Post by Rich RostromI note that aerial bombs were nearly always calibrated
in "round numbers": 1000 ib, 250 ib, 200 kg, etc.
Slightly off reply, the conversion factor is 2.54 cm to the inch, with the
proviso the US in WWII had a slightly different measure of distance so
a statute mile is 5,280 feet or 5,279.9894 U.S. survey feet. It mattered
when it came to precision parts.
Post by Rich RostromThis inspired a few questions.
First, were these designations accurate or nominal?
Accurate or nominal depending on the bomb.
Post by Rich RostromThat is, was the bombs supposed to weigh exactly that
amount, or was the actual spec somewhat more or less,
and the designation just a convenient name?
A convenient name sometimes and accurate other times.
Post by Rich RostromFrom Roger Freeman, Mighty Eighth War Manual. AP = Armour
Piercing, SAP = Semi Armour Piercing (Bomber Command dropped
quite a few of these on oil refineries which gives an idea about how
strong some of the structures were considered), Frag = Fragmentation,
GP= General Purpose, IB Indendiary bomb.
Table is designation, nominal weight, actual weight, both in pounds, with
the note there were always slight variations. I am unsure how much
difference there was in the weights of the various explosives used as
fillings.
M30 GP / 100 / 100
M31 GP / 300 / 260
M34 GP / 2000 / 2050
M38A1 Practice / 100 / 100
M41 Frag / 20 / 20
M43 GP / 500 / 510
M44 GP / 1000 / 965
M47A1 IB / 100 / 120
M47A2 IB / 100 / 100
M50A1 IB / 4 / 3.75
M52 IB / 2 / 2
M56 GP / 4000 / 4201
M57 GP / 250 / 260
M58 SAP / 500 / 500
M59 SAP / 1000 / 995
M66 GP / 2000 / 2050
M69 IB / 6 /6
M76 IB / 500 / 470
M81 Frag / 260 / 260
MK1 AP / 1600 / 1590
Post by Rich RostromSecond, did anyone consider that such weights might
not be optimal? That for a given aircraft on a given
type of mission, best results might be achieved with a
bomb of some other weight?
Yes, but it comes down to how flexible a bomb bay the aircraft
had, IB generally took up more room than HE which in turn
took up more room than AP of similar weights.
In WWII the B-17 bomb bay had been designed to take 12,800
pounds of 1,600 pound AP bombs, it meant the maximum load
of HE bombs was around 6,000 pounds. Same for the B-24.
It is not only bomb weight, it is also how flammable the target
is, how strong it is and so on.
Post by Rich RostromFor instance, a 500 lb bomb might be often ineffective
even if it hits, whereas a 1,000 lb bomb might load
down the aircraft, reducing range and maneuverability,
and making it substantially harder to hit the target
squarely. (I am thinking of a dive bomber here.)
The "optimum" size might be, say, 787 lb.
Simply put nobody at the time had any real ability to do this
sort of calculation and in any case the precision needed to
use such weights was not there. Even today the warhead
required depends on the target.
Post by Rich RostromWith heavy bombers in level bombing... the bomber has
a bomb bay of fixed dimensions with a fixed number of
shackle points. It also has a given engine power and
resulting paylaad. One might load out with that number
of 250 lb bombs, and find that the plane could handle
more bombload. But 500 lb bombs would be too much; a
"middleweight" bomb would be wanted.
No, you would put in a mixture of 250 and 500 pound bombs,
accepting the increase in error due to the different ballistics.
The Lancasters involved in the raid on the night of 2 December
1944, 86 assessed as attacking, they dropped 86 4,000
pound bombs (47 HC, 37 M2), 269 1,000 pound MC, 18
1,000 pound GP, 49 US 1,000 pound, 152 US 1,000 pound
SAP, 182 500 pound MC, 148 500 pound GP, 20 US 500
pound, 4 US 500 pound SAP. No incendiary.
