Fast bombers for the USAF, 1941-45

[ThomasP]

Turbo-supercharged 'C' series R-2800 engines would certainly get the speed up on the A-26 Invader, partly due to the increased rated altitude of course, and partly due to the higher mechanical strength of the 'C' series.

 

[tomo pauk]

The problem with the XB-42, in comparison with the A2D, is that the XB-42 has at least 30% more wetted surface, and about a 30% increase in the flat plate area (this is just an estimate on my part via scaling drawings and figuring the volume and area). At flying weight the XB-42 weighed ~40% more than the A2D, both in clean condition. With the engines listed in the Wiki article (2x 1375 = 2700 BHP) there is no way that the XB-42 could be anywhere as fast as the A2D (which had ~5100 HP effective). The best the A2D could do was 425-430 mph clean at 27,000 ft.

I have been assuming that the V-1710s were turbo-supercharged - is this correct?

The XB-42 have had 2-stage supercharged V-1710s, similar what P-63 or P-82E used. (Wikipedia horse-power figures are often unusable when the power setting is not noted). The 'dry' WER rating was 1400+ HP, with water injction it was 1800+ for the early engines on the XB-42, and 1900 HP for the later engines. Later engines also used better S/C and were supposed to run 3200 rpm.

 

[Shortround6]

A-20s, aside the very early ones, had 400 US gallons of fuel and ended with 725 gallons internal. All additional fuel was in the fuselage.
A-26 could hold 925 US gallon, 800 gallons in the wing a 125 gal fuselage tank.
Both had bomb bay ferry tanks and other options, including external stowage.

A-20G was supposed to do 314mph at 12,000ft at max continuous power burning 290 gal an hour for a theoretical range ( no warm up or climb allowance) of 690 miles. (725 gallons)
If it slowed down to 264mph (Normal power) the fuel burn dropped to 140 gph and the range (no including warm up and climb) went to 1050 miles.

An A-26B did 334mph at 12,000ft using max continuous (as the A-20) burning 386gph for a theoretical range of 780 miles.
If it used normal power the speed dropped to 296mph and the range (including warm up and climb ) went to 1365 miles while burning 209 gph.

Any twin engine bomber using P & W R-2800s would have a similar fuel burn at similar power settings. Two stage engines burn a bit more fuel to drive the aux supercharger but the plane is in thinner air for less drag.

For the Allison fans the engines in a P-38L gave 1600hp WER while burning 360 gph (both engines)
For "cruising" at max continuous (1100hp per engine 2600rpm and 44in MAP) the fuel burn was 226gpm. (both engines)
at max cruise lean (795hp per engine at 2300rpm and 35in MAP) the fuel burn was 126gph. (both engines)
P-38 numbers are from the engine chart and actual fuel burn did vary with altitude.

Plan your bombers accordingly. If you want to go fast and fly further than spitting distance you need a lot of fuel.
The Allison will allow better streamlining but P-38L engine was about as good as it got for power in a mass produced Allison. That 1100hp per engine is going to be the climb rating.
Older Allison's were limited to 1000hp at 2600rpm for climb and max continuous cruise.

 

[wuzak]

I think the V-3420 could have been a viable bomber engine earlier.

Early models had around 2,300hp max power, and power improvements for the V-1710 should translate to the V-3420, so by 1944 you could be looking at a 3,000hp engine (by then the historic V-3420s were making 2,600hp).

A B-26 with twin V-3420s, unarmed, or with just the tail gunner, would be quite a quick machine.

Without the turret, fewer crew and less guns and ammo to be carried, the bomb load could also be bumped up a little.

Or, if the small wing is retained, the weight could be brought down a little, lowering the wing loading.

 

[GrauGeist]

An enlarged Do335 bomber variant is a scary concept, if you could find the engines to give it enough power.

The Do335 did have a bomb bay and was capable of carrying over 2,000 pounds of bombs.
Not sure about the engines part, as the two DB603s gave it impressive speed.

 

[tomo pauk]

A-20G was supposed to do 314mph at 12,000ft at max continuous power burning 290 gal an hour for a theoretical range ( no warm up or climb allowance) of 690 miles. (725 gallons)
If it slowed down to 264mph (Normal power) the fuel burn dropped to 140 gph and the range (no including warm up and climb) went to 1050 miles.

The A-20G was a bit draggier than the earlier models, partially due to the turret it gained. It also gained weight.
The max cruising power was 855 HP at 18000 ft, and a bit better at low altitude. Not sure about max range power.
Max continuous power (1275 HP at 11800 ft and ~950 HP at 18000 ft) = normal power? Max cont used about double the fuel vs. the max cruising power setting, the max cruising is what I believe you're noted in the last sentence quoted.

