High Altitude P-51: turbocharged Allison or special Merlin?

[Lucio]

Hi!
Several years ago I saved a very interesting drawing I have found in a "what if" modeling fórum. Someone envisaged a high altitude, long-span Mustang that could have been developed using P-82 parts. Contrary to some very imaginative but technically impossible contraptions one can find in such forums, this one is viable.

However, there´s the engine dilemma...
Such an airplane, for very high altitude operations, must have a very special engine. In my opinion, an Allison could have been used IF coupled with a turbocompressor and supercharger, P-38-style. But where to mount the turbo? I can only think on the fuselage side. The aft fuselage would be a plumber´s nightmare but I think it could have been made to work.
The other option would be a special, high compression, RR Merlin.
Of course, I´m asking this because I´m contemplating the idea of building a model using a Monogram 1/72 F-82 kit with a P-38 turbocharger grafted in the side fuselage OR a P-51H nose. But, because my question is technical, I decided to post it here and not in the modeling section.
What do you think?
Thanks!
Lúcio

 

[MiTasol]

That means you will be running a large diameter extremely high temperature pipe inside a large cooling shroud, which will still be very warm at least, inside the left side of the cockpit about where the engine flap and landing gear controls are so where are you going to put those rather essential components?

 

[pbehn]

Would it be better than a Spitfire, bearing in mind its weight just as a normal P-51?

 

[Lucio]

That means you will be running a large diameter extremely high temperature pipe inside a large cooling shroud, which will still be very warm at least, inside the left side of the cockpit about where the engine flap and landing gear controls are so where are you going to put those rather essential components?

I know about the hot gas pipe problem. One solution would be the external pipe, just like in the FW-190V-18.

 

[Lucio]

Would it be better than a Spitfire, bearing in mind its weight just as a normal P-51?

Consider the long span, high altitude potential (pressurized cockpit needed!) and fuel tankage (range!), I think the "what if" P-51HA is a lot better than a Spitfire for reconnaissance (I didn´t buy the "interceptor" idea). But where to put the cameras? Rear fuselage? An underwing camera pod? The more I think about these problems, the more I like the Merlin option.

 

[pbehn]

Consider the long span, high altitude potential (pressurized cockpit needed!) and fuel tankage (range!), I think the "what if" P-51HA is a lot better than a Spitfire for reconnaissance (I didn´t buy the "interceptor" idea). But where to put the cameras? Rear fuselage? An underwing camera pod? The more I think about these problems, the more I like the Merlin option.

The original post clearly states "interceptor" if you are discussing photo recon carry huge amounts of fuel internally and lots of cameras like a Mosquito. All those external tanks on that P51 don't give a longer range they just allow it to fly so far it cant get back.

 

[tomo pauk]

Merlin is a way simpler option, and it works great. No need for a 'very special' engine, the V-1650-3 from the P-51B will do it just fine.

[I've recalled the 'very special' not just 'special' - agent Tony DiNozzo from NCIS ]

 

[Lucio]

The original post clearly states "interceptor" if you are discussing photo recon carry huge amounts of fuel internally and lots of cameras like a Mosquito. All those external tanks on that P51 don't give a longer range they just allow it to fly so far it cant get back.

Sorry for not making it clear that I was not going for the interceptor option. I think USAAF would ask for such interceptor only if they think the german and japanese high altitude planes (bombers and recconaissance) then in the development stage could have been a real threat. In this case the what if P-51HA wings would be armed and carry a lot less fuel for a shorter range but high altitude capability.
In either case, four external tanks are counter-productive.

 

[pbehn]

Sorry for not making it clear that I was not going for the interceptor option. I think USAAF would ask for such interceptor only if they think the german and japanese high altitude planes (bombers and recconaissance) then in the development stage could have been a real threat. In this case the what if P-51HA wings would be armed and carry a lot less fuel for a shorter range but high altitude capability.
In either case, four external tanks are counter-productive.

The P-51 was already 1 ton heavier than a Spitfire with the same engine, that is a lot of lift required at extreme altitudes, when it comes to long range recon those tanks on the outside throw away much of the P-51 superiority in aero dynamics and as I said could easily result in it flying to a place it couldn't get back from.

 

[wuzak]

There is always the Griffon.

Good for 50,000ft in the PR.XIX and equipped with a cabin blower.

 

[Lyall]

That Allison in the later F-82 is already a high altitude engine plus it has about 2250 hp. They had second stage mechanical supercharging plus water injection which was rarely ever used.

 

[wuzak]

That Allison in the later F-82 is already a high altitude engine plus it has about 2250 hp. They had second stage mechanical supercharging plus water injection which was rarely ever used.

At what altitude?

