Winch launch

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Winch launch from gliders

Transition of a glider into the climb phase

Glider in the climb phase

Glider after notching

The winch start is a technique with which an aircraft without its own drive is brought to a speed and altitude sufficient for the onward flight. It is pulled into the air with a long rope attached to a winch . At the highest point of the runway, the connection between the rope and the aircraft is broken and the aircraft continues to fly freely.

Winch types

Reeling winches

Drum winch with six ropes

Stationary Aufrollwinde for kites and gliders

Although the towing winch is usually mobile for transport, the furling winch remains in a fixed location during the entire towing action. The towing winch consists of a motor that drives a cable drum via a tension-regulating mechanism. The reeling winch is the most widely used variant.

To prepare for take-off, the rope is pulled out with a car or motorcycle (usually called Lepo in aviation circles ) on the towing area. At the other end of the 400 m to 3000 m long route, the aircraft is attached with a release latch. As soon as the winch driver starts the winch and begins to roll up the rope, the aircraft is pulled. The aircraft ascends due to the pulling force . This phase of the winch start requires special concentration from the pilot and also from the winch operator. The acceleration when towing gliders is 2 to 4 seconds from 0 to 100 km / h.

The height that can be reached is limited by the length of the towing route, as well as the climbing performance of the aircraft and the strength of the wind. In gliding , rope lengths around 1000 m are usually used, although in individual cases up to 3000 m (high wind start) can be found. The towing height is a little less than half the pitch when there is no wind and a little more when there is a strong headwind.

Unwinding winches

The cable winch is mounted on a motor vehicle (car, motorcycle, boat). The rope is wound on the drum. The aircraft is attached to the end of the rope with a release latch.

Then the vehicle drives off and the cable winch begins to unwind the cable. Since the cable from the braked cable drum is unrolled more slowly than the vehicle is moving, a preset tensile force is exerted on the aircraft. The aircraft then begins to ascend and gain altitude .

The height that can be reached is limited geometrically by the length of the secant length of the last existing rope arch (= slightly less than the free rope length) and by the three factors length of the drivable route, climbing power of the aircraft and wind strength .

Towing

At the glider

Ka8 on the winch cable

When gliders take off , reeling winches with an output of 130-250 kW and a cable length of 1000 to 1200 m (in individual cases 600 to 3000 m) are used, typical cable loads are somewhat greater than the weight of the aircraft. The optimal towing speed for a glider depends on the type of aircraft and is between 80 and 120 km / h , 1.3 to 1.7 times the minimum speed is recommended. After the take-off phase, the rate of climb is considerably greater than the rate of roll-up due to the steep angle of the aircraft.

The winch start is divided into three phases.

Tow and take off

Winch launch assembled from 8 individual images

Winch start at the Wasserkuppe

At the beginning the winch driver slowly pulls in the rope until it is taut between the glider and the winch. If it is taut, the winch driver accelerates the aircraft above its take-off speed. Now that the glider has lifted off, the pilot must take care not to climb too steeply within the first fifty meters of gain in altitude (maximum 30 ° angle of climb). If the tow rope breaks or if the cable pulls out due to a malfunction in the winch (e.g. engine or gearbox), the speed of the aircraft is reduced very quickly. There is then only a little time to return to normal flight position before the speed falls below the minimum speed and a crash occurs due to the flow breaking off .

Please note that the rope load increases the minimum speed by a factor of 1.3 to 1.7. A load-independent assessment of the angle of attack in order to avoid the stall can be done by means of a side thread .

Climb

Once the safety altitude of around 50 m has been reached, the pilot can gradually “hang” more tightly on the rope, that is, using the elevator to control the speed with the optimal speed - depending on the aircraft between 80 and 140 km / h -. As a rule, the glider then climbs at 45–50 ° and around 10–20 m / s.

Final phase, notching

In the last phase of take-off, the cable pulls as the winch driver takes the gas out. The pilot releases the elevator to bring the glider into normal flight position.

At the highest point of the tow, the rope is disengaged from the tow coupling . With gliders this usually happens automatically as soon as the angle between the rope and the fuselage exceeds approx. 70 °. The pilot can also trigger the clutch manually at any time. The coupling piece at the end of the rope then falls down on a small rope parachute while the rope is pulled in completely by the winch.

