AHC: A better Allison V1710

Hardly seems worth the effort to retool and deal with the logistics of tracking different cams, etc. for a 1-2% gain.
Yeah, that's my thought, too. Even if we allow a generous 25hp.

Don't overestimate the logistics issues. The cams'd be retrofittable, so all you'd need is an *AD from the AAF to ensure the cams are swapped in pairs (so both sides run the same spec), & to be sure the cam & valve timing is adjusted for the new cam in the older-marque engine. Just the same as swapping in a '90s or '00s grind in a '57 283.
The Allison might have been improved by the much faster valve action of a race type roller cam follower setup. In aviation, roller cam followers were used in most radial engines (because of high cam surface velocity rather than to permit rapid actuation.
That's an interesting idea. I had no idea roller followers were even around yet.

Which brings me back to my idea of "faster" cams: new cam profiles, so they reach max lift sooner & stay there longer.
 
1931 was the Allison's first run and 1937 was the first time an Allison engine lasted 150 hours and the Allsion only went into full production in 1939/1940.

The Merlin for comparison was first run in 1933 and passed a 150 hour test in 1935, went into full scale production in 1936.
Just for giggles - what if Allison looked at their maturing 1937 engine, looked at developments in Germany and at their round-engine competitors, and somehow (rohypnol?) persuaded the Air Corps that continuing development but in V-2150 form would be Just The Thing to ensure a technical lead?
 
Just for giggles - what if Allison looked at their maturing 1937 engine, looked at developments in Germany and at their round-engine competitors, and somehow (rohypnol?) persuaded the Air Corps that continuing development but in V-2150 form would be Just The Thing to ensure a technical lead?

The Air Corps can issue a request for a 35-40L V12 in 1937, and we'd probably have Chrysler, Ford, Continental and Lycoming enter that. May the best 2 engines win it. However, it would require that AAC first admits that hi-per engine aproach (making the most power from a cu in of an engine) is a big mistake, and that 'classic' aproach (making the most power from lb of an engine) is better. Allison might enter this, hopefully (= good thing) killing their X24 and W24 projects in process.
 
Understanding of combustion chamber design was progressing rapidly in the late thirties, both in aviation and automotive engines. In the absence of computer technology such approaches as casting top dead center volume in plaster, then spherically milling material away at constant radius from the sparkplug to create models of non-turbulent combustion propagation, then correcting for mixture turbulence (visualized by other equally primitive means), and guessing at the effects of surface quenching, resulted in knock-free combustion at increasing compression ratios. Combustion chamber evolution was not needed in aviation engines beyond WW2, but progressed very effectively for automobiles in the late forties/early 50s.

The technology for the creation of smooth combustion in larger aircraft engine cylinders was there for the taking in the thirties but no one (with the possible exception of Sir Harry Riccardo) did much analysis.

I know the Germans tended toward larger, more lightly built, lower BMEP engines, and the American emphasis, for some time, was concentrated on small cylinders operating at high BMEP.

The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.

Dynasoar
 
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The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.

Dynasoar

(my bold)
'Militarize' the RR 'R' engine.
 
The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.Dynasoar


I like the way you think. Could that also permit a two V-12 contraprop of 4600 cubic inches? Then fitted with turbochargers or better yet as a turbo-compound and then we have the perfect engine for Jack Northrop's B-35. I think there would be uses found for those other engines too. :)
 
Understanding of combustion chamber design was progressing rapidly in the late thirties, both in aviation and automotive engines. In the absence of computer technology such approaches as casting top dead center volume in plaster, then spherically milling material away at constant radius from the sparkplug to create models of non-turbulent combustion propagation, then correcting for mixture turbulence (visualized by other equally primitive means), and guessing at the effects of surface quenching, resulted in knock-free combustion at increasing compression ratios. Combustion chamber evolution was not needed in aviation engines beyond WW2, but progressed very effectively for automobiles in the late forties/early 50s.

The technology for the creation of smooth combustion in larger aircraft engine cylinders was there for the taking in the thirties but no one (with the possible exception of Sir Harry Riccardo) did much analysis.

I know the Germans tended toward larger, more lightly built, lower BMEP engines, and the American emphasis, for some time, was concentrated on small cylinders operating at high BMEP.

The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.
I wonder if it's occurred to them, yet, to want a burn that's as spherical as possible, & so dished pistons, rather than domed. (Heart-shaped combustion chambers, to induce swirl, seem extraordinarily unlikely.)

About your notional ideal engine, I'd disagree on a couple of points. One, larger bore but shorter stroke; hp, not torque, is what an a/c engine wants, so max revs. (You might be right about big V8 rather than V12, for less parasitic loss.) Also, you want better breathing, so 4 valves is ideal. (The idea of 5 or 6 wouldn't occur to anybody yet, I don't think.)

I also think a MAF-controlled (hot wire fuel metering) FI system would be a good idea, & just within reach of '40s tech.

I'd also add methanol & nitrous injection. (IDK how well known those were in the U.S. at the time, tho.)
 
