The Lockheed P38 Lightning.

"Fork tailed devil"

I have recently acquired a kit of this aircraft from Tamiya and debated whether it would be worthwhile making a video review. The reason for this indecision mainly has to do with the enviable reputation Tamiya has for manufacturing kits of the highest quality. Problems in manufacture are so uncommon that one is inclined to conclude that any construction issues that appear to come to light may very well be caused by the builder rather than due to some fundamental issue with the assembly or the parts. That being said, I relented and thought that I should make at least one video of this kit as, having looked at it, I found that it contained some most interesting aspects. You can find my review here:

The initial set of parameters which spawned the P38 arose from the jauntily named “circular proposal X-608” written in early 1937. This proposal was quite strenuous for the time, requesting as it did (amongst other things) a maximum speed for the proposed aircraft of at least 360mph at 20,000 feet; the ability to climb to 20,000 feet in six minutes or less and a capability to operate at full throttle for one hour. These requirements came about as a result of the desire to improve on the capabilities offered by the then pursuit aircraft, (the term then applied to fighters, hence the “P” prefix given to aircraft at the time), and were driving manufacturers towards a high altitude and long range capability.

It is said that the term “interceptor” was used in the requirements because this would move the design away from the “pursuit” designation, the guidelines of which were considered to be somewhat restrictive and in fact specified only single engined aircraft. The dual engine design was deemed to be useful, as we will discover later.

Anyway Lockheed, whose subsequent reputation for developing highly advanced aircraft has proved to be unassailable, (as we have seen), formed a team to address the specification as given which included Hall Hibbard and none other than Clarence “Kelly” Johnson. This team worked somewhat in secret, but certainly away from other engineers in the Lockheed team and in a similar manner to the famous “Skunk Works” of subsequent years. In so doing, they came up with several design options, all of which employed two engines. The P38 represented the first military project won by Lockheed.

The eventual design, that with twin tail booms, was advantageous because in the first place, the booms provided accommodation for the turbo-chargers which were required in order to meet the altitude capabilities as laid down. They did so by boosting the power of the supercharged Allison V1710 engines by the way. In the second place, because the pilot accommodation also contained a selection, (dependent upon variant), of machine guns and cannons. This concentration of weaponry within the nose is similar to that deployed in the De Havilland Mosquito and dealt with the well known problem of convergence.

We have raised two challenges here, that of engine power and convergence- let us look at both of them separately.

Allison’s engines were rather good but, like all piston engines, their performance was limited by the degree to which they can take in and compress their air and fuel mixture. At the risk of stating the blindingly obvious, at altitude, there is less air available. For this reason, normally aspirated engines do not operate so well. Some were better at this but all required some form of additional support, especially when the air available to combine with fuel is thinner.

This is where superchargers come into play. You will no doubt understand the fundamental principle of the supercharger- it is a fan assembly that is connected directly to the engine and very rapidly delivers a stream of compressed air which is combined with fuel and burnt. The faster the engine runs, the more compressed air and fuel it delivers.

This is unlike a turbo charger which depends for its motive power on the exhaust of the engine itself. You may have heard of the term “turbo lag,” especially if you are a car enthusiast. This is a delay in the further boosting effect of compressing the air/fuel mixture as the fan that runs the turbocharger will act more slowly than a supercharger to the power output of the engine. The same thing happens in aero engines and it would appear that combining the two components allows such a delay to be mitigated somewhat.

It is also the case that heat is a major challenge in keeping aero engines running smoothly and avoiding unscheduled combustion of the fuel which is more or less guaranteed to occur when the air and fuel mixture is compressed by both a supercharger and a turbo charger. This has to do with the compression of the air/ fuel mixture causing a phenomenon known as kinetic heating. The molecules of gas rub together much more as they have less space in which to move and this creates the heat. A solution to this challenge must be found.

The answer is a device called an intercooler. At an altitude of around 20,000 feet, the temperature outside an aircraft (dependant upon season, latitude and weather conditions) can be anywhere from -15 celsius to -20 which I would suggest is on the frigid side. An advantage of this is that there is plenty of cooling air available to prevent those pesky pre-combustions and this air is channelled through the radiators and other engine components to cool them.

You will note from my review that the turbo chargers for the engines were placed on the tail booms- much further from the engine than in a more conventional design. You will also notice how the fans are exposed to the air flow across the top of the boom which allows this cooling to take effect. Within the tail booms, there are also an array of radiators which allowed heat to be moved away from the engine. Furthermore, the intercoolers (a very necessary part of this system) were in fact placed within the wings with cooling air being channeled through two small ports at the front and to the sides of each wing. It’s really bloody clever.

As an aside, it is said that cockpit heating on early versions of the P38 was not good which caused something of a problem to pilots who got rather cold at altitude- much like the crew of the B17 bomber used to. This is somewhat inexplicable given the prodigious amounts of heat being moved around the twin engines which of course were close by. This problem was resolved however on later variants, much to the relief of pilots I have no doubt.