The height reached in the winch launch depends on many factors. The length of the winch rope, which is limited by the size of the airfield, has the greatest influence. Usually the length is approx. 1000 m, which as a rule enables towing heights of approx. 400 m on average. With very long towing distances, towing heights of over 1500 m have been reached.

communication

As a rule, communication between the take-off point and the winch takes place by telephone or radio, more rarely by means of light signals.

In Germany, an operationally reliable voice connection is prescribed according to the German Sailing Flight Operations Regulations (SBO); the use of aviation radio is not permitted. This outdated regulation arises from early times when the radio links were of poor quality. The smaller interference of the air traffic with the winch start operation is advantageous. The disadvantage of this is that there is no direct connection between the pilot and the winch operator: if the pilot wants to inform the winch operator of a speed that is too high or too low, for example, he must communicate this to the start manager via radio, who forwards it to the winch operator via field telephone long delay and possible communication errors.

Nowadays the quality of air traffic is much improved, while the connection via field telephones is often based on old, unreliable technology. For this reason, it is common in France and Switzerland for the pilot and winch driver to communicate directly with each other via aeronautical radio at the normal frequency. In this way, the winch driver can directly hear the pilot's start message and any information about the towing process (too high or too low a speed), as well as informing the pilot when to release the cable to release and whether to hold up in cross winds. With the usually low utilization of the aeronautical radio frequencies at glider airfields, this additional interference usually does not play a major role.

In some winds with heavily loaded radio frequencies, it is common to install only one radio receiver. This means that there is no additional load on the frequency, but the winch driver can overhear information about the towing that should otherwise be transmitted via the launch ladder with a time delay.

gallery

Starting sequence
Tow winch
Tighten the rope
Rope taut
Done - "Start"
Free - take off
Climb
culmination
Notching

research

Between 2008 and 2010, students and research assistants at the Chair for Flight Dynamics (later the Institute for Flight System Dynamics ) at RWTH Aachen University under the direction of Professors W. Alles and D. Moormann dealt with the flight-mechanical modeling of winch take-offs. The focus of the work was the creation of models to depict the interaction between aircraft, winch, rope, pilot and winch driver. These models allow a flight performance analysis in winch launch. They were later supplemented with aerodynamic models to depict the aerodynamic effects on the control surfaces of the aircraft. Important results of the simulations include:

The rope weight plays a small role in the release height, the air resistance of the rope, often neglected, is at least as important.
Better release heights can be achieved with higher rope loads.

Further investigations into the safety of the winch start (see the section below maximum speed and predetermined breaking points ) have shown that the speeds and maximum loads recommended by aircraft manufacturers today (i.e. predetermined breaking points on the rope) are too low and can therefore lead to dangerous situations. This is because at the time of the approval of older aircraft, much weaker winds were in use.

With the hang glider

Winch launch of a hang glider

When starting a hang glider with the winch , you need a start ladder in addition to the pilot and a winch driver, if the pilot does not have an operator-free radio connection to the winch driver. Since the pilot needs both hands to control the aircraft during take-off, he cannot also use the talk button on a radio device. The start leader is then responsible for communication (radio) between the pilot and the winch driver. He also monitors the start and, if necessary, intervenes independently by radio.

In contrast to paragliding, the pilot is connected to the tow rope by two forked ropes in front of the parachute. The shorter of the two ropes is led above the control handle (the base) and hooked into the tow latch, the longer below it.

The complete tow is divided into six phases:

On the ground

In this phase the final preparations for starting are made. The procedure is best illustrated using the commands exchanged between the pilot and winch driver. The launch leader stands a few meters away from the pilot and passes the pilot's commands to the winch driver and vice versa.

Start leader on winch:
First the pilot has to be registered. The following information is sent to the winch driver for this purpose:

Name of the pilot
Weight of the pilot: live weight, to which you usually add 30 kg for the equipment. This is used to adjust the tension limiter on the winch accordingly.
Hang glider type: manufacturer and type designation
Which rope is the pilot attached to, if several tow ropes are laid out.

Pilot on winch: Pilot and device ready to go.
The pilot confirms that he has done the 5-point check (harness closed, test lying, whether harness is connected to the glider, etc.).

Winch to pilot: winch ready to go.
Serves as confirmation of the previous message and states that the winch driver has started the winch.

Pilot on winch: pilot hooked up.
The pilot confirms that he is attached to the rope and that this has been checked by the start leader.

Winch to pilot: pilot attached.
Only serves to confirm that the winch operator has received the message.

