HISTORY

With the threat of war in Europe growing day by day at the end of the 1930s, British manufacturers found that they could not keep up with the demands of a rapidly expanding air force so attention turned to the United States as a source of additional aircraft. After assessing the available fighters, the New York based British Purchasing Commission ordered substantial numbers of the Curtiss P-40 in 1939. The US Army Air Corps had already placed a large order for the P-40 and Curtiss was unable to produce the number of aircraft that the Royal Air Force required so the British decided to look for a manufacturer to licence build it for them. Attention turned to the North American Aviation Corporation. North American was already building NA-16 Harvard trainers for the RAF but was not keen on the idea of building P-40s. Earlier studies had indicated that the company could design and build an entirely new aircraft that would be better than the P-40 while still using the same Allison V-1710 engine, all in the same time it would have taken to set up a P-40 production line. James "Dutch" Kindelberger, the president of North American, submitted the proposal to the British in January 1940 and on April 10 of the same year, approval was granted to design and build a prototype on the condition that it had to be ready in 120 days.

The speed of the design and construction of the NA-73X was mainly due to the fact that, as mentioned previously, North American had already spent almost a year doing initial design work during their fighter project studies. In a contract approved on September 20, 1940, it was agreed that the fourth and tenth production Mustang Is would be the aircraft transferred to the USAAC and receive the designation XP-51. Meanwhile, the RAF increased their Mustang I order to 620 aircraft on September 24, 1940 and then in December of the same year they increased the order by a further 300. On October 26, 1940, test pilot Vance Breese flew the prototype for the first time and in spite of having the same engine, it was 25 mph faster than the P-40. Further testing, modifications and fine tuning were carried out before the first production Mustang I took to the air on May 1, 1941.

One feature that made the Mustang unique among most of its contemporaries was its use of a laminar flow wing. This was an aerofoil that was made as smooth as possible and had a thickness that kept on increasing far beyond the usual location. (50 percent chord rather than the usual 20 percent). In addition, the wing had very little camber with the underside being almost a mirror image of the upper. In theory, this wing was much more "slippery" than the old profiles, providing less aerodynamic drag at high speeds. However, it provided less lift at low speeds so large and powerful slotted flaps had to be fitted to keep landing speeds from being impractically high.

Following the Japanese attack on Pearl Harbour in December 1941 and America's entry into World War Two, military production in that country was stepped up phenomenally. Consequently, by the time the USAAF decided that they wanted the Mustang, there was no money left in the fighter budget. There was, however, still money available for attack aircraft so the A-36A, a dive bomber variant of the P-51 was developed. This was essentially just a way of getting the P-51 into USAAF service, as they had no real need for a dive bomber.

The Mustang (the name being adopted by the USAAF around mid 1942) soon proved to have one major weakness, its Allison engine. As mentioned previously, the Allison's poor high altitude performance and unsatisfactory rate of climb meant that the aircraft were relegated to the low-level ground attack and reconnaissance role. On April 30, 1942 Ronald W. Harker, a test pilot for Rolls Royce, took a brief flight in a Duxford based RAF Mustang and suggested that it would be a natural choice for the new 2-stage supercharged Merlin 60 series of engines that Rolls Royce were just beginning to produce. Intrigued by the idea, Rolls Royce asked to borrow three Mustangs from the RAF so that they could experiment with fitting and testing various Merlin engines. The standard production model's 3-blade propeller was replaced with a 4-blade one to absorb the extra power of the Merlin and the supercharger intercooler radiator and air intake for the carburettor were mounted together under the nose (the carburettor intake on Allison powered Mustangs was mounted on top of the nose). The change in the performance of the Merlin powered aircraft was amazing; the power drop off problem of the Allison engine Mustangs was cured with a 490 hp increase in power at 25,000 feet. During testing at Boscombe Down, it reached a level speed of 433 mph and took 6.3 minutes to climb to 20,000 feet, about two thirds of the time taken by production models. Torque from the more powerful engine and new propeller did have a detrimental affect on the directional stability of the Mustang X, this was soon cured by the addition of a small dorsal fin just in front of the tail.

