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P51 Mustang, what if?


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2 minutes ago, Aerofix said:

A shame really that jet fighters came along just as piston engines were reaching their peak. 

 

It's not really true that piston engines were reaching their peak, simply the advent of jet engines stopped certain developments of piston engines as the advantages they could bring were overshadowed by the much larger advantages of jet engines. At the same time the development of the piston engine continued with other applications in mind, before being stopped again by the introduction of turboprops and jets in transport types.

Had jets not appeared, piston engines for military aircraft would have developed continuously and they would have reached levels unimaginable in the late '40s. Think of what kind of engines could be designed and built today, with much better materials available and a better knowledge of the aerodynamics of ducts and combustion chambers, the peak would have not been reached yet.

Of course there would still be the matter of building a propeller driven aircraft capable of exceeding Mach 1, a problem that the advent of jet engines made irrelevant

 

Types like the MB.5 and the CA.15 are sure fascinating, and even more fascinating are some more extreme types, like the P-75 or the Boeing F8B. They make for interesting modelling subjects, both in their original form and as basis for what-if models. Had they entered service we'd sure see more kits of these types but at some points there would have been oher piston engined types developed to replace them... it was not to be as jets were so much superior

 

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1 hour ago, Giorgio N said:

One thing I often wonder is how actually useful could a Griffon be on the Mustang. The V-1650 variant used on the P-51H was very close to the Griffon in terms of power, why introduce a new larger engine when the one already in production can be brought to a similar power output ? Really the P-51H would have had little benefit from a Griffon.

As to redesigning the P-51D to use the Griffon, the H was already in development and it would have made little sense to stop this and focus on a new variant.

Well, as I said above, changing to a Griffon would actively make the P-51D worse at almost everything the USAAF actually needed it for. The USAAF had no need for a short-legged point-defence fighter with a very high rate of climb, and rate of climb is really the only significant advantage the Griffon would have given to a P-51 airframe encumbered by the realities of military equipment. Even if it were a tuned-up Griffon. 

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2 hours ago, Giorgio N said:

 

It's not really true that piston engines were reaching their peak, simply the advent of jet engines stopped certain developments of piston engines as the advantages they could bring were overshadowed by the much larger advantages of jet engines. At the same time the development of the piston engine continued with other applications in mind, before being stopped again by the introduction of turboprops and jets in transport types.

Had jets not appeared, piston engines for military aircraft would have developed continuously and they would have reached levels unimaginable in the late '40s. Think of what kind of engines could be designed and built today, with much better materials available and a better knowledge of the aerodynamics of ducts and combustion chambers, the peak would have not been reached yet.

Of course there would still be the matter of building a propeller driven aircraft capable of exceeding Mach 1, a problem that the advent of jet engines made irrelevant

 

Types like the MB.5 and the CA.15 are sure fascinating, and even more fascinating are some more extreme types, like the P-75 or the Boeing F8B. They make for interesting modelling subjects, both in their original form and as basis for what-if models. Had they entered service we'd sure see more kits of these types but at some points there would have been oher piston engined types developed to replace them... it was not to be as jets were so much superior

 

Heard the performance potential in the Napier Sabre in particular was huge, seen figures of 50%-80% greater power output quoted 

Edited by PhantomBigStu
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On 9/21/2019 at 7:34 PM, Troy Smith said:

Packard were not making Griffon engines,  so where would you get the Griffons?

 

And the P-51D was then in full mass production.  the 8th AF had 20 Fighter groups alone at the end of WW2, so you have a very successful type with a established supply chain,  the American's efficient logistics was a major part in their success.

 

The replacement for the D, the P-51H, was pretty much a new plane, but was too late.  AFAIK, some engine problems aside the H model was an improvement on the D.

 

It should be noted that the A model was (despite what is often written), a very successful type in it's altitude envelope,  the lack of supercharger being the problem. The D was apparently a bit of a 'dump truck' in comparison. 

