could the Allison engine have done what the Rolls Royce Merlin did?

[CobberKane]

Okay, here's one for the technophiles (definitely not including me). The Allison engine in it's various guises has always seemed to play second fiddle to it's famous contemporary in the land of hope and glory, the Merlin. Was there any intrinsic design feature that precluded Allison engines from powering single engine fighters over Germany at 25000 feet, of was it all just a case of the American engine being hobbled by the thinking of the time - that high altitude fighters weren't required?
To get full marks, please include an objective comparison of the beers of both countries.

 

[wuzak]

High altitude thinking = turbochargers

So no 2 stage until later, and no 2 speed supercharger (there may have been one prototype?).

In terms of supercharger development, Allison, like other US manufacturers, used GE designs to start with but got better results when they switched to designing their own.

Development was hamstrung by how much funding teh government wanted to pay, and an unwillingness to put money into new developments without a clear requirement and/or orders.

 

[Shortround6]

Was there any intrinsic design feature that precluded Allison engines from powering single engine fighters over Germany at 25000 feet, of was it all just a case of the American engine being hobbled by the thinking of the time - that high altitude fighters weren't required?

This is often repeated but has little basis.

The US wanted high altitude fighters, they were required. The USAAC had turbo P-30s, turbo Airacuda's. 13 YP-37s, the P-38 and P-39 prototypes. A turbo P-35 and a P-35 with a two stage supercharger plus a P-36/Hawk 75 with two stage supercharger were at the 1939 fighter trials that led to the P-40 order.
The 1st problem was that NONE of the high altitude planes were really ready for SERVICE squadron use.
The 2nd problem was that Allison was a very small company when it got the order for the engines to power the 500+ P-40s in the April 1939 order. Plant expansion and tooling up to make engines on a production line basis instead of tool room batches of a few engines per month meant that R&D on the high Altitude versions got put on the back burner (if not back in the refrigerator) until the production thing got sorted out. Production got even more complicated when Allison got permission to export the engine to France and Britain which meant an even higher production volume.
3rd problem was that Allison had spent a bunch of time on other Army requirements like the P-39 remote propeller, the Airacuda remote pusher engine set up, the P-38 handed engine and the V-3420 double engine.
GE was supposed to be handling the turbo for the high altitude planes.
Army was handling the turbo controller?
There is a recipe for success (not).

other factors that hurt US fighter high altitude performance in the early part of the war were, 1. US fighters carried more fuel than most other counties fighters. Given similar field requirements (landing and take-off) this means a bigger airplane, in general. 2. the US slapped a heavier armament into it's early aircraft (I am not saying better, I am saying heavier). 3. The US had a higher "G" limit than some other countries (not all) so the structural weight was higher. It adds up to planes that were hundreds of pounds heavier than their British or German equivalents in the early part of the war. Given roughly equivalent engines the US planes struggled at higher altitudes.

Until Hooker came along the Merlin wasn't that much better at high altitudes. Once he showed up everybody else was trying to play catch-up.

Try slapping a Merlin III into a P-40C and see what kind of performance you get?

 

[tomo pauk]

Great post, indeed.

There was no major hurdle to install the two stage V-1710 (the 'normal' drive equivalent of the E-11 installed in the P-63A) in the P-51 airframe and send it in the ETO in 1944. The altitude performance would not be on par with the Merlin Mustang, esp. vs. the early models with the high altitude V-1650-3, but it should be enough for a decent performance advantage vs. the LW opposition.
Another approach could've been the single engined fighter with turbo V-1710, something along the lines of the XP-60A (3 view). The plane based around that power-plant was feasible as early as P-38.

 

[davebender]

This gets my vote.

Same reason USA couldn't produce a reliable copy of Hs.404 20mm cannon even after Britain provided blueprints.

 

[Shortround6]

Do you have a reason for this?

It gets printed in books and bandied about the internet but I don't believe I have ever seen any actual quotes or memo's about it. It usually comes down to people believing the nonsense performance figures for the XP-39 or thinking that Allison, who from 1930 to though 1938 built a total of 30 engines had the engineering staff and test facilities to design, build and deliver cutting edge supercharger technology when both Wright and P&W could not.

The believers of this theory also ignore the the fact that the USAAC and Navy built and flew more turbo supercharged aircraft and more planes with two stage superchargers (most turbos) than the rest of the world put together before Sept 1939.

A sure indicator of a lack of interest.

The US did a lot of dumb things, thinking that high altitude combat planes were not needed wasn't one of them.

