Penetrator vs. Flechette

[AmmoResearch]

I have been reading a number of different posts in the forums here, and one of the more contested points seems to be the question at which the division occurs between what is a flechette, and what is a penetrator.I am not limiting the question to a simple delineation of size, but even to the definition itself...

"what is the difference between a flechette and a penetrator?"

 

[EODGUY]

Interesting question that I never really thought about before. Technically a penetrator is a flechette. My definition of a flechette is a small fin stabilized dart that is used against personnel or light armored targes. What is "small"...I don't know. With the exception of small arms ammunition that is often loaded with a single flechette, I look at artillery sized ordnance as usually having one large "dart" that I call a penetrator. That is, if there is one large "flechette" in a projectile it is a penetrator, if there are hundreds of smaller "darts" they flechettes. As usual though there are some items that do not fit that definition. I have a "dart" that was loaded in a 76mm projectile that is about the size of a Lazydog. Not sure what I would call that!! I do not recall of ever seeing a definition that broke down at what size a flechette is called a penetrator. As far as I know the term flechette was first used in WWI to name the large steel "darts" that were dropped from aircraft on troops and vehicles. The term then disappeared in the US until the 1950's when the Army began the development of the Special Purpose Individual Weapon (SPIW) program where much smaller flechettes were loaded in various calibers. Hopefully someone can provide a good answer to our question.

 

[AmmoResearch]

Agreed...

'flechette' is the French word for dart, which seems like a word of physical description, and could easily cover the penetrators (which are often described as large 'flechettes') as well.

'penetrator' is a word of description of function, and is equally ambiguous, since most things mentioned on this forum are designed to penetrate.

I get that flechettes and penetrators are different than other things that penetrate (projectiles et. al.), but is there any commonly accepted point of demarcation? I guess another good analogy would be the point at which a bullet becomes a 'canon' round. I generally accept this to be approximately 20mm, but no doubt there are very many examples of other.

 

[ammocat]

The RMCS Handbook defines a flechette as a small arrow or dart, flechettes are projected or released by some type of anti-personnel munitions.

So I would argue that while they are physically the same in appearance, flechettes are anti-personnel and penetrators are armour defeating/piercing.

The handbook does not provide a definition of penetrator. However, it does provide a definition of Shot - A kinetic energy shot is an un-fuzed projectile, which can be in the form of:
A single solid mass of metal
Composite construction launched as a single entity
Composite construction launched as a penetrator with a discarding support sabot
Composite construction launched as a fin-stabilised long rod penetrator with a discarding sabot support.

So from this, it appears the difference may also be flechettes are one piece construction of steel, whereas a penetrator is composite with a variety of components of different strengths and hardness to prevent the penetrator from ricocheting or shattering on impact with an armoured target.

Just my 2 cents and not definitive by any means.

 

[SG500]

Agreed...

'penetrator' is a word of description of function, and is equally ambiguous, since most things mentioned on this forum are designed to penetrate.

I watched a program on the TV a couple of years ago where they were discussing the effect of depleted uranium following the impact of "long rod penetrators" i.e. the middle bit (I'm trying not to use confusing terminology here) from the 120mm APFSDS projectile. That seemed to make it a lot clearer as opposed to all the other things mentioned on the forum that are designed to penetrate.

Dave.

 

[HAZORD]

I'm leaning toward the Flechette is used on flesh and penetrators or darts are used on other targets, but a flechette could be a dart.

To comment on Dave's post, Long-Rod penetrators is a technical way to specify the design of a dart. The length-to-diameter ratio has a major effect on penetration due to the mass behind the small cross section. I'm thinking the "Long-Rod-Penetrators" description would be referring to the latest designs with especially long rods as in the most advanced 120mm ammo.

 

[Tony Williams]

The French word "flche" means arrow. Flechette therefore means "little arrow". I wouldn't call a 120mm long-rod penetrator a "little arrow", it's a thumping great big one!

I agree that "flechette" should be used for the small, anti-personnel darts ("dart" being short-hand for "very high L/D ratio fin-stabilised projectiles") which may be fired singly from rifles (but only experimentally, so far) or in bulk from larger-calibre guns (from 12 gauge upwards to heavy artillery).

