Fast bombers for the USAF, 1941-45

[Shortround6]

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.

First flights were 45 days apart. A-26 program was delayed for a number reasons including the Army balking at the quoted price. delays in getting government furnished equipment (like engines and propellers) didn't help aft the contracts were signed. Army couldn't make up it's mind if the first 500 aircraft were ALL to have a 75mm cannon or glass noses or a mix (or some other armament set up).

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.

At what altitude? the P-61 is faster high up, is it faster at lower altitudes? At 22,000ft the P-61 may be 20mph faster (or more) , at 15,000ft is about 5mph faster.

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.

Not really, the P-61 was already using much of the leading edge of the wing for the air intakes for the two stage superchargers it already had. A lot of the wing was being used for fuel tanks near the Nacelles.

Note the rather large scoops/bulge under the nacelle to help hold the Turbo on the P-61C. Boom at about the area of the wing trailing edge was taken up by the main landing gear wheel well.

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

Well, it could carry more bombs (or at least a greater weight) further and faster than a Martin B-26. Nobody hot much of anything from the stratosphere anyway, regardless of the bombing system unless the target was an entire city. Bottom of stratosphere varies with latitude and season (temperature?) but might be around 33,000ft over Europe?

5 The P-61 could in theory have a solid machine gun nose.

It could but why bother?

6 Would be tempting to remove the 4 gun upper turret and replace with 2 gun.

savings would be minimal.

 

[tomo pauk]

In front of spar or behind?

P-38, Me 110/210/410 all have had fuel tanks both in front and behind the main spar.
P-63 have had fuel tanks only behind the spar; the A-20 only in front of the spar.
I've suggested that another fuel tank is installed behind the spar; already 2x75 gals per aircraft will help with extending the cruise range.

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.

You can note that I've suggested installing the tanks in the wings, ie. fairly conservative suggestion wrt. CoG.
Spars are seldom at the center of gravity, even if we limit that just to the wings with 1 main spar. Spar was at 35% of chord on the P-38, at 37.75% on the Bf 110, and at 38% on the A-20.
The shear web - something like auxiliary spar, that will limit the rear side of the aft tank - was at 65.9% of the chord on the A-20, at ~68.5% on the Bf 110, and at 70% on the P-38.

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.

Probably used as ferry tank in practice?
Manual for the Boston IV notes the belly tank for the 'extra long range operations', that was supposed to be used in conjunction with the bomb bay tank of 325 US gals.

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.

It was certainly far easier to install the bomb bay tanks - bomb bay was rather tall, so both tanks and bombs fit.

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

Two 75, 110 let alone 150 gal tanks would've made the A-20 a very long range bird. What might get in the way is the weight - A-20 was getting very heavy as the war progressed, the later A-20Gs tipping the scales at 26000 lbs (4000 lbs of bombs, 400 US gals).
Mosquitoes with 1-stage Merlins were up to 21500 lbs with 5000 lbs + 600 US gals.

What a fine aircraft Mosquito was.

 

[wuzak]

Mosquitoes with 1-stage Merlins were up to 21500 lbs with 5000 lbs + 600 US gals.

I don't think any Mosquitoes with single stage engines were carrying 5,000lb bombs. At most 4,000lb.

The B.XVI could carry the 5,000lb load.

 

[SaparotRob]

Okay. I'm way too lazy to look this stuff up but weren't all the twin engined U.S. bombers faster than their European and Japanese counterparts? I'm not including the hot-rodded Japanese or German recon birds that carried far less weight of ordnance. Never read that the B-26 was too slow. Ditto the A-26. The A-20 was no slug either. The B-25 would not have been so popular had it been slower than the Sterling.
No, I don't know which variant or at what altitude.

 

[tomo pauk]

I don't think any Mosquitoes with single stage engines were carrying 5,000lb bombs. At most 4,000lb.

4000 + 2x500 on the M.XX: link

Okay. I'm way too lazy to look this stuff up but weren't all the twin engined U.S. bombers faster than their European and Japanese counterparts?

Trick was being fast enough so the enemy fighters have far less chances for interception (helps out also vs. AA guns in some measure). Early B-26s were elusive targets for the Japanese fighters, not so much for the German fighters, while Mosquito stood much better chances vs. German fighters, and by default it was as good as un-interceptable for the Japanese.
This thread is about what US might've done different to have their own fast bomber. Neither B-25 nor the B-26 were fast bombers, and even the 320-340 mph A-20 will not cut it against Luftwaffe unless Allies have the air superiority achieved.

 

[Koopernic]

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.

The P-61 was ready for operations in early 1944 so assuming a Turbo Charged PW R-2800 of 2200hp it should break 400mph but it certainly won't beat the 400+ mph 2 stage Merlin Mosquito into service which manged that fete in early 1943.

