Allison V-3420- Anyone have information on it? It seems like it would have been perfect for the XB-42.

[wuzak]

'It didn't make the war' is not just a footnote, but a major disadvantage. It was not even flown. Advantage in power at 20000 ft and above vs. 100 series Merlin is meagre, even if we believe what Allison said.
Other disadvantages include the length even greater than of the long 2-stage V-1710s, so the ability to be retrofitted on an existing fighter - unless that is P-47/F4U/F6F - is about zero.

Likely the only existing single engine fighter that could have used it was the P-63, because its mid mounted engine location made it easier to dump the exhaust from the turbine overboard.

 

[wuzak]

I've seen some estimates that would give the B-38 Fortress about 1000 more miles range at the cost of a slightly lower operating ceiling. That would make it a very attractive option in the early Pacific campaigns where the B-24 was proving to be a "dog," a very difficult aircraft to operate and maintain. If the B-38 eventually proved successful and had range equal or better than the "difficult" B-24, the B-24 could be cancelled. Production prior to the B-29 could be focused on B-17 and B-38s, with different factories assembling the two variants. Those already turning out standard B-17s, mostly for Europe, would continue. B-24 factories would convert to the B-38, until production of the B-29 was ready.

Where are you getting that?

Doubtful that the XB-38 would get much extra range, if at all.

The XB-38 used the same turbo as the B-17, so it is likely that critical altitude was lower for the XB-38 if using extra boost.

The XB-39 as tested did not have the turbochargers fitted.

I've seen estimates that both were not only faster, but had a range advantage too (over the "standard" B-29 and B-17.

The XB-39 had less range than the B-29.

The XB-39 had 4 x 2600hp, the B-29 (at that point) had 4 x 2,200hp. That is 18% more power.

More power = more fuel used.

 

[tomo pauk]

Likely the only existing single engine fighter that could have used it was the P-63, because its mid mounted engine location made it easier to dump the exhaust from the turbine overboard.

Me, I'd install the 2-stage V-1710 on a P-47, use it's turbine as a power-recovery unit, that is connected via a shaft to the V-1710. Should've lloked like the XP-47H. Speed - comparable with the ordinary P-47, tad a better climb at lower altitudes, the main advantage would've been the considerable increase of the range/radius.

 

[GregP]

Early war, yes. But the altitude gap increased when teh Merlin 45 debuted in 1941.




The Merlin 66 could make 2000hp with PN150 fuel and +25psi boost.




The P-38 engines were turbocharged, so their altitude rating (by themselves) was essentially 0ft. It's not really a direct comparison with the Merlin.




The V-1710-127 was a turbo-compound variation. It had 2 stage supercharger and a power recovery turbine (turbine was from a C-series turbo).

It had run by the end of the war, but I am not sure how ready it was, since it kept melting turbines. Allison would have developed an air-cooled turbine for the engine after the war had it been requested. But it was not.

The turbine added around 1,000hp to the engine output.

Bunk, Wayne, The P-38 IS exactly comparable with a 2-stage Merlin.

The 2-stage Merlins had a second supercharger stage and the two stage Allison in a P-38 also had a second compressor stage, too, but it was run from a turbocharger. Both had a low-altitude and a high-altitude boost system. The late-war Allisons ran very well and had very few issues. The so-called turbine above, was the second-stage boost. It added what it added and the high-altitude power was comparable with Merlins at altitude.

If you really want to separate the second stage from the rest of the engine, then separate the Merlin second stage, too and then do a comparison of single-stage engines. They compare well, too.

 

[GregP]

Before mid-1940, on 100 oct (since V-1710 will not function as desired on 87 oct) Merlin III was far better at lower altitudes, too, by ~250 HP.
From mid-1940 on, Merlin XX sweeps the tables, making same power at 20000 ft as V-1710 is doing at 15000 ft. It is also much better down low.
V-1710-39 and the like from early 1941 are still behind the curve vs. Merlins.
It will took until late 1942 for the V-1710 to equal the Merlin XII from mid-1940, and was not still as good as Merlin 45 from the early 1941.

