Max Speed of P-51H : 487mph or 471mph ?

Dawncaster · Apr 2, 2014

mig-31bm said:
wasn't the different in top speed in different test is only due to different fuel ?
P-51 Mustang Performance

case of your color graphs, only different is fuel.

case of Report No. NA-8284-A and AAF No. 44-64182, x2 bomb racks and x6 rocket racks added.

mig-31bm · Apr 2, 2014

Dawncaster said:
with x2 bomb racks and x6 rocket racks

case of P-51D, x2 bomb racks decrease speed -12mph.

i know rack do decrease speed , but looking in the graph you can see that there is a 100 mph different between test using 46 vs 90 inch hg which is alot more significant

Dawncaster · Apr 2, 2014

mig-31bm said:
i know rack do decrease speed , but looking in the graph you can see that there is a 100 mph different between test using 46 vs 90 inch hg which is alot more significant

"hg = manifold pressure

high manifold pressure = high brake horsepower

with 61"hg = only around 1380BHP at S.L
with 67"hg = around 1490BHP at S.L
with 90"hg = 2240BHP at S.L

of course, much faster.

Dawncaster · Apr 5, 2014

P-51H had best performance with coolant shutter flush position

mig-31bm · Oct 25, 2021

Aozora said:
From the P-51H Pilot's Manual, 1946:

View attachment 444167

The 1949 charts do not allow the use of WEP (War Emergency Power), a rating which allowed boost pressures of up to 76" Hg for 1 minute see http://www.wwiiaircraftperformance.org/mustang/p-51h-na117.jpg the other test used up to 90" Hg with water injection.

By 1949 the engines were restricted to using Military Power with a maximum boost of 61 Hg (15 minutes); that accounts for the difference between the P-51H and F-51H.

Also, take a look at the "Compressibility Correction Table" in particular; none of the reports note whether the figures were corrected for compressibility:

View attachment 444168

Engine chart (note WEP):

View attachment 444169

Instrument limitations

View attachment 444170

can you upload these image again, it can't be viewed now

mig-31bm · Oct 25, 2021

Dawncaster said:
SAC [engine ratings] section was not included max power.

for example, same as F4U-4 SAC http://www.wwiiaircraftperformance.org/f4u/f4u-4.pdf

so, 1949 SCP's max power(wet) = water injection with 90"hg. (7 mins only).

mil-power was not called "wet" or "max" power. especially "wet" means ADI.

and IMO, NA-117 was not standard P-51H. it was prototype. gross weight was just 7302lb, only 105gal fual and 4 guns with 1080rds ammo.

actual P-51H was NA-127. gross weight 9430+lb, 255+gal internal fuel, 6 guns with 1820rds ammo.

here is P-51H test report without water-injection.

P-51H Performance Test

Btw do you know the reason why the speed between these two chart are so different?. The P-51H in coloured chart is much faster even though it is heavier than the chart for F-51H

BiffF15 · Oct 25, 2021

Knots versus MPH.

mig-31bm · Oct 25, 2021

BiffF15 said:
Knots versus MPH.

Not just that though, the value are completely different, and where they peaked also very different
Top speed of P-51H peaked at 485 mph at 25,000 ft = 780 km/h while F-51H peaked at 411 knots at 22,000 ft = 761 km/h
At sea level P-51H peaked at 425 mph = 683 km/h while F-51H peaked at 666 km/h

BiffF15 · Oct 25, 2021

mig-31bm said:
Not just that though, the value are completely different, and where they peaked also very different
Top speed of P-51H peaked at 485 mph at 25,000 ft = 780 km/h while F-51H peaked at 411 knots at 22,000 ft = 761 km/h
At sea level P-51H peaked at 425 mph = 683 km/h while F-51H peaked at 666 km/h

My guess is post wartime restrictions were greater (manifold pressure allowances), fuel was different, or there was a water injection restriction in place. Bill, AKA Drgondog will hopefully chime in.

drgondog · Oct 28, 2021

BiffF15 said:
My guess is post wartime restrictions were greater (manifold pressure allowances), fuel was different, or there was a water injection restriction in place. Bill, AKA Drgondog will hopefully chime in.

There are several factors to consider between 1945 Flight Tests flown at Wright Field by Army, 1945 at NAA before Army test, NAA discovered substandard performance issues for new 1650-9 with WI and Simmonds SA-9 auto Boost control and pressure injection carb - that wasn't sorted out until early 1946. NAA achieved 487mph in Fighter Light (interceptor) with 100 gal internal fuel, full ammo and guns, no wing racks for either combat tanks or rocket stubs.

