Allied/Axis Bomb-Shapes

[Zipper730]

From what it appears: The USAAF/USN both employed bomb-fins that used an X-fin arrangement with a box-fin surrounding it (); the RAF used a cylindrical bomb-fin; the Luftwaffe used either X-fins with some designs having a cylindrical fin, at least one having a circular metal connector between the fins; the USSR seeming to use similarities to the Luftwaffe.

What motivated the decisions for the following

• X-shaped fin with no cylindrical fin
• X-shaped fins with cylindrical fin
• X-shaped fins with box-fin

Were there any advantages and disadvantages

 

[wuzak]

The cylindrical fin on British and German bombs was usually the same diameter, or less, as the body of the bomb.

The box fins are larger than the body of the bomb, so that becomes the limiting factor, rather than the body diameter.

 

[Zipper730]

The cylindrical fin on British and German bombs was usually the same diameter, or less, as the body of the bomb.

So the box-fins are bulkier?

Were the box-fins sturdier or flimsier, easier to build, more accurate?

 

[tyrodtom]

Some of the German bombs were stored in the bomb bay vertically (H-111, maybe others too), fins down, so that fact might have had something to do with the size of the fins on German bombs.

 

[Shortround6]

Some of it has to do with the shape of the bombs.

British 250lb bomb

US 250lb bomb

Please note that the long cylindrical body and very quick taper at the rear of the bomb would not provide good airflow to fins that were the same diameter as the bomb. Supercaliber fins (larger than the body of the bomb) give the needed stability. The long gradual taper of the British bomb means the tail assembly will get good airflow.

 

[wuzak]

MC bombs were closer in size to US GP bombs

Note that tails of some of the bombs were shortened to fit more into a bomb bay (500lb MC for Mosquito, 1,000lb MC for Lancaster) and it was found there was little difference in accuracy.

 

[Zipper730]

Some of it has to do with the shape of the bombs.

Was there a reason for the different bomb-shapes? The British seemed to have a better knowledge of aerodynamics than us, so I'm curious if that's it.

 

[wuzak]

Was there a reason for the different bomb-shapes? The British seemed to have a better knowledge of aerodynamics than us, so I'm curious if that's it.

The British changed the shape of their bombs to something similar to the American shape.

The bomb shown by SR is a GP bomb. British GP bombs were developed in the '20s and early '30s and had a charge to weight ratio of ~25% compared to the American GP bomb charge to weight ratio of ~50%.

The British GP bomb may have been more aerodynamic, it certainly looks that way from the picture, but the shape may have contributed to the low charge to weight ratio.

In the late 1930s the British started developing the Medium Capacity (MC) bombs. I can't recall if that included a 250lb MC bomb, but they did develop 500lb MC, 1,000lb MC and 4,000lb MC bombs. Note that they did not develop a 2,000lb MC bomb.

They also developed the High Capacity (HC) bombs (~70-80% charge to weight). The first was the 2,000lb HC bomb, which was long and slender, the 4,000lb HC bomb (often called the Cookie), 8,000lb HC and 12,000lb HC bombs. The HC bombs were decidedly unaerodynamic, but did include some sort of tails for stability.

When the Mosquito was doing initial testing it was suggested that if the tails were cropped that 4 500lb MC bombs could be carried. This proved to be the case, doubling the design bomb load of the Mosquito. Ballistic tests showed little difference between the long and short tail bombs for accuracy.

 

[Shortround6]

Long, streamlined bombs need longer bomb bays than short fat bombs.
short fat ones need wider/taller bomb bays.

Iron/steel is much heavier per cubic in than high explosive material so bombs with a higher percentage of explosive are fatter than low capacity bombs of the same weight.
Just because certain bombers could carry the right amount of weight doesn't mean they could carry an equal number of all types of bombs of that weight.

 

[wuzak]

An example of how the size changed for the later bombs is the difference between the 1,000lb MC and GP (British) bombs.

From memory, the 1,000lb GP bomb was 13.5" in diameter. The 1,000lb MC bomb was 17.75" in diameter. I can't recall the lengths, but I believe the MC was significantly shorter than the GP.

Depending how the bomb bay is arranged, whether length, width or height is the limiting factor, one type could be favoured over another.

(The 1,000lb GP bomb had about as much explosive filling as the 500lb MC bomb, which was similar in diameter and much shorter, which meant that, potentially, more could be carried.)

 

[dogsbody]

The RAF used lots of American made bombs during the last half of the war. If you see bombs with one lug on one side and two lugs on the other, it's an American bomb. Also, the tail fins were inter-changeable.

RAF bombs:

Chris

 

[Zipper730]

Long, streamlined bombs need longer bomb bays than short fat bombs

And with short fat bombs requiring deeper and wider bomb-bays the lesson evidently is "design your bombers with long cavernous bomb-bays", and never build several small bomb-bays when one huge one will do

 

[Zipper730]

An example of how the size changed for the later bombs is the difference between the 1,000lb MC and GP (British) bombs.

From memory, the 1,000lb GP bomb was 13.5" in diameter. The 1,000lb MC bomb was 17.75" in diameter. I can't recall the lengths, but I believe the MC was significantly shorter than the GP.

Is there any thread on this site regarding bomb-dimensions used by the USAAF, USN, RAF, and RN/FAA if not the Luftwaffe and former USSR?

If not, where would I find such things?

 

[fubar57]

Technical section has manuals for all I believe

 

[wuzak]

Technical section has manuals for all I believe

Certainly there are catalogs for British and American bombs. I haven't seen Russian or German bomb catalogs on here, but there must be something?

There are websites that have that information, too.

And books. I have a book on German bombs at home - "German Air Dropped Weapons", or similar, is the title.

 

[fubar57]

I'll get back to you. I believe I up-loaded both........

 

[fubar57]

This is the Russian one...

​

....and the German one

​

They're in here somewhere

 

[pbehn]

With the accuracy of bomb aiming from 25,000 feet I think most of the aerodynamics was concerned with making sure the bomb exploded when it hit.

 

[wuzak]

The Luftwaffe Resource Center has info on German bombs:

Luftwaffe Resource Center - Drop Ordnance - A Warbirds Resource Group Site

 

[fastmongrel]

The British changed the shape of their bombs to something similar to the American shape.

The British Medium Capacity bomb body shape was inspired by the Luftwaffe SC (Sprengbombe Cylindrisch) but the tail design remained much the same as the older GP bombs. The GP bomb shape was very good aerodynamically and when Jets came along the bomb shapes reverted to the GP style though with much thinner higher quality steel walls to keep explosive capacity high