P-51 Mustang

By Robert Jackson and Lynn Ritger

An illustrated history of the renowned fighter aircraft, ideal for modelers and aviation enthusiasts: “Highly recommended.” —AMPS Indianapolis

The North American P-51 Mustang was one of the most successful and effective fighter aircraft of all time. It was initially produced in response to a 1940 RAF requirement for a fast, heavily armed fighter able to operate effectively at altitudes in excess of 20,000 feet. North American built the prototype in 117 days, and the aircraft, designated NA-73X, flew on October 26, 1940. The first of 320 production Mustang Is for the RAF flew on May 1, 1941, powered by an 1,100hp Allison V-1710-39 engine. RAF test pilots soon found that with this powerplant the aircraft did not perform well at high altitude, but that its low-level performance was excellent.

It was when the Mustang airframe was married to a Packard-built Rolls-Royce Merlin engine that the aircraft’s true excellence became apparent. Possessing a greater combat radius than any other Allied single-engine fighter, it became synonymous with the Allied victory in the air.

During the last eighteen months of the war in Europe, escorting bomber formations, it hounded the Luftwaffe to destruction in the very heart of Germany. In the Pacific, operating from advance bases, it ranged over the Japanese Home Islands, joining carrier-borne fighters such as the Grumman Hellcat to bring the Allies massive air superiority.

Yet the Mustang came about almost by accident, a product of the Royal Air Force’s urgent need for new combat aircraft in the dark days of 1940, when Britain, fighting for survival, turned to the United States for help in the island nation’s darkest hour. This is its story, including plentiful photos and information for modelers.

• Language: English
• Publisher: Open Road Integrated Media
• Release date: Sep 30, 2020
• ISBN: 9781526759917

Robert Jackson

A native of St. Louis, Robert Jackson is the great-grandson of a carpenter who helped build the palaces in Forest Park for the 1904 World's Fair. He has trained for two marathons on the park's restored grounds. Although he has since lived in Chicago, Los Angeles, and New York City, he remains a loyal St. Louisan, especially during baseball season when the Cardinals are playing. Robert Jackson studied American literature and culture at New York University, where he received his Ph.D. This is his first book.

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INTRODUCTION

In the early weeks of the Second World War, with the British aircraft industry strained to breaking point by the demands of home defence, there was no immediate prospect of replacing the obsolescent types in service overseas with more modern equipment. Consequently, in January 1940 the British government realized that British aircraft production would have to be supplemented by purchases from abroad, and to this end the British Direct Purchasing Commission was established in the United States.

British liaison with the USA’s rapidly expanding military aviation industry was not new. The Lockheed Hudson, a maritime patrol version of the Lockheed Model 14 commercial airliner, was already in service with RAF Coastal Command. Early in 1940, the most pressing requirement was for fighter aircraft that could also undertake the ground-attack role, and in this respect the American market seemed disappointing at first sight. The best US fighter then in operational service, the Curtiss P-40, fell a long way short of measuring up to the RAF’s requirements, and two more designs that looked promising, the Lockheed P-38 and the Bell P-39, would not be ready for service until the spring of 1941.

The P-40 was therefore the only option. France had already placed an order for 140 aircraft, but before these could be delivered France fell, and the full order was taken over by the British Purchasing Commission on behalf of the RAF. Although considered unsuitable for operational use by Fighter Command, the P-40s were fitted with four wing-mounted Browning 7.7-mm (0.303-in) machine guns and allocated to Army Co-Operation Command as the Tomahawk I. An improved variant, the Tomahawk IIB, went on to give excellent service with RAF and Commonwealth squadrons in North Africa.

Since the Curtiss production line was fully occupied in meeting the demands of the US Army Air Corps, the Purchasing Commission approached another American manufacturer, North American Aviation Inc., and asked them if they would be willing to build a variant of the P-40 for the RAF under sub-contract. Incorporated in Delaware in 1928, North American had been engaged exclusively in military aircraft design since 1934, specializing in observation aircraft and trainers. Six years later the company was mainly occupied with the production of the AT-6 Texan advanced trainer, which had won a USAAC competition for an aircraft in that category in 1937. It was an important milestone in the young company’s career, and North American’s president, James H. ‘Dutch’ Kindelberger, foresaw a bright future in further military aircraft design.

The Curtiss P-40, seen here in the markings of No. 14 Squadron RNZAF, gave excellent service in the US and Commonwealth air forces, but did not match up to the RAF’s requirement for a day fighter. (RNZAF)

James H. ‘Dutch’ Kindelberger, President of North American Aviation, led the company from 1934 to 1960. (National Air and Space Museum)

Consequently, Kindelberger was reluctant to take on sub-contract work from another company, especially as the work would involve producing an aircraft which he already considered to be outmoded. Instead, after conferring with his staff, he came up with a revolutionary proposal. Starting from scratch, North American would design and build a completely new aircraft for the RAF, a fighter that would incorporate the latest refinements in air combat technology.

The British Air Ministry agreed, and North American sought the approval of the US government – a necessary step before the scheme could be implemented, because at this time Congress was still pursuing an isolationist policy and was not anxious to be seen as an active supplier of military hardware to the Western Allies in their struggle against Germany. Approval was forthcoming in this instance, but on condition that two examples of the new fighter were to be handed over at no cost for evaluation by the Army Air Corps.

