Old 24th Nov 2012, 09:21
  #80 (permalink)  
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
There are only two forces acting on a glider: an aerodynamic force and a gravitational force. The gravitational force is directed towards the center of the earth and is equal to the product of mass m and gravitational acceleration g.

The aerodynamic force is usually represented by its two components: the drag force D acting opposite to the direction of movement, and the lift force L perpendicular to it.

For a glider moving at constant altitude the lift force is equal to the gravitational force: L = m * g ... (equation 1)

There is no force opposing the drag force so according to Newton's second law there results an acceleration a resulting from the equation: - D = m * a ... (equation 2)

(The sign convention is positive for forces and accelerations in the direction of motion, negative in the opposite direction)

Combining equations (1) and (2) we get: a / g = - D / L

No need to discuss momentum or energy.

P.S. If you measure accelerations in kts/second, then g is about 19.05 kts/second

Last edited by HazelNuts39; 25th Nov 2012 at 16:09. Reason: P.S.
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