Comments by "John Burns" (@johnburns4017) on "What made the P-51 Mustang so special?" video.
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The Mustang was basically a British plane they had made in an American factory as UK factories were working 24/7. The British Air Ministry directed a six year old inexperienced company, North American Aviation, to the design points they wanted for their plane. British engineers assisted North American engineers who formulated the design in the British office in New York City over three months. Its prime aim was range so large fuel tank were designed as a part of the plane's structure. The Mustang was a British plane made by an American company for them. There was no US forces involvement in the concept, specifications or design. Many Americans lose sight of these fundamental points.
The Rolls Royce Merlin engine made the Mustang perform superbly. The plane initially used an Allison engine, which was only good at low level. The US were behind the British in engine supercharging with the Tizard Mission giving the USA details of advanced super charging. Also the cylinder head design of the Alison was not good enough for full supercharging. Stanley Hooker of RR developed the auto controlled twin-speed twin-charger supercharging technology which was given free to the USA. The first use of the Mustang by the US military was for ground attack because of the poor high level performance of the Allison engine.
https://www.youtube.com/watch?v=by4lH2whhjk
In the early stages of WW2, the U.S. government allowed the British & French to by-pass them, allowing direct approaches to U.S. aircraft makers, as would the British government approach say Hawker. The British needed all types of planes urgently, even the P-40 which was inferior to their own front line planes. But warplanes they were, being useful in certain theatres and for training.
In early February 1940 the British asked North American Aviation's President Dutch Kindelberger to supply P-40s made under licence from Curtiss, as Curtiss could not supply demand. Unlike Curtiss, North American's factory was far from operating at full capacity. Kindelberger told the British, without any detailed design drawing, "I can build you a better airplane, and I can get it built fast". Contrary to popular belief in the USA, North American did not have a prototype ready design which the Brits just happened to have snapped up under the noses of the US military. The design was developed over three months with British engineers at the British Air Ministry's offices in New York City.
North American were first approached in Jan 1940, who had no "detailed drawings or plans". The British gave this young inexperienced company, who had never designed and built a complete combat plane a chance, but they would have to hold their hands. In Feb 1940 North American still never presented any detailed plans, mailing a design concept drawings to the British delegation in New York. This never had the famed laminar flow wings. The Air Ministry accepted the concept starting the Mustang project. The British Air Ministry accepted the inferior Allison engine as Rolls Royce were working flat out 24/7 unable to meet demand for Merlins. New Merlin shadow factories were being set up, and one in the USA, but not yet fully on-line.
In the interim from Feb to May, three months, the British Air Ministry were forming the fundamentals of the design concepts directing North American to Curtiss and NACA the developer of the laminar flow wings, to ensure a fighter with some leading edge design points, not produce another P-40 fly-alike wasting valuable time. The Air Ministry directed NAA to the Curtiss XP-46 experimental plane with all the leading edge design points of top European designs, with a few of their own, rolled into one.
NAA were ordered by the British Air Ministry to buy the plans and test results of the XP-46 plane from Curtiss and study them as they had never built a fighter, if they wanted the job, at a whopping $56,000, a lot of money at the time. Curtiss engineers always said the Mustang was their design. Not quite as the British Air Ministry had a lot to say in the leading design points - they were paying and calling the shots as it was their plane. There was a danger the Mustang may end up the same way as the XP-46 - a plane with leading edge points that never performed as expected. The plane needed to have long range built into the design. The British Air Ministry took a major gamble with NAA so were active in approving the emerging design points.
The Ministry wanted something better than the poor P-40, being prepared to wait, but realistically never expected Spitfire performance. Initially that was the case with the first deliveries using the Allison engine - better than a P-40 but no Spitfire. The initial Allison engined Mustangs filled an RAF niche, so no problems for the British at that point. A niche the plane filled was that the RAF needed a long range reconnaissance plane that could also perform ground attack being able as a low level fighter if the need was there. The Spitfire was a short range fast interceptor. With the fall of France the RAF needed a plane with range to penetrate over the German border from English air bases, they would now have one.
Reading many US books on the Mustang you would think the concept of the plane was to escort US bombers. That is way off from the truth. The last thing the British Air Ministry were thinking of when laying down the points of the plane was US bomber doctrine. The US were not even in the war. Initially the US military overall didn't want to know the plane. The British gave a handful to the Soviets before the USA was in the war who turned their noses up at it. The Mustang was not even in U.S. service when it was shooting down FW-190s by the RAF over France. The Air Ministry gave the U.S. military two planes which were left in the corner of a hangar for a long period, initially not assessed it. Quite amazing, as the USA never had a decent front line fighter at the time.
