page_title: North American P-51 Mustang variants
section_title: Experimental Mustangs
hierarchical_section_title: North American P-51 Mustang variants / Experimental Mustangs
caption_attribution_description: North American P-51A-NA, ski modification, side view (SN 43-6003). First -A model built
context_page_description: Over twenty variants of the North American P-51 Mustang fighter were produced from 1940, when it first flew, to after the Second World War, some of which were employed also in the Korean War and in several other conflicts. Numerous examples of the aircraft survive to this day, often as heavily modified air racers.
context_section_description: In early 1944, the first P-51A-1-NA, 43-6003. was fitted and tested with a lightweight retractable ski kit replacing the wheels. This conversion was made in response to a perceived requirement for aircraft that would operate away from prepared airstrips. The main oleo leg fairings were retained, but the main wheel doors and tail wheel doors were removed for the tests. When the undercarriage was retracted, the main gear skis were housed in the space in the lower engine compartment made available by the removal of the fuselage .50 in (12.7 mm) Brownings from the P-51As. The entire installation added 390 lb (180 kg) to the aircraft weight and required that the operating pressure of the hydraulic system had to be increased from 1,000 to 1,200 psi (6,900 to 8,300 kPa)). Flight tests showed ground handling was good, and the Mustang could take off and land in a field length of 1,000 ft (300 m); the maximum speed was 18 mph (29 km/h) lower, although it was thought that fairings over the retracted skis would compensate.
  Concern over the USAAF's inability to escort B-29s all the way to mainland Japan resulted in the highly classified "Seahorse" project (NAA-133), an effort to "navalize" the P-51.  On 15 November 1944, naval aviator (and later test pilot) Lieutenant Bob Elder, in a P-51D-5-NA 44-14017, started flight tests from the deck of the carrier Shangri-La. This Mustang had been fitted with an arrestor hook, which was attached to a reinforced bulkhead behind the tail wheel opening; the hook was housed in a streamlined position under the rudder fairing and could be released from the cockpit.  The tests showed that the Mustang could be flown off the carrier deck without the aid of a catapult, using a flap setting of 20° down and 5° of up elevator. Landings were found to be easy, and, by allowing the tail wheel to contact the deck before the main gear, the aircraft could be stopped in a minimum distance. The project was canceled after U.S. Marines secured the Japanese island of Iwo Jima and its airfields, making it possible for standard P-51D models to accompany B-29s all the way to the Japanese home islands and back.
  While North American were concentrating on improving the performance of the P-51 through the development of the lightweight Mustangs, in Britain, other avenues of development were being pursued. To this end, two Mustang Mk IIIs (P-51Bs and P-51Cs), FX858 and FX901, were fitted with different Merlin engine variants. The first of these, FX858, was fitted with a Merlin 100 by Rolls-Royce at Hucknall; this engine was similar to the RM 14 SM fitted to the XP-51G and was capable of generating 2,080 hp (1,550 kW) at 22,800 ft (7,000 m) using a boost pressure of +25 lbf/in² (170 kPa; 80 inHg) in war emergency setting. With this engine, FX858 reached a maximum speed of 455 mph (732 km/h) at 17,800 ft (5,425 m), and 451 mph could be maintained to 25,000 ft (7,600 m). The climb rate was 4,500 ft/min (22.9 m/s) at 1,600 ft (486 m) and 4,000 ft/min (20.3 m/s) at 13,000 ft (3,962 m). 
  FX901 was fitted with a Merlin 113 (also used in the de Havilland Mosquito B.35). This engine was similar to the Merlin 100, fitted with a supercharger rated for higher altitudes. FX901 was capable of 454 mph (730 km/h) at 30,000 ft (9,100 m) and 414 mph (666 km/h) at 40,000 ft (12,200 m).
caption: The P-51A-NA modified with skis
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