Glider winch launch question
 

I saw my first glider winch launch the other day. I understood the principle but had never seen it done before. The first thing that struck me though was what would happen if the the cable release failed?

With an aircraft tow you clearly have time to work the problem. But with a ground winch, which seems to involve release when the cable approaches vertical, then a failure to release looks like it would very rapidly get very serious.

The glider winch-hook has a back-release mechanism, which should operate as the the glider overflies the winch. If that doesn't work,then the winch driver uses a guillotine to cut his end of the cable.

The subsequent landing with >1000' of cable attached should be "interesting" :eek:

From a design point of view, the winch launch is a very important case. At the top of the launch, the wing has to generate lift equal to the weight of the glider PLUS the tension on the cable.

Overlap with Above The Clouds, who points out the weak link which I forgot about!

You would treat it in a similar manner to an engine failure after take-off, depending on the altitude obtained would determine your choice of landing area/field.
If by the top of the winch launch and cable could not be released from the cockpit then there are two fail safes, once the glider has flown past the vertical point of the cable then the tow cable will release aft, if that doesn't work then there is a weak link in the cable system that would break once the downward pull force is exceeded.

Thanks for that. Very interesting.

The other things that struck me...

1. You need a pretty long runway because the glider can only get as high as the runway is long - less the length of cable that the winch has drawn in to achieve the launch.

2. At the end of the launch most of the cable tension must be in the downward direction. The glider must need to be generating a phenomenal amount of lift.

3. The hook (nearly). It is scary as a spectator when you think it is about to hit you from a great height - even if it is on a drag chute.:O

EFATO I know about. Stuff the nose down and aim for something flat. But this I envisage more like being pulled rapidly into a vertical dive with very few manouevering options.!

However I am now clearer what the procedure is. Thanks for that.

Yikes! If you're close enough to be at all worried about the strop hitting you as it comes down, you are far, far too close to the winch for safety.

The only safe place is inside the winch cabin. If the cable breaks, it can violently whip backwards or sideways. I have seen a car written off by a snapped winch cable. I also had the memorable experience of driving a winch when the cable snapped, wrapped itself in a knot and then disintegrated as it hit the rollers, spraying fragments of cable thread all over the place with such force that some of them wrapped themselves around the chicken wire that protected the windscreen.
The spectator who I had insisted joined me in the cabin before the launch (thye had wanted to take photographs) went very quiet.

As with all things to do with aviation there are several different options depending on when the cable breaks during the launch - including landing straight ahead, carrying out 'S' turns or completing a circuit to land (gliders 'glide' therefore have more options than powered aircraft in this situation).

Naturally, preventing a stall, by lowering the nose, and getting rid of the cable are important aspects of the process!

All practised during training and 'par for the course' (in my experience at least).

We were at least 100 metres off to the side of the centreline. It was just that as the drag chute started spiralling down it seemed to be heading our way, possibly due to crosswind. It never really got near us - just a few moments of alarm.

The first thing to note is that a cable break is NOT considered an emergency. I was always told a 1% launch failure (usually cable breaks) was par for the course.

Safety-wise, in many ways, winch launching is much safer than aero-towing anyway. A winch launch can be split into 3 phases:
- Enough runway left to land straight ahead
- Overlap: Enough runway to land straight ahead AND enough height to complete a safe (if abbreviated) circuit
- Enough height to complete a fairly normal circuit
If conditions (wind strength/direction, winch power, runway length) do not provide a sensible overlap then the duty instructor will not allow winching.

Compare that to an aero-tow - in the early stages (once you can't land straight ahead) you often don't have enough height to pick a perfect field/return to the airfield.

OC619

Cable breaks teach you a very good 'get the nose down' reflex That can be life saving if you are flying low inertia, light aircraft when the engine stops!

We used to use solid piano wire, now that went with a bang and came towards the winch like a coiled spring.

There are several ways of severing the connection between the glider and the winch.

Firstly, at the glider, there is the connector that can be either opened manually by the pilot (by pulling the yellow lever/ball/whatever the aircraft has) or will release the ring by itself when pulled back under a certain angle. After the disconnect, the pilot will actuate the release lever a few times by himself to ensure no cable left connected. These are the normal ways to end a winch launch.

Secondly, the cable might break either at the weak link, the parachute or some point in the cable itself. This requires the pilot to fly the above mentioned procedure, not forgetting to drop whatever rope may be still attached to the aircraft again by pulling the release, the ground crew to search for the loose cable and the winch driver to repair the rope using one of the many ways available (occasionally a bloody business).