These are not some differences to help one win the bar bet - engines being second- or 3rd-best in the theater of war were a main brake for the P-40 and P-39 to be competitive against what Axis had.

Small advantage was with V-1710 wrt. ability to be run at low settings for better gas mileage, and that it had a better carb. If the low-altitude power was really desired, there was a host of low-altitude Merlins offering whatever the power the V-1710 was making, while the opposite was not the case.



Turbocharged V-1710's ability to be retrofitted on the most important existing fighters was very low, unlike what was the case with 2-stage Merlins. Installed weight and drag of the 2-stage Merlin was lower, reliability was much higher. There is also a thing of exhaust thrust - equivalent of 10-12% extra power at medium altitudes, even more % at high altitudes, vs. as good as zero on the turbocharged V-1710. Ram effect - worth of 4000-5000 ft on a 2-stage Merlin vs. 1000-1500 ft on a turboed V-1710.
At the end, there was a lot to choose from the 2-stage Merlin, including the easier handling during the flight.
Even the Merlin XX was making power comparable to the early turbocharged V-1710, with less issues, lower weight, extra exhaust thrust, less volume required, lower drag.



'It didn't make the war' is not just a footnote, but a major disadvantage. It was not even flown. Advantage in power at 20000 ft and above vs. 100 series Merlin is meagre, even if we believe what Allison said.
Other disadvantages include the length even greater than of the long 2-stage V-1710s, so the ability to be retrofitted on an existing fighter - unless that is P-47/F4U/F6F - is about zero.

Hi Tomo.

I don't care at all about pre-war Allisons or Merlins. We weren't in the war and there was no wartime development push over here.

The early Allisons had a few issues with the intake manifold and the American-vs-British fuel issue. That took about 7 months to fix, largely because they never sent any British fuel back to the U.S.A. to run in the test cell until then, at which time the issue could finally be replicated in the test cells. Once that was understood and corrected with proper jetting and having everyone run the same fuels, the Allison was a solid engine and made competitive power in similar configurations. By the end of the war, the Alison was nudging 3,000 hp. Fact, not fantasy.

The lightweight Mustangs were done with both Allison and Mein engines, and both had very nearly the same performance. The delta was some 2-5 mph out of about 490 mph, which is well within instrument error. There was little to choose among all 3 of them. I think they went with the Merlin in the P-51H largely because they had a cadre of Merlin-trained mechanics in place and the Merlin choice would make for minimal retraining, powerplant-wise anyway. Had I been in charge, I'd likely have made the same decision, not out of a preference for a Merlin (or lack of it, for that matter), but out of economics of the entire project ... the choice made sense economically. The war WAS an expensive one.

I'm not minimizing or trying to minimize the impact of the Merlin. It was a great engine, no question. But the Allison was not nearly as bad as is being suggested in here. It was a pretty good engine, too. When fitted with a debugged high-altitude boost system, it was every bit as good as a 2-stage Merlin at 25,000 feet.

The Spitfire Mk IX made 415 mph at 27,800 feet altitude and had a service ceiling of about 42.500 feet at 7,485 lbs. T
The P-38L went 414 mph at 25,000 feet and had a service ceiling of about 44,000 feet at 17,500 lbs.

Pretty darned even with very comparable engine power and altitude tuning.

 

[wuzak]

Bunk, Wayne, The P-38 IS exactly comparable with a 2-stage Merlin.

The 2-stage Merlins had a second supercharger stage and the two stage Allison in a P-38 also had a second compressor stage, too, but it was run from a turbocharger. Both had a low-altitude and a high-altitude boost system. The late-war Allisons ran very well and had very few issues. The so-called turbine above, was the second-stage boost. It added what it added and the high-altitude power was comparable with Merlins at altitude.

