Overspeeding on winch launches

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

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 |

On Monday, November 6, 2017 at 6:48:16 AM UTC-6, 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
When our club was winching fairly often, I was one of the winch drivers (with only a 3-4 hundred runs though). As the glider begins to reach the last third of the launch, the power must back off, sometimes to barely above idle. this is especially true if launching into a good brisk headwind.

Q: "I understand that it places stress on the airframe, but to what extent"
A: Up to the breaking strength of the weak link. Max ground launch speed is there to protect the weak link not the glider.

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.

That statement is not true when ground launching gliders certified under the old Glider Criteria Handbook in the USA. In that case the ground launch limit is a structural limit!

Well, you've got that wrong.

I don't agree with:

", i.e. when the climb
starts to flatten, you should release immediately if you're even slightly
above the placarded max winch speed. "

I do agree of course that exceeding the placarded limit is not a problem earlier in the launch when the cable is pulling the glider more forward than down, but that the load on the glider (and the weak link) is more critical towards the end of the launch. However, rather than releasing, I think that safety (and not breaking the weak link) can be achieved by relaxing the back pressure.

The correct weak link should prevent any glider from suffering structural failure, and probably does. But has anyone ever heard of any accident caused by exceeding a placarded maximum launch speed?

On Mon, 06 Nov 2017 16:33:03 -0800, waremark wrote:

The correct weak link should prevent any glider from suffering
structural failure, and probably does. But has anyone ever heard of any
accident caused by exceeding a placarded maximum launch speed?

Not that I've heard of, but that's pretty much a direct quote from any of
the instructors at GRL - especially w.r.t. the Puchacz.

I tend to apply it pretty rigidly to my Libelle because she's an old
lady, 48 this year, and I feel that I should be kind to her.

Actually, Libelles would appear to have a better protection than the weak
link: I was at Eden Soaring at the end of September, where pole-bending
is pretty much de rigeur thanks to a somewhat short field (940m winch to
launchpoint) and the need to get to the hill, 2.5 km away, at least 900ft
above the airfield, so you hear words from the instructor if you're
climbing out at less than 45 degrees during a site check in their K13.
Anyway, I soon found out that doing the same in my Libelle tends to back
release a little before I'd normally pull the bung and certainly before
the weak link went. They have good winch drivers: good brisk acceleration
at the start and spot on 65 kts in the top half of the launch.


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

At 00:33 07 November 2017, waremark wrote:
I don't agree with:

", i.e. when the climb=20
starts to flatten, you should release immediately if you're even
slightly=
=20
above the placarded max winch speed. "

I do agree of course that exceeding the placarded limit is not a
problem
ea=
rlier in the launch when the cable is pulling the glider more
forward than
=
down, but that the load on the glider (and the weak link) is more
critical
=
towards the end of the launch. However, rather than releasing, I
think
that=
safety (and not breaking the weak link) can be achieved by
relaxing the
ba=
ck pressure.

The correct weak link should prevent any glider from suffering
structural
f=
ailure, and probably does. But has anyone ever heard of any
accident
caused=
by exceeding a placarded maximum launch speed?

I watched a fatal winch launch accident happen ,and it still haunts
me.
The climb was not steep but the pilot got into a PIO while trying to
sort it out .1 wing broke off near the root and it came down
side ways.
There were structural faults in the glider wing and the weak link was
doubled,BUT the experienced winch driver said there was little load
on the cable.
We put it down to the change in angle of attack at high speed, the
load hits the wing first, then the hook, it is not until all the bow is
taken from the cable that the load it on the weak link and the driver
feels it.
max winch means max.
However I have not let it stop me, but I never have full back stick at
near max winch speed and I try to be smooth .
Jon May