And thirdly, if the winch driver sees the glider pass behind the winch without dropping the rope or if he is otherwise unhappy with the gliders behaviour (e. g. if it underflies the cables parachute or makes weird movements while under tow), he can use the "guillotine" to cut the cable at the winch. This one typically consists of a blade mounted on a pre-tensioned strong spring that when released will cut through the cable and is required to show its ability to cut several strands of tow line (IIRC, 3 or 5 of them - it has been a while since I last operated a glider winch) at once during the annual check.

This of course leaves the glider with several 100m of cable attached. The options are generally the same as with a breakage plus the silk way down in case of sufficient height: having the line entangled somewhere on the ground during approach will easily lead to nasty consequences, so this option may well be considered as well.

I heartily agree with the words on safety around a winch. A parachute with the weak links to the head can ruin ones afternoon quite well, as can receiving a hit from a broken line. Once after a rather late disconnect of the glider (IIRC, a slight tailwind was involved), I had the parachute assembly come down right beside the winch and hit the roof of the old vehicle used to return the lines to the launch side. The driver was rather white about the gills when he got out, but fortunately received no injuries. He made sure to park a bit further behind the winch after that.

I shall take advantage of having some clearly well informed people taking an interest. So here goes with a couple more observations.

To overcome the downforce of the near vertical cable at the end of the tow, the glider must be producing (I estimate) 3 or 4 G of lift. Is that not a pretty teeth jarring kick in the backside when the cable is released?

The winch must start off fast with low torque while the glider is on the ground, but must rapidly slow down with increasing torque as the glider climbs.That sounds like a job for an electric motor, but the winch is clearly a combustion engine. How is that geared as the torque and speed requirements of this particular usage sounds like a perfect recipe for it to stall?

There are several winch designs around. The one I operated most often had a Magirus-Deutz air-cooled V8 Diesel working on a hydraulic clutch to convert rpm to torque as required. This worked rather nicely and in windy weather with a light glider even allowed the cable drums to run backwards (release heights of above 800m have been achieved that way on a 1100m field), although the clutch had a certain tendency to overheat in hot weather. Rapid-fire launches of heavy gliders and insufficient cooling-down periods made it tend to shed all its oil via the melting fuses. Refilling all the IIRC 15 litres (= nearly 4 gallons) of oil and replacing the fuses was not the most popular job and of course the privilege of the unlucky winch driver. An hour or so under the shower usually followed.

Older designs use a petrol V8 engine (often from an Opel Admiral) and may even have a stickshift gearbox in the drivetrain - I have never operated such a device but have heard that stalling the engine is not impossible on those.

I am not familiar with the newest developments in this field; the last time I operated a glider winch is more than 10 years ago already. An electric motor would sound interesting and like a plausible choice though.

The rope disconnect can be everything from a jolt to hardly feelable. A break somewhere mid-tow is usually on the rougher side, but the earlier or later in the tow it gets, the lighter it is; I had a rope break shortly before disconnect that I did not even notice in the glider and learned about only after landing.

The reason for this is the variable power requirement for a launch: the winch will not always pull with the same force. In order to accelerate the glider, firstly the throttle is rather rapidly opened (how far depends on the individual glider type, its mass, weather etc.). When it is airborne for the first 50 meters of height, a fair bit less power is required in order not to overspeed it: the first 50 meters are climbed rather gently as otherwise altitude would be insufficient to lower the nose in case of a break. Then, when the winch operator sees the glider pull up, he is required to increase power again to keep it at speed during the now more rapid climb. The glider will follow an approximate quarter of a circle then, so in the beginning, more power will be required to "lift" the glider, while in the end, the gliders climb rate will decrease and it will tend to overspeed if the power is not appropriately reduced. Finally, the winch driver will cut the power to idle and the pilot will return the elevator to a more neutral position. Both serves to reduce the tension on the cable and allow it to disconnect without a major jolt.

Operating a glider winch is a bit of a black art involving observing the climb rate of the glider, the slackness of the rope, the engine and drive train sound and many other things. If a guy is proficient on one winch, this does not at all mean he can just switch to another winch and operate it with the same expertise in a second.

Thanks Tu.114.

Clearly I was thinking in terms of kite flying when I was considering the tension on the cable at release! Obviously the glider pilot is not a helpless participant in the process and can take the tension off the cable with some forward stick before releasing. Obvious after it is pointed out.

Yes a hydraulic clutch makes sense too. Perhaps a simple temperature gauge could save some heartache with melted fuses?

