The present rapid increase in the number of light aircraft and private pilots will undoubtedly lead to a more general use of these aircraft. This will also mean more frequent operation under extremes of weather and operating conditions, and will increase the tendency on the part of many users to utilize automotive rather than aviation gasoline as an engine fuel because of its wider availability. Both these factors bring the problem of fuel vapor lock closer, hence it became desirable to study light aircraft fuel systems from the standpoint of vapor handling capacity.
The vapor lock limits of a typical fuel system are presented, and an analysis is made of the factors which control vapor formation and the vapor handling capacity of the system. The limits found indicate that present 7 psi. Reid vapor pressure aviation fuels can be safely used under all practical conditions in a properly designed gravity feed fuel system but diaphragm fuel pump systems are marginal. Vapor lock will occur in either type well within the range of practical operating conditions if automotive fuels are used.