Subject: Number Eighty-Two in the Series--North American P-82 Twin Mustang (1 of2)

From: [email-masked]
Date: 12 Jul 93 14:40:40 GMT

>From [email-masked]

The North American P-82 Twin Mustang was the last piston-engined 
fighter ordered by the USAAF.  It was conceived late in 1943, when it 
was realized that the very long distances over which single-seat 
fighters were operating in the Pacific were imposing very great 
strains on their pilots.  It was not uncommon for fighter pilots to 
spend up to eight hours in their cockpits on maximum-distance 
missions.  Pilots would often return from such missions drenched in 
sweat and would be so exhausted that they would have to be lifted from 
their cockpits.  It seemed that a fighter with a second seat for a 
copilot might be a good idea.  North American Aviation came up with 
the idea of joining two Mustang fuselages together by a constant-chord 
wing midsection and a rectangular tailplane, using standard port and 
starboard outer wings.  The project was given the company designation 
of NA-120.  

On January 7, 1944, the USAAF ordered four prototypes under the 
designation XP-82.  The twin fuselages were basically similar to that 
of the P-51H, but were lengthened by some 57 inches by inserting 
additional sections with integral dorsal fins in front of the 
tailplane.  All parts of the wing had to be completely redesigned 
internally to carry the very much greater gross weight and to 
accommodate the increased fuel capacity.  The center wing section 
carried a full set of flaps and was stressed to carry heavy external 
loads on either one or two pylons.  The outer wings were stressed for 
two pylons.  Because of the greater rolling inertia, each aileron was 
increased in length and divided into inner and outer sections to 
prevent binding of the hinges under high g-loads.  

The engines were 1860 hp Packard Merlin V-1650-23/25 liquid-cooled 
Vees driving oppositely-rotating Aeroproducts propellers.  Each main 
undercarriage leg was attached to the front wing spar under the 
outboard side of each fuselage.  The wheels retracted inwards under 
the fuselage and wing.  Armament consisted of six 0.5-inch Browning MG 
53-2 machine guns with 300 rpg mounted in the new wing center section.  

The two cockpits with dual controls had the same bubble canopies as 
the P-51H.  The port cockpit housed the pilot and was equipped with a 
full set of flight and engine instruments.  The starboard cockpit 
housed the navigator/copilot and was equipped with only a limited set 
of instruments, sufficient only for basic control of the plane.  

At an early stage, it was suspected that once the war was over, the 
Packard Motor Car Company would be unlikely to continue the 
manufacture of V-1650 Merlin engines.  Furthermore, the Allison V-1710 
had by that time matured into an engine which, without a 
turbosupercharger but with two stages of gear-driven blowers could 
give excellent performance at high altitudes.  Consequently, the 
V-1710-119 was specified for the third and fourth prototypes, which 
were to be designated XP-82A.  

XP-82 serial number 44-83887 flew for the first time on April 15, 
1945, piloted by J.  E.  Barton.  The other XP-82 (44-83886) followed 
shortly thereafter.  The performance was excellent, the XP-82 
retaining all the excellent qualities of the P-51: high speed, 
excellent maneuverability, and heavy firepower.  Maximum speed of the 
XP-82 was 468 mph at 22,800 feet.  Normal range was 1390 miles, with 
maximum range being 2600 miles.  Service ceiling was 40,000 feet, and 
an altitude of 25,000 feet could be attained in 6.4 minutes.  Weights 
were 13,402 pounds empty, 19,100 pounds normal loaded, and 22,000 
pounds maximum.  Dimensions were wingspan 51 feet 3 inches, length 39 
feet 1 inches, height 13 feet 10 inches, and wing area of 408 square 
feet.  

