The North American P-51 Mustang
The P-51 was designed as the NA-73 in 1940 at Britain's request. The design showed promise and Army Air Force (AAF) purchases of Allison-powered Mustangs began in 1941 primarily for photo recon and ground support use due to its limited high-altitude performance. But in 1942, tests of P-51s using the British Rolls-Royce "Merlin" engine revealed much improved speed and service ceiling, and in December 1943, Merlin-powered P-51Bs 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, P-51s had destroyed 4,950 enemy aircraft in the air, more than any other fighter in Europe.
Mustangs served in nearly every combat zone, including the Pacific where they escorted B-29s to Japan from Iwo Jima. Between 1941-5, the AAF ordered 14,855 Mustangs (including A-36A dive-bomber and F-6 photo recon versions), of which 7,956 were P-51Ds. During the Korean War, P-51Ds were used primarily for close support of ground forces until withdrawn from combat in 1953.
In 1940 British purchasing agents asked North American Aviation to build more Curtiss P-40s. The P-40 was the only American land-based fighter available at the time but it was also seriously deficient in speed, range, and altitude performance. North American declined to build it but proposed a completely original design and promised to finish it in less than three months. North American completed the NA-73 airframe 117 days later and installed an in-line, liquid-cooled Allison engine. This aircraft first flew on 25th October 1940. During flight tests, the aeroplane exhibited outstanding performance, particularly in level-flight. The British enthusiastically ordered 150 examples of the aeroplane and the Royal Air Force named it the Mustang. The U. S. Army Air Corps also showed interest and in 1941 they ordered 500 ground-attack variants designated the A-36.
The A-36A dive-bomber powered by a 1,325 hp Allison V-1710 was the first Army Air Force (AAF) version of the "Mustang" developed for Britain in 1940. The A-36 fist flew in October 1942; production of 500 A-36A's was completed by March 1943.
Unofficially named "Invaders," A-36A's were assigned to the 27th and 86th Bombardment Groups (Dive), later re-designated as Fighter-Bomber Groups. In June 1943, the plane went into action from North Africa. During the Italian campaign, A-36A pilots flew bomber escort and strafing missions as well as ground support bombing attacks. A-36A's also served with the 311th Fighter-Bomber Group in India. Dive brakes in the wings gave greater stability in a dive, but they were sometimes wired closed due to malfunctions. In 1944, AAF A-36A's were replaced by P-51's and P-47's when experience showed that these high-altitude fighters, equipped with bomb racks, were more suitable for low-level missions than the A-36A's.
Early in 1942, the British tested four RAF Mustangs fitted with the two-stage, two-speed Merlin 65 engine. The supercharger in the Merlin 65 was optimised to produce sea-level horsepower up to approximately 9,150 m (30,000 ft). Urged on by Rolls Royce and British and American fighter pilots who sampled the new Mustang, North American obtained two Merlin 61 engines similar to the 65 and installed them in airframes designated XP-51B's. The new variant had good range and outstanding speed, about 80 kph (50 mph) faster than previous models. Thus was born the world's best long-range, propeller-driven escort fighter.
With improved range and speed, P-51 squadrons could now accompany 8th Air Force bombers on long-range raids over Europe. Bomber losses dropped sharply when fighters could protect them during their entire mission. The Mustang also proved itself in the Pacific theatre. Again, the P-51 had the range, speed, and endurance to escort Boeing B-29 Superfortresses conducting long-range bombing attacks. The U. S. Air Force used the aeroplane during the Korean War for close-support, ground attack missions but it was not suited for this dangerous mission. One of the Mustang's few vulnerable spots was the cooling system. A single bullet through a radiator or pipe was usually enough to down a P-51.
North American built more than 14,000 Mustangs and more D-models (8,302) than all other variants combined. The most significant D-model features were a rear fuselage reduced in height to accommodate a new bubble canopy and an increase in armament from 4 to 6 fifty-calibre machine guns. The Air Force did not withdraw P-51's from service until 1957.
Less than 300 P-51's exist today, about 145 flying.
The P-51D's power plant. Click images for an enlargement
The American built version of the renowned Rolls-Royce
Many famous Second World War aircraft were powered by the Merlin. First tested in October 1933, the engine was continuously developed & its power output more than doubled by the late 1940's. Both the Hurricane & the Spitfire were designed to use the Merlin engine & their brilliant performances were due, in no small part, to its combination of high power & compact dimensions.
In 1941, the RAF's Air Fighting Development Unit at Duxford tested the new American Mustang fighter & concluded that it had better potential than either the Spitfire or Hurricane if only it had an engine with good high-altitude performance. A conversion to fit the Merlin engine was made & the prediction proved correct.
Rolls-Royce concluded a licence agreement with Packard in the USA in September 1940, to produce engines primarily for Canadian-built bombers. As a result more than 13,000 Mustangs were supplied from the factory with American-built Merlins. Of the final total of over 168,000 Merlins constructed, 55,000 were manufactured by Packard & a further 30,000 by Ford of Britain at Trafford Park in Manchester.
12 cylinder with two-stage mechanically
1,650 hp (maximum hp 1,695)
Bore 5.4 inches (137.3 mm)
1,650 pounds (749 kg)
$25,000 (in 1940's Dollars)
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