 

Whoop let's hear it for the logs hogs lol🤔🤪🤣

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4 hours ago, PhantomBigStu said:

Heard the performance potential in the Napier Sabre in particular was huge, seen figures of 50%-80% greater power output quoted 

I love to hear a big piston aero engine operate ("big" for following comments meaning more than about 2000 hp) but I could never with a straight face recommend them as anything other than historical curiosities as soon as turbines in the 2000-5000 hp equivalent class matured - which they did very quickly. 

 

Once over about 2000 hp the piston engine brought nothing but trouble to practical aviation, which is exactly why it was so quickly and gleefully abandoned by designers and military/civilian customers as the fundamentally superior turbine technology matured through its first decade of in-service development.  Even if you really want to turn a prop for your particular aviation application (and there are lots of good reasons to) then the massive increases in reliability and reduction in weight brought by the turboprop made it a no-brainer. Replacing zillions of moving parts, many of them reciprocating, with a much smaller number of parts which all simply go smoothly round and round, is just so much better.

 

The 3000 hp Sabre VII had the highest power to weight ratio of any large piston aero engine  and that weighed 1.1 tons before you put oil and coolant into it.  And it used six gallons of oil an hour at cruise, so in a fighter you'd need to carry at least 18 gallons of oil weighing 180 lb, and about 20 gallons of coolant weighing about 100 lb, plus at least 100 lb of radiators and associated plumbing. So you're not going to get away with an installed weight of less than 1.3 tons.   

 

An early T-56 turboprop out of a C-130A is  0.9 tons including oil, and needs no cooling system, so you've gained 0.4 tons right there. And it's highly reliable at 3750 ehp. Any observer has to admit that the in-service record of highly complex last-gen big piston engines was terrible, even in post-war airline service with armies of highly trained mechanics tending them and nothing shooting at them. These were engines which had benefited from massive amounts of development and wartime experience and yet which routinely required in-flight shut-downs and down-route engine replacements.  They very rarely went more than 500 hours without developing serious trouble. or requiring overhaul. And they required very great care in operation and in-flight handling to achieve even that kind of reliability.  The R-3350, Centaurus and R-4360 were, and remain  today, brittle and finicky engines, and there is nothing in the Sabre's record to suggest it would have been any better in extended post-war service.

 

The piston aero* engine does not scale up well, whereas the gas turbine does. Where piston aero engines remain extremely useful and relevant is at cruising outputs of 300 hp and lower, at 15,000 feet or lower, and on aircraft requiring minimum capital outlay. They are really good in those roles, and are fundamentally little changed from 1940s designs, suggesting that revolutions in piston-engine performance through modern materials and manufacturing are of minor incremental benefit only.  Once the era of the R-2800 passed, every piston aero engine bigger and/or more powerful than that was far more trouble than it was worth, as soon as the superior alternative was available.

 

--

*There have of course been some excellent absolutely HUGE piston engines in ships, trains and other industrial applications, but they are all low-altitude applications and have all had the advantage of not having to be particuarly light or compact in relation to their power.

Edited by Work In Progress
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Rolls-Royce Hucknall developed something of an obsession for producing a Griffon powered Mustang.

 

By late 1942 they had gone as far as the could with conventional installations and thoughts to a buried installation where the engine in contained within the normal structure and not appended to it. Converting an existing was not on. The Airacobra was amenable to such a modification but RR was looking for aerodynamic advantages because they did not want just another flying test bed, it was to be a fighter. From the start RR favoured the Mustang as it possessed a number of factors that dictated that it should be the basis for the design.

 

Hucknall did not have the experience to design an aircraft from scratch or the time as the proposal was to fly by the summer of 1943. Recent experience of converting the Mustang to take Merlin had given an insight into its advanced aerodynamic qualities and it was thought that by utilising essential parts a great deal of time could be saved. These parts were the wings and empennage leaving Hucknall to design a fuselage to accommodate a rear-mounted engine and pilot’s cockpit. 

 

The project was given the title Fighter Aircraft Proposal (Hucknall P.V. ). From the start it was designed around the two-stage Griffon 61 engine, then in its early stages of development, exoected to produce 2500 bhp. At this rating, with an aircraft auw 0f 9400 lb the power loading would be 3.7 lb/hp, which compared with 4.67 lb/hp for  the Spitfire IX and 5.3 lb/hp for the Focke-Wulf Fw 190. As the engine could not be developed to this state in time, for preliminary tests a Merlin 61 was chosen. This would bring down the auw to 8950 lb and power loading up to 4.47 lb/hp.

