On Tue, 22 Jul 2003 11:59:12 -0400, Todd Pattist
wrote:

mosquito wrote:

What is the effect of water ballast on: (a)stall speed,
(b)climb performance and (c)glide angle?

In their answer on page 4, they say "The stall speed and glide angle are
increased..."

AFAIK, the glide angle ISN'T increased - with increased weight, you just
travel down the same glide angle, but faster.

You are correct that for a constant glide angle, the speed
at which that glide angle occurs increases as you add
ballast. Thus, if they had asked about the effect on
maximum glide angle, their answer would be wrong and yours
correct. However, they didn't ask about the effect on
maximum glide angle, nor did they specify a constant glide
angle.

Instead of assuming a constant glide angle, we could equally
well assume a constant airspeed. For a constant airspeed,
the effect varies. At speeds above the ballasted max glide
angle, adding weight increases the glide angle. At speeds
below the unballasted max glide angle, adding weight
decreases the glide angle. There's a crossover somewhere in
between those two speeds.


Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

I don't quite follow what you say in your second paragraph.
Do I understand your point if I make the following changes?

"At speeds above the ballasted max glide angle, adding weight
SHALLOWS the glide angle. At speeds below the unballasted
max glide angle, adding weight STEEPENS the glide angle."

Or is this still not right?