AHC: A better Allison V1710

[phx1138]

Inspired, in part, by this thread.

The OTL V1710, of course, was famously used in the P-40 & P-38. So, what might have been done to it to improve its performance? With a start date of September 1939, & with tech that can be in service before war's end.

My first thought is more carburetors, the first thing any hot rodder worth his salt tries. The V1710 used a single 2-bbl Bendix-Stromberg PD-12K. Even with 3 15/16" throats, that seems mighty small... So, what about four PD-12s? Or six? Synchronization will be a nightmare, however...

Next obvious change is fuel injection, which wasn't unheard of even among hot rodders in that period.

Was there room in the head for bigger valves?

The V1710 already had the Top Fuel-standard dual plugs & racer-preferred mag ignition, so no gain there. Nor in increased compression...

Can the pressure on the cooling system be increased, to raise the boiling point of the coolant (& reduce rad size)?

Hardened valve seats & seals would become desirable later; can they be improved over Stellite?

Can the pistons be lighter without risk of breakage?

Is it possible to fit a "faster" cam? That is, one that gets to max lift sooner. (This is an idea well beyond the existing cam design theory at the time.)

Is it possible to redesign the shape of the valve bowl, so a standard "3-angle" valve job starts with a 22deg angle, instead of a 30deg? It would improve airflow across the entire rev range. (This is also well beyond existing design theory at the time.)

I'm also musing the prospect of something like Teflon being accidentally invented & applied as a coating to moving parts, to reduce internal friction, but that's pushing ASB....

Any other ideas?

 

[phx1138]

Another thought: do improvements to turbo & intercooler count as improvements to the engine?

If it does, what about introducing spot-welded hollow turbine blades?

 

[wizz33]

What about changing the firing order I have read somewhere that 1 of the pistons fired at the wrong moment an thus costing 200 til 400 Hp

 

[phx1138]

What about changing the firing order I have read somewhere that 1 of the pistons fired at the wrong moment an thus costing 200 til 400 Hp

I'll take that.

How about "dishing" the pistons to improve flame travel? Usual theory among hot rodders is, you increase compression either by milling the head or adding a higher-top ("pop-top") piston. Flame travel, however, is improved when its more-nearly circular, & a "dish-top" piston actually works better.

In that vein, what about altering the head design? IDK if it was already optimized as a hemi; if it was, this is moot...except from a cost standpoint. Switching to a "wedge" combustion chamber would provide most of the fuel burn benefits of the hemi, without the attendant higher cost.

 

[phx1138]

No love from the P-38 & P-40 buffs?

 

[Driftless]

No love from the P-38 & P-40 buffs?

I think there's probably reader interest, but not enough of us have the expertise to contribute.

 

[naraic]

Not an engineering pod but a timeline pod.

Between 1931 and 1937 the development of the Allison progressed slowly pace. If you can get the usaac to order a plane (for which the Allison would be appropiate) you can speed up the development significantly.

If you can get the mass produced Allison's of 1941 in aircraft in 1939 the Allsion will be a more mature and ready design in 1941.

Sorry you are looking for a 1939 pod but the Allison historically progressed reasonably in the 1939-1941 period. The failing was the 1931-1937 period when development was slowed.

 

[Archibald]

The V-1710 was a very good engine it suffered from the lack of turbo-charger / super-charger for high altitude combat. The P-38 did fine with it. So did the P-63.

 

[phx1138]

Between 1931 and 1937 the development of the Allison progressed slowly pace. If you can get the usaac to order a plane (for which the Allison would be appropiate) you can speed up the development significantly.

I'm not so much looking to accelerate development as to find things that could have been done once war starts (& the urgency goes up) that weren't done OTL, things within the technological capacity of around 1939 (or sooner!). Which is why I'm suggesting more carbs & bigger valves, which hot rodders had already figured out.

A lot of things that would apply to a car engine, from a blower to zoomie pipes, would already apply to an a/c engine, so I haven't many other ideas. Some others, like aluminum pistons, might be options; IDK if those were already standard, but I think so.

What I'm really thinking is, "Hot rod a V1710", make the best possible one 1939 tech could achieve.

In that vein, what about re-engineered carbs? IDK what the guts of the PD-12 looked like, but if they're anything like Holleys, they'd have large shaft-mounted butterflies, with the butterflies screwed on. Rebuilding individual carbs would be insanely expensive, but if a new model incorporated these changes on the production line... So: thinner mounting shafts, for less airflow turbulence/interruption; flat-headed screws mounting the butterflies to the shafts (ditto); maybe even thinner butterflies (ditto).

Is it ASB to ask for a hot-wire air-fuel metering system for a crude EFI (a bit like early EFI in cars)? My thinking is, the science is understood, & it doesn't require microchips, just capacitors & such, so it should be possible; the breakthrough is the idea of it.

 

[Draconis]

I'm not so much looking to accelerate development as to find things that could have been done once war starts (& the urgency goes up) that weren't done OTL, things within the technological capacity of around 1939 (or sooner!). Which is why I'm suggesting more carbs & bigger valves, which hot rodders had already figured out.

