Bearcat vs Corsair

Bill, great post! You make it easy for me to understand, whish you were my high school math teacher!!

Next - the Flight Test Report of June, 1945 does not represent a fully functioning V-1650-9 and because of the following comments contained in the report, raises questions regarding even the actual power produced by that specific engine. The comments included
"Water Injection System not working"
"Simmons Manifold Pressure Regulator not working"
"A Bendix Stromburg PD-18C-3a carburetor was installed to replace the speed density pump"
"At present time the V-1650-9 has not been calibrated and all power data are extracted from calculated power curves"
"all power figures based on Power curves from Spec. No. AC-10356 dated 29 November, 1944"

These remarks raise questions across the board for this 1650-9 engine with respect to how well it operated even with respect to 46 and 61" of boost. I suspect the fuel metering substitution of a Carb for the faulty Simmonds manifold pressure and speed density pump may have been flawed to metering a higher Rich mixture.

Next - The Flight Test Report dated 15 June, 1945 for the P-51D-15NA is tested at or around 9760 pounds at takeoff and speed/climb runs largely at 9660-9570 pounds. The fully loaded Combat Weight for P-51D is 10,288 for everything except external load out. So, all the resulting data points are for a GW=< 94%, where as the P-51H speed and climb runs were at 9450 to 9350 for a GW=> 98%. So, for every data point the P-51H is laboring under a 4-5% weight handicap when compared to the P-51D.

I will extract the comparative 61" boost figures for comparison - both for level speed and climb.

For the ROC values I will put a suggested 'weight' factor to reflect how uploading the tested P-51D climb rate would be reduced when adding 500+ pounds of Fuselage Tank fuel to complete a Combat Load load out.

drgondog said:

I will extract the comparative 61" boost figures for comparison - both for level speed and climb.

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I did some figures of RoC at 67inHg several pages back.


P 51D Performance Test
P-51H Performance Test

This shows the hp of the engines and highlights the different characteristics of the -7 and -9.

Bill, do you know why the V-1650-9 wasn't cleared for +25psi boost (81inHg) dry, even though the equivalent Rolls-Royce engines were?

FLYBOYJ said:

Bill, great post! You make it easy for me to understand, whish you were my high school math teacher!!

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LOL. Joe a couple of points about 'real world' on the above formulas.

For actual ROC, you have to integrate over the climb trajectory to correctly differentiate the change in Thrust as a function of the changes in velocity, as well as the change in Drag for those comparable velocities as altitude increases and density decreases. The Parasite Drag also adds an Angle of Attack component to account for the increased Form Drag as well as the Propeller stream tube delta for the fuselage - which increases due to the new AoA.

But Point by Point in the trajectory the relationship to Drag and Weight I posed is correct and easier to understand (I think) the way I showed it.

The Corner Velocity Maneuver Point is higher for the P-51H, largely because the increased G limit and wing area offset the lower CLmax for the P51H. I used clean stall speed (difficult to nail precisely) for both the P-51H and P-51D, arriving at 1.65 and 1.77 respectively for data that I have found - but not quite sure of.

The W/L to Clmax ratio for the H is 22.9 and 24.7 implying that Rmin for the P-51H is slightly less ((~7%) for same power. Consequently the rate of turn is greater for the P-51H as well... by the ratio of the square roots of CLmax*N to W/S ratio. For this example the 51H has a turn RATE about 10% faster. This all depends on whether I picked the Clmax correctly.

So far - I haven't found one category in favor of the D, given equal power output. When comparing 1650-7 vs the -3 and the -9 and the -9A, as you know the -7 at 67" is the most powerful from SL to FTH in Low Blower and the 1650-3/-9/-9A were better above Low Blower FTH for the -7... so net, net the P-51D at SL at 67" than the P-51H at SL with a good -9 at SL.

Since the time to climb from sea level to 20,000 feet for the P-51H in the flight test I was using and the P-51D I was using wwere withing about 2 seconds of one another, I'd say either your equation is missing something somewhere or we have an issue with the flight tests.

In the P-51H flight test I used, the P-51H was not having any trouble at 67 inches ... it was having trouble going to 81 inches with ADI, meaning it was having issue getting to the extra power that gives the P-51H it's performance jump over the D model. The engine was running fine at 67" per the report. As you know, the speeds and rate of climb to 20,000 feet were VERY cloe to one another, and that does not agree with your analysis above, Bill.

