Lockheed P-38 Lightning

The Lockheed design incorporated tricycle undercarriage and a bubble canopy, and featured two 1,000 [Vous devez être inscrit et connecté pour voir ce lien] (746 [Vous devez être inscrit et connecté pour voir ce lien]) [Vous devez être inscrit et connecté pour voir ce lien]-[Vous devez être inscrit et connecté pour voir ce lien] 12-cylinder Allison V-1710 engines fitted with [Vous devez être inscrit et connecté pour voir ce lien] to eliminate the effect of engine [Vous devez être inscrit et connecté pour voir ce lien], with the superchargers positioned behind the engines in the booms.

It was the first American fighter to make extensive use of stainless steel and smooth, flush-riveted butt-jointed
aluminum skin panels.

It was also the first fighter to fly faster than 400 mph (640 km/h).

Lockheed won the competition on 23 June 1937 with its Model 22 and was contracted to build a prototype XP-38 for US$163,000, though Lockheed's own costs on the prototype would add up to US$761,000.

Construction began in July 1938 and the XP-38 first flew on 27 January 1939 at the hands of Ben Kelsey.

Kelsey proposed a speed dash to [Vous devez être inscrit et connecté pour voir ce lien] on 11 February 1939 to relocate the aircraft for further testing.

[Vous devez être inscrit et connecté pour voir ce lien], commander of the USAAC, approved of the record attempt, and recommended a cross-country flight to New York.

The flight set a speed record by flying from California to New York in seven hours and two minutes, but was downed by carburetor icing short of the Mitchel Field runway in[Vous devez être inscrit et connecté pour voir ce lien], and was wrecked.

However, on the basis of the record flight, the Air Corps ordered 13 YP-38s on 27 April 1939 for US$134,284 apiece.

(The initial "Y" in "YP" was the USAAC's designation for a "[Vous devez être inscrit et connecté pour voir ce lien]" while the "X" in "XP" was for "[Vous devez être inscrit et connecté pour voir ce lien]".)

Lockheed's Chief [Vous devez être inscrit et connecté pour voir ce lien] angrily characterized the accident as an unnecessary publicity stunt.

According to Kelsey, the loss of the prototype, instead of hampering the program, speeded the process by cutting short the initial test series.

The success of the aircraft design contributed to Kelsey's promotion to captain in May, 1937.

Manufacture of the YP-38s fell behind schedule, at least partly due to the need for mass-production suitability making them substantially different in construction than the prototype.

Another factor was the sudden required facility expansion of Lockheed in [Vous devez être inscrit et connecté pour voir ce lien], taking it from a specialized
civilian firm dealing with small orders to a large government defense contractor making [Vous devez être inscrit et connecté pour voir ce lien], [Vous devez être inscrit et connecté pour voir ce lien], [Vous devez être inscrit et connecté pour voir ce lien], and designing the [Vous devez être inscrit et connecté pour voir ce lien] airliner for [Vous devez être inscrit et connecté pour voir ce lien].

The first YP-38 was not completed until September 1940, with its maiden flight on 17 September.

The 13th and final YP-38 was delivered to the Air Corps in June 1941; 12 aircraft were retained for flight testing and
one for destructive stress testing.

The YPs were substantially redesigned and differed greatly in detail from the hand-built XP-38.

They were lighter, included changes in engine fit, and the propeller rotation was reversed, with the blades rotating outwards (away) from the [Vous devez être inscrit et connecté pour voir ce lien] at the top of their arc rather than inwards as before.

This improved the aircraft's stability as a gunnery platform.

Test flights revealed problems initially believed to be tail [Vous devez être inscrit et connecté pour voir ce lien].

During high-speed flight approaching Mach 0.68, especially during dives, the aircraft's tail would begin to shake violently and the nose would tuck under, steepening the dive.

Once caught in this dive, the fighter would enter a high-speed [Vous devez être inscrit et connecté pour voir ce lien] and the controls would lock up, leaving the pilot no option but to bail out (if possible) or remain with the aircraft until it got down to denser air, where he might have a chance to pull out.

During a test flight in May 1941, USAAC Major Signa Gilkey managed to stay with a YP-38 in a compressibility lockup, riding it out until he recovered gradually using [Vous devez être inscrit et connecté pour voir ce lien].

Lockheed engineers were very concerned at this limitation, but first they had to concentrate on filling the current order of aircraft. In June 1941, the Army Air Corps was renamed the [Vous devez être inscrit et connecté pour voir ce lien] (USAAF)) and a total of 65 Lightnings were finished for the service by September 1941 with more on the way for the USAAF, the [Vous devez être inscrit et connecté pour voir ce lien] (RAF) and the Free French Air Force operating from England.

By November 1941, many of the initial assembly line challenges had been met and there was some breathing room for the engineering team to tackle the problem of frozen controls in a dive.

Lockheed had a few ideas for tests that would help them find an answer.