To exceed 400mph most WW2 aircraft needed either turbo charger or a two stage supercharger with exception of a few (Fw 190, Typhoon, maybe Me 109 with others only in 1944 1944)

Had American planners made the decision to incorporate the turbo charged engine from the get go the same speed as the Mosquito would be possible. The Turbo R-2800 was available on the P-47B in mid 1942 as the Merlin 61 was on the Spitfire VIII/IX in 1942.

There was also the P-61E which was a fighter version of the P-61B but faster and capable of 376mph on mechanical super chargers. It definitely would have cracked over 400mph with turbo chargers.

It should be noted that the P-61 had a reputation for out rolling and out turning even single engine fighters and might have escorted B-17 Over Berlin or B-29 over Tokyo.

The P-61 had a large bulged weapons bay, recessed deeply enough to incorporate a bomb bay and given the massive R-2800 would hardly be slowed by a pair of 1000lb GP under the wings.

Hence the P-61 could have performed the role of
1 Night fighter
2 Day fighter able to out roll and out turn single engine fighters
3 Attack bomber with a solid nose
4 Bomber with a clear Perspex nose (if they can put a Perspex nose on a P-38 they can do so on a P-61)
5 Bomber with H2X in nose
5 Anti Submarine with maritime search radar in the nose, rockets under wings and bombs/depth charges in weapons bay.

 

[Koopernic]

First flights were 45 days apart. A-26 program was delayed for a number reasons including the Army balking at the quoted price. delays in getting government furnished equipment (like engines and propellers) didn't help aft the contracts were signed. Army couldn't make up it's mind if the first 500 aircraft were ALL to have a 75mm cannon or glass noses or a mix (or some other armament set up).


At what altitude? the P-61 is faster high up, is it faster at lower altitudes? At 22,000ft the P-61 may be 20mph faster (or more) , at 15,000ft is about 5mph faster.



Not really, the P-61 was already using much of the leading edge of the wing for the air intakes for the two stage superchargers it already had. A lot of the wing was being used for fuel tanks near the Nacelles.

Note the rather large scoops/bulge under the nacelle to help hold the Turbo on the P-61C. Boom at about the area of the wing trailing edge was taken up by the main landing gear wheel well.


Well, it could carry more bombs (or at least a greater weight) further and faster than a Martin B-26. Nobody hot much of anything from the stratosphere anyway, regardless of the bombing system unless the target was an entire city. Bottom of stratosphere varies with latitude and season (temperature?) but might be around 33,000ft over Europe?



It could but why bother?


savings would be minimal.

A fast bomber variant of the P-61 I argue would outperform the Mosquito in every role from 1944 onward.
-A P-61 with mechanical superchargers would be as fast as a Mosquito with single stage superchargers.
-A P-61 with turbo superchargers would be as fast as a Mosquito with two stage superchargers.
-A P-61 in the day fighter or reconnaissance role would out roll and out turn a Mosquito.
-A P-61 looks like it could carry 4 x 500lb or 2 x 1000lb in the weapons bay at least.
-A P-61B could carry rockets and bombs and drop tanks under wing. Due to the power of the R-2800 speed loss is fairly small.
-The large radar dome allows surface search and ground mapping radar
-The P-61E fighter variant managed 376 mph on mechanical superchargers.

Had American planners asked for turbo integration from the inception the daylight escort fighter would have been viable as would the recon version. Replacing the gun pack in the weapons bay with a bomb bay looks viable.

American aircraft were bombing using AZON. Best way was for a B-24 to drop the bomb but a higher up glass nose P-38 to guide it. That would work with the B-29 from the stratosphere. In fact AZON would likely work well from a P-61.
-

 

[Thumpalumpacus]

According to the USAF Historical Support Division:

The B-26 "Marauder" was used mostly in Europe but also saw action in the Mediterranean and the Pacific. In early combat the aircraft took heavy losses but was still one of the most successful medium-range bombers used by the USAAF. By the end of the war, the B-26 had the lowest loss rate of any American bomber used during the war.

Army Air Forces Aircraft: A Definitive Moment > Air Force Historical Support Division > Fact Sheets

 

[Shortround6]

A fast bomber variant of the P-61 I argue would outperform the Mosquito in every role from 1944 onward.

It should do something, it weighed about 50% more. Fuel burn would be fantastic. What the P-61 could not do was deliver an equal amount of bombs for the same logistical cost. There rest is also debatable.

-A P-61 with mechanical superchargers would be as fast as a Mosquito with single stage superchargers.

NOt would be as fast, was as fast, P-61 did use a mechanical two stage supercharger.

