On Apr 13, 2:09 pm, Gary Nuttall
wrote:
Not as much as it disturbs me that there might be people
out there who will stake their lives against a set
of numbers in a book. The margins of safety are so
much tighter in a glider/sailplane than a powered aircraft
and a minor change in any one part of the equation
could have dramatic results.

Let's be clear here.....Some numbers you can be confident
in becuase they've been measured in a certain, calibrated
and controlled environment and as such I 'trust' them
- e.g. VNE/VDF are tested in still air with a new airframe.
Even then, I'm not going to fly right up to the limits!

The problem I have with calculating a takeoff run is
that there are just so many variables involved that
you cannot consistently and safely rely on the results.
As Todd's post suggests, work out a go/no go point
and if you're not airborne, release.

As a glider pilot I act within both my and the glider's
limits. I trust my instincts that if something doesn't
feel right, I abandon the launch while it's still safe
to do so. Maybe it's a US vs UK thing but here in
the UK we take personal responsibility for our actions.
If you're not sure that you have sufficient distance
to take-off then why would you trust a set of numbers
that say otherwise ? I think the concept of calculating
takeoff runs is actually quite interesting but the
sheer number of variables involved make it an impracticable
exercise.

Gary

At 14:36 13 April 2007, Kilo Charlie wrote:





'Gary Nuttall' wrote in message
...
And keep a note of how much fuel the tug has on board.
How heavy the glider pilot is. How clean the glider
wings are. What time of day it was. Outside Air
Temperature,
pressure and moisture content. Local CAPE and Lifted
Index. Length of rope (and its elasticity). Power
setting of tug. What mood each of the pilots were
in. Stick position on ground run. Local thermal
and
wave activity. All can have an effect on take-off
distance and climb rate.

There's so many variables that I'd be dubious of any
metrics developed beyond the fact that high altitude,
high temperature and heavy gliders do not make a good
combination.

Anybody who comes up with a set of explicit numbers
and sticks to them is likely to discover how often
theory doesn't work in practice!

Happy soaring
Gary Nuttall

Continues to amaze me at how much disdain glider pilots
have for
quantitation. I suppose that may be what draws some
of them into the
soaring in the first place. I also enjoy that aspect
but think that
attitude has gotten many powered pilots into bad situations.
To think that
we are immune to it because we don't have engines is
naive.

Casey- Hide quoted text -

- Show quoted text -

The process of acquiring and analyzing the data will establish if it
is reliable or not. If it is not reliable there will be a large
scatter for the same set of conditions. The fundamental set of
parameters include, but are not limited to:
1. Tow plane POH take-off distance (this takes into account density
altitude and type of runway)
2. Glider total weight
3. Glider L/D
4. Wind
All of the other things mentioned are very minor compared to the above
factors, and will be represented as a scatter in the predicted take-
off distance. This can be accounted for with a safety margin, which
MUST be added to any POH calculation anyway. Exactly what are you
proposing as an alternative, launching without regard to available
data? This task is not on the level of a molecular chemical reaction
dynamics calculation. Personally, I would feel much more comfortable
having the data if I were the one being towed. If someone will collect
the data I would be happy to help them analyze it, something I do for
a living.

Tom