What are all those ridges on the cylinder heads of some airplane (and motorcycle) engines? Air-cooled engines, without a radiator or coolant, use the atmosphere all around them to transfer heat. It doesn’t take a brilliant designer to know that, the more surface area you can offer, the more heat you can push out into the world. However, plane engines have to be very compact, so builders have to be smart about getting their additional square footage. The result: an odd-looking pattern of fins over every critical surface of the cylinders.