North American XP-51J Mustang - The Experimental Lightweight Mustang (III)

[Nostalgistic]

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North American XP-51J Mustang

   Hello all! I’d like to suggest the North American XP-51J Mustang for US aviation in War Thunder. It was the third and final member of the three experimental lightweight Mustang models evaluated by the US Army Air Forces. In short, the XP-51J was developed late as a lightweight derivative of the P-51D, much like the XP-51F and XP-51G, to achieve improved performance with the new Allison V-1710-119 engine. Lessons learned from this engine and aircraft combination led to further refinements and its successful application in the P-/F-82 Twin Mustang family.

History

The success of the early Merlin-powered Mustangs led the Allies to appreciate their superior performance compared to the Allison-powered variants. However, concerns arose over the steady weight growth of the Mustang throughout its development into the P-51D/K models. These newer Mustangs found themselves outclimbed by Spitfires (by approximately 1,200 fpm) and outrolled by the Fw 190, which had nearly twice the roll rate. The RAF first approached North American in January 1943 regarding the possibility of a lightweight Mustang design, with the goal of reducing overall gross weight. This request eventually evolved into a joint program when the Army Air Forces formally initiated the contract and program management.

Three XP-51F prototypes, designated NA-105 by North American, were ordered on January 3, 1943, under MX-356 as the formal US Army project designation, before the first P-51D had even been produced. Consequently, the P-51E designation was skipped and never brought to fruition. In June 1943, the XP-51F contract was amended to include five aircraft (43-43332 through 43-43336) powered by the 1,380 hp V-1650-3. This was later changed to the 1,490 hp V-1650-7 while the aircraft were still under construction. The British also agreed to supply five 1,675 hp RM.14SM Merlin engines, which would power the final two aircraft of the amended order, designated XP-51G (NA-105A). The RAF requested one example of each model for its own testing.

Both the XP-51F and XP-51G completed their first flights in the summer of 1944. They were evaluated by the US Army Air Forces and the RAF, but neither type entered full-scale production. With experience gained from these aircraft, the USAAF decided to order two additional lightweight Mustang derivatives, bringing the total number of aircraft under the XP-51F/G contract to seven. The USAAF was particularly interested in evaluating a version powered by the new Allison V-1710-119 engine, which was designated XP-51J.

The XP-51J was essentially an XP-51F airframe mated to the V-1710-119 engine, which featured a two-stage supercharger and water injection. The engine was rated at 1,500 hp for takeoff and 1,720 hp with water injection at 20,700 feet. Installation of the new powerplant lengthened the fuselage by several inches and slightly increased the aircraft’s weight. Externally, the XP-51J could be distinguished by the absence of the carburetor air intake beneath the spinner. Instead, the carburetor air intake was relocated to the ventral radiator duct. The XP-51J retained the redesigned wings of the XP-51F, restricting internal armament to four 0.50-caliber machine guns. A dorsal fin extension was also fitted.

The first XP-51J (44-76027) was completed and made its maiden flight on April 23, 1945. However, the V-1710-119 engine was still immature and prohibited from operating at full power. It was flown again on December 19, 1945, before the aircraft was subsequently loaned to Allison Engine Plant at Indianapolis, Indiana, for additional engine testing and refinement on January 8, 1946. The second XP-51J (44-76028) was never flown and instead served as a source of spare parts to support continued testing of the first aircraft.

After many of the engine’s deficiencies had been corrected, the XP-51J resumed flight testing. It was first flown on January 29, 1946, and for the second time on January 31. However, with the war already at its end and the P-51H already entering full-scale production with the Packard-built Merlin V-1650-9, there was little justification for placing the XP-51J into production. Nevertheless, experience gained by Allison during the development of the V-1710-119 contributed to further refinements of the engine series, which ultimately powered all production Twin Mustangs from the P-/F-82E onward.