Can you think of an explanation other than the engine wasn't calibrated?

I might add that the P-51H flight test I used was from North American and the the P-51D flight test was from the USAAF, not from a private party analysis, and that is not knocking your calculations at all. All I'm saying is that real world flight testing didn't find that amount of differnece between them, on at least several occasions. I like calculations and calculating as well as the next enginer, but I throw them out when real data are avialable ... and in this case, they are, at equivalent power settings.

That does NOT mean that 67" in the V-1650-9 pdocudes the same HP as 67" in the V-1650-7 at the same altitude ... it says they are both set to 67" and 3000 rpm, and that is why I was careful to say power settings, not power levels.

There is Eagledad's reference that says that at equal pwoer settings ( and that was a private flight review), there was little to choose between them, and there are the flight tests I used that say essentially the same thing.

So while I agree with your calculations in principle, they don't seem to track in real life. That is also from two current P-51 pilots who have flown the P-51A, B/C, D/K, H, and careful modifications of some D models. Today, in private hands, none of the P-51's are seeing 67 inches since we aren't flying with gasoline that will sustain it ... except at Reno where high quality aviation fuel is avilable. Today they take off at 45 - 55 inches, sometimes less, and throttle back. So today they are flying at very nearly equivalent power settings ... and don't see much of a difference.

What they really do when flying together is that the leader sets a power level and the other(s) form up in formation, and they talk back and forth on the radio to see who is flying at what power (rpm and MAP). When they do, there isn't much difference, but there is sometimes a small bit. Ed Maloney's P-51D (Spam Can) typically takes about 1 more inch of manifold pressure to keep up with Steve Hinton's P-51D (Wee Willy) at most VFR altitudes, or if did before it got polished and the tail was repaired. Now the pwoer levels required for formation are the same. When they actually fly with a P-51H (on rare occasions), they don't see much difference bewteen Steve's plane and the H while in formation. To me, as an engineer and an observer, that says very close to the same drag when they are running the same MAP and rpm while in formation. And it's mostly at about 235 knots since the speed limit below 10,000 feet is 250 knots, as Joe and Bill well know.

Hence, my post. And since they still fly that way, I'd sat some investigation is in order for anyone really interested. Not being a P-51 pilot nyself, I take our museum and my frinds word for it. The only time I ever flew a P-51D in formation with another P-51, it was another P-51D and I was in the back seat having fun, not playing fight engineer.

And, as I stated erlier, I throw out the calculations when real data are avilable. In this case, they are.

GregP said:

Since the time to climb from sea level to 20,000 feet for the P-51H in the flight test I was using and the P-51D I was using wwere withing about 2 seconds of one another, I'd say either your equation is missing something somewhere or we have an issue with the flight tests.

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These are the flight tests I was looking at:

P 51D Performance Test
P-51H Performance Test

The D test was done in June 1945, the H test in May 1945. This may be the one to which Bill is referring, as it mentions problems with the ADI and pressure regulator.

The condition of the aircraft was similar for the climb tests - ie clean with wing racks in place. Weights were 9,760lb for the D and 9,484lb for the H at take-off for the tests. This suggests to me that the H was relatively more heavily loaded.

Time to climb to 20,000ft with 67inHg MAP was 6.6 minutes for the D and 6.1 minutes for the H. That's a difference of 30s. Or, to put it another way, it took 8% longer for the D to climb to 20,000ft than the H. This is despite the hp advantage the D had at lower altitudes.

The reports don't have climb dat afor the D at 61inHg, but the H climbed to 20,000ft in 6.75s, or 9s longer than the D took at 67inHg.

Greg, since you have repeatedly stated your opinion that the P-51H was not required during WW2 because it never went into combat and therefore was a waste of money, would you say the same of the Bearcat since it never went into combat and was not required to defeat the Japanese?