Turbocharged 2 stage systems work differently than mechanically supercharged 2 stage systems.

Firstly because the turbocharger basically compensates for altitude, the engine stage supercharger can be geared at a lower speed and run at a lower pressure ratio, reducing the power to drive it. The single stage engine separated from the turbocharger would have little or no altitude performance.

In contrast, the Merlin's 2 stage supercharger would still give some altitude performance if the first stage was removed (if that is possible).

If you really want to separate the second stage from the rest of the engine, then separate the Merlin second stage, too and then do a comparison of single-stage engines. They compare well, too.

To be fair, we should compare single stage, single speed engines with each other (Tomo compare V-1710 single stage, single speed with 2 speed Merlin XX earlier).

The Merlin 45 of 1940/1941 had vastly superior altitude performance than the equivalent period V-1710. The 46 or 47 (I can't remember which) had a bigger impeller and even more altitude performance. This was at the cost of low altitude and take-off performance.

The V-1710 had the better low down performance because the engine was a lower altitude engine. The critical altitude could be changed with gearing, to some degree, but it would not match the Merlin 45's performance.

 

[Shortround6]

Turbocharged 2 stage systems work differently than mechanically supercharged 2 stage systems.

Firstly because the turbocharger basically compensates for altitude, the engine stage supercharger can be geared at a lower speed and run at a lower pressure ratio, reducing the power to drive it. The single stage engine separated from the turbocharger would have little or no altitude performance.

yes, no and maybe.

The P-38 turbo engines have a much more complicated history.

You are quite right in that is how they started out. The early P-38 engines Used 6.44 supercharger gears from the YP-38s through the P-38E( F-4 recon) versions and they used the B-2 turbo. They operated as you have described.
However the P-38F used 49/53 engines with 7.48 gears and the B-2 turbo. These are the 1325hp engines, The P-38G s used the same gears but got B-13 turbos. same power rating.
We could assume that these engines would operate much like the engines in the A-36 if their turbos were removed.

The P-38H engines got 8.10 supercharger gears and with the H-5 block got B-33 turbos. One can assume that the engines would operate somewhere between the A-36 engines and the
engines with the standard 8.77 gears.
The engines could make the rated 1425hp at sea level without using the turbo but of you wanted that very high up you are going to need the turbo, if you are happy with the 1150hp of the earlier engines you could get that into the high 4 digit range, maybe 8-9000ft.
The improved turbos allowed for more boost and/or airflow to made as the altitude went up. The B-33 turbos would support 1600hp at at 24,000ft (60in MAP)


The two stage Merlins used a slightly cropped impeller. 10.1 in vs 10.25 in. The gear ratios were also lower but they used several different sets.
The Merlin 60 and 62 used 5.52 & 8.41
The Merlin 61,63, others used 6.39 & 8.03
The Merlin 65 and 67 used 5.79 & 7.06

So in low gear it wouldn't have much power at altitude either. High would have been somewhat better than the Allison considering the bigger impeller.

Standard Merlin 45 used a 9.089 gear set.

 

[don4331]

V-3420 in XB-42 rather than 2 - V-1710s would seem to have whole lot of disadvantages for no advantages.

As I understand it (From Vee's for Victory), the V-3420 used a single supercharger which had mixture distribution issues. Why wouldn't (didn't) Allison bite the bullet and just use 2 regular V-1710 superchargers, I don't know DB-606 used regular and mirrored rather than single large supercharger...

There's also if one bank has issue - e.g. connecting rod failure, the co-joined engines both fail. While two separate engines only have the gear reduction drive as single point of failure. Such a failure is the main issue with the German double V, and I believe the demise of one of the P-75 prototypes.

Lastly with 2 separate engines, you can shut one engine down and run other at peak efficiency - more economic both from fuel and maintenance perspective.