You might be right about big V8 rather than V12, for less parasitic loss.
The advantage of a V12 over a V8 for A/C use is that it is a natually balanced engine design with very little vibration. V8's can be made smooth (90* bank angle, cross plane crank, and/or harmonic balancers, etc.) but that all adds complexity and rotational weight. For smooth power delivery it is hard to beat a V12.

I think for 1940's tech a V12 is still the way to go.
 
phx and EverKing,The intent of using two larger valves rather than four smaller was, primarily to provide piston top area for a relatively large quench/squish region to promote strong turbulence while increasing detonation margin. The reduction of valve area and perimeter would not be a 2 to 1 loss by any means and the combustion chamber shape is intended to permit operation at relatively high boost and increase intake flow.
Simple valve gear would lighten things, tho the cylinder offset from bank to bank to permit simplified rods might introduce some shake.

Dynasoar
 
Dynasoar, you mention a narrow angle V8 as your platform. I am no engine designer so I am curious how you would get it to fire evenly? My understanding is you want one cylinder to fire every 90 degrees with 8 cylinders (720 degrees/# cyl.) Would you have to use an Exotic/complex crank with offsets? Or do you just live with a sputtering uneven firing order and try to smooth the power delivery elsewhere (if so, how?)?
 
EverKing,

You've asked a fair question.

QUOTE="EverKing, post: 15759779, member: 103589"]Dynasoar, you mention a narrow angle V8 as your platform. I am no engine designer so I am curious how you would get it to fire evenly? My understanding is you want one cylinder to fire every 90 degrees with 8 cylinders (720 degrees/# cyl.) Would you have to use an Exotic/complex crank with offsets? Or do you just live with a sputtering uneven firing order and try to smooth the power delivery elsewhere (if so, how?)?[/QUOTE]

When I stated "Narrow angle V-8", no angle was specified however my thoughts were any angle less than the customary 90 degrees. Successful V-8 engines, aircraft and automotive, have been built at 72, 60, 45, 30 and 22-1/2 degrees. The last two were offered by Lancia during the interwar years and employed stepped crankpins like some GM 90 degree V-6s. 72 is not narrow enough, so this leaves 60 and 45.

I'm sure you are familiar with the RR "MeteorITE" (my caps) the Meteor being the tank engine incarnation of the RR Merlin 60 degree V-12, and the Meteorite the same basic engine with the rear four cylinders missing to produce a 60 degree, narrow angle V-8 manufactured by the thousands. I do not know the crank configuration or firing order of this engine, but assume that smoothness was not a problem. Ford produced a similar tank engine conversion, also in the thousands. So, perhaps this satisfies the question, but actually I was visualizing a 45 degree V-8. This was my reason for suggesting hiring Leo Goosens to do the layout, since he did the design work on Harry Miller's 45 degree Indianapolis Speedway
V-8 in the early thirties.

The engine incorporated a 180 degree (flat) crankshaft and the firing order, viewed from above with #1 cylinders of each bank to the front;

1R, 4L, 3R, 2L, 4R, 1L, 2R, 3L.

From page 360 of Mark L. Dees, "The Miller Dynasty" IBSN: 0-9638084-0-0 Quote:
"Taken with the vee angle this resulted in an uneven firing order like four Harley V-Twins loping in rhythm. Surprisingly, "Bunny" Phillips, who raced one of these engines for years, said that for a racing engine it was remarkably smooth." These engines, originally 308 cubic inches and later destroked 1/2-inch to 269 CI to meet the new 1938 rules were rated at 300 HP @5500 RPM. Designed in the fall of 1931, these engines soldiered on at the Speedway thru the early postwar years.

The Liberty engine program first produced a 45 degree V-8 which ran before its 45 degree higher priority V-12, was described as smooth running with Delco coil and battery ignition, and rough with Splitdorf magneto (which I suspect had symmetric E-Gap, despite asymmetric firing order). One of the early prototypes set an American altitude record in a lightly built LFW biplane (Presumably with Delco ignition). The preceeding from"The Liberty Engine 1918-1942" Smithsonian Annals Of Flight. I don't have the Liberty crank configuration or firing order handy, but suspect it was the same as the Miller engine.

Dynasoar
 
phx and EverKing,The intent of using two larger valves rather than four smaller was, primarily to provide piston top area for a relatively large quench/squish region to promote strong turbulence while increasing detonation margin. The reduction of valve area and perimeter would not be a 2 to 1 loss by any means and the combustion chamber shape is intended to permit operation at relatively high boost and increase intake flow.
Simple valve gear would lighten things, tho the cylinder offset from bank to bank to permit simplified rods might introduce some shake.
With OHV/OHC (1/bank), IMO you've got about as simple a valvetrain as you're going to get. About the only gain I see there is in changing from a 30deg valve seat angle to 22deg, & I expect that's beyond the known tech.
For smooth power delivery it is hard to beat a V12.

I think for 1940's tech a V12 is still the way to go.
I would agree completely; I only meant, if we accept the V8 is preferable, it has the advantage of lower parasitic losses.
 
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