Wuzaak,

Just a quick point on the P-51D test... it says that the fuel load was only 209 gallons, the fuselage tank behind the pilot only had 25 gallons, so the D and the H were relatively close in weight. (9760 for the D vs 9484 for the H)

Eagledad

http://www.wwiiaircraftperformance.org/mustang/Comparative_Fighter_Performance.jpg

Just for info, above is a link to a comparative test of three WWII fighters, including a P-51H. If you look at the chart, the power setting used for the P-51H was 3000 rpm and 70 inches. It's not 67 inches like a P-51D would be using, but it is reasonably close.

Take a good look at the numbers. Speed and climb are right where I said they would be. The speed at 20,000 feet is just under 450 mph and the climb rate at that altitude is close to 2600 feet per minute, right where you'd expect to find a P-51D.

So here is another flight test of the P-51H, near P-51D power levels that shows the P-51H right where the P-51D is expected to be. It is dated 12/18/44 and the report appears to be Y-122981. However, I bet M. Williams can tell us for sure if anyone is intetested in asking.

You're starting to sound downright unfriendly for a friend, Wayne.

The Bearcat obviously wasn't required for WWII since it got there but didn't manage to get into combat. It DID get into combat post WWII for France, Thailand, and South Viet Nam.

Virtually every fighter that flew from late 1944 onwarrd didn't make WWII combat and was therefore technically not needed for WWII. That doesn't mean and I never said they are or were bad aircraft ... I said they were not needed for WWII and therefore were a waste of money ... relative to WWII. This IS a WWII forum, after all.

The P-51H served well in the reserve and guard, post war. The P-80 also didn't get into combat, but survived for nearly 50 years in the form of the T-33. It wan't needed for WWII either, but paved the way for future jets. The only thing that saved these planes instead of having them go the way of the Focke Wulf Ta 152 is the fact that we won the war and left these planes in service, albeit in lower numbers than a wartime footing would otherwise dictate.

Had Germny won the war, my bet is the Ta 152 and Me 262 would have equipped not a few squadrons of planes for some years. too, much like the P-51H and P-80, which would have been nearly-forgotten footnotes in history.

Sometimes the future hinges on relatively unimportant-at-the-time events, such as having the USA move toward entering WWI by having the Lusitania, a non-US-flagged ship, sunk without warning.

I'd say that Hitler's decision to invade the USSR was the turning point of WWII. If he hadn't done that one thing, he might have carried the day anyway, even with all the other mistakes the Nazis made. Thank heaven he wanted something in the USSR!

eagledad said:

Wuzaak,

Just a quick point on the P-51D test... it says that the fuel load was only 209 gallons, the fuselage tank behind the pilot only had 25 gallons, so the D and the H were relatively close in weight. (9760 for the D vs 9484 for the H)

Eagledad

Click to expand...

In other words, teh P-51D was more lightly loaded relative to the P-51H. Had they had equal fuel and ammo loads the advantage in climb of the H would have been more pronounced.

GregP said:

http://www.wwiiaircraftperformance.org/mustang/Comparative_Fighter_Performance.jpg

Just for info, above is a link to a comparative test of three WWII fighters, including a P-51H. If you look at the chart, the power setting used for the P-51H was 3000 rpm and 70 inches. It's not 67 inches like a P-51D would be using, but it is reasonably close.

Take a good look at the numbers. Speed and climb are right where I said they would be. The speed at 20,000 feet is just under 450 mph and the climb rate at that altitude is close to 2600 feet per minute, right where you'd expect to find a P-51D.

So here is another flight test of the P-51H, near P-51D power levels that shows the P-51H right where the P-51D is expected to be. It is dated 12/18/44 and the report appears to be Y-122981. However, I bet M. Williams can tell us for sure if anyone is intetested in asking.

Click to expand...

And here is a speed graph of the D

http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_Level.jpg

This is at 67inHg. At 20,000ft the speed appears to be ~420mph (421mph in the table in the test).

I have previously stated the climb rates at 20,000ft for this particular D on that test. The H in the test I posted earlier is recorded as 431.7mph.

Looks like we're all quoting different tests. Maybe a good procedure would be to take 5 tests for each one around the same time, throw out the high and low, and take the average of the remaining three.

After that, go back and recalculated if the P-51D had the V-1650-9 or -11 and see what the differences would be. Of course, that would HAVE to be with calculations since they didn't build one.

