Blanik Weak Link for Winch Launch???

I'm really curious what weak link people are using to winch launch
Blaniks with. If you are using the CG bridle, do you use the blue tost
weak link (in the BGA list) or a stronger one? Blue seems too weak and
wants to break frequently and under only moderate climb angles. The
L-13 manual suggests a 2000 lbs link if you are using the bridle,
however there is no similar wording in the L-23 manual.

Gary

our L-23 has a CG hook and does away with the bridle requirement..

maybe that's why it does not state specifically which strength weak link to
use

BT

"Gary Emerson" wrote in message
. com...
I'm really curious what weak link people are using to winch launch
Blaniks with. If you are using the CG bridle, do you use the blue tost
weak link (in the BGA list) or a stronger one? Blue seems too weak and
wants to break frequently and under only moderate climb angles. The
L-13 manual suggests a 2000 lbs link if you are using the bridle,
however there is no similar wording in the L-23 manual.

Gary

BTIZ wrote:
our L-23 has a CG hook and does away with the bridle requirement..

maybe that's why it does not state specifically which strength weak link to
use

BT

"Gary Emerson" wrote in message
. com...

I'm really curious what weak link people are using to winch launch
Blaniks with. If you are using the CG bridle, do you use the blue tost
weak link (in the BGA list) or a stronger one? Blue seems too weak and
wants to break frequently and under only moderate climb angles. The
L-13 manual suggests a 2000 lbs link if you are using the bridle,
however there is no similar wording in the L-23 manual.

Gary




Our club has hundreds of launches with a L13 on a blue link. Never broken a weak
link, in general the cable fails first. Our winch is a 302cu inch Ford Windsor
motor, so possibly our results may not be representative of newer more powerful
winches. In still wind conditions we get around 1500' launches, dual with a
1800m cable run. Record is 2300', solo into a 25km/h headwind.

One point, if you use a winch and do not transition progressively into the steep
climb angle something is going to break. The Blanik has powerful elevators and
with flaps out can put a huge load on the cable. If the load is applied smoothly
all you get is a descending note from the winch, if you are rough you get a
cable break as often as not.

Similarly the bridle allows the L13 to maintain a large angle of attack at the
top of the launch. This is unwise because of the load on the glider , and will
also break cables. I have seen an over enthusiastic pilot and a strong gust
combine to lift one side (jack and wheel) of our winch right off the ground...
If you do break the cable at this point (and AOA) the probability of a
stall/spin accident is high. Pilots used to the porpoising effect of a CG hook
may inadvertently pull too hard at the top of the launch because the bridle does
not seem to do this?

Our experience is that breaks are usually caused by pilots and winch drivers
trying too hard - result is snatching or "rough" launches, and cable breaks.
Once everyone got used to the idea that a couple of feet was not worth the
regular cable repairs we have had a remarkable decrease in cable breaks.

Bruce,

That's very interesting - what size cable are you using???? I would
have thought it would have been best to have a cable that was
significantly stronger than the weak link to avoid damage to the cable
and rely on the weak link to do it's job if needed.

Also, take a guess at the target indicated airspeed you see when you get
your best launches. I know what the Blanik speed limits are.

Gary

Bruce Greeff wrote:
BTIZ wrote:

our L-23 has a CG hook and does away with the bridle requirement..

maybe that's why it does not state specifically which strength weak
link to
use

BT

"Gary Emerson" wrote in message
. com...

I'm really curious what weak link people are using to winch launch
Blaniks with. If you are using the CG bridle, do you use the blue tost
weak link (in the BGA list) or a stronger one? Blue seems too weak and
wants to break frequently and under only moderate climb angles. The
L-13 manual suggests a 2000 lbs link if you are using the bridle,
however there is no similar wording in the L-23 manual.

Gary




Our club has hundreds of launches with a L13 on a blue link. Never
broken a weak link, in general the cable fails first. Our winch is a
302cu inch Ford Windsor motor, so possibly our results may not be
representative of newer more powerful winches. In still wind conditions
we get around 1500' launches, dual with a 1800m cable run. Record is
2300', solo into a 25km/h headwind.

One point, if you use a winch and do not transition progressively into
the steep climb angle something is going to break. The Blanik has
powerful elevators and with flaps out can put a huge load on the cable.
If the load is applied smoothly all you get is a descending note from
the winch, if you are rough you get a cable break as often as not.

Similarly the bridle allows the L13 to maintain a large angle of attack
at the top of the launch. This is unwise because of the load on the
glider , and will also break cables. I have seen an over enthusiastic
pilot and a strong gust combine to lift one side (jack and wheel) of our
winch right off the ground...
If you do break the cable at this point (and AOA) the probability of a
stall/spin accident is high. Pilots used to the porpoising effect of a
CG hook may inadvertently pull too hard at the top of the launch because
the bridle does not seem to do this?

