Has anyone ever put the prop arc part way through a wing?

[ This would require a slot completely through the wing ] Mine will end up at about 80-90% of the center section airfoil's chord.

From : Don Stackhouse

You can usually get away with this on models, although it hurts the prop efficiency, and it can generate a fair amount of aerodynamic vibration, because of the discontinuous, disrupted airflow into the prop.

On full scale aircraft the same issues exist, only their severity and their potential consequences generally become much more severe. In particular, the vibrational stresses in the propeller blades can easily be severe enough to cause fatigue failures in the blades. Losing a propeller blade, even on the ground, is NOT something you even want to think about! The problem of the broken blade flying off through surrounding airframe and occupants is not the biggest problem. Generally the loss of a blade results in the rest of the prop and engine being ripped completely out of the airplane by the massive unbalance. The centrifugal force on a typical metal propeller blade for a light aircraft is around 40,000 to 50,000 pounds. Even a wooden or composite propeller blade has centrifugal forces of about half that value, still more than enough to overstress most engine mounts. Even if the engine stays at least partially attached, it may get bent around sideways to the airflow, causing massive amounts of drag as well as possible control problems.

Even on a model, the centrifugal forces can be considerable. In giant scale models for example, the centrifugal force per blade can be in excess of several hundred pounds.

I'm thinking of hinging the part behind this slot and using it as a trim tab/elevator. Anyone had experiances w/ this?

On a model it's usually possible to pack enough raw power into the aircraft to overcome the efficiency losses, and the flight time that models accumulate is generally not enough (usually!) to cause fatigue problems. However, fixing a poor design by increasing the engine size will increase weight, which increases the required power, which increases the weight even more, in a vicious cycle. While the end result may fly OK, it will not fly as well as a design that uses the capabilities of the motor and prop more efficiently.

Don Stackhouse
DJ Aerotech