B-17E/F Bomb-Bay Question

[KJ_Lesnick]

The B-17F had a higher bomb-load (8,000 pounds) vs 4,200 lbs.  Was the bay any larger internally or simply structurally strong enough to hold the extra 3,800 pounds of bombs?

[lenny100]

the bomb bay hardly changed over the life of the b17 in all its models , only the hangers were changed as the bomb it was to used changed, when it was first built it was to use bombs up to only 150lb, but as the war changed it roles the bomb became larger and diffrent hangers were used

[KJ_Lesnick]

the bomb bay hardly changed over the life of the b17 in all its models , only the hangers were changed as the bomb it was to used changed, when it was first built it was to use bombs up to only 150lb, but as the war changed it roles the bomb became larger and diffrent hangers were used

So the bay wasn't significantly longer and the B-17F still could theoretically have fitted the lower gun-set up of the early B-17D without a problem?  I'm wondering because of a WHIF idea calling for a B-17 that would have evolved more quickly to include the tail turret and heavier bomb-load

[lenny100]

the bomb bay hardly changed over the life of the b17 in all its models , only the hangers were changed as the bomb it was to used changed, when it was first built it was to use bombs up to only 150lb, but as the war changed it roles the bomb became larger and diffrent hangers were used

So the bay wasn't significantly longer and the B-17F still could theoretically have fitted the lower gun-set up of the early B-17D without a problem?  I'm wondering because of a WHIF idea calling for a B-17 that would have evolved more quickly to include the tail turret and heavier bomb-load

the tail turret was already on the drawing boards of Boeing even before the first flight, as reports German in action over Spain etc and the early action over France and the UK, came in, the number of guns at first was mostly raised by local crew chiefs doing local mods and news of these getting back to Boeing and then changes being made out on  the production lines, even then brand new aircraft were flown from the factory to United Air Lines' Cheyenne, Wyoming, modification center where, among other mods, the B-17 stinger tail gunners compartment was modified for a better tail gun set up with new, larger windows and a "pumpkin" mount for the twin .50 caliber machine guns with larger arcs of fire.
the better weight carring came from mostly improvements in the power of the engines although the model never changed a turbocharged Wright R-1820 Cyclone 9

[wuzak]

the bomb bay hardly changed over the life of the b17 in all its models , only the hangers were changed as the bomb it was to used changed, when it was first built it was to use bombs up to only 150lb, but as the war changed it roles the bomb became larger and diffrent hangers were used

So the bay wasn't significantly longer and the B-17F still could theoretically have fitted the lower gun-set up of the early B-17D without a problem?  I'm wondering because of a WHIF idea calling for a B-17 that would have evolved more quickly to include the tail turret and heavier bomb-load

I doubt the B-17 bomb bay length changed at all after it entered production.

The B-17's bomb bay was very restrictive. It could carry 8000lb in 1000lb bombs, but could only carry a pair of 2000lb bombs internally. The 4000lb HC "cookie" and 4000lb MC bombs were too long, as was the US euivalent, the ANM56A1 Light Case 4000lb bomb. These culd be carried on underwing pylons in Gs, and probably Fs.

When carrying 2 x 2000lb bombs the space above them could be used for other ordinance - like 250lb/500lb GP bombs or incendiaries.

[wuzak]

Here is a diagram from the B-17 manual



Not sure who uploaded it. I pinched it from http://www.warbirdsforum.com/forumdisplay.php?f=10

[KJ_Lesnick]

the tail turret was already on the drawing boards of Boeing even before the first flight

Really?  Why did it take them so long to fit them on the plane?  The B-17E didn't fly until 1941, and the B-17F until Mid-1942.

the number of guns at first was mostly raised by local crew chiefs doing local mods and news of these getting back to Boeing and then changes being made out on  the production lines

Nothing wrong in basic principle with crew chiefs using some innovative spirit in improving the effectiveness of an aircraft.

I doubt the B-17 bomb bay length changed at all after it entered production.

So, if the ability to carry 8,000 pounds of bombs had been adapted earlier, possibly before the ball-turret could be added, the earlier ventral guns could have been retained without issue?

The B-17's bomb bay was very restrictive. It could carry 8000lb in 1000lb bombs, but could only carry a pair of 2000lb bombs internally.