Penetrator refers to something designed to defeat armour; in terms of dart projectiles, that means APFSDS. The smallest in service (IIRC) is in 25x137 NATO calibre, although there have been many smaller experimental ones (most notably the Steyr 15.2mm AMR).

 

[US-Subs]

Not necessarily fin stabilized. Remember that our APDS rounds started out without fins. If you tale that into account then you need to drop it down to 7.62 or less. SLAP, etc. Plenty of small flechettes were finless as well, mass stabilized, Javettes, Lance Jets, etc. Likewise the development never stops, drop back into the flechette thread and look at the Passive Attack Weapon System (PAWS). Several different sizes from nearly normal small size to full-scale roof-to-basement building penetrators. Some things aren't easily stuffed into a definition.

 

[navyman]

Early type fletchette.

Hello,
Here's a pick of a repro WW1 fletchette, they were thrown out of biplanes over enemy trenches. It's five inches long, so definitely a 'little arrow' ! There were many variants, some looked like six inch nails with the end hammered flat to make a crude fin and to make them point heavy. I was told that they were capable of penetrating the top of a steel helmet........big headache for the recipient if that's true?
Cheers,
navyman.

 

[Tony Williams]

Not necessarily fin stabilized. Remember that our APDS rounds started out without fins. If you tale that into account then you need to drop it down to 7.62 or less. SLAP, etc.

I don't agree with that - APDS is spin-stabilised and such rounds are not called flechettes - that name refers specifically to fin-stabilised rounds where gun-fired ammunition is concerned.

 

[AmmoResearch]

I don't agree with that - APDS is spin-stabilised and such rounds are not called flechettes - that name refers specifically to fin-stabilised rounds where gun-fired ammunition is concerned.

I believe that APFSDS is the correct designation for a fin stabilized 'penetrator', while APDS designation is used for rounds such as SLAP...am I correct?

I have also seen APDS to more generally describe any AP round that has a sabot (to which the fin stabilised version would be a subset). Much like speaking about 'armor piercing' (AP) ammunition would include API, etc.

 

[HAZORD]

Well, the SLAP round is an APDS, as it is designed to be an armor penetrator and the sabot does fly off once it leaves the muzzle, but the APDS design goes back at least to WWI 37mm projos, whereas the SLAP design is only around 25 yearrs old. APDS can further be divided into the type of sabot used, if it is a "pot" style or "petal" style, where the pot falls away behind the penetrator, and the petals peel off the side like a modern APFSDS-T Dart/sabot combination.

 

[US-Subs]

I don't agree with that - APDS is spin-stabilised and such rounds are not called flechettes - that name refers specifically to fin-stabilised rounds where gun-fired ammunition is concerned.

I can agree that APDS should not be referred to as flechettes, in my opinion neither should their fin stabilized brothers. But what about the so called "mass stabilized flechettes" and the other similar finless items mentioned?

I haven't seen any definition that requires fins, though admittedly they are more common - When you say " - "that name refers specifically to fin-stabilised rounds where gun-fired ammunition is concerned", this implies that there is in fact a formal definition? At least for small arms?

 

[Tony Williams]

I can agree that APDS should not be referred to as flechettes, in my opinion neither should their fin stabilized brothers. But what about the so called "mass stabilized flechettes" and the other similar finless items mentioned?

I haven't seen any definition that requires fins, though admittedly they are more common - When you say " - "that name refers specifically to fin-stabilised rounds where gun-fired ammunition is concerned", this implies that there is in fact a formal definition? At least for small arms?

I doubt that there is any formally agreed definition, but I've only ever seen the term "flechette" applied to small fin-stabilised anti-personnel projectiles. Of course, there are fins and fins - most of them stick out beyond the diameter of the body of the projectile (the most effective solution for accuracy), but some are kept at body diameter by thinning down the back of the body - in which case it can be difficult to distinguish between fin and mass stabilisation. I've never seen these used in small arms, though - only for convenience in packing them together in large-calibre rounds where accuracy doesn't matter much anyway because dispersion is useful, as long as they all head in vaguely the same direction!

