USAF 1944: ideal multi-purpose 2-engined aircraft?

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See the sizes of the bombs, adding 3-4in in different directions for clearance you need a bomb bay 11 ft long, 4 feet wide and about 2 feet high to carry four 500lb bombs in pairs behind each other or a bay just under 6ft long and 4 feet wide and four feet high. That is enough volume to house 720 gallons of fuel (thickness of self sealing not counted)
Bomb bay has to go about on the center of gravity. Or about where the F7F stored most of it's fuel. Granted you could stretch the fuselage 6 feet or so and by careful fuel management between fore and aft tanks keep the CG from getting to far out of wack (or move some fuel to the wings?

Is the F7F fuselage even 4 feet wide?
F7F single seaters carried 420 gallons of fuel. About 1/2 of what an A-26 carried and the A-26 has trouble meeting Tomo's range goal.
 
tomo pauk said:
Cool, many thanks SR6
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No problem, just want us all working form the same page ( or close to it

The A-26B was capable to hold a 1000 lb bomb on each of 4 bomb racks inside the bomb bays (=4000 lbs total), so it's bomb bay size should be okay?
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Again it depends on your actual goal/requirement. The A -26 could also carry EIGHT 500lb bombs, four in front, two up and two down and four behind, two up and two down and that didn't even fill the bay.

The forward "racks" had seven bomb stations each (one rack on each side of the plane) but only 5 stations max could be used at a time. The rear racks had 5 stations but only 3 max could be used at a time. The Pilots manual does not give the limitations or weight capacities of the stations. You might be able to mount sixteen 250lb bombs or perhaps only sixteen 100lb bombs. And that is without the bomb bay tank which might block 2-3 of the upper stations in the forward racks.



edit: The 2000 lb should be a tricky bomb to install there, I agree. Maybe staggering them - the front bomb attached to the left-side rack, the rear bomb attached to the right-side rack? Racks being suitably strong, of course.
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don't get too tricky, you have to allow clearance for the workers to hoist and attach the bombs and to allow for a bit of side ways movement as the bombs leave the aircraft. Even if the worst that happens is a bent tail fin that bomb will not hit were it is supposed to.

BTW the British 4000lb "Cookie" was 110in long but only 30in in diameter and it's "tail" (hollow drum) was the same size or 1 in smaller than the body diameter. It was smaller across than the US 2000lb bomb tail fins.

This is the BIGproblem with trying to get a US bomber to match the Mosquito's 4000lb "capacity".

And the 500lb bombs used in the Mosquito were 12.9 in diameter, the tail fins were the same size as the body and and for the Mosquito (and perhaps other planes mid/late war) the tail fins were shortened (or made to telescope?) from a 70.6in AOL to 55.6in AOL of bomb.
 
The problem is the "multi-role" specification.

Trying to "ADD" a bomb bay that will hold four 1000lb bombs or eight 500lbs PLUS the fuel needed for 1700-1800 miles of range ( combat radius 600-700 miles?) to an existing fighter/ night fighter/ attack plane requires an awful lot of changes.

The A-26 may very well have been faster ( and cheaper ?) if the bomb bay was sized for four 1000lb or four 500lb bombs only and not the multiple bomb options that were rarely used ( it could even carry TWO torpedoes) and the ventral turret left out.

Or use upper bomb bay to house fuel displaced by fitting two stage Superchargers and inter-coolers.
 
Shamelessly stolen from Joe Baugher's web site.

"At the end of January 1941, a team led by Edward Heinemann and Robert Donovan had come up with a proposal for a new twin-engined attack aircraft that would satisfy these requirements. It had a broad general family resemblance to the A-20 Havoc which was just then entering service with the Army Air Forces. It featured a mid-mounted wing with a laminar flow aerofoil and which was fitted with electrically operated double-slotted flaps. The aircraft was to be powered by a pair of 2000-hp Pratt Whitney R-2800-77 air-cooled radials. The aircraft was to have a large internal bomb bay capable of carrying 4000 pounds of bombs or two torpedoes, and was to be fitted with external racks underneath the outer wings for additional ordnance. The defensive armament was to be provided by a pair of remotely-controlled dorsal and ventral turrets, each housing two 0.50-inch machine guns and operated by a gunner sitting in a separate compartment behind the bomb bay.

The mockup was inspected between April 11 and 22 of 1941, and on June 2 the War Department authorized the construction of two prototypes under the new designation A-26."

Please note that the two Prototypes are ordered six months before Pearl Harbor.
The A-26 may be the first plane in service with double slotted flaps which helped keep the wing small. Wing loading was over 60lb per sq ft on service versions.
 
