Was the B-17's Bomb Bay Really a Fatal Flaw? I'm Doubting the Lancaster's Superiority

[Shortround6]

I think there is some confusion as to B-17 as designed and the B-17 as used in 1942-43-44-45.

Thirteen YB-17's ordered in Jan 1936 after the earlier B-17 (Boeing 299) crashed part way through testing. The 299 was a response to 1934 requirement.
The YB-17s used more powerful engines than the 299 but still no turbos until the 13/14th airframe. Bomb load was 4800lbs (?) eight 600lb bombs and guns were five .30 cal guns. Very strong for 1937-38 but the Thirteen .50s don't show up until the "G" model so the 'design' was never intended for that load of guns.
The overly strong construction allowed for easy upgrading of gross weight (some upgrading was needed). The last YB-17 got the turbos but sorting them out took a while.
The Plane that got the turbos was supposed to be a static airframe for structural testing but when one of the earlier planes survived being flipped on it's back in thunderstorm and surviving they canceled the destructive static testing.
USAAC rated the Wright R-1820 engines used in the YB-17s at 930hp for take-off which rather limits the gross weight. Later versions got the 1200hp engines and weight grew substantially with increased bomb loads, increased gun loads (and ammo) and increased fuel loads.

B-17s could lift over 17,000lbs of bombs off the runway but they weren't going to get far (not much fuel) and two 4000lb bombs hanging underneath were pretty decent airbrakes.
But the external racks were not part of the original design and even with just 1000lb bombs on the external racks they caused a lot of drag.

The B-17 was a rather good adaptation of a good early design. Not what was planned. The B-24 was a 1939 design, or about 4-5 years newer than the B-17.
Designers of the early/mid 30s were usually conservative. The crash of the type 299 could have bankrupted Boeing even though it was pilot error (taking off with controls locked).
A structural failure in flight would have ended any company. By 1939-40-41 the designers knew a lot more about structural design and they had much more powerful engines to get large planes off the ground.
The 299 used 750hp engines. Why design in a bomb bay that would hold 8000lb of bombs, or more, in 1934-35 when even 1000 hp engines were 4-5 years away from production?

 

[Frog]

Just my 2c :

- The Lancaster was complemented by the Halifax.

- The B-17 was complemented by the B-24.

 

[Shortround6]

Spar would've probably remained as-is, since USAAC in the 1930s didn't have the huge bombs in their inventory.
If having the powerful escort was in the doctrine, there would be probably a more modest defensive firepower installed, talk half a dozen of LMGs initially, to be later replaced with 5-6 HMGs?

I would note that in 1935-37 the British had nothing larger than a 500lb bomb. They just preferred to lay out their bombs horizontally (including spreading them out into wing bomb bays) rather than stack them vertically. The British were certainly NOT planning on fitting large bombs inside the bomb bays at this time.
Americans were not thinking about escort fighters as this was the contemporary American fighter.

two .30s or one .50 and one .30 with an 850hp engine. Overload fuel was 200 us gallons.
Trying to escort an B-17 on long range missions was an impossibility.
Don't be fooled by Wiki, the P-35A with the 1050hp engine was a cover designation for the Planes that Seversky was building for Sweden that got embargoed in 1940.

Escort fighters that could accompany even B-17C/Ds needed better engines, and better aerodynamics than really existed in 1938-39-40.

US was not really considering formations of hundreds of bombers at this time (except in fevered dreams) so "escort" might be trying to fly with small formations of faster flying bombers.
US had two possible escort fighters in 1941 but not until 1941. The early P-38s or the P-43 and the P-43 had some problems. And for timing the production P-43 showed up just few months before the B-17E that had the power turrets and the tail guns. Overlapping development.

 

[special ed]

Regarding the comment why the USAAF didn't build larger, better bombers, the design of the B-36 began 1941 but was not on a fast track because of existing production disruption. The XB-36 first flight was 1946. A five year span from designs to prototype for an intercontinental bomber intended to bomb Europe from the U.S.

 

[EwenS]

Just my 2c :

- The Lancaster was complemented by the Halifax.

And the Short Stirling.

 

[Redred]

Spar would've probably remained as-is, since USAAC in the 1930s didn't have the huge bombs in their inventory.
If having the powerful escort was in the doctrine, there would be probably a more modest defensive firepower installed, talk half a dozen of LMGs initially, to be later replaced with 5-6 HMGs?

tomo pauk, that's a very fair assessment, especially regarding the spar!

you're probably right that the central spar was more of a pure structural mandate based on 1930s engineering needs and standard ordnance, totally separate from later grand slam requirements. i appreciate the correction—it makes sense that they wouldn't design against bombs that didn't exist yet.

however, your point about defensive firepower is the real key here. if they had opted for just six hmgs instead of 13, that would have immediately freed up significant weight (guns, ammo, armor plates for the gunners) that could have been directly translated into more fuel for deeper range, or, yes, more payload capacity for standard bombs.

the fundamental design mistake, then, wasn't necessarily the spar, but the massive weight penalty taken in the defense systems, driven by a doctrine that ultimately failed (requiring the p-51 to save the day). this focus on defense trade-offs is also what the video i linked at the beginning addresses when contrasting the two bomber designs.

that weight allocation choice is really what separated the b-17 from the lancaster design philosophy. great insight!

 

[Redred]

Regarding the comment why the USAAF didn't build larger, better bombers, the design of the B-36 began 1941 but was not on a fast track because of existing production disruption. The XB-36 first flight was 1946. A five year span from designs to prototype for an intercontinental bomber intended to bomb Europe from the U.S.

That's a perfect historical check on the feasibility of changing designs mid-war.

you've highlighted one of the biggest constraints faced by any air force: production disruption. the b-36 timeline is a great example—a five-year wait simply wasn't viable in wwii for the needs of the european theater.

this actually reinforces the difference between the us and uk solutions:

1. the us solution was to stick with the b-17 (and later b-29) until a completely new bomber (b-36) could be developed after the war's peak.
2. the uk's solution (the lancaster) was to adapt an existing airframe (the manchester) into something radically different and more capable during the war, minimizing production downtime.

from a design and manufacturing perspective, the british were much more agile in finding a way to meet the specialized need (grand slam) without requiring the massive, long-term disruption of a b-36-style project. that adaptability is exactly what the b-17's rigid structural spar prevented. thanks for the crucial context!