Pilot on winch: tighten rope.
At this moment the pilot is looking for a very firm stance and the winch driver slowly pulls in the tow rope. It serves to pre-tension the rope. This message is not confirmed by the winch operator. When the rope is taut, the pilot gives the next command:

Pilot on winch: rope taut.
This command means that the winch driver will stop slowly pulling in the tow rope. At the same time, the pilot should check the wind direction again at this moment in order to finally make his take-off decision.

Winch to pilot: rope taut.
Used to confirm the last command.

Pilot on winch: start
This is the sign that the winch driver is slowly tightening the rope again. At the same time, the pilot can now be pulled forward by the rope and begins to run. It is important that the pilot really lets himself be pulled and does not just start running and thereby relax the rope again. The hang glider is now started by the pilot.

In contrast to paragliders, the command done is not available at this point .

Should there be any discrepancies during this procedure, it is up to the pilot and the start manager to abort the start by giving the winch driver the stop stop command .

Tow up to safety height

After the pilot has left the ground, he is slowly towed to the safety height of 50 m. Effective use of the rescue parachute is only possible from this height. In this phase, the pilot must always be ready to run and must not lie down in his harness in order to be able to land safely if the winch fails or a rope breaks.

Drag to the latch

After the safety height has been reached, the winch driver increases the pull on the tow rope. The pilot is now gaining altitude faster.

Since the winch driver can only know to a very limited extent which wind conditions prevail at the altitude, the pilot has the option of using "leg signals" to request the winch driver to increase or decrease the tension on the rope. When the pilot starts to walk in the air, this means that the winch driver should increase the pulling force. When the pilot begins to spread his legs (similar to a jumping jack) and close, this means that the winch driver should reduce the pulling force.

Relink

Since the tow rope moves downwards with increasing height (the angle increases), the shorter fork rope presses on the control bracket from above. If the pilot did not change the latch now, the hang glider would be steered towards the ground by the pressure exerted by the tensioned rope on the bracket. In order to initiate the relinking, the pilot gives leg signals (spreading and closing the legs) so that the winch driver reduces the pull on the tow rope. After there is no longer any tension on the rope, the pilot disengages the shorter of the two fork ropes (which is located above the bracket). This makes it possible for the pilot to control freely again.

Then the winch driver increases the pulling force again in order to drag the pilot further. Since this now only hangs on the second fork rope, which is located below the control handle, the towing can continue without any loss of maneuverability.

If the clasp occurs too late, the shorter fork rope pushes the hang glider down, if the clasp occurs too early, the longer fork rope pulls the hang glider up (the angle of attack becomes too steep and the predetermined breaking point in the tow rope will hopefully tear before the current on the glider breaks).

Drag to the notch

After the latching, the winch driver increases the pull on the tow rope. The normal tow, as it was already described above before the relinking, is continued here.

Notching

At the end of the tow, the pilot must actively disengage. This happens when the tow rope points downwards at an angle of approx. 70 °. At this moment he gives leg signals (spreading and closing the legs), which causes the winch driver to stop the winch. As the hang glider continues to fly forward, the pilot recognizes this by the rope sagging. The pilot now operates the tow release.

If there are problems with the latch, the pilot is required to continue to hold towards the winch and to fly over it. Overflying the winch is the signal for the winch driver to cut the tow rope, otherwise there is a risk of falling. If the pilot continues to fly with several hundred meters of rope (due to being cut off or a rope break), he should be careful not to fly over any obstacles. He should spiral down the height above the starting meadow and land on the meadow. If the rest of the rope gets caught in trees, fences, etc., there is an immediate risk of falling. In order to prevent these serious consequences, the pilot should prepare mentally in such a situation to throw the reserve parachute in case the remainder of the rope should get caught in obstacles on the ground.

With the paraglider

To start a paraglider with a winch, you need a pilot and a winch driver as well as a launch leader if the pilot does not have an operator-free radio connection to the winch driver. Since the pilot usually needs both hands to control the glider at take-off, he cannot also use the talk button on a radio. The start leader is then responsible for communication (radio) between the pilot and the winch driver. He also monitors the start and, if necessary, intervenes independently by radio. The optimal towing speed for a paraglider is approx. 20 to 25 km / h.

The complete tow is divided into four phases:

The start on the ground

Paraglider taking off from the winch

In this phase the final preparations for starting are made. The procedure is best illustrated using the commands exchanged between the pilot and winch driver. The launch leader stands a few meters away from the pilot and passes the pilot's commands to the winch driver and vice versa.

