At 21:45 19 July 2009, Del C wrote:

Whilst I agree with Don that the ground run acceleration should be
reasonably brisk to give quick aileron control, if it is too rapid some
types of gliders pitch up dangerously quickly, due to the rotational
couple between the cable pull line to the belly hook and the centre of
gravity. This risks a flick spin on rotation, or making recovery from a
low launch failure almost impossible.

This doesn't affect Grob G103s, which I believe is the type Don
instructs
in, due to its weight (it's not nicknamed the concrete swan for
nothing),
low set wings and hence low centre of gravity, but it does affect
lighter
high winged gliders such as the K6 or K8.

We do hold the tail down for some of the more delicate vintage types,
but
we often don't have enough helpers at the launch point to do this
additional task on a routine basis. OK if you have lots of ATC Cadets
hanging around with nothing much else to do!


There really is no conflict here, the gliders that are likely to suffer
from to brisk acceleration are generally lighter and high winged. The have
an advantage on two fronts in that there is less inertia to overcome so
they do not need the "extra" power to accelerate and of course being
high winged a wing drop is less likely to result in the wing touching the
ground. They can therefore be launched safely with less initial power.
On the other hand, modern glass gliders tend to be heavier and do need the
extra power to accelerate quickly but once this acceleration phase is over
they actually need less power to move them through the air so the throttle
technique needs to be different and this is where knowing what glider you
are launching is important.
On a Skylaunch I find that with wooden gliders and some lighter glass
gliders the throttle needs to be advanced to the adjustable stop. With
heavy 2 seaters the throttle needs go go through the stop and then return
as soon as the glider is moving. The "extra" power is only needed to
overcome the inertia. Many drivers to not provide enough power quick
enough for heavier gliders, maybe because of the caution needed for
lighter ones and not being taught to recognise the difference. The pilot
needs to play his part and establish a positive rate of climb to prevent
overspeed.
As far as holding the tail down, I would have thought this preferable to
having to accept a slower acceleration with the attendant risk of wing
drop/yaw.
We did not hold down the tail of Grob 103s, we did the Janus.
The concrete swan was actually the Astir Del :-)