Originally posted by gripen:
Well, there were couple things fundamentally wrong with the P-38; the concept was wrong and aerodynamics sucked. In practice there were also lot of technical problems which made situation even worse.
I see, you disagree with Kelly Johnson about concept and aerodynamics. Even though Johnson was lead designer of the F-104, U-2 and SR-71, and by extension, should have at least a journeyman's understanding of the science, right?
Hmm, let's see, can you name any other twin engine interceptors (or twin fighters of any kind) that offered performance even remotely close to the XP-38, circa 1938-39?
Perhaps you don't understand the specification that the P-38 was required to meet. It required a rapid rate of climb, high speed and good endurance. None of these could be met with the normally aspirated engines in existance at the time (1936-37). So, it was determined to use the new Allison V-1710, but to have the power required at altitude, Johnson elected to incorporate the new GE turbosupercharger. Gee, he couldn't have been far off the mark as the aircraft exceeded every requirement.
As to the aerodynamics, I suppose you are commenting on the the airfoil section. Well, Johnson knew that this aircraft would need to carry considerable fuel. Where to put that fuel was the issue. He elected to put in the wing, and selected an airfoil design already in use on the Electra. Perhaps not the best choice, but one he believed to be adequate. Several years later Johnson admitted that they never believed that severe compressibility problems would ever be an issue when they did the initial design. Lockheed wasn't the only aircraft manufacturer to find this out the hard way.
As it was, Johnson and his team had originally looked at six different configurations, rejecting one after another for various reasons until only the twin boom design remained. Preferring a much thinner airfoil (chord/thickness ratio), Johnson tried to find the internal volume to pack in 400 gallons of avgas. After weeks of hard work, that produced no easy solution, Johnson was forced to make a decision as the drop-dead date approached. He scrapped the thin wing and (with management's blessing) selected the NACA 23016 section for the inner wing, and the NACA 4412 section for the outer wing. Essentially, this was the same as the Electra. It is also generally believed to be the first fighter to use metal covering on all control surfaces.
Meant to meet the requirements of specification X-608 (the content of which was leaked to Johnson 6 months before being officially released), Johnson was confident that it would win the competition hands down.
On April 13, 1937, Johnson submitted his aerodynamic study to the Air Corps. They reviewed his data, and forwarded it to NACA,
which endorsed the engineering.
So, if you find fault in the aerodynamics, you do so only with the hindsight advantage of 65 years of development in the science of aerodymanics since Johnson first penned the concept in the Fall of 1936.
The twin engine concept with turbocharged engines was very expensive and also mainteance nightmare; actually advanced P-38 develoments were based on mechanically supercharged engines. The twin engine concept also caused poor acceleration in the roll specially at low speed; the P-38 was a high speed energy fighter as it was used in Pacific.
You have overlooked the simple fact that this was the only viable solution with the then available powerplants (1936-37).
However, Johnson tried to take advantage of the new Rolls Royce Merlin engine (in 1941), but the Air Corps, and later, the War Production Board were having none of it.
The aerodynamic problems were more serious; critical mach number was low specially under g load at high altitude. Also Clmax dropped fast when mach number increased. The P-38 was not particularly maneuverable at high altitude.
I think that everyone is aware of the P-38's Mach limits. You also need to understand that the original design was intended to be a high-speed bomber interceptor, and maneuverability at high altitude was not an issue at that time.
With redesigned wing, tail and fuselage the P-38 might have been a good but very expensive long range high altitude escort fighter, something like DH Hornet couple years later. But with original aerodynamics the P-38 was destined to low altitude operations; actually even 5th AF knew this, they choosed the P-51 for escort missions..
As I've explained, a redesign was not going to happen. Recall that the WPB rejected Lockheeds request to close down the production line for two weeks while they make the required tooling changes to incorporate the lower RPM Hamilton-Standard propeller. What chance existed for a major redesign? None. By the way, the P-38 WAS a good high altitude escort fighter. It just wasn't the best. If it was so bad, why did the P-38 maintain a better than 2:1 kill/loss ratio, even during its most troubled 8th AF days in the ETO?
The Hornet benefitted from 7 more years of aviation development, most of it in the war years with the associated rapid advances in engines and aerodynamics. So, this is not a fair example. Although, you may wish to re-examine the layout of the P-82 Twin Mustang. Even with 7 years of technological advances, North American still elected a twin-engine, twin-boom design. Before you point out that they did not incorporate the central pilot gondola, have a look at the F-82s that actually served and take note of that massive radar pod, right there between the engines. Of course, there were other aircraft that used this basic layout as well, with the P-61 and XF-11 coming to mind.
As to the use of the P-51 in the 5th AF, you need to have a look at the force composition of the 5th. Mustangs did not arrive until 1945, and they did not replace the P-38, but rather the P-47Ds then in service. Towards the end of the war, the 5th AF and 13th AF merged to become the Far Eastern Air Force (FEAF). Kenney never gave up his Lightnings, for reasons already expounded upon. The Air Force that first re-equipped with the Mustang (in the Pacific) was the 7th, which went to war at Saipan with P-47Ds. Later, their new Mustangs would escort the B-29s to Japan, along with the P-47N. Kenney's Lightnings were busy working over Formosa and the coast of China from bases in the PI.
My regards,
Widewing
