Twin engined B-17

[wuzak]

On another forum we were discussing what if the B-17 was a failure or behind on its schedule, would they build Manchesters under licence. And if they did, what engines would they use. My answer was that the most suitable US engine for the Manchester was the V-3420.

Which got me thinking. The V-3420 makes about twice the power as an R-1820 and weighs about twice as much. Could there have been a B-17 with two V-3420s instead of 4 R-1820s?

The R-1820 has the same diameter as the R-3350 which the V-3420 replaced on the XB-39. So the firewall would be roughly the same size. On the XB-39 all the coolers and turbos were mounted in the QEC module. The B-17 had the turbos behind the firewall under the nacelle. A V-3420 would need two of the same size turbos, so this could cause a problem in installation. Unless the QEC module is used, as per the XB-39, with all bits together.

The next problem is that the V-3420 was used to swing a rather large prop - the B-17's landing gear would need to be lengthened to cope with that, but the inner nacelles, which have the landing gear, are too close to the fuselage anyway. So the V-3420 would most likely need to be fitted with contra-props.

[rickshaw]

Could you mate the V-3420 to a contra-prop?   That would negate the need to lengthen the B-17's landing legs.

[wuzak]

Could you mate the V-3420 to a contra-prop?   That would negate the need to lengthen the B-17's landing legs.

Yes, the V-3420 could have a contra-prop.

One of the many requirments for its design was the provision for the possible fitment of contra props.

There were two main types of the V-3420 - the A and B models. The main difference between these was the reduction gear arrangements. The A had the two crankshafts rotating in the same direction (as was the case for the Sabre too), while the B had crankshafts rotating in opposite directions. It was a B model V-3420 that powered the Xp-75 and its contraprop arrangement, albeit via extension shafts. I would imagine that a similar reduction gear could be connected directly to teh engine without extension shafts.

[wuzak]

http://www.enginehistory.org/Gallery/JimBuckel/Allison%20V-3420%20for%20Fisher%20P-75A%20Eagle%201-17.JPG
http://gallery.oldholden.com/d/95832-1/Allison+V-3420+for+Fisher+P-75A+Eagle+1-18.JPG

[kerick]

Sounds like major redesign of the wing structure to support the weight and thrust of the one big engine instead of two smaller ones. But this is whiff world, all problems are solved!

[Captain Canada]

What a neat engine !

A twin engined B-17 sounds great, regardless of what engine is powering it. I was thinking the same thing of a Shackleton just the other day....

[jcf]

... or an enlarged Model 298 with a pair of V-3420 instead of a pair of V-1710.


... or perhaps Model 298 combined with Model 299J and V-3420:


As to a Yank-engined Manchester, a pair of R-2800 ala the twin Hercules proposals,
or twin R-3350 as a counterpart to the twin Centaurus version. Twin R-2800 with
turbo-superchargers would be a good late-30s possibility.


Hercules


Centaurus

Oops, posted Herc version twice.

[Captain Canada]

I sure like the look of that 298 ! Stubby fuse and a big wing !

[wuzak]

... or an enlarged Model 298 with a pair of V-3420 instead of a pair of V-1710.

Thanks for these.

A 1600hp Allison proposed in 1934 would have been the X-3420, predecessor to the V-3420 and only built as a wooden mockup.

Looks like a "high speed bomber" - if, indeed, it is a bomber.

As to a Yank-engined Manchester, a pair of R-2800 ala the twin Hercules proposals, or twin R-3350 as a counterpart to the twin Centaurus version. Twin R-2800 with turbo-superchargers would be a good late-30s possibility.


Hercules

Unfortunately the R-2800 would not be available to the British in significant numbers before 1941. And tehy would be the A-series, with about the same (or less) power than detuned Vultures. The turbo would help, allowing it to maintain that power to a higher altitude - but it would have helped immensely with the Vulture Manchester too.

The R-3350 was a troubled engine during the late 1930s/mid to late war period. It may have had more issues even that the Vulture. By the time a 2200hp R-3350 comes along Rolls-Royce (had they persisted with it) could have had a 2500hp+ Vulture. They had already tested the Vulture at 2500hp before its cancellation.

Centaurus

Hercules would not have enough grunt for the Manchester, having less than either the Centaurus or the R-2800.

Centaurus would not be available until 1943, or later.

[rickshaw]

Centaurus would not be available until 1943, or later.

Centaurus production started in 1942.

[wuzak]

Centaurus would not be available until 1943, or later.

Centaurus production started in 1942.

How many made in 1942? At what rating?

[rickshaw]

Centaurus would not be available until 1943, or later.

Centaurus production started in 1942.

How many made in 1942? At what rating?

1. No idea
2. 2,000hp.

[jcf]

Centaurus was under test from 1938, which is why Avro used it as a possible alternative powerplant
in their Type 679 studies. Likewise Bristol was also doing experiments on high-output Hercules, so it was also
considered as an alternative. Four of the current Hercules were also considered, so four R-2800
on a Yank Manchester.  s'all good.


4-Hercules