B-26 with High Altitude Supercharger & Redesigned Bomb-Bay

Zipper730 · May 26, 2020

The idea was inspired by the fact that the B-25 has a cavernous bomb-bay similar to the RAF designs, the RAF Mediums were built for strategic and tactical-bombing use (namely the HP Hampden and the Vickers Wellington -- though I'm not sure if they were classed as heavies initially), and the USAAF tended to favor some high altitude capability in strategic bombing designs.

While I know Martin did propose the XB-27 which was high altitude design, it appeared to have come after the B-26 design, and I figure a bump-up in critical altitude could be useful. There were numerous proposals made which included variants with single-stage/twin-stage and turbocharged variants of the R-2600 and R-2800. While I'm not sure how many turbocharged R-2800 variants were ready, I do know there was an R-2800 with a twin-stage supercharger available by May, 1940 (the F4U used it), and the B-26 made its first flight in November of 1940. It would have increased the plane's top speed and would have made it harder to catch, and with neutral blower, you'd probably retain good power even at lower altitudes.

While I don't remember the chart exactly, I do remember estimates of ram compression adding something like 2,000-3,000 feet of altitude. If this number is correct, you would see a maximum altitude around 800 feet higher (or 200 feet lower) than the F4U-1.

DarrenW , P pinsog , S Shortround6 , W wuzak

Shortround6 · May 26, 2020

Why are we re-inventing the wheel?

There were a number of different proposals for high altitude medium bombers .

The NA B-28 made it to flying status.

People have got to get over the idea that you could just stuff an extra stage into a plane that was designed for a single stage engine.
Doesn't matter if it used a turbo or mechanical drive.

F6F Hellcat engine.

There are 3 scoops in the big scoop at the bottom of the Cowl, the center one fed the carb and oil cooler, the outer two feed a pair of inter coolers. The Intercoolers are visible in the picture above between the exhaust pipes and just forward of the wing. What you can't see is the ducting leading from the aux supercharger to the intercoolers and back to the inlet of the main supercharger.

You could put such an engine in the Martin B-26 but you need bigger cowls/engine nacelles which are going to cause more drag and cut your speed at low altitudes.
Yes you would have the same power at low altitudes but you have to fight the increased drag.
TANSTAAFL.

tomo pauk · May 26, 2020

Zipper730 said:
The idea was inspired by the fact that the B-25 has a cavernous bomb-bay similar to the RAF designs, the RAF Mediums were built for strategic and tactical-bombing use (namely the HP Hampden and the Vickers Wellington -- though I'm not sure if they were classed as heavies initially), and the USAAF tended to favor some high altitude capability in strategic bombing designs.

The RAF bombers (including the Battle) were built for strategic use. B-26 have had two bomb bays, with IIRC 4000+2000 lb capacity - a single bomb bay would've probably allowed for more flexible bomb-load?
Unfortunately, the fuselage was too big since the designers also provided comfortable accommodation for as many crew as the initial B-17 carried. Big -> heavy.
The flap system was very basic.

While I know Martin did propose the XB-27 which was high altitude design, it appeared to have come after the B-26 design, and I figure a bump-up in critical altitude could be useful. There were numerous proposals made which included variants with single-stage/twin-stage and turbocharged variants of the R-2600 and R-2800. While I'm not sure how many turbocharged R-2800 variants were ready, I do know there was an R-2800 with a twin-stage supercharger available by May, 1940 (the F4U used it), and the B-26 made its first flight in November of 1940. It would have increased the plane's top speed and would have made it harder to catch, and with neutral blower, you'd probably retain good power even at lower altitudes.

While I don't remember the chart exactly, I do remember estimates of ram compression adding something like 2,000-3,000 feet of altitude. If this number is correct, you would see a maximum altitude around 800 feet higher (or 200 feet lower) than the F4U-1.

The proposals were made before the B-26 took flight.
At any rate, the nacelle of the B-26 was very long in front of the wheel bay, so there is a lot of place for the longer 2-stage engine if the up-engining is attempted. The intercoolers' scoops will need to go in the leading edge similar to the P-61 or F4U, ditto for the ram air intake (now probably just one, but bigger).
For the best speed, the bomber will need to go above 15000 ft in order to make use of the extra HP at altitude - as people expect.

Zipper730 · May 26, 2020

Shortround6 said:
Why are we re-inventing the wheel?

Well, the premise would be the design was configured from the outset to use this engine, not fitted with it after first flight. I figure the XB-27 and XB-28 flew later so it would kind of have improved performance earlier.

People have got to get over the idea that you could just stuff an extra stage into a plane that was designed for a single stage engine.

As I said, the premise was that the plane would have it from the outset.

I'm aware that inter-coolers would be required for a twin-stage design short of carrying a lot of water and methanol around. I didn't consider that the scoops would take some performance away at low altitudes.

