P-38 Lightning vs P-51 Mustang: Which was the Better Fighter?

[kool kitty89]

The P-38 also had the high lift airfoil (23000 on inner wings, 4400 outer) and the twin propwash. And don't forget the fowler flaps.

And the chart doesn't show 450+ mph it shows ~440 mph at ~26,500 ft for the P-38L at 1,725 hp WEP.

And I was wrong, the P-51 does have a small top speed advantage between 5,000 and 14,000 ft. (most pronounced at ~11,500 ft where the P-51D has a ~20 mph speed advantage)


And iirc the trials were done with full main tanks with LE wing tanks dry. (300 US gal total)

I don't know the P-51's condition (probably fuse tank empty, 184 gal), but the charts shows a max speed of ~435 mph at 25,000 ft. And an initial climb of ~3,300 ft/min.

[drgondog]

Originally Posted by kool kitty89

The P-38 also had the high lift airfoil (23000 on inner wings, 4400 outer) and the twin propwash. And don't forget the fowler flaps.Interesting, and perhaps important for either landing speeds or lift calculations

And the chart doesn't show 450+ mph it shows ~440 mph at ~26,500 ft for the P-38L at 1,725 hp WEP.

At what loading, amx internal fuel.. and what does the MP and WEP Hp profile look like for all altitudes.. 'sawtooth'??

And I was wrong, the P-51 does have a small top speed advantage between 5,000 and 14,000 ft. (most pronounced at ~11,500 ft where the P-51D has a ~20 mph speed advantage)

A small advantage. the real key is an 'out' manuever' when caught by suprise. Can the P-38L intiallially out turn a pursuing 51D and say, out roll and reverse to attain a superiorior tactical positiion. Can it climb too steeply to enable a 51 to cut the corner and pull deflection?.. in other words what is its 'out manuever' to a a.) escape and b.) reverse a tactical advantage?


And iirc the trials were done with full main tanks with LE wing tanks dry. (300 US gal total).

The 51 trials were done with full internal fuel, oil and full ammo and guns plus external racks

I don't know the P-51's condition (probably fuse tank empty, 184 gal), but the charts shows a max speed of ~435 mph at 25,000 ft. And an initial climb of ~3,300 ft/min.

No, the 51B/C/d and H tests on Mike Williams site were performed with full internal fuel including fuselage tanks.. you need to compare the P-38L at the same tactical load to maintain perspective.. the 3,330 fpm is probably close from Sl area.

[kool kitty89]

Thanks for the correction.

But wan't it unsafe to carry much more than a 1/2 full fuse tank due to stability (CoG) problems?

In service, however, the directional instability caused by the presence of a full fuel tank behind the pilot's seat was a hazard for new or inexperienced pilots, and the tank was usually restricted to 65 US gallons. This extra tank, nevertheless, still made a crucial difference in combat radius, and it was standard equipment in all future production versions.

And on the pylons, according to FLYBOYJ, the P-38's pylons were integral to the airframe.


Agree on the load, to compare you'd need figures with the full LE wing tanks. (2x 62 US gal) and the P-51 with the max safe fuel limit. (around 250 US gal) In which condition both would have very similar range.


And on the roll rate, the P-38's boosted ailerons meant roll rate kept increasing as speed increased. In the chart a roll rate of just over 90*/s is shown at 350 mph and ~95 degrees/s at 400 mph.



But another advantage of the P-51 is that it cruised well at high speed, making cruise speeds aproaching 400 mph practical. (and above 400 w/out drop tanks) At ~410 mph the P-51D could still manage almost 800 mi. (granted, with a full fuse tank, so practical closer to 700 mi)
Try that with the P-38 (with 425 gal) and it's down to less than 500 mi at ~380 mph.

as seen here:

[FLYBOYJ]

Originally Posted by kool kitty89

Thanks for the correction.
And on the pylons, according to FLYBOYJ, the P-38's pylons were integral to the airframe.

When did I post that?

[drgondog]

Originally Posted by kool kitty89

Thanks for the correction.

But wan't it unsafe to carry much more than a 1/2 full fuse tank due to stability (CoG) problems?

