RAF Second World War 500lb MC bomb fins

[FrankC]

Hello everyone, following the excellent response to my last post on here a few weeks ago, I'm hoping some of you might be able to help me again.

I am helping a new not-for-profit museum at the site of RAF Witchford (1943-45) near Ely, UK. My last post led us to acquiring two inert 500lb MC bombs for the new display but now I am looking for information on the fin assemblies which will have to be fabricated from scratch to make the bombs, well, look more like bombs for the visitors. My non-expert eyes see there may be a few options for these but I wonder if any of you can point me toward any detailed drawings of fin assemblies that could help with making these key elements for the display?

As ever, thank you for your assistance in advance - what a great resource this forum is.

Frank

 

[Dreamk]

Take into account that you'll need to make a choice as different models of tails could be mounted on these bombs depending of whether they were mounted on internal or external racks and of the type of the bomber aircraft:

On MC 500 lb Mk I, II or III, Mk VI, Mk VII, Mk VIII, and Mk X, Tails could be the "long" No 25 Mk I, II or III or the "short" No 28 Mk I or II

"Long" tail No 25 Mk II was a strenghtened tail intended for carriage on external racks when there was room for a long tail
However for high speed aircraft, on external racks, "Short" tails No 28 Mk I or Mk II were preferrred

Height of "Long" tails No 2 Mk1 and No25 MkI or MkII was 71.1 cm
Height of "Short" tails No 26 MkI and No 28 Mk I was 35.6 cm

On the MC 500lb Mk IV and Mk IX. the tails used were different:
The long tails were the No 2 Mk I or the No 77 Mk l (No 77 was a strenghtened tail and replaced the former No 26 - No 2 was to be used till the stocks were exhausted then replaced ny the No 77)
The short tails were the No 26 Mk I, II or III, for use "when the bombs were to be carried externally on high-speed aircraft, or when their use enabled a greater number of bombs to be carried internally on other types of aircraft".

On the MC 500lb Mk V, only the "long" tail No 25 Mk I , II, or III could be used (No "short" tail available for this bomb)

And in the post war period the remaining 500 lb were equipped with the conical Mk 112 tail (offically from 1955 onwards, though I have seen a photograph from 1953 in Korea showing such a tail on a 500lb MC mounted under a RAAF Meteor jet - possibly a trial of a pre-production model)

 

[FrankC]

Take into account that you'll need to make a choice as different models of tails could be mounted on these bombs depending of whether they were mounted on internal or external racks and of the type of the bomber aircraft:

On MC 500 lb Mk I, II or III, Mk VI, Mk VII, Mk VIII, and Mk X, Tails could be the "long" No 25 Mk I, II or III or the "short" No 28 Mk I or II

"Long" tail No 25 Mk II was a strenghtened tail intended for carriage on external racks when there was room for a long tail
However for high speed aircraft, on external racks, "Short" tails No 28 Mk I or Mk II were preferrred

Height of "Long" tails No 2 Mk1 and No25 MkI or MkII was 71.1 cm
Height of "Short" tails No 26 MkI and No 28 Mk I was 35.6 cm

On the MC 500lb Mk IV and Mk IX. the tails used were different:
The long tails were the No 2 Mk I or the No 77 Mk l (No 77 was a strenghtened tail and replaced the former No 26 - No 2 was to be used till the stocks were exhausted then replaced ny the No 77)
The short tails were the No 26 Mk I, II or III, for use "when the bombs were to be carried externally on high-speed aircraft, or when their use enabled a greater number of bombs to be carried internally on other types of aircraft".

On the MC 500lb Mk V, only the "long" tail No 25 Mk I , II, or III could be used (No "short" tail available for this bomb)

And in the post war period the remaining 500 lb were equipped with the conical Mk 112 tail (offically from 1955 onwards, though I have seen a photograph from 1953 in Korea showing such a tail on a 500lb MC mounted under a RAAF Meteor jet - possibly a trial of a pre-production model)

Thank you - sorry I should have specified - the site in question was home to Stirlings and, mainly, Lancasters so let's assume Lancasters from 1944-45. The bombs only have one lug so that I believes makes them MkI to IV? In that case we'd be after reference material for a long-tail MkI? All expertise and advice much appreciated!

 

[Dreamk]

A Mark X with short tail is more probable for Lancasters
"The short tails were the No 26 Mk I, II or III, for use "...... when their use enabled a greater number of bombs to be carried internally on other types of aircraft"
A typical Lancaster charge agains V1 site was 1 4000 lb HC "cookie" and 18 500lb MC with short tail (instead of the regular load of 14 500lb GP/MC with a long tail) loading 4 500lb MC in each of the 2 front rows (instead of the usual 3) and 2 MC bombs in tandem on each side of the cookie, then 2 rows of 3 MC bombs .
A similar disposition was used for SBC carrying incendiaries,

 

[FrankC]

Amazing - thank you. So the next question would be where could I find technical drawings of a short tail? One was sold at an auction a few years back!

 

[Dreamk]

Digging in the forum, it appears that number of years ago Investment (https://www.bocn.co.uk/members/investment.159/) posted diagrams of the No 26 Mk I-IV tail fins - though the image is small and you cannot read dimensions:

British bomb tail assembly

Does anyone have a picture (preferably a diagram) of a No.26 Mk.I tail assembly for a 500 lb bomb? Thanks for any help.

www.bocn.co.uk

Howvever, contact him to see whether he has better quality drawings.

Meanwhile you can also use that, as the overall dimensions of the 500lb GP bomb are known (This is a GP with drop-shaped body not a MC with cylindrical-shaped one):

 

[Dreamk]

The RAF historical section has Some details on the MC 500lb Tail issue:
"The 500 lb. M.C. bomb tail
The rather complicated story of the development of the 500 lb. M.C. bomb had so far been confined to the body structure. In conformance with a principle long established, this was provided with a clip on tail. The design for the new tail was produced by C.S.D., and production of the part was undertaken by a civilian contractor, for a small quantity for development purposes.
By June 1941, production of the 500 lb. M.C. bomb had commenced, and a production order for the tail was placed with Messrs. Fisher Ludlow, who were already the contractors for the G.P. bomb tail, a number of whose components wer used in the M.C.
The design was recommended for approval by the Ordnance Board in the following month. By November 1941, dropping trials had shown the bomb to be quite stable, and in this month its acceptance for service use was recommended by D.Arm.D.
One but very minor modifications were made to the original tail which received the service title of No. 25 Mark IA and which continued to be used in the majority of 500 lb. M.C. bombs throughout the war.
Towards the end of 1941 however, the need arose for the carriage of M.C. bombs in Mosquito aircraft, and the space available did not allow the orthodox tail to be fitted. A short drum type tail was specially designed for this aircraft, and a series of trials made at Orfordness to test its ballistics. These trials were combined with ballistic trials of the bomb with a standard tail, and showed that when fitted it had good ballistic consistency with a terminal velocity of 1,460 feet per second. The effect of fitting the special drum tail was to reduce the te rminal velocity by 70 feet per second and to increase the ballistic errors in range by 70 feet.
This shortened tail was given the designating Number 28.
Bombs with short tails were in fact very near the limit of stability, and the A.O.C.-in-C., A.E.A.F. reported to the Air Ministry in June 1944 that this instability was the probable cause of bomb failures. This instability was most noticeable in bombs carried externally on fighter-bombers, and was ascribed to some extent to weakness in structure.
Accordingly a stronger type of tail was designed for external use in fighter-bombers, and numbered 77."

Strangely enough there is no mention of the No 26 tail which apparently was the most frequently seen on these bombs !