What if V-3420 available earlier?

The V-3420 program was stop-start all through its life. It was cancelled a few times and then re-instated.

For this thesis suppose that Continental's IV-1430 project was cancelled early and the engineering resources put under the direction of Allison to help in development of the V-1710 and V-3420. One of the problems Allison had was a shortage of engineering resources and facilities, so having Continental's development team available would go some way to alleviate Allison's shortage.

There are a few aircraft that would benefit by the V-3420 being available earlier - notably the B-39 could have been tested and compared with the B-29 at the same time.

In the No B-17s prior to WW2 thread it was discussed which engines would be suitable for the Manchester had it been built in the US. To my mind the V-3420 would be the only engine with sufficient power that early in the war.

Could a twin V-3420 B-17 or B-24 work?

The early V-3420 was about 2300lb with 2300hp. That makes it about twice the power plus twice the weight (not including cooling system) of the R-1820 of the B-17. The V-3420 would need two B-series turbos so would add weight there as well. The offset is (presumably) less drag from the two nacelles vs 4 and, with hindsight, much more power potential.

The R-1830 was about 100lb heavier than the R-1820.

There was a V-1710-powered B-17 and it was faster than the R-1820/1830-powered version, but not significantly enough to make it a different weapon. The tactics with the V-1710-powered plane would have been essentially the same.

I think a twin V-3420-powered version with possibly a slightly smaller aircraft would have been a good idea, but I have some doubt of the V-3420 would suffice to power the full-size B-17 airframe as a twin, though I might be wrong there.

What I mean is simple.

The B-17 had four 1,200 HP engines for a total of 4,800 HP. With two V-3420's, it would have about 4,600 HP for roughly the same weight, and I'm not too sure the reduced drag would significantly help the airframe. Although it could get up to a bit over 300 mph, the cruise speed was about 185 mph or so with the radials. If the V-3420 version could up the cruise to over 275 mph, you might have something, and big inlines tended to cruise significantly faster than big radials …. probably due to less inline drag and the radials being pretty thirsty at high cruise power. I believe they generally cruised slower to gain range.

So the real issue would be whether or not the substitution would render the airframe a different weapon by making if faster at cruise or not, and it is very likely that the cruise with the V-3420's would not achieve a quantum jump in speed with the attendant change in tactics afforded the mission planners. If the resulting aircraft wound up being used the same way as the radial-powered version, what would the gain be? On the other hand, if it could cruise 100 mph faster, then the tactics might be significantly different, with different results that could be better or even worse if the change in cruise speeds affected bombing accuracy. I doubt that since Mosquitos didn't suffer bombing accuracy at higher speeds, but you never know in the real world.

I admit the prospect is interesting, but wonder how we would ever answer the question unless we did a pretty thorough design analysis of the proposed new aircraft.

A 1942 version may have 4600hp. By mid 1943 you are probably looking at 5200hp (2600hp each), but some weight increase. By 1944 a 3000hp version of the V-3420 shouldn't be too much of a stretch. Assuming production started in 1941/42.

I agree that there wouldn't be a big leap in performance or capability - not, at least, until more powerful versions of the V-3420 became available.

As the V-3420 was evolved as a bomber engine it ran higher compressions ratios, at least in early versions, to gain in efficiency.

I have my doubts that the USAAF would have allowed the use of a big liquid cooled engine on any of their heavy bombers; liquid cooled engines were considered to be too vulnerable to relatively small amounts of damage, particularly when there was a selection of reliable radial engines available which were already giving enough power and could be developed to give more.

Another question would be would be how many other useful aircraft types could be powered by V-3420s? Certainly not the Fisher P-75, which was a waste of time and resources from go to woe.

P-47 - Why? Apart from the 56th FG and Iwo Jima based units it became a useful fighter-bomber and would not have benefited by being converted to a liquid-cooled engine.

Possibly the Douglas A-26 and Martin B-26, but their role as medium bombers, operating in "flak-rich" environments would have precluded the use of liquid cooled engines, and the R-2800 was more than reliable and powerful enough for both these aircraft - unless the V-3420 powered mediums proved to have substantial performance advantages over their R-2800 versions.

B-29? The R-4360 proved to be a better bet.

So, again, why bother ordering large numbers of an engine just to power one or two types of aircraft?

