"Ian" wrote in message
ups.com...
On 15 Oct, 14:19, (Richard Casady) wrote:
On Sun, 14 Oct 2007 23:31:30 -0700, Ian
wrote:

What force do you think does work against gravity to allow aeroplanes
to ascend?

Thrust from the engine, of course.

Nope. How many aircraft do you think are capable of vertical takeoff?

A Boeing 747-400 has a take off weight of 875,000 lbf and a total
thrust of 4 x 63,300 = 253,200 lbf.

My own aircraft has a take off mass of 370kg and no thrust whatsoever,
and yet I can get it to go up.

Ian

But in your example, gravity is still causing you to descend through the
air. Unless converting excess speed to height, you only climb because the
air in which you are flying is rising faster than your sink rate.

Presumably, if a boat's motion is generating apparent wind from dead ahead
and a fully battened sail (I say fully battened because it's a better
aerofoil shape) could be set far enough out to achieve sufficient angle of
attack to produce some lift, then a keel boat "may" go a little quicker.
Would the lift produced be greater than the drag though?

Graham.