Single stage V-1710: options for improvements?

[tomo pauk]

One of widely used, yet rarely celebrated engines, was the Allison V-1710. It was there when needed, particularly the single stage variant, being eclipsed with other Allied engines of ever-increasing capabilities. So was there a way to increase it's capabilities (particularly high altitude ones), before going to the 2 stage variant? Eg. NAA was proposing the 2-speed V-1710 in the time they were testing the P-51. Anything else, like the bigger supercharger (sorta V-1710-AS, like DB-605-AS)?

The contests between engines, let alone the post war engines' capabilities, can have their own thread. Thank you

 

[krieghund]

Without going to a two-stage you would need something like the hydraulic supercharger similar to the one fitted to the DB603 series engines. However I still think the best option is this one......

 

[GregP]

There weer a number of options that could have been pursued. In point off act, the US Government owned the design and dictated all improvements. If Allison Engineering had owned the design they could have done any or several of the following:

1) The supercharger could have been turned into a multi-speed unit, possibly of slightly bigger diameter.
2) The mechanical drive could have been changed to an internal hydraulic drive. This eliminates the "dogtooth" in the top speed versus altitude curve.
3) They could have designed an internal, 2-stage unit similar to the Merlin. It would have been best to "borrow" Sir Stanley Hooker for a few months and do a unit with him, the master.
4) The turbosupercharger could have been made part of the power package for all Allison installations. If this one had happened, they would have ironed out the issues a bit earlier. The P-39 and P-40 would have slightly bigger airframes with the high-altitude portion of the Allison power system intact instead of being made into low-to-medium altitude aircrafta s they were in the event.
5) They could have added the intake turbulator venturi sooner to help with even mixture for all cylinders.
6) All piston engines should be run at the factory on the fuels they will experience when deployed BEFORE being deployed. If they had done that, then the Allison carburetors would have been jetted correctly to start with and we could have avoided almost a year of fiddling around with problems in Great Britain.
7) Alernately, they could have gone with fuel injection. I think this would have been the biggest improvement for the mixture problems though it COULD have introduce a whole new raft of issues. I think not.
8) They could have designed the accessory housing (supercharger housing) such that a simple gear change could be used to change the supercharger impeller drive ratio to help with mission adaptability. Higher drive ratio for higher altitude missions and power drive ratio for lower altitude missions. A simple cover with gaskets could have been made with quick-change impeller gears. Thuis may or may not have introduced mixture issues. If so, then select a single gear for a particular use at the factory.
9) They could have eliminated, by design, 3 or 4 very troublesome screws/bolts. One at the base of the intake on the accessory housing, two up front in the interior of the oil transfer passage, and a couple on the very bottom of the water pump that are almost impossible to work with without magnets abd some luck. This serviceability complaint is one from someone who works on them, not one from an operation standpoint, and should not be considered major by anyone unless YOU have to assemble the engine and said fasteners.

Most of the above could have been done without too much effort had Allison owned the engine design. They didn't and it never happened.

 

[MikeGazdik]

How much bigger or longer, is the Allison with the auxillary 2 stage such as in the P-63, as compared to the Rolls Royce / Packard Merlin as installed in the P-51? Could that engine be placed into the Mustang if the U.S produced Merlin was not available?

In my thinking, because altitude performance was King, the absolute number one improvement would have been a 2 stage supercharger for the Allison. A close second would be fuel injection as in the Daimler IV-12.

 

[krieghund]

Why not use the V-1710-119 as pictured above?

 

[Shortround6]

The V-1710-119 was a bit late in the day.

The V-1710-33 (C-15) had a supercharger as good as anybody else's in 1939/40, unfortunately if got a bit stuck at that point. Allison did a make few modest improvements as things went along but nothing like the improvement that Hooker performed on the Merlin 45 and XX engines. A slightly bigger impeller and housing (10.25in?) with a 2 speed or variable drive and a Hooker inspired intake would have gone a long way in adding 3-5,000ft to the critical altitude of the Allison without needing a two-stage supercharger.
A "G" model with a 10.25 in impeller and a two speed drive (-131 Model) was good for 1150hp MAX CONTINUOUS at 15,500ft at 2700rpm. The 25 more HP power as a -99 at 15,000 using it's Military rating and 3000rpm. The "G" had some other improvements so an earlier engine might not match it but there was certainly room for improvement.

