To the on Mog
By Geoff and Lynn We RAAus pilots have flown for years on 98 octane Mogas with no fuel related issues. Things were different more than 35 years ago when Ray Hodges, an academic of Chemistry was granted approval from DCA (or CAA then CASA) to experiment and test Mogas for GA use. He soon confirmed the real issue was related to volatility of winter blends of petrol. Some hot conditions caused vapour lock where the fuel pressure fell to zero (lean mixture). But an unexpected one occurred with this winter blend when still cold in the tank, but used on a hot day. Under pump pressure, this petrol remained liquid in the lines until it entered the float bowl of the carburetor at atmospheric pressure – some vaporised to gas and gave pressure pushing excess fuel through the main jet (over rich mixture). Ray experimented with modifications to his Beech Musketeer until DCA accepted cooling static ducts etc. and issued a Supplemental Type Certificate (STC) for his Musketeer. Since 1989, via a US partner, Ray has been supplying STCs for over 100 GA types to run on Mogas, as well as a Fuel Volatility Tester he designed. 20 / SPORT PILOT