This has been an interesting discussion, but it appears to me that it got
off-track somewhere because "forward" has two meanings (see the attached
illustrations):
(i) The LIFT does not have a "forward" component, under any
circumstances, if FORWARD means the direction of the aircraft's flight.
Reason: LIFT is by definition always perpendicular to the direction of
flight, as DRAG is always opposite to the direction of flight (i.e.
perpendicular to the LIFT).
(ii) If, however, one refers to FORWARD as the direction of
the aircrafts centerline, then LIFT has a "forward" component as soon as the
centerline points up at the nose relative to the direction of flight. The
higher the nose points up, the greater this forward component is. At some
point it may, as I read the discussion, become larger than the wing DRAG's
component parallel to the centerline in the opposite direction, giving a net
"forward" force on the wing.
(iii) The LIFT does not contribute, under any circumstances,
to moving the aircraft forward through the air, as there is no lift
component parallel to the direction of flight. A glider is "propelled" by
the forward - in the direction of flight - component of the aircraft's
WEIGHT only.
Regards,
Svein
LN-SKJ
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