-A P-61 with turbo superchargers would be as fast as a Mosquito with two stage superchargers.

Well this rather depends on which version of the turbo R-2800 we are talking about. Might also depend on which version of the Merlin.
P-47B&C and early D used an engine and Turbo that could give 2000hp to about 27,000ft in level flight but only to about 23,000+ ft when climbing (loss of RAM). Turbo was limited to 18,250 rpm.
When fitted with water injection (in late 1943/early 44) in the field the engines were up graded to 2300hp. A new turbo was fitted to the P-47D-10? In tests the new turbo was limited to 20,000rpm by the regulator. A later regulator (or adjusted?) allowed 22,000rpm. However the use of any manifold pressure over 52in required water injection. The higher rpm limits on the turbo allowed for higher altitudes.
In the spring of 1944 they increased the amount of water injection and cleared the engines for 2535hp using 64in of MAP using 100/130 fuel.
In the summer of 1944 they were doing tests with 44-1 fuel and could get to 70in MAP with water injection and 65 in without.

The engines used in the P-61C were the same engines (and turbos/regulators?) used in the P-47 M & N. These were "C" series engines with different cylinders with much improved cooling and were allowed to run at 2800rpm instead of the 2700 rpm of earlier engines. These are the 2800hp engines.

Yes you probably could have stuffed turbos into an earlier P-61, but you weren't going to get the 2800 hp engines until the spring of 1945. Or the 2535hp engines until the late spring of 1944.
A water injected two stage R-2800 was good for 2250hp at sea level, 2135hp at 12,5000ft no ram and 1975hp at 17,000ft no RAM. Add 2500-3000 ft for max level speed RAM.
Turbos will help, just not as much as some people think.

-A P-61 in the day fighter or reconnaissance role would out roll and out turn a Mosquito.

That is going to take a lot of swallowing. Out roll seems plausible. Out turn???? Are we talking about instantaneous turn or sustained turn? Maybe a very light P-61 against a very heavy Mosquito. Pilot reports vary.

-A P-61 looks like it could carry 4 x 500lb or 2 x 1000lb in the weapons bay at least.
-A P-61B could carry rockets and bombs and drop tanks under wing. Due to the power of the R-2800 speed loss is fairly small.

Using a plane that is near (or over) 30,000lbs to deliver four 500lb bombs or two 1000lbs seems rather uneconomic.
Especially considering what the A-26 could do, And the A-26 did it using single stage engines that gave only 1600hp at 13,500 ft at Military rating in high gear.
P-61 at 28,000lbs is 10mph faster at 15,000 ft using hundreds more HP per engine. Which means it is burning a lot more fuel per minute.

-The P-61E fighter variant managed 376 mph on mechanical superchargers.

Yep,

Except the P-61E was doing it at 17,000ft using around 300hp more per engine than the A-26. Does something seem a bit off with the P-61?

Had American planners asked for turbo integration from the inception the daylight escort fighter would have been viable as would the recon version. Replacing the gun pack in the weapons bay with a bomb bay looks viable.

Possible to do something (viable?) doesn't mean it is the smart thing to do.

 

[nuuumannn]

I couldn't possibly reply with details about the US types as my knowledge of them is limited, but it seems that the most logical path would have been for a US manufacturer to start from scratch. Adapting an existing type is just not going to do what any fast bomber requirement asked. Removing weight by deleting turrets and localised strengthening around turrets weakens the structure, and removing turrets and moving fuel around alters the CG, all of which might introduce potential unforeseen handling issues.

Douglas was an excellent firm that made exceptional aircraft and there's no reason not to believe that an entirely original design for a fast bomber would have been as great as the A-20 was for its generation, or its replacement the A/B-26 (I mean the post-war Invader, not the Martin Marauder) would have been. I'm sure North American and Martin would have come up with some slick machines each, but I bet they would have all been clean-sheet rather than based on the B-25 and B-26 respectively.

 

[wuzak]

If the P-61 was converted to a bomber, would it need a longer central nacelle to house a decent bomb bay?

 

[Shortround6]

A/B-26 (I mean the post-war Invader, not the Martin Marauder)

Douglas made around 2400 A-26s before the end of the war. Granted it didn't show up in combat until late fall of 1944 but it was not a post war aircraft.

If the P-61 was converted to a bomber, would it need a longer central nacelle to house a decent bomb bay?

Heck, it would need a longer or much modified central nacelle just to house the fuel.
Drop tanks are NOT the answer for a high speed long range bomber.

 

[Shortround6]

The US got what the US Army wanted, mistaken as that may or may not have been.

There was a Feb 1938 requirement for a twin engine attack aircraft. There were several modifications to this requirement. The Original requirement spawned the Martin 167, the Douglas DB-7, the North American NA-40 (which lead to the B-25) and an entry by Stearman.

