Overspeeding on winch launches

On Monday, 6 November 2017 12:48:16 UTC, Dan Schmitz wrote:
I'm wondering what the consequences of overspeeding on winch launches are? I understand that it places stress on the airframe, but to what extent?

I find it near impossible to control the airspeed on the top third of a launch and have found myself over speeding the placarded max. speed by 5 - 10 knots a few times despite signalling to the winch driver.

Should I be taking the approach of releasing at 2/3 of typical launch height (e.g. 700 - 800 foot) if my airspeed isn't under control at this point?

Thanks in advance

Dan, my response is "yes".

The physics suggest that there is substantially greater risk to the airframe (and you) over 1/2 way up the launch, and even more as it progresses (with little risk below half-launch situation) because of increasing resolved forces acting 'downwards' (relative to the glider). Yes the weak link should provide protection - BUT are you sure the weak link is the correct one? Is your airframe perfect (in manufacture, later storage, repair, infestation, rot, corrosion, etc )?
Fortunately we have not seen many situations where the structure has failed through over-speeding. We have seen more damage and death with too low airspeeds or failed launches. A little off this particular thread but please may I reiterate the advice that we should all take a (repeated) look at the BGA advice, arrived at through a proper scientific analyisis to the 'BGA safe winch launching initiative' to reduce accidents (proven to help). The basic advice is at
https://members.gliding.co.uk/wp-con...fely_Part1.mp4
The whole programme is at
https://members.gliding.co.uk/bga-sa...safe-winching/

Pete.

At 11:22 07 November 2017, Peter Whitehead wrote:
On Monday, 6 November 2017 12:48:16 UTC, Dan Schmitz wrote:
I'm wondering what the consequences of overspeeding on winch launches
are=
? I understand that it places stress on the airframe, but to what extent?
=20
I find it near impossible to control the airspeed on the top third of a
l=
aunch and have found myself over speeding the placarded max. speed by 5 -
1=
0 knots a few times despite signalling to the winch driver.
=20
Should I be taking the approach of releasing at 2/3 of typical launch
hei=
ght (e.g. 700 - 800 foot) if my airspeed isn't under control at this
point?
=20
Thanks in advance

Dan, my response is "yes".

The physics suggest that there is substantially greater risk to the
airfram=
e (and you) over 1/2 way up the launch, and even more as it progresses
(wit=
h little risk below half-launch situation) because of increasing resolved
f=
orces acting 'downwards' (relative to the glider). Yes the weak link
should=
provide protection - BUT are you sure the weak link is the correct one?
Is=
your airframe perfect (in manufacture, later storage, repair,
infestation,=
rot, corrosion, etc )?=20
Fortunately we have not seen many situations where the structure has
failed=
through over-speeding. We have seen more damage and death with too low
air=
speeds or failed launches. A little off this particular thread but please
m=
ay I reiterate the advice that we should all take a (repeated) look at
the
=
BGA advice, arrived at through a proper scientific analyisis to the 'BGA
sa=
fe winch launching initiative' to reduce accidents (proven to help). The
ba=
sic advice is at=20
https://members.gliding.co.uk/wp-con...04/1430311979=
_HowToWinchSafely_Part1.mp4
The whole programme is at=20
https://members.gliding.co.uk/bga-sa...safe-winching/

Pete.

There is another aspect to this, which unfortunately cannot be evaluated.
My understanding from a BGA Technical Officer a long time ago, was that the
designer does not calculate the maximum speed that the specified gust load
can be withstood safely, but rather decides on a speed, and then does the
calculation to show that that speed is safe. We don't know, but it may well
be safe at a much higher speed. Some years ago the BGA National Coach tried
to get the Puchacz max winch speed increased above 59 kts. This gives a
very narrow window when you don't really want to be below 55 kts in the
full climb.
Dave