Rolls Royce proposed the production of 500 Merlin 65 engines to be fitted to most of the RAF's Mustang fleet, bringing them up to Mark X standard. Unfortunately, because of wartime pressures, there was nowhere available in Britain to do the conversions so the idea was scrapped. However, North American Aviation, who had been had been fully briefed by Rolls Royce on the Mustang X project, had started planning their own Merlin powered Mustangs. On July 25, 1942, they received authorisation to install Merlin 65 engines imported from England into the two P-51s that had not gone to the RAF or USAAF. The aircraft initially received the designation XP-78 but this was later changed to the XP-51B. Unlike the situation in Britain, a ready supply of Rolls Royce engines was available from the Packard Motor Car Company of Detroit, Michigan who had signed a deal to licence build the Merlin in the United States. North American now had source of engines for the new XP-51B and based partly on this, as well as on estimated performance, an order for 400 P-51B Mustangs was placed in August 1942, before the first prototype had even flown.

The first XP-51B, powered by a 1,590 hp Packard Merlin V-1650-7, flew on November 30, 1942 and the increase in performance over earlier Mustangs was even greater than that achieved with the Mustang X. It achieved a level speed of 441 mph at 29,800 feet, over 100 mph faster than the Allison powered P-51 at the same altitude and at all heights, the rate of climb was almost doubled. Design changes included moving the carburettor air intake to below the nose to accommodate the new engine's updraft induction system and the addition of an intercooler radiator located in an enlarged under-fuselage duct that also housed improved coolant and oil radiators. By mid 1943, it was becoming clear that American heavy bombers of the 8th Air Force could not protect themselves adequately on daylight raids over Germany and were in desperate need of fighter escort. With its already exceptional range, the Mustang was a prime candidate for this role. The P-51B and C had an 85 US gallon self-sealing fuel tank installed behind the pilot's seat, bringing the total fuel capacity (including two drop tanks) to 419 US gallons. With the extra fuel, the Mustang was now able to accompany Boeing B-17 Flying Fortress and Consolidated B-24 Liberator bombers on the 1,100 mile round trip to Berlin. This came as a nasty shock to the German defenders. As reports of the first dogfight over German soil reached Hitler's deputy and head of the Luftwaffe, Reichsmarshall Hermann Goering, he refused to believe them. He was adamant that no Allied fighter had the range to fly so far into Germany. When he was finally convinced this was true, he was reported to have muttered, "We have lost the war."

Large numbers of P-51Ds began arriving in Europe from March 1944 and it was one of the few allied fighters to shoot down the Messerschmitt Me-262 jet fighter/bombers. With a speed difference of almost 100 mph, the Mustang was unable to compete on equal terms in the air. It easily out turned the jet but usually only got the chance for one quick burst of fire before the jet made its getaway.

New Zealand's involvement with the Mustang began in August - September 1945 when the RNZAF received the first 30 P-51Ds of what was to have been a total order of 370 intended to replace the F-4U Corsair. However, by the time they had finally arrived, the war was over and all 30 aircraft were promptly mothballed with the remainder of the order being cancelled. They were reactivated in 1951 and served with four Territorial Air Force squadrons until an 'alleged' undercarriage fault caused them to be removed from service in 1955 (although four remained at Ohakea with No. 42 Squadron as drogue tugs until early 1957). Finally, all surviving RNZAF Mustangs (with the exception of 3) were sold as scrap in 1958.

Our aircraft is painted in the colour scheme of NZ2415 from No. 3 Squadron (TAF), flown in the early 1950's by Squadron Leader Ray Archibald, the squadron's CO. It was originally built in 1944 at Inglewood (P-51D-30-NA, Ser no 44-74829, c/n 122-41369) and served with the Royal Canadian Airforce. It was imported into New Zealand in 1984 by Sir Tim Wallis and first flew here in January, 1985. Tim Wallis subsequently sold the aircraft and it was operated by a trust set up to keep it in the country, before passing to an Ardmore based syndicate.