Bearcat vs Corsair

[GregP]

Great post Eagledad, and it says it all. If the power were the same in both planes there was little to choose between them. If they fitted the -9 / -11 engines of the H to the D, they again would have been very much the same plane, albeit with the H being a bit more stable with full fuel. I have no worries there because there was almost nobody stupid enough to try to attack a 1000-plane raid while it was forming up near home base. That would be virtual suicide.

The fact that the war ended made the P-51H unneeded. Had the war continued, I'm sure it would have been a good mount , at least while the ADI was flowing. After that, it was basically a D ... not at all a bad thing to emulate.

All in all a good plane that was unneeded and had a very short poast-war service life in front-line service.

 

[drgondog]

I'll have to say that I already allowed the H was very slightly faster, on the same power, as the P-51D was. The rest of it I dispute. Will it be more maneuverable by a small bit? Sure. Enough to make a diffference? I don't think so, and the H didn't even make WWII as a combat plane, neither did the Bearcat and Tigercat, though they were really very close to being there until the war ended what might be called somewhat prematurely due to the the Atomic bomb. Any end to a war is a good thing as far as I'm concerned, as long as it ends.

Ah, Greg, generous in your praise always. Pick up your slide rule. Harken back to the good old days when you were modeling P-51B canopies as an undergrad and pick up a slide rule. Assume the CDo of both the P-51D and P-51H is the same. Stick a 1650-3 or 7 in both airframes. Look up the charts on HP vs boost vs altitude. Take the P-51D at empty and the P-51H at empty for case A. Take both and load to full combat load of internal fuel plus ammo plus oil, pilot as case B.

Note that the Empty Weight of the P-51D without fuel, pilot guns or oil is 7205 pounds while the P-51H Empty Weight is 6,586 pounds (for reference the P-51B/C Empty Weight is 6988 pounds).


To me, the "improvement" the P-51H represented is not and never was worth the development costs. To a P-51 lover like Bill, it probably WAS worth the cost.

Perhaps in March 1944, Hap Arnold thoughtfully looked at emerging intelligence regarding LW development projects and said, "Hmmm - I MAY or MAY Not be a P-51 Lover, like Bill- but methinks we have to proceed with continued Development and improve on what we have because the P-80 isn't going to help us until next year and this proposal from NAA offers 40mph advantage, better climb, same range and no aft Cg problems. Seems like a good idea to me".. "Oh wait, he says, I understand there is a really smart fella with the handle "GregP" that can see into the future and wants to tell me that the P-51H is a waste of money"

In the end, they DID develop it but made only a few that didn't last very long in post-war first-line service.

Hmm, it lasted longer than the F6F which was a pretty good airplane. It lasted longer than the F8F and F7F and about as long as the P/F-80. It was around and available in front line USAF units when Korea broke out but it was deemed more valuable than the P-51D (and P-47N and P-38L) and retained in SAC for long range escort and Interception continency.

I suppose had the war continued, we'd have some combat statistics to discuss. But it didn't and we don't. So I'll say it was a very modest improvement and allow that anyone else in the world may differ in opinion. If that's what you think, then by all means think it in good health and be happy.

Of course, hindsight DOES have 20-20 vision, doesn't it? It was quite possibly not so clear when the P-51H was conceived and proceeded with.

Now prove it Greg. You have the weights, the physical data and can take the P-51H 80 and 90" Boost out of the equation.

Calculate W/L and then explain your thesis regarding why the higher W/L (the P-51B/D) translate to better climbing and turning performance that the lower W/L P-51H

Calculate SL velocity for the two and explain why the heavier one with the same horsepower and higher W/L and higher induced drag seems slower.

Calculate ROC and explain why the heavier one seems to climb slower at all altitudes with same HP, same prop, same thrust, same activity factors as the lighter one.

Calculate Acceleration and explain why the heaver one seems more sluggish with same HP, thrust, same prop, same activity factors than the lighter one.

If you want to explore the CDo of the P-51H do some reverse engineering on the NAA calcs of November 1945. Then re-plug the drag with slightly better CDo, better CL, lower CL^^2 and thus lower induced drag and figure out why the P-51H had a higher calculated range on internal fuel than the P-51H (slight - but it had 14 gallons less fuel).

