Fast bombers for the USAF, 1941-45

[Shortround6]

Things changed and they changed fast.

In 1938/39 a fast bomber barely broke 300mph, had a three man crew and carried around 1000lb of bombs or bit over. Pair of 1000 hp engines, give or take. This was for flying prototypes.
By early 1941 the Americans had the A-26 on the drawing board and the North American B-28. Wiki "The order for a high-altitude medium bomber was put out on 13 February 1940; the XB-28 first flew on 26 April 1942. "
First flight of the A-26 was in July of 1942.
Note that the US had little or no experience with twin engine medium bombers in combat (A few B-26s at Midway ) when the A-26 flew and the B-28 flight pre dated Midway.

There are the turbo-charged R-2800 engines. top speed 372mph at 25,000ft
However with a 5 man crew and the 3 remote aimed powered gun mounts added a lot of weight and bulk. As did the pressure cabin.

With it's size and weight would it have been any faster than the B-26 Marauder or Vega at low altitude?

 

[swampyankee]

It's well-known that US industry had some very good aircraft designers. What would be needed for them would be a spec. One problem with this was that the USAAF was too concerned with bomber self-defense firepower, so they would not write a specification for a truly fast bomber.

What would that specification look like? I'd suggest something like this:

• Cruise speed of no less than 300 knots (true) at 18,000 to 25,000 feet with engine at no more than 65% max continuous power
• Combat radius of no less than 500 miles with 2,000 lb bomb load at 300 knot cruise.
• Stall speed no greater than 100 knots at landing weight
• Full instruments for flying at night and in adverse weather
• Minimum control speed no greater than 115 knots
• Landing weight is to be sufficient to land with internal bomb load and 50% of internal fuel
• Crew of two (pilot and navigator).
• Tricycle landing gear preferred but not required.
• Appropriate words about stall and spin behavior, load factors, etc.

These specs aren't that much different from those of the Mosquito, so they're not (too) unreasonable. The problem isn't the designers; it's that the USAAF won't specify an aircraft of this sort before WW2 is underway.

 

[Shortround6]

Part of the problem with designing a fast bomber is that it takes longer than designing a fast fighter.
With a fighter you may be designing 3-4 years down the road. The Bomber may be 4-5 years down the road.

Another problem is the Range. The US seemed to value range more than speed, which is understandable given the size of the US and the small numbers of aircraft purchased before 1940.

From Joe Baugher's website on the Martin B-26
" The history of the Martin Marauder dates back to early 1939. Both the North American B-25 Mitchell and the Martin B-26 Marauder owe their origin to the same Army Air Corps specification. On March 11, 1939, the Air Corps issued Proposal No. 39-640 for the design of a new medium bomber. According to the requirements listed in the specification, a bombload of 3000 pounds was to be carried over a range of 2000 miles at a top speed of over 300 mph and at a service ceiling exceeding 20,000 feet. The crew was to be five and armament was to consist of four 0.30-inch machine guns. The proposal called for either the Pratt & Whitney R-2800, the Wright R-2600, or the Wright R-3350 radial engine. "

They didn't get what they asked for. But how do you pare down this requirement?
Lower the bombload to 2000lbs so you need 50% more bombers to deliver the same tonnage of bombs? (assuming same bombsight and bombing techniques).
The US was not planning on penetrating 500 miles of defended air space at this time. While a high cruise speed might have been useful for getting to an invasion site on America's shores quicker, having to stop to refuel means the slower plane will get there at about the same time. Americans thought that 8-10 hour missions required two pilots. Plus the navigator and a dedicated radio operator.

Maybe we can take out the tail gun and cut the crew to 4?
And take another look at the spec, the idea that American bombers were well armed in 1939/40 is pretty much a myth.

Once the US was in the war the early A-20s were disliked in the SWP because of short range and there was a scramble to add tankage.

