Tracy reported a marked increase in cooling when changing the inner/outer radius of the duct inlet. The outer radius of the lip should apparently be greater than the inner radius of the lip. He got the optimum ratio from an NACA paper, but don't remember which.

I think the goal is maximum pressure recovery at low speeds (100 mph) and high angle of attack and of course minimum drag at low and high speeds (output cowl flap to lessen flow at high speeds making the air flow easily around the inlet and cowl at higher speeds).

I've been trying to locate that paper but keep finding papers on turbine inlets and supersonic inlets.

Does anyone know what that NACA paper may be? Or even just the optimum radius ratio?

Finn