It was easy to carry 1000 lbs of bombs 200 miles away; it gets trickier when carrying 2000 lbs 600 miles away


You mean something like this? One pilot's manual (a more 'colorful') indeed does not have this table, this is from another one:




Agreed. Wonder whether that cunning British trick would've worked here (cropping a bit the tail fins of the bomb)?


Thanks again. Some fin cropping might be a good idea.

About the F7F A-26: the F7F, as is, needs a bomb bay. Second, it does not need the cannons and ammo, so some amount of fuel can go there (in the wings).
The A-26 has ample space outboard of the nacelles, later versions carried ammo and/or HMGs there (6 per plane).

Edit2: place to download a better flight manual for the A-26B/C:
http://napoleon130.tripod.com/sitebuildercontent/sitebuilderfiles/a26.pdf
 
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tomo pauk said:
You mean something like this? One pilot's manual (a more 'colorful') indeed does not have this table, this is from another one:
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Thank you, I don't know what is going on but the forward bomb bay with more stations is holding fewer of the small bombs, Plane is fitted with bomb bay tank?

Drop the requirement/s for the small bombs, torpedoes, fragmentation clusters and so on (maybe even the eight 250lb bombs?) and you could certainly 'shrink" the bomb bay by quite a bit and still hold four 1000lb bombs.

Depends on your bomber "requirement".


Agreed. Wonder whether that cunning British trick would've worked here (cropping a bit the tail fins of the bomb)?
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Depends on what accuracy you were expecting from the bomb, British 4000lb cookies weren't noted for stable flight or much accuracy unless dropped from rather low levels.



Thanks again. Some fin cropping might be a good idea.
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British used a round tail about equal in diameter to the bomb but had a more tapered tail to the bomb body giving better air flow to the tail, the US had blunter tail taper and used a "box" section fin arrangement with fins protruding from the box and and having a greater span the bomb body.





Granted they are different size bombs but the pictures show the different basic shape. Shortening the tail on the British bomb may still give "acceptable" accuracy, Not so sure about shorting the tail or reducing the span of the fins on the American bombs. It does depend on target and bombing technique. Trying to hit a city or trying to hit one big building ( bridge or????) in the city?
 
Shortround6 said:
Thank you, I don't know what is going on but the forward bomb bay with more stations is holding fewer of the small bombs, Plane is fitted with bomb bay tank?
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Seems so, the 125 gal tank was to be installed in the upper portion of the front bomb bay.


The bomb bay from A-26 looks okay, maybe even the one from the A-20? A resulting plane can be smaller lighter than A-26, since we don't need 2 turrets and a gunner.


I surely wouldn't go for tailless bomb like cookie was. A little bit of tweaking with tails fins should save on the size of a bomb bay, and hence on size of the plane, with benefits in performance, range and maneuverability.

Further re. F7F: Grumman was proposing a 'F7F with a bomb bay', the XTSF1. Not some sizeable bomb bay, but an useful one - with torpedo, it was to beat 400 mph mark. Only the mock-up of the fuselage was being built, the end of the ww2 brought cancelation. wiki
 

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  • XTSF-1_Tigercat_ACP_-_1_August_1944.pdf
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You really don't want to screw around with the bombs a whole lot, especially for one airplane. Chances of the wrong tails being the only tails available are too great. Having ground crew shorten/trim tails with hack saws or cutting torches? do-able for a few special missions but as standard practice?

From the other A-26 manual. at 10,000ft flying 5mph faster than the bomb sight is set for will cause the bombs to fall 200 feet short, flying 100 ft high but at the correct speed will cause the bombs to 65 over the target.

Do you really want to be dropping bombs on a "point" target that use undersized fins and don't stabilize properly?

Dropping bombs on city a number of miles long and wide it doesn't matter.

Bombs were not only test dropped but in some cases special guns/mortars were designed, built and used to "fire" aircraft bombs to eliminate some of the variables in air drop testing.

As far as the XTSF1 Tigercat goes,( or doesn't) it carries about 1/2 the load (2000lb torpedo) about 1/2 as far as your spec on internal fuel. It requires an additional 7.8 ft of wing span (and 45 sq ft more wing area).

Note again the bomb bay capacity. FOUR 1000LB ARMOR Piercing bombs. ONLY TWO 1000LB GP (demolition) bombs.
 

Fair points - bombs need to be the run-on-the-mill. Seems like the requirement for two 2000 lb bombs is a deal breaker for a compact bomb bay?