In other words - lay out some facts and present them. It would help if you could define "Very Slightly", "Slightly" and "darned good, by gum" to help frame your reported calcs

 

[davparlr]

Well, I haven't commented much on this subject but I'll pontificate some. First, the F4U-4 and the F4U-5 were both noticeably faster than the contemporary F8F-1 and F8F-2 (the F4U-5 was some 20 mph faster than the F8F-2). Climb rate was an F8F forte however the F8F-2 was only slightly better than the F4U-5. I am sure maneuverability was also a strength of the lighter F8F, however both of these aircraft would be of diddly squat use in Post 1945 air-to-air combat with Me 262s (and possibly other advanced German jets) and Mig 17s, so maneuverability is somewhat negated. F4U ruggedness and air-to-ground capability was well known but the F8F performance in air-to-ground combat was unknown. F4U had a small advantage in range. Lots of F4U logistics capability existed. So, I think the Navy decision was correct.

 

[GregP]

As always Bill, you discuss by attacking, putting people down, and trying very hard to be superior and condescending. Unfortunately it comes across in a way I'd best not describe in here as it would be against forum policy.

You're doing a good job of it, so hark back and do it yourself. I already know the P-51D and H fly just about the same at the same power levels ... I don't need a slide rule for that as I also know people who have flown both. And I already mentioned that had the war dragged on, the P-51H would have had its chance to garner a combat record worth discussion. I already stated that the main reason it was a useless exercise was the end of the war coupled with the dawn of jet age ... not any specific shortcoming of the P-51H ... it was just a development that was at the wrong time and turned out not to be needed.

My slide rule collection works just fine but I use Microsoft Excel these days and have since the day after it was a product. You should try it. That way, at least you might find something you like other than the P-51 and yourself. And I did, in fact, put some numbers out for speed and climb. Must not have been looking for it, huh?

Almost everyone else in here is civil. You should try it on a regular basis. If you want to talk with me, please be civil. It makes things a lot easier.

Last, When I called you a P-51 lover, it was not in any way an intended insult. I like 'em myself and thought you would be pleased to see it, given your history with the P-51. Just goes to show you that perception is not always reality. OK, if it makes you feel better, perhaps you are NOT a P-51 lover ... I don't know anymore and it is not on my list of things to investigate.

 

[drgondog]

As always Bill, you discuss by attacking, putting people down, and trying very hard to be superior and condescending. Unfortunately it comes across in a way I'd best not describe in here as it would be against forum policy.

I guess if you listen very hard you will hear the strains of violin music as I struggle to comprehend your insults. Wuzak, Tomo and I raised specific points to your assertions of equivalence between the D and the F which seemed to elude your attention - but each deserved a thoughtful reply other than your normal vapid platitudes.

You're doing a good job of it, so hark back and do it yourself. I already know the P-51D and H fly just about the same at the same power levels ...

Just as you were quite sure that the F6F could perform the long range escort mission in the ETO independent of a blizzard of readily available facts? You have no clue what the relative performance is unless you substitute 'the same power levels' but you wish to evade calling me out by demonstrating that you REALLY do know what you are talking about - via facts as demonstrated by the Engineering method. That is beyond you - whether slide rule or excel - so your modus operandi falls back to what I call the Soren Method of counter attack and fling a blizzard load of BS to see what sticks.

I don't need a slide rule for that.

No, you need a Pete Law to help you understand how wrong you are based on engineering. Go find him and present the same basic points and let him help you muddle through it. Maybe you will learn something?


And I already mentioned that had the war dragged on, the P-51H would have had its chance to garner a combat record worth discussion. I already stated that the main reason it was a useless exercise was the end of the war coupled with the dawn of jet age ... not any specific shortcoming of the P-51H ... it was just a development that was at the wrong time and turned out not to be needed.

When confronted with a simple test of understanding a physics/aero problem - you fall back into your Safe zone of generalities and platitudes... how many times have you avoided comparing W/L, CL, Drag comparisons by throwing this (again) up as your shield?


My slide rule collection works just fine but I use Microsoft Excel these days and have since the day after it was a product. You should try it. That way, at least you might find something you like other than the P-51 and yourself. And I did, in fact, put some numbers out for speed and climb. Must not have been looking for it, huh?

Your normal attempt at numbers without context.

Almost everyone else in here is civil. You should try it on a regular basis. If you want to talk with me, please be civil. It makes things a lot easier.

Last, When I called you a P-51 lover, it was not in any way an intended insult. I like 'em myself and thought you would be pleased to see it, given your history with the P-51. Just goes to show you that perception is not always reality. OK, if it makes you feel better, perhaps you are NOT a P-51 lover ... I don't know anymore and it is not on my list of things to investigate.

