Bearcat vs Corsair

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When the light weight Mustang developments began the war was far from over.

To not try and improve the breed would be unthinkable.
 

67inHg MAP (+18psi boost) was WEP, a 5 minute limit.

61inHg MAP (+15psi boost) was Military Power, a 15 minute limit.

If WEP was required for a second or third time then, sure, ADI would be of no help.

I still can't fathom why the V-1650-7 (Merlin 66) was cleared for +28psi boost (87inHg MAP) dry, the 100-series Merlins were cleared for +25psi boost (81inHg MAP) dry, but the V-1650-9 (Merlin 100-series) was only cleared for +18psi boost (67inHg MAP) dry.
 

The weight difference should make a noticeable difference in climb rates, at least. The problem in comparing climb rates between the D and H is that the D makes more power down low (at 67inHg MAP). But the H still beats the D to 20,000ft by a half minute using the 67inHg limit.

At 20,000ft the V-1650-9 is making 1,320hp, the V-1650-7 1,455hp, despite the V-1650-9 using 67inHg and the V-1650-7 65inHg. The climb rate for the D is 3,050ft/min at that altitude, the H is 3,060ft/min. Not much difference, but the D is using 10% more power.

Given the same engine I'm sure the climb rate difference would be larger.
 
I think 600 lbs in the climb or cruise would make a bit of an impact, it's when you start to turn that it would show. 600lbs at 1 gravity (g) is only 600lbs. However at 4 g's it would be 2400lbs (or is my thinking off here)...

The lessor weight in the turn means less airspeed bleed or altitude given up to hold / sustain speed.

Cheers,
Biff
 

The Reno thing is not a good example...those planes are so highly modified it doesn't really matter which version you start with...also, I'm sure the rarity of the H models would be a huge factor too...I heard there's only like 1 or 2 still in existence...
 

Greg - post the P-51D flight test you want to use, but make sure it has all the data for GW, load of fuel, ammo and ballast - as well as the HP 'from tables' that you want me to compare.

In the meanwhile - ponder this.

From the NAA Drag and Power Analysis Report:
The P-51H Zero lift Parasite Drag at 9x10^^6 R.N is .0151 vs .0160 for P-51D at R.N. of 9x10^^3
The P-51H Wing area is 235.73 vs 233.19 for the P-51D
The P-51H Empty Weight is 6586 pounds vs 7205 for the P-51D
The P-51H Combat Gross weight for 255 gallons of fuel plus water and 1820 rounds of ammo = 9544 pounds vs P-51D with 269 gallons, 1820 rounds, no water = 10,208 pounds

P-51H Limit Load = 7.5G at 9500 pounds----------> 7.46G at 9,544 pounds
P-51D Limit Load = 8.0G at 8000 pounds----------> 6.26G at 10,208 pounds

P-51H W/L at Combat GW = 9544/235.75 = 40.5
P-51D W/L at Combat GW = 10,208/233.19 = 43.7

P-51H CDo = .0153 at RN=9x10^^6
P-51D CDo = .0160 at RN=9x19^^6 Both Values at ~ 150mph at SL with zero correction for compressibility

Corrections at .5M ~ 1.1, at .65M = 1.2

So, You decide on the "Best Airframe". The one with 95% of the Parasite Drag, 94% of the mass, 93% of the W/L, 86% of Induced Drag at all comparable speeds - or the "other one"?

Given the SAME power at all altitudes the P-51H will outperform the P-51D 'significantly'

When I looked at the only chart with raw data plotted, namely the Rate of Climb vs Boost for the P-51H test in which the test report discussed issues with both the WI and carburetor, it was clear that there was significant spread of plotted values for both 61" and 67" Hg - look for yourself and decide whether you think the -9 engine was putting out HP to the Packard Standard Chart as plucked by the test pilots?
 
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There is a Report out there which has the P-51H-5 using 90. 80, 67, 61 and 46" with 130/100 fuel which was basis of 1949 SAC report - which I am looking for as the -9 had less HP for most altitudes below 24,000 feet when compared to the 1650-7.

I don't recall checking to see if the table pick ups from Packard were faithfully transcribed to the Flight test reports but I have found many errors in the flight test reports for the included HP in the data.
 

The 67 in Hg was the limit for 130 grade fuel, the colored power charts on the Williams' site do show 70 in Hg - that being for post-war 145 grade fuel? On 150 grade fuel, the earlier Merlins in Mustang being cleared for +25 psi in RAF use, albeit only (or 'only') 75 in Hg in USAF use? The +25 psi only for low gear?
The V-1650-9 have had a similar 'hi-alt' supercharger gearing as did the -3, unlike the -7 that was 'mid-alt' engine - will heat the charge less on same boost, so the -7 could use a bit more boost than the -3 and -9?
On ADI, it was 90 in Hg for the -9, though.

