Two engine R-3350 powered bomber

kool kitty89 said:

The A-20 itself seems like it might have fared well enough in a mosquito-like role, though the internal bombload was more limited. (more limited than the Ju-88's maximum internal load too, though not limited to the small, vertically oriented bombs as on the Ju-88 )

Click to expand...

The DB-7 flew for the first time about 15 months before the Mosquito (and about 10 months after the DB-7B, which was just about a totally different aircraft) And the DB-7s first used 1000-1100hp for take off R-1830 engines with single speed superchargers. They were good for 900hp at 12,000ft. The DB-7/A-20 bomb bay was larger than the Mosquito's and somewhat more flexible. Later A-20s could carry pretty much the same "standard" bomb load as a Mosquito, four 500lb bombs.
The later A-20s got a 140 US gallon fuel tank in the upper part of the bomb bay which did NOT affect it's ability to carry the four 500lb bombs inside. Mosquito still carried more fuel. Even later A-20Gs could take 325 US gallons in the bomb bay and still hold the four 500lb bombs. JU-88 had a choice, small bombs inside (carried horizontally not vertically) and about the same fuel as an A-20 without upper bomb bay tanks or cut way down of the internal bombs and carry more fuel.

Switching from R-2600s to R-2800s would be less dramatic, though more so if consider 2-stage or turbocharged R-2800s. The dimensions and weights of the A-20 are fairly close to the F7F ... if obviously not as clean of an aircraft.

Click to expand...

Well, having an internal bomb bay will do that, make for an aircraft that is not as clean. So will using older cowling designs and older airfoils and..............

Still, it might have already been close enough to be modified (without a total redesign) into an unarmmed fast-bomber configuration with more powerful engines. (logistics of turbocharger supplies or 2-stage R-2800s would have limited matters, though, and just stripping down the existing A-20s probably wouldn't have gained enough performance to be really good 'fast' bombers)

Click to expand...

They broke a B-25 re-engined with R-2800s by pulling up too sharply at the end of a low altitude high speed pass.

A DB-7 went about 15,030lbs loaded (Normal, not overload) or less than the F7F did empty.

Now please remember that US light/medium bombers were commonly built to an ultimate stress factor of 6 "G"s. Or 4 "G"s in service with a 50% safety factor.

A-20s with R-2600 engines went to about 20,000lb pretty quickly and had the wing structure reinforced to handle the higher weight (they also got the larger tail)

Later Versions went to 24,000lbs with a 27,000lb over load rating. Many bombers were restricted in the maneuvers they could perform to begin with and in over-load condition even more restrictions are mentioned in pilot's manuals.
How much beefing up the later ones got I don't know.
You can certainly beef up the structure to handle the R-2800s but at what cost in weight? and engineering time?
The engines used in the majority of A-20s went about 1940lbs.
R-2800s as used in early B-26s went about 2270lbs and the two stage Navy engines went about 2480lbs without intercoolers and ducts. Of course you need bigger props, engine mounts, exhaust systems etc. Power plant is going to go up a lot more than dry engine engine weight and that is already 1/2 ton.
Leaving out seven .30 cal Brownings (at under 25lbs each) and their ammo ( 65lb per 1000rounds?) isn't going to cut it.

I don't think I am smarter than Edward Heinemann and if he thought in Jan of 1941 that starting over with clean sheet of paper to start designing the A-26 was the way to go I am certainly not going to say he was wrong. The Xa-26 prototype went 21,150 pounds empty. How much of that was due to the gun turrets I don't know but "empty" weight often includes the turrets but not the guns.

The A-20's wing was stressed for R-2600 + turbo. That powerplant will not induce heavier load than R-2800?
The wing was also eventually stressed for external payload.
Both the A-20 and F7F used the NACA 230 series wing profile, granted the F7F was at 15% TTC at root vs. 18%.

tomo pauk said:

The A-20's wing was stressed for R-2600 + turbo. That powerplant will not induce heavier load than R-2800?

Click to expand...

Single stage R-2800 or two stage/turbo? Weight of propellers, Weight of total power-plant. Do you think the turbo installation on the R-2600 added 500-1000lbs per engine?

The wing was also eventually stressed for external payload.

Click to expand...

Where maneuvers or speed restricted when carrying external load?

Both the A-20 and F7F used the NACA 230 series wing profile, granted the F7F was at 15% TTC at root vs. 18%.

Click to expand...

And there is no difference between the two?

BTW Pilots manual for a Boston IV says:
Maximum weights are-
For normal take-off and gentile manoeuvrers........26,000lbs
For overload take-off and gentile manoeuvrers......27,600lbs (the 6 is penciled in)
For all permitted forms of flying and landing.........24,000

all aerobatics and intentional spinning are NOT permitted.

Stalling speed in a 2 G turn (60 degree bank) at 24,000lbs is 170-180 mph IAS

Diving speed was 400mph IAS before being crossed out with pencil.
Diving speed was 300mph IAS with under wing loads (not specified)
Bomb doors were not to be opened over 320mph IAS.

2000hp R-2800s should produce 25% more thrust than 1600hp R-2600s.

Empty weight of a A-20G/BostonIV was 17,200lbs. 725 gallons of fuel (4350lbs ) and 4000lb of bombs puts you at 25,550lbs with no guns, no crew, no ammo and no engine oil. Granted you don't have to carry the outside bombs ( and shouldn't for a Mosquito like mission) but adding 1500-2000lbs of powerplant weight is sure going to cut into the usable load and not help landing a whole lot, landing instructions (recommended speeds at different points in the approach) are for 20,000lbs.

Oil is listed at 23 US gallons per engine which seems a bit light. Early B-26s could carry 41.25 gallons, granted they were planning longer missions but when you swap engines you have to change a lot of things besides just the engine.

wuzak said:

You could, perhaps, run 6 R-2800s on a B-29.

Click to expand...

The XB-39 powered by the Allison V-3420-11 seemed to be the backup plan.

Shortround6 said:

They broke a B-25 re-engined with R-2800s by pulling up too sharply at the end of a low altitude high speed pass.

Click to expand...

Glad they tried though and that we're not the only ones exploring these ideas

Unfortunately the pilot and perhaps what crew/passengers were on the test flight died. And seeing as it was a test flight, no bombs, no over load fuel tanks, no full crew.

Shortround6 said:

Unfortunately the pilot and perhaps what crew/passengers were on the test flight died. And seeing as it was a test flight, no bombs, no over load fuel tanks, no full crew.

Click to expand...

Beechcraft XA-38 Grizzly

While designed as an attack aircraft fitted with a 75mm cannon, it could also perform a secondary mission as a bomber, mine layer or smokescreen duty. Could carry up to 2000lbs in up to six external racks. Not very indicative of what sort of bomb load a twin 3350 could do, but it does give a decent idea of performance as it is medium bomber sized. At some point this was the intended A-20 replacement.

I wonder what it could do without the 75mm and small bomb bay taking replacing the bottom turret.

To me, the biggest advantage of twin 3350s would be fuel economy and thus range. Maybe instead of the XB-33, do something that is as small as possible a departure from the B-26.

It would probably be the US equivalent of the He-177

Large, fast, good payload and a certain tendency to leave a trail of smoke and flames behind.