Must agree with downunder (no it's not an aussie conspiricy!) Example: had a big scale model with a 120 4 stroke & a big radial cowl using a Master 16x8 prop (those supposedly in the know in oz call them paint stirrers). Performance was a little lacking so a friend lent me a fancy german scimitar shaped 16 x 8 carbon fibre prop, yes you could see the weave of the carbon - beautiful thing, and the motor picked up about 15% more RPM. Great I thought, performance plus! In practice the performance was so poor I was lucky to make a circuit & land. For what it's worth I tried APC props on my 40 FP's in a 4 engined scale model & went back to the Masters, reason, I got sick of cutting myself on the sharp, pointed tips working around the model cleaning, fueling & preparing it. The thought of sticking a hand in a spinning prop is just scary. Do I work for Master or hate APC for some reason - no. For electrics I use APC's all the time because they make special electric props which are very efficient. For an FP 40 in a trainer I'd go for the Master, efiicient enough, stronger & safer. Whatever you use make sure you sand off the sharp edge where they came out of the mould & balance them. - John.