Two stage V-1710: looking for good airframes

[tomo pauk]

Hello,
The conventional wisdom states that single stage V-1710 was a lousy performer above 15-20000 ft, due to numerous reasons. The 2 stage variant was better, but it never played a role in the outcome of the ww2. The main user, P-63, went to VVS, and records about the use are scarce.
So what airframe could put the two stage V-1710 into a good use? The performance* is 1150 HP at 22400 ft (military power), WER dry of some 1450 HP at sea level, WER wet 1800+ HP at sea level. Weight is comparable with single stage Griffon or 2 stage Merlin, but it's longer.

*for the engines available in late 1943/early 1944. Late 1944/early 1945 increases the altitude of mil power to 25000 ft

 

[wuzak]

P-51. They did shoehorn the two stage V-1710 into the P-51 at one point (XP-51J), and the P-82 had them as well.

 

[GregP]

The so-called two stage Allison was realy a single stage Allison with an auxilliary stage supercharger with a hydraulic drive. Any airframe witha Merlin in it might be candidate, but I'd have asked for a true two-stage mechanical unit for less complexity and less weight, though in truth the Aux stage isn;t very heavy. The shop where I work on V-1710's has two aux stage blowers and they add maybe 150 -200 pounds. A case for a emxahical 2-stage would ALSO add some weight and might save about 100 pounds or so.

If you look at the speed graph fior any Merlin-powered, 2-stage fighter, you'll see the top speed has a dogtooth look. That is the speed increases until a max is reached and then the speed drops off until the pilot switches to the higher gear, then it increases again until another max is reached and then falls off again. Typicaly and normal.

If you look at the top speed chart of a Bell P-63 equipped with the auxilliary supercharger, it has no dogtooth due to the hydraulic drive and is one smooth curve.

I'm not sure there is a tactical or strategic lesson in there, but it well might easilty be the plane to beat anywhere near the gear change points of the mechanical 2-stage engine powered fighters since it had no performance fall off at internediate height. There easily could have been development, too, if widely produced, but that, again, is another "what if," so I'll not pursue it.

Atfer the intake issues were solved, the Allison was a first class engine that, in developed form, ran right with a Merlin at most heights up to and including 35,000 feet plus. The US Government dictated most of the development of the Allison and got exactly what it directed from Allison Engineering. People may have wanted better power or whatever, but when they order a V-1710-111, then Allison is required by contract to deliver a V-1710-111, not some developed engine that is not Army Air Corps approved or on the contract.

I bet Allison wished they had never accepted US Government ownership of the design of the 1710, but once done, it could never be retracted. Rolls Royce never had to ask permission from the British government for developments, and they were much better off for it than it might have been otherwise.

 

[drgondog]

The Allison ended up the war with a very fine engine. Having said that, the USAAF dictated -143/145 series never quite drove the P-82 as fast as the Merlin 1650-9...

 

[wuzak]

The Allison ended up the war with a very fine engine. Having said that, the USAAF dictated -143/145 series never quite drove the P-82 as fast as the Merlin 1650-9...

Dictated what Bill? That the P-82 be powered by Allisons?

 

[GregP]

You know Drgondog, I have often wondered if the fact that the Allison P-82 was a small bit slower than the m,erlin P-82 was due to the propellers. Allison tended to concentrate on the Curtiss Electric prop and the Merlins used an Aeroproducts or Hamilton-Standard. I wonder if they tested opposite props with each of the V-12's?

Don't know and may never know, but prop selection could have an impact, depending on a few factors. After all, both V-12's were cleared for 3,000 rpm and the installations were quite similar except for the updraft / downdraft carb installations on the engines. Might make an interesting research project ...

 

[bob44]

How bout the P38.
Should be able to fit her in without too much redesign.

 

[Shortround6]

The major problem with the two stage Allison was fitting a decent inter-cooler into the airplane. Good inter-cooler= good high altitude performance. No inter-cooler = mediocre to poor altitude performance. The P-63 had no inter-cooler but used ADI (water injection) which helped but post war Merlins and Allisons used BOTH inter-coolers AND ADI to get their peak performance numbers.

The P-51 had the fuselage volume to accommodate a proper inter-cooler for the two stage Allison as did the even bigger P-82. Trying to shoehorn in inter-coolers on such air frames as the P-40 or P-63 was a lot harder. The Inter-coolers could also cause a loss of speed at the lower altitudes due to drag.

 

[wuzak]

How bout the P38.
Should be able to fit her in without too much redesign.

Lockheed did propose a P-38 with 2 stage V-1710s (along with studies for Merlin P-38s). The drawing shown in Vees for Victory looks pretty sleek. It didn't use an intercooler, thus having a smoothly transition from spinner to nacelle/boom.

