Can X penetrate Y?

December 28, 2008 7:05 PM

DensityFilter: What happens when you throw a nickel really fast at the fuselage of an F-16?

I remember an old issue of The Uncanny X-Men, in which the flight-enabled, super-strong Rogue is battling some fighter jets. If I recall correctly, she throws one or more coins at the jets. The coins penetrate the planes, and they explode, or are otherwise disabled.

In reality, would this work? Is it strictly a question of the relative density of the coin and the jet's fuselage? How much does the coin's inertia matter? I got a C+ in Physics 11, or I'd answer this myself.

posted by dbarefoot to science & nature (18 comments total)

It's not really a question of relative density. The aluminum skin of an aircraft has a certain strength and impact resistance. It will take a certain amount of energy to break the bonds in the material to penetrate it. A projectile's energy is the product of its mass and velocity squared. So if you hurl anything fast enough it will do damage.

The problem with coins is that their surface area to weight ratio is pretty low, so they lose lots of momentum to aerodynamic drag (that's why throwing coins off a tall building isn't so dangerous). This would not be a problem if Rogue had the ability to continuously push the coins during their flight.
posted by Popular Ethics at 7:17 PM on December 28, 2008

The coin's inertia is what it's all about. If she throws them fast enough, they'll penetrate the skin, and also be hot enough (through the friction with both the air and the skin of the aircraft, and then the walls of the tank) to ignite the fuel.

Oh, on re-reading, I'm assuming you hit a fuel tank, for the cool explosion.

Still, you can make it work with enough inertia.
posted by pompomtom at 7:29 PM on December 28, 2008

Considering the airflow around the skin of something like an f-16 flying at speed, there is a high chance something like a coin would just be caught up in that airflow and carried off around the aircraft without striking much more than a glancing blow.

On the other hand, one wonders what might happen if something like a jar of coins were thrown into the air intake of a jet engine. Maybe they're small/soft enough not to do much damage, but maybe not. Something like a goose or a duck can do a fair chunk of damage to a jet engine if it's sucked in that way, so coins--who knows? Could be substantial . . .
posted by flug at 7:33 PM on December 28, 2008

(NB: you don't actually need to penetrate the skin to take the vehicle out: British HESH anti-tank rounds were designed to take out tanks without actually piercing the armour. The point is to simply transfer the energy into the target - so again in your scenario, it's more about the inertia than the density of the projectile.)
posted by pompomtom at 7:35 PM on December 28, 2008

Think about a bullet. It's shaped a little differently, but the point is the same. A small metal object could penetrate the relatively weak skin of an aircraft. I doubt any human could throw a nickel hard enough to get through a fuselage, but if the coin could be moving fast enough, I'm sure it's possible.

As for disabling or destroying the plane, I suppose it would depend on what else the coin hit inside the aircraft. The plane could fly along with a hole in it, no problem. If the coin ruptured a fuel line or some other critical part of the aircraft, then it might cause it to explode or be disabled.
posted by JuiceBoxHero at 7:37 PM on December 28, 2008

A coin would certainly damage a jet engine is thrown in. Since a F-16 only has one engine it'll have to be shut off and the pilot has the fun of a dead-stick landing in plane that doesn't glide very well. It certainly won't explode in an exciting way but the plane will be out of commission until the engine is replaced.

Read more about FOD here and here.
posted by Confess, Fletch at 7:46 PM on December 28, 2008

Here is video of an actual, real-life fighter jet getting taken down because Nature lobbed some blobs of meat at it at very low speed (<250mph).
posted by ROU_Xenophobe at 7:54 PM on December 28, 2008

Thanks to lousy writing, superheroes often seem to warp space-time around them to let them achieve things that even someone with their powers should not be able to do. Throwing stuff at ultra-speed is one of those things.

Superman, like several other Flying Bricks, has super-speed as well as super-strength. So he, or a speedster like the Flash, could plausibly throw a rock, a coin, or a cupcake for that matter, fast enough that it'd punch a hole through, or just violently annihilate, any non-superpowered object it hit. The thrown object might just be a cloud of superheated gas by the time it hit the target, but it'd still do the damage.

(See also Superman's mysterious breath powers - super-blowing, and super-cold-blowing. His ability to blow up a typhoon on demand is strange - where's all the air coming from? The comics give some cock and bull story about how his lungs can compress the air they contain - thereby explaining the cold breath, because as air decompresses it becomes cold; never you mind why he doesn't blow cold all the time, or where the heat from compressing the air went. How cubic kilometres of air get into Superman's lungs in the first place also remains unexplained.)

Lots of superheroes are super-strong but only able to move at normal human speed, though. Rogue is one of those; she's got a few Flying Brick powers she soaked up from Ms Marvel, but I don't think those include super-speed. Characters like this may be able to throw a 40-kilo dumbbell as far as a baseball pitcher can throw a rock, but they shouldn't be able to turn bullet-ish objects into actual de-facto bullets, because you can't throw anything any faster than you can move your hand.

Heroes that can fly could fly at top speed and then fling something ahead of them at top-speed-plus-throwing-speed, but you've got to be super-tough to fly super-fast without dying if you hit a bird - another point that's glossed over in most comics. If you're super-tough, you'd think you could just fly through the target rather than toss mundane objects at it.

Super-strong heroes could also throw heavy things much faster than they could by hand if they used an appropriately strongly-built sling-like device. But that'd give them an attack like a 18th-century cannon, not like a handgun.

