In rec.aviation.student WingFlaps wrote:
On Apr 27, 11:23?am, Michael Ash wrote:

My personal decision height for the analogous glider launch emergency is
*usually* a shade under 200 feet. Conditions, performance, obstacles, and
landing opportunities ahead can all modify this value.

What's your glide ratio? If it were 40:1 would that equate to 800' in
a 10:1 Cessna?

The things I fly regularly range from 20:1 on the low end to 37:1 on the
high end. The 200ft number remains the standard for all of them. Glide
ratio can adjust it but it's more a matter of having a comfortable safety
margin. I once talked to an instructor who did a 180 in a 34:1 machine at
only 100ft, and he said it was a piece of cake. With that kind of
performance the turn costs no altitude at all so the decision height is
basically all safety margin. Flying something with reasonable performance
out of an airport where the landing sites ahead look deadly then I
probably would reduce the decision height to something like 100ft.

A direct multiplication isn't going to work here for several reasons.

First because of the safety margin. You don't need four times as much of
that.

Second because of speed differences. The power plane needs to go
significantly faster to maintain best glide or min sink, resulting in a
larger turn, more altitude lost in that turn, and more corrective action
to regain the runway centerline after it. The power plane starts out
either around best glide or slower than it, whereas the glider generally
has extra speed which means extra energy. (This will of course depend on
the performance speeds of the plane in question, but most power planes
have faster performance speeds.)

Third, reaction time. When you hear a bang and your rope goes away it
makes the situation obvious instantly. Engine trouble can take more time
to diagnose. (One of the more difficult scenarios for a glider is when
this happens to the tow plane. You could end up low and slow before
realizing what's going on and 200ft may very well not be enough in that
case.)

Overall I don't think it makes sense to extrapolate from the glider case.
From what the power guys are saying, it sounds like you want at least
several hundred feet, with the exact number depending heavily on the skill
of the pilot and the performance of the airplane.

--
Michael Ash
Rogue Amoeba Software