300 lb Triplex Rocket

[TallEng]

I've bought myself a Trumpeter Spiteful, and while checking my references, I found a picture
in an Old 'Aeroplane' (July 2001) magazine in an article about the Spiteful, which shows Spiteful
RB516 carrying "4 Triplex rockets, which consist of a 7.2inch howitzer shell propelled by a cluster
of three 3inch rocket motors" 
Does anybody know anything about these? pictures/drawings would be nice
I've tried 'google' but found nothing. (apart from a couple of questions asking the same thing!!)

Regards
Keith

[Mr.Creak]

I think there's at least a mention in BSP: Hypersonics and Missiles. I know I've read something about them in the last couple of weeks...

Ah, found it:
Page 88, under Uncle Tom.
Apparently only tested on Seafangs. But no drawing or further detail. 

[kitnut617]

Well there's a photo in the book 'Spitfire' by Albert Price (page 271), which shows RB516 with a full load of 4 Uncle Tom's and a 180 Gal centerline drop tank (similar in appearance to what the Hellcat center drop tank looks like)

Checking on UK Serials website, RB516 was a Spiteful Mk.14 and the photo clearly shows no hook or other RN paraphernalia on it.  I think the confusion to it being a Seafang was while at Boscombe Down, RB516 was fitted with the lengthened carburettor air intake that the Seafangs were fitted with later.  And the photo clearly shows this air intake system on it.

[Mr.Creak]

Well there's a photo in the book 'Spitfire' by Albert Price

Alfred has a brother?

[kitnut617]

Well there's a photo in the book 'Spitfire' by Albert Price

Alfred has a brother?

My bad -- it's Alfred

[TallEng]

AH Ha! I've been doing some more googling
And I found this over at Secret Projects: http://www.secretprojects.co.uk/forum/index.php?topic=5300.0
Which looks very much like that what is pictured under the Spiteful's wing
What do you lot think?

Regards
Keith

[Mr.Creak]

Good find, and I think Red Admiral is wrong.
Here's a quick sketch I've just done:


It's based on nominal sizes only, i.e. the 3" rockets are drawn at 3" diameter and the 6" warhead (inner of the two big circles) is actually 6". The other large circle is for 7.2".
Does anyone have actual sizes for each of these weapons (I did have a quick Google for 7.2" artillery shell to see if I could find a dimensioned drawing, but no joy)?
If I can get some genuine dimensions it shouldn't take long to knock up a workable drawing from these photos.

[kitnut617]

From what I've read the pipe used for a 3" rocket motor was nothing more than standard 3" pipe.  Standard 3" pipe is refered to as 'nominal size' and the outside diameter of the pipe is actually 3 1/2".  It's nominal because it comes in various wall thicknesses, standard (or Sch40) being .226" whereas Sch80 (or Extra Strong) has .318" wall and Sch160 (or Double Extra Strong) would have .636" wall.  All having the same OD of 3 1/2". As you can see Std 3" pipe has an inside diameter of 3.048" but Sch160 has less than 2 1/4" ( 2.228") inside diameter, but it's still refered as 3".

I would re-draw you section M.C. using 3 1/2" OD for the rocket motors then see where it stands with the 7.2" shell diameter.

[Mr.Creak]

Looks even worse!


Of course I've drawn the 7.2 inch at 7.2 inches diameter. I wouldn't be at all surprised if it were larger.

Looking at the photos there does appear to be a collar at the base of the shell, maybe that "covers" some of the overhang seen here?

Okay, Wiki says 3" diameter and this page, http://www.bocn.co.uk/vbforum/threads/3795-3-60Lb-S-A-P-rocket-British-WW2, says 83 mm dia.
I'll try 83mm:

[rickshaw]

I will check I.V.Hogg's "British and American Artillery of WWII" when I get home this evening.  However, 7.2 would be IIRC the diameter of the driving bands, not the actual shell.  Calibre measures are invariably taken from land to land across the tube of a barrel (from groove to opposite groove, for laymen).  The shell actually has to be smaller to fit into the tube.  The driving band however has to be slightly larger as it is a band of soft metal (copper usually, sometimes sintered iron for the Germans) which is used to seal around the shell.  Some shells had multiple driving bands, depending on their length and calibre.

The British use of artillery shells for rocket warheads was actually an ingenious way of using a readily available source of warheads which were already aerodynamically stable.  All they needed to do was change the fuses so they no longer needed a "set back" to be armed (the shock of firing).  This of course made them a lot less stable though.  The original 3in rocket used a 6in shell, so using the next size up, 7.2in was logical.  Clustering 3, 3in rocket bodies was as well, 'cause it used the existing rockets.  All that was required was an adapter ring which screwed onto the base of the 7.2in shell to accept three 3in rockets.

[TallEng]

Well... this is all very interesting and educational for me
But another question comes to mind: What sort of damage could/would
be inflicted by a 7.2in shell fired as a rocket? And did they have different
heads as well? like A.P. or H.E.
I'd guess they wouldn't be very accurate?
Oh and what colour would they be?

Regards
Keith (with an enquiring sort of mind)

[Mr.Creak]

Aha! Just found this (although why it didn't come up the last two times I googled I have no idea): http://nigelef.tripod.com/72inchsheet.htm
This says that the body dia is 7.185" (which gives a negligible 0.381 mm smaller diameter than that drawn) and the shell length is 35.07. Something to work from.

@ TallEng: with 28 lbs of explosive filling it has compares more than "favourably" with the 12.3 lbs in a 60 lb rocket. Not to mention a total (shell weight) of 202 lbs. Travelling at rocket speed I'd imagine there'd be quite a noticeable impact.

[Old Wombat]

... but, as with all unguided rockets, accuracy would be an issue (to some degree).

[Mr.Creak]

What he said. 
What's the figure? 6%? 1%
Something appallingly low, despite the fearsome reputation they gained.

[PR19_Kit]

But if you were in the target area would you want to rely on that? I think not, you'd be getting the H**L out of there!