 

[tomo pauk]

you're probably right that the central spar was more of a pure structural mandate based on 1930s engineering needs and standard ordnance, totally separate from later grand slam requirements. i appreciate the correction—it makes sense that they wouldn't design against bombs that didn't exist yet.

Yeah, the Grand Slam (in)suitability is a red herring.

however, your point about defensive firepower is the real key here. if they had opted for just six hmgs instead of 13, that would have immediately freed up significant weight (guns, ammo, armor plates for the gunners) that could have been directly translated into more fuel for deeper range, or, yes, more payload capacity for standard bombs.

+1 on that.

the fundamental design mistake, then, wasn't necessarily the spar, but the massive weight penalty taken in the defense systems, driven by a doctrine that ultimately failed (requiring the p-51 to save the day). this focus on defense trade-offs is also what the video i linked at the beginning addresses when contrasting the two bomber designs.

IMO:
- the spar and it's placement was not any kind of a design mistake
- that video is made more for the clicks and revenue, rather than as a fair historical assessment

 

[Greyman]

Yeah, the Grand Slam (in)suitability is a red herring.

Re: bomb types -- a factoid from the US's Strategic Bombing Survey examining the Oil Campaign gives a better indication of the difference. Looking at the hundreds of thousands of HE bombs dropped by both air forces, the average US bomb was 388 lb and the average British bomb was 660 lb. The survey was explicit in its praise of the effectiveness of larger bombs vs smaller bombs.

Granted, we're not just isolating the Lancaster and Fortress here, but I think it's possible the difference would be even greater if you did.

As others have mentioned, this is in addition to the roughly double overall load the Lancaster carried.

 

[Shortround6]

The B-17 is going to get more clicks but from a stand point of time the B-24 was closer in timing to the Lancaster.
And going back to design vs use, The British were a bit late introducing bombs of over 500lbs. So they needed big bomb bays to hold lots of smaller bombs.
They lucked out in that they could stick the big "cookies" in the existing bays with only small (or not so small) modifications and still have room for other bombs or large numberso f incendiaries. But the incendiary bundles were not part of the original specifications either.

B-17 and B-24 were built for longer ranges (Pacific Islands?) and flying around the coasts of the US rather than European distances.

 

[yosimitesam]

Rarely mentioned in the discussions is the effect of RADAR, when bomber theories were being made RADAR didnt exist at all, in a few years it changed everything.

Indeed. Because using "standing patrols" was wasteful (expensive) to the point of being unsustainable, and because the "sky" is so huge, the "bombers will always get through" was the generally accepted paradigm in the 1930's. Radar eliminated the need for standing patrols and made fighter defense a workable and effective strategy. Up to a point. The paradigm was changed to: some bombers will always get through but the attrition from fighter defense MIGHT eventually cause the enemy to cease bombing in daylight. Worked in the BoB.

 

[GrauGeist]

1930's bomber ideology shifted drastically when put to the test.

The Stirling was Britain's answer to a heavy bomber and the Lancaster was a further shift in heavy bombing strategy.

In the case of the B-17, it's conception was based on the need for the U.S. to defend itself from foreign navies, not carpet bomb industrial targets.

As the U.S. entered WWII, the B-17 was the most available bomber platform, as the great depression had slowed military development to a certain degree.

The USAAC was aware of a potential need for extra long range heavy bombers and had several manufacturers submit proposals by way of their 1935 "Project D", the Douglas B-19 (XBLR-2) being the one selected for further development, the others were Sikorsky's XBLR-3 and XBLR-1 (XB-15)

 

[Bretoal2]

- that video is made more for the clicks and revenue, rather than as a fair historical assessment

There are far more true and essential facts freely presented on this site than the more or less conjectural informations introduced for commercial purpose by numerous videos.

 

[MikeMeech]

The B-17 is going to get more clicks but from a stand point of time the B-24 was closer in timing to the Lancaster.
And going back to design vs use, The British were a bit late introducing bombs of over 500lbs. So they needed big bomb bays to hold lots of smaller bombs.
They lucked out in that they could stick the big "cookies" in the existing bays with only small (or not so small) modifications and still have room for other bombs or large numberso f incendiaries. But the incendiary bundles were not part of the original specifications either.

B-17 and B-24 were built for longer ranges (Pacific Islands?) and flying around the coasts of the US rather than European distances.

Hi
Not strictly true as before the war the British had the 2,000 lb AP bomb on hand, the Stirling could carry up to seven in its divided bomb bay and the Wellington could carry two (the Wellington was modified to carry a 4,000 lb, dropping the first on 1 April 1941). However, the first 2,000 lb AP bombs were dropped by a Beaufort on 7 May 1940, and Hampdens also dropped them during 1940. The 'Disney' bomb used a scaled up version of the 2,000 lb body/warhead for its design:

(from 'Bombs Gone' by MacBean & Hogbean, page 50)

(from 'The Mighty Eighth War Manual' by Freeman, page 228)
The RAF also had five million 4 lb Incendiary bombs available at the outbreak of war, these were packed in containers, story related in 'Bombs Gone' below:

So pre-war designs for the 'new' monoplane bombers. I hope that is of use.

Mike

 

[Shortround6]

The 2000lb AP bomb was pretty much an anti-ship bomb or anti-fortification bomb.
As to size it was 13.5in in diameter and 113in long compared to the "standard" 500lb GP bombs 12.9in diameter and 70.6 in length (long tail).
The real problem for operational use was that the 2000lb AP held 166lbs of HE and the 500lb GP held 144lbs of HE.

The next kicker was that, according to one source, the British dropped just over 20,000 500lb GP bombs in 1940 compared to just over 80,000 250lb GP bombs.
In 1941 the 500lb bombs just edged out the 250lb bombs. with over 79,000 to over 78,000 each.
For comparison they seem to have only dropped 159 1000lb GP bombs in 1940. They dropped 11,662 of these in 1941 but since we are talking about design in 1936-1940
British design of bomb bays was going to be different.
We also have the Halifax.