Winch for start! Wind hears!
The pilot is registered. The following information is sent to the winch driver for this purpose:

Name of the pilot
Pilot weight: live weight. This value is used to set the tension limiter on the winch.
Type of paraglider: manufacturer and type designation.
Which rope is the pilot attached to, if several tow ropes are laid out.

The winch operator confirms the data by repeating and notes them in his notebook.

Start leader to winch: "Pilot and device ready to go."
The pilot confirms that he has done the 5-point check .

Winch to start ladder: "Winch ready to go."
Serves as confirmation of the previous message and states that the winch driver has started the winch. The yellow all-round light only lights up after the winch driver has engaged.

Start leader on winch: “Pilot hooked up.”
The pilot confirms that the harness straps are closed (and this has been checked by the start leader).

Winch to start
ladder : "Pilot hooked up." Only serves to confirm that the winch driver has received the message.

Start leader on winch: "Tighten the rope."
At this moment the pilot is looking for a firm stance and the winch driver slowly pulls in the tow rope. It is used to slightly pretension the rope.

No feedback from the winch driver. The winch driver slowly pulls the tow rope.

Start leader on winch: “Tight rope.”
This command means that the winch driver can stop pulling the tow rope in further. At this moment the pilot can check the wind direction again in order to finally make his take-off decision.

Winch on start leader: "Tighten the rope."
Used to confirm the last command.

Start
ladder on winch: “Ready.” This is the signal for the winch driver to slowly pull the rope (60 kp for safety start). Again there is no confirmation. Now the pilot can be pulled forward by the rope, begins to run and thus pulls the paraglider up. The screen that was previously on the ground behind the pilot now rises over the pilot. The pilot has to control the glider while running. If this does not come over the pilot “cleanly”, the start is to be aborted. In the event of problems, the start manager is obliged to abort the start with the command: “Stop stop, stop stop, stop stop!”.

Start leader to winch: “Staaaaaart.”
If the glider is clean over the pilot, he gives this command. The winch driver now raises the pull and the pilot takes off. Should there be any discrepancies during this procedure, the start leader breaks with a three-time command stop stop! the starting process. The winch driver then reduces the rope pull by disengaging it immediately.

Halt Stop, Halt Stop, Halt Stop
The towing process can be aborted at any time, if e.g. B. the pilot stumbles, the rope gets stuck somewhere, or the glider goes in the wrong direction in the wind.

The tow up to the safety height

After the pilot has left the ground, he is slowly towed to the safety height of 50 m. Up to this height there is a risk (if the pull is too strong) that if the rope breaks, you will swing and hit your back. From this height, the effective use of a rescue parachute is also possible. In this phase, the pilot must remain ready to run and must not sit in the harness. This enables him to make a safe landing in the event of a winch failure or a cable break .

The tow to the notch

After the safety height has been exceeded, the winch driver increases the pulling force on the tow rope up to the preset maximum value. The pilot is now gaining altitude faster. Since he now has more height and time for a counter-reaction in the event of any disturbances, he can sit in his harness. During the following climbing phase, the pilot can use leg signals to ask the winch driver to increase or decrease the pull on the rope. With running movements, he asks the winch driver to increase the pulling force. If the pilot spreads his legs several times like a jumping jack, the winch driver should reduce the pulling force.

Notching

At the end of the tow, the pilot must actively disengage. This happens when the tow rope points diagonally downwards to the cable winch at an angle of approx. 70 °. At this moment he gives the winch driver the command to remove the pulling force with a leg signal. As soon as the rope sags due to a lack of tensile force, the pilot can operate the tow latch and release the rope. The pull rope now falls down on a small rope parachute, while the winch driver winds the rope completely onto the rope drum.

If there are problems with the pawl, the pilot is required to point towards the winch and to fly over it. Overflying the winch is a sign for the winch driver to cut the tow rope, otherwise the pilot is in danger of falling.

If the pilot has a long piece of rope still hanging on the latch due to the rope being cut or broken, he should avoid any contact with obstacles and reduce his altitude above an open meadow by a circling flight path. It is also advisable to grasp the hanging piece of rope with one hand as soon as possible, then release the latch and only hold the rope loosely in your hand. If the remnant of the rope gets caught in trees, fences or the like, it threatens to fall if the rope is still firmly attached to the latch. In an emergency, the rescue parachute must be deployed.

