Why didn't Allison work harder on developing it? Did it have some serious flaw? (Hard to believe because the V-1710 seemed to be more reliable and easier to build than the Merlin. I'm beginning to think that the Allison got a really bad rap.) Like the P-38, a 1942 XB-42 COULD have gotten one (or two) good turbochargers... Of course the XB-42 might have been even better if it was a tractor ala the R2Y than a pusher...
Allison V-3420- Anyone have information on it? It seems like it would have been perfect for the XB-42.
- Thread starter Kilkenny
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ThomasP
Senior Master Sergeant
It is not so much that the Allison got a bad rap, as it is that it did not get as good a rep as the Merlin.
The reason is simply that the Allison was about 2-3 years behind the Merlin in advanced high-altitude performance, re it did not receive an ~equivalent 2-stage SC until post war. The Merlin 60 series entered production in mid-1942, while the ~equivalent 'G' series Allison did not enter production until early-1945? Even then, the Allison 2-stage SC was not as compact as the RR 2-stage.
On the other hand, even the early-war V-1710 had a few detail aspects in terms of reliability that were better than the Merlin.
The reason is simply that the Allison was about 2-3 years behind the Merlin in advanced high-altitude performance, re it did not receive an ~equivalent 2-stage SC until post war. The Merlin 60 series entered production in mid-1942, while the ~equivalent 'G' series Allison did not enter production until early-1945? Even then, the Allison 2-stage SC was not as compact as the RR 2-stage.
On the other hand, even the early-war V-1710 had a few detail aspects in terms of reliability that were better than the Merlin.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The XB-42 was a bomber and it was felt that the Bombardier should be in the nose, not an engine (or two).
Peter Gunn
Master Sergeant
An engine (or two) in the front of the bomber?
UGH! How gauche.
*** EDIT ***
Not trying to hijack the thread but found this, that last footage at rooftop level, jeezus the windows must have come out of the houses...
UGH! How gauche.
*** EDIT ***
Not trying to hijack the thread but found this, that last footage at rooftop level, jeezus the windows must have come out of the houses...
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Peter Gunn
Master Sergeant
More to the OP's question, I thought Allison was being pulled in too many directions with resources getting stretched a bit thin, what with the 1710 and the budding jet engine technology i.e. J-35 being tops on the "To Do' list.
Ergo the 3420 rather fell by the wayside so to speak.
Ergo the 3420 rather fell by the wayside so to speak.
GregP
Major
The Allison W-3420 had potential. to be sure, and four were fitted to a B-29.
It was faster than the normal R-3350 version, but would have also interrupted production. You'd think they could have anticipated that had it been adopted, it would have interrupted production since they declined to improve the F6F-5's rolling characteristics for the exact same reason ... it would have interrupted production.
They also tried an Allison-powered B-17, though they were V-1710s rather than W-3420s.
It was also faster than the radial-powered variety but, are you ready for it, it would have interrupted production! Go figure, huh?
It was faster than the normal R-3350 version, but would have also interrupted production. You'd think they could have anticipated that had it been adopted, it would have interrupted production since they declined to improve the F6F-5's rolling characteristics for the exact same reason ... it would have interrupted production.
They also tried an Allison-powered B-17, though they were V-1710s rather than W-3420s.
It was also faster than the radial-powered variety but, are you ready for it, it would have interrupted production! Go figure, huh?
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The B-19 was also fitted with the V-3420 engines in place of the R-3350 radials and it's performance increased with that swap.
There was a lot to improve on V-1710, a much more important engine than the V-3420.
Merlin was probably more reliable.
V-1710 was a decent engine, Merlin was far better.
- Thread starter
- #9
As far as the V-3420, the propulsion system on the XB-42 was a coaxial system, meaning one engine drove one propeller, the other engine drove the other propeller. This allowed independent control of the Curtiss Electric propellers including feathering on both and reverse on the aft propeller. Those functionaliity would have been lost on a V-3420 powered XB-42. XB-42 Props
GregP
Major
I seriously doubt it was far better overall, but it definitely had better altitude performance once the 2-stage supercharger was fitted to the 60-series and later engines. Late-war Allisons were everything the Merlin was and more. During the hard-hitting years of 1943 - 1944, and even into 1945, the Merlin was better-suited to the ETO environment. It certainly didn't run as long as a V-1710 before needing overhaul, but longevity doesn't win fights. Performance does.