Aozora said:

I have my doubts that the USAAF would have allowed the use of a big liquid cooled engine on any of their heavy bombers; liquid cooled engines were considered to be too vulnerable to relatively small amounts of damage,

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The XB-15 was intended to be powered by X/V-3420s (or V-1710s according to some sources).
The XB-19 was to be powered by the V-3420.
The XB-38, powered by V-1710s was developed as a possible way to improve B-17 performance.
The XB-39 was developed as a backup to the troubled B-29, replacing the R-3350s with the V-3420.
A B-26 powered by the V-3420 was proposed.

The V-3420 was developed as a bomber engine.

Aozora said:

particularly when there was a selection of reliable radial engines available which were already giving enough power and could be developed to give more.

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"Enough power"?

The R-3350 was underpowered for the B-29.

None of the contemporary radials could compete with the V-3420 for power during the middle of the war. Nor could they compete with the potential power development. The R-4360 didn't start development until aboout teh time the V-3420 could have been in production.

I don't think the R-1820 and R-1830 had significant power development in them.

Aozora said:

P-47 - Why? Apart from the 56th FG and Iwo Jima based units it became a useful fighter-bomber and would not have benefited by being converted to a liquid-cooled engine.

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The P-47 was proposed with the Chrysler IV-2220, a liquid cooled inverted V-16.

P-51s, P-38s, Spitfires, Typhoons, Tempests and Mosquitoes all did fighter bomber/ground atack roles, and all had liquid cooled engines. Not a deal breaker.

But, as above, the V-3420 was mainly seen as a bomber engine.

Aozora said:

Possibly the Douglas A-26 and Martin B-26, but their role as medium bombers, operating in "flak-rich" environments would have precluded the use of liquid cooled engines, and the R-2800 was more than reliable and powerful enough for both these aircraft - unless the V-3420 powered mediums proved to have substantial performance advantages over their R-2800 versions.

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There was a proposed V-3420 Martin B-26.

The B-26 only ever got the A series R-2800 - so the power was adequate rather than more than enough. The A-26 got later R-2800s, but not the most powerful versions.

Both would have improved performance with V-3420s, especially the Martin B-26.

British liquid-cooled-engined bombers operated in flak rich environments and did fine.

Aozora said:

B-29? The R-4360 proved to be a better bet.

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Did it? By the time the B-50 was developed Allison basically had given up on the V-3420. Allison certainly weren't spending money on its development at the time.

The XB-39 had higher performance (maximum speed) than the B-50. 3 or 4 years ealier. A V-3420 version of the B-29 could have flown as long as the B-29 did in WW2 had the V-3420 been developed continuously.

Aozora said:

So, again, why bother ordering large numbers of an engine just to power one or two types of aircraft?

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You would have to ask the USAAF Materiel Command that since they did fund the development of the V-3420 from the mid to late 1930s. The first cancellation was to allow Allison to concentrate on the V-1710 at a critical time (September 1940). After that the USAAF changed their minds as to whether or not they needed the engine.

More money was wasted on programs such as the IV-3420.

The timing is key.
If the V-3420 is produced from 1942 on, the B-29 seem like a good airframe to take it. In a turbo iteration, we can look at military power levels of 2300 HP in 1942, 2650 in early 1943, 2850 in late 1943 (using the turbo V-1710 as base). That easily dwarfs any US built wartime engine, even without going into WER, let alone without ADI. Ie. USAF would get a B-50 equivalent already in early 1944.
The P-47 would be another potential airframe, hopefully the layout of liquid cooling system would've get worked decently. It would have had, under military power setting, the amount of power equal to late B series and early C series of R-2800 operating on WER. With WER, it's some 3200 HP - so USAF fields the equivalent of P-47M/P-72 from late 1943/early 1944.

The main thing going vs. the V-3420 was that the complete power plant weight was above 5000 lbs, two stage variants with counter-rotating prop. For example, the 2 stage R-2800 was under 4000 lbs.

The interesting airframe for the V-3420 might've been the P-61, in two stage variation would provide some 40% more power at 20000 ft, but at price of a good tonne just for power plant weight, without necessary reinforcements. So with some 3000 lbs of extra weight, the 'basic weight' would go up, from some 23000-26500 to 26000-30000 lbs, or under 10%. Less percentage for normal take off weights (historically, 28200-40000 lbs).
It would be interesting to see weight penalty the XP-61D paid, when the trbo C series R-2800 installed.

