SCENARIO: A transport plane is transporting some artillery shells. Suddenly, one of the crewmembers is a terrorist, so when the plane is flying over a city, he takes the shells out of their boxes and drops them one by one onto the city, facing downwards.
The plane is flying at 5 kilometers above the city, and the shells hit: a heavily crowded rugby field, a skyscraper rooftop, a horse racing field and a radio tower.
SCENARIO: A military base has been constructed in a war zone. An opened box of artillery shells lies on it’s side inside the base, and a sleeping soldier on a chair with a pack of beer next to him is near the box, which is hidden from sight by various objects. A man outside with a jetpack jumps over the base’s wall and steals five HE artillery shells and flies off. Suddenly, he spots a group of 5 M113A2 APCs patrolling around the base.
The man flies over them at a altitude at 1 kilometer and drops the shells with incredible precision on the rooves (roofs?) of the APCs.
Do the shells explode? If not, what other damage would they cause in both scenarios? I imagine they would make quite the dent in the second scenario. NOTE: The shells are of excellent quality and well-designed.
The shell first has to undergo the proper setback caused by the high acceleration of being fired. This releases the next mechanism. Now the shell must spin at very high rpm (over 20,000) before the impact trigger is armed. Nothing happens in your scenarios.
Looks like none of them would explode as artillery would be expected to. They might explode as a result of the impact setting off the propellant, but that’s going to be minor compared to the shell itself going off as expected.
An APC hit from a kilometer up with a non-exploding shell is still going to have a whole punched straight through it. APCs being what they are, it might well strike something else that’s inclined to go boom, so it may well be a very bad day for everybody involved.
“How could it put a hole straight through the APC? It hits the roof, but that’s still a fair amount of metal and material it goes through.”
From kinetic energy alone. Heck, a bunker buster bomb penetrates many, many feet of earth or even concrete before it explodes. If you have the particulars of this shell, we can calculate how much kinetic energy it will have.
“Anyway, the APCs in question have flak cannons mounted on top”
No they don’t. Picture a lightly armored mini van. Do you know how large an artillery piece that fires anti-aircraft round is? They can’t hit a dropping shell anyway.
Now a radar guided Phalanx might, but they weigh 15,000 lb without the ammunition.
I don’t think that last part is necessary – given the shape of the shells, the air resistance will automatically turn them to point downwards (unless dropped close to the ground).
It’s only a kilometer, though. Let’s say it’s a M107, which only weighs about 42 kilograms, about less than twice that of a expensive desktop computer.
Okay, the APC has a M61 machine gun on top instead with incendiary rounds that are set to go off when the rounds reach a certain prerequisite that is useful for annihilating large numbers of tiny, densely-packed, twitching “aircraft”.
As long as you are designing a fantasy piece of military equipment, you might as well design some lightweight, 2" thick, titanium-beryllium-ceramic armor that can withstand the impact.
The artillery pieces which normally fire the rounds have rifling to gyrostabilize the shell so it keeps going nose first when shot nose first. If it would naturally go nose first when fired at any angle (with respect to gravity) you wouldn’t need to waste propellant energy on every shot by having rifling.
We know a smooth bore mortar round with fins will drop nose first because it needs to have strong positive nose first course stability without spin. But a rifled shell doesn’t have to, and doesn’t necessarily. We could be sure it would drop nose first if the internal weight distribution was nose heavy enough, not just by aerodynamics. But for typical modern HE shells the shell wall at the base is relatively thicker than at the nose, and shell wall is much denser than the explosive filler: they are tail heavy.
For example in this case of an M107 155mm shell (a common type), the shell’s length is given as 698mm and the center of gravity 459mm back from the nose.
Anyway I agree just dropping it nose first doesn’t mean it will stay nose first, and same for any other attitude at which you initially drop it. It might not be course stable at any attitude and naturally tend to tumble.
Aside from typical fuse safety measures, they shouldn’t even have a fuse installed in either of those scenarios. Typically one of various types of fuses get screwed into the nose before firing. That means no detonator.
You know, mythbusters did a segment on shooting hand grenades out of the air. So I’m going to say that based on that, it’s not entirely accurate to say that artillery shells with their fuses in won’t go off under any circumstances.
TLDR, they found that if you shoot an hand grenade with a high powered rifle dead center, the bullet will set off the blasting cap inside and the grenade will go off.
So there might be scenarios where a live artillery shell, when subject to exactly the right kind of impact (like dropping it out of a plane and it impales itself on a metal rod on the ground or something), might have it’s internal blasting cap explode from the shock and thus set off the shell. It does not require the detonator to arm, the internal blasting cap is made of sensitive explosives.
I would imagine this is why artillery shells are stored without the fuses installed until right before use.
Interesting. This is arty only, right? What’s the highest RPM tolerable by winged or finned air-dropped bombs? Or am I confusing bombs with missiles? (And if wings are deployed only in terminal phases.) Which raises the question of their arming mechanisms.
While I’m at it, whats the RPM of rifle or handgun bullets in flight?
Missiles’ mechanisms are all over the map. But since a missile is guided, it has electronics on board. So it’s trivial to implement a timer that arms X seconds after the launch signal. Where X is chosen as just big enough to get the missile far enough away that if the fuze fires instantly when armed the warhead won’t kill the shooting aircraft.
The maximum energy of your 95 lb shell dropping 3200 ft will be nearly 300,000 ft-lbs. This is you ignore air resistance and it reaches 450 ft/sec velocity. But you can’t do that.
It’s pretty streamlined so perhaps it reaches 3/4 of that velocity. So, 160,000 ft-lbs. of pointy thing landing on the roof. You’re gonna need a bigger vehicle.