If you've ever looked under the bonnet of a car, the engine can seem like a maze of metal parts, pipes and wires. In reality, its job is quite simple: it turns fuel into the power that moves your car.

That lump under your car's hood? Yep, that's an engine. Duh, right? That thing spinning the propeller on a Piper J-3 Cub? Also an engine. That said, they're about as similar as a catapult and a ...