If I read that graphic correctly the limits were

Within Maximum Load
24 x 100 lbs
20 x 300 lbs           
16 x 500 lbs
6  x 1,000 lbs
4  x 1,600 lbs
5  x 1,600 lbs* (asymmetrical-load)
2  x 2,000 lbs

Overloaded
8 x 1,600 lbs

The 4000lb HC "cookie" and 4000lb MC bombs were too long, as was the US euivalent, the ANM56A1 Light Case 4000lb bomb. These culd be carried on underwing pylons in Gs, and probably Fs.

The USAAF had a cookie or an equivalent?  Did they have some kind of streamlining to it (front and rear) as that thing was like a flying log.  It sounds like it would have horrible performance shortcomings

When carrying 2 x 2000lb bombs the space above them could be used for other ordinance - like 250lb/500lb GP bombs or incendiaries.

Makes sense

[wuzak]

So, if the ability to carry 8,000 pounds of bombs had been adapted earlier, possibly before the ball-turret could be added, the earlier ventral guns could have been retained without issue?

I think the ability was down to the power of the engines. So not really available earlier.

I sould suspect the ventral guns could have been carried on a later mark with more powerful engines, but why? The reason for replacing that was surelyto get a more effective defence system?

The B-17's bomb bay was very restrictive. It could carry 8000lb in 1000lb bombs, but could only carry a pair of 2000lb bombs internally.

If I read that graphic correctly the limits were

Within Maximum Load
24 x 100 lbs
20 x 300 lbs           
16 x 500 lbs
6  x 1,000 lbs
4  x 1,600 lbs
5  x 1,600 lbs* (asymmetrical-load)
2  x 2,000 lbs

Overloaded
8 x 1,600 lbs

I would have to check later, but I think overload was restricted to 6 x 1600lb bombs. And I think you are correct - 6 x 1000lb bombs or 16 x 500lb bombs.

The 4000lb HC "cookie" and 4000lb MC bombs were too long, as was the US euivalent, the ANM56A1 Light Case 4000lb bomb. These culd be carried on underwing pylons in Gs, and probably Fs.

The USAAF had a cookie or an equivalent?  Did they have some kind of streamlining to it (front and rear) as that thing was like a flying log.  It sounds like it would have horrible performance shortcomings[/quote]

Yes, they had the AN-M56A1 Light Case bomb. It had a rounded nose and tailfins.

The British built the 4000lb HC bomb (about 75% charge to weight ratio) and the 4000lb MC (about 50% charge to weight ratio).

I willl look up the AN-M56A1 stats later.

Problem was that the bomb couldn't be carried internally in the B-17 (or B-24 either, I think), so it had to be placed on pylons under the wing. Not sure what other US aircraft could carry them.

[rickshaw]

While this may lay outside the scope of the thread, why did Boeing go for a low wing position on the B-17 when it was obviously going to cause problems with the bomb bay?  And why did they repeat the problem with the B-29, adopting two separate bomb bays instead of one continuous one?

[jcf]

Perhaps because it wasn't "obvious" in 1934/35?
The Model 299 was a private venture that was not designed to an issued specification,
and it was a direct outgrowth of the Model 247. Thus the low wing.

Unlike the British bombers of the period, it was not designed to a specification
that required the capability to carry troops, the troop requirement was one of
the reasons that the Brit aircraft ended up with the long, under floor bomb-bays.
The Sterling had a multi-cell design that couldn't carry anything larger than
the 2,000 pounders. The unimpeded bomb-bays of the Lancaster and Halifax
were the result of the original specification requiring the ability to carry torpedoes.
The later ability to carry cookies, and other out-sized ordnance, was a matter of
serendipity, not clairvoyance.

BTW the Model 299 was designed to carry eight of the Air Corps 600 lb bomb.

Also what makes you think the dual bomb-bays of the B-29 were a "problem"?

[wuzak]

While this may lay outside the scope of the thread, why did Boeing go for a low wing position on the B-17 when it was obviously going to cause problems with the bomb bay?  And why did they repeat the problem with the B-29, adopting two separate bomb bays instead of one continuous one?

I would say the B-29 was more of a mid-wing design.

The big difference is that the B-29's wing structure continued through the fuselage, and the B-17's did not (at least I think that was the case).

As for the size and shape of the B-17's bomb bay you have to consider the size of the bombs around in 1935 and before. I think there would have been generally smaller bombs available.

The B-29 program began before teh war, or at least before US involvement.

