While several aviation concerns of World War 2 (1939-1945) entertained the idea of mating two fuselages of existing successful aircraft lines, only a few projects actually bore fruit - the Heinkel "Zwilling" (twin He 111) and the North American P/F-82 "Twin Mustang" come to mind. The Twin Mustang was originally brought about to fulfill the required role of long-range fighter escort for the four-engined, long-range, high-altitude Boeing B-29 "Superfortress" heavy bomber. In the end, the Twin Mustang missed out on combat actions in World War 2 altogether, was turned into a night fighter and served with distinction during the Korean War (1950-1953), netting the first air kills of the conflict.
While World War 2 had officially begun in September of 1939, the United States did not formally enter the war until late-1941 following the Japanese attack on Pearl Harbor. The nation mobilized the following year and its large war industry ramped up to meet demand. The initial primary focus was on the European Theater leaving forces in the Pacific to made due for the interim - the survival of Britain and the Soviet Union were key factors in the demise of the Axis powers in Europe. Once the situation across the Atlantic had stabilized, American attention then turned to the West and the Empire of Japan where territory now spanned across the Pacific Ocean. Each holding was essentially helped by long distances of open water which would force invaders to commit considerable naval assets and manpower in forcing Japanese defenders from their entrenched positions. Such offensives - through "Island Hopping" - would eventually claim the lives of millions of participants.
One of the unique challenges facing American warplanners was the range required to support ground, naval and aerial actions. While the Boeing B-29 was slated to bomb far-off targets (including Japan proper), it required capable fighter escorts with similar long-range qualities. Long-range qualities in aircraft required sufficient fuel stores and multiple crewmembers to share the workload. In 1943, North American Aviation started development of a possible contender for the long range escort role, taking its excellent P-51 Mustang fighter as a starting point. It was deemed that the principle qualities of the base P-51 could be largely retained though expanded upon by way of simply joining two P-51s as one. Modifications would seem relatively minor but proved rather deep to the point that the resulting product was considered an all-new aircraft. This involved the joining of the inboard wing surfaces (the main span and the tail), concentration of armament in a center section, new landing gear arrangement and altered cockpits with redundant flight controls and systems. The primary pilot would be seated in the left fuselage cockpit with the navigator/co-pilot in the right fuselage cockpit - the workload being theoretically shared between the two men. The use of two powerplants ensured a failsafe should one engine fail over the unforgiving Pacific waters. From this thinking was born the North American NA-120 proposal which was approved by the United States Army Air Force (USAAF) on January 7th, 1944, giving rise to two prototypes (s/n 44-83886 and MX-485) intended to test the viability of the project. North American workers christened their unique concept as the "Twin".
The prototypes were collectively designated as "XP-82" and the powerplant of choice became the Packard series inline piston engine, license-produced versions of the excellent British Rolls-Royce Merlin Vs. The engine proved a heady performer and, with two units coupled, offered double the power output. As each unit drove their own propeller assembly, "torque" (the natural occurring pull of the airframe in one direction caused by the spinning propeller blades) was neutralized by assigning the other propeller to spin in the opposite direction. Each engine was to drive a four-bladed propeller.
The XP-82 incorporated a list of changes over the original P-51 airframes: each fuselage was extended by 57 inches behind the air scoop, a strake was added along the ventral seam and each tail rudder was increased in height. The undercarriage was wholly redrawn to accommodate for the repositioned center of gravity as well as revised dimensions. Single-wheeled main landing gear legs were now positioned under the mass of each fuselage nacelle (at the point where the wing element met the fuselage). These units retracted inwards towards centerline. Each empennage was given a single-wheeled tail leg which retained the "nose-up" appearance of the original P-51 when the aircraft was at rest. Along with the center section of the main wing joining the two fuselages, a new horizontal stabilizer was drawn up and added between the two tails to complete the XP-82 look. The outboard portions of the main wing spans were given ordnance and fuel hardpoints as well as de-icing technology. The central wing section held a flap.
In the case of standard armament, it was decided to concentrate 6 x 0.50 caliber Browning heavy machine guns along the central joining wing span. Original P-51 fighters held three such machine guns to the leading edges of each wing. In the XP-82, the outboard guns were dropped altogether and the three inboard triplets were mated as a single battery of six guns. Support for conventional drop bombs and rockets was also added as was plumbing for jettisonable fuel tanks.
In March of 1944, the USAAF granted North American an official production contract which covered the "P-82B" model. This form varied slightly from the prototype in that it was to incorporate a central underslung gun pod containing 8 x 0.50 caliber heavy machine guns. Additionally, four underwing hardpoints were requested to carry ordnance or fuel stores. The combined firepower of this development was massive, numbering no fewer than fourteen machine guns with the capability of dropping 4 x 1,000lbs on ground targets. Up to 10 x 5" HVAR (High Velocity Aircraft Rocket) air-to-surface, high-explosive rockets could be called on for ground attack sorties. Conventional ordnance-carrying capabilities totaled 4,000lbs of external stores. The USAAF commissioned for 500 of the type while the war still raged.
