Wing Launch - Can it pull your wings off?

On Aug 17, 6:16*pm, bildan wrote:
On Aug 17, 4:50*am, Derek C wrote:





On Aug 15, 7:51*pm, Andreas Maurer wrote:

On Sun, 15 Aug 2010 10:12:03 +0200, John Smith

wrote:
Derek C wrote:
The site in question is a narrow strip 800 metres long, sloping
downhill at about 1 in 10, on top of a hill and totally surrounded by
small unlandable vineyards. They always launched downhill,
irrespective of wind direction. Once above about 200ft, but below
circuit height, the only cable break option to get back onto site was
a 180 degree turn (teardrop circuit) to land back uphill.

And where's the problem?

The timing.

With such a short field it might be necessary to execute this teardrop
circuit at very low altitude because it's not possible anymore to land
straight-on.

Little error margin for finding the right compromise between executing
the turn ionto final at a healthy altitude and not too close to the
airfield.

It's definitely more relaxed to execute this teardrop circuit at
300ft+.

Cheers
Andreas

Here is a video of a German pilot getting a teardrop circuit wrong
after an 80 metre (about 250ft) cable break:

*http://www.youtube.com/watch?v=_xCct...os=zqLm5HhNvPc

Derek C

Andreas, Derek, your posts reveal, in great detail and in ways you
obviously don't realize, just how screwed up many UK winch operations
are. *The real danger for US operations is if they take your posts as
"normal" operations - they aren't. *I hope they will ignore the UK and
study Continental, *specifically German operations instead.

Dyneema doesn't just "break", clumsy, incompetent operations break
it. *Clearly your Dyneema is being damaged by poor winch design and
rough handling. *You don't let Dyneema "fall", you pull it to the
winch.- Hide quoted text -

- Show quoted text -

I note from his profile that Andreas has a German email address, so I
guess that he lives and flies in Germany!

In fact German and UK practices are pretty similar, apart from the
German land line telephone requirement for communication between the
launch point and the winch. The standard European winch used to be the
German Tost, but it is now becoming the British Skylaunch. The French
National Gliding Centre have recently ordered two turbo-diesel engined
Skylaunch 2 winches, with one already delivered and in service.

Derek C

On Aug 17, 6:19*pm, bildan wrote:
On Aug 17, 4:50*am, Derek C wrote:

On Aug 15, 7:51*pm, Andreas Maurer wrote:

On Sun, 15 Aug 2010 10:12:03 +0200, John Smith

wrote:
Derek C wrote:
The site in question is a narrow strip 800 metres long, sloping
downhill at about 1 in 10, on top of a hill and totally surrounded by
small unlandable vineyards. They always launched downhill,
irrespective of wind direction. Once above about 200ft, but below
circuit height, the only cable break option to get back onto site was
a 180 degree turn (teardrop circuit) to land back uphill.

And where's the problem?

The timing.

With such a short field it might be necessary to execute this teardrop
circuit at very low altitude because it's not possible anymore to land
straight-on.

Little error margin for finding the right compromise between executing
the turn ionto final at a healthy altitude and not too close to the
airfield.

It's definitely more relaxed to execute this teardrop circuit at
300ft+.

Cheers
Andreas

Here is a video of a German pilot getting a teardrop circuit wrong
after an 80 metre (about 250ft) cable break:

*http://www.youtube.com/watch?v=_xCct...os=zqLm5HhNvPc

Derek C

Yes, and it's obviously a landing accident, not a winch accident. *The
pilot had a perfect opportunity to make a safe landing and failed to
do so.- Hide quoted text -

- Show quoted text -

This crash is known to have occured after a cable break at about 80
metres (listen to the commentary) and the pilot attempted to fly a
teardrop circuit to a downwind landing. He looks almost reasonably
high on baseleg, but obviously didn't have enough airspeed, hence the
spin (speed and height being interchangeable). There appear to be
houses and trees in the overshoot field, so landing there might not
have been an option. Does anybody know the runway length at Magdeburg?

Derek C

Derek C wrote:
Does anybody know the runway length at Magdeburg?

Plenty. http://eddh.de/info/landeinfo-ergebnisb.php?ueicao=EDBM

On 8/17/2010 6:25 PM, Andreas Maurer wrote:
On Tue, 17 Aug 2010 16:51:29 -0500, brian whatcott
wrote:


is the crucial issue abrasion, or UV degradation?

I guess it's a combination of less-than-perfect winch design, not
completely level airfield and using already damaged cable that results
in shorter than expected lifespan of the Dyneema cable and a
comparably high number of cable breaks.

One problem is that in case of a cable break the latter often falls
into a little wood from which recovery is difficult (pulling the cable
trough the wood usually damages it sufficiently that it needs
replacement).