I for one think there wouldn't be enough difference to warrant the devlopment costs of the P-51H. There may be some justification, but I can't see it or agree with it. We all know it was built, so the decision was made already ... during the war, to do it. With hindsight, I'd change a lot of things, not just this one small decision.

Hindsight is like experience, you get it right AFTER you need it.

You can't see how 600-700lbs weight saving would be a good thing?

Are you being obtuse on purpose, Wayne? Have you even read my replies? I was using actual data and actual calculations from the manufacturer and USAAF, not calculations based on numbers I mostly can't seem to find. I didn't make any claims the data didn't show.

I already said the H was a small bit better than the D, not very much ... at equal power. At full rattle it was significantly better.

If you won't believe real data, then you won't. It makes no difference this long after the war anyway. I won't try to confuse you with manufcturer's and USAAF data anymore if your mind is made up.

Confusion about V1650-9 power settings

The data indicates that the V1650-9 produced 2200+ hp with 90" Hg using water injection and about 1600 hp with 67" Hg dry using 130 octane fuel. Something is missing here: what is the power output using 145 octane fuel without water injection? Wouldn't it be about 2000 hp? And shouldn't the comparison being made be between the P-51D using 145 octane fuel (widely available since mid-1944) at 75 Hg and the P51H using 145 octane fuel at 80 Hg, and also using water at 90Hg?

When water ran out for the P-51H, it would still be able to produce power at 80 Hg, somewhat better than the P-51D at 75 Hg.

From other sources, the max speed of the P-51D using 75 Hg was about 450MPH. The P-51H (not a P-51 at all but a complete redesign based on the P-51) at the same power setting was about 10MPH faster than the P-51D. We can now answer the central question: what part of the improved performance of the P-51H was due to improved aerodynamics and what part was due to using water injection. The P-51H gained about 10MPH from better aerodynamics and 10+MPH from using water injection. Was the overall improvement, 20+MPH, worthwhile? Greg says no. But what if the war in Europe had continued and the allies has had to face numbers of 335's and 152's. The extra speed would have been useful and the higher rate of climb even more so. Wouldn't have helped against the 262 though.

What about the future? The Hawker P1030 and the Supekrmarine 391 both had projected speeds of about 510MPH using the 3500 hp RR Eagle engine. That seems to represent the absolute limit for a combat aircraft that the combination of reciprocal engine and propellor was capable of, at least using a WWII wing.

Wayne - I think I see where he is missing the obvious. Greg seems to be equating Manifold Pressure setting results as 'equal power". If so, he is missing the very obvious data points of different HP for same boost between 1650-7 and -9 (and thus the -3 and -9A) leading to another conclusion that he forgot that T=D at top speeds for any given altitude and that Boost does Not equal HP, nor does HP = Thrust.

For the moment I suspended belief that the -9 Engine tested actually achieved the 'HP picks of the Flight Test, when they had to run with fuel metering carb instead of the Simmons manifold Pressure system with speed density pump.

Will run some numbers for the May flight test on the H with the 61" HP data. Do you suppose Greg realizes that the P-51D-15 was tested with an fuselage fuel tank was 400 pounds shy of full while the H ran full Combat load with 100% fuel and ammo load out?

drgondog said:

Will run some numbers for the May flight test on the H with the 61" HP data. Do you suppose Greg realizes that the P-51D-15 was tested with an fuselage fuel tank was 400 pounds shy of full while the H ran full Combat load with 100% fuel and ammo load out?

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I didn't mention fuel specifically, but I did mention that the D was, relatively speaking, more lightly loaded.

Eagledad pointes out the fuel load of the D earlier.

I noticed on tests of British aircraft that the figures were often corrrected to 95% of MTOW. Was there any standard like that in the USAAF?

GregP said:

Are you being obtuse on purpose, Wayne? Have you even read my replies? I was using actual data and actual calculations from the manufacturer and USAAF, not calculations based on numbers I mostly can't seem to find. I didn't make any claims the data didn't show.

Greg - Wayne has forgotten more about Physics than you know, and easily understands the applications ON HIS OWN. If something doesn't smell right, he questions it. The May, 1945 Flight Test results didn't quite 'smell right' so your repeated 'replies' using actual calculations and contractor data didn't make any sense to him or me. So when NAA issues a revised Report which downgrades ALL of the 1650-9/Simmons data to 1650-9 Fuel Metering Carb data - You missed it even though it was explained in detail in all 97 pages of the NA-8284-A report you threw at him and me.

