Overspeeding on winch launches

On Mon, 06 Nov 2017 05:25:52 -0800, Tango Whisky wrote:

Le lundi 6 novembre 2017 13:48:16 UTC+1, Dan Schmitz a écritÂ*:
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

If you are overspeeding on winch launch, ease the stick forward as
needed to stay in the flight enveloppe. If this doesn't help, release
and talk to the winch driver when back on the ground.

If you are overspeeding while flying a high angle of attack, remember
that the whole load generated by the winch is fed via the fuselage into
the wing (and you won't feel a thing unlike while pulling g's in free
flight). If you have a weak ling popping at say 1000 daN, that is like
you had added 1000 kg to the weight of your fuselage. If you fuselage
weights 200 kg, adding 1000 kg translates to a "g-load" of 6 g.

What Tango Whisky says.

Quite a high degree of overspeed (5-10 kts) is acceptable in the first
half of the launch because most of the cable tension is pulling you
forward rather than down, but above that point, i.e. when the climb
starts to flatten, you should release immediately if you're even slightly
above the placarded max winch speed.

The ideal launch speed for most single seaters is about 5 kts[*] below
the placarded max: you get almost as high and the launch feels nicer and
a bit more controllable.

[*] Vwinch for an ASK-21 is 80 kts, but we virtually never exceed 70kts
on the winch with out club gliders - there's simply no need to launch
them that hard.

My H.201 Libelle has a Vwinch of 65 kts, which I strictly observe
in the top half of the climb and almost never exceed below that, but
it definitely feels a lot nicer at 60kts. That speed reduction costs
me no more than 100 ft. We normally place the winch 1200m (4000ft)
from the launch point and I expect to get 1300-1400 ft in typical
wind conditions.


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

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 this
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 transmission
surging
can add loads. That is what the weak link protects against. The
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 a
habit.

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

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

of gusts.

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

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

I am going to purchase the kit for our expedition winch and auto-tow outfit, and one for my glider. A small price for higher and safer launches, compared to what we spend on 'gizmos'. I have no connection with Skylaunch though they have always provided great service and everything I have needed in terms of launching accessories.
The 'wheel has been invented'. We don't need to anguish over the question - "should I pull off before my wings are pulled off?"!