The US had a bit of problem with engines for fast bombers in 1939/40. Plenty of designs on paper or in the shops, not much in the way of actual hardware. (the companies saying they were developing two stage superchargers and turbo installations). In 1939 P & W had two stage R-1830s but not a two speed single stage engine.
The B-26 being the first production plane to use the R-2800 and the version it got was good for 1850 for take-off and 1500hp at 14,000ft at 26000rpm. Max continuous was 1450hp at 13,000ft at 2400rpm. the engine weighed 2270lbs.
In the Spring of 1939 Allison was trying to sell the C series engine with the long nose and was delivering a couple of engines a month. What was promised and when for 1940-41 I don't know.

 

[Koopernic]

I suspect the P-61 Black widow could be adapted as a fast bomber with an internal bomb bay.

 

[Shortround6]

I suspect the P-61 Black widow could be adapted as a fast bomber with an internal bomb bay.

And what do you get????
A plane that is only about 10-15mph faster than an A-26, that holds hundreds of gallons less fuel, and the modifications not to just have an internal bomb bay but one that will hold FOUR 1000lbs are what?

The A-26 maybe somewhat under appreciated as an airplane. The Douglas engineers managed to build a high speed attack bomber (or modern medium bomber) with a wing 120 sq ft smaller (about 82% ) of the wing on the P-61, it was also about 60 sq ft smaller than the 'small wing" Martin B-26.

Performance of an early B-26 was " Performance: Maximum speed 315 mph at 15,000 feet. Cruising speed 265 mph. An altitude of 15,000 feet could be attained in 12.5 minutes. Service ceiling 25,000 feet. Range was 1000 miles at 265 mph with a 3000-pound bombload. Weights: 21,375 pounds empty, 32,025 pounds gross."

The USAAC didn't get what they asked for in 1939.

They were a bit faster with lighter loads but then the range was truly crap, 400 gallons doesn't last long with a pair of R-2800s

Granted a smaller fuselage would have less drag but on a 32,000lb airplane the amount of guns on the early B-26 shouldn't have been a big problem, one .30 cal out the nose, the two .50s in the top turret, a single .30 out the bottom hatch and a single .50 in the tail. Who manned the bottom .30 is a question. a very athletic and agile top gunner? or the co-pilot ran (wormed?) his way through the bomb bay to the rear compartment when needed ? or the tail gunner tried to move back and forth?
5 man crew listed, 4 gun positions.

A fast bomber for the US not only needs to leave a few crewmen out, it needs a lighter bomb load (smaller bomb bay) and shorter range than what the USAAC was looking for.

An A-20/DB-7 with Allisons in 1941/42 might have worked, such a plane in 1940 might have been a disaster. Allison couldn't build engines fast enough for the P-40s and first few hundred C-15 engines needed to be sent back to Allison for extensive reworking. You get better streamlining than the radial engines but you don't get as much power for take-off.

 

[Thumpalumpacus]

I definitely agree that the A-26 is underappreciated.

 

[wlewisiii]

Once the US was in the war the early A-20s were disliked in the SWP because of short range and there was a scramble to add tankage.

One thing they did with the A20 was with a droppable conformal fuel tank that fit along the bottom of the bomb bay holding 374 gal. That would have to be dropped before the bombs could be salvoed.

 

[Shortround6]

while it may have been conformal in a technical sense that word conveys a more sophisticated shape than the tank really had.

Makes a Spitfire belly tank look good.

 

[wlewisiii]

The drawing in the manual looked better!

 

[GrauGeist]

I wonder if they could have adapted "Tokyo Tanks" to the A-20?

 

[Shortround6]

Already had fuel tanks in the spaces forward of the main spar just outboard of the engines. There is a joint in the wing just out board of the fuel tanks where the outer wings were detached for shipment (deck cargo).
Not a lot of space left in the outer wings

Later versions got up to 325 gallons in the upper bomb bay. 3 fuel cells, not all of which had to be fitted at the same time.
early A-20s grossed under 21,000lb max with the R-2600 engines. Late A-20s could operate at 27,000lbs max gross weight (field length permitting.)
325 US gals is about 1950lbs without the weight of the tanks.
There was only so much weight you could stuff into a plane that started out at 17,031lbs (French DB-7) max gross.

Many WW II planes were weight limited and not volume limited, although trying to stick things in between ribs and into other nooks a crannies might be difficult.

P-39 went from 200 (?) gallons to 120 gallons when they introduced self sealing tanks.