Yep - but for flight tests at Eglin and Wright Pat, they carried a full combat load at take off. The tests you see on Mike Williams site are pretty explicit about the loads. The aft CG was a serious problem for turns primarily.

I haven't seen the flight plan(s) but a couple of thoughts occur to me. First, if the plan called for high altitude runs I would also be looking for climb to altitude times at MP and other throttle and RPM settings - but just one climb to say 25,000 feet would by itself would burn off 15-20 gallons.

SOP in the field was to reduce the fuse tank 'fill' level to 65 gallons. Most of the guys I talked to like to drain that tank before switching to external tanks which meant forming up and flying to the Dutch or French coast before the tank was fairly well drained - then SOP varied.. but still most like to drain it completely

And on the pylons, according to FLYBOYJ, the P-38's pylons were integral to the airframe.

I did not know that but it wouldn't make a lot of sense to have a non-removable pylon if for no other reason simple maintenance of little things like fuel lines. Photo recon versions of the L for example could perform many of their missions w/O external fuel. I would want the extra 10-20 kts instead.

Agree on the load, to compare you'd need figures with the full LE wing tanks. (2x 62 US gal) and the P-51 with the max safe fuel limit. (around 250 US gal) In which condition both would have very similar range.


And on the roll rate, the P-38's boosted ailerons meant roll rate kept increasing as speed increased. In the chart a roll rate of just over 90*/s is shown at 350 mph and ~95 degrees/s at 400 mph.



But another advantage of the P-51 is that it cruised well at high speed, making cruise speeds aproaching 400 mph practical. (and above 400 w/out drop tanks) At ~410 mph the P-51D could still manage almost 800 mi. (granted, with a full fuse tank, so practical closer to 700 mi)
Try that with the P-38 (with 425 gal) and it's down to less than 500 mi at ~380 mph.

The charts above are the same Lockheed Charts I posted for you several months ago. The thing about them is that we know nothing about the test conditions. I have known Marketing and Sales to occasionally Not disclose everything in test comparisons against a competitor - which is why I tend toward believing Flight Tests with no axe to grind or impression they want conveyed. For example - where did they get the Fw 190 test data? or how was the P-38L loaded relative to internal wing tanks.. take a couple of hundred gallons out and the rolling inertia will be improved.

The post war tests against Fw 190D's for example always leave you wondering how the tests would have been run if say a Focke Wulf factory team with spares and new engines had been pitted against North American and Lockheed and Vought factory reps - and the all the aircraft flown by factory test pilots?

Actually I trust the war time tests more than post war simply because I believe the USAAF, RAF and USN for example - really cared about conveying to the combat operations the strengths and weaknesses of the respective a/c? We can always debate whether the engines were at Spec or the controls properly rigged - but I doubt that the intentions were to 'sell' one aircraft over another in the case of enemy a/c performance.

[kool kitty89]

That was a quote from wmaxt:

BTW: The P-38s racks/pylons were structural components of the aircraft and not removable in normal terms. Even Yippee, the show plane, kept its racks.

http://www.ww2aircraft.net/forum/avi...ts-4970-4.html (Interesting P-38 Comments)



However you're right Bill that doesn't make much sense, and there was another argument here:
http://www.ww2aircraft.net/forum/pol...er-444-11.html (Best Pacific Fighter?) (anonymous is RG Lunatic)



And I cant find the condition for testing now, someone listed it on an old therad, but I can't seem to find it. (pertaining to the planes and pilots of WWI site's climb speed and roll charts)

So I'm not totally sure on the testing conditions. (climb and roll would be the most affected by weight changes, speed would a little but not nearly as much)
But I'm almost certain it said pylons were on.
The wing tanks thing might not have been for that chart, but I though it was.


wmaxt hasn't been on in a while (2 years) though.

Maybe syscom3 knows about it.

[merlin]

Originally Posted by syscom3

If it was designed as a fighter, why was it given the A-36 designation?

