On Wed, 7 Jan 2004 23:29:16 +0000, Ian Strachan
wrote:

The static on-the-ground measurement of where the glider GC is with
respect to the belly hook position is not what matters. It is what
happens on a launch (dynamic, not static conditions). What matters is
the angle-of-pull of the cable with respect to the centre of motion and
control effectiveness of the glider in that dynamic launch situation.

If you measure where the CG is statically, that is, on the ground, and
placed a tow hook directly underneath it, I think that you would find
the subsequent launch pretty unstable either on winch or air tow.

The best (static) procedure I know for correctly locating the tow hook
on a free flight model glider (launch for these is equivalent to winch
launch with the controls fixed for a minimum sink glide condition) is
to:

- locate the CG on the wing chord (A)
- draw the wing chord on the fuselage
- draw a perpendicular to the wing chord running through the CG
- a line through the tow hook and point A should slope forward
at an angle of 16 degrees from the perpendicular.

On most models that approximates to 18-20 degrees forward of a
vertical line through the CG. In other words, the optimum winch launch
hook position is in front of the CG by an amount that is related to
the vertical distance between wing and hook.

HTH

Martin

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :