On Mar 11, 3:15*am, Derek Copeland wrote:
Remember that a glider has to produce more lift when climbing.

Er .. say what?

Any constant rate of climb (including flying level or constant
descent) requires exactly the same amount of upward force -- identical
to the weight of the aircraft.

In a powered aircraft flying level the weight and lift balance, and
the thrust and drag balance.

In a glider gliding, the lift from the wings is slightly less than the
weight (it is multiplied by the cosine of the glide angle), and the
balance of the upward force comes from drag (multiplied by the sine of
the glide angle).

In a glider being towed upwards, the lift from the wings is also less
than the weight (by the cosine of the climb angle), with the balance
of the upward force coming from the difference of the tow rope force
and the drag (multiplied by the sine of the climb angle).

If you're climbing at only a few hundred feet per minute while being
towed at 60 or 70 knots (6000 or 7000 fpm) then these angles are tiny
and the lift is essentially equal to the weight, but if a powerful
towplane could climb at, say, 45 degrees, then (far from having to
generate more lift than usual) your wings would only have to generate
lift equal to 70% of your weight.