- Yes, as a tech tree vehicle
- Yes, as a premium vehicle
- Yes, as an event vehicle
- Yes, as a squadron vehicle
- No, I would not like to see the XP-51G in game.
- Yes, I would
- No, I would not
- I voted no on the first question
Introduction
The story of the North American Aviation P-51 Mustang is a story of collaboration between the United States and United Kingdom, producing one of the most vital fighters for Allied operations in Europe and arguably the best fighter of World War II. The P-51D (Mustang Mk.IV) has cemented itself as a legendary aircraft, but even its designers recognized that it had room for improvement. The continuation of the Mustang saga began with the “Lightweight Mustangs” - the NA-105 prototype aircraft. As the Mustang had begun, so too would it evolve, with collaboration between NAA and Supermarine producing the fastest Mustang variants ever. The ancestor to the P-51H was trialed not only by the USAF but by the Royal Air Force in the form of both the XP-51F and XP-51G. This is the story of how the Mustang reached its zenith - and why the RAF wasn’t interested in it at all.
TL;DR
- High performance redesign of the venerable P-51
- Fastest Mustang variant ever
- Lighter weight and aerodynamic redesigns provide increased performance
- Reduced armament akin to the P-51C but with less ammo
- Lower wing loading for more agility
- Superior stalling characteristics
- Large, high mounted canopy for better visibility
- Rolls-Royce RM.14.SM gives similar horsepower to the P-51H without the water injection limit
History
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The history of the P-51 as a whole has further reading readily available, so its genesis does not require too much examination. The Mustang arose from Britain’s purchasing requirements for a new American fighter to supplement British equipment. Outsourcing production in this way would allow the RAF to take advantage of America’s excellent industry while being able to commit their home factories to existing designs like the Spitfire and Hurricane. However, none of the currently available (in the late 30’s) aircraft met British standards. Reluctantly, the British decided to buy some P-40 Tomahawks, but because Curtiss-Wright was using all of its production, they tried to source some license-built versions from North American Aviation. Instead, NAA promised a new fighter aircraft which could outperform the P-40, and after some back and forth on the design details, the P-51 was born.
The Mustang came into an element of its own once Rolls-Royce engineers installed Merlin 65 engines with two-stage supercharger to the five Mustang X prototypes, while NAA for their part installed Packard V-1650-3s (Merlin 61s) in two XP-51Bs. At altitude, the aircraft delivered speed improvements of around 50 miles per hour. Between the excellent high altitude performance and its very good fuel capacity, the USAAF became very interested in the Packard Merlin-powered Mustangs, producing the P-51B, then C, and eventually D variant which had a V-1650-7. However, the Mustang lineage underwent an interesting split even before the XP-51B had left the ground.
The question that prompted the beginning of the “Lightweight Mustang” was simple: why is the Mustang so much heavier than the Spitfire? Despite occupying similar footprints in terms of size, the Mustang was 1,500 pounds heavier empty and the disparity was even larger loaded (due to the Mustang’s greater fuel capacity). When the Spitfire was already struggling to deal with the Focke-Wulf Fw 190, the heavier and less maneuverable Mustang would surely fare no better. Edgar Schmeud, the Mustang’s chief designer, got the idea to create a new Mustang that weighed less while also investigating new engines to produce more power. The combined effect of both of these ideas would be a significant improvement in performance. Upon putting forward a proposal for a new design, known by the company code NA-105, Schmeud secured a contract from the USAF for five prototypes.
The NA-105 would be produced in three versions: the XP-51F, XP-51G, and XP-51J, the latter of which was added later on to test an Allison engine. In order to prepare for production, the NAA design team first had to figure out how to save weight in the first place. To this end, Schmeud visited Supermarine in Britain to examine the Spitfire for inspiration. After Supermarine had weighed the individual parts for the Spitfire, their findings were interesting - because British standards did not require the same structural rigidity as American aircraft, the components weighed less. Other weight savings were introduced by using new aluminum alloy for the plane’s skin, incorporating plastic components, using a thinner wing with redesigned shape, removing the fuselage fuel tank (though the wing fuel tanks were slightly increased in response) and lightening the ammo load to just 250 rounds per gun. In all, despite appearances, the NA-105 might as well have been a new aircraft. These changes resulted in a plane which, while still heavier than the Spitfire, was much closer to its weight than before, with an empty weight in the 5,700 pound range.
