Jumpin on the P-38 bandwagon

[HoHun]

Hi Bolillo_loco,

>I do not doubt that at high speeds that the P-51 has a better CL max. however of what importance is this when the mustang does not have the hp to support this.

At 30000 ft, turn radii are wide, and sustained turns are slow - in the region of 60 s for a full circle. Serious combat up there involves losing energy, and the Clmax advantage of the P-51 means that it's better at instantaneous turns.

Remember that kinetic energy increases with the square of true air speed - and while indicated air speeds are quite low up high, true air speeds provide the aircraft with quite a lot of energy to burn in instantaneous turns.

Additionally, the HP number doesn't tell the entire story as the Merlin engine adds a good amount of exhaust thrust to the propeller thrust which the turbo-supercharged Allison does not.

>the 443 is a plane of similar care and no rear fuselage tank and the 440 is one with the tank in place, but empty on take off. that is also in americas hundred thousand.

"P-51 Mustang" by William Grant quotes a 440 mph speed for the P-51B, so I'd say 450 is in the ballpark. Even if you subtranct 20 mph from the P-51B's speed at all altitudes, the graph shows it'll still be faster than the P-38J except around the supercharger gear change altitude (22500 ft). The P-38J at best holds a 10 mph advantage at that altitude.

With regard to the empty rear fuselage tank: The combat radius of the P-51B as listed in the document I quoted still exceeds that of the P-38J listed in the same document, so I'd call it a fair comparison.

Regards,

Henning (HoHun)

[bolillo_loco]

I am not talking about ranges, the mustang for a fair compairison must take off in combat trim with out sanded and filled and waxed wings with full fuel on board. this means the mustang does 425-430 mph. it is in AHT I do not make this up. 440 and 450 mph speeds are once again specially prepaired mustangs with sanded and filled wings and highly waxed taking off 1,200+ lbs light. that is why they are so fast and climb in excess of 3,000fpm.

the mustang has 900 hp at 30K vs 3,100 hp for the lightning. I am to believe exaust gas and a propeller will make it turn better because this adds a lot of power to a under powered plane? the propeller does not improve high speed, it is to make the plane climb better and accelerate better at low speeds. both the P-47 and P-51 saw benifit from this propeller. it was added to improve poor rate of climb and acceleration, look at the speeds of the P-47 before and after. no significant gain in speed, but climb went up and that is what the prop was made to do.

if you are to use high data for the mustang then high data for the 38 should be used. warren bodie states 1,725hp for the 38L and 440 tas top speed and climb in excess of 4,000 fpm

[HoHun]

Hi Bolillo_loco,

>the 450 mph in the test states all the improvements and special care taken to make the P-51B much faster than a common front line fighter. special sanding of wings and care to improve the fit of cowlings, special high octain fuel, rear tank removed, etc.

When the US Navy tested the P-51B against different models of the F4U, their Mustang achieved 358 mph at sea level and 450 mph at 29200 ft at a weight of 9423 lbs.

Their comment on the condition:

"The P-51B, as flown, was in a drag condition slightly superior over that of a standard production airplane, by reason of minor changes in the external radio installation and smooth sanding of the wing."

For comparison, one of the Corsairs had received much more attention (wing fold hinge line sealed and faired, tail hook removed, cowling precisely fitted, faired and smoothed skin), and the total speed gain was estimated to be about 8 mph at upper critical altitude. The benefit the P-51B experienced from the skin smoothing alone certainly was less than even these 8 mph.

But anyway: The fighter squadrons of the 8th Air Force often not only smoothed and sanded their aircraft, but actually polished them. The P-51 in operational condition in this case obviously were superior to standard production aircraft, too.

>the one the 38 was subjected to will lead to lower results than the one the mustang was subjected to so the chart is very decieving making the mustang look like it has better CL max numbers at all speeds when it is two different tests ploted on the same chart.

You might have noticed that the report relied on a number of independend tests (including wing tunnel tests with models not affected by surface roughness problems) to confirm the findings, and the drop of the P-38's maximum lift coefficient with Mach number was validated that way. Perhaps a carefully maintained P-38 would lose slightly less than the quoted 40% of its lift at medium speeds in high-altitude combat, but there can be no doubt it lost significant amounts of lift.

Just look the the graph for the F6F which was in a better condition than the P-38F - it lost lift just the same.