A = Attack

P = Pursuit

Because of 'politics'! The USAAC already had the fighters they wanted, they didn't need a British inspired aircraft to enter the ring. It was a case of - 'all right I suppose we could use it as a dive-bomber'. And again after that, it was a struggle, with a lot of lobbying, to get the US to order the Mustang with the Merlin engine in quantity.

The P-38 with its allison engine, I believe, had problems with the cold air over northern Europe, so the Pacific was a better place where it could be more effective, and where the extra engine gave a better safety margin over the long stretches of ocean.

[kool kitty89]

It had nothing to do with the allison engine, the main engine problem at high alt was due to inadequate intercoolers, this was solved on the J model with the chin intercoolers. The major problem with cold was the lack of adequate cockpit heating on early models, also solved on the J.

There were some less frequent at high alt, some with overcooling of the engines, and sometimes the turbochargers freezing up iirc. These were also solved on the J model.


That quote from syscom3 is very old and has already been answered (if you read through the first couple pages) but:

The Mustang wasn't inspired By the Brits, NA already had it on the drawing board as a private project when they were asked to build P-40's, that's why the prototype was made so fast. The political issue with the USAAC/AAF was that it was a private project, not built to compete in one of there specifications, so it was ignored at first. It was the Brits' request for export P-40's which spurred development though, but they had nothing to do with the actual design of the airframe.

See: North American P-51 Mustang

And the A-36 wasn't the first version of the Mustang to see service with the USAAF and the A designation wasn't a political move. The A-36 was a dedicated GA aircraft, it even had dive breaks for dive bombing! It was capable of dogfighting below 15,000 ft though. The P-51/F-6A (NA-91, Mk.1A in British service) North American P-51/F-6A Mustang armed photo-recon a/c was the first to see service and they were direct conversions from the Mustang I.

And before that several Mustang I's (NA-73's) were taken by the USAAF as XP-51's North American XP-51 Mustang

And also on that page the political/bureaucratic problems:

At that time, the Army was overloaded with other test programs, the Lockheed P-38 Lightning, Bell P-39 Airacobra, and Republic P-47 Thunderbolt being thought to meet all the Army's requirements for fighter aircraft. Furthermore, the Mustang was a "foreign" type not built to any American specification, and was therefore way down on the Army's list of priorities. ... The Mustang may have been the victim of the "Not Invented Here" (NIH) syndrome, in which the Army looked askance at an upstart aircraft which had not been designed in response to any of its official requirements.

[renrich]

Don't forget the P38 "problem" withe cold air over Europe and the compressibility situation.

[kool kitty89]

I did address the cold problem at the beginning of my post.

It had nothing to do with the allison engine, the main engine problem at high alt was due to inadequate intercoolers, this was solved on the J model with the chin intercoolers. The major problem with cold was the lack of adequate cockpit heating on early models, also solved on the J.

There were some less frequent at high alt, some with overcooling of the engines, and sometimes the turbochargers freezing up iirc. These were also solved on the J model.

[renrich]

KK, what I am talking about is the problem the P38 had where at high altitudes in the cold air over Europe the P38 could exceed it's Mach limit(compressibility) if it went into a dive, become uncontrollable and possibly suffer structural failure. This was not as much of a problem in the Pacific as the air was warmer. As you know the speed of sound varies with the air temperature. That problem was solved to a great extent in the late models by the addition of dive brakes.

[kool kitty89]

Technically they weren't just dive breaks though, but I get the point. (the flaps changed the pressure distribution of the wing, reducing the shock wave, and both improoved the lift distribution in compressibility and allowed some elevator controll to be regained)


Hoever the compressibility problems were the main limting factor in the P-38's development, as it would hit compressibility at just over 450 mph at 30,000 ft, so it couldn't compete with the level speed of the P-47N/M, and P-51H (and 109K, 190D-13, Ta-152, late model Spits etc) let alone the dive speed.

The only way to fix that would be to redesign the wing to a new airfoil, which couldn have been possible to do without altering most of the wing structure its self, and it shouldn't have been unduely difficult. (the simplest way would be to keep thickness and main wing structure and increase the chord allong with altering the airfoil type)

But there my have been other Issues I don't know of.