The Lancaster had a long bomb bay because the Manchester had been designed around a requirement to carry one or more 18" torpedoes. Other British aircraft, liek teh Short Sterling, did not have the long, unobstructed bomb bay.

[wuzak]

The Model 299 was a private venture that was not designed to an issued specification,

Yes it was.

and it was a direct outgrowth of the Model 247. Thus the low wing.

No, it wasn't.

[rickshaw]

Perhaps because it wasn't "obvious" in 1934/35?
The Model 299 was a private venture that was not designed to an issued specification,
and it was a direct outgrowth of the Model 247. Thus the low wing.

Unlike the British bombers of the period, it was not designed to a specification
that required the capability to carry troops, the troop requirement was one of
the reasons that the Brit aircraft ended up with the long, under floor bomb-bays.
The Sterling had a multi-cell design that couldn't carry anything larger than
the 2,000 pounders. The unimpeded bomb-bays of the Lancaster and Halifax
were the result of the original specification requiring the ability to carry torpedoes.
The later ability to carry cookies, and other out-sized ordnance, was a matter of
serendipity, not clairvoyance.

BTW the Model 299 was designed to carry eight of the Air Corps 600 lb bomb.

Also what makes you think the dual bomb-bays of the B-29 were a "problem"?

To answer the second question first - the B-29 had problems carrying long bombs such as the Tallboy internally.  As it was designed after the war had begun and after the bomber offensive was already started, I was rather surprised that the British experience had not been taken into account.  While I agree that the B-17 was a case of insufficient experience to suggest bigger bombs would be wanted (as the Stirling did as well), the B-29 appears to have been a case of insufficient foresight.

The B-24 was designed both as a bomber and a transport, in a comparable time period to the B-17 but even it, despite its high wing position had split bomb bays, so it appears to have been a case of not thinking outside a certain box IMO.

[wuzak]

To answer the second question first - the B-29 had problems carrying long bombs such as the Tallboy internally.  As it was designed after the war had begun and after the bomber offensive was already started, I was rather surprised that the British experience had not been taken into account.  While I agree that the B-17 was a case of insufficient experience to suggest bigger bombs would be wanted (as the Stirling did as well), the B-29 appears to have been a case of insufficient foresight.

The B-29 design began at least 18 months before the US became directly involved in WW2. At least 6 months before the Manchester became operational, and at least 20 months before the Lancaster became operational. Bomber Command's inventory at the time included Wellingtons, Whitleys, Blenheims and Hampdens.

The B-29 design predated the paper Barnes Wallis presented on a 10 ton bomb. And the B-29 was designed 4 years before the 6 ton Tallboy entered service.

The B-29 proposal was presented to the USAAC in mid 1940. The XB-29 first flew in 1942, only a month or two after the first 8th AF operations in Europe.

The B-24 was designed both as a bomber and a transport, in a comparable time period to the B-17 but even it, despite its high wing position had split bomb bays, so it appears to have been a case of not thinking outside a certain box IMO.

Not sure that it was designed as a transport. It was designed because the Consolidated team thought they could do better than just build B-17s. It was designed to carry the same bombs as teh B-17, just more of them. No thought would have been given to the longer bombs.

[KJ_Lesnick]

I think the ability was down to the power of the engines. So not really available earlier.

Once the turbos were added (B-17B?), they could have bumped it up to 8,000 right away no?

I sould suspect the ventral guns could have been carried on a later mark with more powerful engines, but why? The reason for replacing that was surelyto get a more effective defence system?

I understand that, I already created a thread based on the US developing an independent air-force earlier (1922-1924), and I assume they'd have more money to their disposal than the USAAC would (even though there were economical limits due to the depression).  The B-17 was pretty technologically advanced for this purpose, I just figure that development could have occurred faster if they had a greater budget.  The RAF developed all kinds of bombers.

Truthfully, the requirements might have looked totally different in such a situation though.

I would have to check later, but I think overload was restricted to 6 x 1600lb bombs.

I simply counted the number of mountings that could carry 1,600 lbs.  Still 9,600 lbs of bombs ain't bad.

Yes, they had the AN-M56A1 Light Case bomb. It had a rounded nose and tailfins.

That would improve aerodynamics

I willl look up the AN-M56A1 stats later.

Thank you

The B-24 was designed both as a bomber and a transport

I know the B-24 was used as a transport, but I was under the impression it was designed as a bomber from the start.