Fin Stabilised
 

I was in Atlanta Georgia earlier this week, and visited the superbly restored Cyclorama depicting the Battle of Atlanta during the US Civil War/War of Northern Aggression/War Between the States (you choose which name suits you!). Almost 400 feet long x 40 odd feet high, it is an impressive painting.

Associated with the Cyclorama is an excellent museum of Civil War objects, including a wide range of rifles and pistols with good, detailed captions, not the 'one liners' we so often see in museums these days. There is also a fine collection of ordnance and projectiles, including this rather interesting 'fin stabilised' experimental projectile manufactured by a Confederate armory. The caption states it was a winged projectile for increasing the range and accuracy of smooth-bore cannons. The wings were spring-loaded and extended upon the projectile leaving the bore.

Seems to be very much like the principles of the modern-day fin-stabilised anti-tank rounds. I say 'modern', but of course, the principle has been in Western use since at least the late 1950s, with the 106-mm RCL HEAT round, which had wings which extended once the round left the barrel.

Just though it was interesting that 'fin stabilisation' had been thought of as far back as the 1860s (at least).

Mike

Ahh, museum captions. I hope one day there will be a museum that records and displays all those one liners!

The projectile shown is not for a smooth bore cannon. It has "buttons" that engage with rifling, which was used in the Armstrong breech loading rifled barrels.

Hi Tony,

I see no buttons....?

Seriously,Tony, I'm familiar with the Whitworth & Armstrong systems, but I didn't see any lugs/buttons on the projectile's outer edge that could engage any form of rifling. The caption was quite specific about the development (but of course, we all know how accurate many museum captions really are!)

Mike

Fin stabilization was hardly new, even then. Arrows spring to mind!

My apologies, Mike. I need to open pics and look closer, or clean my computer screen. :doh: While not as large as the big brass pads on British projectiles, I thought I saw small "nipples" or lugs, which I thought were the American version of an experimental round.

Happens to us all, Tony: I made the same error when I took a quick look at Colin's post on the smoke dischargers - didn't comprehend the scale and assumed (embarrassingly!) that the spent cart was a 12 # not a .303!! :bang:

Mike

I think currently all the major powers have smooth bore main armament in many of their tanks ( or are coming in to service) with finned projectiles.

Obviously a finned projectile will absorb a great deal of energy from the fin drag as it spins decreasing velocity and range. A very slow spin can still help stabilize finned projectiles and the current smooth-bore projectiles have the fins very slightly off-set to create a slow spin.

To get no spin or slow spin with finned projectiles with traditional grooved barrels they have "Obdurating Rings" which is a collar that seals the gas but slips on the projectile. There are also various discarding sabot designs that seal the gas but fall off once the projectile leaves the barrel. These are extremely bad news if infantry have close support from tanks firing over their heads!

I believe Mike's projectile would have been shot from a smooth-bore weapon but may be wrong.

Lang

British practice is still to use a rifled gun for HESH projectiles.

Yes Adrian. The British are unique in having their main battle tank the only one of all the NATO countries to have a rifled barrel.


Here is an interesting discourse on fin and spin stabilised projectiles.

https://www.globalsecurity.org/milit...ets2-types.htm

There's no mention of shaped charges (or did I miss it?). I've read that one reason smooth-bores are back in fashion is that if the projectile is spinning, the effect of a shaped charge is reduced. Maybe that's another myth.

Ed

I would surmise that a spin of say 10/20 turns per second for a finned projectile would not have much of an effect on an explosion initiating at many thousandths of a second. On the other hand a rifled barrel producing a spin between 2,000 and 3,000 rpm could well have some effect as you say.

It appears that the high tensile penetrating "bolt" is the go now to get the charge igniting after the armour has been penetrated rather than just a surface explosion from squash-head, shaped or conventional HE.

They are getting so sophisticated with Infantry man-carried anti-tank weapons that the tank-on-tank weapons we are talking about are almost superfluous as more than ever before in a conventional war with well equipped armies a tank is little more than a steel coffin and this is not taking into account aircraft like A10's, Mi-28 and Apaches. I think they are brave men surviving psychologically on a hope-over-experience mind-set.

This is pretty depressing if you are a tank man.
https://www.youtube.com/watch?v=CDctxC-7P9k

and this one
https://www.youtube.com/watch?v=y5xKCzdhAC8

And this would make you want to give the game away.
https://www.youtube.com/watch?v=myv7CAJ5Zpk

Lang

I seem to remember hearing/reading somewhere that shaped charge projectiles have limitations on them as regards maximum velocity. They depend on the blast being focused due to the distance from the armour when detonated and if travelling too fast may even be knocked out of shape at the time of detonation. Maybe how squash heads were invented.
As I understand it, delivery systems for shaped charge projectiles tend to be relatively low velocity.

David

Dave,

MV of rounds fired from an L7A3 105mm tank main armament (eg Leopard AS1):

L52A2 APDS/T = 1,478 m/s
L35A2 HESH/T = 732 m/s
M456A1 HEAT/T = 1,174 m/s

I'm certainly no expert on the physics of shaped charges, but it seems to me the 'stand off' distance of the PIBD (Point Intitiating Base Detonating) initiator ie the distance from the initiator to the shaped charge, would be the critical factor. The higher the velocity at impact, the greater that distance would need to be to allow development of the slug by the shaped charge?

The M456A1 was fitted with a rotating Nylon band - the band rotated in the rifling, but did not impart appreciable spin to the projectile (which I think answers your query, Ed). The projectile included a set of tail fins for flight stability.

Mike

I was always surprised that the M456 didn't have some sort of ballistic cover; it was counter-intuitive that that shape should fly right. But it seems that is exactly what the shape does:

http://sturgeonshouse.ipbhost.com/to...jectiles-work/

Hi Tony,

I agree - the spigot sticking out the front of a cylindrical, flat-faced projectile just seems all wrong, but it works, as the linked you provided shows.

In contrast to the M456A1's protruding spigot ,the 106mm HEAT rounds for the M40A1/M40A2 Recoillesss Rifle have a conical, hollow nose cap (as do the various Soviet Bloc RPG rounds). In the case of the 106mm HEAT round, the spin imparted by the rifling is only about 12 clock-wise revolutions per 100 metres, with flight stability provided by six fins protruding from the base of the projectile. These are housed within the cart case, and spring out after the round leaves the barrel. In this case, the MV of both the HEAT and High Explosive Plastic (HEP) rounds are about the same: about 503 m/sec for the HEAT and 498 m/sec for HEP. (HEP is the US equivalent to the Brit HESH).

Mike