henning (HoHun)
According to this,
the fifth production P-51H did 487 mph , unfortunately there is no additional information about the test
1.JPG
2.JPG
3.JPG
4.JPG
 
Hi Ronny,

How about the F4U-5 , do you have any data?

I had a look at the engine description, as the combat power graph has an unusual shape. The R-2800 variant in question appears to have some quite complex features, but unfortunately I don't have any books covering it, or the F4U-5.

Regards,

Henning
apparently, overlap the F-51H SAC chart (data from NA-8284A) with estimation data for F4U-5 will show something like this
comparison.jpeg
comparison 2.jpeg
 
Hi Ronny,

apparently, overlap the F-51H SAC chart (data from NA-8284A) with estimation data for F4U-5 will show something like this

According to ...


..., the F4U-5's engine (R-2800-32W) is characterized by:

"Dual Auxiliary Blower, Variable Speed, Dual Aux. Stage Impellers with Variable Speed Main"

I'm not quite sure sure how to parse that. By the descriptions, probably a two-stage engine with a single 'engine' stage compressor ("Main") and two compressors acting in parallel ("Dual Auxiliary Blower") feeding into that. I'm not quite sure whether the double mention of "variable speed" means that both stages' speeds could be varied independendly of each other.

I suppose "Pratt & Whitney's Dependable Masterpiece" would answer that question, but that's a book I don't have.

The F8F-2's R-2800-30W might be sort of similar, but is described as "Variable Intermediate with fixed High Ratio Main Imp."

In conjunction with the supercharger gear ratio data, I end up throroughly confused. I think these engines have more complex features than the design of the table allows to be notated without introducing ambiguity.

Regards,

Henning (HoHun)
 
Hi Ronny,

apparently, overlap the F-51H SAC chart (data from NA-8284A) with estimation data for F4U-5 will show something like this

According to ...


..., the F4U-5's engine (R-2800-32W) is characterized by:

"Dual Auxiliary Blower, Variable Speed, Dual Aux. Stage Impellers with Variable Speed Main"

I'm not quite sure sure how to parse that. By the descriptions, probably a two-stage engine with a single 'engine' stage compressor ("Main") and two compressors acting in parallel ("Dual Auxiliary Blower") feeding into that. I'm not quite sure whether the double mention of "variable speed" means that both stages' speeds could be varied independendly of each other.

I suppose "Pratt & Whitney's Dependable Masterpiece" would answer that question, but that's a book I don't have.

The F8F-2's R-2800-30W might be sort of similar, but is described as "Variable Intermediate with fixed High Ratio Main Imp."

In conjunction with the supercharger gear ratio data, I end up throroughly confused. I think these engines have more complex features than the design of the table allows to be notated without introducing ambiguity.

Regards,

Henning (HoHun)
do you have any data of F4U-5 roll rate, dive limit ? is it similar to previous version?
 
Hi Ronny,

some additional data about P-51 version

Thanks a lot! What book are these pages from?

It actually makes things more confusing as it states that the XP-51F aircraft were ordered with the V-1650-3, but actually built the V-1650-7 instead.

That followed the development in the B/C/D Mustang series, which started off on a V-1650-3 and changed over to the V-1650-7.

However - and that's a big one -, if the XP-51F really achieved 493 mph on a V-1650-7, it would have been dead easy to get a 500 mph+ Mustang by simple switching this engine against a V-1650-3. The latter achieved its optimum performance at a higher altitude, where the air is thinner and air resistance is lower, consequently allowing the Mustang to reach higher true air speeds.

Just as a coarse indication:

P-51B-15-NA with V-1650-7: 426 mph @ 23900 ft using 3000 rpm/67" Hg


P-51B-5-NA with V-1650-3: 442.5 mph @ 29400 ft using 3000 rpm/67" Hg

So you can gain around 15 mph simply from swapping the engine from one mass-production engine variant to an earlier one, no experimental models required. If "North American worked very hard" to break the 500 mph barrier, they probably missed an opportunity there as 493 mph on a V-1650-7 could probably have translated to 500 mph+ on a V-1630-3, if these 493 mph was real, and actually achieved on a V-1650-7 as claimed by the book.

What's more, the statement about the 493 mph speed is quite interesting in yet another and somewhat surprising way:

"Bob Chilton flew the first XP-51F (43-43332) on 14 February 1944 from Mines Field, Los Angeles. Although the aircraft was limited to 475 mph and required full rudder by 480 mph to compensate for a yaw tendency, it eventurally reached 493 mph."

First off, fighter aircraft are normally limited to IAS numbers, not to TAS numbers, because that's what the pilot sees in the cockpit. These IAS limits are universally so high they can only be reached by diving. The P-51D was limited to 505 mph IAS ... it would seem reasonable to assume that the XP-51F might be limited to a lower value than that, being a light-weight aircraft with relaxed strength requirements.