 

[Wavelength]

Its been awhile, but as I recall in the book about Schmued: Mustang Designer Schmued explains that when the Gov wanted them to use the Allison in the P51J and the F82, he finally diagnosed the problem of the Allison not liking boost to a flaw in the intake manifold design. He could not get GM to listen to him, however. The deafness wasn't Allison themselves but their coporate masters in Warren.

 

[krieghund]

Kind of looks sexy

 

[Readie]

Kind of looks sexy

It does....all that is missing is ROLLS ROYCE on the camcovers

 

[Readie]

Seriously....

http://www.ww2aircraft.net/forum/engines/superchargers-early-v-1710-vs-merlin-17590.html

The answer is within this thread.

Cheers
John

 

[tomo pauk]

Not sure it's there, John. What post did you have in mind? Seems there is no mentioning/analysis the 2-stage V-1710, nor the turbo variation.

 

[dobbie]

The Allison could have made the high altitude horsepower with the proper supercharger set up, but no money was allocated for such a project until late in the war. I think the urgency of the war and production kept the redesign off the boards. As it was, Packard was already producing the Merlin under license, so possibly it was considered a waste of time. The Allison, even if the time and money would have been spent to develop to do so, wouldn't have made that much difference in performance which the Merlin already had. Wartime is a bad time for lengthy developments.

 

[tomo pauk]

V-1710 actually made the 'high altitude horsepower,' rather early in the war. Earlier than the Merlin or DB-601.
As for 'difference in performance which the Merlin already had', maybe we should calculate in the airframe capabilities of the P-51 to get the whole picture?

 

[dobbie]

V-1710 actually made the 'high altitude horsepower,' rather early in the war. Earlier than the Merlin or DB-601.

With a mechanical supercharger? Turbochargers are great, but then you end up with a monster sized fighter such as the P-47. Great aircraft, but a gas hog.

 

[tomo pauk]

With a mechanical supercharger? Turbochargers are great, but then you end up with a monster sized fighter such as the P-47. Great aircraft, but a gas hog.

Why would one end up with a monster-sized fighter powered by a turbo V-1710?
The gas hog was patiently faster, more rugged and heavier armed than any fighter of ww2.

 

[dobbie]

Don't get me wrong...."the gas hog" is my favorite! I suppose that if you made the fuselage long enough and wide enough to pack all of the plumbing necessary, you could have had something to show at high altitude. But that would take a clean sheet of paper to make it all work. Just like the P-47-it was designed around a turbocharged R2800. They did attempt the XP39 which didn't turn out so well, and the YP37 too.

 

[Shortround6]

The Allison would use the smaller "B" series turbo (P-47s used the "C"series) but you are right it would take more volume in the fuselage. What people keep forgetting is that the mechanical drive two stage supercharger just gets rid of the turbo and the exhaust plumbing. It still needs the second supercharger casing, a drive system and to be effective, an inter cooler and the associated plumbing/ducting to go with it.

P-51B was 7 in deeper top to bottom than a a P-51A, in part to fit the Merlin and the intercooler/larger radiator and larger duct.

An air/liquid intercooler is more compact than an air/air intercooler but adds another "system".

And it's volume is still not zero.

 

[CobberKane]

The gas hog was patiently faster, more rugged and heavier armed than any fighter of ww2.

Possibly to number one, probably to number two, definitely not to number three.

 

[tomo pauk]

It was carrying more weapon weight than any single-engined fighter, along with awfully big heavy ammo load. Anyway, my point is that one cannot get something for nothing.
We might add the 1000 miles escort capability there, too.

Don't get me wrong...."the gas hog" is my favorite! I suppose that if you made the fuselage long enough and wide enough to pack all of the plumbing necessary, you could have had something to show at high altitude. But that would take a clean sheet of paper to make it all work. Just like the P-47-it was designed around a turbocharged R2800. They did attempt the XP39 which didn't turn out so well, and the YP37 too.

SR6 covered this.
USA have had all what it takes to field the single-engined turbo V-1710 fighter contemporary with P-38, but the only firm that got layout correct (Republic), decided to go with R-1830 for their new fighter (P-43).

 

[Sid327]

I think,

if both the Merlin and Allison were tested without a supercharger there'd be very little in it; both being fine engines for the day.
It was just right place, right time for RR when they (Hooker) re-designed the supercharger system and applied it to the Merlin family.
The Allison by all accounts was a sweeter running engine(?)