There were also a bunch of paper proposals.

Just from Douglas in Oct 1938 there were
7C..............P & W R-2180
7D.............Wright R-2600
7E..............P & W R-2800 SA1G
7F.............P & W R-2800 SA2G
DB-10......Continental O-1430
DB-10 Lycoming O-1230

By March of 1939 things were a bit more refined.
DB-7C..........P & W R-1830 turbo
DB-7D..........P & W R-1830 two speed supercharger
DB-7E...........P & W R-2180 turbo
DB-7F.........Wright R-2600 2 speed
DB-7G.........Wright R-2600 turbo.

Other manufacturers also had proposals and the proposals also included cost estimates for a 100 plane order.

Interestingly the cheapest plane would have been the Douglas B-23.

The specification that lead to the Martin B-26 came later in timing than the attack bomber specification.

How well the A-20 with a turbo R-2600 would have performed is certainly open to speculation. of the 70 ordered only one was completed and it had chronic cooling problems.
The rest of the order got two speed engines and most (all?) became P-70 night fighters.

 

[swampyankee]

6 Would be tempting to remove the 4 gun upper turret and replace with 2 gun.

Remove the turret, its mechanisms and structures, and gunner entirely.

7 P-61 fast bomber wouldn't need forward armament and should be faster.

I suspect that the incremental drag from the gun troughs for the four 20 mm cannon was much less than the drag due to any turret. On the other hand, getting rid of them would free up weight and volume.

----

While I think the P-61 was an interesting and potent aircraft, Northrop was also a small company. Even modifying the P-61 into a bomber may have been beyond their capabilities.

 

[Shortround6]

Please note that in the above lists the O-1430 and Lycoming O-1230 didn't even exist as complete 12 cylinder engines at the end of 1938.
While the Allison isn't listed it is not too surprising. Allison had built a total of 30 V-1710s from 1930 to the end of 1938. This total was made up of 18 different models.
The two "O" engines were the Army's favored hyper engines.

Also note that the P & W R-2180 would soon be dropped by P & W with about 30 engines built. The R-2800 used 18 of the same sized cylinders the 14 cylinder R-2180 used.

Turbo R-1830 sounds interesting but please remember, you are going to need a cowling the size of the one on the B-24 to get full benefit from a turbo R-1830.

Or stick one of those air scoops in the wing???
Engine air, oil cooler and turbo intercooler air. Intercooler took up one scoop by itself.

 

[Koopernic]

Remove the turret, its mechanisms and structures, and gunner entirely.

I suspect that the incremental drag from the gun troughs for the four 20 mm cannon was much less than the drag due to any turret. On the other hand, getting rid of them would free up weight and volume.

The Northrop F15 Reporter wouldn't look out of place with quad of AMRAAM missiles like its McDonald-Douglass aka Boeing name sake F-15.
The F-15 Reporter (later RF-61) photographed much of North Korea. Capable of over 440mph the gun pack was replaced with a 5 camera camera pack.

----

While I think the P-61 was an interesting and potent aircraft, Northrop was also a small company. Even modifying the P-61 into a bomber may have been beyond their capabilities.

If something become important enough engineers, technicians and workers can be transferred in. I suspect that had Northrop based the night fighter variant on the P-61E without remote control guns they would have had the aircraft in service sooner. The radar directed turret of an experimental version is interesting.

 

[Koopernic]

If the P-61 was converted to a bomber, would it need a longer central nacelle to house a decent bomb bay?

There seems to be plenty of room under the wing spar for bombs. The P-61 were upper wing aircraft. The US GP 1000lb bomb had a diameter of 1ft 6.78 inches (47cm). Width might be more of an issue than length but then a 400llb might work.

The aircraft was used as a fire fighting water bomber by attaching a tank to where the gun pack went. The gun pack was deeply recessed into the fueselage.

 

[wuzak]

here is the Hawker P.1005 (4,000lb bomb load)

View attachment 222391

Could the US have based a project on the Hawker P.1005, proposed to specification B.11/41?

The engines were a problem for the P.1005, using a pair of Sabres. An alternate engine may have been the Centaurus, but neither of these were available in teh quantities required for production.

A US version could have used V-3420s, with alternatives of R-2800s or R-3350s. R-3350s would have been a supply issue due to the B-29 program.

 

[ThomasP]

Hey wuzak,

re the Hawker P.1005 . . . interesting. I wonder what the top speed would have been and how soon it could have been in service? In service date maybe 1944?

 

[Conslaw]

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.

Yes, I think the procurement foul ups on the A-26 were the worst procurement mistakes the AAF made, maybe with the exception of not giving the P-47 good drop tanks from the beginning.