So, Excel person - what did you use for your HP vs altitude plots for 61" and 67" of HG, for which engines, which prop efficiency, which CDo, which Thrust delta and why - if you used a different engine between the comparisons? Do you have a V-1650-9 Power Spec which is different from a V-1650-3 and if so, where do you source it? What is your CDo for the P-51H and how did you derive it? What is your source for the CL vs Alpha and CL vs CD plots for the NACA/NAA 45-100 and the NACA 65-(1.8) 15.5?

Or is it back to your usual flailing about how I treat you like a stepchild?

 

[pbehn]

Discussion about whether the P51H was needed or necessary depended on the A Bombs working, the Russians halting when the Germans surrender and solutions to jet engine reliability and thirst. The bombs did, the Russians didn't and jets were sorted, hind sight is very clear. A lack of war record doesn't detract from an aircrafts abilities, many great planes were not used because the situation changed, others time in the sun came too late, it doesn't detract from the AC. If the Germans had swept across Belgium and France then started attacking England in 1939 the Hurricane not the Spitfire would be England's saviour (if it won).

 

[GregP]

Typical Bill. Almost anyone in here can look up a Merlin in any of the dash numbers and find specs. I did and I bet YOU can, too. I have faith in you there.

I didn't mention a lot of aerodynamics, not that they are all that difficult. I DID mention that at eqivalent power levels the P-51H could hit about 450 mph at the same altitude where the P-51D, using the same power, can hit it's best speed, which is typically quoted as 437 mph. That's about 2.97% faster on the same power. Doesn't seem like much math is needed here to me. I'm sure you know the best height as well as I do.

From the difference in speed, you can find the difference in drag. Go do it ... or don't, I don't care ... I already KNOW the speed difference, and that's all I need to know to realize it isn't a major change in aerodynamics at least as far as drag goes.

My entire contenion was not an aerodynamics course, which is NOT the purpose of this forum or the thread or what the thread has morphed into, it was a simple observation that at similar power settings they perform quite similarly. If I can find that out, you probably can, too. Eagledad left you a link if nothing else comes to mind.

So as I said above, hark back and go to it all you like. I'm VERY comfortable with my observations since they are shared by pilots who flew and continue to fly them. Your opinion seems to differ. OK, it differs. By now that is apparent to anyone who gets this far in the thread.

I do not appear to ge the one flailing about here. You do.

I like the P-51H and have so stated, It just wasn't a factor in WWII combat and if you contend differently, then we must be reading different accounts. There is nothing whatsoever wrong with the P-51H ... it just wasn't needed at all ... but that's just my opinion.

Go bury your head in aeroidynamics if you seriously need to, but don't go asking me to do so. I will when I want to, and that's usually when some undeveloped version is comtemplated by me ... not by you. When a real live plane that has performance numbers is available I don't need an aerodynamic estimate, I have real-world numbers. Aerodynamics is all about predicting the performance. You don't need it at all when you HAVE the performance.

Take away the 81" and ADI of the -9/-11 engine, which could have been installed in the P-51D had anyone desired to do so, and how much beter is the P-51H? I know the answer and so do you. The fact that someone doesn't agree with you seems to rankle your intellectual sense of pride for some reason, but it has nothing to do with you personally or aerodynamics at all. The real numbers of these 2 planes at equivalent power levels are what matter, and I've already said what I need to say.

So how important was it to go 450 mph instead of 437 mph at full throttle sometime about May - Aug 1945 over Japan? On my reality scale, it rates a zero. Maybe I'm missing something here as none of the Japanese oppostion was that fast except the very few jets that flew,and they didn't attack anything. After the war, the P-51D would have served just as well as the P-51H ... and it DID. It also served in Korea, not because the P-51H was too vlauable a resource as you suggest, but because there were more of them around with more spare parts scattered over our bases in the vicinity.

Settle down, Bill, before you have a heart attack, this isn't personal and won't be. And it certainly isn't worth an aerodynamics argument in a non-aerodynamics forum as the performance numbers are already known, so we don't need to make aerodynamic predictions. If you think the P-51H was a wonder plane, by all means erect a monument to it. I simply don't agree.

Big surprise there, huh?

Here's a link to a test when the high boost didn't work. How much difference IS there between a D and an H at equal horsepower? Huh? OK, make your case, as you asked ME to do. This report, where the boost wasn't available, say otherwise. If the same power was available in the D, it would be VERY close ... because it IS.

file:///E:/pdf/P-51H%20Performance%20Test.html

 

[pbehn]

Range: The P-51D has a slightly longer radius of action than the P-51H due primarily to the larger internal fuel supply(269 gallons for the P-51D as compared to 255 gallons for the P-51H); but this advantage was considerably reduced by the fact that the P-51D is not sufficiently stable with full fuselage tank to permit violent manurvering.