“Convergence” is the problem that must be solved by aircraft manufacturers and pilots when guns are mounted on the wings of aircraft. A decision must be made with respect to how the guns are to be directed in order to concentrate fire onto a point in space ahead of the aircraft so as to create the most destructive effect from firing weapons. This means that wing mounted guns must be angled slightly inwards to a notional point- typically around 400 yards ahead of the aircraft. It is easy to imagine how the bullets behave in this sort of circumstance- they converge at 400 yards and then spread out rapidly after that and this leads to the weapons having much less effect at ranges outside the 400 yard mark. When the guns are very close together, as in the case of the P38, dealing with convergence is much less of an issue. Nose positioning of the weaponry confers the larger advantage that the deployable range of the guns may be up to 1,000 yards in the hands of an experienced pilot.

It is also notable that the oft mounted 20mm canon was arranged at a slightly more upward angle than the 0.5” calibre machine guns in order to take account of the greater “bullet drop” for the heavier round. This meant that “going to guns” against an enemy at ranges between 400 and up to 1000 yards was much more potent in terms of damage done when firing.

After a period of pretty secretive development, the XP38 made its maiden flight at the end of January 1939. The process of bringing the aircraft to flight wasn't without problems, but what new aircraft flew without any issues at all? Flap linkages failing and brake problems were two issues solved “on the fly” if I may use such an aphorism.

Proving the capability of this new aeroplane was done in a rather public way in the sense that the Lockheed team sought to challenge the speed record for travelling across America. This record was held at the time by a little known individual called Howard Hughes who took about 7 1/2 hours in his “Hughes H1 racer.” The XP38 made the journey in a fraction over 7 hours, but the record was not established as the aeroplane crashed onto a golf course prior to landing in a more expected way at the end of the flight. Nevertheless, the reputation of the P38 for speed was nicely set up and the US Army Air Corps ordered 13 examples for testing and evaluation.

As the P38 was somewhat unusual in its design, it took several years and a number of iterations to arrive at the form we see in the first operational variant. Beyond the brake and flap issues, problems with turbulence owing to the cockpit side windows being inadvertently left open were overcome and issues with compressibility were eventually overcome by the addition of dive flaps underneath the wings, but these were not seen until the J variants and beyond.

The inability to pull out of high speed dives in a P38 perhaps deserves a brief explanation, so I will attempt one. In aerodynamic terms, air flowing over the wings at high speed (near to and at the speed of sound) caused the centre of gravity of the aircraft to move forwards and lessened the authority of the elevator to such an extent that the aircraft increased its dive angle in a cumulative way which, beyond certain speeds which was not always recoverable. This was known as “mach tuck.”

We can once again see the effects of compressibility which I have discussed before in my article on the Tempest and we see that this increasingly became a feature of earlier high performance aircraft operating in the trans sonic domain. Many pilots met their ends when unable to pull out of high speed dives owing to insufficient elevator or aileron authority caused by this (at the time) little understood phenomenon.

The first P38 Lightnings to enter service did so in the Mediterranean and North Africa and it seems to be here that it came by its well known soubriquet- the “fork tailed devil.” The nickname appears to have been coined by a German aviator who was shot down by a P-38 and doubtless represents his frustration at being downed.

Lockheed began an illustrious career of producing high performance military aircraft when they produced the P38 Lightning. In the three years it operated from 1942 to 1945, it was deployed in a number of theatres including the Pacific against the Japanese and North Africa and distinguished itself in those areas by being one of the most versatile fighter/ bomber/ aerial reconnaissance aircraft of the second war. It was much liked by the pilots who flew it and, despite its shortcomings, it was an operationally tough and enormously capable aircraft. It is this operational toughness which we repeatedly see in allied second world war aircraft.

In operations in the Pacific theatre particularly, two engines were a real advantage especially when there was a necessity to fly over vast tracts of water and where engine failure of a single engined aircraft of any kind would place the pilot in real danger of being lost at sea. The ability of the P38 to fly on one engine was extensively demonstrated by test pilots in the early days of its development and the aircraft was shown to be benign when being driven by only one engine. Some video footage exists of this and would invite you to take a look around a local internet to you.

The P38 was, like many WW2 American aircraft, built in large numbers with just a shade over 10,000 rolling off the production lines. It was also the first military aircraft to fly faster than 400 mph. Much admired and liked by pilots, it was the first of many exceptional machines to subsequently emerge from the Lockheed stable.

I think it likely that I will scheme this aircraft to the Pacific theatre variant used in “Operation Vengeance” and make an effort to depict a well worn and highly used example. The challenges of doing this are many fold and whilst I have some skills in this area, (not that many you understand) it is good to develop them, hence my choice. There will be a short series of videos of the project which I hope that both of my viewers will watch and thank them in advance.