In article . com,
Tina wrote:

As best I can tell, it seems for a given configuration air speed for
best glide angle (I will define best as most shallow angle) changes
with weight, but the angle itself doesn't change much. Hi performance
gliders carry water to increase penetration into headwinds, dump it
to increase time aloft, but still go down about foot for every 20 some
they move thru the air, don't they?

I need, for a fictional piece I'm writing, an efficient long range low
power consumption airplane and don't want it to fail because of
technical errors.

Thanks for your comments

An aircraft drag coefficient is defined by:

Cd = Cdp + Cd0 + Cl**2/(pi*A*e) whe

Cd = total drag coefficient;
Cdp = sum of the parasite drag coefficients;
Cd0 = airfoil basic drag coefficient;
Cl = lift coefficient (a function of angle-of-attack [alpha])
pi = 3.14159732......
A = wing aspect ratio (sqrt[span**2/S)
e = wing planform efficiency factor
S = wing area

The third term represents the induced drag contribution, due to lift
production.

Best L/D will occur when Cl/Cd = min.


In unaccelerated flight, L = weight = Cl*q*S,

where q = dynamic pressure = 0.5*rho*V**2, whe
rho = air density;
V = velocity through the air

Within limits, best glide occurs at a set alpha; speed varies with
weight.