Lockheed P-38 Lightning
Lockheed P-38 Lightning
What would become one of the best fighters in World War II was created more by happenstance than by design. The Lockheed P-38 Lightning was originally designed as a bomber-interceptor and was never intended to be a fighter. Weight was kept to a minimum and it was far more advanced and faster than its U.S. counterparts, the Bell P-39 Airacobra and Curtiss P-40 Warhawk. It caught the attention of the US Army Air Corps (USAAC) very quickly and it would be in great demand. It was faster than the Zero—even on one engine. It shot down more Japanese airplanes than any other fighter during World War II—seven of the top scoring USAAF aces in the Pacific flew the P-38. It was as versatile as the de Havilland Mosquito, but it was the only truly successful twin-engine fighter of World War II.
It was basically a hand-built airplane and was never meant to be mass produced. All skin sections were butt-joined using flush riveting, and all flight controls were metal covered. The total order was expected to be only fifty aircraft, so when orders started coming in by the hundreds, Lockheed had to scramble to find room to increase production. Over lunch, Lockheed’s president, Bob Gross, made a deal to buy the old 3-G whiskey distillery for $20,000 to make room for an additional production line. However, initial production was slow and by the time Pearl Harbor was attacked, on December 7, 1941, only 69 Lightnings were completed.
When first introduced in 1939, the Lightning was able to fly a steady course at 413 mph (665 km/h) making it the fastest production airplane in the world and it remained one of the fastest climbers right up to the end of the WW II. It wasn’t as fast as the Messerschmitt Me 209 which was able to attain a record 469 mph (755 km/h), but this record setting machine was built for the purposes of promoting the Messerschmitt Bf 109 and only four aircraft were built.
In 1937, the USAAC sent out specification X-608 to the leading aircraft manufacturers for a new pursuit aircraft. It would be a radical departure for existing fighters and required the following specifications:
• 360 mph (580 km/h) airspeed at 20,000 ft. (6,095 m).
Lockheed had previously competed in 1936, but lost against Bell’s XFM-1 Airacuda. Lockheed was new in the military aircraft market and by competing against Boeing and Douglas, many felt they it was overstepping its boundaries. However, this view wasn’t shared by Lockheed’s president Robert E. Gross and he gave the go ahead for his design team to proceed with a plan.
Lockheed’s chief engineer, Hall Hibbard and the then young Clarence “Kelly” Johnson, and their design team would come up with one of the boldest departures from traditional American fighter development. Hibbard realized that there wasn’t an engine in the world that would meet all of the specifications for speed, range, climb, firepower and other specifications. What they needed was two engines. Hibbard looked at the new Allison V-1710 engine which had just been tested to deliver 1,000 hp (745 kW) for 150 hours. Their airplane would require two of these engines and the aircraft design was narrowed down to six selections. With the final choice decided, the Lightning was a complete break from conventional airframe design, power and armament. It had twice the power and was almost twice the size of its predecessors. It had four .50 calibre machine guns plus a 20 mm cannon—enough firepower to sink a ship—and sometimes did. By locating the guns in the central fuselage pod, this eliminated a need for propeller synchronization and the twin booms provided extra space for the engines, landing gear and turbochargers.
The Lightning’s tricycle landing gear and twin-boom configuration completed the list of major deviations from what might be considered conventional Army fighters. In this respect, it was very unusual that the Lightning design progressed beyond the testing stage—such radical concepts seldom achieved production status. But the simple fact was that the P-38 was needed more than ever. The Messerschmitt Bf 109 and Supermarine Spitfire had a top speed of around 350 mph (563 km/h) with a ceiling over 30,000 ft. (9,144 m) and now the Army finally had a competitor that exceeded their requirement by 40 mph (65 km/h).
The XP-38 (c/n 37-457), was built under tight secrecy and made its inaugural flight on January 27, 1939, flown by test pilot Lt. Benjamin S. Kelsey. Heavy vibration was encountered on the first flight and this was due to tail flutter, which was eventually corrected in the YP-38 by installing fairings or “fillets” at the wing roots to improve airflow, installing elevator counterweights, and changing the horizontal stabilizer angle of incidence.
The XP-38’s initial performance justified Lockheed’s investment of nearly $600,000 of its own funds to produce the prototype. Although further development was still required, the Army decided to lift the wraps of secrecy and scheduled the sole prototype for a transcontinental speed-dash on February 11, 1939 from March Field, California to Mitchell Field, New York. It was a critical decision that would haunt them for years.