How much would you estimate?

Shortround6 · May 26, 2020

tomo pauk said:
The proposals were made before the B-26 took flight.
At any rate, the nacelle of the B-26 was very long in front of the wheel bay, so there is a lot of place for the longer 2-stage engine if the up-engining is attempted. The intercoolers' scoops will need to go in the leading edge similar to the P-61 or F4U, ditto for the ram air intake (now probably just one, but bigger).

There is not a lot space if you take in everything else that was in the Nacelle.
If the proposal was adopted in time then perhaps it could be done, but the resulting airplane would have a lot of changes from the B-26 as we know it/

Experimental B-26 installation to improve cooling. The oil tank was in nacelle forward of the wheel well.
The forward spar of the B-26 was quite close to the wing leading edge with fuel tanks in the inner wing between the fuselage and nacelle and more tanks just out board of the nacelle.
The wing leading edge held the control runs.
Standard B-26 nacelle

You do have to be able to cool the engine if it is making more power in the higher/thinner air.

wuzak · May 26, 2020

Zipper730 said:
While I'm not sure how many turbocharged R-2800 variants were ready, I do know there was an R-2800 with a twin-stage supercharger available by May, 1940 (the F4U used it), and the B-26 made its first flight in November of 1940. It would have increased the plane's top speed and would have made it harder to catch, and with neutral blower, you'd probably retain good power even at lower altitudes.

The XF4U-1 used a prototype A-series R-2800. Likely only a handful of them available in 1940.

The first production 2 stage R-2800s (a B-series) was delivered to the USN in November 1941.

When are you expecting the B-26 to be available?

Zipper730 · May 27, 2020

Shortround6 said:
There is not a lot space if you take in everything else that was in the Nacelle.

As I said, the idea assumes the plane would have been designed with this feature from the start. That means it would have been designed to accommodate these things off the bat, and the nacelle would be different by the time first flight occurred.

If the proposal was adopted in time then perhaps it could be done, but the resulting airplane would have a lot of changes from the B-26 as we know it

Correct, and the propulsion system would be the most heavily changed.

You do have to be able to cool the engine if it is making more power in the higher/thinner air.

Of course, but it was clearly doable as other aircraft pulled it off.

wuzak said:
The XF4U-1 used a prototype A-series R-2800. Likely only a handful of them available in 1940.

I didn't know there were so few of them. Do you have the image of the chart that listed engine options for the B-26? I'm just curious what was available for the time period.

The first production 2 stage R-2800s (a B-series) was delivered to the USN in November 1941.

Since I don't know how much time was required for engine development, and how much was used based on the demand for such engines.

When are you expecting the B-26 to be available?

The actual aircraft was available in February, 1941. That said, I figure if the two-stager wasn't ready in time, one could simply adopt a single-stage design for an interim -- provided it wasn't something so serious as to cause the USAAF to have pulled the plug.

I should point out the F4F's had a number of variants that ran on a single-stage supercharger instead of a twin-stage design, I think some of the earliest P-61's had a single-stage set-up too.

wuzak · May 27, 2020

Zipper730 said:
I didn't know there were so few of them. Do you have the image of the chart that listed engine options for the B-26? I'm just curious what was available for the time period.

There were 2 production R-2800s built in 1939 and 17 in 1940.

There were 1,733 built in 1941, almost all being single stage engines.

http://enginehistory.org/Piston/P&W/P&WProduction/P&WProduction.shtml

Zipper730 said:
Since I don't know how much time was required for engine development, and how much was used based on the demand for such engines.

Since the 2 stage engines were required for the F4U, the F6F and the P-61, the demand for these engines was high in 1943.

Engine development depended on what was being developed and who was doing the development.

The R-2800 started development in 1935(?), first ran in 1937 and first flew in 1940.

Zipper730 said:
The actual aircraft was available in February, 1941. That said, I figure if the two-stager wasn't ready in time, one could simply adopt a single-stage design for an interim -- provided it wasn't something so serious as to cause the USAAF to have pulled the plug.

The 2 stage engine was definitely not ready in 1941. So you'd end up with a B-26 with the single stage engine, as was historically the case.

A 2 stage version would likely not appear prior to 1943.

Zipper730 said:
I should point out the F4F's had a number of variants that ran on a single-stage supercharger instead of a twin-stage design, I think some of the earliest P-61's had a single-stage set-up too.

The prototype XP-61, the pre-service YP-61s as wel as all P-61As and P-61Bs had 2 stage R-2800s. The same version as the F6F, in fact.

Some F4Fs didn't get the 2 stage engines because there were not enough of them at the time. I don't know what changes were required to the airframe.

Zipper730 · May 27, 2020

This is the chart I was referring to by the way...

Zipper730 · May 28, 2020

wuzak said:
There were 2 production R-2800s built in 1939 and 17 in 1940.

