Dynamic stalling of delta wing a/c (wrt MiG 21)

> Once past 
>(Cl/Cd)(max) further increases in alpha might boost Cl but the 
>corresponding increase in Cd is greater, so the glide angle (and hence the 
>sink rate) increases.

It is certainly true that below the speed for (Cl/Cd)(max)
further increases in alpha cause a worse glide angle, but
that's not the same thing as an increase in sink rate.
Glide angle is altitude lost per unit distance.  Sink rate
is altitude lost per unit time.  As airspeed slows below
(Cl/Cd)(max), sink rate continues to decrease (alt/time)
even as the glide angle (alt/dist) worsens. 

> Hence low-aspect ratio deltoids require phnomenal 
>amounts of power to fly at the very low speeds that the high-alpha 
>capability of the configuration permits. 

Between (Cl/Cd)(max) and the minimum sink rate, power
requirements decrease even as the glide angle worsens.  For
a while, as speed decreases below (Cl/Cd)(max) power
requirements fall because the decrease in airspeed more than
makes up for the increase in induced drag.  It's not until
the speed drops below the minimum sink/min. power required
speed that power requirements start to increase, and that is
exactly the "region of reversed command" or "back side of
the power curve."  The delta simply has a larger range below
min sink/min power prior to stall than other more
conventional designs, so the power required can grow very
large without hitting stall.

Todd Pattist
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