The 'new multi role plane' can also carry drop tanks to achieve the range. I know that XTSF-1 was to have too small a bomb bay - eg. the A-26 was able to carry 2 torpedoes internally, vs. one for the XTSF-1.
 
The Ta-154 has an interesting shape, that might do the trick. A high-wing layout, with a teardrop shaped fuselage (when looking from above). The bomb bay should house gun armament ammo in a night fighter version. Of course, do it in metal.
picture via Wikipedia

 
It's got a shape but that is all it has.

Look at the Mosquito MK XVI, it has about 35-36% more wing area, about 17% more power, about 13-14% more max gross weight and it won't meet you specification for range or bomb load (or bomb load without the "cookie" bomb)

AS far as "just" adding a turbo-charger to the R-2800 engine, P-61C (with turbos) picked up about 2000lbs empty over the P-61B. Empty weight does NOT include guns, armor sighting equipment, etc.
 

Mosquito XVI can fulfill the specification, if it does not have to carry 2 x 2000 lb bombs, and I've already admitted that such bomb load is a game breaker. A-20/26 was not able to carry 2x2000, for example, despite being capable to carry 4000 lbs internally. The US 4000 lb demolition bomb should fit in the Mossie's bulged bomb bay?
Picture of the German 1800 kg bomb (3965 lbs), the US 4000 lb bomb should be of about same size?




AS far as "just" adding a turbo-charger to the R-2800 engine, P-61C (with turbos) picked up about 2000lbs empty over the P-61B. Empty weight does NOT include guns, armor sighting equipment, etc.
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'No free lunch' applies as always. The bomber with same 'genes' as the P-61 does not carry turret, cannons, gunner, ammo; only ammo weighted more than 900 lbs, cannons and turret with HMGs further 1400. More than making up for weight of the turbo installation. Lack of the turret should add some speed, too.

Some more details above the XB-42: there was indeed an auxiliary blower for cooling the engines' coolant, that was switched on/off with pressure on U/C legs, so the engine will not overheat when plane is standing still or when at low speeds. The reduction gear was the same as used on the P-75, here attached on two engines, instead of one 'double' engine.
 
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The Mossie would be lucky to hold a US 2000lb bomb but that is because of the tail fins. They are bigger across than the diameter of the 'cookie'.
The US 4000lb bomb is a lost cause, the 7" longer may not be a problem but the body is 4.25" bigger ( mosquito bulged the bomb bay 6 in to fit the cookie) and tail fins a wopping 17.6in bigger than the cookie.

The Mossie, even with bulged doors never carried more than two 1000lb stores ( target marking devices). These were supposed to the same size as a "normal" British 1000lb bomb and I could be corrected on this but there were two British 1000lb bombs. The 1000lb GP bomb which was 16.16in diameter (with a 16in tail) and either 71in or 86.5in long depending on tail and with a wall thickness of 0.77 in, HE content 33% and the 1000lb medium case bomb which was 17.75in diameter (17.5 in tail) 72.6in long and had a 0.48/0.58in thick wall and an HE content of 47% and was in mass production in the spring of 1943. There was a rack ( never used in WW II ?) that would let the Mossie carry six 500lb bombs.

From that source you kindly provided a few days ago;

http://legendsintheirowntime.com/Content/1943/Fl_4301_bombs.pdf
http://legendsintheirowntime.com/Content/1943/Fl_4310_bombs.pdf

There are a few other articles on bombs and bombing, please remember that these are wartime articles and are a bit propogadish (or more than a bit), but help to illustrate the thinking of the time (1942/43) a good deal of which was found to be wrong and the discontinuance of the small bombs (100lb bombs of various varieties) and even 250lb bombs lost much of their appeal. But if you were designing a "bomber" in 1941/42 the ability to use large numbers of these soon to obsolete bombs would be of interest by the Army. Not so much the Navy who was more interested in ship killing. This is shown ( or interpreted by me in the loads given for the "Tigercat bomber" four 500lb GP bombs or four 1000lb AP bombs. the 1000lb AP , while longer is smaller in diameter and tail span than the 500lb GP bomb and actually not much greater than the 250lb GP bomb except for being much longer.

Even four 1000lb US GP bombs calls for a rather sizable bomb bay.

AS for the big stuff, A B-17 could only carry the 4000lb bombs on outside racks and could carry only two 2000lb bombs inside because of the central walkway down the middle of the bomb bay. The bomb racks tapered or slanted inwards as the rose from the bottom of the plane ( to prevent bombs scrapping their way down and out) so there wasn't room to stack 2000lb bombs.