I wonder about weight balances, though. The V-1710 with auxiliary supercharger is longer than the 2 stage Merlin, roughly the same weight, and a significant weight is being removed from behind the wings (ie the turbos). I suppose with the remote set up of the auxiliary supercharger it could be placed somewhere near the position of the turbo, using an extension drive. As was done with the auxiliary supercharger for the R-4360 in the XP-72.

 

[wuzak]

The major problem with the two stage Allison was fitting a decent inter-cooler into the airplane. Good inter-cooler= good high altitude performance. No inter-cooler = mediocre to poor altitude performance. The P-63 had no inter-cooler but used ADI (water injection) which helped but post war Merlins and Allisons used BOTH inter-coolers AND ADI to get their peak performance numbers.

The P-51 had the fuselage volume to accommodate a proper inter-cooler for the two stage Allison as did the even bigger P-82. Trying to shoehorn in inter-coolers on such air frames as the P-40 or P-63 was a lot harder. The Inter-coolers could also cause a loss of speed at the lower altitudes due to drag.

The intercooler they used was similar to that on the Merlin - ie a liquid:air intercooler. Thus the space required wasn't that much. Just need to provide an additional radiator. which would be smaller than the intercoolers fitted to teh P-38.

 

[Shortround6]

The provision of the engine part of a liquid:air intercooler isn't that hard. It is the provision of the extra radiator. Much like the difference between the MK V Spitfire and a MK IX. The MK IX had enough extra power to over come the extra drag at low altitude.
The P-63 avoided the extra drag by using ADI. 1700-1800hp WEP at sea level but 1100-1150hp at 25,000ft, A good intercooler would have been worth several hundred horsepower at 25,000ft but would have cost speed at sea level.
A two stage Allison with intercooler instead of ADI might have had 1700-1800hp at sea level but the plane would have been slower.

 

[wuzak]

The provision of the engine part of a liquid:air intercooler isn't that hard. It is the provision of the extra radiator. Much like the difference between the MK V Spitfire and a MK IX. The MK IX had enough extra power to over come the extra drag at low altitude.
The P-63 avoided the extra drag by using ADI. 1700-1800hp WEP at sea level but 1100-1150hp at 25,000ft, A good intercooler would have been worth several hundred horsepower at 25,000ft but would have cost speed at sea level.
A two stage Allison with intercooler instead of ADI might have had 1700-1800hp at sea level but the plane would have been slower.

The P-38 already had a location for an intercooler radiator - where the intercoolers were fitted on the -J and -L. Though the sketch of the proposed 2 stage V-1710 installation in the P-38 shown in Vees for Victory doesn't have one there. I can't recall if it actually had the intercooler, though.

 

[tomo pauk]

Maybe the A-20 + two stage V-1710 equals US Mosquito? Not being a fighter means that intercooler is not a necessity?

 

[Shortround6]

There are reasons the US used the R-2600 as a bomber engine inspite of some difficulties. One thing is that even the "A" series engines in the A-20 were good for 1600hp for take-off without water injection of WEP power settings that require extra maintenance. Another is that the "A" series was good for 1350hp at 5,000ft and 1275hp at 11,750ft max continuous. An early A-20 could make just over 300mph at 12-15,000ft using max continous power as long as the fuel held out, which at just over 300 gallons an hour wasn't going to be that long.

The V-1710 used in the P-63A was good for 1325hp for take off, While it offered more power at higher altitudes like 20,000ft and up it's max continuous rating was hundreds of horsepower lower than the R-2600 at lower levels, Will the better streamlining make up for it?

You do have to get bombers off the runway and it is better if you don't plan from the beginning to use WEP power levels to do so. The use of WEP power settings can allow for growth ( still not a good idea) or operations in emergency settings, like hot and high with overloads.

 

[GregP]

The A-20 could cruise at max continuous power of about 75% max HP. The Allison V-1710 could do the same. So, what is your point?

Most late war Allisons were 1,425 HP miltary and 1,600 HP WER. A 75% cruise is pretty decent. The Allison powered aircraft will be much slicker and will cruise just as fast or faster than the R-2600 powered aircraft. I mkight remind you that the P-38 wa no slouch in cruise, climb, or top speed. Was it the best at anuything? No. Was it pretty darned good? Yes.

 

[tomo pauk]

The two stage V-1710 from P-39A has 1050 HP at 10000 ft, max continuous, or 1000 HP at 20000 ft. That compares well with V-1650-1 - 1080 HP at 9500 ft, or 1010 HP at 16000 ft. Two stage V-1710 will weight more, but the drag penalty is almost the same. The historical A-26 has 2 x 1275 at 11800. Streamlining worked well in Mosquito's case, so why not for the A-20.