Regards,

Henning (HoHun)

[HoHun]

Hi Bolillo_loco,

>I am not talking about ranges, the mustang for a fair compairison must take off in combat trim with out sanded and filled and waxed wings with full fuel on board.

For the surface condition, see above.

With regard to the rear fuselage tank, there's a good reason it's usually not included in performance figures: It was intended to be emptied before entering combat. When the P-51 dropped its tanks in combat operations, it was down to the fuel in the wing tanks. When the P-38 dropped its tanks in combat, it was down to full internal fuel. These are the two matching configurations that you have to compare for a meaningful performance assessment.

>if you are to use high data for the mustang then high data for the 38 should be used.

I quoted the above document since it provided detailed set of matching figures on both types that are of interest to us. The combination of P-38J and P-51B data sets in this report was not selected by me, but by the authors of the original report.

When I compared the P-51B data to the most detailed report I've come across, the Navy comparison to the F4U (that certainly is free of any pro-Mustang bias!), the P-51B's top speeds were confirmed with good accuracy.

>warren bodie states 1,725hp for the 38L and 440 tas top speed and climb in excess of 4,000 fpm

As discussed previously, Warren Bodie's figures apparently rely on the 64" Hg power settings that were never cleared for operational use by the USAAF. The US Navy figures for the P-51B rely on the 67" Hg power setting that apparently was the accepted standard power.

Regards,

Henning (HoHun)

[bolillo_loco]

it still falls down to mustangs with special attention payed to them while the 38 that is tested are always ragged out.

If you have americas hundred thousand page thru to the charts inside for the mustang and look at what the P-51B did for top speed when it took off with the rear tank inplace and full and was not a specialy trated mustang. it did 425 to 430 mph max this is much slower than the "specialy treated mustangs that do 440+ mph" so this is not representative of common 8th airforce pratice. also note the 150 oct. fuel used for these tests.

since it was pointed out that a mustang must burn its 85 gallons of internal fuel before it goes to drop tanks, what happens to the mustangs range when it must drop the external tanks that are still full due to enemy action? its range suffers, also the added drag of the tanks has to also cut down on the range because it had to carry the tanks much farther because it did not burn them as soon as it took off.

I only see it as fair that if the P-51 mustang is to recieve the highest rate of climb and speed figures then it sould be so for all other planes, be they russian, german, japanese, and or american.

[gripen]

bolillo_loco,
Well, there several errors on engine ratings in the AHT. Forexample that graph 37 for the V-1650-7 is without RAM as text states but values for the V-1650-3 are with RAM (there is same error in the next page on table 46. With RAM the V-1650-7 did at least that what I stated, check manual if you don't believe. Also in the case of the P-38 there is errors too; ratings for the P-38H wrong (rammed WER should  be 10k and so on) and again there is rammed and unrammed ratings mixed for the P-38J and L (unrammed WER should be 25800ft and rammed 28700ft for both, check manual again). Also it should be noted that limiting factor for the B-33 turbo (same for the J and L) is overspeed 26400rpm for WER, not regulator or what ever.

About Clmax advantage of the P-51 it should be noted that at 30k mach 0.3 less than 150mph IAS (assuming standard conditions) so the P-51 tend to be better all over speed range. I wonder from where you have got a idea that the P-51B or P-51D did not have the power to use this advantage? As noted earlier even with the V-1650-7 the P-51 had power at 30k. BTW typical combat loads for the P-51B or D are around 9000-9800lbs and around 17000lbs for the P-38J, I wonder how many times I should point this out?

About test results for the P-38 it should be noted that I have seen three separate and different datasets for various P-38J and L models and decrease of the speed below critical altitude exists in every one of them. AFAIK the smooth finish in the wings was a standard for the P-51, even planes with metal finish had actually wings painted with metal color (see pictures, you can actually see it). And about tests (A&AEE, RAE, NACA, USAF), generally you should prove that these were somehow unfair otherwise you are just wasting bandwidth and blaming people who just tried to make their best for their country. BTW I have also additional wind tunnel data which supports those Clmax values in that NACA report. And surface finish does not change the fact that aerodynamics of the P-38 sucked at high altitude and high speed.