The third prototype was completed as the XP-82A and was fitted with a 
pair of Allison V-1710-119 engines of 1500 hp each, driving propellers 
rotating in the same direction.  This change to the Allison brought 
the Mustang design full circle.  The serial number was 44-83888.  The 
Allison installation now looked not unlike that of a Merlin, because 
the -119 engine had an updraft inlet and an injection-type carburetor 
upstream of the two-stage supercharger, so that the inlet was on the 
underside of the engine behind the spinner.  The inlet was about a 
foot further back than with the Merlin.  The other XP-82A prototype 
was cancelled.  

The first production model was the P-82B (Model NA-123), with a pair 
of Packard Merlin V-1560-19/21 engines.  Five hundred production 
P-82Bs were ordered by the USAAF.  These P-82Bs were basically similar 
to the XP-82, but differed in having provisions for underwing racks 
capable of carrying four 1000-pound bombs, two 2000-pound bombs, or 25 
5-inch rockets.  A central pod carrying eight additional 0.50-inch 
machine guns could also be fitted.  

The P-82B was one of the hottest piston-engined fighters of the war.  
Maximum speed was 482 mph at 25,100 feet.  Normal range was 1390 miles 
at 227 mph, 1280 miles with a 4000-pound bomb load.  Service ceiling 
was 41,600 feet, and an altitude of 20,000 feet could be attained in 7 
minutes.  Weights were 13,405 pounds empty, 19,100 pounds normal 
loaded, and 22,000 pounds maximum.  Dimensions were wingspan 51 feet 3 
inches, length 38 feet 1 inches, height 13 feet 10 inches, and wing 
area of 408 square feet.  

Only twenty of these P-82Bs had been built by the time of V-J Day 
(serials were 44-65160/65179).  None of these planes managed to get 
overseas before the end of the war.  The end of the war against Japan 
resulted in the cancellation of the remaining 480 of these P-82Bs.  

On February 28, 1947, P-82B serial number 44-65168 piloted by Robert 
E. Thacker and his copilot John M. Ard flew nonstop without 
refueling from Hickam Field, Hawaii to LaGuardia Airport, New York, 
covering a distance of 4968 miles in 14 hours 31 minutes 50 seconds 
for an average speed of 342 mph.  This airplane, named *Betty Joe* 
after Thacker's wife, carried four external fuel tanks under the wings 
for this flight.  This was the longest unrefuelled flight ever carried 
out by a piston-engined fighter.  The record still stands.  

The tenth P-82B (serial number 44-65169) was modified during 
construction as a night fighter with the mounting of a SCR-720 
airborne interception radar housed in a large bulb-shaped housing 
underneath the center wing.  The SCR-720 was the same radar 
installation which was carried aboard the Northrop P-61 Black Widow, a 
considerably larger aircraft.  In order to avoid interference of the 
radar beam from the propellers, it was necessary to position the radar 
antenna ahead of them, which mean that the entire pod had to be 
cantilevered well ahead of the pylon, placing severe nodding loads on 
the pylon, pod, and wing.  The right-hand cockpit became the radar 
operator's position.  The designation P-82C was applied.  The first 
flight took place on March 27, 1946.  

The eleventh P-82B (serial number 44-65170) was also modified during 
construction as a night fighter, but with an APS-4 radar installation 
in place of the SCR-720 set of the P-82C.  The APS-4 was a much 
smaller set than the SCR-720, and operated in the 3 cm waveband.  The 
designation P-82D was applied.  The first flight took place on March 
29, 1946.  

Sources: 

  Classic Warplanes: North American P-51 Mustang, Bill Gunston, Gallery 
  Books, 1990.  

  Fighters of the United States Air Force, Robert F.  Dorr and David 
  Donald, Temple Press Aerospace, 1990.  

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.  

  War Planes of the Second World War, Fighters, Volume 4, William Green, 
  Doubleday 1964.  

  American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 
  1982.  

  United States Military Aircraft Since 1909, Gordon Swanborough and 
  Peter M. Bowers, Smithsonian, 1989.  

Joe Baugher		AT&T Bell Laboratories   	
2000 North Naperville Road      Naperville, Illinois 60566-7033