Aircraft Spotter Challenge/World War II  

  PLANE 010
Level 3

This plane was designed as the NA-73 in 1940 at Britain's request. The design showed promise and AAF purchases of Allison-powered planes began in 1941 primarily for photo recon and ground support use due to its limited high-altitude performance. But in 1942, tests using the British Rolls-Royce "Merlin" engine revealed much improved speed and service ceiling, and in Dec. 1943, Merlin-powered aircraft first entered combat over Europe. Providing high-altitude escort to B-17s and B-24s, they scored heavily over German interceptors and by war's end, they had destroyed 4,950 enemy aircraft in the air, more than any other fighter in Europe.



In late 1939, with the likelihood of full scale war in Europe a major concern, the British Royal Air Force was looking seriously at methods of quickly increasing its fighter strength. In April 1940, the British Air Purchasing Commission approached the manufacturer with the intent of having them build P-40's for the R.A.F. Instead, they offered to build an entirely new fighter using the same Allison V-1710-39 engine as the P-40. The British agreed only on the stipulation that a prototype be on hand within 120 days. Designers Raymond Rice and Edgar Schmued immediately set about meeting the requirements. Schmued had been a part of Willy Messerschmitt's design group in Germany; no doubt the somewhat angular lines of the new fighter came from this relationship.

The Allison-powered prototype NA-73 was assembled within the specified period, but the engine was not yet ready, causing a delay of some six weeks before the NA-73 could fly. In the meantime, on May 4, 1940, the U. S. Army released the design for export sales with the condition that two of the planes be delivered to them for evaluation. At this time the NA-73 was assigned the XP-51 designation. The first and tenth airframes were sent to the Army for testing; these were given the serial numbers 41-38 and -39. An order for 150 planes followed. These planes were named "Apache" for a short time.

The airplane was an immediate success. It outperformed even the Spitfire, but the Allison engine placed limitations on the performance. In England, a mock-up was devised to use the Rolls Royce Merlin in the existing airframe. One concept was to locate the new engine behind the cockpit, but this idea was rejected and the Merlin was mounted in the conventional position in the nose. Four airframes were adapted in England to take the Merlin engine. These planes had deep intakes below the engine for carburetor air. In the meantime, the manufacturer had undertaken a similar conversion project and was building two Packard Merlin-powered planes. The results of the British tests were passed on to the manufacturer; and even before the Army's Merlin -powered planes had flown, the U. S. Army ordered 2,200 of the more powerful fighters. For a short time, this model was designated P-78.

To say the Merlin engined planes were successful would be an understatement. This aircraft became one of the aviation world's elite. The total number of 14,819 planes of all types were built for the Army. American planes destroyed 4,950 enemy aircraft in Europe to make them the highest scoring U. S. fighter in the theater. They were used as dive-bombers, bomber escorts, ground-attackers, interceptors, for photo-recon missions, trainers, transports (with a jump-seat), and after the war, high performance racers.

The Merlin -powered "B" version and its Dallas-built twin, the "C" version, began operations in December 1943. A further improvement was introduced when a graceful teardrop canopy was installed to eliminate the dangerous blind area created by the faired cockpit. First tested on two planes, they became standard on the "D" version and all later models. The "D" became the version produced in the greatest quantities, 7,954 being completed. The "D" model carried six .50 cal. machine guns instead of the four mounted in the "B's"; and other refinements, such as moving the wing forward slightly and providing for rocket launchers, were included. The first "D" types were delivered without dorsal fins but this feature was added to compensate for keel-loss when the bubble canopy was adopted.

Later developments to the series included the final production type, the "H" with several changes which made it the fastest production variant with a maximum speed of 487 mph at 25,000 feet. Five hundred fifty-five H's were delivered before VJ Day led to cancellation of the production program.

The "D" represents the typical configuration. It had a 37-foot wingspan with an area of 233 square feet and was 32 feet 3 inches long. Height was 13 feet 8 inches. The Packard-built Merlin V-1650-7 was capable of delivering 1,695 hp which provided a speed of 437 mph at 25,000 feet. Weights were 7,125 lbs. empty and 10,100 lbs. normal gross, but an additional 2,000 lbs. could be carried. Internal fuel capacity was 105 gallons, giving a range of 950 miles at 362 miles per hour at 25,000 feet. Armament was six .50 cal. wing-mounted machine guns with 1,880 total rounds.

This aircraft was one of the first fighters to use a laminar-flow airfoil, a high-speed shape which became standard on most later high performance fighters.






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