Your 4000lb bomb load and 400mph speed requirement are somewhat at odds. To carry 4000lbs inside in a flexible or varied manner requires a large bomb bay. To hit (or exceed) 400mph requires a low drag fuselage. Throw in the range requirement which requires a lot of fuel and things get very difficult.






True. While the F-15A reporter could meet the speed requirement with ease



It has trouble with the range and bomb load. Assuming the basic (not empty) weight is around 24,000lb and Max gross was 36,200 you have 12,200lb to play with. Two man crew? 400lbs. oil 563lb , internal fuel 3876lbs, two drop tanks 544lbs fuel in two drop tanks 3600lbs. 8983lbs, bomb load is 3217lbs and you don't have the required range. Yard stick Range ( no take-off allowance, no combat allowance, no reserve) is about 1900 miles. P-61s did operate at higher gross weights (up to 41,000lbs) but the performance rather goes to pot.

Please note that the 440mph performance at 33,000ft also required not only turbo chargers but the same engine/turbo used in the P-47M and N. First P-61C with the turbo engine was accepted by the Army in July 1945.
Engine would deliver 2800hp at 32,500ft. Engines in late model "D"s could deliver 2600hp at 25,000ft. Mid P-47d's had 2300 at 31000ft, early "D"s with water injection could pull 2300hp at 27,000ft.

If you use the early "D" water injected engine you are down 1000hp total (17.8%) and flying 6000 ft lower in denser air (more drag). Faster than a normal P-61, yes, as fast as a P-61C or F-15A, no.
 

I'm not sure whether this was sure for all US bombs, so any corrections are welcome: The tail fins are not necessarily oriented in cross, or '+' layout, but in x layout once the airplane is bombed-up. Therefore we need to divide the tail fin span with 1.41 to arrive at it's real width. For the 4000 lbs bomb that would make 33.77in, compared with the diameter of 34.25in. Here is a picture of a bomb of unknown size that illustrates my point.
The other picture shows, however, the fins in '+' layout - was it possible to attach fins differently?


Agree all the way. The only way for the Mossie to carry more than 2000 lbs internally was to carry a cookie, that was okay of course.
Will have to read the stuff from that site, not a problem during winter



Agreed again. The bomb bay as was on the A-26 seem to fit the bill nicely here.


The 2000 lb bomb really makes a mess here. Should be deleted from my requirement.


Everybody knew how to make a 350 mph bomber, it would not make any worthwhile thread if I've stipulated that.
We might read this as 'how to beat Mosquito' on mid-ww2 technology, and, out of all belligerents, the USA have had the best means to do so. They decided not to pursue the XB-28 further (delete turrets, install the R-2800-21 with ADI), the A-26 went in combat in 1944 with lowest powered R-2800 (install the 2-stager instead, or even better the turbo, while deleting the turrets), the XB-42 was too late to matter etc. The A-20 with multi-stage V-12 looks also as a contender. All fine - the USAF didn't have, or felt the need to do otherwise, but technology was there.


There is quite a difference between 36200 lbs and 41140 lbs The difference of almost 5000 lbs 'buys' us another pair of 310 gal drop tanks. The performance was anyway measured with planes in clean configuration, and our bomber has less drag than even the turret-less P-61A/B.


Think you can note that I was careful not to mention the 'P-61C' verbatim anywhere here (at least I think so), I know it used the engines not available for this thread. The P-61A/B without the turret was capable for ~370 mph at 20000 ft (on 1930 HP WER, lousy use of ram to elevate the FTH), how much of the exhaust thrust was lost via the NF-suitable exhausts? The 400 mph should be achievable with turbos, at 27000 ft it was 2300 HP vs. ~1550 for the P-61A/B (355 mph at 27000 ft?), at least without any guns protruding and chutes. With 2000 lbs of bombs it would still be lighter than a historical night fighter.
 

The Mosquito did, indeed, carry both the 1000lb GP and 1000lb MC bombs operationally during WW2.

Also, regarding the 2000lb bombs, the UK didn't build any 2000lb MC bombs, the closes thing being teh pre-war 1900lb GP bomb. Which was next to useless.

There was also the 4000lb MC bomb, which had similar dimensions to the cookie. This could be carried in teh bulged bomb bay.
 
To further illustrate my point - the 4000 lb bomb should fit in a bomb bay 35 in wide and tall (make it 36 in, so the bomb is unlikely to hit any part of the airplane between installation and dropping), despite the fins having the span of 47,62 in.

 
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