The excuse not to take up the plane by U.S. forces was that it was liquid cooled and vulnerable in frontal attack. This was a poor excuse to reject the plane because it wasn't theirs. What went over their heads was that the world's two best fighters locked horns in the Battle of Britain, both with liquid cooled engines. With British support, the Mustang finally was noticed by the U.S. Army Air Force. The US military had to go to England to fully assess the plane as it was finished off in Liverpool being flow by the RAF. They did eventually adopt the plane calling it the Apache and P-51 when in U.S. service.
UK and U.S. Mustangs for the European war theatre were finished off in Liverpool. They were test flown then delivered to the units by young English girls, many of them teenagers. The Mustang was built to British specification and design guidance without a doubt. They specified and paid for it. It never performed at all like the short range interceptor the Spitfire, not having the maneuverability of the Spitfire and was about useless above 15,000 feet. It was 'fine' and reasonably fast at low altitude with the Allison engine. It could operate over France and even Germany at a push, escorting bombers because of the longer range that the British Air Ministry specified. The Mustang filled an initial niche role for the British. continued......
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...Continued...
Rolls Royce. Rolls engineers under Ron Harker went to North American to advise on how to install a Merlin engine in the Mustang. They also gave advice from their work with the RR Mustang X. Rolls-Royce made the first proposal to North American regarding a Merlin 45 engine Mustang in 1940, after Stanley Hooker improved the power by 30%. This was before the plane was operational an still in the R&D stage. The RR Merlin was superior to the Alison engine, also to what it was in February 1940 when North American were first approached by the Air Ministry. The later Merlin 61 had the two-stage auto controlled supercharging developed by again by Stanley Hooker. This gave an extra 70 mph and 15,000 feet of operation to the Merlin. A quantum leap. The pilot just went where he liked without degradation in performance.
RR sent three engineers led by James Ellor to supervise the adaption and manufacture of a Merlin 61, built under licence in Detroit, the same type that was already being considered for the Rolls Royce Mustang X experimental series.
On 9 June 1942, the first memos from W/C I.R. Campell-Orde of the RAF Air Fighting Development Unit at Duxford, revealed that an effort was being made to convince North American to adopt a Merlin-powered Mustang. Work in the US was setback due to an initial lack of interest and also to mechanical failures of the first Merlin engines built under licence in the USA. Both projects commenced at nearly the same time with the first Mustang X in the air about a month earlier than the North American XP-51B.
The RR Mustang-X programme was 5 or 6 airframes each with different experimentation. RR attempted to have North American accept British Merlin 61s (the two-stage superchargers) in American airframes, it is clear that the prime contractor (NAA) wanted to control the project as control was looking like it was to move over to the UK. NAA was essentially building production-standard aircraft rather than the experimental series that saw each of the RR Mustang Xs trying out new variations of design. An offshoot was the mid-engine RR Griffon engined Mustang that actually made it to the mock-up stage, albeit with a Merlin installed amidships. On the success of the RR Mustang-X built in Nottingham, the Air Ministry ordered hundreds from RR, who declined wanting to remain specialising in engines. NAA remained the prime contractor.
Rolls Royce mass produced Merlins in Crewe, Manchester and Glasgow, also licensing Packard in the USA, using idle US industry. The US made Merlins were to supply the Canadian aircraft factories - to avoid a two-way trans-Atlantic trip and give extra manufacturing when the engine proved very popular with many airframe makers. An agreement was reached in September 1940, with the first Packard built Merlin engine running in August 1941.
Early in 1944 the P-38, P-51B Mustang and P-47C, were dived by the British for compressibility testing at the RAE Farnborough, England at the request of the USAAF. They had trouble when these planes dived onto attacking German fighters when providing top cover for the bombers. The results were that the Mach numbers, the maneuvering limits, were Mach 0.68 for the P-38, Mach 0.71 for the P-47, and Mach 0.78 for the Mustang. The corresponding figures for the FW-190 and Me109 was Mach 0.75. The tests resulted in the Mustang being chosen for all escort duties. - Page 70, Wings On My Sleeve by Eric Brown, who did the test.
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