 

[GrauGeist]

The DB610 used a coupling gearcase that had the ability to disengage either engine, enabling the remaining engaged engine to drive the output shaft.

 

[tomo pauk]

I don't care at all about pre-war Allisons or Merlins. We weren't in the war and there was no wartime development push over here.

It is not about what you care, but what it was.
Before September of 1939, UK was also not in the war, still Merlin was being mass produced and powering combat aircraft in service, while V-1710s were being produced (produced??) in ones and twos.

The early Allisons had a few issues with the intake manifold and the American-vs-British fuel issue.

Any other American engine run just fine on 'British' fuel.
Only the 'Merlin was a hand-made engine' myth is more persistent than 'it was British fuel' myth.

Once that was understood and corrected with proper jetting and having everyone run the same fuels, the Allison was a solid engine and made competitive power in similar configurations. By the end of the war, the Alison was nudging 3,000 hp. Fact, not fantasy.

"In similar configurations" - that is the kicker. V-1710 never gotten a big enough 1-stage supercharger, there was no 2-speed supercharger, the 2-stage S/C was 1 year later, was without intercooler and was not making the same high-altitude power in 1944 vs. what Merlin 61 did two years earlier. Best 1-stage supercharged V-1710 was as good as the 3rd best Merlin, the 1-stage 1-speed types with small impeller.
Engines running on test beds don't win the wars, not even the single air combat.

The lightweight Mustangs were done with both Allison and Mein engines, and both had very nearly the same performance. The delta was some 2-5 mph out of about 490 mph, which is well within instrument error. There was little to choose among all 3 of them. I think they went with the Merlin in the P-51H largely because they had a cadre of Merlin-trained mechanics in place and the Merlin choice would make for minimal retraining, powerplant-wise anyway.

There is a lot to choose from the XP-51J vs. it's Merlin-powered brethren - timing. XP-51J 1st flew in April 1945 . XP-51F started flight tests in late October of 1943, the XP-51G in August 1944, the XP-51H in February 1945.
Flights of the XP-51J were limited to 54 in Hg and 2700 rpm, for 1150 HP max (per 'Vees for victory', pg. 189)- talk 400 mph, rather than 490 mph, until/unless the engine problems are solved.
The Merlin choice was right due to engine actually being there and making power. Allison with V-1710 was unable to emulate that.

I'm not minimizing or trying to minimize the impact of the Merlin. It was a great engine, no question. But the Allison was not nearly as bad as is being suggested in here. It was a pretty good engine, too. When fitted with a debugged high-altitude boost system, it was every bit as good as a 2-stage Merlin at 25,000 feet.

Last sentence is dead wrong. Thing with V-1710 was not that it was a bad engine - and I've never suggested that - but that it was not as good as Merlin. But the real problem was that German engines were also making better power above 10000 ft, apart vs. turboed V-1710s that were with limitations of their own.

To be fair, we should compare single stage, single speed engines with each other (Tomo compare V-1710 single stage, single speed with 2 speed Merlin XX earlier)

I am being fair, and compare the Merlins with V-1710s from the same era. A 2-speed S/C drive on a lot of Merlins was a feature, lack of the 2-speed S/C drive on the V-1710 was a bug.

 

[GregP]

Turbocharged 2 stage systems work differently than mechanically supercharged 2 stage systems.

Firstly because the turbocharger basically compensates for altitude, the engine stage supercharger can be geared at a lower speed and run at a lower pressure ratio, reducing the power to drive it. The single stage engine separated from the turbocharger would have little or no altitude performance.

In contrast, the Merlin's 2 stage supercharger would still give some altitude performance if the first stage was removed (if that is possible).




To be fair, we should compare single stage, single speed engines with each other (Tomo compare V-1710 single stage, single speed with 2 speed Merlin XX earlier).

The Merlin 45 of 1940/1941 had vastly superior altitude performance than the equivalent period V-1710. The 46 or 47 (I can't remember which) had a bigger impeller and even more altitude performance. This was at the cost of low altitude and take-off performance.