About dive characters of the P-51 it should be noted that overall the P-51B was better than P-51D because it had better directional stability. Fabric covered elevators were not a big problem if the plane was trimmed nose heavy (actually Borsodi made his tests with a early P-51D which had fabric covered elevators). And later modified planes actually had critical mach number around 0.8 (metal covered elevators and stabilizer incidence change).

I believe there is no reason to discuss about those 1725hp claims until some one comes out with verifyable and more accurate data, BTW use of the +25lbs can be verified in the case of the Mustang.

gripen

[HoHun]

Hi Bolillo_loco,

>it still falls down to mustangs with special attention payed to them while the 38 that is tested are always ragged out.

The Mustang tested by the US Navy was in poorer condition than operational 8th Air Force Mustangs.

I have no indication that the P-38J tested for comparison with the XF4U-4 was ragged out.

With regard to lift coefficient Mach numbers, you missed that the F6F which was not ragged out was almost as badly affected as the P-38. I'd also like to point out that the P-63A which did not receive the same surface treatment as the P-51 or the YP-80 but had a laminar-flow airfoil displayed the same kind of behavior as the other laminar wing fighters, and the same superiority to non-laminar fighters too.

>it did 425 to 430 mph max this is much slower than the "specialy treated mustangs that do 440+ mph" so this is not representative of common 8th airforce pratice.

Well, the Navy had no reason to try and make the P-51B look better than their F4U - in fact, if there's a bias in the report, it's pro-Corsair. Still, their P-51B achieved 450 mph on standard power settings.

>also note the 150 oct. fuel used for these tests.

Since the 8th Air Force operationally and on a large scale used grade 150 fuel with the P-51 in the summer and autumn of 1944, and from February to April 1945, there's nothing wrong with it. The 67" Hg WEP used to achieve 450 mph is a setting for grade 130 fuel, though, so it's actually a conservative figure.

>since it was pointed out that a mustang must burn its 85 gallons of internal fuel before it goes to drop tanks, what happens to the mustangs range when it must drop the external tanks that are still full due to enemy action?

Even with fuselage tank empty, the P-51B's range is longer than that quoted for the P-38J on full internal fuel by the same report.

>its range suffers, also the added drag of the tanks has to also cut down on the range because it had to carry the tanks much farther because it did not burn them as soon as it took off.

Relying on the Flight Operation Charts in AAF Manual 51-127-5, the difference in range yielded by 85 gallons fuel burned with 2 x 110 gallons long range tanks under the wings and the same amount of fuel burned with empty wing racks amounts to 35 statue miles based on a fast cruise at 25000 ft at 46" Hg.

Regards,

Henning (HoHun)

[bolillo_loco]

Hi grippen, I have noticed errors you speak of in AHT and even pilots manuals and you are correct. I remember the P-38H, J, and L have incorrect data for critical altitude, I think it is the H model and you are correct in saying that wep (1,600hp for the H) at 26,400 ft is incorrect. that was the theory, but the pilots manual states 10,000ft is max and even in the pilots manual for the 38H it states military power is possible at 26,400 ft. from what I have read the usable power is probably 1,240hp at that altitude as stated in warren bodies book if I am not mistaken.

correct me if I am wrong on the weights for the P-38J/L and P-51D. full internal fuel and ammo and oil with external hard points, but not external stores with a pilot.

as stated in americas hundred thousand

P-51D 10,208lbs
P-38J/L 17,699lbs

this does not include any fuel burn for start up and take off allowance.

with the link you posted grippen for Cl max,  I just wanted to point out it clearly states the P-51's wing was sanded and filled and waxed and that the 38F had dull paint and suface condition was rough (the poorest of the 7 types tested) and had holes in it.

I feel this is not a fair compairison. I am not however saying that the Cl max for a 38 is higher than a P-51 at speeds above mach .6 tas. just that I am sure that the 38 would have higher numbers than shown if it had the special wing work done. this is very important in how the airflow sticks to the wing as well as the leading edge is also critically important.

you were also very correct in stating this thread is very long  

[gripen]

bolillo_loco,
The limiting factor for WER (60", 7k, 10k with RAM) in the case of the P-38H is intercooling capacity with both possible turbo versions (B13 and B-33). But for MIL (54") critical altitude  for the P-38H depends on turbo being around 22k with RAM for the B-13 and  between 23-25k depending on RAM for B-33 (manual I have claims ratings exactly just for the B-33, 24900ft with RAM and 22k without RAM). But it should be noted that after early problems with WER most P-38Hs were limited to 54" WER (see Whitney: Vee's for Victory).

