Wing mount engine clearance

[Garry s]

Am converting a Sig Kadet (high wing floaty trainer) to a cameraship. Power will be twin Axi 2826/10's in the wings. For CG reasons I'd like them as far back as possible (but not pushers, mechanically too difficult). Most multi's have the props a fair way ahead of the LE - is there an airflow related reason for this or is it just for CG? I'd like to have the props clearing the LE by the narrowest possible margin.

Thanks, G

[Brandano]

the biggest issues with prop/wing interaction are the noise caused by the prop wake and the fatigue stresses caused by the "pressure pulses" behind the prop, stressing both the motor mounts and the prop blades. Why is it mechanically difficult to mount the motors as pushers? With brushless motors getting them to run in reverse is just a matter of swapping two of the wires.

[Garry s]

Thanks Brandano. It's a long way from the main spar to the trailing edge - would be weight consuming and complex to build sturdy enough nacelles, also takes up real estate I want for flaps (which should be highly effective in the propwash).

[Brandano]

anyway, try to leave some clearance behind the prop. Switching o a 3 blade prop might mitigate some of the wing-prop interaction issues, as well as mounting the engine nacelles underslung or over the top surface of the wing. Since this is not a scale ship and you don't need to perform engine maintainance from under the wing mounting the nacelles on top will give you better prop clearance from the ground and still provide a high energy airflow over the top of the wing, like in the AN-72/AN-74 Coaler

[Garry s]

Thanks again. Will certainly experiment with 3-bladers, and in fact my layout is as you sugest, with the motors slightly above the wing.