The V-1710 had the better low down performance because the engine was a lower altitude engine. The critical altitude could be changed with gearing, to some degree, but it would not match the Merlin 45's performance.

Hi Wayne.

You said,"Turbocharged 2 stage systems work differently than mechanically supercharged 2 stage systems.? Ya' think?

It is not about what you care, but what it was.
Before September of 1939, UK was also not in the war, still Merlin was being mass produced and powering combat aircraft in service, while V-1710s were being produced (produced??) in ones and twos.



Any other American engine run just fine on 'British' fuel.
Only the 'Merlin was a hand-made engine' myth is more persistent than 'it was British fuel' myth.



"In similar configurations" - that is the kicker. V-1710 never gotten a big enough 1-stage supercharger, there was no 2-speed supercharger, the 2-stage S/C was 1 year later, was without intercooler and was not making the same high-altitude power in 1944 vs. what Merlin 61 did two years earlier. Best 1-stage supercharged V-1710 was as good as the 3rd best Merlin, the 1-stage 1-speed types with small impeller.
Engines running on test beds don't win the wars, not even the single air combat.



There is a lot to choose from the XP-51J vs. it's Merlin-powered brethren - timing. XP-51J 1st flew in April 1945 . XP-51F started flight tests in late October of 1943, the XP-51G in August 1944, the XP-51H in February 1945.
Flights of the XP-51J were limited to 54 in Hg and 2700 rpm, for 1150 HP max (per 'Vees for victory', pg. 189)- talk 400 mph, rather than 490 mph, until/unless the engine problems are solved.
The Merlin choice was right due to engine actually being there and making power. Allison with V-1710 was unable to emulate that.



Last sentence is dead wrong. Thing with V-1710 was not that it was a bad engine - and I've never suggested that - but that it was not as good as Merlin. But the real problem was that German engines were also making better power above 10000 ft, apart vs. turboed V-1710s that were with limitations of their own.



I am being fair, and compare the Merlins with V-1710s from the same era. A 2-speed S/C drive on a lot of Merlins was a feature, lack of the 2-speed S/C drive on the V-1710 was a bug.

Hi Tomo,

Your second sentence says it all, Allison V-1710s were not being produced much before the war, and development was almost nothing until the war started or at least was looked at with some concern, even though the engine power section itself was basically a 1929 design. The early Merlins WERE better, but not by much.

A Merlin C made 1,029 hp at 2,650 rpm and 11,000 feet. A V-1710-C made between 1,050 and 1,150 hp at 2,600 - 3,000 rpm, altitude unknown and so assumed to be sea level. Pretty even. I'd say making that power at 11,000 feet was better than making it at sea level.

The "British fuel" was a fact, not a myth. The difference was the amount of aromatics included in the fuel. But, you know that. Once it was figured out, if there was no problem with it, why then did they make changes so we all used the same fuel? The answer is rather obvious; it DID make a difference ... along with the Allison intake issue that was solved.

I'm not trying to make the Allison better than it was or the Merlin worse than it was. The Merlin was and is a great engine. The P-40F WAS a bit better than a P-40E. But not by much. The difference wasn't worth betting your life on. You needed to fly the aircraft well if you were in either one.

 

[GTX]

This book might be of interest:

 

[GregP]

The advantage was not meager, Tomo.

Both Allison and Rolls-Royce had test-stand engines that never flew, but ... they all make the power charts since they ran and COULD have been produced. The R.M. 17 certainly makes the power charts ... at about 2,350 hp in one instance with 150-grade fuel and about 2,620 hp in another instance ith 150-grade fuel and water injection. It didn't fly but is widely bandied about as what was possible in Rolls-Royce literature and charts.

The Allison V-1710-127 put out a solid 2,950 hp.