 

[tomo pauk]

Welcome, SR6; thanks for pointing me to the -131

Looking at tip speeds: the Merlin XX/Packard V-1650-1, in high gear gear, was doing 1273 fps (SC diameter 10.25 in, SC gear ratio 9.49:1), or just around the speed of sound. The V-1710, with SC diameter of 9.50 in and 9.60:1 SC gear ratio, was doing 1194 fps. Now the next step up for the SC gear ratio is/was 10.52:1, but that makes tip speed going at 1308 fps, thus breaking sound barrier comfortably - not a best thing to do here.
The V-1710-131 went for SC gear ratios of 7.48:1 (low gear) and 9.60:1 (high), so the tip speed was up to 1288 fps.
Further data about the -131: 1475 lbs, 1600 HP/3200 rpm/61.7" at SL (for take off), 1220 HP/3000 rpm/52" at 15500 ft.

Obviously, if we want a 2 speed V-1710 in service in, say, 1943, the max RPM is to be 3000. So in the best case the engine can be as good as the Merlin XX.

The induction system of the V-1710 had one of it's major shortcomings (even discounting other supercharger issues). The supercharger inlet area was 24.4 sq in, so even with bigger carburetors (with 41.3 sq in of throat area) that small inlet area acted more or less as a restrictor (over 1 in Hg of pressure is lost there, plus what ever is lost upstream). Contrary to that, V-1650-1 had a carburator of 38.3 sq in area, feeding the similarly sized supercharger inlet. The 'very much enlarged induction system' of the Melrin II was noted by Wright Field engineers, already in 1938.

the data is from 'Vee's for victory' book

Any hope going to 6:1 compresssion ratio, vs. 6.65:1?

 

[Shortround6]

"Any hope going to 6:1 compresssion ratio, vs. 6.65:1?"

Certainly nothing to prevent it except interchangeability of spare parts. However, lowering the compression allows a higher boost to be used before hitting the detonation limit. The supercharger had to be capable of supplying the extra boost. Lowering the compression would allow higher power at low altitudes but would do little or nothing ( or might even lower power) at the altitudes above the normal FTH or critical height. Lowering the compression also hurts fuel economy.

I can think of nothing to prevent a larger supercharger and better drive being used on the Allison in 1943 except lack of engineering capacity. The Hooker designed Merlin supercharger was in production in the summer of 1940, you don't need 150 PN fuel to make it work, you don't rare or exotic metals, The Basic Allison engine Block was rated as being good for 1425-1500hp in a P-38 at this point. P-38s generally used less power to drive the engine supercharger (lower gear) than the regular engines but 1425-1500hp seems reasonable for low gear in a two speed ( or variable hydraulic ) drive. A 9.60 gear supercharger needs about 64% MORE power to drive than an identical supercharger using 7.48 gears so high gear needs to adjusted accordingly.

 

[tomo pauk]

For the airflow between 8000 - 13000 lbs/hr, the 7.48:1 supercharger was using between 80-150 HP, the 9.60:1 SC was using 200-330 HP.

Interestingly enough, the 10.25 in impeller, rotating at 7.48 times the crankshaft speed was using about the same amount of power as it was the case with a commonly used 9.50 in impeller, at same 7.48:1 ratio.

 

[GregP]

The Allison V-1710 with Auxilliary supercharger is about nine inches longer than a two-stage Merlin and that is the primary reason it was not used in the P-51 ... it would mean moving the firewall and that would interrupt production. All of the Allison Aux-stage superchargers used a 12 3/6 inch diameter impeller.

The V-1710-127 made 1,740 HP at 3,000 rpm and 52.5" HgA, 33,000 feet dry. It made 2,320HP at 3,200 rpm and 85" HgA at 28,000 feet dry. At WER (wet) it made 3,090 HP at 3,200 rpm and 100" HgA at 28,000 feet. Maximum cruise was 1,340 HP at 2,700 rpm at 26,000 feet. That ain't no slouch, but was basically a prototype.

The V-1710-131 mentioned above (a G3R made in -Hi and -Lo version with a different supercharger ratio) was made in a total quantity of 8 and was used on the XC-114, basically an Allison engined version of the C-54 transport. Would have been a good transport, but all out power is not desirable in a transport engine; reliability is. It was pretty reliable with the lower power made for XC-114 specific use.

