A "well-formed lip" is one that resembles an airfoil in cross-section, with
the upper surface outward. More specifically, a non-laminar section, with
the maximum thickness fairly far forward. When resistance in the cowling
(from a closed cowl flap) forces more air to spill around the inlet rather
than enter it, the stagnation line on the inlet moves inward and
high-velocity flow around the leading edge of the inlet produces suction,
reducing the total drag.

Generally, in my opinion, inlet leading edges tend to be a bit too sharp. I
get the impression that designers think that the sharp lip cuts through the
air, forcing some of it to go through the inlet whether it wants to or not.
Air, however, is like the clothes in a over-full suitcase in a Charlie
Chaplin film. It just keeps spilling out somewhere.

Peter Garrison

Peter,

Do you like any of these?

Sandy McNabb

A and B are my personal faves.

PG