Winch Launch Fatality

On Jun 26, 10:30*am, Don Johnstone wrote:
You should not necessarily point the glider at the winch, you should point
it in the direction that the cable is going to take. If there is a bow in
the cable then the glider should not point at the winch but towards the
bow so that yaw is not induced.

A typical answer for a steel cable user. Steel digs in to the ground
as it is puled out. You don't know if a steel cable will maintain its
initial direction or 'twang' back to center jerking the glider around.

UHMWPE/Dyneema rope will take a dead straight line from the glider to
the winch as it is tensioned. The stuff is so light that it easily
skips sideways over weeds and grass. If it fails to straighten out,
it's likely caught on something solid and you'd best investigate.

Yet another reason to dump steel cable.

When we did a trial with Plasma (similar to Dyneema) cable on one drum and
steel cable on the other drum of a two drum winch, I can't say that I
noticed any difference between the two in terms of straightening out. The
Plasma cable did give higher launches, by a hundred feet or so, but the
cost is unfortunately rather prohibitive.

It is a good idea to keep the airfield grass as short as possible so that
cables will slide over it and straighten out as they are tensioned. This
also reduces the chances of groundloops or cartwheels if a wing drops.

At my club we pull the cables just past the launch point so there is
enough slack to reach the second glider, normally on the upwind side by
just over half a wingspan. There is therefore a small amount of offset,
but this generally does not cause a problem. The upwind side is preferred
as you launch the downwind cable first, which tends to drift away from the
second cable, reducing the risk of picking it up. Also reduces the chance
of the cables crossing at the winch end during the wind in.

Derek Copeland



At 19:35 26 June 2009, bildan wrote:
On Jun 26, 10:30=A0am, Don Johnstone wrote:
You should not necessarily point the glider at the winch, you should
poin=
t
it in the direction that the cable is going to take. If there is a bow
in
the cable then the glider should not point at the winch but towards
the
bow so that yaw is not induced.

A typical answer for a steel cable user. Steel digs in to the ground
as it is puled out. You don't know if a steel cable will maintain its
initial direction or 'twang' back to center jerking the glider around.

UHMWPE/Dyneema rope will take a dead straight line from the glider to
the winch as it is tensioned. The stuff is so light that it easily
skips sideways over weeds and grass. If it fails to straighten out,
it's likely caught on something solid and you'd best investigate.

Yet another reason to dump steel cable.