The Bridi airplanes site says that anything from a .40 to a .60 can be used so the .40 is on the low side and the .60 is on the high side. I only have experience with the .46FX/AX engines so I don't know how much of a power difference there is between those and the Magnum .40. I think that if the .40 is close to the same power as the .46FX that it would work great on the Aircruiser. Anyone have experience and can compare these engines?