The first solution tried was the fitting of spring-loaded servo tabs on the elevator trailing edge; tabs that were designed to aid the pilot when control yoke forces rose over 30 lb (14 kg), as would be expected in a high-speed dive.

At that point, the tabs would begin to multiply the effort of the pilot's actions.

The expert test pilot, 43-year-old Ralph Virden, was given a specific high-altitude test sequence to follow, and was told to restrict his speed and fast maneuvering in denser air at low altitudes since the new mechanism could exert tremendous leverage under those conditions.

A note was taped to the instrument panel of the test craft, underscoring this instruction.

On 4 November 1941, Virden climbed into YP-38 #1 and completed the test sequence successfully, but 15 minutes later was seen in a steep dive followed by a high-G pullout.

The tail unit of the aircraft failed at about 3,000 ft (910 m) during the high-speed dive recovery; Virden was killed in the subsequent crash.

The Lockheed design office was justifiably upset, but their design engineers could only conclude that servo tabs were not the solution for loss of control in a dive.

Lockheed still had to find the problem; the Army Air Forces personnel were sure it was flutter, and ordered Lockheed to look more closely at the tail.

Although the P-38's [Vous devez être inscrit et connecté pour voir ce lien] was completely skinned in aluminum (not fabric) and was quite rigid, in 1941, flutter was a familiar engineering problem related to a too-flexible tail. At no time did the P-38 suffer from true flutter.

To prove a point, one elevator and its vertical stabilizers were skinned with metal 63% thicker than standard, but
the increase in rigidity made no difference in vibration.

Army [Vous devez être inscrit et connecté pour voir ce lien] Kenneth B. Wolfe (head of Army Production Engineering) asked Lockheed to try external mass balances above and below the elevator, though the P-38 already had large mass balances elegantly placed within each vertical stabilizer.

Various configurations of external mass balances were equipped and dangerously steep test flights flown to document their performance. Explaining to Wolfe in Report No. 2414, Kelly Johnson wrote "... the violence of the vibration was
unchanged and the diving tendency was naturally the same for all conditions."

The external mass balances did not help at all. Nonetheless, at Wolfe's insistence, the additional external balances were a feature of every P-38 built from then on.

After months of pushing [Vous devez être inscrit et connecté pour voir ce lien] to provide Mach 0.75 wind tunnel speeds (and finally succeeding), the compressibility problem was revealed to be the center of lift moving back toward the tail when in high-speed airflow.

The compressibility problem was solved by changing the geometry of the wing's underside when diving so as to keep lift within bounds of the top of the wing.

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.

Late in 1943, a few hundred dive flap field modification kits were assembled to give North African, European and
Pacific P-38s a chance to withstand compressibility and expand their combat tactics.

Unfortunately, these crucial flaps did not always reach their destination.

In March 1944, 200 dive flap kits intended for [Vous devez être inscrit et connecté pour voir ce lien] (ETO) P-38Js were destroyed in a mistaken identification incident in which an RAF fighter shot down the [Vous devez être inscrit et connecté pour voir ce lien] bringing the shipment to England. Back in Burbank, P-38Js coming off the assembly line in spring 1944 were towed out to the tarmac
and modified in the open air.

The flaps were finally incorporated into the production line in June 1944 on the last 210 P-38Js.

Despite testing having proved the dive flaps were effective in improving tactical maneuvers, a 14-month delay in production limited their implementation with only the final 50% of all Lightnings built having the dive flaps installed as an assembly line sequence.

Johnson later recalled :


I broke an ulcer over compressibility on the P-38 because we flew into a speed range where no one had ever been before, and we had difficulty convincing people that it wasn't the funny-looking airplane itself, but a fundamental physical problem.

We found out what happened when the Lightning shed its tail and we worked during the whole war to get 15 more kn [28 km/h] of speed out of the P-38. We saw compressibility as a brick wall for a long time.

Then we learned how to get through it.

[Vous devez être inscrit et connecté pour voir ce lien] was another early aerodynamic problem, difficult to sort out from compressibility as both were reported by
test pilots as "tail shake". Buffeting came about from airflow disturbances ahead of the tail; the airplane would shake at high speed.

Leading edge wing slots were tried as were combinations of filleting between the wing, cockpit and engine nacelles.

Air tunnel test number 15 solved the buffeting completely and its fillet solution was fitted to every subsequent P-38
airframe.

Fillet kits were sent out to every squadron flying Lightnings.

The problem was traced to a 40% increase in air speed at the wing-fuselage junction where the chord/thickness ratio was highest.

An airspeed of 500 mph (800 km/h) at 25,000 ft (7,600 m) could push airflow at the wing-fuselage junction
close to the speed of sound.

Filleting forever solved the buffeting problem for the P-38E and later models.

Another issue with the P-38 arose from its unique design feature of outwardly rotating counter-rotating propellers.

Losing one of two engines in any twin engine non-[Vous devez être inscrit et connecté pour voir ce lien] aircraft on takeoff creates sudden drag, yawing the nose toward the dead engine and rolling the wingtip down on the side of the dead engine.

