One detail about flying fuel engines in gliders that is missed by inexperienced flyers is the use of freeflight fuel tanks. In fact, freeflight timer shutoffs to limit the engine run make a lot of sense for modelers who want the challenge of winch like launches.

Flying a fuel engine glider with no means to shut off the engine really has little challenge. It can be boring for most modelers. The biggest test is to your patience waiting for the engine to stop. On good glider days, the problem is often just keeping the altitude down and the model in sight. But add a fuel shutoff and you model has it's own "winch". Of course, you gotta make your own unless you've got a history of freeflight.