Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
'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.
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.
I've seen estimates that both were not only faster, but had a range advantage too (over the "standard" B-29 and B-17.
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.
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.
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.
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.
yes, no and maybe.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.
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.
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.
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.
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)
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 Tomo,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.
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?
At least the Allison passed the 150-hour type test DURING the war. The Merlin never did until after the war.
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.
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?
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.
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.