R-3350 vs. V-3420

[gjs238]

The Wright R-3350 Duplex-Cyclone seems to have been rushed into production for the B-29 with many problems.
Eventually it was ironed out and went on with fine service in the Lockheed Constellation, Douglas A-1 Skyraider and many others.

With hindsight, is it feasible that had more development been committed, the Allison V-3420 may have been a better choice for the B-29?

 

[Timppa]

With hindsight, R-2800 would have prevented many B-29 losses. R-3350 was rushed to service too early.

 

[tomo pauk]

According to the Vee's for victory book, the XB-39, with V-3420s (but without turbos) was managing 405 mph at 25000 ft, vs. regular B-29 making 365 mph at same altitude. The mileage, on different air speeds and at 10000 ft was to be improved from 7.5% up to 17.1%.

 

[davebender]

I agree.

U.S. Army Air Corps was too aggressive introducing the new engine before it was technically ready. R3350 engine should have been an upgrade after further development to improve reliability.

 

[wuzak]

With hindsight, R-2800 would have prevented many B-29 losses. R-3350 was rushed to service too early.

Not sure that the R-2800 was powerful enough.

At least not during the time the B-29 was in its design stages. Even 1944 R-2800s would have struggled with the B-29.

Takeoff performance was one of teh big issues with the B-29. Overloaded and taking off from insufficiently long strips the R-3350s were at their limits.

 

[wuzak]

The Wright R-3350 Duplex-Cyclone seems to have been rushed into production for the B-29 with many problems.
Eventually it was ironed out and went on with fine service in the Lockheed Constellation, Douglas A-1 Skyraider and many others.

With hindsight, is it feasible that had more development been committed, the Allison V-3420 may have been a better choice for the B-29?

Interestingly the R-3350 development started at about the same time as the R-2800.

The V-3420 would have provided vastly improved takeoff performance, not to mention the improved top speed performance (shown by Tomo).

Development wise, the V-3420 was not untroubled. It suffered from mixed messages from the powers-that-be - it was on-again, off-again for years. And GM-Allison didn't develop it when it wasn't wanted. Then the USAAF wanted it as a backup for the R-3350, but then tied its testing to an experimental turbo on the XB-19, then changed tack and wanted it for the XP-75 long range fighter program. That meant that the XB-39 flew much later than it should.

Then there was the claim that changing over would slow production. This is despite the fact that the V-3420 installation qas designed as a QEC module that would have bolted up to the standard firewall. If the V-3420 nacelles were in production in time, they could have been swapped out at the modification centres in Kansas.

 

[GregP]

The V-3420 was and IS a good engine that was not heavily stressed at 3,000 HP or so. But, the USAAF simply wasn't going to support it despite some potential improvvements over other engines of the time. It was powerful, faster than the radials of the day in actual flight performance, and could have been developed into a still more powerful unit. I'm glad it was a QEC module because maintenance on the inner cylinder banks would have been ... interesting, to say the least.

Regarding the R-2800, four would have been stressed very hard for less performance than the R-3350 variant, but how about six R-2800's on a B-29 derivative? Alternately, how about four R-2800's on a B-17 or B-24 variant?

 

[Shortround6]

The trouble with trying to switch engines on something like the B-29 program is when do you do it?

The Government had financed a brand new plant for Wright just for the R-3350 engine that started production in 1943, (means work on plant had to start in 1942) and produced over 5,000 engines in 1944.

While Allison might have had the capacity to build the V-3420 in late 1944 (just in time?) it was building 2000 engines a month through May of 1944 and production doesn't really fall a lot until Sept 1944. Granted P-40 production could have stopped somewhat earlier. The decision as to what engine to use would have to have been made in 1943 to have an real effect or not to screw up things too bad.

Take-off power is just one aspect of engine performance. The R-3350 had more "Normal" (max cruise) power and "regular" cruising power than any war time R-2800. You might have been able to match the R-3350 powered B-29s perfomance numbers but only by thrashing the the R-2800s rather hard. And by doing things like cruising in the rich settings range vs the lean settings the R-3350 used and having the smaller engine actually use more fuel.

Sticking R-2800s on a B-17 is the same problem as using R-2600s. The late model planes are already operating at overload conditions, having gained 20,000lbs or more from early versions. switching engines can raise the empty weight 2-3 tons, maybe more for the R-2800. Sure you now have power but some of the restrictions on the heavily loaded aircraft include taxiing, allowable runways, and permitted flight maneuvers. You either redesign the aircraft for higher weights (including new landing gear) or operate with several tons of fuel/bombs less. That is assuming the new engines don't break the airplane to begin with.

They lost a prototype B-25 with R-2800 engines because the pilot exceeded the allowable flight envelope, (too sharp a pull up after a high speed pass). I don't know if a R-2600 powered plane would have survived an identical maneuver or not but it would have been going slower.

 

[fastmongrel]

but how about six R-2800's on a B-29 derivative?

Someone has got to do a picture of that. How about it Tomo.

 

[Timppa]

The trouble with trying to switch engines on something like the B-29 program is when do you do it?

The Government had financed a brand new plant for Wright just for the R-3350 engine that started production in 1943, (means work on plant had to start in 1942) and produced over 5,000 engines in 1944.

Take-off power is just one aspect of engine performance. The R-3350 had more "Normal" (max cruise) power and "regular" cruising power than any war time R-2800. You might have been able to match the R-3350 powered B-29s perfomance numbers but only by thrashing the the R-2800s rather hard. And by doing things like cruising in the rich settings range vs the lean settings the R-3350 used and having the smaller engine actually use more fuel.

Remember this is one of those "with hindsight" threads.

With hindsight B-29 did not need cabin pressurization nor most of the gun turrets. Also the engines themselves would have been lighter. Quite a weight saving.

From AHT (P-47D-5):
Take-off power: 2,300hp (with water injection)
Military: 2,000 hp
Normal: 1,625 hp ( to 25,000 ft)

You have the figures for R-3350 ?

 

[Shortround6]

Military and take-off were both 2200hp but 'Normal' was 2000hp to 25,000ft. on the early B-29 engines. Later versions with water injection were rated for 2600hp take-off.

It is a little hard to tell but economical max for the R-2800 as used in the P-47 may have been 1200hp in auto lean while the R-3350 may have been good for as high as 1540hp in certain conditions but 1300-1400 seems quite obtainable according to the B-29 Manual in a lot (but not all?) conditions.

 

[GregP]

Think six R-2800's ...

Alternately, to balance things, maybe you could mount one set in pusher configuration behind the inner pair.

 

[Shortround6]

"Alternately, to balance things, mayne you could mount one set in pusher configuration behind the inner pair."

Nah, can't happen, everybody KNOWS that Dornier held the world wide patent on tandem engines and nobody but they could use them

 

[GregP]

I was thinking that, but not of the ability to cant the rear engines upward to clear the water spray.

Of course, we COULD add a hull to the B-29 and make it into a flying boat bomber. Maybe some hydraulic actuators to raise the wings for takeoff and landing? Or lower the bottom of the hull like Blackburn did?

Nahhhhh ... I have it, four R-2800's and one V-3420 in the nose!