The single stage V-3420 were some 500 lbs lighter (dry engine), would need also smaller lubricating cooling system, along with smaller prop (not the monster 850 lbs counter-rotating prop like the one used on P-75). All of that might bring down the powerplant weight to some 4000 lbs, while providing 50% more power at altitude than single stage R-2800 (in A-26, B-26). Finally a fast B-26?

wuzak said:

The XB-15 was intended to be powered by X/V-3420s (or V-1710s according to some sources).
The XB-19 was to be powered by the V-3420.
The XB-38, powered by V-1710s was developed as a possible way to improve B-17 performance.
The XB-39 was developed as a backup to the troubled B-29, replacing the R-3350s with the V-3420.
A B-26 powered by the V-3420 was proposed.

The V-3420 was developed as a bomber engine.

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The key words are "intended, possible and proposed." The USAAC/USAAF did not want liquid cooled engines for its bombers - period.

The main reason there was so much chopping and changing in opinion over the V-3420 was because of the political lobbying by, and on behalf of GM, which owned Allison. The main consequence of this was the design and development of the awful P-75, which was to be one of the main recipients of the V-3420.

wuzak said:

"Enough power"?

The R-3350 was underpowered for the B-29.

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Really? The main problem was it's unreliability - one of the few truly unreliable radials developed by the Americans - and that was the main reason for testing the XB-39.

wuzak said:

I don't think the R-1820 and R-1830 had significant power development in them.

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You're forgetting the existence of the R-2600, which "filled the gap" between the R-1830s and R-2800s.

wuzak said:

The P-47 was proposed with the Chrysler IV-2220, a liquid cooled inverted V-16.

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Proposed flown and rejected because it was outperformed by the P-47M and N series. Plus the P-72 with the R-4360 promised much greater performance improvements.

wuzak said:

There was a proposed V-3420 Martin B-26.

The B-26 only ever got the A series R-2800 - so the power was adequate rather than more than enough. The A-26 got later R-2800s, but not the most powerful versions.

Both would have improved performance with V-3420s, especially the Martin B-26.

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Again possibly, but there's also the very real possibility that at the altitudes at these aircraft operated any performance advantages gained would have been negated by the extra weight and complication of the cooling systems, not to mention the increased vulnerability. The B-26 had the lowest loss ratio of any of the light/medium bombers - with a liquid-cooled engine this could easily have changed.

wuzak said:

P-51s, P-38s, Spitfires, Typhoons, Tempests and Mosquitoes all did fighter bomber/ground atack roles, and all had liquid cooled engines. Not a deal breaker.

British liquid-cooled-engined bombers operated in flak rich environments and did fine.

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How many were lost because of one bullet or shell fragment in the cooling system? Purely hypothetical, but it could be argued that the Typhoon, for example, would have suffered fewer losses had the British been able to develop the Centaurus installation properly: ditto the Tempest II.

wuzak said:

None of the contemporary radials could compete with the V-3420 for power during the middle of the war. Nor could they compete with the potential power development. The R-4360 didn't start development until aboout teh time the V-3420 could have been in production.

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Possibly dry power to weight ratio, but when cooling systems etc are added the power to weight ratio changed in favour of the radials, particularly the R-2800.

Another consideration: by the middle of the war the Americans had developed cowlings for radial engines that more than offset the drag of their greater frontal area - there were radial engine installations that had less drag than some liquid-cooled equivalents.

An interesting discussion but, as noted by GregP, without specific details it is impossible to know whether the V-3420 would have been better than the radial engines the Americans were already building.

Aozora said:

The key words are "intended, possible and proposed." The USAAC/USAAF did not want liquid cooled engines for its bombers - period.

The main reason there was so much chopping and changing in opinion over the V-3420 was because of the political lobbying by, and on behalf of GM, which owned Allison. The main consequence of this was the design and development of the awful P-75, which was to be one of the main recipients of the V-3420.

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This depends on which year you are talking about. For much of the 1930s the Army was very much in favor of liquid cooled engines. They thought they could get more power from smaller, lighter engines and bury them in the wings or fuselage and use extension shafts to eliminate engine nacelles and their drag. Programs that dragged on during the 30s and early 40s were the Army designed ( and Continental built) O-1430/I-1430 engine and the Lycoming O-1230 (later doubled to become the 24 cylinder H-2470). The opposed engines were thought to be ideal for burying inside the thickness of the wing.

The Allison V-3420 was proposed in late 1936 by Ron Hazen as a way to cut development cost and problems with the Army's proposed X-3420 ( four con rods per crank journal, like a Vulture). Well be fore the Fissher XP-75 was even a gleam in anybody's eye.