Specifications

North American XP-51J Mustang

General Characteristics

• Crew: 1 (Pilot)
• Dimensions:
  • Length: 32 ft 11 ft (10.03 m)
  • Height: 13 ft 8 in (4.17 m)
  • Wingspan: 37 ft (11.28 m)
  • Wing Area: 233 sq ft (21.64 sq m)
• Propeller: 1 x four-bladed Aeroproducts A-542-B1 propeller
• Powerplant:
  • Type: 1 x Allison V-1710-119, two-stage supercharged, water-injected
  • Power Output:
    • @ Takeoff
      • 1,500 hp (1,520.81 PS) @ 3,200 RPM @ S.L. @ 58.0 hg
    • @ Combat
      • 1,720 hp (1,743.86 PS) @ 3,200 rpm @ 20,000 ft (6,096 m)
• Fuel Capacity:
  • 180 US-gal (681 L)
• Weight:
  • Empty: 6,030 lb (2,735 kg)
  • Gross: 7,550 lb (3,425 kg)
  • Max. Takeoff: 9,140 lb (4,146 kg)

Flight Performance

• Power-to-Weight Ratio: 0.23 hp/lb (0.51 ps/kg)
• Wing Loading: 32.4 lb/sq ft (158 kg/sq m)
• Max Speed:
  • 471 mph (790 km/h) @ 27,400 ft (8,352 m)
• Climb Performance:
  • Rate of Climb: 4,000 fpm (20.3 m/s)
  • Time to Altitude: 5 minutes to 20,000 ft (6,096 m)
• Service Ceiling: 43,700 ft (13,320 m)

Armament

• Guns:
  • 4 x 0.50-cal M2 Browning machine guns (250 rpg; 1,000 rds)
• Bombs:
  • 2 x 500-lb bombs
• Drop Tanks:
  • 2 x 75 US-gal drop tanks

Images

Related Suggestions

• XP-51
• P-51A-10
• P-51B-1
• P-51B-5 (Malcolm Hood)
• P-51C-10 (Malcolm Hood + Dorsal Fin)
• XP-51F
• XP-51G

Sources

1. Bert Kinzey, P-51 Mustang Part 3: P-51D and Subsequent Variants, Detail & Scale Series Volume 23 (2026)
2. Malcolm V. Lowe, North American P-51 Mustang, Crowood Aviation Series (2009)
3. Bill Norton, US Experimental & Prototype Aircraft Projects: Fighters 1939-1945 (2008)
4. David McLaren, North American P-51H Mustang: Includes Lightweight Fighters XP-51F, XP-51G, & XP-51J, Air Force Legends Number 209 (2003)
5. William Green & Gordon Swanborough, The Complete Book of Fighters: An Illustrated Encyclopedia of Every Fighter Aircraft Built and Flown (2001)
6. Francis H. Dean, America’s Hundred Thousand US Production Fighters of WWII (1997)
7. Graham White, Allied Aircraft Piston Engines of World War II (1995)
8. Robert F. Door, US Fighters of World War Two (1991)
9. F.G. Swanborough, United States Military Aircraft Since 1909 (1989)
10. Enzo Angelucci, The American Fighter: The Definitive Guide to American Fighter Aircraft from 1917 to the Present (1987)
11. P-51 Mustang in Action, Aircraft No. 45, Squadron/Signal Publications (1981)
12. William Green & Gordon Swanborough, World War Two Fact Files - US Army Air Force Fighters Part 2 (1978)
13. William Green, War Planes of the Second World War Fighters Volume Four (1973)
14. North American XP-51F, G, J Mustang

Thank you for taking the time to read my suggestion! 😃

[CharAznable3]

great post

[BACKRAGE44428-live]

+1 please techtree

[BasherBenDawg8]

+1 for the last of the experimental lightweights, hope to see it ingame with the others!

[GTP_Paulie-psn]

790km/hr

[Scärlett]

@Nostalgistic

Max Speed:

• 471 mph (790 km/h) @ 27,400 ft (8,352 m

+1
this so cool plane and very fast 790km o.o

i wonder what br mr snail will put it at like 6.3?

[Nostalgistic]

@Scärlett

i wonder what br mr snail will put it at like 6.3?

Could be. Or 6.0, I don’t know. I cannot predict where Gaijin will put it.

Do note that its ammunition capacity is lower than the F8F-1 Bearcat’s.

[CharAznable3]

But at what cost?

What did they gut to get this way? Only 4 M2 (with late war belts) 250 rpg is a issue. I think reading somewhere the Lightweight mustangs had some other stuff cut or swapped out as the goal was to push the design to the limit. One might have been the armor.

I will try to find the article. might have been another program.

[RDXRooster63]

@Nostalgistic

Max Speed:

• 471 mph (790 km/h) @ 27,400 ft (8,352 m)

bro 790km/h is fast as hell holy…

@Nostalgistic

Time to Altitude: 5 minutes to 20,000 ft (6,096 m)

that engine is crazy

@Nostalgistic

Guns:

• 4 x 0.50-cal M2 Browning machine guns (250 rpg; 1,000 rds)

uhm…P-51A has more ammo

+1 for a speed demon