 

[Koopernic]

And what do you get????
A plane that is only about 10-15mph faster than an A-26, that holds hundreds of gallons less fuel, and the modifications not to just have an internal bomb bay but one that will hold FOUR 1000lbs are what?

The A-26 maybe somewhat under appreciated as an airplane. The Douglas engineers managed to build a high speed attack bomber (or modern medium bomber) with a wing 120 sq ft smaller (about 82% ) of the wing on the P-61, it was also about 60 sq ft smaller than the 'small wing" Martin B-26.

Performance of an early B-26 was " Performance: Maximum speed 315 mph at 15,000 feet. Cruising speed 265 mph. An altitude of 15,000 feet could be attained in 12.5 minutes. Service ceiling 25,000 feet. Range was 1000 miles at 265 mph with a 3000-pound bombload. Weights: 21,375 pounds empty, 32,025 pounds gross."

The USAAC didn't get what they asked for in 1939.

They were a bit faster with lighter loads but then the range was truly crap, 400 gallons doesn't last long with a pair of R-2800s

Granted a smaller fuselage would have less drag but on a 32,000lb airplane the amount of guns on the early B-26 shouldn't have been a big problem, one .30 cal out the nose, the two .50s in the top turret, a single .30 out the bottom hatch and a single .50 in the tail. Who manned the bottom .30 is a question. a very athletic and agile top gunner? or the co-pilot ran (wormed?) his way through the bomb bay to the rear compartment when needed ? or the tail gunner tried to move back and forth?
5 man crew listed, 4 gun positions.

A fast bomber for the US not only needs to leave a few crewmen out, it needs a lighter bomb load (smaller bomb bay) and shorter range than what the USAAC was looking for.

An A-20/DB-7 with Allisons in 1941/42 might have worked, such a plane in 1940 might have been a disaster. Allison couldn't build engines fast enough for the P-40s and first few hundred C-15 engines needed to be sent back to Allison for extensive reworking. You get better streamlining than the radial engines but you don't get as much power for take-off.

1 The P-61 was running about 6-7 months ahead of the A-26 getting into service: May versus September in the ETO and in that case the P-61 was shipped by sea wheras A-26 ferried.
2 Speed is Life. If the P-61 is 10 mph faster then that is significant if the intercepting fighter is now only 10 mph faster instead of 20mph.
3 The twin booms of the P-61 readily allow accommodation of turbo chargers and a 400+ mph speed faster than the Mosquito with two stage Merlins.
4 A-26 is a "Attack Aircraft" not a fast bomber that could hit and run like the Mosquito or drop a bomb or target mark from the stratosphere using Oboe radio bombing.
5 The P-61 could in theory have a solid machine gun nose.
6 Would be tempting to remove the 4 gun upper turret and replace with 2 gun.
7 P-61 fast bomber wouldn't need forward armament and should be faster.
8 It should be possible to use the nose of the P-61 for ground bombing radar given its wide sweep.
9 The Mosquito's manoeuvrability made it very hard to shoot down, Mosquitos could evade long enough to hide in clouds. The P-61 was MORE manurable than the Mosquito,

 

[GrauGeist]

The P-61 proved to be devestating in the ground attack role with it's cannon (some didn't have the upper turret in place), so perhaps remove the radar from the airframe and install a gun-ship style nose with 4/6/8 .50MGs?

 

[wuzak]

3 The twin booms of the P-61 readily allow accommodation of turbo chargers and a 400+ mph speed faster than the Mosquito with two stage Merlins.

Do you mean a faster top speed or being able to get to 400mph before the Mosquito?

If it was the latter, the Mosquito IX was in production and service in 1943 and could produce a top speed over 400mph. This was around the same time, or before, the P-61A started operations.

If it was the former, the Mosquito B.XVI had a maximum speed, at mean weight, of 408mph at 26,000ft with Merlin 72/73s, or 415mph @ 28,000ft with Merlin 76/77s. The XVI started production in early 1944. The B.IX had similar performance. This was about a year before P-61C production began.

It is not certain that a bomber based on the P-61 using turbocharged R-2800s would have higher performance than the Mosquito if it was produced at the same time as the P-61A/B, as it would have had to use earlier generation R-2800s.

