Dave S wrote:
I have an Excel Spreadsheet application that does W&B and plots it on a
graph... The form also lists certain speeds that are "static": Vx/Vy,
Vne, etc.. I would like to modify this form to list Va dependent on
the given calculated gross weight

Easy. Va as published is for max gross weight, and goes down with the
square root of weight. So:

MGW = Max Gross Weight
W = Weight of the aircraft at a given moment
Va = Maneuvering speed as published in the POH
Va,w = Maneuvering speed for a given weight

Va,w = Va * sqrt (W / MGW)

Stall speeds (Vs0 and Vs1) both follow the same formula, and so does
your final approach speed, which is usually calculated as 1.3 * Vs0.
So, if you really want to do landings right, you should calculate your
weight at the end of the flight (taking into account fuel burn),
calculate a Vs0 based on that, and multiply by 1.3 to get your proper
final approach speed (keeping in mind that the multiplication needs to
be done in CAS, not IAS).

It turns out that for the majority of light airplanes, the difference
between max gross and a reasonable minimum landing weight (pilot and
minimum fuel) is a small enough percentage of max gross that stall speed
only varies a few knots between the upper and lower limits. As a
result, most people don't bother with this (nor is it often taught in a
private pilot course), and they never have a problem. On a bigger plane
where half the takeoff weight can be fuel, it's a much more significant
issue and these calculations are done for every takeoff and landing.

If you were really paranoid, you could calculate Vfinal and Va for three
loadings: pilot and minimum fuel, max gross, and halfway in between,
then keep these on your cheat sheet. In flight, just take a WAG which
of those you are closest to and use the appropriate number.