Plenty of question marks, I'd love to have more information on this
 
I cannot believe that a weight difference of 600 pounds is insignificant. It takes a lot of work to raise 600 pounds to 25,000ft and keep it there for 6 hours. An increase in weight may not have a great difference on top speed but must have a greater influence on climb, time to climb and consumption at altitude. Similarly having an extra 30 mph, if only for 5 minutes cannot be insignificant. In the BoB 30 mph extra would have the Spitfire completely outclassing the 109 and the Hurricane fighting on par. 30 mph extra for the 109 would have completely changed the BoB in the LW favour. Many, if not most combats last less than 5 minutes.
 

It makes a difference. Under same power output the P-51B outclimbs and out turns the P-51D for combat load GW and all comparable load outs. Having said that, for full combat load the P-51B has two less machine guns and 600 rounds less ammo...

The P-51H on the other has the same combat capability with 600 pounds less weight - which is another reason that the 51H had the same reason with 14 gallons less fuel - and no cg problems for any loading
 
I'll revisit this one more time just for completeness.

If you go to the WWII Aircraft Performance website you can find a calculated test for the P-51H. It is report NA-8284-A. There it lists the calculations for the P-51H airplane. It lists speed and rate of climb at two combat power ratings, 90" and 80" Hg. at 3000 rpm, War Emergency Rating of 67" at 3000 rpm, Military rating of 61" at 5000 rpm, and Normal rating of 46" at 2700 rpm.

If you go to the Mustang Performance website you can find two reports for the P-51D airplane. One is USAAF report 44-15342 with flight test data and the other is report NA-46-130 with calculated data from North American.

These are not MY calculations, these are official reports from North American and the USAAF.

Since my contention is that the P-51D and P-51H airplanes were very similar at similar power levels, I'll use the WER rating of 67", 3000 rpm, and blower in appropriate gear for the altitude, the Military rating of 61", 3000 rpm, and the Normal rating of 46", 2700 rpm. I ignored the 90" and 80" M. P. numbers because the P-51D can't make those power settings and is thus not relevant to this post. Let's see what the reports say.

Please note the critical altitudes change with manifold pressure, as expected.

P-51H at critical altitude:
WER, 29800 feet, 447 mph
WER, 17800 feet, 433 mph
WER, sea level, 360 mph
Military, 32000 feet, 441 mph
Military, 20400 feet, 431 mph
Military, sea level, 342 mph
Normal, 32000 feet, 407 mph
Normal, 21900 feet, 397 mph
Normal, 301 mph
Time to climb from sea level to 20000 feet at 67" M. P. and 3000 rpm is 6.37 minutes.

P-51D at critical altitude:
WER, 26000 feet, 442 mph
WER, 10000 feet. 417 mph
WER, sea level, 375 mph
Military, 28000 feet, 439 mph
Military, 13200 feet, 413 mph
Military, sea level, 364 mph
Normal, 29400 feet, 420 mph
Normal, 16200 feet, 387 mph
Normal, sea level, 323 mph
Time to climb from sea level to 20000 feet at 67" M. P. and 3000 rpm is 6.4 minutes.

So, overall we see that the P-51H at 67" M. P. and 3000 rpm climbs from sea level to 20000 feet 0.03 minutes faster than a P-51D at the same power setting. That's a whole 1.8 seconds quicker, assuming the 6.4 minutes was really 6.40 minutes. It was quoted at 1 decimal place. Less than one half of one percent seems pretty similar to me. So the 500 or so pounds of weight savings in the P-51H bought you nearly nothing in climb, at least to 20000 feet.

The P-51H goes 447 mph at 29800 feet at WER while the P-51D goes 442 mph at 26000 feet at the same power setting. A whole 5 mph delta. So the P-51D is 1.1% slower at a slightly lower altitude where we would expect it to be slightly slower.

The P-51H goes 433 mph at 17800 at WER while the P-51D goes 417 mph at 10000 feet at the same power setting. Most of the 16 mph delta is due to the large difference in altitude between the aircraft due to engines developing their best power at different critical altitudes.

The P-51H goes 360 mph at sea level at WER while the P-51D goes 375 mph at sea level. The P-51D makes better power at sea level than the P-51H does. Again, almost entirely engine-related.

You can read the numbers above as easily as I can and they rather heavily support my contention that the P-51H and P-51D were VERY similar at similar power levels. Hence my claim that had they fitted the P-51D airframe with the same engine as the P-51H had, the P-51D would have performed VERY similarly to the P-51H.
 
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As an observer on the sidelines, I'll throw this in here - I see speed and climb data, lots of it, where are we on wing loading, turn and roll performance and acceleration between the D H?

*EDIT - I think Bill was starting to go in that direction on the last page...
 