But our main problem is completely different: As I already wrote in
another posting in this thread, the Dyneema cable gets blown all over
the place in case of a cable break with even a medium crosswind,
forcing us to cease all operation till the cable has definitely been
cleared out of the way.
We've been badly surprised several times about how long the Dyneema
cable stays in the air and how far it can be blown.

Andreas


I see, abrasion and low density blow down. Perhaps a little drogue and
post partum pull back - or is that the way it is?

Brian W

On Wed, 18 Aug 2010 06:16:56 -0500, brian whatcott
wrote:

I see, abrasion and low density blow down. Perhaps a little drogue and
post partum pull back - or is that the way it is?

That's the way it is, unfortunately.

Generally we found that Dyneema is simply much less fault-tolerant
than a steel cable - small handling errors (like using a little too
much power to pull it out of the wood) often result in a really
expensive damage.

Andreas

On Wed, 18 Aug 2010 13:54:38 +0200, Andreas Maurer wrote:


Generally we found that Dyneema is simply much less fault-tolerant than
a steel cable - small handling errors (like using a little too much
power to pull it out of the wood) often result in a really expensive
damage.

I'm not altogether surprised. I once tried using a light (5-10Kg) woven
Dyneema line the control tailplane release for VIT and d/t on a small
(F1J) power model, which required it to slide round a 3mm alloy tube that
converted the movement from fore and aft through the fuselage to vertical
travel as the tail surface moved. It was a miserable failure -the mere
act of threading the line into the fuselage caused it to fluff into total
unusability. I threw it away and replaced it with woven Dacron. Problem
solved.

Since then the only Dyneema I've used has been 100 lb kite bridle, which
I used as the towline for an F1A competition model glider. This line has
a core of straight Dyneema fibres inside a woven Dacron sheath and is
excellent: no tangles, nice to handle, abrasion resistant. Its very stiff
too. The total stretch is about 150mm in a 50m length under the nominal
5Kg test tension - and even that stretch is mostly pulling the kinks out.

On this showing I'd be wary of any Dyneema rope that lacks a Dacron outer
casing: the ease with which the naked Dyneema line fluffed up was really
a shock.


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

On Aug 18, 11:47*am, John Smith wrote:
Derek C wrote:
Does anybody know the runway length at Magdeburg?

Plenty.http://eddh.de/info/landeinfo-ergebnisb.php?ueicao=EDBM

If the runway length is 1000m as claimed, from 80 metres high (260ft)
it should have been possible to just open the airbrakes and land
straight ahead, especially as the windsock in the crash video is
showing a reasonably stiff headwind. In the UK we always encourage
pilots to land ahead as the primary option, if reasonably possible, as
no low turns with a risk of spinning are involved. My club also
charges a much reduced winch launch fee for landing straight ahead as
a futher incentive.

Derek C

Some translation from Free Flight Duration Model Airplane speak.

I'm not altogether surprised. I once tried using a light (5-10Kg) woven
Dyneema line the control tailplane release for VIT -- Variable Incedence Tail
....and d/t -- DE-THERMALIZER (brings the plane down quickly after a
set time) on a small
(F1J) (.051 Cubic Inch Displacement) power model, which required it to slide round a 3mm alloy tube that
converted the movement from fore and aft through the fuselage to vertical
travel as the tail surface moved. It was a miserable failure *-the mere
act of threading the line into the fuselage caused it to fluff into total
unusability. I threw it away and replaced it with woven Dacron. Problem
solved.

Since then the only Dyneema I've used has been 100 lb kite bridle, which
I used as the towline for an F1A competition model glider. This line has
a core of straight Dyneema fibres inside a woven Dacron sheath and is
excellent: no tangles, nice to handle, abrasion resistant. Its very stiff
too. The total stretch is about 150mm in a 50m length under the nominal
5Kg test tension - and even that stretch is mostly pulling the kinks out.

On this showing I'd be wary of any Dyneema rope that lacks a Dacron outer
casing: the ease with which the naked Dyneema line fluffed up was really
a shock.

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

On Aug 18, 5:54*am, Andreas Maurer wrote:
On Wed, 18 Aug 2010 06:16:56 -0500, brian whatcott

wrote:
I see, abrasion and low density blow down. Perhaps a little drogue and
post partum pull back - or is that the way it is?

That's the way it is, unfortunately.

Generally we found that Dyneema is simply much less fault-tolerant
than a steel cable - small handling errors (like using a little too
much power to pull it out of the wood) often result in a really
expensive damage.

Andreas

And yet there are many user finding Dyneema is far, far more tolerant
than steel. Go to a manufacturer's spec sheet and look at the
numbers. It has 15x the abrasion resistance of steel and absolutely
no tendency to twist or kink. It handles shock loads much better than
steel. It has only three weaknesses - chlorine bleach, heat and sharp
edges.