[drgondog]

Originally Posted by kool kitty89

Technically they weren't just dive breaks though, but I get the point. (the flaps changed the pressure distribution of the wing, reducing the shock wave, and both improoved the lift distribution in compressibility and allowed some elevator controll to be regained)

ouch. the only solution for the P-38 was to keep the dive (and level) flight speed below .75+ Mach. It is true that flaps increase the CL but really has nothing to do with shock wave or compressibility 'reduction'. To deploy flaps of any kind at those kinds of speeds would mean you intended to make a lot of connected parts 'disconnect'.

Hoever the compressibility problems were the main limting factor in the P-38's development, as it would hit compressibility at just over 450 mph at 30,000 ft, so it couldn't compete with the level speed of the P-47N/M, and P-51H (and 109K, 190D-13, Ta-152, late model Spits etc) let alone the dive speed.

The only way to fix that would be to redesign the wing to a new airfoil, which couldn have been possible to do without altering most of the wing structure its self, and it shouldn't have been unduely difficult. (the simplest way would be to keep thickness and main wing structure and increase the chord allong with altering the airfoil type)

I have never seen any of the airflow/wind tunnel data on any version for the P-38. It was a real hog, drag wise, compared to say a Mustang or even a 190 or Spitfire. So, a much more complex analytical problem from a wing/body combination in trying to figure out exactly where the compressibility started - like inboard wing and fuselage? if so, the the outboard wing may have been relatively Ok until a higher mach?

From a 'profile drag' standpoint I have always been curious how much the nacelles/boom contributed versus the fuselage

But there my have been other Issues I don't know of.

Compressibility and 'masking' the elevator as well as the elevator flutter issues were the dominant problems preventing it from being a superb high altitude fighter. They solved the flutter issues with the 38J IIRC and the dive/speed brake kits, then the factory 38L solved the 'instant compressibility' issue when entering a dive at high speed and altitude

- but only by keeping the airspeed to .68-.7Mach where it really could not catch up to a 109 or 190 - which did not have the compressibility issue at higher speeds - at least not until they were doing maybe 50-75mph faster speed

The engine/supercharger problems pre 38L were high altitude reliability issues

the cockpit heating issues made for extremely uncomfortable flying and increased fatigue for the pilot on long range, high altitude escort

[syscom3]

I saw the P38 and P51 fly at Chino yesterday.

No doubt about it, the P38 looked better.

Therefore, the P38 is better than the P51.

[kool kitty89]

ouch. the only solution for the P-38 was to keep the dive (and level) flight speed below .75+ Mach. It is true that flaps increase the CL but really has nothing to do with shock wave or compressibility 'reduction'. To deploy flaps of any kind at those kinds of speeds would mean you intended to make a lot of connected parts 'disconnect'.

No, I didn't mean the normal flaps, I was talking about the dive recovery flaps, located under the wing just outboard of the nacelles.
(similar ones later fitted to the P-80's wingroots, and also used on late P-47D's and P-47M/N's)

Lockheed P-38J Lightning

The problem was eventually traced to a shock wave that formed over the wings as the Lightning entered the transonic regime, the shock wave preventing the elevators from operating. In order to counteract this problem, starting with the P-38J-25-LO (Model 422-81-23) production block, a small electrically-operated dive flap was added underneath each wing outboard of the engine nacelles and hinged to the main spar. These dive flaps would change the characteristics of the airflow over the wing, offsetting the formation of the shock wave and permitting the elevators to operate properly. This innovation largely solved the problems encountered by diving P-38s.

Also (wikipedia)

In February 1943, quick-acting dive flaps were tried and proven by Lockheed test pilots. The dive flaps were installed outboard of the engine nacelles and in action they extended downward 35° in 1½ seconds. The flaps did not act as a speed brake, they affected the center of pressure distribution so that the wing would not lose its lift.

Republic P-47D Thunderbolt

The high diving speeds of which the Thunderbolt was capable pushed the aircraft into the edge of compressibility, and new blunt-nosed ailerons were fitted to improve controllability at these high speeds. In order to help in dive recovery at these high speeds, an electrically-operated dive recovery flap was fitted on the undersurfaces of each wing.