A lot of things that would apply to a car engine, from a blower to zoomie pipes, would already apply to an a/c engine, so I haven't many other ideas. Some others, like aluminum pistons, might be options; IDK if those were already standard, but I think so.

What I'm really thinking is, "Hot rod a V1710", make the best possible one 1939 tech could achieve.

In that vein, what about re-engineered carbs? IDK what the guts of the PD-12 looked like, but if they're anything like Holleys, they'd have large shaft-mounted butterflies, with the butterflies screwed on. Rebuilding individual carbs would be insanely expensive, but if a new model incorporated these changes on the production line... So: thinner mounting shafts, for less airflow turbulence/interruption; flat-headed screws mounting the butterflies to the shafts (ditto); maybe even thinner butterflies (ditto).

Is it ASB to ask for a hot-wire air-fuel metering system for a crude EFI (a bit like early EFI in cars)? My thinking is, the science is understood, & it doesn't require microchips, just capacitors & such, so it should be possible; the breakthrough is the idea of it.

I think the POD timeline change is more productive and realistic. There were already many practical improvements designed into the V-1710 through the war years. An earlier start on these OTL improvements would have been helpful. Aircraft engine design is a balance between getting as much horsepower out of the engine as possible without greatly decreasing the reliability. That constrains the things that you can do. I think the Allison engineers had already considered all the practical improvements that could be feasibly applied using 1940s technology.

Getting the 1941-42 advancements in production 2 to 3 years earlier would have been helpful. Or for a different example Allison finished up V-1710 design in 1945 with the turbo-compound engine that was more fuel efficient and capable of producing 2700 HP using a P-47 turbo-supercharger turbine linked to the crankshaft. It was not pursued because of the advent of jet engines. Now if these engines were available in 1943 they would have proved useful.

Some of the design features you're suggesting would certainly boost the horsepower but what would they do to the engine reliability? I'm thinking of race cars and the need to rebuild their engines after every race.

 

[phx1138]

Allison finished up V-1710 design in 1945 with the turbo-compound engine that was more fuel efficient and capable of producing 2700 HP using a P-47 turbo-supercharger turbine linked to the crankshaft. It was not pursued because of the advent of jet engines. Now if these engines were available in 1943 they would have proved useful.

That's exactly the kind of thing I was thinking of! Now, that's a bit outside the window I imagined, but it's within reach of entering service by war's end, or sooner, so...

Some of the design features you're suggesting would certainly boost the horsepower but what would they do to the engine reliability? I'm thinking of race cars and the need to rebuild their engines after every race.

They shouldn't affect it. An a/c engine run at combat power would do as much damage (probably) as a fueller engine on a couple of passes; how often would fighter engines be rebuilt? After every mission?

Most of the changes I'm suggesting are street-legal kinds of mods, not insane increases in boost or adding nitro(methane) to the avgas. (Yeah, you'd see a performance boost from that, right before you'd see a rod thru the block. {Maybe only 90% nitro... Or, to borrow a phrase, "You sure you used enough nitro, there, Butch?"}) They'd require some new engineering in the production pipeline (new carb parts, new intake manifold, new valve seat angles), but nothing so wild you'd risk engine failure on ops.

All fighter a/c engines in this period, including the V1710, are so close to the best auto engine tech I've seen, it's hard to think of ways to improve on it without ASB.

 

[naraic]

1939-1940 the Allison engine was transitioning from prototype to mass production and being reengineered front that purpose. I think the design team are doing the best they can at that stage.

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.

I honestly think if you can have the Allsion first run in 31, pass a 150 hour test in 35 and go into full scale production in 1936 you will have a much better engine in 1941.

 

[Just Leo]

There have been several decades use of Allison, Merlin and Ford engines used in drag-racing, tractor pulling and unlimited hydroplanes. Your question would have been better put as what has been done, rather than what nascent AH hot-rodders would do.

 

[phx1138]

There have been several decades use of Allison, Merlin and Ford engines used in drag-racing, tractor pulling and unlimited hydroplanes. Your question would have been better put as what has been done, rather than what nascent AH hot-rodders would do.

"Several decades"? More like "a few years", because the V1710 was too heavy to be really effective. More to the point, any postwar changes would rely on tech not (necessarily) available in 1939 or 1940.

 

[ennobee]

No love from the P-38 & P-40 buffs?

I don't know. I'm not that familiar with engine design, but from what I gather, there seemed to be a general consensus to blame everything that went wrong with the US Army Air Force on the P39 and P40 rather then on more far fetched explanations like policy, logistics and tactics. And again there seems to be a general consensus to blame everything wrong with the P39 and P40 on their engines. A good deal of that coming from the Wright and Prat&Whitney crowd favoring radial engines over linears out of principle as a tenet of faith.

So I wonder how much difference a 'better' Allison engine would make as compared to having the engine around long enough to have experienced ground crews mastering the art of fine-tuning the controls or simply having an ample supply of spare parts.

 

[Andras]

The USAAC prevented Allison from working on a two speed second stage supercharger, insisting that they use turbochargers instead. If Allison went ahead and worked on it anyway, they'd have a viable hi-altitude power plant, that makes more power on less boost then the Merlin.

