Glide distance vs. weight

On Sat, 26 Feb 2005 17:11:46 -0600, Don Hammer wrote
in ::


Glide distance is determined by the glide ratio (L/D ratio for the
airplane as a whole) and the altitude. If you're 1 mile up, and your
L/D is 10, you can glide 10 miles. Since the best L/D ratio for an
aircraft doesn't change with weight (although the SPEED to fly at best
L/D goes up with increasing weight), the distance you can fly isn't
dependent upon weight.

The heavier you are, the faster you'll get there, but where you get TO
is the same :-).

Howzzat?

That's what they do in gliders. Put on 400 pounds or more of water
when conditions are strong and dump it when it gets weak or before
landing.

Glide ratio is a function of the design and doesn't change with weight

While your statement above is generally accurate, it's not absolutely
true (as was pointed out to me by a glider pilot in e-mail). Here's
some empirical evidence of L/D changing with a change in weight (note
the right hand polar graph under 'Technical data'):
http://www.dianasailplanes.com/szd55.html

According to the e-mail I received, this weight induced change in L/D
is apparently more significant on aircraft with wing aspect ratios
(length/chord) from 22-26, so the OP may not find it of too much help
in correcting his instructor's assertion depending on the particular
aircraft they were discussing.