My guess is that the poor winch driver is a glider pilot himself/herself most of the time? Just taking a turn on the rota.

Yep - some of my 'longest days' were left and forgotten at the far end of the airfield for hours on end manning and operating the winch.

Yep!

In my case the winch driver was me an impoverished student and lowly member of the gliding club who spent an entire day winching (and mending cable breaks) in return for a quick circuit in the K7 at dusk.

Often got : nah it's too dark now.

Gave up gliding and G Club membership soon afterwards.

Cusco

When the glider is approaching the top of a normal launch the cable is at a significant angle to the glider and therefore the glider forward speed will be a lot higher than the cable speed. (a comparison is a water skier doing tight turns, when his forward speed is much more than the boat speed).

To compensate for this, the winch driver steadily backs off on the throttle as the glider approaches the top of the launch.

The winch driver can further cause the cable to back release from the glider under minimal cable tension by closing the throttle completely. The cable disconnection is then barely noticeable other than as a minor click. This minimises stresses on the hook and cable and is also great for early pupils who can be discommoded by an almighty bang if the cable is released by the instructor under full tension.

Full tension cable releases are normally caused by the instructor at about mid point in the launch in order to give the pupil practice in dealing with mid-height cable breaks (i.e. he/she has to decide whether there is room to land straight ahead or turn a turn is necessary after getting the nose down and adequate airspeed.

The sudden release of tension and the "elasticity" of the cable can then cause loose loops of cable to form on the winch drum and/or the cable to fall off the side of the drum, creating a mega birds nest and the winch driver to swear about f****** instructors doing simulated cable breaks!

Astir8,

ouch, had totally forgotten about these ones. Beside a broken cable, the pull-out car driver not keeping a steady speed and pulling out the cable at about the same speed the drums deliver them was a frequent cause of such a mess. Much cursing ensued; more than once I have had to take the chisel, simply cut the knot up in order to untie it and then resplice the cable - this was sometimes the fastest method to unjam the cable. It was most fun during thermal season with all the cross-country guys waiting over at the launch pad, the phone keeping ringing every 4 seconds ("Are you done yet?" - "NO!" (SLAM!)) and the flight instructor coming over to berate You for taking so long, but then at least lending a hand.

At my club, everyone wanting to fly plastic gliders had to get the winch license and got half a day on the winch about once every 4 to 6 weeks. Procedures at other fields were different.

A nice thread btw - the winch driver is an oft forgotten hermit at the far end of the field.

Me too. I often wonder how many folk were lost to gliding through that sort of inexcusable experience.

My first experience of driving the winch went something like:
Instructor: "You're a solo pilot, aren't you?"
Me: "Yes"
Instructor: "Go and drive the winch then"
Me: "I've never done it"
Instructor: "Tell whoever is in it to show you 2 cables then"
Me: "I'm worried I'll get it wrong / give people cr*p launches"
Instructor: "Good practice for them"

Another time I heard:
Instructor: "Go and drive the winch"
Volunteer: "I'm scared"
Instructor: "Never been anyone killed that end of the cable"

And the most important bit of advice when converting from winch to aerotow...
Instructor: "What's the most important difference between winch and aerotow launching"
Student: Runs through the expected list...
Instructor: "As a glider pilot you can't kill the winch driver ... always remember that"

OC619

P.S. In both cases (mine and the "volunteer") we had both been gliding for a some time, whilst skillfully avoiding winch duty - so it wasn't nearly as bad as the snippets above sound. Also it was many many years ago.

Am I not right in remembering that one of the pre flight checks is the cable release by pulling backwards on the cable to check it comes off cleanly?

Usually done at first flight of day. Cable on-release with cockpit release under no tension. Cable on- back release. Cable on-release with cockpit release under tension.

Interesting reading this thread, unlike a power question everyone seems to be more or less in agreement!

unlike a power question everyone seems to be more or less in agreement...

Darwin?

Well of course glider pilots are higher up the evolutionary scale...:)

The pilot needs a bit of (re)training to lay off for the x-wind, then. That amount of drift shouldn't be tolerated.

FBW

On my first day of gliding with the ATC I actually witnessed a Tutor glider come straight down from the top of a winch launch. The outer section of one wing broke away as it fell. As far as recall, it was thought that the cable did not release. Sadly the pilot was killed.

Spectra is Lovely
 

Just make sure you get it thick enough.

We had lots of practice with cable breaks with the thin stuff. Our winch went back to the manufacturer for upgrade -- which took two years -- and is just back with thicker Spectra.