22ft long bomb bay holding nine bombs. The 3 bays in each wing root can hold one 500lb bomb in each bay.
What you don't have in each wing root is a fuel tank. This is a design choice.
Not to beat up on the British too badly here, The Americans were switching over from their 100, 300, 600 and 1100lb bomb sizes to the 100, 250, 500 and 1000lb sizes in this period.
The early B-17s could hold only eight 600lb bombs in the bomb bay in two vertical racks of 4 each.
The Early B-17s could hold 1700 US gallons (1414 Imp) in the wing tanks and then we have to consider designed weight vs operational weight as the the war went on and more powerful engines were used and longer runways built. The USAAC managed to get a B-17E running very light (40,260lbs) to take off and clear 50ft in 2150ft. (717yds?)
Late production B-17Fs and all Gs got the self sealing "toyko" tanks in the outer wings that held 1080US gal of fuel so there was a real trade off between fuel and bomb load.

 

[Geoffrey Sinclair]

That point about the design era is absolutely crucial, and I think it perfectly highlights the constraints the B-17 designers faced. You're right—it was essentially a pre-war design built for a theoretical mission (patrol/defense), which meant structural integrity (like that central spar) was probably non-negotiable at the time.

What was non negotiable at the time was the USAAF August 1934 specification of 2,000 miles with 2,000 pounds of bombs at 200 mph, while having engines rated at 850 HP for take off, that meant lifting 1,700 gallons of non 100 Octane into the air plus crew plus bombs, apart from its extra energy 100 Octane was about 5% lighter than 80 Octane. So the B-17 design set maximum bomb load at 4,800 pounds (8x600 pound). This would give twice the load and range of the 1936 B-10B cruising at about the B-10B top speed. The B-17 would have 5 defensive machine guns, the B-10 had 3, the B-17 having been dubbed the Flying Fortress in July 1935. The USAAF went with the B-18 as its 1937/38 bomber, performance about that of the B-10 but carrying up to nearly 3 times the bomb load (not all internal), with maximum bombs its range started to look much more like that of the P-36. The B-18 was about half the price of the B-17 and gave way to the better B-18A end 1938.

It meant Boeing was limited to 13 Y1B-17 in 1937, and set about proving the design was the future of air power, including how much it would cost. The Y1B-17A was the 1938 working example of turbo supercharging, the 39 B-17B from mid 1939 the production version, with a top speed of nearly 300 mph at altitude it was very difficult to intercept, and had even more machine guns to defend itself, coupled with the new very accurate bomb sights and the known assumed devastating effect of small bombs it was all set for its wartime role. It was also the only 4 engine design the USAAF could have in some sort of numbers in the 1940 to 1942 period but the 1935 design limits hung around in things like the bomb bay volume.

The Lancaster, conversely, was a direct product of battlefield necessity and the realization that the initial designs needed much bigger payloads for area bombing. It's a perfect example of design evolution in wartime.

It was not battlefield necessity. In the second half of the 1930's the RAF had a clear target and was well aware heavy bombers were the most economical per ton of bombs delivered. The result was a series of designs, initially in the hope of 2,000 HP class engines but reverting to 4 engines in the 1,000 HP class. 1941 Normal Bomb Load, Halifax I 12,000 pounds, Manchester I, 10,350 pounds, Stirling I 14,000 pounds. Since it was assumed they could not base a large bomber force in France ranges were set from British bases, with various ideas about whether the Netherlands and Belgium would be neutral, those who believed in air power could see great advantages of keeping them and Denmark neutral in shielding Britain and Germany from each other.

It makes me wonder: do you think the USAAF should have been faster to adapt its heavy bomber design once the war showed them the B-17's structural limits on specialized ordnance? Or was the sheer number of B-17s produced (and their survivability) a better strategic asset than starting a new design like the Lancaster?

If you wish to keep claiming the B-17 was more survivable consider a greater percentage of 8th Air Force B-24 losses on combat missions were Category E, that is they made it back to base, whether that is due to the B-24 being more able to take more battle damage and keep flying or more likely to take more damage in a crash landing or crash on landing is another matter.

The B-17 dates from 1934/35, the Manchester/Lancaster from 1936. There is a saying WWII was fought by obsolete or obsolescent aircraft, as there was always something better already flying or available "soon". The bigger the aircraft the longer the design period, the B-24 design started in early 1939, despite all the urgency of a world at war and shortening the development cycle it was a second half of 1942 bomber in terms of arriving in numbers, and took until the second half of 1941 to create a combat worthy version. If the USAAF wanted a bomber with B-17 performance in 1940/41 it was the B-17 and with the assumptions about effectiveness it was clearly good enough, the B-17E in 1941 upped the defensive armament and put much of it into the more accurate shooting turrets. Once the production lines were laid down the cost of stopping them was high. The only alternative to the B-17 was the B-24. The second and third B-17 production lines started in June 1942, the second B-24 line in April, a short run assembling kits sent to it, the third in August, again a short run assembling kits, the fourth in September (Ford) which would assemble its own plus send kits to the second and third lines, the fifth in March 1943.

On your counterpoint about the combat box not being sustainable: You're absolutely correct about the brutal losses in '43. But doesn't that reinforce the pragmatism of the B-17's heavy defensive focus, even if it wasn't a perfect strategy?

No. For a start every defensive measure cuts into the offensive ones and the bomber defensive measure that worked was fighter escorts. In the January to May 1944 fighting, Luftwaffe versus 8th Air Force it looks like the Luftwaffe broke about even in terms of numbers of aircraft lost, they easily won on economic cost as a heavy bomber was worth about 3.5 fighters, and overwhelmingly won in terms of personnel casualties. Now run that again with the 8th Air force consistently using self defending bombers, say with tripe or quadruple power operated turrets to up defensive power with corresponding decreases in bomb loads. It took about 12 months to create a bomber group, the 1944 air commanders had to make things work with aircraft put into production well before what was actually required was known.

If the USAAF was committed to daylight precision bombing, they had to double down on defense, even if it meant structural compromises on payload (the spar) and heavy crew losses. They chose to survive the mission, even if they couldn't carry the Grand Slam.

This starts to sound like working backwards to a conclusion. The 8th Air force from near the start of operations on Germany was taking unsustainable losses and they were trending upwards through 1943, losses to targets in France were lower but also trending up and heading to unsustainable. Meantime the USAAF heavies in the MTO were usually staying within escort range. Part of the cost from moving from the B-17C and D to the G was a loss of around 40mph in top and therefore cruising speed.