Two Packard Merlins would consume 185-195 US an hour, or 2/3rds of what 2 R-2600s will, the 2 stage Allison is in the ballpark with Packard Merlin. So the fictions A-20 with 2 stage Allisons can take off with 2/3rds of the fuel, in order to attack the same target the historical A-20 will - instead of 540 gals, we can take off with 360, or with almost 1100 lbs less.
Alternatively, with the full load of fuel, it can attack the target located 50% further.

 

[krieghund]

I prefer this installation.....

 

[Shortround6]

The two stage V-1710 from P-39A has 1050 HP at 10000 ft, max continuous, or 1000 HP at 20000 ft.

From a P-39A?

OK, I have done a lot mistyping myself

The historical A-26 has 2 x 1275 at 11800. Streamlining worked well in Mosquito's case, so why not for the A-20.

Assuming your V-1710 installation can knock about 20% of the drag off the radial engine version you actually come out about the same. 20-22% reduction is what they got on a single engine fighter, I doubt a twin engine bomber would see the same reduction unless you play some real games with the fuselage.

So the fictions A-20 with 2 stage Allisons can take off with 2/3rds of the fuel, in order to attack the same target the historical A-20 will - instead of 540 gals, we can take off with 360, or with almost 1100 lbs less.
Alternatively, with the full load of fuel, it can attack the target located 50% further.

It doesn't work quite that way. 1. even a single stage Allison burns 109-115 GPH at maximum continuous. A two stage might use a little less due to more efficient supercharger but you are only using around 4-5lbs of boost. 2. once you back off the max continuous the radials get somewhat better. An A-20 can do about 253mph true at 12,000ft burning 147gph. Maybe best case but few missions were flown at max continuous from leveling off after take-off to slowing down for approach to landing. At max continous the Radials are running extra rich and using some of the fuel as a coolant. Once they are running lean in a more normal cruise setting the fuel burned per HP/HR is a lot closer to the liquid cooled engines. The liquid cooled engines see a large drop going to lean condition but not as much as the radials.

 

[Shortround6]

The A-20 could cruise at max continuous power of about 75% max HP. The Allison V-1710 could do the same. So, what is your point?

The point is that 75% of 1600 is a lot more than 75% of 1200-1325hp.

Most late war Allisons were 1,425 HP miltary and 1,600 HP WER.

And these were used in??????
P-38 engines gave more power than the non-turbo V-1710s because at most points in time the P-38 engines used a lower gear ratio to the supercharger which allowed for more net HP to the propeller for the same indicated or gross HP because the supercharger was taking less power.
The P-63C got a 1425hp for take-off Allison but since they don't show up until Jan of 1945 it is a poor engine to base a "what if" on compared to a 1600hp R-2600 that showed up in winter of 1940/41.

I mkight remind you that the P-38 wa no slouch in cruise, climb, or top speed. Was it the best at anuything? No. Was it pretty darned good? Yes.

The P-38 was a very good airplane and perhaps under rated by many. That does not mean that sticking non-turboed (or even turboed) V-1710s in a bigger, heavier bomber instead of R-2600s is a real good idea. The drag of the engine installation is a smaller percentage of the total drag on an A-20 than on a P-38.

 

[wuzak]

Here are some numbers I got from the RRHT a while back for the Vulture II (would be X-2600 in US parlance, or XX-2600 for the experimental versions) and the Merlin XX.

Vulture II
(Moderate gear):
Max t/o (SL) - 1800bhp, 3200rpm, 6lb boost, 162gph;
Max climb - 1700bhp, 2850rpm, 6lb boost, 142.5gph;
Max cruise - 1480bhp, 2600rpm, 5lb boost, 0.61 pt/bhp/hr
(High gear):
Max cl - 1455bhp, 2850rpm, 6lb boost, 134.5gph;
Max cr - 1290bhp, 2600rpm, 5lb boost, 0.66 pt/bhp/hr

Merlin XX
(Moderate gear):
Max t/o (SL) - 1280bhp, 3000rpm, 12lb boost, 0.64-0.71 pt/bhp/hr;
Max climb - 1220bhp, 2850rpm, 9lb boost, 0.57-0.63 pt/bhp/hr;
Max cruise - 1080bhp, 2650rpm, 7lb boost, 0.54-0.59 pt/bhp/hr
(High gear):
Max cl - 1130bhp, 2850rpm, 9lb boost, 0.63-0.70 pt/bhp/hr;
Max cr - 1015bhp, 2650rpm, 7lb boost, 0.57-0.64 pt/bhp/hr

A Vulture type engine (with reliability sorted) would be at least as good as the R-2600, though weighing more. Bear in mind that the Vulture's figures are derated due to technical and reliability issues. Teh Vulture would be available in 1940/41, but not after that.