Our experience is that breaks are usually caused by pilots and winch
drivers trying too hard - result is snatching or "rough" launches, and
cable breaks. Once everyone got used to the idea that a couple of feet
was not worth the regular cable repairs we have had a remarkable
decrease in cable breaks.

Hi Gary

We use 2.51 or 2.75mm Spring Steel single strand cable, in grade C temper.
This gives 1860 to 2070MPA breaking strain, which is theoretically significantly
more than the blue link.

Full spec is:
2.51 mm
1860/2070 MPA
Code: 46 /0264/1862 1 / A
Din 17222 Grade C

Tests have been done on knotted wire and the reason for the situation found.
Quite simply , the first knot in the wire lowers the strength to around 900KG at
the knot - which is where it breaks. Since we always knot the wire to our
parachute, the weak link is superfluous, but we keep it for insurance.

The single strand spring steel is very resistant to wear in our rough gravel
strip, and is very easy to repair. We get about 1000 launches on a cable before
it work hardens to the point where the increasing frequency of cable failures
prompts replacement.

Speed on the launch is fairly simple, let the L13 fly itself off the ground at
around 75-80Km/h.
Hold attitude steady as the speed increases to around 100Km/h and altitude goes
up to around 100'. Rotate smoothly into steep climb, knowing that you have
enough energy to recover from a break. Speed generally touches 110-120km/h
before slowing to a climb out at a target speed of 95-100Km/h, with half flaps.
We stow the flaps if speed exceeds 100 because the force required at higher
speeds is too high.

This gives best results on our winch, which I suspect is a little underpowered
for the Blanik. Standard procedure on the winch is to smoothly roll on full
power in four seconds and hold it until the last seconds of the launch. (when
you hear the winch stop labouring, you know it is time to start backing off the
power, or you will overspeed)

Maximum height tends to be achieved when the transition to steep climb is early
in the launch, so a headwind makes a big difference.

Hope this helps.
Bruce

Gary Emerson wrote in message .com...
I'm really curious what weak link people are using to winch launch
Blaniks with. If you are using the CG bridle, do you use the blue tost
weak link (in the BGA list) or a stronger one?... The
L-13 manual suggests a 2000 lbs link if you are using the bridle,
however there is no similar wording in the L-23 manual.

My club autotow-launched a Blanik L-13 1995-2000; we used dacron rope
and the standard bridle with no weak link because we tested the actual
breaking strength of the rope with a tensiometer and found it to be
1800 lbs. new. The standard L-13 bridle has a factory-supplied weak
metal link that meets their criteria. After we had tested our rope, I
simply removed this weak link because we found that if the weak link
is at the glider end of the system and a break occurs, the bridle
falls off into a corn field or a factory roof and is never seen again,
and at about $200 per bridle this is a bit much.

Auto-tow lauching is hard on the truck-end of the rope, creating a
natural weak link through abrasion; when this end of the rope breaks,
it's also very easy to find the bridle.

I've written a long manual based on our ground-launching experiences,
located at
http://amygdala.danlj.org/~danlj/Soa...nch/index.html

Dan Johnson

Our club has hundreds of launches with a L13 on a blue link. Never broken a weak
link, in general the cable fails first. Our winch is a 302cu inch Ford Windsor
motor, so possibly our results may not be representative of newer more powerful
winches. In still wind conditions we get around 1500' launches, dual with a
1800m cable run. Record is 2300', solo into a 25km/h headwind.

One point, if you use a winch and do not transition progressively into the steep
climb angle something is going to break. The Blanik has powerful elevators and
with flaps out can put a huge load on the cable. If the load is applied smoothly
all you get is a descending note from the winch, if you are rough you get a
cable break as often as not.

Similarly the bridle allows the L13 to maintain a large angle of attack at the
top of the launch. This is unwise because of the load on the glider , and will
also break cables. I have seen an over enthusiastic pilot and a strong gust
combine to lift one side (jack and wheel) of our winch right off the ground...
If you do break the cable at this point (and AOA) the probability of a
stall/spin accident is high. Pilots used to the porpoising effect of a CG hook
may inadvertently pull too hard at the top of the launch because the bridle does
not seem to do this?

Our experience is that breaks are usually caused by pilots and winch drivers
trying too hard - result is snatching or "rough" launches, and cable breaks.
Once everyone got used to the idea that a couple of feet was not worth the
regular cable repairs we have had a remarkable decrease in cable breaks.

Our winch at the PSA is big block powered and has no trouble breaking a
blue link when towing the L-13. We have Plasma rope which does not fail.
Sounds like a good reason for the Winch Telemetry System. YO BILL, any
updates??

Craig-