You've hit on something really important: static threat assessment in design is a killer. It's an almost unforgivable flaw for planners to assume the Luftwaffe would stand still for 2+ years. The rapid introduction of things like the Fw 190 and heavy cannon packs (which you mentioned) fundamentally invalidated the "self-defending bomber" concept almost immediately.

Flaming Wellingtons and other RAF bombers in 1939, Luftwaffe during the Battle of Britain largely removed the self defending bomber ideas there and then. The USAAF did assume more defensive firepower, tighter formations, higher and faster flying would mean fewer losses to interceptors, all of which is correct, another assumption was overwhelming the defences, the number of 300 heavy bombers became fixed even as known Luftwaffe fighter strength increased. The everything that can fly mission on 24 December 1944 aw 2,046 sorties, 1,884 effective, 12 aircraft MIA, 23 category E, or about half the famed 1943 raid losses. The Luftwaffe would have needed to shoot down around 100 bombers to make the loss rate unsustainable.

As a designer, this is the core failure: if the USAAF had predicted the actual threat level, would they have focused less heavily on cramming in all those .50-cals and that structural spar, and instead gone for a design with more flexibility for specialized ordnance?

In an organisation as big as an air force you can usually find a memo that accurately predicts the future, but usually never written by the same person twice. That memo comes with lots of wrong predictions by other writers.

Sure if the USAAF predicted the war would begin in 1939, that it would be hundreds of miles from base to target over hostile airspace, so all the way to target escorts were needed, that radar was going to make Ground Controlled Interception work in 1940 and beyond, that average bombing accuracy was much lower that proving ground, that a 4,000 bound bomb was about the best weight for target destruction and bomber carrying capacity and so on it could come up with a much better design.

In short the USAAF would have turned up with a Lancaster type bomb bay, along with many more escorts whose the external tanks began being tested in late 1939. In early November 1944 the 8th Air Force had 2,455 heavy bombers and 1,326 fighters on strength, call it 2,400 bombers to 1,300 fighters. A B-17 cost 3.5 times that of a P-51 and a B-17 unit had 3.5 times the personnel. Double the average bomb load and turn 1,200 bombers into 4,200 fighters, so 5,500 fighters to escort 1,200 bombers and watch the Luftwaffe wilt. How about 1,800 bombers which is a 50% increase of bomb lift, add 2,100 fighters and instead of 1 fighter per 2 bombers, you now have nearly 2 fighters per bomber. One fighter stays with its personal bomber all the way, effectively replacing the bomber guns, the other standard 8th Air Force fighter escort. The early Merlin 60 testing went remarkably well, about the least troublesome Merlin upgrade of them all, send the blueprints to the US plus an early production engine in 1941, have a Merlin Mustang flying in Britain in late 1941 or early 1942 thanks to earlier work on trying a Merlin P-40, cancel bulk single stage Merlin orders from the US and Ford in the UK for 2 stage.

The B-17 was designed for the expected war, but the Lancaster was adapted for the actual war. That distinction, I think, is what made the difference in payload capacity. Great perspective!

The short answer is no, the Lancaster ended up with more design features that proved to be a good choice compared with the B-17. The British armoured carriers had remarkable defensive capacities, no British carrier burned like some IJN and USN ones did, Kamikaze hits on the Illustrious class were generally shrugged off with many fewer casualties than USN carriers took, but the price was an air group significantly smaller than a US design of the same tonnage and unable to sustain operations for as long. That was the trade off.

If the USAAF had acknowledged the need for long-range escort from the beginning, do you think they would have still committed so much design weight and internal space to the 13 machine guns and the spar that limited bomb size? Or would they have stripped down the defense, focused on speed/payload, and relied more on the escort, moving the design closer to the Lancaster's philosophy?

By definition knowing the answer makes the problem easy. A bomb bay capable of 4,000 pound bombs and total HE load more like the B-17 total AP load weight wise. A day bomber needs defensive power, say 4 twin power operated turrets, less if you increase the escorts, losing 5 0.50 inch machine guns plus mounts plus a pair of gunners plus ammunition is over 1,000 pounds. It looks like a twin 0.50 inch gun turret on a heavy bomber was about as lethal to a fighter with 20mm cannon as the fighter was to the heavy bomber in a straight shooting match.

this actually reinforces the difference between the us and uk solutions:

1. the us solution was to stick with the b-17 (and later b-29) until a completely new bomber (b-36) could be developed after the war's peak.
2. the uk's solution (the lancaster) was to adapt an existing airframe (the manchester) into something radically different and more capable during the war, minimizing production downtime.

No. The bomb bay area is the strongest and generally central part of the airframe, it is not easy to make changes to the area. What happened reflects the original design decisions backed by expected tactics, the prewar RAF expected its power operated turret carrying bombers to be self defending as did the US, while the Luftwaffe went more with low interception and loss rates from the Spanish civil war. The Manchester to Lancaster change was minimal, it meant almost no loss of production, helped by making the decision early, while the 2 open lines were still working towards maximum output.

To think of it another way if changes to the bomb bay area were simple enough then the 1943 Halifax and Stirling would have been routinely carrying 4,000 pound bombs, if changes to designs in production were also simple then the RAF would not have had more Halifax production lines than Lancaster and the Stirling would have been phased out much earlier nor would it have appeared in transport and glider tug versions. Same for the Halifax.

from a design and manufacturing perspective, the british were much more agile in finding a way to meet the specialized need (grand slam) without requiring the massive, long-term disruption of a b-36-style project. that adaptability is exactly what the b-17's rigid structural spar prevented. thanks for the crucial context!

The USAAF went with the B-29 as the next generation bomber, it could carry larger bombs and despite the average sortie distances carried more bombs on average than the Lancaster, the B-36 was more about what if Britain is lost.

Please drop the Grand Slam ideas, even the Tallboy ones. There does not appear to be much of a case for a HE bomb much over 4,000 pounds for the usual targets the heavy bombers went after, admittedly no one was dropping many heaver HE bombs. Pre war the RAF had the 2,000 pound AP bomb, meant for warships, 30 September 1940 first use of 1,000 pound bomb by Bomber Command.