There were 1,733 built in 1941, almost all being single stage engines.

http://enginehistory.org/Piston/P&W/P&WProduction/P&WProduction.shtml

Fascinating

Engine development depended on what was being developed and who was doing the development.

And the demand for the development, which according to the chart, seemed to have begun in 1939. The F4U-1 began in 1938, so it would have a leg-up in time-table. That said, with it entering service in late 1942 (USMC), I would say that the B-26 would probably be a little later.

The prototype XP-61, the pre-service YP-61s as wel as all P-61As and P-61Bs had 2 stage R-2800s. The same version as the F6F, in fact.

I didn't know that, I remember seeing something that (I guess) was wrong.

Some F4Fs didn't get the 2 stage engines because there were not enough of them at the time. I don't know what changes were required to the airframe.

But it would be okay to design for a two-stage engine and fit for one-stage if needed, correct?

Shortround6 · May 28, 2020

It's a lot easier to leave stuff out than try to put stuff in a smaller airplane later on in it's life.

wuzak · May 28, 2020

Zipper730 said:
Fascinating
And the demand for the development, which according to the chart, seemed to have begun in 1939.

That is a production list. Production started in 1939. Development began ~1935 (as an R-2600).

Zipper730 said:
The F4U-1 began in 1938, so it would have a leg-up in time-table. That said, with it entering service in late 1942 (USMC), I would say that the B-26 would probably be a little later.

Since the F4U entered service in December 1942, I doubt there is any way a 2 stage R-2800 B-26 would be available before mid 1943.

Zipper730 said:
But it would be okay to design for a two-stage engine and fit for one-stage if needed, correct?

It would be pointless to design for a 2 stage engine that may delay the introduction of the aircraft 2 years.

How easy it is to change between 1 and 2 stage engines depends on the details of the installations, weight balance, etc.

Note that the B-26 (and B-25) was never intended to be a high-altitude bomber.

Also note that the R-2800-8/10 was not a particularly high altitude engine. The P-61A, which was about the same size and weight as the B-26, had maximum performance at 20,000ft and a service ceiling of 33,000ft.

*My earlier post said that all P-61As and P-61Bs had the R-2800-10. This is not correct - only the early P-61As had the -10, later ones and (presumably the B) had -65s, which was only slightly different to the -10.

Reluctant Poster · May 28, 2020

I don't see a requirement for a high altitude medium bomber. The types of missions they flew resulted in quite low loss rates. Higher altitude has a major negative impact on accuracy

Zipper730 · May 28, 2020

S Shortround6 W wuzak

The engine list I posted -- what did the B-26 fit into? I assume 6 or 9

wuzak · May 29, 2020

6 I think. Don't think they had the long nose case. But I could be wrong.

Another option for a B-26 derivative for service in mid/late 1943 may have been the V-3420 powered proposal.

That would have required more rework, but would have provided 500-600hp more power per engine than the B-26's B-series R-2800s.

gjs238 · May 29, 2020

Reluctant Poster said:
I don't see a requirement for a high altitude medium bomber. The types of missions they flew resulted in quite low loss rates. Higher altitude has a major negative impact on accuracy

I would love to hear more about this.
How did the Mediums get away with lower altitude missions w/o getting clobbered?

wuzak · May 30, 2020

gjs238 said:
I would love to hear more about this.
How did the Mediums get away with lower altitude missions w/o getting clobbered?

Maybe the targets were "softer"?

Shortround6 · May 30, 2020

The targets usually weren't as deep in enemy air space.
The mediums were faster.

This limited exposure but on some raids losses were still very high.

Zipper730 · Jun 25, 2020

I'm working on putting everything in the B-26 engine selection chart into an Excel document. It makes it easier to read and stuff.

Conslaw · Oct 5, 2020

The medium bombers ideally went in at an altitude that was too high for light flak, and too low for optimal performance of heavier flak. (It didn't always work out this way, of course.) Because they specialized in shorter-ranged missions, they were more likely to have fighter escort. Moreover, the targets of the mediums were more likely not to be the "high value" industrial targets justifying larger defensive fighter coverage. Also, the shorter strikes and lower altitudes meant that there was less warning for the defenders. The B-26's attributes came into play as well when it came to loss rate. They were somewhat faster than the heavy bombers. They had defensive firepower that almost matched the heavies. And they took a lot of damage and came home. One B-26 named "Flak Bait" survived 200 missions and 1,000 shrapnel and shell hits. For many years Flak Bait's front fuselage was on display at the Smithsonian Air and Space Museum on the National Mall. As of early this year, Flak Bait was under restoration at the Udvar Hazy Restoration Center, putting the entire aircraft back together for eventual display in the Udvar Hazy Museum.

B-26 with High Altitude Supercharger & Redesigned Bomb-Bay

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