AP rounds fired by arty

[Marcello]

Yah, 5kg sabot dart traveling at 1500 m/s isn´t going to expend any enrgy going through a canvas or a windshield or some regular car bonnet.

Pretty much.Most of the mechanisms that an APFSDS uses to inflict damage on a tank, from spalling to thermal effects, don't work well against thin skinned vehicles (bar hits on the engine and similar of course).Artillery cluster munitions should be a different matter however, as these use explosive bomblets.
Against tank fired HEAT rounds it should boil down to how much the fuze is sensitive and if it impacts something hard enough to trigger it.If that happens then you have a very dead Land Rover.

[PlasmaKrab]

Regarding the sensitivity of HEAT fuzes, I'm not sure that the material hit is very relevant at the impact velocities considered.
Think about the "necklace" of the Merkava Mk3/4: there are simple weighted chains dangling from the turret basket, and they are supposed to (and I guess reliably tested to do so) detonate RPG rounds at a standoff from the turret.

I'm out on a limb with my physics here, but I'd say that the inertia of the chains (in this example) prevents them from being significantly displaced before the fuze fires.
The same thing can probably be said of any unarmored vehicle bonnet, given the material is hard enough.
Admittedly, a canvas top has a chance of folding around the fuze probe, or ripping open, letting the fuze tip through, and stop only the thin and conductive warhead cover,making the round a dud. As far as I know that was how RPG fences worked back in Vietnam.

Just my 2c, don't ask me to back that up with calculation!

[Mobhack]

Note the ball on the end of the chains on the "necklace" - these are needed to provide enough resistance to trip the fuse, I think?. Modern HEAT fuses are designed to not trigger on twigs and other foliage - the ball on the chain end will likely make the thing think the impact is more substantial than some piece of incidental shrubbery.

As to chicken-wire RPG fences, these stopped the rounds by trapping them in the gaps (there was not that much forward velocity) without triggering the fuse, and also by shorting the fuse if it touched the wires as well (early RPG used a crush pezio-electric fuse). Or it could also trigger the fuse - hence the need for the chicken wire to be some distance from the protected vehicle. All if I remember correctly - the details were in the old 1976 Jane's Infantry weapons section on the RPG, but I foolishly sold that off at a second-hand book shop back in 95 or so. Exellent reference work - but nowadays fiendishly expensive .

Anyway - the early RPG's simple pezio electrical fuse was a weakness and there was a proposed "electrical" defence which generated a field to set these things off at a certain distance from a field generator. It was just a bit big to cart around (so would only have been good for static observation posts etc), and a simple change in fuse design would have made the thing obsolete. Later RPG fuses tend to be more sophisticated.

Oh - and another way to defend against RPGs was to fight on a windy day - the thing tended to "weathercock" at longer ranges as the wind acted on the extended stabilising vanes at the rear end of the round, and so it would end up flying more sideways than end-on..

Cheers
Andy

[PlasmaKrab]

Thanks for the update, Andy, I didn't know the fuse technology had changed so much over time.
Considering this, most old HEAT warheads (say, up to and including the PG7VM) should go off at a whim, even (case considered here) when hitting the canvas top of a soft-skin vehicle. And I guess this should also be the case for most first-generation ATGMs (AT-3, SS-11, Cobra, Vigilant...) which have equivalent technology and similar velocities (not above 1000 ft/s).

Now we agree about the way RPG fences used to work, by trapping the fuse tip between the wire and in some cases crushing the conductive warhead cover. My point was that with a high enough velocity and an insensitive enough fuse, a vehicle canvas (or even bonnet) could act the same way if the fuse tip managed to rip through without detonating.

If you want some more RPG references of the olden days, I've found this TRADOC manual from 1976, building on Vietnam and Israeli experience, with info on RPG fences, weathercocking and riding the wind, and of course those damn aiming procedures.
Probably not worth the Jane's data, but worth a look for everyone.