 

Considerable modification was necessary to the engine. The propeller reduction gear was eliminated and replaced by a spur driving an identical one splined on to a shaft and rotating in the opposite direction to the crankshaft. The shaft then proceeded forward within a torque tube that ran through a trough in the cockpit floor between the pilot’s feet and splined into the rear of the repositioned reduction gear in the nose. The torque tube was splined at both ends and transmitted the torque reaction from the reduction gear case directly back to the engine and was capable of absorbing slight rotational deflections. This design feature was especially beneficial as the forward fuselage monocoque was of light construction because of the lack of engine mass. For accessibility many of the units mounted on the rear of the engine were transferred to this structure. These units, driven by the reduction gear, were the constant speed unit, generator, hydraulic and vacuum pumps and air compressor. Other items such as the radio, oxygen and electric equipment were also repositioned from their traditional rear-fuselage mounting to the forward fuselage to provide ease of access. Contra-rotating airscrews were finding favour at this time and a Rotol pair 11 ft diameter was chosen. With no engine up front 20 mm cannon firing through the spinner was relatively simple to fit. The specification was completed with the installation of full armour protection and special magnesium alloy bulletproof fuel tanks.

 

To assist in its construction a complete wing assembly and empennage of a Mustang was utilised and mated to a wood and paper fuselage to give a good idea of the shape of the finished fighter. The mock-up later received a Merlin engine as no Griffon was available. In this form it was inspected by officials from MAP. At this time it was still a private venture.

 

About this time preliminary performance figures with a Griffon 71 were calculated that showed a top speed in MS gear of 403 mph at 4800 ft and 451 mph at 20,400 ft in FS. Boost was +18 lb in each case.

 

The result of the ministerial visit was the suggestion that three aircraft should be constructed as flying test beds only, the fighter idea was a dead duck.

 

In June 1943 RR present MAP with its cost estimates for three flying test beds powered by Griffon 65 Specials. The first aircraft would cost £35,000, the second and third £25,000 each. A further £3,500 per aircraft for Rotol contra-rotating airscrews and their constant-speed units. Asum of £5,500 was quoted for a mock-up and wind tunnel model. MAP agreed and issued instructions to proceed on the 12th November 1943, although work on the mock-up had started on the 1st November.

 

To provide the three sets of wings and empennage for the test beds MAP allocated three surplus Mustang Mk 1 aircraft, AL960, AM148 and AM245, which were dismantled to provided these and other parts.

 

The mock-up was built from aluminium to fine limits. It had been decided from the beginning to produce a fully engineered model that would reduce installation problems to minimum by enabling the positioning of such thing as pipe and control runs and other items to be accurately assessed thus easing manufacture of the aircraft proper. This raised the mock-up’s price to £15,000.

 

The RAE became involved, undertaking preliminary wind tunnel testing with a 1/10 scale model. Tests indicated that the tailplane area should be increased by 60% and, because of the high solidity of the wash from the contra-props, the fin area should also be increased. None of this was implemented on the mock-up but it was decided that the first aircraft would have a Tempest tail unit and one was duly delivered.

 

 

The project did not have a high priority and progress on the mock-up was slow. On the 28th February 1945 it was decided to end the contract. A number of components for the first aircraft had been completed; cockpit, forward fuselage, engine mounting, shaft an torque, hood, and other bits and pieces. Total expenditure came to £11,000 plus the cost of the mock-up.    

 

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First mock-up, paper and wood.

 

61b42c90-c1f9-4738-80d0-8ccbae702149.jpg

 

Second mock-up.

 

4b133477-be44-4b54-a94b-2abf8e3861d3.jpg

 

Wind tunnel model.

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I remember a 1/72 Unicraft resin conversion for what I know understand was this project. Sold it a while ago to a fellow modeller on the forum, he will sure more capable of building a better model than I am. Have to say that back then I wasn't really aware of this project, very interesting but also one of those projects that rarely result in a production machine

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