my limited exposure to Rotaxs in VLA in the training envoroemnt shows them to burn around 12 lts an hour and thats a hell of a saving compaired to an o-200 or o-235.
Something worth mentioning there - the 912 is a lot lighter than any of the usual Lycontinental lumps. Because the engine is such a large part of the aircraft's empty weight - put a lighter engine in, and you can make a lighter aeroplane, and the smaller lighter aeroplane will of course have a lower fuel burn. Lower fuel burn, means you need to carry less fuel, which brings fuel burn down again.
Aircraft design weights tend to spiral either inwards or outwards - the art is to make it spiral inwards.
G