 

[Tony Williams]

Well, the SLAP round is an APDS, as it is designed to be an armor penetrator and the sabot does fly off once it leaves the muzzle, but the APDS design goes back at least to WWI 37mm projos, whereas the SLAP design is only around 25 yearrs old. APDS can further be divided into the type of sabot used, if it is a "pot" style or "petal" style, where the pot falls away behind the penetrator, and the petals peel off the side like a modern APFSDS-T Dart/sabot combination.

I wasn't aware that APDS was used in WW1. The first work on it that I know of was by Brandt in France in the late 1930s. This was transferred to Canada when France was overrun in 1940, and from there went to England where it was perfected (or, at least, made workable enough to be useful) for service entry in 1944, in the 6 pr and 17 pr tank/anti-tank guns. The UK remained the main user of APDS until the British 105mm L7 (arguably the first service tank gun specifically designed around APDS) became adopted as the NATO standard in the late 1950s.

The tank APFSDS rounds were developed from APDS through following a logic chain which went something like this: armour penetration by solid shot is essentially a function of the energy delivered for every square millimetre of the penetrator's frontal area. Therefore, for any given weight and velocity, the narrower the projectile, the better it will penetrate. But the narrower it is, the longer it has to be, so you rapidly exceed the length limit for spin-stabilisation, which is roughly six times the diameter. Therefore it is necessary to switch to fin-stabilisation for the very long, thin APFSDS projectiles. If you're not using spin-stabilisation, barrel rifling becomes a nuisance, so it makes sense to use a smoothbore gun. The first in the field with APDSFS were the Russians, in the 1960s.

The British (and Indians) are an exception in sticking to rifled 120mm tank gun barrels. They do this because they like to use full-calibre HESH rounds, which are more accurate with spin stabilisation. They get around the problem of the rifling destabilising APFSDS rounds by fitting the sabot with slip rings so the projectile isn't spun very much. There is a small loss in APFSDS performance, though.

The SLAP rounds are just APDS which uses a plastic sabot rather than the original light-alloy type. Obviously the lighter the sabot the better because its weight just reduces the velocity of the projectile.

 

[paul the grenade]

maybe fin stabilized rounds are older that you all think. heres a pic if a cannon from 1326 firing whats thought to be a metal dart.:tinysmile_grin_t:
cheers, paul.

 

[Tony Williams]

Yes, I know - below is a picture of a full-sized model at the Artillery Museum. But a fin-stabilised round is not necessarily an APFSDS, just as a saboted round is not necessarily an APDS (crude wooden sabots were sometimes used in 18-9th century smoothbore guns).

 

[AmmoResearch]

maybe fin stabilized rounds are older that you all think. heres a pic if a cannon from 1326 firing whats thought to be a metal dart.:tinysmile_grin_t:
cheers, paul.

They go back to nearly 10,000BC with the invention of the arrow, but the use of the sabot to use the larger caliber barrel to fire a subcaliber round is a far more recent technology.

Is it perhaps safe to say that there is a LOT of ambiguity between flechettes and other items in terms of definition (similar to the gun/cannon analogy). In some cases it appears that they are near synonyms.

 

[E-tech]

They may not be so similar actually- aside from the fins on modern models, there is a big difference in construction and mission.
No one expects a small-arms or gravity propelled flechette to penetrate armor, and no one really plans on using 120mm APFSDS rounds against a single person wearing body armor....
Flechettes also seem to be made pretty simply- a single piece of metal hammered into a sharp point with some integral fins.
Penetrators are optimized for material density with metals like tungsten or depleted uranium- but, only in the penetrator portion, which usually has a dull, rounded point, protected by a ballistic windshield with a very sharp point, made of a softer metal, that acts like a "shock absorber" to prevent the hard material of the penetrator itself from shattering on impact with armor.
Optimized design for hard-material defeat, compared to simple metal designs- maybe this, and the target intended is the defining point between the two.....

 

[SG500]

no one really plans on using 120mm APFSDS rounds against a single person wearing body armor....

Now that would be nasty!
Dave.