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.

Thanks everyone for your feedback. My take aways from this a

1. Speak with the winch driver. I've had fast launches a few times with no reduction in power when signalling.
2. Get the airspeed under control early in the launch.
3. Release early if over speeding past the first 1/2 of the launch.
4. Smooth control inputs and don't give full up elevator towards the top of the launch if over speeding.

Thanks,

Dan

Having a little engine I don't winch launch but reading through
the earlier posts it sounds like little has changed in 40 years:
why, in the 21st Century, don't the pilot and winch driver
communicate by radio? Surely all this waggling the wings
about stuff should long ago have been scrapped?

I would repeat what Scott said above as well. I've done quite a few launches as driver on our winch here at Utah Soaring, and we are always back to 1/3 or 1/4 throttle as the climb rate begins to slow and the glider begins to arc over at the top, and sometimes get all the way to idle by the time the back release engages. The less tension on the line the better the back release works, at least on our Astir.

I assume "signaling" is done by radio? If not, that seems to be a "weak link" in the process chain, as Dave suggests.

Mike

On Tue, 07 Nov 2017 09:00:58 -0800, Mike Hendron wrote:

I would repeat what Scott said above as well. I've done quite a few
launches as driver on our winch here at Utah Soaring, and we are always
back to 1/3 or 1/4 throttle as the climb rate begins to slow and the
glider begins to arc over at the top, and sometimes get all the way to
idle by the time the back release engages. The less tension on the line
the better the back release works, at least on our Astir.

I assume "signaling" is done by radio? If not, that seems to be a "weak
link" in the process chain, as Dave suggests.

Where I fly, glider-winch signalling is visible: lower the nose of the
launch is too slow and use the rudder to wave your tail at the winch if
its too fast.

Our duty launch marshal uses radio, rather than lights, to pass glider
details to the winch driver and to manage the launch, but that doesn't
use an airband frequency and we do not have an airband radio in the
winch.

Our airband frequency is used for glider-tug, glider-glider comms and for
blind calls as we join the circuit. The launch marshal has an airband
receiver to help him maintain situational awareness, but he is primarily
concerned with managing winch launching and co-ordinating launches with
aerotow operations. On a typical day winch launches considerably
outnumber aero tows.

I know that at least one Scandinavian club experimented with using radio
telemetry to display the glider's airspeed to the winch driver, but I
don't know if they still use it or what their conclusions about its
benefits were.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

At 17:28 06 November 2017, George Haeh wrote:
https://members.gliding.co.uk/bga-sa...safe-winching/

The BGA has published a an excellent winch launching resource.

Well worth memorizing at the beginning of every season.

The winch driver should be reducing power at the top of the launch as thi
is
where overspeed becomes critical.

Do remember to have a correct weak link.

I managed to break one just as I was releasing. Gusts and transmissio
surging
can add loads. That is what the weak link protects against. Th
manufacturer
airspeed limit gives some margin for gusts; so yes, on a calm day a small

airspeed exceedence might not break the weak link. But don't make it
habit.

We qualify in a 2-seater, but a single seater handles differently. Th
winch
generally has to run at the max for a 2-seater, but has excess power for
single
seater.

Tension can go up or down a few hundred pounds in very few seconds becaus

of gusts.

You can always invest in a Launch Assistant from Skylaunch. An ASI
transmitter in the glider, and a receiver/readout in the winch. Not that
expensive, and doesn't have to be a Skylaunch winch.
Dave

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

On Monday, November 6, 2017 at 1:48:16 PM UTC+1, 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 - if you are overspeeding in the last third of the launch, your winch driver is inept and needs some supplemental training! He needs to back off the power much more when launching a light single seat glider compared to a heavy K21 or TwinAstir. Ideally, the winch operator retards the engine to the point where the glider over-flies the line and executes a very soft back-release.

Uli
Winchmeister, Carolina Soaring Assoc.

On Tue, 07 Nov 2017 18:15:23 +0000, David Salmon wrote:

You can always invest in a Launch Assistant from Skylaunch. An ASI
transmitter in the glider, and a receiver/readout in the winch. Not that
expensive, and doesn't have to be a Skylaunch winch.
Dave

So I see. That answers all my questions about size/weight/how it is
installed in the glider. Thanks.



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

At 20:56 07 November 2017, Martin Gregorie wrote:
On Tue, 07 Nov 2017 18:15:23 +0000, David Salmon wrote:

You can always invest in a Launch Assistant from Skylaunch. An ASI
transmitter in the glider, and a receiver/readout in the winch. Not
that
expensive, and doesn't have to be a Skylaunch winch.
Dave

So I see. That answers all my questions about size/weight/how it is
installed in the glider. Thanks.



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

It is a small lightweight plastic box, from memory around 75x25x10. Needs
tee-ing in to the pitot and static lines, and also needs a 12v supply. So
light, it could be velcro'd under the panel, or tie wrapped. It detects the
start of the launch, at around 25kts, then transmits the airspeed to the
receiving unit in the winch, which has an analogue airspeed readout, then
after the launch, switches itself off. Check out the Skylaunch web site.
Dave