MAS props can take divets out of grass runways and usully not sustain any damge. You can also see them flex out of shape at high revs which makes them less efficient than APC props. APC props are more solid and won't flex therefore put more load on an engine for the same size and pitch than a MAS. I have tried wood props and don't like them. If the prop touches anything, even lightly while the engine is running the prop will instantly break with a loud snapping noise! Re; "Master Airscrew even though durable don't produce enough thrust in most trainers off grass runways."< I have trained a lot of newbies and haven't seen this myself. As long as you use a 10-5 or 10-6 prop for a 40 size engine and an 11-5 or 11-6 prop for a 46 size engine either MAS or APC props will work just fine. I do uggest that new flyers use MAS type for the toughness factor. [8D]