I want to throw this in here. Everyone wants to know about "Hot and Cold". To put it simply hot and cold refer to the plugs ability to transfer and retain heat. A "Cold" plug transfers heat away easily. Thus in a high rpm or high nitro/compression situation this is a desirable feature.

A "Hot" plug however would transfer heat slowly. Thus it would retain heat easily. This would help in a low rpm or low nitro/compression situation. This is why 4 stroker plugs are the hottest out there.

One last point to throw out there. Any internal combustion engine is basicly a heat pump. You convert chemical energy (fuel) into kinetic energy (in our case prm's and heat). The heat generated in copmbustion must be eliminated or at least lowered. Thus the cooling fins on our engines. The heat left in the engine can affect the operation of a glow plug. A coweled engine may benefit from a cooler plug. Whereas one in the front of an ugly stick may benefit from a hotter plug even if both planes use the same engine.

Picking a plug can cause your hair to fall out. I would reccomend picking a favorite manufactuer (Fox in my case) and just buy a couple of each of thier plugs. Try them all in your application. You will find that one will work the best in your unique set-up. Then use it religeously. Don't forget that changing fuels or radical changes in temprature may cause you to have to change plugs. Flying at low temps in the winter will probably need a hotter plug.

I hope this helps clear up a totally muddy subject.

Mark Shuman