By the time the Allison was ready to make 2,900 hp (V-1710-127, Sea Level; 1,550 hp @ 29,000 feet), jet engines were spelling out the demise of the piston fighter, and kerosene burners were all the rage. Allison V-1710 development was like German aviation development ... too little, too late.
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Merlin have had better altitude performance from day one.
Pick a late-war V-1710 and compare it with a late-war Merlin.
1944 and 1945 were the late-war years, Merlin proving itself time and again in the MTO, Eastern Front and Asia/Pacific, too.
Agreed pretty much.
wuzak
Captain
Why would changing to a V-3420 change the propeller system?
The V-3420 could be configured with a single rotation propeller, or dual rotation, as in the Fisher XP-75.
The Fisher P-75 system is pretty much would have been used in teh XB-42 had they opted for teh V-3420 instead of twin V-1710s. The main difference being that the XB-42 was a tractor arrangement, the XB-42 a pusher.
The engine and driveshafts can be seen in the 3rd photo down on this page:
Allison V-3420 24-Cylinder Aircraft Engine
The Allison V-3420 24-cylinder engine was more than just two coupled V-1710s. The large engine showed promise, but other priorities and a lack of aircraft applications regulated the V-3420 to obscu…
oldmachinepress.com
wuzak
Captain
The V-3420 installation was to be an engine module that bolted up to the airframe. That is, they unbolt the R3350 engine module and bolt up the V-3420 module. The engine module contained the engine, radiator, turbos, coolers, etc.
No (major) airframe mods were necessary, though there may have bene some controls that needed changing.
The XB-38 had radiators installed in the leading edge between the nacelles. The chin scoop fed an intercooler, replacing the one in the wing on the regular B-17. The turbo was in the same place.
The XB-39 would not have interrupted B-29 production much. But V-3420 production was virtually non-existent, the engine modules were not in production and Fisher, who developed the engine module, were mucking around with the XP-75. The XB-39 only had its first flight in December 1944, by which time the B-29 was in service. Production probably would not have made the war (due to engine availability).
Had the XB-39 flown in December 1943 I would think that its added performance (at the cost of some range) would warrant production.
The XB-38 did require more extensive modifications to the airframe, but this could have been avoided by putting the radiators in the nacelles. The performance gain over the regular B-17 was not that great, and not worth the effort. Later, higher performance V-1710s would have stretched the advantage over the regular B-17,
Changing to the XB-38 would have cost some production, so probably a wise choice to abandon it.
GregP
Major
By a tiny bit, yes. They were about even as single-stage units, with the Allison giving slightly better performance lower and the Merlin slightly better performance up higher by maybe 2,000 feet or so.
The Merlin's performance was great, all the time during the war. In the 60-series, it topped out at about 1,710 hp @ 3,000 rpm @ 6,400 feet (Merlin 38 / 69 as fitted to P-51 B/C and D/K). The post-war Merlin 130/131 topped out at about 2,070 hp @ 3,000 rpm. At 25,000 feet, the 2-stage Merlin was about 1,300 hp or so.
The V-1710 lagged a bit behind for a good bit of the war. But, a representative unit would be the V-1710-89/91 as flown in the P-38J. It made 1,600 hp @ 3,000 RPM @ 10,000 feet and 1,425 HP @ 3,000 @ 24,900feet. Not much to choose, really, once the issues were worked out, as they were by early 1944. The late-war V-1710-127 made 2,950hp @ 3,000 rpm @ 11,000 feet, which was 400+ hp more than any flying wartime Merlin made. It didn't make the war, but was running and ready if needed.
Rolls-Royce ALSO had Merlins that were running and ready if needed but not flown, but both the Rolls and the Allison units weren't really needed. In their late models, they were very close to having nearly equivalent performance when they were eclipsed by jets.
I'll say this; there's NOTHING wrong with a good Merlin. It was a great engine, especially for the ETO. I happen to think the Allison was a great engine, too, but not really in the same niche for a good deal of the war. Later, it was as long as it had a high-altitude boost system in the form of a turbo OR a 2nd stage supercharger. If it stayed a single-stage unit, then the 2-stage Merlin had better altitude performance.
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GregP
Major
Am familiar with the quick engine change packages. Cheers. Still, the W-3420 never got much development. It makes you wonder sometimes. What were the priorities? The R-3350 was an EXPENSIVE engine that took a long while to develop. The W-3420 was WAY ahead of it, development-wise, and could have been great much sooner and much cheaper, had they gone with it.
But, that's a definite "what-if" since it didn't happen.
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wuzak
Captain
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.
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.
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.
