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 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.

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

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