"Gary Drescher" wrote in message
news:HDSLb.15032$I06.94614@attbi_s01...
"Dave S" wrote in message
.net...
Wonderful.. Thankyou Blanche... I only have to tweak the name of the
variable A6 to plug this in..

This was exactly what I was lookin for.
Dave

Dave, please forgive me for saying so, but if you found the statement "the
speed is
proportionate to the square root of gross weight" to be unhelpful, but
Blanche's "full_va*SQRT(A6/full_weight)" is "exactly what you were looking
for", then with all due respect, you do not understand the calculation
well
enough to base a life-or-death piloting decision on it.

Especially since both the statement and the equivalent
expression are just plain _wrong_. To clarify this (since
there are safety implications):-

1) Va by definition is just a number and _does not_ scale
with weight.

2) What you really looking for is some speed (lets call it
Va'(w)), a function of weight, below which you can tug on
the controls and not have things break.

3) Va' is the _lowest_ of several speeds where individual
components might overstress -- controls break, engine mounts
crack, cargo bends the floor, wings fall off, etc.

4) Some of these component Va' don't scale with weight, some
scale as sqrt(w), and some no doubt scale in other bizarre
ways.

5) Since you don't know without access to the engineering
design reports what these component Va's are, you can
never be certain how they scale with weight or which of
them is the limiting factor in any configuration.

6) Even at gross, Va' doesn't guarantee you protection
against full control movement. For that you need Vo, which
isn't available for older aircraft anyway.

--
Dr. Tony Cox
Citrus Controls Inc.
e-mail:
http://CitrusControls.com/