The Army did not want liquid cooled engines for attack planes due to vulnerability from ground fire. The big bombers were supposed to fly out of small arms/light AA range/altitude. The lower drag promised higher speeds/longer range.

Due to the absurdly small R&D budgets the liquid cooled engines were behind the commercial air-cooled radials in development and the Army had to take what engines it could get. The Army first contracted with Continental in 1932 but didn't get it's first 12 cylinder engine until 1938 and it didn't pass any sort of test until 1939. It wasn't "airworthy" until 1942 or 43 and even then was down on promised power and woefully lacking in reliability.

Air cooled engines for bombers were not the Army's first choice. Circumstances forced the adoption of the air-cooled engines and once programs were put in place it was hard to change them.

GM owned Fisher and that may have had as much to do with the selection of the V-3420 as anything else. Allison was also having trouble delivering the number of V-1710s wanted for much of the war ( at least until some point in 1944) which also affected the the choice of the V-3420 for a number of programs. A new factory would have been needed to meet any increased demand. Several GM divisions were already acting as sub contractors to Allison, such as Cadillac making crankshafts and connecting rods and other parts.

Aozora said:

The key words are "intended, possible and proposed." The USAAC/USAAF did not want liquid cooled engines for its bombers - period.

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Sorry, that is incorrect. Covered by SR6.

There was a thought in the early '30s in the USAAC that the air-cooled radial was not suitable for high altitude becuase they could not take the boost pressures required.

Aozora said:

The main reason there was so much chopping and changing in opinion over the V-3420 was because of the political lobbying by, and on behalf of GM, which owned Allison. The main consequence of this was the design and development of the awful P-75, which was to be one of the main recipients of the V-3420.

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The main reason for chopping and changing was the war situation and production situation. Production took priority over development in many areas. New engines was one of them.

Aozora said:

Really? The main problem was it's unreliability - one of the few truly unreliable radials developed by the Americans - and that was the main reason for testing the XB-39.

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Reliability was the main problem, and remained so after the B-29 went into service.

The B-29 was also underpowered, and often struggled to get airborne off the shorter than ideal Pacific Island runways.

Aozora said:

You're forgetting the existence of the R-2600, which "filled the gap" between the R-1830s and R-2800s.

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I am not at all.

The R-2600 was significantly heavier than the R-1820 and R-1830, and significantly thirstier. A single R-2600 could not do the job of two R-1820s or R-1830s, buta V-3420 probably could.

Could you give some examples where an R-2600 was substituted for the R-1820 or R-1830?

Aozora said:

Proposed flown and rejected because it was outperformed by the P-47M and N series. Plus the P-72 with the R-4360 promised much greater performance improvements.

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Not sure that it flew against them. May have actually been earlier.

The engine was not put into production because it was, basically, a dead end. But not because it was liquid cooled.

Not sure that the claim that the "R-4360 promised much greater performance improvement" is accurate.

FWIW a V-3420 with cooling system would come in at about the same weight as the R-4360, and should, at a minimum, match the power of the R-4360.

Aozora said:

Again possibly, but there's also the very real possibility that at the altitudes at these aircraft operated any performance advantages gained would have been negated by the extra weight and complication of the cooling systems, not to mention the increased vulnerability.

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Installed power to weight of air-cooled engines and liquid-cooled engines was not dissimilar. But some installations were better than others.

I have said this before, the increased vulnerability of liquid-cooled engines is, IMO, overstated.

Aozora said:

The B-26 had the lowest loss ratio of any of the light/medium bombers - with a liquid-cooled engine this could easily have changed.

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I doubt it would change much, if anything.

The main reason for the B-26's low loss rate was tasking. Genrally shorter range missions, well within escort fighter range and not necessarily the most high value targets.

Put the B-26 in the Mosquito's shoesm and see how well it goes. ie Unescorted daylight bombing of Germany, unescorted PR work over Europe, pathfinding at night. diversionary raids designed to lure in nightfighters.

Aozora said:

How many were lost because of one bullet or shell fragment in the cooling system? Purely hypothetical, but it could be argued that the Typhoon, for example, would have suffered fewer losses had the British been able to develop the Centaurus installation properly: ditto the Tempest II.

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That may be so, but it is impossible to say.

The Centaurus, when it was eventually fitted, was much more powerful than could have been offered to the Typhoon mid war.