If you had a a scintilla of understanding regarding what was written and documented in detail, you would have apologized to Wayne. Why, you ask? Because NA lowered the HP for each of the performance values to match the actual performance. The AVERAGE reduction was nearly 200 HP per line of entry. A case example is that the "original" HP values for 358mph at SL for 67"@3000 RPM was Revised to 358mph at SL for 67"@3000 RPM. That is a NET Thrust reduction of 150-200 pounds of Thrust to achieve the May Flight Test values. AT 25,000 Ft for 67"@3000 RPM, the HP was revised from 1311HP to 1150 to achieve the May, 1945 speed of 435mph. That is a reduction in Thrust of 113 pounds from 925 to 812. At 30000, 67" @3000RPM, the HP was revised from 1310 to 1170 HP, from 917 pounds of thrust to 802 pounds to achieve 448mph

By contrast the 'Light' P-51D-15 with 1650-7 at 25000 ft. achieved 438mph with 989.7 pounds of thrust. That would be an increase of 22% Thrust to achieve +3mph. At 30,000 feet the P-51D-15 achieved 429mph with 1180HP, 845 pounds of thrust. So, the P-51H at design GW, at 30,000 feet achieves 19mph more speed with 4.5% less thrust. That means the P-51d-15 at 400 pounds less penalty, achieves 19mph less with 4.5% MORE THrust.

Summary - MUCH better performance without 80" or 90" HG, with LESS HP, much less equivalent HP-THRUST equivalency. and still has 7 minutes of 90" Boost plus 80" when the 80 gallons of water run out.

You still think aerodynamics doesn't matter? You think the H might be more economical? Ya think that even with lower boost settings and a lower HP engine at 46, 61 and 67" that it doesn't outperform a D?

Summary for this discussion
What you consistently and repeatedly do is place your money on comparisons by Manifold Pressure rather than Velocity vs HP for specific test runs at specific altitudes.

What you consistently and repeatedly do is ignore the effects of one Mustang running ~ 400 pounds under the full up combat load versus the other Mustang with full up combat load.

What you repeatedly miss is that the V-1650-9 Power Charts for 46", 61" and 67", 90" and 90" using a Fuel Metering Carb differs Significantly from the September 1944 Preliminary Spec for the Simmons version so that the "correct HP" of the actual engine could not be extracted from the Simmons equipped Power Chart.

Having said that, you still quoted from the NA-8284-A report but failed to mention the Revised HP Charts prepared by NAA on pages 57 through 64. If you bother to look you will see that the May, 1945 Flight Test HP data has been significantly lowered to obtain Required Thrust HP vs SL, 5, 10, 15, 20, 25, 30, 35, 40K for 46", 61", 67", 80" and 90".

What you are intellectually devoid of, is curiosity, when confronted with statements such as the Introduction to the NAA Report 8284-A when it starts like this

"INTRODUCTION

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 dated September 25, 1944. This report presents the results of the revised calculations together with a discussion of the data and methods used.



SUMMARY OF CALCULATED PERFORMANCE

All performance figures are based on N.A.C.A. standard atmospheric conditions and gross weight as given in item (2) except as noted.

(1) Condition Design. Full Combat Load plus wing racks but no stores - Gross Weight 9450 lbs, 255 Gallons of Fuel, 1820 rounds of Ammo, Wing Loading 40.5 lbs./ft.2




I already said the H was a small bit better than the D, not very much ... at equal power. At full rattle it was significantly better.

I think I have just trashed your belief system. At reduced manifold pressures and associated HP, it was significantly better

If you won't believe real data, then you won't. It makes no difference this long after the war anyway. I won't try to confuse you with manufcturer's and USAAF data anymore if your mind is made up.

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Greg - If you won't read what Ed Horkey signed off on, on all 97 pages, then you are simply lazy and ill-informed on this subject. You should start these discussions with the following disclaimer.

"I Have a 1st Amendment Right to express an opinion independent of a.) the facts available, or b) my ability to comprehend them" - because both of these conditions seemingly apply.

What you should Really do is apologise to Wayne.