page_title: North American P-51 Mustang variants
section_title: P-51D and P-51K
hierarchical_section_title: North American P-51 Mustang variants / Merlin-engined Mustangs / P-51D and P-51K
caption_attribution_description: English: North American P-51D prototype in flight SN 43-12102; Modified P-51B
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: Following combat experience the P-51D series introduced a "teardrop", or "bubble", canopy to rectify problems with poor visibility to the rear of the aircraft. In America, new moulding techniques had been developed to form streamlined nose transparencies for bombers. North American designed a new streamlined plexiglass canopy for the P-51B which was later developed into the teardrop shaped bubble canopy. In late 1942, the tenth production P-51B-1-NA was removed from the assembly lines. From the windshield aft the fuselage was redesigned by cutting down the rear fuselage formers to the same height as those forward of the cockpit; the new shape faired in to the vertical tail unit.  A new simpler style of windscreen, with an angled bullet-resistant windscreen mounted on two flat side pieces improved the forward view while the new canopy resulted in exceptional all-round visibility. Wind tunnel tests of a wooden model confirmed that the aerodynamics were sound.
  The new model Mustang also had a redesigned wing; alterations to the undercarriage up-locks and inner-door retracting mechanisms meant that there was an additional fillet added forward of each of the wheel bays, increasing the wing area and creating a distinctive "kink" at the wing root's leading edges. 
  Other alterations to the wings included new navigation lights, mounted on the wingtips, rather than the smaller lights above and below the wings of the earlier Mustangs, and retractable landing lights which were mounted at the back of the wheel wells; these replaced the lights which had been formerly mounted in the wing leading edges.
  The engine was the Packard V-1650-7, a licence-built version of the Rolls-Royce Merlin 60 series, fitted with a two-stage, two-speed supercharger.
  The armament was increased with the addition of two more .50 in (12.7 mm) AN/M2 "light-barrel" M2 Browning machine guns, the standard heavy-calibre machine gun used throughout the American air services of World War II, bringing the total to six. The inner pair of machine guns had 400 rounds per gun, and the others had 270 rpg, for a total of 1,880. The B/C subtypes' M2 guns were mounted with an inboard axial tilt, this angled mounting had caused problems with the ammunition feed and with spent casings and links failing to clear the gun-chutes, leading to frequent complaints that the guns jammed during combat maneuvers. The D/K's six M2s were mounted upright, remedying the jamming problems. In addition, the weapons were installed along the line of the wing's dihedral, rather than parallel to the ground line as in the earlier Mustangs.
  The wing racks fitted to the P-51D/P-51K series were strengthened and were able to carry up to 1,000 lb (450 kg) of ordnance, although 500 lb (230 kg) bombs were the recommended maximum load.  Later models had removable under-wing 'Zero Rail' rocket pylons added to carry up to ten T64 5.0 in (127 mm) H.V.A.R rockets per plane. The gunsight was changed from the N-3B to the N-9 before the introduction in September 1944 of the K-14 or K-14A gyro-computing sight. Apart from these changes, the P-51D and K series retained V-1650-7 engine used in the majority of the P-51B/C series.
  The addition of the 85 US gallon (322 l) fuselage fuel tank, coupled with the reduction in area of the new rear fuselage, exacerbated the handling problems already experienced with the B/C series when fitted with the tank, and led to the same fillet being added to -B, -C and initial -D-series versions in the field, to be quickly standardized as a normal rear-fuselage airframe component on later production blocks of the -D version. P-51Ds without fuselage fuel tanks were fitted with either the SCR-522-A or SCR-274-N Command Radio sets and SCR-695-A, or SCR-515 radio transmitters, as well as an AN/APS-13 rear-warning set; P-51Ds and Ks with fuselage tanks used the SCR-522-A and AN/APS-13 only.
  The P-51D became the most widely produced variant of the Mustang. A Dallas-built version of the P-51D, designated the P-51K, was equipped with an 11 ft (3.4 m) diameter Aeroproducts propeller in place of t
caption: The tenth production P-51B 43-12102, prototype for the P-51D, showing the modified rear fuselage and new canopy and windscreen.
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