Hi paul, good luck with your project. but perhaps you could give us some more info? what kind of BL motor is it? i assume it's an inrunner, but what size? 36 (540), 28 (380/400)? long/medium/short can? what sort of ESC have you got? props come in different pitches not just diameter sizes. If you're using an M4 prop stub you can use the graupner K-series props. I've tried the other kinds from Robbe and Graupner and have to say i'm not impressed at all (too much flex and don't seem to work much)....keep us posted will ya? Some other useful posts you can consult though - i think one thread "prop geometry" should be interesting....also see the predator outrigger project by fiend...he's experimented quite a bit on a similar setup.

Best,
A