Excellent post eagledad. Just one question. The D version had an 85 gallon rear tank but had to burn off approximately 60 gallons before switching to external tanks I believe. Therefore any P51H forced to drop its tanks would probably have more internal fuel than a D in the same situation. The D would be burning internal fuel while having maximum weight and drag so the H probably had approximately the same range or possibly more than the D. Or do I read it wrong?

 

[eagledad]

Pbehn,

I am out of my league here trying to answer your question, as I am not a pilot, but will give it a try. My understanding is that both aircraft would take off using internal fuel, I believe that was SOP for safety reasons (Drgondog, feel free to chime in on this). So neither aircraft would have full internal fuel when drop tanks are released. I went to my copies of the P-51 H and P-51 D flight manuals and found that if both aircraft are clean (wing racks only), and are carrying the same amount of internal fuel, (in this case 240 gallons), the manual claims that at the best crusing speed, the P-51H has a range of 1270 miles, the P-51D has a range of 1330 miles. The P-51D with 220 gallons would have a range of 1220 miles, and with 200 gallons a range of 1110 miles. So (pilots correct me if I am wrong, ) a P-51D with 210 gallons (269-60, about 210) would have a range of 1165, (half the value of 220 and 200) about 105 miles less than the P-51H.
So according to the flight manuals I have, the D has a slightly longer range carrying the same amount of fuel as the H has, but would have a shorter range if the 60 gallons of internal fuel was burned from the fuselage tank before switching to drop tanks. If you re-read my first post, the evaluators stated that even though the P-51D had a greater combat radius than the P-51H, the CG problems encountered with fuel in the D's fuselage tank offset that advantage. It appears it would be unusual for the P-51D and P-51H to enter combat with the same amount of internal fuel. (the P-51H should have more as most P-51D pilots would use the 60 gallons of internal fuel mentioned)

Eagledad

 

[grampi]

Greg P...where did you get the top speed of 450 for the P-51H? It's top speed is generally listed as 487 MPH...

 

[Milosh]

Greg P...where did you get the top speed of 450 for the P-51H? It's top speed is generally listed as 487 MPH...

That is with 67" of boost most likely.

P-51 Mustang Performance

 

[GregP]

I was looking at the performance at 67" as Milosh says. I was putting out an estimate of the top speed of the P-51H at 67" at anywhere from 17,500 feet to 21,500 feet ... which is close to where the P-51D achieved it's top speed. The entire discussion above is centered around the fact that while the P-51H DOES have great performance at 81" and using ADI, there isn't very much ADI in the plane and the sparkling performance is only for about 5 minutes or so. After that, the engine performs much like the engine in the P-51D and puts out just about the same HP, albeit at slightly different critical altitudes.

Hence my assertion that the P-51H wasn't a big step over the P-51D, it was an incremental improvement at best, and not much at that unless the power was screwed in hard. Had they simply put the -9 or -11 engine in the D, they'd have had almost the same thing without the very slight incremental improvement to the stability with full fuel and external load. I don't think it was all that unstable anyway since many thousands of P-51D pilots flew them many thousands of miles over Europe escorting B-17s and B-24s.

As it turns out, when the war in Europe was over, they got transferred to the PTO where the enemy planes were somewhat slower than the German planes, so they didn't need the extra 5 minutes of speed as they were already faster than the opposition and so could dictate combat or not as they chose anyway.

It was not and IS not that the P-51H wasn't a good plane, it was, but the war was essentially over and the next generation was going to be a jet generation. So the P-51H, which otherwise would have been a very good step, turned out to be the last gasp of the piston fighters that basically came into service just when the wer ended. It's production was cut short due to the elimination of the wartime need for it and, through no fault of the designers or the people who acquired it, it just wan't really needed at all.

It was probably a good thing they pursued it at the time, though, since the war was still on, and hindsight does have pretty good vision. When I say the plane was a waste of effort, it is nothing against the aircraft at all. It just means the war was won by the existing planes already in the field and the expense of the P-51H didn't play a part in the victory, that's all. After the war it didn't stay active for long and was sent almost immediately to the reserves and the guard. I call that reserve service, not first-line active service.

So the "useless" part was relative to WWII, not the quality of the aircraft. This is a WWII forum and I try (maybe don't always succeed) to stick with WWII in general while I'm in here. There is a "Modern" forum where post war is discussed.