Step drag

An extended launch technique is the step tow . Here the aircraft is pulled into the air with a rewind winch as described above. If the aircraft has arrived shortly before the winch, it is not disengaged, but only the pulling force is removed from the rope by the winch driver. The aircraft can now fly back to the starting point (or further) with the rope attached and its altitude gained. There the aircraft turns again in the direction of the winch and can be pulled again by the winch. With this technique, a greater altitude can be reached. This is only limited by the length of the rope and its weight. This technique is currently not possible in gliding due to the technical design of winches and tow couplings.

Rope types

Predetermined breaking points in metal protective sleeves on the lead rope of a winch rope (glider flight)

Rope clamp and defective "nail point"

Traditionally, steel tow ropes with a thickness of 4 to 5 mm and a length of 1000–1500 m are used in the area of glider pilots . Current systems nowadays have plastic ropes , which leads to a considerable reduction in weight and thus to a slightly better notch height.

The advantages of synthetic ropes are:

Lower weight (8–15 g / m instead of 60–80 g / m for a steel cable). This increases the towing height (around 50 m) and makes handling on the ground more comfortable
Less friction on the ground and often less air resistance
Higher elasticity, which results in a smoother start.
With good care, a synthetic rope can withstand around 2000–4000 starts, a steel rope around half.
Easier to repair a rope break (see below)

Disadvantages of synthetic ropes are:

Higher price, at least three times higher than for a steel rope (over € 1 / m against € 0.30–0.50 / m, as of 2015)
Sensitivity (wear on sharp-edged parts in the winch, cannot remain wound on the drum for a long time under tension, you cannot drive over it with vehicles)
Greater load on the drum due to its elasticity and low friction
High price for the conversion (depending on the construction of the winch around € 5,000-10,000)

Plastic ropes have long been used in paragliders and hang-gliders because they work with lower tensile forces.

A broken steel cable can be repaired in two different ways:

It is first temporarily patched ("nail point") with rope clips (aluminum sleeves in oval shape) and must be permanently repaired by splicing at the next opportunity (at the latest before the start of the next flight day) .

Advantage: Inexpensive, only (cheap) splicing tool required.

Disadvantage: Slow execution (> 30 minutes), practice required.

It is permanently repaired with special rope clips (tinned copper sleeves in the shape of an “8”) (“nail point”). An approved, often used, permanent clamp is e.g. B. "Nicopress" from the US company "The National Telephone Supply Company".

Advantage: quick execution (a few minutes), easy handling.

Disadvantages: Expensive connection (approx. 3 € / nail point) + purchase of Nicopress pliers (approx. 300 €), as of 2014. Less durable than a splice point and unsuitable for some winches with narrow rope guides.

Torn plastic ropes are spliced. However, this is much easier (and faster) than with steel ropes and can be done in about 10 minutes in just a few simple steps.

A rope can be repaired several times. Usually ropes are changed when they have more than 5–10 repairs.

Winches

The design of the towing winch always depends on which aircraft it is to be used for later. A small winch motor is sufficient for paragliders that only need to reach low speed ranges. With modern gliders, with high speed ranges, larger engines are necessary. Automatic transmissions are mostly used to transfer the pulling force smoothly and smoothly. The widespread double drum winches are equipped with converted truck rear axles on which the cable drums sit. Special roller constructions ensure safe rope guidance. In the case of wide drums with a small diameter, a spooling device is also required in order to cover the drum evenly with rope.

Older sailplane tow winches have engines with much less power than today's ones. But for the aircraft that were available at the time (e.g. Baby or FES), this performance was sufficient, because they weighed less and took off at lower speeds. An example of such a winch is the Maybach winch, which was widespread in GDR territory. Her successor in the GDR was the versatile and widespread Hercules III .

Modern towing winches for gliders have drive motors with over 200 kW in order to bring even heavy gliders safely into the air. For paragliders, motors are used that exert a pulling force of approx. 1–1.3 kN . In addition to car, combine, ship and motorcycle engines, electric motors are also increasingly used today.

The control is almost always done manually, whereby the aircraft weight, the towing speed specified in the flight manual, the current flight attitude, rate of climb, rope slack, wind speed and direction as well as the “material feel” of the winch driver result in a certain engine speed. An aid to improve flight safety is a telemetric display of the aircraft speed for the winch driver. Automatic controls are much more complex and therefore not widely used. So u. a. the Segelfluggruppe Wershofen has developed its own PLC- based motor control, which allows each take-off to be identical. The winch driver is thus relieved and only needs to sit in the driver's cab to observe the winch. Before take-off, a saved setting is selected for the respective aircraft type and the wind is set, then the towing process is initiated and the controller takes over control until it is released. A semi-automatic control system was developed by the Skylaunch company: Before take-off, the type of aircraft and the wind speed must be set with auxiliary levers on the throttle in order to have a guide value for the throttle position in the towing process.