Also, I believe that the Typhoons and Tempests intended for ground attack missions had armoured cooling systems.

Aozora said:

Possibly dry power to weight ratio, but when cooling systems etc are added the power to weight ratio changed in favour of the radials, particularly the R-2800.

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The R-2800 was exceptional for a radial. But not the normal for air-cooled radials. Installed power to weight was similar for air and liquid cooled engines, some installations being better than others.

Aozora said:

Another consideration: by the middle of the war the Americans had developed cowlings for radial engines that more than offset the drag of their greater frontal area - there were radial engine installations that had less drag than some liquid-cooled equivalents.

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There were some (drag vs hp), but there were also ones that were opposite. There were good and bad examples of both. The Typhoon/Tempest V wasn't a very good installation aerodynamically. The Tempest I was superior.

Usual problem for a purely hypothetical proposition.."I say tor-mato you say to-may-to etc etc..." Without solid data there is simply know way of knowing whether more widespread use of the V-3420 would have been worthwhile cf the radials. It might have been better than the R-3350 in the B-29, but enough of an improvement over the radials in other applications? I say po-tayto you say petayta..."

wuzak said:

Could you give some examples where an R-2600 was substituted for the R-1820 or R-1830?

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Didn't the R-1830 powered Douglas DB-7 evolve into the R-2600 powered A-20 Havoc?

gjs238 said:

Didn't the R-1830 powered Douglas DB-7 evolve into the R-2600 powered A-20 Havoc?

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It required a lot of modifications, though.

It actually wasn't too bad, A much bigger tail fin though.

The B-23 was developed from the B-18 and switching engines.

The Martin Baltimore?

The Lockheed twin 14/18 managed to go from R-1820s/R-1830s to R-2600/R-2800s.

Part of the problem is that few people left the airplane alone ( only changed what needed to be changed for the engine swap), Changes in crew layout, defensive armament, equipment, bomb load and so on impacted the size of the "New" version ( B-23 and Baltimore). but increasing power by 33-42% makes it hard to say no to "improvements" when the plane in question has noticeable deficiencies.

Please note that on a 4 engine plane switching from R-1830s to R-2600s could also suck up close to 2 tons of gross weight after the larger power-plant weights (bigger props, bigger engine mounts, bigger exhaust systems and so on) are figured in. The A-20 went from just over 15,000lbs gross weight to just over 20,000lbs on the first R-2600 models with the same MG armament very little more fuel (30 gal) and only a bit bigger bomb load. Structural changes included steel wing to fuselage forgings instead of the aluminium ones used on the R-1830 models.

The bigger engines will suck more fuel, especially if the extra power is used. The extra power will enable the heavier aircraft to get of the ground but sticking four R-2600s into a B-17 or B-24 is like trying to stick one in an F4F Wildcat. Every engineer that looks at it will figure that you are better off ( get better results) sticking the engines in a new air-frame.

There was an experimental B-25 that was powered by R-2800s - if I remember correctly I saw an article on this in an old American Wings or Airpower magazine I had borrowed a couple of years ago...must see if I can find the article.

There was, It crashed when the pilot exceeded the structural limitations of the aircraft. A high speed low level run with too sharp a pull up at the end. The wings came off or folded?

The wings and/or wing attachment points could have been beefed up on a production version but at the cost of more weight and more design/test time.

Some planes had more "margin" for re-powering or increased weights than others. A lot of planes had already had rather large weight increases from the original design/early models.

Aozora said:

There was an experimental B-25 that was powered by R-2800s - if I remember correctly I saw an article on this in an old American Wings or Airpower magazine I had borrowed a couple of years ago...must see if I can find the article.

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Shortround6 said:

There was, It crashed when the pilot exceeded the structural limitations of the aircraft. A high speed low level run with too sharp a pull up at the end. The wings came off or folded?

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R-2600 -> R-2800 isn't as big a jump in power and installed weght as from R-1820/R-1830 to R-2600, though.

A real V-3420 engined plane, something like a P-38 on steroids. With V-3420 available earlier, a night fighter better than P-61? 6000 HP on board.

Lockheed XP-58 Chain Lightning - Wikipedia, the free encyclopedia

Just realised that with the proximity of the inner nacelles to the fuselage and the length of the landing gear the V-3420 would have to drive a smaller propellor than would be desirable. Unless it had contra props, or the V-3420 was put on a new wing structure..

What's the airplane in the question?