Yes, I do spend quite a lot of time thinking about things like this. Doesn't everybody?
posted by dansdata at 8:02 PM on December 28, 2008 [3 favorites]

Trust me, you're never going to get a better or more authoritative answer than this:

Quantum Ravioli

...in which a physicist answers the question "Would a chunk of metal (can of ravioli) impacting another, larger, rest mass structure (star destroyer) produce an "explosion" effect, or simply punch an appropriately shaped hole as it passed through?"
posted by NortonDC at 8:09 PM on December 28, 2008 [2 favorites]

Seconding the FOD explanation. And it actually could cause the engine and subsequently the plane to explode if damage occurred to the turbine and or turbine blades such that the engine becomes rotationally unstable and then catastrophically fails.

Come to think of it, I actually had a scenario like that once...
posted by squorch at 8:24 PM on December 28, 2008

Assuming that we ignore dansdata's excellent analysis.

A sufficiently fast nickel is identical to a bullet. (Most) Aircraft skins aren't bulletproof. It would penetrate. The effects of the penetration, as with a bullet, depend on what it hit inside the airplane. A modern fighter, as I understand it, hasn't got a lot of free space inside it. It's likely to hit something necessary. I'm sure most pilots would disengage and return to base if their plane weren't just spot on.
posted by Netzapper at 9:14 PM on December 28, 2008

that's why throwing coins off a tall building isn't so dangerous

It isn't? I'd always heard that dropping a penny off the CN Tower would go right through a person.
posted by Manhasset at 9:20 PM on December 28, 2008

It isn't? I'd always heard that dropping a penny off the CN Tower would go right through a person.

No, it's not. MythBusters covered this in one of their very first episodes. Here's a quote from the wiki:

"A penny's terminal velocity is too low and its mass too small for it to penetrate human skin - let alone penetrate concrete or asphalt. Even when fired from a rifle, the penny was unable to penetrate concrete. It did, however, decimate the ballistics gel dummy."
posted by joshrholloway at 9:31 PM on December 28, 2008

A coin would certainly damage a jet engine is thrown in.

Not necessarily. One of the tests required by the military before they'll accept a jet engine for production use is the chicken test. They have a running jet engine on a test stand, and use a rail gun to throw a dead chicken into the air intake of the engine at about 400 MPH. (They buy whole chickens from the grocery store for this.) The engine has to survive and keep running.

The reason for that test is that it simulates a bird strike, a case where the engine sucks a duck or sea gull into the air intake. That's a pretty common event for this kind of jet and they don't want to lose airframes when it happens. (For the Navy, especially sea gulls.)

A coin is a lot smaller and while it's possible it might damage a small number of rotor blades, even that isn't certain. And losing rotor blades doesn't necessarily cause the engine to fail. If the engine were that fragile, the military would lose a lot of airframes to engine failure. For $40 million per jet, they want them more sturdy than that.

As to hitting the fuselage, these kinds of jets are also designed to stand up to machine gun fire and shrapnel. Anything that flies can be shot down, but it takes a lot more than one bullet to do it when you're talking about American combat jets. They put armor around critical components, and the fuel tanks are self-sealing.
posted by Chocolate Pickle at 9:36 PM on December 28, 2008

Chocolate Pickle - that's bollocks, I'm afraid. I don't know of any military engine that can take that kind of punishment. I've seen the damage done by small pebbles sucked into a Pegasus turbofan, a large/midsized bird will rip fan blades off the rotor and dump them down the engine to cause further damage.

You may be thinking of the infamous canopy test, where they fire the chicken at the aircraft cockpit canopy to ensure a birdstrike won't cause penetration (up to certain speeds, anyway). There's an apocryphal tale of nation 1* copying nation 2**'s chicken-to-the-canopy test and destroying the cockpit; when asking nation 1 for advice, the answer comes back as a simple four word response:

"Defrost the chicken first".


* Insert according to nationality and prejudices: US, UK, France, Italy, Canada etc
** Insert according to nationality and prejudices: US, UK, France, Italy, Canada etc
posted by Nice Guy Mike at 3:30 AM on December 29, 2008

As to hitting the fuselage, these kinds of jets are also designed to stand up to machine gun fire and shrapnel.

Ground attack aircraft like the A-10 and the AH-64 are armored to withstand a moderate amount of small arms fire.

But fighter planes, especially previous generation aircraft such as the F-16 (which entered service 30 years ago!!!), tend to be very thin-skinned.
posted by randomstriker at 4:00 AM on December 29, 2008

Someone should write a book called the physics of Chris Claremont. I remember his run having a lot of fun little 'facts' like this.

I think you can get over the terminal velocity issue if you throw the coin sideways and if the coin is stable to not flip in flight. Your surface area is much smaller when thrown like a skipping stone. I would imagine Rogue could toss a coin that would travel at a fraction of the speed of a bullet and hit a plane to pierce its skin, but the amount of damage from this kind of attack is minimal.

Im guessing the author thinks a handful of nickels is a lot like Anti-Aircraft fire. AA fire works because the rounds are actually little bombs that are launched at the aircraft. These little bombs go off spreading shrapnel in all directions. This makes it much easier to hit the plane. Or its a 20mm cannon with a high rate of fire. Even then its difficult to shoot down a fighter yet.


I dont see how Rogue, even with all her superpowers, could have the accuracy to hit a plane. If this is a given then I could see some damage from the nickels, but not enough to actually shoot down the plane like AA fire does. It would do some damage and a lucky shot is still a lucky shot, but generally I would think the pilot could launch a missile at her before she got a chance to throw another handful of change. This assumes that sci-fi figher jets have missiles that can hit flying humans. I think the idea here isnt if enough shrapnel will disable a plane (yes it will) but if there is enough time and damage from this kind of attack to disable the plane before the plane disables you or fininishes its mission.
posted by damn dirty ape at 8:11 AM on December 29, 2008

Comic book nerd here, It was a 1/2 dollar
posted by kanemano at 4:04 PM on December 29, 2008 [1 favorite]