Normal training in flying twin-engine aircraft when losing an engine on takeoff would be to push the remaining engine to full throttle; if a pilot did that in the P-38, regardless of which engine had failed, the resulting engine torque and [Vous devez être inscrit et connecté pour voir ce lien] force produced a sudden uncontrollable yawing roll and the aircraft would flip over and slam into the ground.

Eventually, procedures were taught to allow a pilot to deal with the situation by reducing power on the running engine, feathering the prop on the dead engine, and then increasing power gradually until the aircraft was in stable flight.

Single-engine takeoffs were possible, though not with a maximum combat load.

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The engines were unusually quiet because the [Vous devez être inscrit et connecté pour voir ce lien] were [Vous devez être inscrit et connecté pour voir ce lien] by the [Vous devez être inscrit et connecté pour voir ce lien] turbo-superchargers on the twin [Vous devez être inscrit et connecté pour voir ce lien].

There were early problems with cockpit temperature regulation; pilots were often too hot in the tropical sun as the canopy could not be fully opened without severe buffeting, and were often too cold in northern Europe and at high altitude, as the distance of the engines from the cockpit prevented easy heat transfer.

Later variants received modifications (such as electrically-heated flight suits) to solve these problems.

On 20 September 1939, before the YP-38s had been built and flight tested, the USAAF ordered 66 initial production P-38 Lightnings, 30 of which were delivered to the USAAF in mid-1941, but not all these aircraft were armed.

The unarmed aircraft were subsequently fitted with four .50 in (12.7 mm) machine guns (instead of the two .50 in/12.7 mm and two .30 in/7.62 mm of their predecessors) and a 37 mm (1.46 in) cannon.

They also had armor glass, cockpit armor and [Vous devez être inscrit et connecté pour voir ce lien] cockpit controls.

One was completed with a pressurized cabin on an experimental basis and designated XP-38A.

Due to reports the USAAF was receiving from Europe, the remaining 36 in the batch were upgraded with small improvements such as [Vous devez être inscrit et connecté pour voir ce lien] and enhanced armor protection to make them combat-capable.

The USAAF specified that these 36 aircraft were to be designated P-38D.

As a result, there never were any P-38Bs or P-38Cs.

The P-38D's main role was to work out bugs and give the USAAF experience with handling the type.

In March 1940, the [Vous devez être inscrit et connecté pour voir ce lien] and the [Vous devez être inscrit et connecté pour voir ce lien] ordered a total of 667 P-38s for US$100M, designated Model 322Ffor the French and Model 322B for the British.

The aircraft would be a variant of the P-38E. The overseas Allies wished for complete commonality of Allison engines with the large numbers of [Vous devez être inscrit et connecté pour voir ce lien] both nations had on order, and thus ordered for the Model 322 twin right-handed engines instead of counter-rotating ones, and without turbo-superchargers.

After the fall of France in June 1940, the British took over the entire order and christened the plane "Lightning".

By June 1941, the War Ministry had cause to reconsider their earlier aircraft specifications, based on experience gathered in the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien].

British displeasure with the Lockheed order came to the fore in July, and on 5 August 1941 they modified the contract such that 143 aircraft would be delivered as previously ordered, to be known as "Lightning (Mark) I", and 524 would be upgraded to US-standard P-38E specifications, to be called "Lightning II" for British service.

Later that summer, an RAF test pilot reported back from Burbank with a poor assessment of the 'tail flutter' situation, bringing the British to cancel all but three of the 143 Lightning Is.

Because a loss of approximately US$15M was involved, Lockheed reviewed their contracts and decided to hold the British to the original order. Negotiations grew bitter and stalled.

Everything changed after [Vous devez être inscrit et connecté pour voir ce lien] when the United States government seized some 40 of the Model 322s for [Vous devez être inscrit et connecté pour voir ce lien] defense, subsequently all British Lightnings were delivered to the USAAF starting in January 1942.

The USAAF loaned the RAF three of the aircraft which were delivered by sea in March 1942 and were test flown no earlier than May at Swaythling, [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien].

These three were subsequently returned to the USAAF; one in December 1942 and the others in July 1943.

Of the remaining 140 Lightning Is, 19 were not modified and were designated the USAAF as RP-322-I
('R' for 'Restricted', because non-counter-rotating props were considered more dangerous at takeoff), while 121 were converted to non-turbo-supercharged counter-rotating V-1710F-2 engines and were designated P-322-II.

All 121 were used as [Vous devez être inscrit et connecté pour voir ce lien]; a few were still serving that role in 1945.

A few RP-322s were later used as test modification platforms such as for smoke-laying canisters.

The RP-322 was a fairly fast aircraft under 16,000 ft (4,900 m) and well-behaved as a trainer.

Some of the fastest post-war racing P-38s were virtually identical in layout to the P-322-II.