Bomber Command bombing raids only,
1940, HE/AP 30x2000 AP, 153x1000, 20,258x500, 61,248x250 pound
1941, HE/AP 397x4000, 1,189x2000 (only 181 HE, rest AP), 482x1900, 94x1100 (B-17 raids), 10,447x1000, 73,767x500, 38,509x250 pound

According to the USAAF it dropped 6,284,271 HE bombs in the MTO and ETO,
158x4500 lb, 48,575x2000 lb, 564,969x1000 lb, 712x600 lb, 1,645x550 lb, 3,089,916x500 lb, 12x350 lb, 1,055,289x250 lb, 79x160 lb, 1,520,209x100 lb, 2,707x40 lb

Of the above the 9th Air force dropped 21,931x2000 and jettisoned another 876x2000 pound bombs, plus around 110,000x100 pound bombs.

 

[Shortround6]

What I wonder about in the design phase of the B-17 and Lancaster and in this case lets look at the B-17E/F and the Lancaster MK I as the early B-17s didn't carry that much in way of armament.
B-17E/F carried Eleven .50 cal guns but only two power turrets.
Lancaster MK I carried Ten .303 guns which are much lighter but they used 4 power turrets. One quad and 3 twins. Weight of the power turrets?
Granted the US .50 cal ammo was heavy, almost 5 times as heavy as .303 ammo but the British provided for 10,000 rounds of ammo for just the rear turret.
The upper and nose turrets carried much, much less and the lower turret was soon removed as it didn't work well.
But saying that the American design philosophy was to use a lot of heavy guns and and few bombs and the British philosophy was to use little defensive armament and a lot of bombs seems simplistic.
It might have wound up that way in effect but in 1940-41 design philosophies don't seem that far different.
On the other hand many US crews took much more ammo than they were supposed to into their B-17s, over loading the aircraft but that was not fault of the designers or of the Air Force planners.
Weight of the B-17 increased in fits and starts and some existing planes were either up graded or were OK'ed to operate at higher gross weights than original.
At some point even the B-17Fs (or late versions) were OKed for 65,000lbs that may be a better basis for comparison?

 

[Greyman]

Lancaster MK I carried Ten .303 guns which are much lighter but they used 4 power turrets. One quad and 3 twins. Weight of the power turrets?

front FN5: 670 lb
mid-upper FN50: 700 lb
under FN64: 300 lb
rear FN20: 1350 lb

w/ turret, guns, and ammo.

Couldn't get everything from a single concise source -- so the measuring criteria might be different for each.

 

[Shortround6]

front FN5: 670 lb
mid-upper FN50: 700 lb
under FN64: 300 lb
rear FN20: 1350 lb

w/ turret, guns, and ammo.

Couldn't get everything from a single concise source -- so the measuring criteria might be different for each.

Thank you
So roughly about 1 1/2 tons of guns, turrets and ammo. Not as much a B-17 but that is not a small amount either.

 

[Geoffrey Sinclair]

Think of this as a make your own early Lancaster sales brochure, with options but not soft top. Australian Archives Series MP450/1 control 123. Lancaster weights in pounds and performance

1,300 Wing Ribs including engine and fuel tank mounting ribs
1,380 Wing front spar
955 Wing rear spar
101 Spar joints
170 Wing stringers
1,025 Wing skin covering
149 Flaps, centre section
125 Flaps, outer wing
125 Flap operating tubes and links
200 Wing tips
190 Ailerons
130 Wing centre section leading edges
770 Wing sundry fittings, bolts, joints to fuselage, paint, trailing edges, dummy spars, shrouds etc.
150 Access doors for fuel tanks.
6,770 Total Wing structure weight

497 Fuselage formers
343 Fuselage stringers
721 Fuselage skin covering
980 Fuselage main floors
74 Fuselage walkways
180 Canopy
63 Windows
110 Seats
51 Fuselage former extensions below main floor
58 Flying control guards
170 Cabin heating
490 Bomb doors
233 Fuselage sundry fittings, doors, bolts etc.
3,970 Total fuselage weight

464 Tailplane
206 Elevators, including mass balance
164 Fins
117 Rudders, including mass balance
951 Total tail unit weight

640 Undercarriage shock absorber struts and bracing
100 Wheel axles
252 Undercarriage radius rods and locks
230 Undercarriage retracting jacks and bracing
1,180 Undercarriage main wheels and tyres
110 Undercarriage brakes
280 Tailwheel and shock absorber strut
2,792 Total undercarriage and tail wheel weight

463 Engine sub mounting frames, undercarriage beams and bracing on front spar
130 Inboard engine sub mounting frames
6 Inboard sub mounting bolts
285 Outboard sub frames
40 Outboard front spar attachment channels
12 Outboard rear spar attachment channels
5 Outboard sub mounting bolts
941 Total weight, sub mounting frames on wings

702 Fuel tanks including protective covering and fuel jettisoning (Centre section)
550 Fuel tanks including protective covering and fuel jettisoning (Inboard - Outer wing)
200 Fuel tanks including protective covering (Outboard - Outer wing)
244 Oil tanks including protective covering
100 Tank mounting straps
1,796 Total fuel and oil tanks weight (Lancaster by Harry Holmes says later upped to 1,990 then 1,999 pounds)

580 Nacelle fairings aft of fireproof bulkheads
600 Hydraulics - general services
300 Flying controls, including dual

18,700 Total Structure weight: wings, fuselage, tail, undercarriage, fuel tanks, engine sub mountings, nacelle fairings, general hydraulics, flying controls.

1,200 6 Crew and including parachutes

15,336 2130 gallons of fuel
1,026 114 gallons of oil
7,000 Bomb load
208 Bomb carriers
23,570 Load for maximum range

9,796 1361 gallons of fuel
639 71 gallons of oil
12,750 Bomb load
385 Bomb carriers
23,570 Load for maximum bombs

Military load weights

Fixed	Removable	Note
261​	179​	Front turret (FN.5A) Guns and ammunition (2,000 rounds)
320​	179​	Mid Upper turret (FN.7) Guns and ammunition (2,000 rounds)
370​	490​	Rear turret (FN.20) Guns and ammunition (6,000 rounds)
240​		Turret hydraulic systems
105​		Ammunition boxes, tracks and mountings for rear turret
385​	6​	Fixed bomb gear and fusing gear
20​	38​	Bomb sighting and mounting
49​	245​	Pyrotechnics, pistol, distress signals, training and reconnaissance flares and mountings etc.
740​	5​	Electrics, including generators and accumulators
203​	90​	Instruments, engine, flying and navigational, including 6 sea markers and dead reckoning compass
8​	39​	F.24 Camera
109​	233​	Oxygen equipment (16 bottles)
97​		Automatic controls
35​	54​	Dinghy
145​	94​	Miscellaneous, including fire extinguishers, safety belts, rations, water bottles and mountings.
91​	142​	Wireless Telegraphy, Direction Finding and power supply
25​	5​	Intercommunication
7​	28​	Pilots TR9F radio
35​	40​	Lorenz blind approach
15​	33​	R.3003
230​		De icing equipment, tail and airscrews
120​		Anti barrage equipment
300​		Armour plating
3,910​	1,900​	Total weight, fixed and removable military loads

Engine weights (4 engines and propellers)

Merlin XX	Hercules VI	Twin Wasp S3C4-G
5,200​	5,900​	4,800​	Take off power, BHP
5,720​	7,460​	5,940​	Engines - dry
9​	10​	10​	Air compressors
66​	172​	172​	Electric starters
10​			Hand turning gear
31​	29​	29​	Constant speed governor unit
16​	16​	16​	Vacuum pumps
168​	120​	113​	Air intakes, hot and cold
	70​		Auxiliary gear boxes
328​	440​	400​	Engine mountings
228​	588​	500​	Exhausts
1,282​			Cooling system and coolant
182​	260​	220​	Oil coolers and mounting
130​	130​	130​	Oil system, pipes, filters etc.
210​	210​	210​	Fuel system, pipes, filters etc.
200​	200​	200​	Engine controls
1,480​	1,480​	1,440​	Airscrews (Rotol)
140​	160​	140​	Fireproof bulkheads
520​	360​	340​	Engine cowling
	160​	140​	Additional cowling behind engines
	220​	200​	Cooling gills and mechanism
10,720​	12,085​	10,200​	Total engine and airscrew weight

4 engine performance

300​	315​	265​	Maximum level speed mph
21,000​	17,500​	13,100​	At altitude, feet
260​	270​	217​	Cruising speed, maximum economic power - weak mixture
21,000​	21,500​	17,000​	At altitude, feet
16​	16​	24​	Time to climb to 15,00 feet, minutes
25,800​	23,800​	17,100​	Service ceiling, feet

3 engine performance

250​	270​	230​	Maximum level speed mph
12,250​	17,500​	5,000​	At altitude, feet
205​	218​		Cruising speed, maximum economic power - weak mixture
13,800​	14,000​		At altitude, feet
20,300​	18,100​	12,000​	Service ceiling, feet

2 engine performance

180​	216​	170​	Maximum level speed mph
12,250​	7,500​	5,000​	At altitude, feet
54,500​	57,500​	51,500​	Maximum gross weight at which level flight can be maintained, continuous cruising power on rich mixture.
5,000​	5,000​	5,000​	At altitude, feet

Summary

Merlin XX	Hercules VI	Twin Wasp S3C4-G
18,700​	18,700​	18,700​	Structure weight: wings, fuselage, tail, undercarriage, fuel tanks, engine sub mountings, nacelle fairings, general hydraulics, flying controls.
10,720​	12,085​	10,200​	Power plant weight
29,420​	30,785​	28,900​	Empty weight sub total
3,910​	3,910​	3,910​	Fixed military load and armour
1,900​	1,900​	1,900​	Removable military load
1,200​	1,200​	1,200​	6 Crew and parachutes
36,430​	37,795​	35,910​	Weight less fuel, oil and bombs sub total
23,570​	23,570​	23,570​	Fuel, oil, bombs
60,000​	61,365​	59,480​	Gross weight

Dimensions

Feet	Inches
102​	0​		Wing span
69​	4​		Overall length - tail up
68​	10​		Overall length - tail down
19​	3​		Overall height - tail up
19​	6​		Overall height - tail down
		8.02​	Wing aspect ratio
102​	0​		Wing span
16​	0​		Root chord
12​	8.6​		Mean chord (Geometric)
		4​	Wing incidence, degrees
		7​	Wing dihedral - outer wing, degrees
45​	7​		Span of wing fitted with flaps
18​	0​		Span of Ailerons (one)
23​	9​		Undercarriage track
33​	0​		Tail plane span
8​	6.5​		Tail root chord
12​	2​		Height of end pin and rudder

Sq Feet
1297​		Gross wing area including ailerons
1205​		Nett wing area including ailerons
90.3​		Aileron Area (total)
146.3​		Flap Area (total)
237.2​		Tail plane and elevator area (gross)
87.5​		Elevator area including balance and trimmers
	29.53​	Percentage balance area
4.22​		Area of elevator servo trimmers
2.85​		Area of elevator adjustable trimmers
111.6​		Area of end fins and rudders
72.4​		Area of end fins
39.2​		Area of rudders including balance and trimmers
	18.2​	Percentage balance area
2.21​		Area of rudder trimmers
	0.533​	Control volume: Tail plane and elevator
	0.624​	Control volume: Fin and rudder
	0.033​	Control volume: Aileron

Avro Lancaster by Harry Holmes, weights in pounds, load is Crew, removable military load, fuel, oil, bombs and carriers

Month	Jan-42​	Sep-42​	Nov-42​	May-44​	Early 1945
Mark	I	II	I	I & III	I & III Overload
Structure	17,064​	17,064​	17,776​	18,033​	17,633​
Power plants	10,720​	12,335​	11,304​	11,610​	11,610​
Fuel and oil tanks	1,796​	1,796​	1,990​	1,999​	1,999​
Empty weight	29,580​	31,195​	31,070​	31,642​	31,242​
Fixed military load	4,120​	4,120​	4,334​	5,169​	4,589​
Tare weight	33,700​	35,315​	35,404​	36,811​	35,831​
load	26,300​	24,685​	27,596​	28,189​	36,169​
Gross Weight	60,000​	60,000​	63,000​	65,000​	72,000​
take off power bhp	5,120​	6,200​	5,120​	6,440​	6,440​
Wing load lb/sq ft	46.26​	46.26​	48.57​	50.12​	55.51​
Span load lb/sq ft	5.77​	5.77​	6.06​	6.25​	6.92​
Power load lb/bhp	11.72​	9.68​	12.30​	10.09​	11.18​

Back to the archives file. General Description
The Avro Lancaster is a four-engined mid-wing monoplane of all metal construction, designed to operate as a heavy bomber.
The aircraft may also be used as a long range general reconnaissance type.