If you can find an Allison G5, it makes 2,200 HP at sea level and max power.

They made 375 Allison G6R (right hand turn) and 375 Allsison G6L (left hand turn) engines for P-82 use, and these are the engines that are most desired for hot applications. Basically 1,700 HP at 21,000 feet. All the top Merlin guys at Reno run Allison G6 rods since the stock Merlin rods won't handle the power developed at higher rpm and MAP levels. Just FYI.

Total G series production was around 763 engines and they are rare these days.

Our shop can build about 12 - 15 G6 engines (R or L) depending on parts fallout when reconditioned for overhaul use. Need one? Call Yancey Enterprises, Rialto, California, U.S.A. We can do it.

 

[GregP]

Hi Tomo,

To get best horsepower, they should have tried less than 6.0 compression ratio. That's about what all the top unlimited racing guys at Reno are running and all are getting 3,800+ HP from their engines, both inline and radial. More boost without detonation requires a lower compression ratio to start with; that's how they can run 130"+ MAP ... but the engine won't run below about 5.0 or so at idle power, or even start in the first place at the low rpm generated by the electric starter.

I suppose 6.1 in WWII would have been pretty good.

 

[wuzak]

The V-1710-127 made 1,740 HP at 3,000 rpm and 52.5" HgA, 33,000 feet dry. It made 2,320HP at 3,200 rpm and 85" HgA at 28,000 feet dry. At WER (wet) it made 3,090 HP at 3,200 rpm and 100" HgA at 28,000 feet. Maximum cruise was 1,340 HP at 2,700 rpm at 26,000 feet. That ain't no slouch.

The V-1710-127 was the turbo-compound.

 

[GregP]

Yes it was, and it was an E series engine, not a G. The E series were not equipped with propeller shafts, but instead powered a driveshaft to a remote propeller case, such as in the P-63 or whatever experimental aircraft was being made with a remote engine installation. It was not a high-volume engine. Grade 115/145 fuel was specified and it was intended for the P-63H, but was never shipped and ran its life in a test cell. Interest in jet engines killed further development of not only the "hot" Allisons, but also the Merlins, Griffons, etc.

I believe the only aircraft V-12 engine developed after late 1944 to early 1945 was the Swiss Saurer YS-2 / YS-3 used in the Doflug D-3802 / 3803 fighters of 1947. These engines were developed from the basic Hispano-Suiza powerplants and were the "last hurrah" for the big pistons. Still, from 1944 onward, if production interruption were not a major "no-no," many great-performing aircraft COULD have been developed. Alas, they were not and the big pistons simply dies from lack of interest.

Luckily, there are still some left around and we get to see them fly!

 

[GregP]

Hi Tomo,

Regarding post #7, Allison proposed a 2-stage engine in both 1937 and 1942. Both proposal would have entailed a complete redesign of the accessory housing. The US Government declined to participate in the proposal in 1937 and forbade the new development in 1942. Allison also proposed further development of the turbocharger system on at least 3 occasion and was turned down on all 3 occasions.

General Arnold sent threatening letters to Allison asking for immediate development or possible repurcussions. The intent was clearly to get Allison and GM to proceed with development on their own initiative. We might recall that Allison was a small subsidiary of General Motors by 1939, and a sound business decision could not be made to proceed with developments that the primary customer was not enough interested in at the time to at least help with funding.

The situation in 1937 was different from that 1942, and the Government may well have been justified in declining, but so was Allison justified in not proceeding since the customer for the entire development was the US Government. Almost nobody else was buying or would have been allowed to buy the developed product.

Everyone concerned, including Allison knew what needed to be done, but the development that WAS done was that approved and funded by the primary customer and user. By late war, the Allison and the Merlin were very much comparable at any altitude, regardless of the lack of participation or approval of the US Government in Allison development.

In hindsight, Allison should have insisted on ownership or co-ownership of the rights. They never made that mistake again, just as Northrop will very probably never again develop and advanced jet fighter on their own money after the idiotic F-20 program result. You can bet all other manufacturers took notice of that one, too.

 

[tomo pauk]

Thanks for your input here, Greg. As you can notice, I was asking specifically about the feasible improvements of the single stage engine, while not going for second stage version ("So was there a way to increase it's capabilities (particularly high altitude ones), before going to the 2 stage variant?").

