Camouflaged/Hidden Field Obstructions

In the spirit of the season - northern hemisphere winter, I mean, of course! -
another RAS thread raised the question of how Joe Glider Pilot might go about
assessing how much more field will be necessary if his chosen field has an
obstruction along/near its downwind border. (They all do, of course...have
some sort of obstruction, I mean.)

By way of avoiding thread drift, since in the other thread it was soon pointed
out that there are more considerations than "merely" field-edge-obstructions -
f'r'example, powerlines crossing a field - I thought an obstruction-specific
thread might serve a useful purpose...

Powerlines - "For all practical purposes," don't count on EVER actually seeing
powerlines' actual wires; it's far safer to practice learning how to see
"stuff" related to their supporting infrastructure, e.g. individual poles,
bespoke towers, an old installation/maintenance track, etc. In parts of the
eastern U.S. mountains, it's not unknown for such lines to actually be
attached to *trees* in which case only luck - or, possibly, an "apparent pole
interruption" on either side of such tree use might be a possible visual
tipoff. Fact is, it's impossible to eliminate 100% of the non-loss-of-control
risks associated with off-field landings.

It likely goes without saying that hitting a metal line (power, single-strand
fence, etc.) in a glider is immediately life-threatening (for multiple
reasons)...definitely not something you want to do.

Not all line-related news is bad though. The poles carrying power lines often
can serve as a useful field-length guide. Your standard tree-trunk-based pole
(of the sort carrying power to those transformers stepping voltages down to
the 120/240V range used by houses/non-heavy-inductrial busisnesses) are
typically 200 (occasionally, nearing 300) feet apart. (Don't take my word for
it; go pace off a few random test cases in your neck of the woods.)
High-voltage power lines (the ones strung along tall metal towers) tend to run
about 500' apart, wherever I've paced 'em off on reasonably flat land.

In broad brush terms, if you've learned how to recognize "hidden" fence lines
from an airborne glider cockpit (typically, a narrow unmowed/uneaten stretch
of biomass runs beneath the lowest strand, and it'll be some combination of
different color/shading in contrast to greenery slightly farther away), the
same skill set should serve to help spot individual tree-trunk-based power
poles. Don't count on a tree-trunk-based pole's shadow tipping you off,
especially if you're landing with the sun still high in the sky (i.e. "You're
falling out!" while it's still soarable).

If there's a structure (e.g. house, barn, pump-hut [a western U.S. 'thing'])
nearby, assume it's got power running to it, and try and find its poles
*before* you get to pattern altitude; far better to be paranoid than dead.

And, of course, many many excellent books have been written covering "the OFL
topic"...on both sides of the pond. (Re-)Reading one or two is a great
wintertime way to help reduce "winter doldrum-induced cobwebs."

Bob W.

---
This email has been checked for viruses by AVG.
http://www.avg.com