On Sun, 02 Jan 2011 07:38:29 -0800, Andy wrote:

All I have read here is that the D2, because of its very low angle of
incidence, may have a downward pull on the nose (and even here downward
would mean below the glider longitudinal axis, not necessarily below the
horizon). I'm quite sure that my ASW 28 being towed on the CG hook has
no downward force on the nose.

Hmmm, My Libelle glides at around 55 kts with the trim full forward so
should need its nose held down a bit when being towed at 60-65 kts on the
nose hook. Its possible that I am holding the nose down - all I can say
is that I'm not aware of doing so once I'm off the ground, stabilised
behind the tug and waiting for it to unstick, gain speed and start to
climb.

There is a noticeable catenary in the tow rope and, since that is a thin,
flexible rope the pull on the nose hook will be at the same angle as the
rope leaves the nose and not on the direct line between my nose-hook and
the rope attachment point on the tug. This probably puts the force line
above the glider CG and so is contributing a nose down moment.

FWIW I estimate that climbing at 600 fpm at 60 kts is a 5.67 degree climb
and that the tow rope tension is 37.62 kg for my glider (10 kg is drag
due to the glider and the rest is due to the glider hanging from the
rope).

However, I don't know rope weight or exact length or how to calculate the
sag in the rope and hence can't estimate the distance of the force line
above or below the CG.


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martin@ | Martin Gregorie
gregorie. | Essex, UK
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