HC has more explosive than MC which has more explosive
than GP.
So the nominal average bomb load was a 4,000 pound, 5.7
1,000 pound, and 4 500 pound. If you multiply the bombs
by their official weight you end up with 450.4464 long tons,
versus the official tonnage of 450.4, so the bomb tonnages
you see published are probably using the official weights,
not the actual ones.
On the 4th the bomb load was a similar mixture of 4,000, 1,000
and 500 pound HE plus a mixture of 4 pound, 500 pound and
750 pound incendiaries, the latter two being clusters of 4 pound
bombs (106 and 158 respectively). The pathfinder Lancasters
also had 1,000 pound and 250 pound marker bombs. All up
incendiaries accounted for around 20% of the bomb load,
which averaged 11,102 pounds per aircraft credited with
attacking.
Post by Rich RostromDid anyone attempt or implement bomb designs of non-round
weights?
Sort of. Remember the bomb had to physically fit into the bomb
bay in optimal numbers, then the aircraft has to lift the bomb load,
asking for specific special bombs for your aircraft is setting up
a logistics problem as well as limiting flexibility given there are
so many different types of targets.
So the air forces developed a series of bombs and the aircraft
were expected to lift some or all of them. Bigger aircraft
allowed for bigger bombs and mixed loads.
Post by Rich RostromI know this was done to some degree with the super-heavy
British bombs - the "Tallboy", "Earthquake", and "Volcano".
Tallboy was designed within the parameters of the Lancaster of
1943, specifically the bomb bay size and maximum weight lift
with enough fuel to go somewhere useful. Plus of course the
ability of the materials available to build a bomb that would
penetrate deeply without breaking up and then explode. The
Grand Slam required removal of equipment and use of overload
weights.
Post by Rich RostromBut was this ever done anywhere else?
There is a two way street, aircraft designed to take existing
weapons and new weapons designed exploiting the capabilities
of the aircraft.
The incendiary clusters used by the Lancasters above were a
wartime design taking into account the capabilities of the
bombers.
Post by Rich RostromThis also raises a question about the loading-out
practices of Bomber Command. It's said that BC tried
to maximize bombload, with planes often straining
their undercarriages on take-off. How did they adjust
bombloads, and how "fine" could they tweak? Were small
adjustments made in fuel load instead?
Fuel loads were calculated according to track miles plus a fixed
reserve, after that came what was available for a bomb load plus
any weight safety margin for things like take off and altitude
performance.
In gallons the Lancaster fuel load was track miles divided by 0.95
plus a 200 gallon reserve. Given the weather forecasting and the
logistics of landing large numbers of aircraft when the weather
turned bad there was no fine tuning of fuel loads, just the basic
rules.
At 1,200 track miles the Lancaster had about 14,150 pounds
available for bomb loads, the Halifax III 9,260, the Halifax II
8,320, the Stirling 6,625.
All air forces tried to maximise the bomb loads and post war the
air forces rarely if ever flew their aircraft to the weight limits
routinely used in wartime.
The main effect of extra bombs on range is they reduce the
fuel load you can carry, extra internal weight does not do a
great deal to range for a given fuel load. It does make a
difference to the altitude you can fly at. So number 1
Group Bomber Command tended to load more bombs on
its aircraft, which meant they flew lower and resulted in some
crews for a time jettisoning some of the load in order to fly
higher and therefore safer.
It looks like at times the 8th AF put fewer bombs on its B-24s
even though the B-24 had a better load at distance than the B-17,
in order to allow the B-24s to fly higher.
In summary no real fine tuning, the bomb loads depended on
the target and the capabilities of the aircraft used, living largely
within the standardised bomb sizes available but also using
new designs that the bombers could then carry and also affected
by the state of the defences.
Or in short, it depends, within the constraints of requiring the degree
of standardisation needed by mass production and mass consumption.
Geoffrey Sinclair
Remove the nb for email.