The P-38G with 75 or 150 (165?) gal tanks (might be a better ballpark wrt. drag expected from a bomber than it is a case with clean P-38G) was supposed to cruise at 300 mph at 20000 ft using 115 gph total. At 12000 ft, it was to be 275 mph, fuel used 110 gph. On 613(?) gals of fuel and with allowance for warm up and climb to 5000 ft (leaving 570 gals for the flight) range was 1290 miles. Those are figures for lean mixture. Power used was up to 535 HP?
Best range at rich mixture, 2300 rpm, was 1070 miles; speed of 320 mph with 154 gph at 20000 ft (35 in Hg boost), or 285 mph with 142 gph at 12000 ft (32 in Hg). Power (max cruise setting) up to 740 HP? All power figures were up to 30000 ft.
At max continuous (up to 1100 HP at 24000 ft; 2600 rpm and up to 41 in Hg), it will be using 228 gph for 350 mph at 20000 ft, and 228 gph for 330 mph at 12000 ft.

I'd have to do a proper fuel consumption vs. power vs. altitude (3-dimensional?) table one of these days...

(P-38G clean and with racks/support for the tanks adds ~30 mph to these figures, but that is much sleeker than we'd expect from most of the bombers of the day)

A Mosquito IV with Merlin 21s, 644 US gals and 2000 lbs of bombs was good for 1620 miles at 265 mph and 15000 ft, or 1360 mph at 320 mph and 15000 ft. All after the allowances for T.O. and climb to 15000 ft, all for lean (weak) mixtures.
A P-38G with those drop tanks and at 15000 ft will do 1600 miles 260 mph, and will need to move from auto-lean to auto-rich to do 320 mph at 15000 ft, with range taking a dip ( 920 miles). With a turboed V-1710, we'd want to fly at higher altitudes - talk 20000 ft and above for good range and high cruise speeds, eg. 1280 miles at 310 mph at 20000 ft for our P-38G, or at 330 mph at 25000 ft.

 

[ThomasP]

Hey tomo pauk,

Thanks for the info on the XB-42 engines.


Hey GrauGeist,

re:"The Do335 did have a bomb bay and was capable of carrying over 2,000 pounds of bombs."

I did not know that. Learn something new every day.

 

[ThomasP]

I am thinking we might need to define the 'bomber' part of fast bomber a little more precisely? Although we are getting a lot of neat info and ideas just the way it is.

 

[ThomasP]

Maybe the Do335 would fit the bill for the 1945 speed. Since it already had a bomb bay, and a Vmax of ~470 mph, maybe it would not have to be enlarged very much to get what a fast 'bomber' variant would need.

 

[GrauGeist]

How about the Lockheed B-34 (Navy PV-1 Ventura)?
It entered service in 1941, powered by two R-2800s, capable of carrying bombs, depth charges or a torpedo with a max. speed of 322 mph and a range of 1,600 miles.

With a little engine work (and perhaps ditching the upper turret), it might hold promise.

 

[ThomasP]

re: PV-1

Wiki gives first service delivery in late-1942 with the US, did it enter service with the UK earlier?

 

[GrauGeist]

Yes, the RAF took delivery of the Ventura Mk I in September '41.

 

[tomo pauk]

I'd try the complete wing of the Ventura installed on an A-20...

 

[GrauGeist]

The B-34 was a mid-wing and a little larger at 51 1/2 feet long (wingspan being 65 1/2 feet) where the A-20 was a high-wing and 48 feet long (wingspan being a bit over 61 feet wide), so there would need to be some work done.

 

[tomo pauk]

The B-34 was a mid-wing and a little larger at 51 1/2 feet long (wingspan being 65 1/2 feet) where the A-20 was a high-wing and 48 feet long (wingspan being a bit over 61 feet wide), so there would need to be some work done.

More than just some work, perhaps up to the point to why bother. Wings differ too much.

 

[wlewisiii]

The earliest A-20G model aircraft did not have the turret but still had the single flex .50.

The manual gives the same performance with and without the turret.

43.5"/2300rpm, Autorich, 12000 ft altitude gives TAS 322 max. Burning 290 gal/hour so you won't go that fast for long...

I would be curious if the lighter early models could have benefited from the more powerful R-2600-23?

 

[Shortround6]

Douglas started work on the A-26 in the fall of 1940, By Jan the made a proposal to the USAAC. By mid April the mock up was being inspected.

Trying to stick bits and pieces of existing aircraft together would only have slowed things down. Douglas was already proposing using laminar flow wings and double slotted flaps so you weren't going to get a much more advanced wing.

A-26s delayed entry into service was due to other things than the basic design.

 

[Koopernic]

I wonder if the two seat P38 could be given a bomb pannier.

 

[Shortround6]

Fast bomber.
1. Speed
2. Bomb load
3. Range

Pick 2

If you go too extreme on one factor then you only get one attribute.

2 seat P-38 (bomb aimer in nose) with bomb pannier has 300 gallons in the wing until the J model, then 410 gallons.
P-38s were used as bombers, either short range or with one bomb and one drop tank.
Not that fast with external loads. Not long range with large bomb load.

 

[tomo pauk]

We'd probably want a proper bomber with a bomb bay and no reliance on drop tanks in order to have our US fast bomber, while trading fuel load for bomb load and vice versa, while going very modest on guns' armament.