And this is just my opinion. Bill's opinion is no less valid or valuable. Perhaps North American learned something that helped the F-86 from the P-51H effort, I don't know. If so, maybe it was a good thing after all. Whatever the case, it's worth maybe a discussion but not an acrid argument. I hope that isn't a vapid plattitude ...

 

[snowmobileman]

I just had a quick look at the posted link...some of that P-51H altitude performance looks a little suspicious to me! Really, almost 5000 fpm climb at 20K feet, with a 47,000' ceiling? This beats the XP-51G by a large margin!

 

[tomo pauk]

The top speed figure of 487 mph might come from factory estimates, eg. the chart in the Williams' site, dated as of 1944 (here). One of the charts is with just 105 gals of fuel and 4 HMGs (here).
There is a test, on 90 in Hg, where the top speed is just 451 mph (here). Contrary to that, the SAC for the F-51H (redesignated post-war P-51H) show max of 412 kts, or 474 mph (here, browse a bit until F-51H docs). The colored speed charts at the Williams' site show 480+ mph, without racks and on 90 in Hg (here) and 480 mph with racks (here). In the ballpark with factory estimates.

 

[GregP]

Looks that way to me, too. But I wasn't there and don't know for sure.

When the engine was at full rattle, the P-51H appears to have been a great ride, doesn't it? But a mission can last 6 - 7 hours and that great performance is available for about 5 minutes at best, which is why I was trying to look at the performance after the ADI was gone in the first place.

You could, of course, say the same for all the planes that had a wet max power system. Some of the Focke Wulf Fw 190 series had good performance wet and then were back to regular performance the rest of the time, too, just as we were. It would be useful to look at performance at rated power dry since that is what was encountered MOST of the time.

I doubt any pilot would automatically go to wet power for combat since it might be gone when he really needed it to save his own life later if he got jumped. Maybe rookies would. I doubt veterans would.

 

[tomo pauk]

Even if the mission is 6-7 hours long, that does not mean that LR fighter will routinely spend like 30 min or more in combat during a mission. The USAF rule of the thumb was 5 min on WER (whether dry or wet) and 15 min on military power, even for LR work.
Five minutes, multiplied with so much LR aircraft = so many combats can be decided in the favor of the LR fighters if more engine power is needed.

 

[cimmex]

Wasn't the emergency power actuator lead sealed? I read somewhere that the pilot had to write a detailed report if the seal is broken.
cimmex

 

[bobbysocks]

iirc my father said there was a wire that acted as a stop. going to the wire was full throttle and to get WEP you pushed and broke through the wire. and i dont recall him saying anything about having to write a report if he used it. he probably told his crew chief if he used it alot so that they could pull spark plugs and check them for leading.

 

[grampi]

Hence my assertion that the P-51H wasn't a big step over the P-51D, it was an incremental improvement at best, and not much at that unless the power was screwed in hard. Had they simply put the -9 or -11 engine in the D, they'd have had almost the same thing without the very slight incremental improvement to the stability with full fuel and external load. I don't think it was all that unstable anyway since many thousands of P-51D pilots flew them many thousands of miles over Europe escorting B-17s and B-24s.

QUOTE]

Even if the power being used is equal to that of the "D" model, the "H" model's 600 lb weight difference alone is enough to make a considerable difference in performance...600 lbs less weight is nothing to shake a stick at!

 

[GregP]

It doesn't make a considerable difference.

If you fight them at the same power level, there is nothing to choose between them.

And I'm not saying the 5 minutes WEP was never used or was a bad thing or was useless at all. The point is the main difference between them, at full performance, was the extra 14 inches of boost available in the -9 and -11 engines over the -7 engines in the D models. The -9 / -11 would have fit into the D models, too. Had they done thath, the performance increase would have been very close to the same, at LEASST in speed, and climb would not be far behind, either. 500 pounds to a 9500 pound airplane doesn't make a huge difference. Some, yes ... not much.

You know, I've said it too many times already so this is it.

Nothing above knocks the H as a bad airplane. The war was won without it, making it unnecessary, and my main point is stated above, that the main diffrence in performance was power avilable. If there is ANYONE out there who thinks otherwise, you are welcome to do so in peace and harmony.

It won't change the fact that at the same power level, the performance was just about the same between the D and H model P-51s, which goes a LONG way to proving my point ... Add the extra power to the D and they STILL won't be that far apart.

Heck, go to Reno and watch it happen in person ... if these guys thought an H model was faster in any meaningful sense, they'd have raced it a LONG time ago. It's not like they weren't available when the planes were surplussed.

And that's all for this thread. Cheers.