Early in February 1940, a delegation led by Kindelberger and Leland Attwood, North American’s vice-president and assistant general manager, travelled to London for a design conference with Air Ministry representatives. Having studied the Air Ministry specification, the North American team came prepared with several preliminary design sketches which had been drawn up by Raymond H. Rice, who was to be chief engineer for the project, Edgar Schmued, North American’s chief designer, and their assistants Larry Waite and E. H. Horkey.

The design conference was held in a London hotel room, and the Air Ministry representatives were enthusiastic about the concept with the exception of the proposed armament. The original North American design specified an armament of either four.50-calibre guns or a mix of two 0.50s and two 0.30s, similar to that of the Curtiss P-40, but the Air Ministry requirement specified an eight-gun armament similar to that incorporated in the Spitfire and Hurricane. In the end an agreement was reached: the aircraft would carry eight, comprising two .50 Browning MG53s in the lower front fuselage beneath the engine and one in each wing just outside the propeller disc, plus two 0.30 Browning MG40s in each outer wing, the MG53s having 400 rounds per gun and the MG40s 500 rpg.

Agreement was also reached on the powerplant. Early in 1940, the most powerful in-line engine available in the United States was the Allison V-1710 series of liquid-cooled V-1 powerplants. The engine selected was the Allison V-1710-F36, which drove a Curtiss three-blade constant speed propeller of 10 ft 6 in diameter and was rated at 1,500 hp at 11,800 ft. It was an engine designed to produce optimum performance at low and medium altitudes, which was exactly what the RAF required in a tactical fighter.

With the preliminary negotiations successfully concluded, North American received a letter of intent from the British government on 10 April 1940 and went ahead with detailed design work on the project, which was now designated NA-73X. The letter of intent was followed by a formal contract on 23 May, with North American predicting a completion date for the prototype in January 1941.

Work on the new fighter prototype made a tremendous impact on North American’s routine in Mines Field, near Los Angeles, where the 150-strong workforce had been concentrating on production of the AT-6. Personnel in the fabrication shops worked 16-hour shifts, seven days a week, and the basic airframe was completed in just 102 days. A further two weeks saw the systems installed and the airframe, minus its engine and resting on wheels and tyres borrowed from the AT-6 production line, was rolled out. Twenty days later, the Allison engine was delivered and mated with the airframe in less than 24 hours.

The NA-73X was a clean design. For ease of assembly the airframe was divided into five major components – forward, centre and rear fuselage and two wing halves – all of which were fitted with their wiring and piping systems before being joined together. (North American)

Design & Development

At first sight, the design of the NA-73X was that of an orthodox fighter, featuring a clean, low-wing monoplane with an in-line engine and square-cut wing and tail surfaces. Close examination of detail, however, revealed some exciting innovations, the most important of which was the use of a laminar flow wing, the aerofoil section for which had been partly developed by the National Advisory Committee for Aeronautics (NACA).

In designing this aerofoil, as well as making use of information supplied by the NACA and other technical institutions, North American, who had no experience in the design of high-performance aircraft, bought wind tunnel data from Curtiss, a move that gave rise to a completely false rumour that the new aircraft was little more than a revamped Curtiss design.

The all-metal airframe featured a semimonocoque fuselage and a twin-spar, cantilever stressed skin wing. All control surfaces were also metal-skinned, and large split trailing-edge flaps took up the whole space between ailerons and wing roots. The wide track main undercarriage retracted inwards into wells recessed into the wing leading edge; immediately aft of each wheel well was a self-sealing fuel tank with a capacity of 90 US gallons. The tail wheel was steerable and fully castering, retracting forwards into the rear fuselage. Undercarriage, flaps and brakes were hydraulically operated.

The choice of a liquid-cooled engine was another primary consideration in making the airframe as streamlined as possible, as was the siting of its radiator. Wherever the radiator was positioned it was bound to create drag. In the end North American opted to locate the radiator below and behind the cockpit area, streamlining it as much as possible and fitting it with a retractable scoop that stood clear of the fuselage underside to avoid turbulence from the airflow. Air passing through the radiator was expanded and accelerated before being ejected through a controllable rear flap, providing a propulsive force that more than compensated for the extra drag produced by the radiator assembly. It was a clever arrangement, but it required considerably more plumbing to connect the radiator to the engine. Also, as later operations would show, it was highly vulnerable to ground fire.

Ground testing of the Allison engine proceeded with relatively few problems, and North American contracted a well-known high-performance aircraft test pilot, Vance Breese, to make the NA-73X’s maiden flight, which took place on the morning of 26 October 1940. The 20-minute flight, always within sight of Mines Field runway, was smooth and without problems, its most noteworthy feature – apart from the aircraft’s enormous performance potential, which was readily apparent – being that the NA-73X needed a lot of right rudder on the take-off run to counteract the strong torque produced by the engine.

A fine study of the NA-73X prototype in flight, as yet unpainted. (North American)

Front view of the NA-73X, showing the under-fuselage radiator scoop and three-blade constantspeed Curtiss propeller. (North American)

Breese made three more test flights in the NA-73X before handing over the test programme to North American test pilot Paul Balfour, who took off for his first flight in the aircraft on 20 November. Balfour made several high-speed runs over the airfield, but as he turned to make another pass the Allison engine began to run roughly and then cut out. Losing altitude rapidly, Balfour lowered the undercarriage and flaps and took the aircraft down for an emergency landing. Unfortunately, the main undercarriage dug into soft ground and the aircraft turned over on its back. Balfour escaped unhurt, but the aircraft was severely damaged. A subsequent investigation showed that the engine had stopped through fuel starvation;