Cruise missile graphite engine

Cited as the existence proof that brittle-material jet engines can be built — when the engine only has to last an hour, the inspection problem becomes tractable. Graphite is tougher than most ceramics; coatings prevent burn-up.

So as long as you make a jet engine with no imperfections larger than half or one-tenth the size of a human hair, it'll run at great temperatures. We've already done that. It's called a cruise missile. The cruise missile engine is made out of graphite. Graphite's not particularly tough, but it only has to last for an hour, and the bigger problem is keeping it from burning up in an hour. They put coatings on it. But graphite's tougher than most of the ceramics.

Cited in passing as another "limited-life engine, hour-and-a-half service" parallel to NASCAR magnesium use.

Yeah, a NASCAR vehicle is worth how much, about a half a million to a million dollars, right? You can afford it, and you only have to drive it for 500 miles. Sort of like a cruise missile — it has to last for an hour and a half, the engine in a cruise missile, limited time life. So NASCAR. But there are actually a lot of people driving around on magnesium wheels — mag wheels — on a car. Turns out most mag wheels today are actually aluminum. In the old days they were magnesium, and they would start pitting after a year. They'd put clear coat on them and all this other stuff, and they would still start pitting when they're made out of magnesium. So they mostly make them out of aluminum, but they'd love to make them out of magnesium, and they did make them out of magnesium.

Cruise missile rocket motors made of carbon composites because life requirement is short.

We do just the spray, because we wouldn't want to spend $2 million for something that we were going to throw away after one use — less than an hour's use. You're only using it for about three and a half minutes. It's the four or five tests you do to make sure it's okay that get the life. So we just do the spongy white zirconia. I haven't ever worked on them, but it's my understanding that cruise missile rocket motors are made out of carbon composites.

Designed to last only 2 hours because the missile is then destroyed; carbon composite engine that would oxidize away in 10 hours but only needs to fly 2.

He brought me this thing and it had failed, it had split. No one got killed but they were worried about the safety. He explained to me: for America's Cup yachts, if the thing doesn't fail every now and then, you made it too heavy as a designer. A different philosophy. You should be shaving it down and making it thinner and thinner until it fails on a regular basis. These are fairly expensive yachts in that you usually are expecting parts to fail and you just replace them, because it doesn't have to last very long. America's Cup has to last for a few hundreds of hours before you trash it and go on to the next America's Cup. There's only one other component that I know — well, there are five things in nuclear weapons that have to last for a fraction of a second before they're no longer useful. But the engine on a cruise missile only has to last for about two hours. They make it out of carbon composites, and they can keep it from oxidizing away at high temperatures, but it won't last for 10 hours because it will oxidize away in 10 hours. It only has to operate for two hours, because then you're going to blow it up.

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