Dave Windle - Profiles of Flight: North American P-51 Mustang: Long-Range Fighter

First published in Great Britain in 2011 by
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Copyright Dave Windle & Martin W. Bowman, 2011

9781783461158

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The Mustang story begins in April 1940 when British Direct Purchasing Commission officials visiting America sought a new long-range fighter to supplement the Spitfire and Hurricane. A number of US aircraft manufacturers were called to a conference in New York on 5 April and the delegates included James H Dutch Kindelberger, president of North American Aviation Incorporated, who was accompanied by the companys executive vice-president, J. Leland Attwood. When Curtiss-Wright Corporation offered to supply the Curtiss H-87 (P-40D), which was already in production, it was suggested that North American could ease the supply problem by assisting in production of the aircraft. Then Kindelberger offered to design and build a new and infinitely superior fighter specifically developed to meet the British requirement using the same 1,150-hp Allison V-1710-39 engine. The British Purchasing Commission accepted their proposal but the contract also called for various types of other fittings and armament to be provided by the British, who specified that the cost of each aircraft should not exceed $40,000. North Americans only previous experience in fighter design and construction was limited to the NA-50A, which had been designed in 1939 for Siam (now Thailand). However, Kindelberger had studied accounts of air combat in Europe and he had already conceived the broad outlines of a new combat-worthy fighter, designated NA-73. Also, much useful technical data was obtained from the Curtiss-Wright Corporation. The first prototype was not built from production drawings, but rather from design layouts so that a faster rate could be achieved. All told, 3,500 original drawings were required, in addition to a wind-tunnel test programme and a structural test programme, which had to be virtually completed prior to the first flight. The design and production team worked sixteen hours each day, six days a week, finishing at 1800 hours.

Kindelberger and Attwood called a meeting of the design team at North American, including: Raymond H. Rice (chief engineer); chief design engineer, German-born Edgar Schmued, who had previously worked for Fokker and Messerschmitt; E. J. Horkey (aerodynamicist); and Ken Bowen (project engineer). Arthur G. Patch and John F. Steppe were to oversee wing and fuselage design respectively. Rice ordered a low-drag, high-lift wing, while Horkey submitted what were then considered radical ideas for an aerofoil section. Rice and Schmued planned the NA-73 for mass production with a low, square-cut wing, whose laminar-flow aerofoil had its maximum thickness well aft, similar to aerofoils introduced by the National Advisory Committee for Aeronautics (NACA), giving it the lowest drag of any fighter yet built. A radiator scoop was streamlined into the underside of the fuselage underside behind the pilot, while keeping the fuselage cross-section to the smallest depth possible. The low-drag wing was perfect for high-speed flights over long distances but it meant the aircraft would have a high landing speed so flap design was of vital importance. North American engineers were worried that all of these advanced features would cause long delays when the aircraft went into production but, in the event, their fears proved groundless. Even before the first flight took place, design for production had already started and Ken Bowen was given the job of chief production project engineer.

The NA-73X prototype was assembled in an astonishing 78,000 engineering hours, 127 days, although the 1,100-hp Allison V-1710-39 (F3R) engine was not yet installed and the wheels were borrowed from an AT-6 basic trainer. After several modifications the NA-73X was flown for the first time on 26 October 1940 from Mines Field (now Los Angeles International Airport) in the hands of project test pilot Vance Breese. The prototype showed excellent handling characteristics and early test flights proved to be a great success; the NA-73X soon achieved 382mph at 14,000ft, equal to the British Spitfire. However, during the fifth flight on 20 November 1940 the NA-73X ran out of fuel after a fuel switching error. The pilot attempted a wheels-down landing on farmland and the prototype flipped over onto its back after entering a newly ploughed field. The aircraft was deemed to be a write-off but the British Direct Purchasing Commission had been more than satisfied and production was assured. The first Mustang I was flown on 23 April 1941 and was then retained by the company for necessary testing. The first production model for the RAF (AG345) flew on 1 May 1941. On 4 May the Mustang was cleared for sale to Britain by the US Government, on condition that two of the initial batch were transferred to the Army Air Corps for testing. The fourth and tenth aircraft were allotted the designation XP-51 and the first was flown to Wright Field, Ohio, on 24 August, while the second aircraft (AG346) was accepted by RAF representatives in September. It began a long journey by American cargo ship through the Panama Canal to England and was unloaded at Liverpool docks on 24 October 1941. On 29 May 1941, 320 NA-73s were ordered. A further order was placed for 300 slightly improved NA-82 aircraft, the order being completed in July 1942. At least twenty Mustang Is were lost at sea and another ten were diverted to the Soviet Union before the end of 1941 and were used against Finland.