William wrote: "Is there any evidence that motor gas will affect the fibre-glass fuel tanks in our KR's? I have a continental and have always used avgas, but with the increasing costs i am considering mogas"
I recently went through this type of research when trying to decide fuel tank configuration in a design of my own. I was tossing up whether to just seal the aluminum skins of to make a fuel cell inside the skin. Anyway, The research led me to the understanding that properly cured resins are also impervious to fuel. The Rutan based composite constructions, along with many others, have fuel tanks made using the same materials as the rest of the aircraft and they have no troubles at all, regardless of their fuel type. Of greater concern is the compression ratio and valve guides in your existing engine, since aircraft engines are designed to use the higher octane AVGAS (100LL), the compression ration is higher than in an equivalent automotive engine. Use of lower octane ULP can lead to pre ingnition problems which can dramatically shorten engine life. I'm not sure of the price of premium unleaded fuels over there, but here they are not a great deal cheaper, and the octane rating is still a couple of points lower than the AVGAS The other concern with ULP is that Aircraft engines are designed for use of a leaded fuel, and as such, the valve guides are lubricated by the lead content of the fuel. You will need to have bronze guides installed or use an additive to deal with it, or the guides will wear rapidly, also dramatically shortening your engine life. Cheers, Peter Bancks. strange...@dodo.com.au