Users with excellent rope handling winches see no breaks until it
wears out. If it's breaking before it's worn out, it's getting
damaged - most likely by the winch. Undamaged Dyneema just doesn't
suffer random breaks like steel.

Poor fairlead design is the biggest culprit. Allowing the rope to
contact sharp edges somewhere in the rope path runs a close second.
Airfield surfaces, even really rough ones, do little damage.

Fairleads must use sheaves, not rollers. The grooves in the sheaves
must have a very specific cross section called out by the rope
manufacturer. Industrial studies have shown this is critical to long
life. On every winch I've seen without a Dyneema-specific sheave,
I've been able to pull strips of melted Dyneema off the fairlead.

Drums must be boxed. It's not unusual for a loop to form on the drum
for a fraction of a second and whip the rope against a sharp edge on
the winch frame before it gets pulled tight on the drum again. One
winch operator declared this couldn't happen or he would have seen
it. I pointed to bits of torn rope on a frame bracket 8 feet behind
the drum as evidence it was happening.

Dyneema is wonderful stuff and it will last up to 15x steel but it
needs a different rope path design and handling protocol.

On Aug 12, 4:12*pm, Frank Whiteley wrote:
On Aug 12, 3:16*pm, ContestID67 wrote:



I was sent this link from a UK soaring friend of mine about a death
when the wings came off of a glider during a winch tow.http://www.dailymail.co.uk/news/arti...lunged-death-b...

Sad story. *A few things;

- My friend's thought was that the wing pins were left out. *Howerver,
this was the second flight of the day. *Both winch launches. *So I
would think that the wing pins were installed but the wings failed
under a winch load. *Which glider was it? *Older? *Wooden spars?
Never having had a winch launch, what happens if you don't release
back pressure at the top? *Can you pull your wings off? *Maybe
safeties on the pins were missed and the pins wiggled out on the
second flight after staying in for the first.

- I was under the impression that the BGA required parachutes for all
pilots. *Wrong? *1000 ft should have been enough to get out in time
but who knows what was happening in the cockpit or if she was 1000 MSL
or AGL at the time.

Thanks.

- John DeRosa

It was aFoka4.

Foka-4was a derivative of theFokalinehttp://en.wikipedia.org/wiki/Foka_%28glider%29
Cobra was the next to last iteration, with 17m being the last.http://en.wikipedia.org/wiki/SZD-36_Cobra_15
Note the comments on failures.

I don't know that the4had the same wing join design, but suspect it
was very similar.
There was a wing failure on a Cobra in the US and a sobering analysis.http://www.sylacaugasoaring.com/SZD%...%20WARNING.htm

The SHK has an expanding vertical pin. *There's an anecdotal story of
someone who used the right-hand to expand the pin, and finished the
job with left-hand, in the opposite direction. *The wings reportedly
departed at the top of the launch. *The pilot reportedly pulled the
tail chute on the way down.

I believe that some German studies found that successful egress and
parachute deployment below 600m is unlikely, of course there are
exceptions. *The better emergency chutes are life saving from 100ft
agl at 100kts horizontal.

Wing failure on a winch launch is very rare. *There was a K-7 at RAF
Dishforth in the UK a while back, but the investigation determined
there was prior damage to the spar which was not found following
another incident. *There was a homebuilt in Colorado that had a wing
failure due to aileron flutter during a winch launch. *After two weak
link breaks, the pilot doubled the weak link (unknown to the winch
crew). *The described flight path was one of climb, level off, climb,
level off, climb, glider breakup, crash. *The wing inspection hatch
was found early in the flight path. *What did not appear in the NTSB
report was that the pilot was refused further tows at the local FBO
after the glider had suffered significant aileron flutter on aero tow.

I winched at RAF Bicester when it was the RAF/GSA Centre. *Appropriate
weak links were always used, like any UK club. *It's not a long run,
but easy enough to climb away on the thermal day.

Steel wire rope used in many places typically has a breaking strength
of 2800-3500lbs. *The new UHMWPE 12-strand ropes (Spectra, Plasma,
Dyneema, Amsteel) now in common use are nominally 3500-5400lbs
breaking strength at similar diameters, thus use of correct weak links
are essential to avoid damaging a glider as some winches have
substantial power and there are also gusts and thermals to allow for.

Frank Whiteley

Reading the UK URAS new group today, I see someone posted a link to
this FAA doc
http://www.ntsb.gov/recs/letters/1974/A74_100_101.pdf
which gives another mode of failure specific to the Foka 4.

The AAIB analysis will prove interesting.

Frank Whiteley