The Merlin in the P-82B gave higher maximum speed at a higher altitude with a higher ceiling than the V-1710 P-82E (later ones had the big radar pod, so not really worth comparing them).

 

[Lyall]

40,000 feet. With the P-82B its service ceiling was suppose to be 41,600 feet with Merlin's and the "G" was 38,900 feet with the pickle and the Allison's. I had thought that Allison engine in the F-82 was rated at 1500hp-1600hp for years because of the books of Bowers & Wagner. Then in 1981 I got to hear an F-82 pilot who said "that's BS!" He also implied that the Allison version was faster than the Merlin.

 

[wuzak]

40,000 feet. With the P-82B its service ceiling was suppose to be 41,600 feet with Merlin's and the "G" was 38,900 feet with the pickle and the Allison's. I had thought that Allison engine in the F-82 was rated at 1500hp-1600hp for years because of the books of Bowers & Wagner. Then in 1981 I got to hear an F-82 pilot who said "that's BS!" He also implied that the Allison version was faster than the Merlin.

There is no way that the V-1710s had 2,250hp @ 40,000ft. The only way that would happen is with a very high altitude turbocharger, which I don't believe was made in the B-series turbo (there was in the C-series for the P-47).

The 2,250hp was achieved with increased boost, which has the effect of lowering the altitude at which the peak is produced.

From your previous post:

That Allison in the later F-82 is already a high altitude engine plus it has about 2250 hp. They had second stage mechanical supercharging plus water injection which was rarely ever used.

The 2,250hp was only available with ADI.

Not sure if the V-1710s in the P-82 had intercoolers - most 2 stage Allisons did not.

 

[Lyall]

There is no way that the V-1710s had 2,250hp @ 40,000ft. The only way that would happen is with a very high altitude turbocharger, which I don't believe was made in the B-series turbo (there was in the C-series for the P-47).

The 2,250hp was achieved with increased boost, which has the effect of lowering the altitude at which the peak is produced.

From your previous post:



The 2,250hp was only available with ADI.

Not sure if the V-1710s in the P-82 had intercoolers - most 2 stage Allisons did not.

 

[Lyall]

It didn't have a exhaust gas driven turbocharger like the P-38/P-47. It had a variable speed (Auxiliary) impeller hydraulically powered off the engine feeding into the carb then the first stage supercharger. So it wasn't a fixed two system as on the "B". No intercooler system but a cold ram air & heated air system.

I screwed up replying to you - The maximum horsepower is 2250 and the service ceiling was 40000 feet for the "E". I don't have a chart to give you the horsepower at what altitudes which seems to be what asking. Apparently they had a lot of problems because the government mandated using as much of the left over parts they bought to support WWII Allisons.

 

[jmcalli2]

The only V-1710 I've heard of (disclosure: I am NOT an expert.) that approaches that performance would be the V-1710-127 turbo compound engine designed for the P-63H.

Allison V-1710TC

 

[mad_max]

This might be a crazy idea, but add a 3rd gear to the supercharger of the merlin.

 

[wuzak]

This might be a crazy idea, but add a 3rd gear to the supercharger of the merlin.

The two stage Merlins were designated as RM.#SM.

R stood for Rolls-Royce, M for Merlin, the # was the development specification number (up to 17). The S and M referred to the supercharger - S meant fully supercharged (ie high altitude) and M meant medium supercharged.

When the Griffon went to 3 speed supercharging, the suffix became SML - fully supercharged, medium supercharged and low supercharged. The third gear was for low altitude performance.

it is unlikely that adding a higher gear to the existing supercharger would provide much gain, beyond the existing high altitude versions (the V1650-3 and -9 were higher altitude engines than the -7). A new supercharger may be required.

Late in the war Rolls-Royce developed the RM.17SM, which used larger supercharger impellers - 10.7/12.7 inches vs 12.0/10.1 inches for regular 2 stage Merlins (if I am remembering correctly).

Though the RM.17SM was not a high altitude engine, the supercharger may have been used for a future high altitude Merlin.

 

[mad_max]

The two stage Merlins were designated as RM.#SM.

I know all about the Packard Merlin -3/-9 and -7.

When the Griffon went to 3 speed supercharging, the suffix became SML - fully supercharged, medium supercharged and low supercharged. The third gear was for low altitude performance.

Didn't know that. Thanks for the info.

Adding a 3rd gear is the logical choice for an increase in boost at high alts. Both the German and Japanese developed motors with 3 speed 2 stage superchargers. Would've it made a difference? Who knows; but for a relatively easy change with a slight increase in weight, it could've been produced rather quickly and be able to be installed in airframes already being produced that used the 2 stage merlin without much weight increase with a small addition of ballast to keep the CG proper.

Just my thoughts without any aircraft motor background.