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I'd love to explore an answer to that Joe but, unfortunately, the fight test and calculated data don't enumerate turn rates. I think the P-51H is almost certainly a bit better than the P-51D, as I have said numerous times, but I don't believe the difference between the P-51D with a -9 / -11 engine and a P-51H with the same engine is enough to justify the development cost.

Apparently, Bill does.

Our disagreement is NOT about whether or not the P-51H was a good plane, it was. It is entirely about whether or not the difference with equal engines would be worth the cost.

In the relative scheme of things, it's a very minor disagreement after all and, in the end, they DID proceed with the development of the P-51H. It's really nothing to get excited about. We apparently have a different idea about whether or not they should have spent more money than was required in WWII for P-51 development that was never used in the war. 80 years after the fact, it makes no difference at all. I feel we could have gotten substantially the same aircraft with a simple engine change and he thinks the P-51H's new airframe was significantly better.

From the real-world data I can find, it wasn't quantitatively much better, top speed wise or climb-wise. He thinks otherwise.

That's nothing much to get upset about from my end, but I will respond to sarcasm and personal attacks, hopfully within the rules of the forum. I've been trying to stay focused on the point I was trying to make but, alas, am not very good at turning the other cheek, so to speak. Perhaps we just like to explore alternative "what ifs" differently.

I'd be happy to discuss it ... without having it escalate into personal attacks just because we don't think alike.
 

Joe - I went there early. What I didn't want to do is deal solely with the single flight test on Mike Williams' site that a.) clearly had engine issues with 80" and 90" boost, and b.) confusing HP values for -9 in the report for 61 an67". When I looked at those I noted quite a few 'pick and insert' errors from the V-1650 Power tables for B/C/D tests
 

I was being polite, the bomb load carried by "strategic" bombers like the stirling and fortress were not in many cases strategic. A 4 engined bomber dropping 1.5 tons is light to medium bombing with little accuracy is no strategy at all. I know you cannot extrapolate directly from a single to a four engined aircraft but to say a S/E aircraft can carry 600 LBs to Berlin and back with no detriment is also to say all allied bombers could carry an extra ton (or tonne) of bombs with no ill effects, obvious nonsense.
 
Good find, Eagledad.

Thanks.

I believe that Spitifre IX in the chart had to be a clipped wing version, not a full universal wing.

Also, I've read in at least 15 texts on the subject that there was no other WWII fighter that could out-roll an Fw 190, particularly the radial engined models. This is the first time I have seen anything that even suggests a Spitfire could out-roll one, even with a 50-lb stick force.

Let's remember, it came from Sport Aviation. Is there any otehr corroboration out there that anyone has seen? Not saying anything in particular except that it is contrary to what I've read for a lot of years.
 
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The graph kindly posted by eagledad does not have the roll rate for the serial produced P-51. The roll capability of those was lower than the Fw 190A at 10000 ft until up to 350 mph indicated. Above that, the P-51 was better. Graph from NACA report no. 868: pic.

BTW, that might also explain why the later Fw 190D were to receive hydraulically operated ailerons, those help in achieving maximum aileron movement (where the pilot does not have enough strength for that), and hence roll rates at high speed,
 
Just a few more observations here...

As a pilot (and a sometimes wanna be fighter pilot), in a close in engagement I'd want a mount under me that 1) accelerated well, 2)good turning and roll rates, 3) good climb rate and lastly speed. It seems the P-51H might have brought those to the table with only a marginal "mark-up" in speed and climb, depending where you were on the flight envelope. (Biff, chime in and let me know if my priorities are in order)

As far as time and cost for a slight or marginal improvement (in some folks opinion) I think it would depend on how much commonality the P-51D had with the H, how much would it cost to convert tooling and manufacturing methods and lastly if the customer (Uncle Sam) was willing to fork out the expense of modifying the production line. IMO, if all these factors can easily be incorporated with no disruption of production, degradation or quality or excessive add-on costs, I see no reason why the P-51H should have been continued, especially with P-51D production lines still rolling.



 
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Joe - I am going to break this out in two parts.

First - I will use the Relevant physical attributes stated by NAA for the P-51D and P-51H as the basis for Performance comparisons.

Then I will use the best case P-51D Flight Tests obtained by AAF in June 1945 for Dash speeds at specific altitudes with the V-1650-7 and the P-51H during the May 1945 Flight test with the V-1650-? and make some comments regarding the Test conditions of each airplane, but particularly the 1650 used in the P-51H test as reported.