BTW:

General Arnold sent threatening letters to Allison asking for immediate development or possibl repurcussions.

Any way to check out the threatening letters?

Regarding post #7, Allison proposed a 2-stage engine in both 1937 and 1942.

I'm not sure that post #7 and two stage Allison are connected?

 

[PWR4360-59B]

R-3350 and R-4360 had a CR of 6.7 . 6.0 would be fine if you were burning nitro and boosting it way up. The problem with a low cr is that usually makes less turbulent combustion space. But then again the big bores are very prone to detonation, and is why the big engines run on old time tractor compression ratios.

 

[tomo pauk]

Those big radials could (and were) relying to the displacement to provide power; their RPM and boost levels were not that high. Se also the DB-601/605, Jumo 211/213 etc.
The small V-1710 was, well, small; 27L vs 34/35.7 for the DBs, 35L for Jumos. So it needed the boost, and RPM, if the power was to remain worthwhile. The RPM, for wartime engines was limited to 3000 rpm, not such a great value. The RPM got up to 3200 eventually, but none of such engines ever seen ww2. So we're left to boost. The greater compression ratio, the lower the boost the engine can 'swallow'. The late war V-1710s were mostly 6:1 CR engines, yet, again, none seen the ww2.
Merlin, the engine of similar displacement and RPM, had the CR of 6:1, that being one of the factors the engine achieved enviable boost levels, and hence power.

 

[GregP]

Hi Tomo,

I think going to a primary hydraulic drive instead of a mechanical one, increasing the impeller size and intake area, and dropping the compression to about 5.2 - 5.8 would have done the trick. The new impeller could have been as small a change as going to a 12" impeller with hydraulicly-coupled drive, with the slightly bigger intake opening, and the lowered compression ratio.

It is possible and probably likely that changing the gearing in the nosecase and slowing the prop down, coupled with a slightly larger prop would also help some.

I'd also opt for fuel injection, but that wasn't as necessary as the preceeding steps.

Just my two cents worth, and no, they didn't actually DO any of them.

Just FYI, today and yesterday at the shop, we were boring the cylinder liners for a Bristol Centaurus rebuild. BIG cylinders! 5.75 inch bore and 11 inch stroke. Looks like the monkey-motion sleeve valves would be the weak point if you increase the RMP above stock levels, and that is true in ral life ... they give up at a slight RPM increase over stock levels, but the stock Centaurus is a very strong stock engine and gives plently of grunt for a Sea Fury.

 

[PWR4360-59B]

Hi Tomo,

I think going to a primary hydraulic drive instead of a mechanical one, increasing the impeller size and intake area, and dropping the compression to about 5.2 - 5.8 would have done the trick. The new impeller could have been as small a change as going to a 12" impeller with hydraulicly-coupled drive, with the slightly bigger intake opening, and the lowered compression ratio.

It is possible and probably likely that changing the gearing in the nosecase and slowing the prop down, coupled with a slightly larger prop would also help some.

I'd also opt for fuel injection, but that wasn't as necessary as the preceeding steps.

Just my two cents worth, and no, they didn't actually DO any of them.

Just FYI, today and yesterday at the shop, we were boring the cylinder liners for a Bristol Centaurus rebuild. BIG cylinders! 5.75 inch bore and 11 inch stroke. Looks like the monkey-motion sleeve valves would be the weak point if you increase the RMP above stock levels, and that is true in ral life ... they give up at a slight RPM increase over stock levels, but the stock Centaurus is a very strong stock engine and gives plently of grunt for a Sea Fury.

Wow 11 inch stroke? Same Bore as 4360. I would like to visit that place some time. I guess your place is about the only one around that does any Centaurus engines. Is that for some restored brit plane? Cool stuff. Are those new liners? Or just a clean up on the factory bore using same pistons etc?

 

[GregP]

Hi Engguy,

Actually, we specialize in the Allison V-1710, but can easily work on other engines if required. It so happens we seem to be the only shop around that can bore a Centarus cylinder liner and have it stay round ... so we are doing a complete engine's worth of cylinder liners for a customer who likes the fact that our cylinders run pretty dry and are round when installed.

We've done Merlins, too, and the odd Griffon, but prefer the Allison as a core business. The important thing is whether or not you understand the engine and have the specifications for the critical fitments. Then the trick is to FIT the engine per the specs, not just accept what comes when you bolt it together.