Martin Gregorie wrote:


* * * "Thats why you NEVER push a glider by its wingtips."

From DG:

Pulling an aircraft
von friedelweber am Do Okt 25, 2007 1:36 pm
Is it okay to pull an aircraft on the wingtips?

The question tends to pop up in the gliding society. There is always a
concern that wings could suffer damage if the ground crew pulls on the
wingtips. Therefore we’d like to give you a short insight – without
going into too much detail – on the force that can be applied in a
longitudinal direction. Water tanks and other specific items are left
out in this abbreviated description. The length of the lever enable to
calculate the max. force a wing has to withstand without suffering any
damages.

The building describes a force of 400N as specification for every
glider. This will result in a force of 40kp (longitudinal). A normal
adult will commonly not be able to develop a force of 40kp in a
longitudinal direction without any problems. In other words – it is
save to pull a plane on its wingtips.