IIRC 150 octane fuel was discontinued after 1945, reducing max potential even with WI. I'm search my files but not very well organized and I am consumed by indifference at the moment.

So, the SAC values represent the 1650-9 with 130 octane fuel - which I don't believe permitted 90" Mp. (Memory)

AFAIK, the P-51H wing rack resulted in parasite drag equivalent to 3+ mph, vs P51D racks at ~6mph and P-51A/B/C racks at 11mph.

BiffF15 · Oct 28, 2021

drgondog said:
There are several factors to consider between 1945 Flight Tests flown at Wright Field by Army, 1945 at NAA before Army test, NAA discovered substandard performance issues for new 1650-9 with WI and Simmonds SA-9 auto Boost control and pressure injection carb - that wasn't sorted out until early 1946. NAA achieved 487mph in Fighter Light (interceptor) with 100 gal internal fuel, full ammo and guns, no wing racks for either combat tanks or rocket stubs.

IIRC 150 octane fuel was discontinued after 1945, reducing max potential even with WI. I'm search my files but not very well organized and I am consumed by indifference at the moment.

So, the SAC values represent the 1650-9 with 130 octane fuel - which I don't believe permitted 90" Mp. (Memory)

AFAIK, the P-51H wing rack resulted in parasite drag equivalent to 3+ mph, vs P51D racks at ~6mph and P-51A/B/C racks at 11mph.

Thanks Bill!

mig-31bm · Oct 29, 2021

drgondog said:
There are several factors to consider between 1945 Flight Tests flown at Wright Field by Army, 1945 at NAA before Army test, NAA discovered substandard performance issues for new 1650-9 with WI and Simmonds SA-9 auto Boost control and pressure injection carb - that wasn't sorted out until early 1946. NAA achieved 487mph in Fighter Light (interceptor) with 100 gal internal fuel, full ammo and guns, no wing racks for either combat tanks or rocket stubs.

Do they fly test the prototype for this chart below or is this purely calculated/estimated performance:

How about the chart below, fly tested or purely calculated/estimated?

drgondog said:
IIRC 150 octane fuel was discontinued after 1945, reducing max potential even with WI. I'm search my files but not very well organized and I am consumed by indifference at the moment.
So, the SAC values represent the 1650-9 with 130 octane fuel - which I don't believe permitted 90" Mp. (Memory)

I found this in the F-51H manual, 2220 HP and 3000 RPM would be representative of 90" Mp right?

drgondog said:
AFAIK, the P-51H wing rack resulted in parasite drag equivalent to 3+ mph, vs P51D racks at ~6mph and P-51A/B/C racks at 11mph.

How come there is such a massive different? do their rack have significantly different shape and size?

mig-31bm · Oct 29, 2021

Also, why the P-51H so extremely slow in this test even with 3000 RPM and 90 MP?

P-51H Performance Test

pinehilljoe · Oct 30, 2021

Forgetting the specifications, do you think the H would have given the pilot an edge in speed over a 109 or 190?

drgondog · Oct 31, 2021

mig-31bm said:
Do they fly test the prototype for this chart below or is this purely calculated/estimated performance:
View attachment 646416

mig-31bm said:
otype for this chart below or is this purely calculated/estimated performance:

A mystery for me. NAA Performance Calculations would clearly state whether external pylons were present, would have NAA standard Plot/Report Block format, Report number, Date, Page number. The plot looks like standard AAF/USAF summary plot in summary form - Basic Form implies zero external racks/pyons and 1/2 wing fuel. Four machine guns is interesting because AFAIK SAC never assigned P-51H in interceptor role with less than 6x50 and full ammo (1800+).

Missing is date and possibly location like Wright/Eglin Field.

mig-31bm said:
View attachment 646416

How about the chart below, fly tested or purely calculated/estimated?
View attachment 646418

The plot above is probably a Performance Plot (calculated) at NAA, but unusually - does not so state and the P-51H NA-8284 Report labels all Performance plots as Calculated Performance. Additionally the plot labeled pg 11 is NOT from NA-8284-A. 8284was dated 9-44 BEFORE first flight and as this plot has 8284 and Not 8284-A dated 11/45 it MUST be a Calculation.

mig-31bm said:
I found this in the F-51H manual, 2220 HP and 3000 RPM would be representative of 90" Mp right?

