page_title: North American P-51 Mustang variants
section_title: XP-51F, XP-51G and XP-51J
hierarchical_section_title: North American P-51 Mustang variants / The "lightweight" Mustangs / XP-51F, XP-51G and XP-51J
caption_attribution_description: XP-51F
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: The lightweight Mustangs had a new wing design. The airfoil was switched to the NACA 66,2-(1.8)15.5 a=.6 at the root and the NACA 66,2-(1.8)12 a=.6 at the tip.  These airfoils were designed to give less drag than the previous NAA/NACA 45-100.  In addition, the planform was a simple trapezoid, with no leading edge extension at the root.
  In 1943, North American submitted a proposal to redesign the P-51D as model NA-105, which was accepted by the USAAF. Modifications included changes to the cowling, a simplified undercarriage with smaller wheels and disc brakes, a larger canopy, and an armament of four .50 Brownings. In total the design was some 1,600 lb (730 kg) lighter than the P-51D. In test flights, the NA-105 achieved 491 mph (790 km/h) at 21,000 ft (6,400 m). The designation XP-51F was assigned to prototypes powered with V-1650 engines (a small number were passed to the British as the Mustang V), and XP-51G to those with Merlin RM 14 SMs.
  A third lightweight prototype powered by an Allison V-1710-119 was added to the development program. This aircraft was designated XP-51J. Since the engine was insufficiently developed, the XP-51J was loaned to Allison for engine development. None of these experimental lightweights went into production.
caption: An XP-51F (one of three built) with three-bladed Aeroproducts propeller
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