Discussion 1
P-51H Limit Load = 7.5G at 9500 pounds----------> 7.46G at 9,544 pounds
P-51D Limit Load = 8.0G at 8000 pounds----------> 6.26G at 10,208 pounds

P-51H W/L at Combat GW = 9544/235.75 = 40.5
P-51D W/L at Combat GW = 10,208/233.19 = 43.7

P-51H CDo = .0153 at RN=9x10^^6
P-51D CDo = .0160 at RN=9x19^^6 Both Values at ~ 150mph at SL with zero correction for compressibility

Corrections at .5M ~ 1.1, at .65M = 1.2

So, what does it mean that the P-51H has 95% of the Parasite Drag, 94% of the mass, 93% of the W/L, 86% of Induced Drag at all comparable speeds?

FIRST - take the engine out of the equation - for two reasons.
A.) any of the V-1650 engine/prop combinations could have been used including the -3, -7, -9 and -9A and "GregP" suggested using only the one P-51H Test Report of the -9 which a.) The Water Injection System and Simmons Manifold Pressure regulator system were malfunctioning, and b.) the delivered V-1650-9 had not been calibrated and c.) that HP data in the report had been pulled from the Engine Spec AC-10356 Dated November 1944.
B.) Assigning the SAME engine/prop system to both the P-51D-15NA and the P-51H-1NA eliminates debates about "plot vs spec sheet vs actual HP' for any altitude or any speed run so any equation below which depends on THRUST can assign the Same Thrust to each airframe and focus on the Physical attributes to derive Acceleration, Climb, Corner Speed(Maneuver Point on the V-n Diagram), Rate of Turn.

Given the SAME power at all altitudes the P-51H will outperform the P-51D 'significantly'.

For example: Acceleration

For equal Power, equal prop efficiency The aircraft with less weight and Same drag will out accelerate the greater weight a/c. In the case of the P-51H is has both less Drag (=greater net Thrust) AND lower mass. Net THRUST = Thrust available - Thrust required. Acceleration is Thrust/Mass. Acceleration is inversely proportional to Mass for a given Thrust. The Mass of the P-51H at full combat load at 9544 is 92.7% of the P-51D at full combat load of 10,288 pounds.

For same Power, same Thrust, starting at same velocity, with same engine and prop the Acceleration of the P51H is 1/.927 = 7.8% greater than the P-51D.

This is before taking into account the lower Drag of the P-51H. The Induced Drag of the P-51H and the Zero Lift Parasite Drag will individually and collectively be less than the P-51D at the same airspeed for same combat load out. At top speed of the P-51D and the same speed for the P-51H. the Induced drag for the P-51D will be slightly greater than the P-51H, but for the sake of clarity, assume both are = zero. For that assumption, the Drag comparisons are:

Drag of P-51H = 96% of the P-51D (.0153/.016 at RN=9.6x 10^^6. The Drag of both increased as the velocity increases but maintain their relationship for level flight)

Therefore the Net Thrust for the P51H = Thrust Available - .96 Drag of P-51D ----> driving incremental acceleration more positive for the P-51H over the P-51D.

The same logic and process follows for ROC. ROC = Excess Power/W where Excess Power = T*V-D*V
For the same Prop/engine system, and the same Trust developed at same Velocity, the P-51H once again has greater Power Available than the P-51D because the P-51H Drag = 'K'( 9544/10288)/(235.75/233.19) where K= 1(.5*Rho*V^^2) and same for both the P-51H and D.

Therefore the P-51H Drag as a % of the P-51D = .927/1.011 = 91.7% of the P-51D Drag.

Extending that back to the ROC equation Excess Power for the P-51H compared to the P-51D;

V*(T-.917*D) for the P-51H and V*(T-D) for the P-51D,

Now, the ROC of P-51H = V*(T-.917*D)/9544 while the ROC for the P-51D = V*(T-D)/10288

As we don't know either Thrust or Drag as we have not specified at Velocity (or Power) we can get a rough understanding of the comparison by using P-51D Drag = 1/2 Thrust and 3/4 Thrust for illustration:
Case 1 D=1/2*T
P-51H ROC = V*(T-.917(.5*T)/9544 = V*T*(.542)/9488= V*T*(5.68x10^^-5)
P-51D ROC = V*(T-.5*T)/10288 = V*T*(4.86x10^^5)
The ROC advantage for the P-51H in this case is 17%.
Case 2 D= 3/4T
P-51H = V*(T-.917(.75*T)/9544= V*T*(.312)/9544 = .0000327*V*T
P-51D = V*(T-.75*T)/10288 = V*T(.25)/10288 = .0000243*V*T.
The ROC advantage for the P-51H in Case 2 is 34%

Summary - For same Power at same altitude with the same engine, the aerodynamic superiority of the P-51H gives it a decided advantage in Acceleration and Climb - as well as Velocity but for this exercise the actual value for power is not introduced.

I will lay out the May 1945 P-51D-15 vs P-51H-1 Flight Test Reports using Military Power in the next post.
 
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