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

[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/aviation/interesting-p-38-comments-4970-4.html



However you're right Bill that doesn't make much sense, and there was another argument here:
http://www.ww2aircraft.net/forum/polls/best-pacific-fighter-444-11.html (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]

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]

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.

 

[drgondog]

KK - you will note that I posed 'inboard wing body' considerations re: shock wave and or 'masking the elevator'.. out board of nacelle should not be much of an issue regarding the elevator issues?

You will also note I passed on your 'Flap' comments and focused on the dive/speed brake.. virtually the same approach used on the F7F.

NOBODY deploys flaps at high speed although a 51 could deploy 10 degrees at high speed to a.) lose a lot of energy, and b.) cut a turn - but it better get the result the pilot was looking for because it negated a lot of energy maueverability advantage it may have had..

 

[renrich]

My reference states that the P38 was limited to the equivalent of a dive speed of .65 Mach and that was placarded in the cockpit.

 

[kool kitty89]

And I think it was raised to .68 Mach with the dive flaps intalled.

 

[HJERIA]

P 51 Was faster and more maneuverable, The Lightning was stronger and had better volume of fire, with its guns in the nose.... I guess always the hands make the difference, but I think the Mustang was a little superior.

 

[kool kitty89]

Maneuverability depends on the context and models each having advantages, though overall maneuverability of the pre-G P-38 had mediocre maneuverability in every respect. (the G model received combat flaps which nearly doubled the turn rate)

And initial roll rate was rather poor until the boosted ailerons on the late J models.

 

[parsifal]

one thing that does not appear to be brought up in this thread. The P-38 cost, on average about $91000 US dollars to build, wheras the P-51D only cost $51000. For comparison, the P-47 cost about $67000 per unit.

 

[trackend]

P51 for me, one lump, lower maintenance time, easier to keep flying, easier to manufacture these go towards IMO making it a better fighter. a fighter on the deck and not in the air is not a fighter Impressive though the Lighting undoubtedly was I believe the Mustang to be more suited to the task.

 

[drgondog]

one thing that does not appear to be brought up in this thread. The P-38 cost, on average about $91000 US dollars to build, wheras the P-51D only cost $51000. For comparison, the P-47 cost about $67000 per unit.

And that reflects 1945 unit costs. The 51 went from 12,000 hours to build the A-36 to 2200 hours for the P-51.

IIRC the P-38 in 1943 was around 111K and the 51 was near 59K? The P-47 was around 80K in 1943 I think.

Syscom had the actuals on all three by tables on one of the other posts.

 

[drgondog]

Maneuverability depends on the context and models each having advantages, though overall maneuverability of the pre-G P-38 had mediocre maneuverability in every respect. (the G model received combat flaps which nearly doubled the turn rate)

And initial roll rate was rather poor until the boosted ailerons on the late J models.

The P-38L was the only version that finally approached manuevering equivalency in several, better than some, and worse than a few factors vs P-51

 

[kool kitty89]

Yeah, the roll rate was a major limiting factor (which had continually degraded up to the J model, particularly with full LE tanks, until the boosted ailerons were added)

And Bill, you do understand I was talking about dive flaps (dive recovery flaps) which are mounted outboard of the nacelles under the main spar. They obvioulsy would have a significant drag effect, but the main purpose was to prvent the pitch-down behavure iirc. Granted that earlier statement about shock-wave reduction/delay doesn't make sense.

And AFIK the P-38 never had actual airbrakes/dive-brakes.

Wikipedia seems to have gotten it right:

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