Those weights you claimed can be confirmed from the AHT and actually I have claimed them too. But we are interested about typical combat weights which are those I claimed above and relevant comparison for the ETO is P-51B vs P-38J. BTW your earlier claim 8lbs fuel burn for the P-51D when it climbs to the 30k...

About finish of the P-51B it should be noted that smooth finish was a standard for wing. The  P-38F had also standard finish and some problems with surface but it was also around 1200lbs lighter than the P-38J at typical combat weight while the P-51B weighed about that P-51B used to in combat. I see no reason to believe that results are not valid nor that test favors P-51B. And as noted earlier the P-38J needed higher Clmax for same turning performance as the P-51, so we can see that the P-51 has clear advantage at hole speed range at high altitude. BTW wind tunnel tests also support results.

Well, IMHO the main reason for long thread appears to be that someone can't accept documented tests, weights and engine ratings.

gripen

[Vermillion]

Isn't this thread dead yet? let it die , jeez 170+ posts.

Start another for Cod's sake it takes over a min to load even with DSL

[HoHun]

Hi Bolillo_loco,

>correct me if I am wrong on the weights for the P-38J/L and P-51D. full internal fuel and ammo and oil with external hard points, but not external stores with a pilot.

>as stated in americas hundred thousand

>P-51D 10,208lbs
>P-38J/L 17,699lbs

The P-38J as tested for comparison with the XF4U-4 weighed 16415 lbs with 300 gallons of fuel.

The P-51B as tested for comparison with the XF4U-4 weighed 9300 lbs with 180 gallons of fuel.

These are the operational meaningful numbers to compare.

Since you're insisting on a full internal fuel load: The P-51B with 85 gallons of internal fuel would weigh 9840 lbs. The P-51D in similar conditions would weigh 10090 lbs.

Be careful what you do with these numbers though: The internal tank was only full when the Mustang was still carrying its droptanks, so operationally, the weight of the fuel in the fuselage tank was meaningless. If you use these numbers as basis for a comparison of combat capabilities, I'll have to assume you're merely interested to make the P-38 look better.

>with the link you posted grippen for Cl max,  I just wanted to point out it clearly states the P-51's wing was sanded and filled and waxed and that the 38F had dull paint and suface condition was rough (the poorest of the 7 types tested) and had holes in it.

>I feel this is not a fair compairison. I am not however saying that the Cl max for a 38 is higher than a P-51 at speeds above mach .6 tas.

The results of the NACA report were carefully double-checked wind tunnel tests of aircraft models in the Ames and the Langley 16 ft wind tunnels which confirmed the findings. The Ames 1 by 3.5 ft wind tunnel tests of wing sections however matched the other test results closely except for those for the P-38F. This confirms that the P-38 not only had the same wing section compressiblity problem as the other fighters with conventional airfoils, but that the rest of the airframe contributed to the compressiblity problem as well.

Here's the comparison of the Mach-induced drop of the P-38F's and the P-51B's lift capabilities:

Mach - IAS - P-38F - P-51B

0.3 - 138 mph - 100% - 100%
0.4 - 184 mph - 88% - 93%
0.5 - 230 mph - 74% - 92%
0.6 - 276 mph - 58% - 94%

In other words, the P-38F loses significant amounts of lift through the entire speed range, while the P-51B loses only a very small amount.

The NACA report leaves no room for the assumption that the observed Clmax drop is the result of poor surface condition.

Have a look at the numbers for the F6F (which uses a similar wing to the P-38F but is not affected by its airframe-induced compressiblity problems) and the P-63A which had a similar surface condition (data for  25000 ft):

Mach - IAS - F6F - P-63A
0.4 - 194 mph - 100% - 100%
0.5 - 243 mph - 82% - 96%
0.6 - 291 mph - 63% - 109%

>I am not however saying that the Cl max for a 38 is higher than a P-51 at speeds above mach .6 tas.

The NACA report clearly shows that at high altitude the maximum lift coefficient of the P-38 drops quickly with increasing speed - starting right at the stall. This is not a phenomenon limited to high speeds, it affects the entire speed range.

Regards,

Henning (HoHun)

[bolillo_loco]

thanks for the explanation hohun and grippen


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I have to go now, my mummy is calling for me