P-82 Twin Mustang

Extending the escort range

Design changes

Production & first flight

Variants

Operational service

Survivors

Specifications

Serial numbers

3-Way drawings

 

 

Extending the escort range

Long range escort missions led to a problem that was no issue in earlier fighters: pilot fatigue. Sitting in a tight cockpit for up to 8 hours is one thing, managing fuel from takeoff untill landing, flying formation and the constant stress of air combat all (often in poor European weather conditions) combined was enough to drain pilots completely. On more than one occasion, pilots had to be helped out of their cockpit when they returned to base.

Further more, the USAAF was looking for fighters with even more range than the P-51 to operate in the extreme long escort missions, escorting B-29s on missions exceeding 2,000 miles over the Pacific (from the Solomons or Philippines to Tokyo).

NAA's Edgar Schmued came up with the idea to link two Mustangs together with a common center wing and horizontal stabilizer in November of 1943. In January of 1944, US General Herny H. “Hap” Arnold was shown the concept and became enthousiastic with the idea. As a result, NAA was given the go-ahead to proceed with the design.

XF-82 (Photo by USAF)

The North American P-82 Twin Mustang (NA-120) was born. As it turned out, the Marines captured islands close enough to Japan that P-51s were easily able to escort the B-29s all the way to Japan and back. As a result, P-82s never saw combat during WWII.

 

Design changes

Although the idea of mating 2 P-51 fuselages together seemed very simple, the P-82 was in fact an entirely new aircraft. Longer range meant carrying more fuel which lead to a bigger fuselage. A bigger fuselage meant a higher weight. A higher weight meant that the wings and landing gear had to be stronger. It also meant that the control surfaces needed to be larger. In the end, the
P-82 had less then 20% parts in common with the P-51.

Amongst the most noticeable changes were:

 

  • Two P-51H fuselages were chosen to be joined together with a common center wing and a horizontal stabilizer section. The fuselages were extended by 4'9” (1,45 meters).
  • The center wing housed six 0.50 caliber machine guns with 440 rounds each.
  • The center wing also housed a slotted flap.

  • The outer wing parts were smaller than that of two P-51s and were thus strengthened to handle the higher wing load.

  • In order to improve the roll response, the outer wings were fitted with longer two-piece ailerons with hydraulic power boosting.

  • A total of six underwing hardpoints were available (two underneath each outer wing section and two underneath the center wing) for carrying bombs, HVAR rockets and/or drop tanks. The center section could carry an external pod for a night-fighting radar, extra machine guns or reconnaissance cameras.
    XF-82 44-83886 (Photo by USAF)
    Above: XF-82 44-83886 carrying two 1,000lbs bombs, ten 5-inch rockets and two 500lbs bombs (also note the six 0.50 caliber machine guns in the center wing)

  • The two vertical tails ware taken from the XP-51F, but had large dorsal fins for added stability in case of an engine failure.

  • The XP-82 had an unusual four-point landing gear (two mains and two tail wheels) which was strengthened to carry all the extra weight. Both main wheels retracted across the fuselage, into bays underneath the common wing.

  • Fuel tanks were incorporated in the outer wings and in each fuselage, bringing the total internal fuel capacity to 574 US gallons (2,180 liters).

  • The cockpits were redesigned. The pilot in command flew in the left cockpit which was fully equipped, while the copilot flew the right cockpit with more simplified controls. Both engine throttles and both propellers were controllable from either cockpit by manually operated levers. The pilot's cockpit on the left contained the normal flight and engine instruments, while the co-pilot/navigator on the right had sufficient instruments for relief and emergency operation. A simplified cockpit arrangement improved pilot comfort, including a tilting, adjustable seat to reduce fatigue during long flights. It is interesting to note that only the pilot in the left fuselage had full IFR instruments. On such missions in the "soup," the second pilot would be able to provide little help in the way of relief.
    Twin Mustang cockpit
    Above: the left and right cockpit interior of the F-82

  • Engines were two Packard V-1650-23 with a gear reduction box to allow the left propeller to turn opposite to the right engine. In this setup, both propellers would turn upward as they approached the center wing. However the XP-82 refused to get airborne during its first flight attempt.

    After a month of work, NAA engineers finally discovered that rotating the propellers to meet in the center of their upward turn created sufficient drag to eliminate the lift from the center wing section which was equal to one quarter of the total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn. This resolved the problem.

 

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