So, a 250 hp advantage for an early Merlin over an early Allison is significant, but a 500+ hp advantage for the later Allison V-1710-127 over the R.M. 17 is not to be considered? Who is trying to fool who here?

The R.M. 17 and the V-1710-127, though both very impressive by any measure from a technical standpoint, were not proceeded with directly because jet engines WERE being proceeded with. There was no other reason. Had pistons been carried on with, both could have been good, serviceable engines. As it is, they both made recorded engine runs at whatever power they made at the time.

At least the Allison passed the 150-hour type test DURING the war. The Merlin never did until after the war.

None of which stops the Rolls-Royce Merlin from being the generally-accepted top inline Allied engine of the war.

That doesn't mean the Allison was less than a good engine. It wasn't. Being a "fan" of one engine doesn't mean all the others are trash. I'll venture to say that very few "bad" engine ever made production status. What would be the point of producing something nobody wanted to buy or use?

 

[tomo pauk]

Both Allison and Rolls-Royce had test-stand engines that never flew, but ... they all make the power charts since they ran and COULD have been produced. The R.M. 17 certainly makes the power charts ... at about 2,350 hp in one instance with 150-grade fuel and about 2,620 hp in another instance ith 150-grade fuel and water injection. It didn't fly but is widely bandied about as what was possible in Rolls-Royce literature and charts.

The Allison V-1710-127 put out a solid 2,950 hp.

So, a 250 hp advantage for an early Merlin over an early Allison is significant, but a 500+ hp advantage for the later Allison V-1710-127 over the R.M. 17 is not to be considered? Who is trying to fool who here?

I'm trying to compare the in-service engines, since those really mattered for the Allied war effort and contributed to the eventual victory. Along with the other engines that were limited to the test benches (and without offense to the people behind them), the -127 contributed nothing for the Allied war effort.
I'd be fooling other people if I'd say that V-1710 was equal to the Merlin.

At least the Allison passed the 150-hour type test DURING the war. The Merlin never did until after the war.

If only Germans knew that, they would've simply decimated the RAF in 1940.

 

[GregP]

I'm trying to compare the in-service engines, since those really mattered for the Allied war effort and contributed to the eventual victory. Along with the other engines that were limited to the test benches (and without offense to the people behind them), the -127 contributed nothing for the Allied war effort.
I'd be fooling other people if I'd say that V-1710 was equal to the Merlin.



If only Germans knew that, they would've simply decimated the RAF in 1940.

Whether or not the Merlin passed anything had zero to do with the German experience. The only thing that mattered were combat results, as I'm pretty sure you know.

 

[wuzak]

Both Allison and Rolls-Royce had test-stand engines that never flew, but ... they all make the power charts since they ran and COULD have been produced. The R.M. 17 certainly makes the power charts ... at about 2,350 hp in one instance with 150-grade fuel and about 2,620 hp in another instance ith 150-grade fuel and water injection. It didn't fly but is widely bandied about as what was possible in Rolls-Royce literature and charts.

The Allison V-1710-127 put out a solid 2,950 hp.

So, a 250 hp advantage for an early Merlin over an early Allison is significant, but a 500+ hp advantage for the later Allison V-1710-127 over the R.M. 17 is not to be considered? Who is trying to fool who here?

The Merlin RM.17SM was cleared for flight at around 2,300-2,400hp. It was type tested and rated at 2,200/2,100hp hi and low gear. 2,600hp was achieved with higher rpm (3,150), higher boost (+36psi), higher grade fuel (~PN160) and water injection.

The V-1710-127 was a turbo-compound engine. I can't recall if it passed a type test, but it had problems with its exhaust being too hot for the power recovery turbine. It was also longer than an already long engine (2 stage V-1710). The turbine recovered as much as 1,000hp.

The RM.17SM would plug into a Spitfire or Mustang without much issue. There weren't too many aircraft that could take the V-1710-127 without extensive modification of the airframe or engine.