There is an automatic cable tension control with airspeed transmitted from the hookup.

Now we get to see how it works.

50+ years ago, when Aberdeen Gliding Club operated at Aberdeen Airport, I saw a solo pilot allow enough crosswind drift to drop the cable over a Tiger Moth towing a glider off the main runway. It caught round the propellor.The teenage winch operator had no guillotine - just an axe. He hacked through the cable as it tightened. The ex-Spitfire pilot released the glider, and successfully landed, with the cut winch cable attached to the prop. There were no injuries. I think that cable was the stranded stuff we used before pianowire. Instructors didn't need to do simulated cable breaks - they were too common.

All so familiar, good to see the amount of agreement by everyone involved in gliding.

If the cable is guillotined and the cable hung up, then the procedure is to fly a tight spiral over the field aiming to land in the centre. I know someone who did it for real once, he says it was no big drama.

Once, I did see the cable get struck by lightning before the glider released. The glider pilots were aware what had happened, but the winch driver just thought it was a cable break. However, the cable couldn't be found. It had vapourised!

Going back to the original question of the risk of the glider being unable to release the winch cable.

Clearly that would be a pretty serious situation even given the presence of cable guillotines on the winch etc.

The automatically releasing hook ("back releasing" hook) was invented pre WW II to counter this risk and as has been said, its action should be checked daily before the first flight. It's a very reliable system even if (say) the cable release knob comes off in the pilot's hand.

The remaining risk of a winch cable "hang up" these days is if at the start of a launch, after a slightly enthusiastic taking up of the slack in the cable, the glider rolls forward, runs over the cable and picks it up around the mainwheel.

This risk is countered by the last few metres of the cable ("the strop") near the glider being encased in a relatively stiff length of plastic hose. Also the launch should be aborted by the signaller if the glider is seen to overrun the cable at all prior to the "all out" signal being given to the winch driver

All these security systems have evolved over the last 90-odd years since the gliding movement took hold. The risk of a "hang up" is one of the first things an onlooker thinks about when he first sees a winch launch, but in reality the risk is now tiny (never say never)

Many years ago, I was doing a 80 nm cross-country tow with a two-seat Lark (IS-28B2) behind me. We were parallel to and about 10 miles down-wind of the Canadian Rocky Mountain Front Ranges on a wave day.

It was quite rough, so we were using a long rope. About half-way, our CFI, who was flying from the back seat of the Lark, called me up and said incredulously "We're off tow!". Sufficient slack had developed to cause the Tost hook to back-release.

I'll draw a veil of the subsequent field landing and takeoff, other than to say there was no damage, except for grass stains on the belly of the tow-plane - a C182 Lawnmower. :E

The moral of the story was that we subsequently disabled the back-release, since we only aero-towed.

A lot of gliders have two hooks. They are all made these days (and for many years) with a CoG hook for winching, some have an extra hook added further forwards for aerotow as a/t on a CoG hook can be 'interesting'. (in some cases the a/t hook is right in the nose)

Some older gliders have a compromise hook which does neither that well.

The a/t hooks usually don't have a back release, though the one in my glider does.

Was there no training at all for a winch driver!? True, a glider pilot can abort the launch by dumping the cable if he is unhappy, but will a student pilot reliably do so? Also, one can do a little bit of damage driving a winch beside that. I have heard about bicyclists on a road beside the glider strip getting caught straight off their bike by the cable parachute after the winch driver failed to pull in the falling rope sufficiently fast; another one removed a fence post or two. So there surely must be some insurance requirement around. Also, who teaches the winch driver to splice a broken cable, handle the various malfunctions and - not to forget - drive the often rather rustic truck the winch is mounted upon? A 1960s truck with a non-synchronized gearbox and pneumatic brakes is a bit different from todays cars most people are used to: an uninitiated person would likely not even get the engine started or stopped.

In my club, every aspiring winch driver had to do 150 tows on at least 10 days under supervision of one of the nominated trainers, then pass a test consisting of 10 tows, a theoretical examination and two splices (a broken cable and an eye) with an examiner. Then, one would receive the winch license. From that moment on, one would spend half a flying day on the winch every 4-6 weeks according to schedule, and be allowed to fly not only K13 and K8, but also the plastic types.

This is what a modern glider winch looks like. Made by Skylaunch whose advertising strap-line is, 'Its like going up on rails.'

http://www.skylaunchuk.com/images/evo1.jpg

And it taught me not to stick my tongue out during take off.

Bitten tongue bleeds a lot.