The XP-51G promised incredible performance due to its Merlin 100 powerplant. However, because of the engine’s temperamental nature, it took the XP-51G much longer to make ready than the XP-51F. Between its high-power engine and its significant weight reductions compared to the P-51D, the XP-51G handily outpaced it as the fastest Mustang ever, achieving a maximum level speed of 495 mph (797 km/h) compared to the P-51D’s 440 mph (708 km/h). In addition, the rate of climb was superior, with a time to 20,000 feet (6,100 m) of 3.4 minutes compared to 7.3 minutes for the P-51D. Maneuverability was enhanced by the lower wing loading, making the XP-51G a clear improvement over the P-51D for short range operations at nearly any altitude. Provision for drop tanks was kept in the event that the plane would be used for escort missions, though the significantly reduced internal fuel capacity would hamper its effectiveness.
The second XP-51G was sent over to the RAF in February 1945. Supermarine test pilots who took its cousin, the XP-51F, for a spin provided some insights on the airframe in general. Issues inherited from the XP-51F would include poor rudder/aileron control at high speed and a pointless hydraulic raised seat, while it would maintain the type’s exceptional stall control and innovative hydraulic sliding canopy. The main issue with the XP-51G was not its performance or even lack of range, but rather the engine. The RM.14.SM wasn’t fully developed at the time and would require further refinements before it could be applied to British planes like the Hornet in the form of the Merlin 130. Even if it was functional and ready for production, the XP-51G would have had to contend with late model Spitfires and jet powered planes like the Meteor and Vampire. Meanwhile, Packard made their own experiments with water injection and created the V-1650-9 engine which was chosen to power the P-51H, the most potent service Mustang. The RAF struck FR410 off charge in 1947, ending the lightweight Mustang program for good. Had the Merlin 100 been ready earlier, the XP-51G almost certainly would have found an American order and maybe even a British one. Unfortunately, this is another “what if” to add to a long list of aviation industry ventures.
Specifications
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North American Aviation XP-51G
Dimensions:
- Length: 32 ft 3 in (9.82 m)
- Span: 37 ft 0 in (11.29 m)
- Height: 13 ft 8 in (4.17 m)
Weight:
- Empty: 5,750 lb (2,608 kg)
- Loaded: 8,885 lb (4,030 kg)
Propulsion: 1 x Rolls-Royce RM.14.SM 12-cylinder inline engine
- Takeoff horsepower: 1,700 hp
- Max combat power: 2,200 hp
Maximum speed: 495 mph (797 km/h) at 25,000 ft (7,620 m)
Ceiling (estimated): 44,800 ft (13,655 m)
Armament (provisional):
- Guns:
- 4 x .50 caliber (12.7 mm) AN/M2 Browning heavy machine gun (250 rounds per gun, 1,000 rounds total)
- Drop tanks:
- 2 x 75 gallon (284 liter) drop tanks
Crew: 1
Additional equipment: N/A
Why it should be in the game
The XP-51G would provide an interesting lighter weight version of the Mustang to the British and/or American tech trees at superprop tier. With similar power to the P-51H, enhanced stalling characteristics, and lighter weight, the XP-51G will be by far the best dogfighting Mustang in the game. However, pilots would have to be conservative with their ammo as the provisions for 250 rounds/gun are not as ample as other Mustang variants or U.S. planes in general. As I said in the introduction, the Mustang is a story of Allied cooperation and I would personally be happy to see this plane and its cousin, the XP-51F, in both tech trees.
Sources
- The Mustang that might have been
- [2.0] The Merlin Mustangs
- North American XP-51F, G, J Mustang
- THE LIGHTWEIGHT MUSTANG PROGRAMME - Mustang: Thoroughbred Stallion of the Air
- North American XP-51G : North American
- Mustang XP-51F/G/J prototypes | Secret Projects Forum
- North American XP-51G
- Various charts from P-51 Mustang Performance