Can you destroy a hundred million dollar fighter with a hand grenade?

December 24, 2009 4:22 PM

In a lot of movies, large fighter jets and other aerial battle vehicles are destroyed by using just a small explosive to their air vents. Are fighter jets in real life so vulnerable that even a hand grenade can bring them down?
posted by zain to Technology (19 answers total)

Well, actual fighter jets don't actually encounter a whole lot of hand grenades at 10,000 feet.

Fighters (and bombers, for that matter) are built for light weight; if you armor them up enough to withstand a hand grenade, they'll still get wrecked by the kind of ordnance another jet is carrying, except it now it can't fly at all, because it's carrying its weight in steel plating.
posted by Tomorrowful at 4:30 PM on December 24, 2009

I'm not sure they would detonate dramatically on the ground while the hero dives for cover. I have seen engines destroyed by as little as a loose bolt getting sucked into the intake. The first thing you come to on the inlet side of a jet engine is a very high speed rotating fan. It doesn't take much damage to rotating machinery to unbalance it or make parts with close tolerances come into contact. That plus a bunch of extra shrapnel in there would make the engine eat itself when it was operating. A hand grenade would do the trick nicely.
posted by ctmf at 4:36 PM on December 24, 2009

Does this question come from that silly movie Avatar? If something explodes inside of a jet engine (it's not clear to me that the engines into which grenades were tossed in Avatar are jet engines though), the engine would quickly lose power and that plane would crash.
posted by dfriedman at 4:43 PM on December 24, 2009

Having worked in the aerospace field, it's been my experience that bird strikes are a far bigger threat, and a lot of testing is performed specifically for these scenarios. Some examples of the tests in action include (Warning: videos of birds being shot into turbines): 1,2,3.
posted by Cody's Keeper at 4:45 PM on December 24, 2009 [2 favorites]

Response by poster: Yeah, it was the movie Avatar that prompted me to wonder. At the time, it seemed totally unbelievable that there's no defense against throwing something at a fighter jet's vents to destroy the aircraft.
posted by zain at 5:12 PM on December 24, 2009

There is a defense against throwing something into a fighter jet's vents to destroy the aircraft, you secure the airfield from which it takes off and lands.
posted by Good Brain at 5:16 PM on December 24, 2009 [3 favorites]

Best answer: The general term for the effect is F.O.D, which stands for Foreign Object Damage. More info here and here.
posted by Confess, Fletch at 5:47 PM on December 24, 2009

Best answer: At the time, it seemed totally unbelievable that there's no defense against throwing something at a fighter jet's vents to destroy the aircraft.

It all depends on the design of the aircraft. The A-10 Thunderbolt is designed for close air support of ground forces, so its entire design reflects that, from being able to carry a shit load of weapons to being built to withstand a lot of punishment, including armor piercing rounds and small arms fire. It does that well, based on an incident in the Iraq invasion of 2003 where one had its fuselage and wing severely damaged, but the pilot was still able to fly and land the craft successfully because the craft was designed in a way that such damage and loss of systems was anticipated and multiple back up systems were put into place to make it still functional.

So could an aircraft survive a hand grenade thrown in its air vent? Probably, if the creators of the craft took that scenario into account and came with ways to defeat or minimize such damage.
posted by Brandon Blatcher at 6:39 PM on December 24, 2009

No idea how the engine felt, but a human being has gone thru a jet engine, and survived
posted by nomisxid at 6:54 PM on December 24, 2009

There's no defense against a pterodactly-mounted half-human half-smurf throwing grenades into the vanes of the current generation of imaginary future airships. I guess they could have put a wire mesh to protect the vanes, though (they weren't jets), but then the movie would have a sad ending.
posted by jewzilla at 7:00 PM on December 24, 2009 [4 favorites]

To add to Brandon's post the A-10 has 2 engines for a reason.
posted by Max Power at 7:55 PM on December 24, 2009

a human being has gone thru a jet engine, and survived

Actually, he was sucked into the engine's air intake, the engine shut down, and he was able to crawl backwards out of the intake.