Aerotow on CG Hook
 

It does require just as much attention behind a towplane as a winch when close to the ground as a cartwheel is very bad news.

Once you have 50' I find it easier in my 27 (70% CG) with a CG hook than the K-21, even when the towpilot takes a thermal. A forward hook produces a yaw couple in turns that requires compensation with rudder.

The 20 with 80% CG is considerably more frisky;)

RBF
Agree that aerotow also requires attention. I have a '20' which does not have a nose hook, so aerotowing is a little tricky, particularly in the initial ground run as there is not a lot of aileron authority. I use full, negative flap up to 25 kts which gives a bit more authority but she still wants to drop a wing especially in nil-wind conditions - much course stick input needed. At 25kts, flaps are brought back (carefully) to zero and off we go. I think the big difference in wing drop on winch is the rapidity at which it can occur if you get a snatched launch.

I had a K6E that has an offset to the left belly hook. Aerotows could be very interesting! It would attempt to ground loop as soon as the tug moved, lots of left everything and stay awake!!

Definitely BEWARE when accepting a winch cable in your glider, your hand MUST be on the release because if a wing drops and the glider cartwheels there have been fatalities and the poor basket never even got off the ground.

Winch cables are bloody dangerous. To spectators, passersby, and to power planes that ignorantly fly over a gliding site. One power pilot departed our airfield after visiting (we think) a local pub, and he flew through the wire as a glider was being launched; why his wing didn't get sawed off I will never know. The pillock should have landed immediately. Instead of which he blithely flew back to Wellesbourne. I wonder how he explained the damage to the flying club?

Neighbouring our gliding site is a very active karting circuit. Wind may blow cables over the track....so we have to choose a different runway and accept a crosswind.

I learned to fly at Booker, on aerotow, then moved to Shenington near Banbury and used to be totally freaked out by winch launching. The acceleration is astonishing. But I did get used to it, and ended up as an instructor having to teach winch launching. This never fails to bring out the sadist in the instructor (me too!) because when the pupil is getting near solo, he will have a LOT of practice winch failures. The instructor tries to be as sneaky as possible before pulling the release.

My favorite way of making the pupil suffer was to tell him that on the next launch we would have a practice launch failure.

And then I wouldn't. All the way to the top of the launch, maybe 1,200 or 1,400 feet, the poor guy is expecting the "BANG!" of the simulated cable break, most likely at the most awkward height for what do you do next! and it doesn't happen.

The lesson is it COULD happen at any moment, so one should be ready and have a plan of action ahead of time.

We used to winch using piano wire, and that was horrid for the poor winch driver, it frequently broke, and descended over the cab of the winch like spaghetti. Best thing for the pilot to do in this case was to soar for at least an hour until he got over it!

I was a towplane pilot, so declined to learn to drive the winch, at my age I shouldn't be having to wrestle splicing the braided steel cable we use now. We considered using the fancy new plastic line called Dynema, but it lays out on the top of the grass when taken to the glider, and is much more likely to be picked up if a glider or car or whatever has to cross over the wire. Which you do not do if it is at all likely to be suddenly in use.

The new winches are very simple, I am told. We used to employ a retired and possibly classic German Fire Engine converted into a winch that served us well for years.

Some clubs use a light signal. We use radio to the winch; once the glider lifts into the air, the winch driver is keeping an eye on it, and if you need to call STOP (anyone can do this if they see danger) he would not be looking at the light. Paddles were used in the olden days.

The drill for the wingtip holder, who MUST be trained and alert, is to carefully look around above and behind and in front in case there are gliders soaring over the winch. If OK to go, he levels the wings. Then naming which cable is being used, he says
"Launch to winch, K13, Take up Slack!" The winch driver stops reading his magazine, starts the engine, and slowly draws in the cable until the wingtip holder (or whoever is doing the radio) says and signals with his OTHER arm
"ALL OUT ALL OUT!!" The winch driver floors the throttle and the glider accelerates incredibly fast, rotates when it is safe to do so, and goes for the ride up the wire.

We know the back release works, we test it first launch every day. There are different weak links on the cable according to the weight of the glider.
Red, Blue, or Black. And we hope that the winch driver knows how to use the guilllotine......

though I know of no time when it has been used! except by mistake.

If the glider is then dragging the cable, and can't drop it, it probably wont make all that difference to the performance if he keeps his speed up when turning toward the pre-selected landing spot. If it drags over a fence or trees, that probably won't yank very much....I've done it with a tow plane.

Any questions?