 

[GregP]

So, did the R.M. 17 fly? If so, in what? Packaging issues are variable and the package can be changed in shape as required, as long as all the pieces are somewhere. Look at the very large and cumbersome-looking turbocharging system employed by the P-47. It seems unlikely, but it resulted in one of the finest high-altitude fighters of the war, and also the fastest of any at just over 500 mph, with service versions making in the 470s at high altitude.

In point of fact, the V-1710-127 made considerably more power than any Merlin ever operated, much less flown. The only Merlin that came close ALSO didn't fly, but ran quite well on the test stand.

None of the above denigrates the operational Merlin accomplishments which were considerable and of which we are all aware. It also doesn't lessen the development effort Allison put into the V-1710, even if it came along too late to be in combat. Allison did, in fact, exceed the power levels generated by any running Merlin. It's just that you guys can't seem to acknowledge the fact without screaming about it being wrong or somehow unimportant or irrelevant.

But, that's OK. It happened anyway in Indianapolis, Indiana, right across from the Speedway.

It doesn't turn a P-40 into a Spitfire by any means. The fastest ocean liners came when ocean liners were being obsoleted by air travel, just like the big piston engines were obsoleted by jet engines and turboprops,

 

[wuzak]

So, did the R.M. 17 fly? If so, in what?

I'm not sure if the RM.17SM flew, but it was cleared for flight testing at (IIRC) 2,380hp in late 1944.

If it did fly it would have been in one of Rolls-Royce's test hacks.

Packaging issues are variable and the package can be changed in shape as required, as long as all the pieces are somewhere.

The RM.17SM was very much a Merlin. Most of the changes were internal and to the supercharger.

To fit it in an aircraft fitted with a 2 stage Merlin should not have required very many modifications, if any at all.

In point of fact, the V-1710-127 made considerably more power than any Merlin ever operated, much less flown. The only Merlin that came close ALSO didn't fly, but ran quite well on the test stand.

You asked if the RM.17SM flew, and then state that it did not.

I am not sure, but it was cleared for flight testing.

The V-1710-127 was a turbo-compound. The turbine added ~1,000hp to the power output.

I'm sure Rolls-Royce could have done the same for the Merlin, though it would have taken more re-engineering to get it to work, since it was less modular than the V-1710.

The V-1710-127 was based on the 2 stage engine, which was long to begin with. And then there is a large turbine bolted on the back of that. It would take considerably more engineering to fit that to an existing airframe The only proposed use for the engine seems to have been the XP-63H.

To my knowledge, the V-1710 was never type tested (the RM.17SM was), and was never cleared for flight.

Reliability was an issue, as the exhaust temperature at WEP was too high for the turbine. Had it continued, Allison would have designed a new turbine with air-cooled blades. But that didn't happen before the project's cancellation in 1946.

When did the V-1710-127 first run on the test bench?

 

[ThomasP]

As far as I am aware, the V-1710-127 was run up to 2800 BHP on the test stand, never to 2920 BHP. I have never been able to find any official info saying that it was run at the higher output - if there is any out there I would very much like to see it?

The NARA records include a planned flight test program outline and orders to proceed with developing the preliminary rating for the flight test engine, installation and flight testing of the test engine in the Bell Model 45/XP-63H (a modified P-63E-1) - but the orders were cancelled before the V-1710-127 engine installation occurred. NOTE that all of the above was to occur in 1945-1946.

Dry Weight of the engine with all normal ancillaries + 2nd stage SC + turbo-compound exhaust driven turbine/gear box equipment was about 2000 lbs.

 

[ThomasP]

Preliminary V-1710-127 engine ratings for the engine flight tests were to be:

Normal_1100 BHP at 2000/2600 rpm from SL to 30,000 ft
Military_1550 BHP at 3200 rpm from SL to 29,000 ft
TO_____1450 BHP at 3000 rpm