However, not sure on the feasibility due to high rpm output of a rotary engine. Also can aircraft use car petrol (95/97 octane) if a car engine is adapted to a light aircraft, eg mazdas RX-8? Why is AVGAS used for aircraft?
(1) High RPM isn't a new problem, 2-stroke microlight / homebuilt engines such as the Rotax 582 handle it with a gearbox or belt / chain reduction drive.
In my experience, if you can keep tipspeeds consistently below 0.7M then the system should work. Torque will drop out from power and speed, propeller pitch setting will drop out from that.
(2) UK Airworthiness Notice No. 98, contained in CAP 455 contains the rules on using unleaded MOGAS in aircraft. It is possible - in fact for many engines, it's a better fuel.
(3) AVGAS, which in it's 100LL form has 100 octane rating, and about 3 times the lead of old 4-star is used because (a) many aircraft engines were designed for this sort of makeup, (b) because it comes from a "regulated" aviation fuel source - which keeps the CAA happy, and probably most of all (c) habit. Actually rotaries are incredibly tolerant of different fuels and will run on just about anything with a bit of tweaking.
With the improvements in efficiecy, minimal vibration and more power to weight ratio than a piston engine a rotary engine would proberbly be good enough to use in small GA single props!
Mazda conversions are quite popular in some countries, particularly for Gyroplanes where the engineering problems aren't all that different to a conventional SEP.
But, they are thirsty, and the aircraft / motorcycle rotaries such as the Norton have only ever been used for unmanned aircraft applications because of a relatively poor reliability. Without doubt the Mazda is a much more reliable unit (and I'm sure there are others), but they aren't all that light - not necessarily because they can't be, but because they don't need to.
- I think that if you take a look at websites dealing with Ultralights and Gyroplanes, particularly in Australia, you'll find some information about Mazda rotary conversions for aircraft use. Also look in Janes at the work done in the UK for UAVs using Rotary engines, and look up a company called "Midwest" who were developing aircraft rotaries based somewhere near Gloucester before they moved to Germany about 4 years ago in frustration at CAA not letting them do anything (although rumour has it, CAA were equally frustrated that Midwest would never give them the information that they asked for).
Good luck with your project,