Notes on V-speeds
-----------------

  The most important speed is Vs, clean stall speed (at
max gross weight).  From this we can calculate actual 
stall speed as
                 _______________
    Vsnew =     / new weight 
	       /  ------------            x    Vs
             \/   max gross weight 


  This means the new stall speed is the square root of
the ratio of current weight over max gross weight 
multiplied by the max gross stall speed.

  For example, if the plane has max gross of 6000 pounds
and is currently 5000 pounds, and the Vs is 69, the new
Vs for current weight is the (sqrt of .833) x 69.
This is about 63.

  This is a useful speed because it also describes minimum
rotation speed (if a pilot rotates before this the
aircraft may stall on takeoff once out of ground effect).

  Another useful speed is best glide.  Vgnew is 
calculated in the same way:

                 _______________
    Vgnew =     / new weight 
	       /  ------------            x    Vg
             \/   max gross weight 

  Be very careful, however, when using best glide.  Yes
the best glide velocity goes down as weight decreases, but 
if you fly into a headwind, you are better off with too
much airspeed rather than not enough.  

  We can also determine Va for this weight, by using the
equation
              ____ 
     Va =    /         
           \/  n     x    Vsnew

  For normal category aircraft, the value of n, the design
load limit, is 3.8 G's.  So Va is 1.949 x 63 = 122.7 
So 122 is Va for this weight.

  Vs also gives us slow flight and final approach speeds,
which are 1.2 x Vs.  At max gross this is 83, and at
.83 of gross, this speed is 76 (63 x 1.2).  Landing at an
airspeed which is higher than this may cause the plane to
float, landing at an airspeed lower than this is likely 
behind the power curve, resulting in too high of a
vertical descent.