Thanks Martin

I did use the "vector" word talking about the winch case - because the
cable has mass (our steel cable is ~150Kg so not insignificant) and
there is a pull at a downward angle. At top of launch cable angle
approaches 90 degrees to fuselage - If you want proof look at one of the
videos on you tube.

http://www.youtube.com/watch?v=v2Qh95I_YM0

http://www.youtube.com/watch?v=np8OGPZ2pvE

As Doug Greenwell points out - there is constant acceleration on winch
launch because the flight path is curved, describing a horisontal S. I
don't know how what magnitude the acceleration has, but subjectively it
is only significant in the brief rotation to steep climb, and possibly
on the level out if you are less than smooth...
Generally it is a relatively small change from a little over 1g to a
little under 1g at release.
Anyone have the maths capability to calculate for a known situation?

Cheers
Bruce

On 2011/01/04 1:43 PM, Martin Gregorie wrote:
On Tue, 04 Jan 2011 10:57:01 +0200, BruceGreeff wrote:

Of course - the angle that the flight path can make relative to the
ground is proportional to the excess power available - hence the low
rate of climb behind the cub, versus the extreme angle on a winch.

Aerodynamics guys - Am I confused?

Sounds fair to me except that you omitted two fairly significant forces:
- the weight of the cable
- the tension in the cable.

Both will add to the load carried by the wing. The tension should add a
fairly constant load to the wing once the glider has rotated into full
climb since the throttle setting remains fairly constant[*] from rotation
until the glider is near the top, but the effective cable weight will
increase as more of it is lifted off the ground and then as the whole
cable gets closer to vertical.

[*] this is true on a calm day but is obviously incorrect in the presense
of turbulence or a significant wind gradient.



--
Bruce Greeff
T59D #1771 & Std Cirrus #57