The mention of a strong yaw tendency requiring "full" rudder input fits the idea of a dive very well, as 480 mph IAS is a lot faster than 480 mph TAS at medium to high altitudes (and you would neither to high-speed dive testing at low altitudes, nor would any Mustang be able to achieve 480 mph TAS at low altitudes). If the aircraft would have required full rudder in level flight, Chilton would probably have broken off the test and told the ground crew to fix the aircraft, as it would have been unsafe to fly. So, if 493 mph were "eventually reached", from the context in which these statements are made, that would have to be an indicated air speed achieved in a dive.

At least, that's my opinion without any more detailed data to go by! :)

Regards,

Henning (HoHun)
 
First off, fighter aircraft are normally limited to IAS numbers, not to TAS numbers, because that's what the pilot sees in the cockpit. These IAS limits are universally so high they can only be reached by diving. The P-51D was limited to 505 mph IAS ... it would seem reasonable to assume that the XP-51F might be limited to a lower value than that, being a light-weight aircraft with relaxed strength requirements.
The mention of a strong yaw tendency requiring "full" rudder input fits the idea of a dive very well, as 480 mph IAS is a lot faster than 480 mph TAS at medium to high altitudes (and you would neither to high-speed dive testing at low altitudes, nor would any Mustang be able to achieve 480 mph TAS at low altitudes). If the aircraft would have required full rudder in level flight, Chilton would probably have broken off the test and told the ground crew to fix the aircraft, as it would have been unsafe to fly. So, if 493 mph were "eventually reached", from the context in which these statements are made, that would have to be an indicated air speed achieved in a dive.

At least, that's my opinion without any more detailed data to go by! :)

Regards,

Henning (HoHun)
I don't think that 493 mph top speed is achieved in a dive. Since that would be pretty meh and nothing to be brag about
Besides, the lower weight of XP-51F might reduce initial acceleration. But the top speed of the dive would still be limited by its drag which decided by the wing and the fuselage. For example, P-51H has lower weight but higher top dive speed

dive limit of varius fighter.jpg

P-47N Dive.JPG
 
Hi Ronny,

apparently, overlap the F-51H SAC chart (data from NA-8284A) with estimation data for F4U-5 will show something like this

According to ...


..., the F4U-5's engine (R-2800-32W) is characterized by:

"Dual Auxiliary Blower, Variable Speed, Dual Aux. Stage Impellers with Variable Speed Main"

I'm not quite sure sure how to parse that. By the descriptions, probably a two-stage engine with a single 'engine' stage compressor ("Main") and two compressors acting in parallel ("Dual Auxiliary Blower") feeding into that. I'm not quite sure whether the double mention of "variable speed" means that both stages' speeds could be varied independendly of each other.

I suppose "Pratt & Whitney's Dependable Masterpiece" would answer that question, but that's a book I don't have.

The F8F-2's R-2800-30W might be sort of similar, but is described as "Variable Intermediate with fixed High Ratio Main Imp."

In conjunction with the supercharger gear ratio data, I end up throroughly confused. I think these engines have more complex features than the design of the table allows to be notated without introducing ambiguity.

Regards,

Henning (HoHun)
I found some additional data about F4U-5 and its engine
 
Hi Ronny,

I don't think that 493 mph top speed is achieved in a dive. Since that would be pretty meh and nothing to be brag about
Besides, the lower weight of XP-51F might reduce initial acceleration. But the top speed of the dive would still be limited by its drag which decided by the wing and the fuselage.

These 493 mph, if they're a dive speed, are IAS, and depending on altitude and conditions, they translate to a much higher speed than 493 mph TAS.

See the attached graph from the P-51D manual ... the P-51D was "redlined" at 505 mph, but at altitude, the real limit was actually lower. A 475 mph limit would be relevant below 8000 ft only.

The whole point of the P-51F was building a light aircraft by relaxing all kinds of requirements, so having a lower allowable dive speed makes perfect sense.

This was not about how fast the P-51F would be in a dive if it went all out, it's about how fast it can safely go in a dive. I am not sure which factors played a role in determining the lower dive speed limit, but structural strength could have been one of them, and that certainly was reduced on the P-51F.

(Most fighters at the time would accelerate in a dive to the point of either loss of control or self-destruction, initial acceleration really wasn't much of a concern. If it was, then often in the sense that it was a factor increasing the difficulty for the pilot to stay in control - the P-38 had a combination of good initial acceleration and low safe limit that made it really dangerous to dive in combat.)

If the dive limit was set to 475 mph, and you'd be able to dive to 493 mph without any bad effects, that certainly would be worth mentioning as it demonstrated that the aircraft had a good safety margin.

Regards,

Henning (HoHun)
 

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