The overall dimensions area: Span 102 feet, length 70 feet, height 19 feet 6 inches, wing area 1,300 square feet. The maximum loaded weight is 60,000 pounds. A crew of six is usually carried.

Fuel tankage for a still air range of 3,000 miles, at an economical cruising speed of 200/215 m.p.h. is provided. All the fuel tanks are in the wing and they are of the self sealing type. Jettison valves are fitted to jettison 1,000 gallons.

For reinforcing flights where very long distances have to be covered, additional fuel tanks can be mounted inside the bomb compartment.
The official test figures for the prototype Lancaster gave a cruising speed of 285 m.p.h. at the continuous cruising power of the Merlin XX engines using weak mixture, but at this cruising speed the range with standard tankage is reduced, as shown in the accompanying charts.
Bomb loads of up to 12,750 pounds can be carried.

All the bomb load is carried in one large compartment which forms the lower portion of the fuselage and which is closed by means of two long doors which conform to the streamline shape of the fuselage and are hydraulically operated. This arrangement of bomb compartment enables all the standard sizes of bomb to be accommodated, including the latest very large bombs.

The bomb carriers and bomb housings are of the Avro type, which has been standardised for use in the R.A.F.

An effective bomb sighting position is provided in the extreme nose of the fuselage.

An important feature of the design is that a large variety of different types of power plant can be installed. This is made possible by the use of easily detachable sub-mounting frames.

The Lancaster can be supplied either as a twin engined aeroplane or a four engined aeroplane, using engines of 2,000 h.p. or 1,000 h.p. For example power unit installations are already designed, or are in the process of design to accommodate the following engines:- Four engined, Rolls Royce Merlin XX or Pratt and Whitney Twin Wasp or Bristol Hercules. Twin engined, Rolls Royce Vulture, Bristol Centaurus, Napier Sabre.

The Lancaster is at present in production using the Rolls Royce Merlin XX engines.

The airscrews are of the fully feathering, constant speed type.

Design developments are in hand to adapt the aircraft for ultra high altitude operation.

The Lancaster is provided with a very effective defence, consisting of three power operated gun turrets. These comprise, a twin gun nose turret, a four gun tail turret and a twin gun mid-upper turret. All the guns can be brought to bear on the beam converging at a distance of about 100 yards from the aircraft, and the mid upper turret provides effective reinforcing fire for both the rear and forward turrets.

This strong defensive armament, coupled with the very high speed of the aircraft, makes the Lancaster a very difficult machine to attack by fighters.

The Lancaster is remarkably controllable for its size, which enables it to take effective evasive action when attacked and also during bombing operations.

Excellent armouring is provided. This consists of an armour plate bulkhead in the form of two large doors, which completely bulkhead off the forward crew compartment. The pilot's seat is provided with separate armour and the fire control station alongside the pilot is fitted with a bullet proof glass shield to protect the fire control officer's head and shoulders.

The construction of the Lancaster airframe is simple. A great deal of care was taken during the design stage to simplify both the main components and the details; this simplicity of construction has been well proved in actual manufacture.

The materials mainly used throughout the airframe are aluminium alloy and steel, aluminium alloy forming the major portion of the constructional material.

Hydraulic power is provided for the operation of undercarriage, landing flaps, bomb doors, gun turrets, airscrews, etc.
Electrical power is provided for engine starting, radio, intercommunication telephones, lighting, instrument operation, bomb fusing and firing, etc.

Cabin heating is provided and this has been tested to high altitudes and low temperatures with very satisfactory results. The cabin heating is controllable and can be varied to suit the temperature at which the aircraft is operating.

The pilot and fire control officer are accommodated in a roomy cabin which has a completely transparent top raised above the general top of the fuselage and carefully streamlined. This raised canopy gives them an exceptionally good all round field of view, which is considered to be a valuable military asset, particularly when the aircraft is subjected to air attack.

The pilot's windscreen is provided with a clear vision panel which can be opened without any draught entering, and in addition the main windscreen is fitted with windscreen wipers.

The pilot's seat and rudder pedals are bit adjustable for height and distance, so that pilots of different heights can be comfortably seated.

Single control is provided for the pilot, but dual controls can be installed for instructional purposes.

An automatic pilot is fitted to relieve the pilot of flying strain during the long flights, or under conditions of blind flying.
Blind landing apparatus is installed.

The large dimensions of the fuselage enable all the standard military equipment to be accommodated and the Lancaster is particularly well equipped in this respect.

For reinforcing flights, additional seats can be fitted in the fuselage to seat twelve squadron personnel.

Side light and roof lights are fitted along the fuselage so that the interior is sufficiently light to enable work to be carried on during the day time without artificial lighting.

Curtains are fitted for night operations.

Emergency parachute exits are fitted in the bottom of the fuselage and emergency exits on the top of the fuselage for use in the case of a forced landing with the undercarriage up and where the main door maybe jammed.

Construction.
Fuselage
The fuselage is a straight forward light alloy monocoque, built up on a framework of hoops and stringers with flush rivetted skin.

To facilitate manufacture and transport, the fuselage is divided into five sections which are fastened together by rings of bolts at the transport joints. This sub division of the fuselage has proved of great value, as it enables a large number of work people to operate at the same time without interfering with one another.

Where strong points are necessary, use is made of high grade aluminium alloy forgings and castings.

The hoops or formers are developed from sheet in presses. The stringers may be either of extruded aluminium alloy sections or drawn sections made from strip.

Alternatives are provided in the drawings.

Wing
The wing is of the two spar type with pressed ribs and flush rivetted covering.

Like the fuselage, the wing is constructed in a number of sections which are bolted together. This is done to facilitate construction and transport.

Compartments are fitted in the wing to contain the fuel tanks, the undercarriage and the emergency dinghy.

The leading edge of the wing is fitted with B.B.P. gear.

Frise type ailerons are employed and these are mounted on self aligning ball bearings.

The trailing edge flaps are of the conventional split trailing edge type.

The centre section leading edge is arranged to fold upwards easily to give access to the engine controls, electrical cables, hydraulic piping, etc.

Inspection doors are fitted wherever necessary to give easy access to interior piping, wiring, etc.

Tailplane
The construction of the tailplane is on the same lines as that of the main plane.

The elevator is a welded tubular structure with fabric covering and is both mass balanced and aerodynamically balanced.