Without the additional boost at high altitudes from the turbo or 2spd/2Stg SC, it will never be a useable high altitude engine no matter what additional mods you do to it. The P-82 finally had 2 stage 1710s, but they lacked several extra features the Merlin had (anti backfire screens, etc)

 

[tomo pauk]

What the man above said.
The 'power' part of the engine was good, superchargers were lacking for several years (though the 2-stage S/C was introduced on the V-1710 a full year before the Jumo did it on the 213E). Allison didn't used 2-speed drive for any of their V-1710s, though, the auxiliarx stage was driven via the variable-speed drive, while engine stage was always driven via 1-speed. drive.
Allison also suggested direct fuel injection, USAAC/F said no - the direct FI solves intake and backfire issues (= no backfire screens = less intake losses = more power), and air has less restrictive path towards the S/C. But, say, for production of 1941, get the strengthened supercharger drive in production, so the S/C can be turned faster (9.6:1 S/C rpm vs. crankshaft, instead of 8.8:1) - buys 2500 ft worth of rated height, so you P-39D does 380 mph, the P-40D does 370, P-51 does 410 mph, all above 15000 ft.
Get the 2-stage supercharger working during the second half of 1942 and in production in early 1943, shove them on the P-51s and P-40s. The intercooler in late 1943 (no intercoller was one of the shortcomings of the V-1710s installed on the P-82 vs. Merlin-powered variant), as well as operation at 3200 rpm, plus the water injection as per OTL - 2000+ HP in 1944 even on 130 grade fuel vs. 1850 per OTL, with better hi-alt power too. Water injection also for the turbo version on the P-38, ASAP.

 

[Draconis]

What the man above said.
The 'power' part of the engine was good, superchargers were lacking for several years (though the 2-stage S/C was introduced on the V-1710 a full year before the Jumo did it on the 213E). Allison didn't used 2-speed drive for any of their V-1710s, though, the auxiliarx stage was driven via the variable-speed drive, while engine stage was always driven via 1-speed. drive.
Allison also suggested direct fuel injection, USAAC/F said no - the direct FI solves intake and backfire issues (= no backfire screens = less intake losses = more power), and air has less restrictive path towards the S/C. But, say, for production of 1941, get the strengthened supercharger drive in production, so the S/C can be turned faster (9.6:1 S/C rpm vs. crankshaft, instead of 8.8:1) - buys 2500 ft worth of rated height, so you P-39D does 380 mph, the P-40D does 370, P-51 does 410 mph, all above 15000 ft.
Get the 2-stage supercharger working during the second half of 1942 and in production in early 1943, shove them on the P-51s and P-40s. The intercooler in late 1943 (no intercoller was one of the shortcomings of the V-1710s installed on the P-82 vs. Merlin-powered variant), as well as operation at 3200 rpm, plus the water injection as per OTL - 2000+ HP in 1944 even on 130 grade fuel vs. 1850 per OTL, with better hi-alt power too. Water injection also for the turbo version on the P-38, ASAP.

A fine wish list to be sure. Do you know what was the Air Corp's objection to fuel injection?

 

[marathag]

A fine wish list to be sure. Do you know what was the Air Corp's objection to fuel injection?

The early mechanical FI ran best at a single speed.

Problem is, what RPM do you want that to be at, cruise or WOT?

 

[phx1138]

What the man above said.
The 'power' part of the engine was good, superchargers were lacking for several years (though the 2-stage S/C was introduced on the V-1710 a full year before the Jumo did it on the 213E). Allison didn't used 2-speed drive for any of their V-1710s, though, the auxiliarx stage was driven via the variable-speed drive, while engine stage was always driven via 1-speed. drive.
Allison also suggested direct fuel injection, USAAC/F said no - the direct FI solves intake and backfire issues (= no backfire screens = less intake losses = more power), and air has less restrictive path towards the S/C. But, say, for production of 1941, get the strengthened supercharger drive in production, so the S/C can be turned faster (9.6:1 S/C rpm vs. crankshaft, instead of 8.8:1) - buys 2500 ft worth of rated height, so you P-39D does 380 mph, the P-40D does 370, P-51 does 410 mph, all above 15000 ft.
Get the 2-stage supercharger working during the second half of 1942 and in production in early 1943, shove them on the P-51s and P-40s. The intercooler in late 1943 (no intercoller was one of the shortcomings of the V-1710s installed on the P-82 vs. Merlin-powered variant), as well as operation at 3200 rpm, plus the water injection as per OTL - 2000+ HP in 1944 even on 130 grade fuel vs. 1850 per OTL, with better hi-alt power too. Water injection also for the turbo version on the P-38, ASAP.

Bravo. To which I'd add, Allison should have gone ahead & developed FI anyhow, AAF be damned; when it was learned the Germans used it...

That said, how much does this affect the P-38, presuming turbos aren't used?

The early mechanical FI ran best at a single speed.

So there was some motivation to find a way to meter fuel at varying speed... That suggests a hot wire air mass flow sensor (of some variety) might cross somebody's mind...

Also, let me be clear: I'm laying no blame on the failings of the P-39 or P-40, merely thinking about what the best possible V1710 might have looked like.