Yes.

mig-31bm said:
View attachment 646419

How come there is such a massive different? do their rack have significantly different shape and size?

Massive? Significant between P-51A/B/C and A-36 - all the same pylons and all possesed some external 'plumbing. The D/H pylons were similat but the H slightly cleaner. Both had simple and clean glass 'elbow' from fuel feed near leading edge and no other drag components.

The first plot is closer to AAF format - but not Flight Test report format.
Any NAA or AAF Flight test plot would show flight test data points for context on the interpolated curve. Conclusion - either summary plots from prior flight tests or plots by third party (i.e. NAA Marketing of Army Public Relations).

mig-31bm · Oct 31, 2021

drgondog said:
A mystery for me. NAA Performance Calculations would clearly state whether external pylons were present, would have NAA standard Plot/Report Block format, Report number, Date, Page number. The plot looks like standard AAF/USAF summary plot in summary form - Basic Form implies zero external racks/pyons and 1/2 wing fuel. Four machine guns is interesting because AFAIK SAC never assigned P-51H in interceptor role with less than 6x50 and full ammo (1800+).

Missing is date and possibly location like Wright/Eglin Field.

The plot above is probably a Performance Plot (calculated) at NAA, but unusually - does not so state and the P-51H NA-8284 Report labels all Performance plots as Calculated Performance. Additionally the plot labeled pg 11 is NOT from NA-8284-A. 8284was dated 9-44 BEFORE first flight and as this plot has 8284 and Not 8284-A dated 11/45 it MUST be a Calculation.
Yes.

So basically, if i understand you correctly, this F-51H chart below would be accurate to the real P-51H performance

while all other charts such as this one below is incorrect because it only rely on calculation?

As a side note, how about the F-4U5 chart below, is it a real test performance or just estimated? If it is real performance then it would seem that F4U-5 is faster than F-51H correct?

davparlr · Nov 4, 2021

mig-31bm said:
Also, why the P-51H so extremely slow in this test even with 3000 RPM and 90 MP?

P-51H Performance Test

Seems strange to me. Charts show a speed of 448 mph at 25k, 90" boost for the P-51H. Other charts show 444 mph at 25k, 75" boost for the P-51B. This doesn't make since. Tis a puzzlement.

Generally, charts that identify test aircraft tail number, military test, signed, are the most accurate and trustworthy. A military test, unsigned, next, but good. For test that are not military, and no tail number, I always assume the data is engineering estimates. Engineering estimates are usually made to sell a product, or to show product will meet sales performance requirements and, in my mind, are almost always optimistic. Both of the above test show tail number??

drgondog · Nov 4, 2021

davparlr said:
Seems strange to me. Charts show a speed of 448 mph at 25k, 90" boost for the P-51H. Other charts show 444 mph at 25k, 75" boost for the P-51B. This doesn't make since. Tis a puzzlement.

Generally, charts that identify test aircraft tail number, military test, signed, are the most accurate and trustworthy. A military test, unsigned, next, but good. For test that are not military, and no tail number, I always assume the data is engineering estimates. Engineering estimates are usually made to sell a product, or to show product will meet sales performance requirements and, in my mind, are almost always optimistic. Both of the above test show tail number??

The 1650-9 (IIRC) was first delivered to NAA in December 1944. It had many different issures associated with the new carb that were not fully ironed out until EOW. From May 1945 Flight 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. However, this information will be obtained and test results will be submitted as an addendum to this report. "

Mike Williams · Nov 4, 2021

davparlr said:
Seems strange to me. Charts show a speed of 448 mph at 25k, 90" boost for the P-51H. Other charts show 444 mph at 25k, 75" boost for the P-51B. This doesn't make since. Tis a puzzlement.

Generally, charts that identify test aircraft tail number, military test, signed, are the most accurate and trustworthy. A military test, unsigned, next, but good. For test that are not military, and no tail number, I always assume the data is engineering estimates. Engineering estimates are usually made to sell a product, or to show product will meet sales performance requirements and, in my mind, are almost always optimistic. Both of the above test show tail number??

It had bomb and rocket racks. See attachment:

mig-31bm · Nov 5, 2021

Mike Williams said:
It had bomb and rocket racks. See attachment:

I thought bomb and rocket rack on P-51H only reduce speed by 3 mph?

Max Speed of P-51H : 487mph or 471mph ?

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