The Mosquito B.35, produced in 1945, used Merlin 113/114 engines had a maximum speed of 422mph.

 

[tomo pauk]

I wonder if they could have adapted "Tokyo Tanks" to the A-20?

Already had fuel tanks in the spaces forward of the main spar just outboard of the engines. There is a joint in the wing just out board of the fuel tanks where the outer wings were detached for shipment (deck cargo).
Not a lot of space left in the outer wings

The P-38, P-63 and Bf 110/210/410 also have had fuel tanks installed behind the main spar (Bf 110 was carrying almost 120 - imp? - gals behind the main spar and inboard the nacelle). If anything, A-20 have had a generous wing, and not thin at 18% t-t-c at root, leaving a lot of volume for fuel tank aft the main spar and inboard of the engines.
Or they could've done it like on the P-38, when the new part of the outer wing was designed and manufactured, loosing intercoolers and ribs there, while gaining a 55 gal fuel tank on each side.
Early A20G shave had the smaller bomb-bay tanks, for 144 US gals total.

P-39 went from 200 (?) gallons to 120 gallons when they introduced self sealing tanks.

P-39 have had problems that it didn't have 1, 2 or perhaps 3 fuel tanks, but 12 fuel cells all together - 6 per side, interconnected, with ribs between them. P-39C was already down to 170 gals in the non-protected taks, the P-39D introduced the s-s fuel tanks that 'stole' a big chunk of internal volume, indeed bringing down the fuel tankage to 120 gals.
P-63 was designed with two 'proper' tanks, but the designers left the volume in front of the spar without fuel tanks, thus frittering the opportunity to make an useful fighter from the USAF perspective. Yes, there was the ammo bay in front of the main spar for the HMG.
A-20 went from 540 to 400 gals (all for wing tanks only) when s-s tanks were introduced.

 

[Shortround6]

In front of spar or behind?

Fuel tanks have to near the center of gravity. Not just where there is unused volume.

Spar may or may not be on the center of gravity.
A-20 carried 136 US gallons in the inner wing tanks and 64 in the outer tanks.
As noted before, a number of different tank set ups were used in the bomb bay.
The tank in the picture in post #48 was not self sealing was 'supposed' to allow the bomb bay to carry bombs, Belly tank being dropped on the approach to allow the bomb bay doors to open. I don't know if it was ever used in combat or just rarely.

One would think that if it was easy to put in extra wing tanks they would have done it an not resorted to some of the set ups they did use.

 

[wuzak]

The Mosquito was slightly smaller than the A-20, but had 536 imperial gallons of internal fuel, all carried in the wing structure. The wing was one piece, and also formed the roof of the bomb bay.

https://upload.wikimedia.org/wikipe...ay_at_RAF_Museum_London_Flickr_5316144656.jpg

This site shows the restoration of a Mosquito:
SpitfireSpares.com - warbird Reference

One of the pictures shows the incomplete wing from below, the fuel cell bays visible.

Mosquito was able to carry drop tanks when production changed the the universal wing in 1943. They used tanks that attached to the leading edge and bottom of the outer wings

https://upload.wikimedia.org/wikipe...._544_Squadron_RAF,_26_July_1944._CH14264.jpg

Could something similar have been used for the A-20?

 

[GrauGeist]

When the A-20 was designed and accepted by the USAAC, drop-tanks were not an option per the powers-that-be.
So the A-20 (and anything else designed in the late 30's) did not have provisions for that feature.

 

[wuzak]

When the A-20 was designed and accepted by the USAAC, drop-tanks were not an option per the powers-that-be.
So the A-20 (and anything else designed in the late 30's) did not have provisions for that feature.

Nor did the Mosquito in early versions.

 

[ThomasP]

A-20G/Boston IV were equipped to carry upto 1000 lb (2x500 lb) under each outer wing. Since the wing was strong enough, I do not think there would be a problem rigging for a DT. There would be no reason that at least a 75 USgal DT (~500 lb) could not be carried in place of 1 of the 500 lb bombs, and if a 4-point carrier set-up was used the DT could probably be larger (unless there were some unusual aerodynamic problems).