Those engines have a small chip that controls their startup process. First, they spin the turbine up with a DC electric motor (the small pod right on the intake of the turbine). Once the computer senses they are at full electric motor supplied rpms, it injects propane into the combustion area and ignites a spark igniter. The propane usually comes from a tiny cartridge very similar to a CO2 cartridge used in pellet guns. Once the propane cycle has ignited, the DC motor turns off and the engine continues to spin faster and faster. Once the computer senses it has reached enough RPM for the JP4 (somewhat similar to kerosene), it starts feeding in the real jet fuel and shuts off the propane feed. From there it's simply a matter of metering the JP4 for throttle control. It's really quite a spectacle to just see one of these relatively tiny things ignite, chuff and spit fire, then whine up smooth as silk as the exhaust outlet turns cherry red and the noise becomes almost unbearable.

It is also quite a spectacle to see a twin turbine propelled model jet turn into a 200mph Frisbee when a homemade fake air to air missile implement breaks off and takes out the horizontal stabilizer. <img src="http://www.catsailor.com/forums/images/graemlins/crazy.gif" alt="" />