Power for the F-82B was served through 2 x Packard V-1650 inline piston engines developing 1,380 horsepower. Maximum speed was 482 miles per hour with a listed cruise speed of 280 miles per hour. Range was 2,200 miles giving the crew good reach while operating ceilings maxed at 39,000 feet. Dimensionally, the F-82B featured a running length of 38 feet, a wingspan of 51 feet, 3 inches and a height of 13 feet, 8 inches. Maximum take-off weight was 24,800lbs.
The original XP-82 prototype was trialed for the first time on April 15th, 1945 with V1650-11/12 engines of 1,380 horsepower (though rotating in the same direction) and it failed to go airborne. After some of her weight was reduced, the aircraft went airborne for the first time on June 16th. The Mustang evolution proved sound with much of her handling retained. A second, still incomplete, XP-82 achieved flight on August 30th (only the original XP-82 was ever officially completed). The USAAF liked what it had and pushed the program further, resulting in the "XP-82A", a third prototype (s/n 44-83888) now fitted with Allison V-1710-119 engines of 1,500 horsepower in the case that the British pulled Packard production rights of their Merlin. A second XP-82A followed (s/n 83889) and both A-models fitted the 119-series engines.
The war in Europe came to a close in May of 1945 and Japan followed in August. Its conclusion brought many ongoing military programs to a slow crawl while many others were cancelled outright as the post-war drawdown began. The Twin Mustang endeavor fell under threat for the original 500-strong order of F-82Bs was drastically reduced to 20 airframes. As a historical aside, the F-82 went on to become the last prop-driven fighter to be procured in number by the United States Air Force (USAF) as the jet age loomed (the USAAF officially became the USAF in 1947).
At this time, the Northrop P-61 Black Widow night fighter was nearing retirement and this proved a saving grace for the Twin Mustang's continued development. A pair of P-82Bs were selected for conversion to the night fighter role and these became the "P-82C" and "P-82D". The primary difference between these mounts lay in the choice of radar systems installed: the C-model was handed the SCR720 series radar system while the D-model was given the APS-4 series system (pods fitted under the center wing section). Both airframes were appropriately coated in black.
Work on other P-82s continued: the P-82E became an all-weather day fighter which 100 were produced. The P-82F became a dedicated night fighter outfitted with APS-4 radar, production also numbering 100 units. The P-82Gappeared in 50 examples and was equipped with SCR720 radar. This became the final Twin Mustang production form. All aircraft were manufactured at the North American Inglewood plant of California, the final unit coming off the lines in March 1949. In all, 273 P-82s/F-82s were produced
The Korean War
Air Defense Command adopted the F-82G radar-equipped night fighter (all "P" fighters were redesignated to "F") and, by the time of the Korean War (1950-1953), those based in the Far East became some of the some of the first American fighter groups to respond to the North Korean invasion of the South. P-82Gs claimed the first three North Korean air kills of the war on June 27th, 1950.
During the conflict, the F-82 used its formidable machine gun firepower to strafe unfortunate North Korean troops and convoys while rockets handled devastating attacks on key positions and infrastructure. Her bomb load was brought to bear against more precise targets, adding another tool in the arsenal of the impressive machine. The end of the F-82 over Korea was signaled by the arrival of the new generation of fighter jets who could equally excel in the ground attack role. As more and more jets entered the American inventory, F-82 use dwindled and further restricted by a general lack of replacement parts. After the Korean War, surplus P-82G models were handed to Alaskan Air Command for defense of the North against possible Soviet invasion or patrol incursion. These mounts were appropriately modified for cold weather service.
The Hawaii-to-New-York Record-Setter: "Betty-Jo"
One F-82B holds the distinction of the longest non-stop flight of a piston-engined/prop-driven military fighter aircraft covering 5,051 miles over 14 hours, 33 minutes when "Betty-Jo" (s/n 44-65168) flew from Hickam Field, Hawaii to New York during the span of February 27th-28th, 1947. The aircraft was outfitted with four oversized, jettisonable 310 gallon fuel tanks and averaged a speed of 334 miles per hour. Her flight dynamics were somewhat hampered when three of her fuel tanks refused to release. "Betty-Jo" - named after pilot Lt Colonel Robert Thacker's wife - now resides as a museum showpiece at the National Museum of the US Air Force in Dayton, Ohio. Thacker was aided by copilot Lt John Ard during the record-setting flight.