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Aviation History Month Day 9 - 9th of November 1956

The second prototype of the Martin XP6M-1 Seaplane, BuNo 138822 with c/n XP-2, crashed on this day in aviation history in 1956. The aircraft had made its first flight on the 18th of May 1956. All four crew members ejected and safely landed by parachute. The cause of the crash was determined to be a change made to the horizontal stabilizer control system which what not properly evaluated prior to the test flight. A failure in an actuator caused the aircraft to pitch up at an altitude of 21.000 feet (6400 meters), the aircraft would not respond to nose down inputs from the crew. After the crew abandoned the aircraft it falls towards earth gaining speed and finally breaking up in the air at approximately 6000 feet (1800 meters) before impact. Only 11 months before the first prototype had been lost, killing all four crewmembers when a horizontal stabilizer failure caused the aircraft to be subjected to 9 g and as result breaking up mid-flight.

The Martin XP6M-1 Seaplane

The Martin P6M Seamaster, a strategic bomber flying boat was a product of the Glenn L Martin Company.

The aircraft was designed as a strategic nuclear weapon delivery platform for the US Navy. It was 'overtaken' by the Polaris Ballistic Missile launched from submarines.

The aircraft had some unique characteristics;

- Mach 0.9 (1100 km/h) just above sea level

- Strongly built airframe, for example, the "skin at the wing root was 1" 25 mm thick


There were also some negative characteristics;

- Severe compressibility effects at speeds above Mach 0.8, leading wing drop, trim issues and buffeting

- When on the water the wing tip floats had a tendency to dig into the water due to roll issues. The manufacturer had these problems solved at the same time the government gave the US Navy some stringed requirements for budget cuts. This resulted in the US Navy having to cut programs, one of the programs that got cancelled was the Martin XP6M-1 program.

A total of 16 airframes were built in 3 different versions;

  • XP6M-1 Two prototypes were built, both crashed

  • YP6M-1 Six pre-production aircraft. Scrapped when the program for cancelled

  • YP6M-2 Eight production aircraft built Three were completed and flown Five were completed but not flown The contract for a further 6 production aircraft were cancelled

Specifications for the production version;

  • Crew: 4

  • Length: 134 ft 4 in (40.94 m)

  • Wingspan: 102 ft 7 in (31.27 m)

  • Height: 33 ft 10 in (10.31 m)

  • Wing area: 1,900 sq ft (180 m2)

  • Empty weight: 97,439 lb (44,198 kg)

  • Gross weight: - 184,280 lb (83,588 kg) (at take-off) - 162,392 lb (73,660 kg) (in combat)

  • Max takeoff weight: - 190,000 lb (86,183 kg) in calm water - 160,000 lb (72,575 kg) in rough water (6 to 9 ft (1.8 to 2.7 m) swell)

  • Powerplant: 4 × Pratt & Whitney J75-P-2 turbojet engines, 17,500 lbf thrust

Performance

  • Maximum speed: 686 mph (1,104 km/h, 596 kn) at 20,000 ft (6,096 m)

  • Cruise speed: 535 mph (861 km/h, 465 kn)

  • Stall speed: 152 mph (245 km/h, 132 kn) (Power off, flaps down, T.O. wt)

  • Range: 2,083 mi (3,352 km, 1,810 nmi)

  • Combat range: - 750 mi (1,210 km, 650 nmi) (Carrying 30,000 lb (14,000 kg) payload) - 1,726 mi (1,500 nmi; 2,778 km) with one AAR from a P6M-2 tanker

  • Service ceiling: 50,000 ft (15,000 m)

  • Rate of climb: 7,380 ft/min (37.5 m/s)




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