Mark, I think Janos was talking about winch launch. The land ahead/turn
height for winch launch depends greatly on the winch site although at 25% of
the altitude expected without a wire break, say 500 feet or 150 meters, a
landing straight ahead on the runway should be possible. The ideal,
available at most sites, is an overlap between the two options where a 360
degree turn with a landing into the wind can be made from 300 feet AGL and a
straight ahead landing can be successful at 450 feet.

For airtow, there are certainly conditions where a low altitude rope break
will not allow the glider to get back to the airfield. Tailwinds, high
density altitudes and heavy gliders make conditions worse for rope breaks.
I have often been at 1000'AGL (300 Meters) before I felt comfortable about a
return to the runway. Under these conditions, airtow weak link strength
becomes a life or death matter.

Conditions like these make me far more comfortable with winch launch where I
can be sure of landing the glider on the airfield without a scratch.

Bill Daniels


"Mark James Boyd" wrote in message
news:4023f76a$1@darkstar...
Janos Bauer wrote:

What are the standards altitudes for such incident? Here are the list
I learnt: 50 straight landing, 50&100 one 180 degree turn, 180 two
turns or small circle. Of course in strong wind I would increase these
values.

I have been VERY surprised a few times by the effect of a slight
tailwind on my rope break practice. Since then I pay a lot
more attention to when the towplane rotates. If he rotates
much further down the strip, then I know I have either
a tailwind, heavy glider, high density altitude, etc.

Of course this assumes the towplane pilot rotates at the same speed
each time (in my experience they are very consistent).

In the cases when this happens
I know we ain't doin' very much "up" for the amount
"forward." So I SWAG a higher 180 altitude (maybe 300 or 400 feet).
The worst was an open canopy L-13 with two people on a hot
day with a 3-5 knot tailwind and only 180hp towplane. I dunno
if even 400 feet AGL woulda been enough.

Anybody else use the point of towplane rotation as
a hint?

I've wondered why airliners don't have some spot on the
ground (GPS) some distance down the runway, and abort
at that spot if they haven't reached a certain airspeed.
Seems simpler than doing all them calculamications for
wind, density altitude, etc. which may have changed since
you did them. Why not observe instead of predicting?

It doesn't work if you have ice/frost on the wings,
or if the ASI malfunctions (reads too high AS),
or you're misconfigured, but otherwise it seems to make
sense to me...

Of course when's the last time anybody de-iced a towplane or
glider, for goodness sakes! ;O