Trimming tabs are fitted for operation by the pilot.

Fins and Rudders.
The twin fins and rudders are both metal covered structures and the rudders are fitted with trimming tabs to relieve the load on the pilot's foot when flying with one or two engines stopped on once side. The trimmers are sufficiently powerful to enable this to be done without any load on the pilot's foot.

Undercarriage.
The undercarriage is of a very simple design for so large an aeroplane. Two independent units are used, one under each of the inboard engine supporting points. The undercarriages are hydraulically operated and retract backwards onto a fairing which is a continuation of the inboard engine nacelles.

When retracted, the undercarriages are completely enclosed by means of doors which are coupled to the undercarriage themselves and thus automatically open and shut when the undercarriages are lowered and raised.

A long travel is provided on the shock absorber struts, which are of the air-cum-oil type, the air acting as the taxying spring and the oil providing the hydraulic energy absorption.

Efficient wheel brakes are incorporated, which are operated by compressed air from a control on the pilot's wheel.

Tail wheel.
The tail wheel is not retractable.

The shock absorber is of the air-cum-oil type.

The tail wheel can rotate through 360 degrees for manoeuvering on the ground and the whole unit can be removed from the aircraft by the removal of one large bolt.

Flying controls.
The flying controls are of the column and wheel and foot pedal type; either single control or dual control can be fitted. The dual control consists of attachments to the single control.

The rudder pedals are quickly adjustable to suit pilots of different heights.

The forces from the control column and foot pedals are transmitted through the aircraft by means of push-pull control rods.

All control services are mounted on ball bearing hinges of the self aligning type.

A folding seat alongside the first pilot's seat provides a side by side pilots' station.

Engine controls.
Particular care has been taken in the design of the engine controls to provide easy and exact operation of the carburettor, mixture, airscrews, etc.

The system is mechanical and consists of levers connected by means of chains and sprockets and tie rods.

The engine control system is given a small degree of pretension which eliminates all backlash.

The engine controls are mounted throughout on ball bearings.

This system of engine controls, whilst somewhat elaborate, is remarkably free of friction and enables the rather heavy loads which have to be dealt with in large sized engines to be easily overcome by the pilot.

Freedom from backlash gives the accuracy of the control necessary for Constant Speed airscrews.

These engine controls are very free from maintenance troubles.

Bomb Installation.
The bomb installation is very simple, consisting of one long compartment forming the bottom portion of the fuselage.
Fifteen bomb housings are provided in five rows of three.

The bomb gear is in two parts, consisting of a carrier which is attached to the bomb and a housing for the carrier which is built into the aircraft structure. The housing contains a supporting hook and an adjustable crutch.

The method of loading the bomb into the aircraft is as follows:-
The bomb carrier is placed on the bomb and the electro magnetic release slip engaged with the lug on the top of the bomb.

The crutching jaws on the carrier are then screwed down by means of the two integral handles and the bomb is then ready to be hoisted into position.

Whilst this is being done, another man inside the aircraft removes the cover from the housing and lowers down the hoisting cable. The cable has a ball at its end which engages with a socket on the bomb carrier.

The man inside the aircraft then winds up the bomb and the bomb carrier automatically engages in the bomb housing.

The loader then screws down the crutching jaws and the bomb is thus secured in position.

He next engages the hoisting cable, plugs in the electric lead to the carrier and re-fits the cover over the housing.

Two men can load a 500 pound bomb into the aircraft in two and a half minutes. As it is possible for several teams of men to work at one time, the aircraft can be re-bombed in a very short space of time.

This system of bomb carrying and loading was produced by A.V. Roe & Co., and has been adopted as the standard system for the R.A.F. new type aircraft.

The bomb compartment has been designed to take all the different types of bomb, including small bomb containers and the new very large size bombs.

Bomb Aimer's Station
The bomb aimer's station is in the extreme nose of the fuselage and the bomb aimer is provided with a cushioned kneeling position, which is considered to be more comfortable that either a prone position or a seated position. A large hemispherical transparent dome gives him a very good field of view.

The actual bomb sighting is done through a large diameter circular glass panel of special design which can be electrically heated to avoid frosting and misting.

Brackets are provided to carry a variety of bomb sights.

The official flight trials of the Lancaster have proved this aircraft to be both stable and controllable.

The Lancaster is particularly manoeuverable for such a large machine and its controls are light and effective so that it is not tiring to fly for long periods.

The machine responds exceptionally well to the automatic control, which can be used to relieve the pilot of flying strain.

The take off and landing is straight forward and easy.

The Lancaster can be described as an easy aircraft to fly, which makes it particularly suitable for night operations.

The pilots have a particularly good view in all directions, including a backward view which is provided by the raised canopy over the cockpit.

Very efficient cabin heating is installed so that the crew can perform their duties in comfort when flying under conditions of very low temperature.

Structural Strength
The Lancaster aircraft structure is designed for a normal loaded weight if 50,000 pounds with an increase of 20% to 60,000 pounds as an overload weight occurring at the commencement of the flight.

The maximum weight at which the normal landing requirements are met is 50,000 pounds.

The strength of the structure is up to the following standards: (Edit to add missing table)

At 50,000 lb	At 60,000 lb	Flight Cases
5.7​	4.75​	1. Normal horizontal flight C.P Forward
4.0​	3.5​	2. Normal horizontal flight C.P back
2.0​	2.0​	3. Steady diving flaps up at 400 m.p.h.
2.0​	2.0​	4. Steady diving flaps down at 200 m.p.h.

5. The requirements of A.P.970 and all current A.D.M's applicable to this type of aircraft, and met at the normal weight of 50,000 pounds.

Landing cases
1. The aircraft at the weight of 50,000 pounds is able to withstand impact with the ground at a vertical velocity of 12 feet per second. At this velocity the impact does not exceed three times the weight of the aircraft. The ultimate factor for the undercarriage when subjected to this impact load is 1.33 and for the remainder of the structure is 1.5

2. The landing requirements of A.P.970, Chapter 3, Paragraph 4, are met at the weight of 50,000 pounds. The main governing requirement is the "combined loading" case of 4W upwards, 1 W backwards with 0.4W sideways on one wheel inwards and 0.35W sideways on the other wheel outwards.

3. At the overload weight of 60,000 pounds the ultimate factor when the aeroplane is at rest is 4.0.