John: It's been 16 years since your posts here, and I'm just now discovering your Bootstrap Approach to assessing small aircraft performance. Are you still around? If so, please respond. I'd like to buy additional background information directly from you since your book is now out of print. I have my fingers crossed for good luck.

Gary Lanthrum


On Tuesday, September 28, 1999 at 12:00:00 AM UTC-7, John T. Lowry wrote:
Here's the formula for Vbehw = speed (in knots) for break-even headwind (to
be explained):

Vbehw = dRB*Theta*(1-hRho/70000)/(5*VR)

where dRB is your airplane's Base distance to Rotation (on a flat runway
with the same type surface at the same altitude with no wind); Theta is the
slope of the actual runway in degrees; hRho is the density altitude in feet;
and VR is your airplane's rotation speed in KCAS.

Vbehw is the wind speed for which it makes no difference whether you take
off uphill into the wind or downhill with the wind. If the actual wind is
greater than Vbehw then go uphill into it; if actual wind is less than Vbehw
then go downhill with it.

Derived on pp. 375-379 of Performance of Light Aircraft. Remember that it's
perfectly possible, if you have two airplanes about to take off on the same
sloped runway at the same time, that one of them (the one with more power)
is better off taking off uphill, the other one better off taking off
downhill.

John.
--
John T. Lowry, PhD
Flight Physics; Box 20919; Billings MT 59104
Voice: 406-248-2606

Newps wrote in message ...
John, I read an article in Mountain Pilot from you about how to figure
out when to take off uphill into the wind or downhill with the wind. It
gave a formula and directions on how to use it. I've since lost it.
Could you post it here with the directions? Thanks.


"John T. Lowry" wrote:

Dear Matthew, and All:

My first Editor-in-Chief at AIAA, Paul Zarchan, suggested MatLab and I
looked into it. With the possible exception of the de novo propeller
chart
calculation, which I expect almost no geneal aviation types to actually
perform, MatLab was way way overkill. Most of the bootstrap calculations
are
on the high school level, just plugging numbers into algebraic relations.
The bootstrap approach is NOT some sort of massive curvefit or simulation
program. Just basic physics, propeller theory, and elementary
aerodynamics.
A spreadsheet is nice to have, granted, because you may want to use the
same
formula with say ten different values of air speed or for four different
weights or half a dozen different density altitudes. And so a hand
calculator can get tiresome. But no computational tour de force is
needed.