During the flight, the average airspeed was 340 mph (547 km/h) and a heavy tailwind provided a groundspeed of 420 mph (675 km/h). Two refueling stops were made at Amarillo, Texas, and Dayton, Ohio. However, on approach to Mitchell Field, Kelsey pulled back power and stalled the right engine, sending him into a steep right turn. Kelsey cut the throttle again and the plane slipped down and sheared off the tops of trees bordering the field. The undercarriage caught in a 35 foot (10 m) tree, and the plane plunged down into a sand pit on the Cold Stream Golf Course, 2,000 ft. (610 m) short of the runway. An Army investigation attributed the engine failure to carburetor ice.1 Kelsey survived and remained an important part of the Lightning program, but the airplane was a total loss. Despite the crash, the Army felt the aircraft showed promise and Lockheed received a contract for thirteen YP-38s along with the usual list of improvements. The XP-38 crashed after only 16 days with an airtime of 11 hours and 50 minutes.
The flight was just 17 minutes longer than Howard Hughes’ record breaking flight in the H-1 racer, but more importantly, the crash was a major setback and delayed development of the P-38 for at least two years. Once it became operational, technical problems surfaced that could have been corrected before the aircraft was placed into service. Martin Caidin, author of “Fork-Tailed Devil: The P-38” was very critical of the USAAC decision to publicize the airplane. He suggests that the speed-dash with the sole prototype was a foolish publicity stunt that led to many casualties that could have been prevented.
A major problem that surfaced was the loss of control in a dive caused by aerodynamic compressibility. During late spring 1941, USAAC Major Signa A. Gilke encountered serious trouble while diving his Lightning at high-speed from an altitude of 30,000 ft (9,120 m). When the airplane reached an indicated airspeed of about 320 mph (515 km/h), he encountered sever buffeting and the airplane’s tail began to shake violently. The airspeed increased rapidly and the nose dropped until the dive was almost vertical. With great effort, Signa barely recovered from the dive and landed safely. However, many unsuspecting pilots would not be so lucky and would plummet to the ground.
The P-38 suffered from two different problems, tail flutter and compressibility. Compressibility could tear the tail off the P-38 and this phenomenon was common to all high-speed fighters. Both P-47 Thunderbolts and P-51 Mustangs lost tails during high-speed dives. Compressibility caused buffeting on the P-38, not flutter. Flutter was corrected by installing wing fillets and making tailplane changes. Compressibility deflects airflow up & down away from the leading edge and prevents proper flow of air over the wing. Lockheed engineer Hall Hibbard said, “It is appreciable at 425 mph (684 km/h), and serious at 500 mph (805 km/h) and higher.”
- Crew: One
- Length: 37 ft 10 in (11.53 m) (11.53 m)
- Wingspan: 52 ft 0 in (15.85 m) (15.85 m)
- Height: 12 ft 10 in (3.91 m) (3.91 m)
- Wing area: 327.5 ft² (30.43 m²)
- Airfoil: NACA 23016 / NACA 4412
- Empty weight: 12,800 lb (5,800 kg)
- Loaded weight: 17,500 lb (7,940 kg)
- Max. takeoff weight: 21,600 lb (9,798 kg)
- Zero-lift drag coefficient: 0.0268
- Drag area: 8.78 ft² (0.82 m²)
- Aspect ratio: 8.26Powerplant: 2 × Allison V-1710-111/113 V-12 piston engine, 1,600 hp (1,193 kW) WEP at 60 inHg, 3,000 rpm each
- Maximum speed: 414 mph (666 km/h) on Military Power: 1,425 hp at 54 inHg, 3,000 rpm at 25,000 ft (7,620 m
- Cruise speed: 275 mph (443 km/h)
- Stall speed: 105 mph (169 km/h) (170 km/h)
- Range: 1,300 mi (2,100 km) combat (1,770 mi / 3,640 km)
- Service ceiling: 44,000 ft (13,000 m) (13,400 m)
- Rate of climb: 4,750 ft/min (24.1 m/s) maximum
- Wing loading: 53.4 lb/ft² (260.9 kg/m²)
- Power/mass: 0.16 hp/lb (0.27 kW/kg)
- Lift-to-drag ratio: 13.5
- 1× Hispano M2(C) 20 mm cannon with 150 rounds
- 4× M2 Browning machine gun 0.50 in (12.7 mm) machine guns with 500 rpg.
- 4× M10 three-tube 4.5 in (112 mm) rocket launchers; or:
- Inner hardpoints:
- 2× 2,000 lb (907 kg) bombs or drop tanks; or
- 2× 1,000 lb (454 kg) bombs or drop tanks, plus either
- 4× 500 lb (227 kg) bombs or
- 4× 250 lb (113 kg) bombs; or
- 6× 500 lb (227 kg) bombs; or
- 6× 250 lb (113 kg) bombs
- Outer hardpoints:
- 10× 5 in (127 mm) HVARs (High Velocity Aircraft Rockets); or
- 2× 500 lb (227 kg) bombs; or
- 2× 250 lb (113 kg) bombs