Could a person go through a jet engine and survive? Nah. Too many small pieces, impossible to sew them back together.
posted by exphysicist345 at 8:17 PM on December 24, 2009 [4 favorites]

A grenade has a fair amount of destructive power in this scenario. Not because of the blast (there are certainly similar, though steady-state, forces elsewhere in the engine) but because of the mess it makes. Even designed with durability in mind, a modern jet engine has a lot of pieces all under high loads with high temperature differentials across them. Once one little thing deforms or breaks, it gets out of hand very quickly.

A diagram to explain how delicate the whole assembly really is. Imagine it all spinning very, very quickly and throwing in a fist-sized steel ball. Good shit is not going to happen.
posted by milqman at 11:46 PM on December 24, 2009

It's a matter of design, but by and large, yes. Fighter craft engines are designed around the idea of pushing air through them as fast as possible to make as much thrust as possible, not with being durable to foreign object damage. Where they operate, the environment pretty much precludes the idea of having to deal with solid chunks of things entering the turbine. Which is one of the reasons there are constant walkdowns to scan aircraft carrier decks for any foreign matter that might be sucked into a turbine during aircraft launch.

Also, let's not forget Captain Sully and his landing in the Hudson in January because his plane ate a couple of birds and lost both engines to exactly this kind of damage.
posted by barc0001 at 12:30 AM on December 25, 2009

Captain Sully - totally threw me as the lead character in Avatar is called Sully
posted by A189Nut at 7:35 AM on December 25, 2009

The large military transport planes like the C-130 use turboprops because they are less vulnerable to random rocks and debris encountered on unprepared runways like fields or grassy areas, among other reasons.
posted by Rhomboid at 9:35 AM on December 25, 2009

Best answer: "The large military transport planes like the C-130 use turboprops because they are less vulnerable to random rocks and debris encountered on unprepared runways like fields or grassy areas, among other reasons."

I'm gonna have to offer a contrary viewpoint on that one as it's somewhat of a misconception... the C-130 uses an Allison T-56 engine, the same as used in the E-2C Hawkeye. I only know this because I am/was a Naval Aviator who flew around in them. Turboprops are actually jet engines that rotate the propeller. The propeller produces the vast majority of the thrust (4000 lbs vice 800 approx), but it's turned by a 14-stage compression cycle lighting off and turning a shaft linked to the prop - think of a big volume of air being compressed by smaller and smaller fan segments until it gets to the ignition chamber, which in turn turns the prop through a reduction gear box.

Back to that thrust: The engine is extremely efficient at carrying heavy loads as compared to a fighter jet. It also has a better fuel burn rate - it's obviously not built for Hornet-like speed. That makes it good at operating at a moderate altitude, with a heavy payload, for an extended distance when compared to a fighter.

The intake of a turbo-prop engine is just as prone to FOD than any other jet engine. One difference with the C-130 is that the engine is VERY high off the ground when compared to fighter aircraft. But then, even C-130's take off from groomed runways - not always PAVED runways, but groomed ones. That makes a huge difference.

In other words, the turboprop issue has little to nothing to do with FOD avoidance. On the deck of an aircraft carrier, E-2C's (using the same engine family as the C-130) FOD out just as often as the fighter jets.

Here's an image that breaks down the differences between types of engines better than I can probably explain it... just keep in mind the common component of the compressor stages in all types of engines - all easily susceptible to FOD.

http://www.solarnavigator.net/aviation_and_space_travel/aviation_space_images/jet_engine_diagrams.jpg
posted by matty at 1:05 PM on December 25, 2009

Previously
posted by Confess, Fletch at 9:53 PM on December 25, 2009

Some aircraft (MiG-29, Su-27) have screens over their intakes (or alternate intakes) so they can operate from rough or unprepared fields. (The screens are retracted at altitude because they reduce the performance of the engine.)

Example: the MiG-29 has doors that block off the main intakes, and louvres on the upper surface that open. The upper-surface intake is much less likely to ingest debris.
posted by phliar at 5:58 PM on December 28, 2009