So that the winch driver can wind the tow rope onto the rope drum without loops after the release process, it is braked by a rope parachute when it falls and thus kept under tension. After being released, the rope parachute opens automatically by the wind, while it is pulled taut during the take-off process by the pull on the rope and cannot open.

Modern winches mostly use special gears that allow the use of large diameter rope drums. This has four important advantages:

The large, narrow drum no longer needs a winding device
The rope is bent less, with less wear
The centrifugal forces on the drum are smaller with the same rope speed and larger radius
With a small drum, the diameter changes considerably when the lower layers of rope are wound up. This means that the winch can have a large pulling force at the beginning of the towing process and a high speed at the end of the towing process. The opposite is necessary, especially in bad winds. With a large drum, the change in diameter is less.

Typical prices vary from a few thousand euros for an old, used winch to over one hundred thousand euros for a modern winch.

Winch launch and aircraft tow

Compared to aircraft tow, winch launch has advantages and disadvantages. The winch launch is inexpensive (around € 3–6 / take-off at 350–500 m altitude versus around € 3–6 / 100 m in aircraft tow) and enables a high take-off rate. The operation of the winch is sufficiently easy and safe that the winch drivers can be trained in around 10–20 hours (at least 100 starts on at least 10 different days). The lower noise pollution from the winch launch is advantageous in the vicinity of built-up areas; In particular, the rest period of 1 p.m. to 3 p.m., which is often prescribed in Germany, does not have to be observed.

Apart from the aircraft crew, several people are involved in the winch launch: A launch ladder (fails if there is a direct radio link to the winch), a winch driver, possibly a rope retractor, a wing holder (not absolutely necessary for aircraft towing).

With aircraft towing, however, the release location and height can be freely determined and a shorter towing distance is required with sufficiently powerful aircraft: While a winch launch with less than 800-1000 m is hardly practical, an aircraft tow is often possible with a 500 m runway.

Flight safety

The safety of winch towing depends on the experience of the winch operator, the pilot and the system used. Possible dangers are described below.

If the rope breaks or the predetermined breaking point breaks , the tensile force on the aircraft suddenly and surprisingly decreases. The first measure in this case is to bring the aircraft into level flight with sufficient speed. The remainder of the rope hanging on the aircraft is released as soon as possible. Depending on to what extent this is done and how many runways are present, is then landed directly in the starting direction, served by a curve a transverse web, landed at low wind after a reverse curve in the opposite direction or a normal landing Voltage initiated.

If the angle of attack of the aircraft is too steep at high speed, the aircraft may be overloaded. To avoid this, a predetermined breaking point is built into the winch cable just in front of the aircraft. The predetermined breaking point tears above a load that is predetermined by its design.

High angle of attack at low speed can be used to by the additional load of the rope (higher than the aircraft weight often) stall lead. In this case, too, the speeds recommended by the aircraft manufacturers should often be adapted to the modern, stronger winds in order to allow safe and efficient winch starts. A direct measurement of the angle of attack can be made with a side thread on the hood.

If the winch fails during towing, the pulling force will decrease and the aircraft cannot gain any further altitude. As with a rope break, the aircraft is stabilized and the rope is disengaged. Then, depending on the altitude, the pilot has little time to land again.

Aircraft whose flight direction deviates too far from the pulling direction of the winch can get into a lockout . In this case, the aircraft continues to turn to the side without the pilot being able to counter-steer and threatens to fall to the ground at high speed. As a countermeasure if a lockout has already been initiated, the only thing that helps is to reduce the pulling force immediately by releasing or cutting the tow rope.

One possible problem is the rope getting caught in the drum. In the case of the reeling winch, this leads to a stop in the pulling force, at which the pilot of the aircraft must immediately return to normal flight position. The release pawl is activated at the same time as possible in order to separate from the tow rope. In the case of the unwinding winch, on the other hand, entanglement of the rope in the drum can lead to increased tensile force and consequently to a dangerous lockout. In this case, the rope must be released or cut immediately.

Another possible event is the rope getting stuck on the ground. The aircraft behaves as if it is being pulled by a winch with a considerably shorter rope. In this case, too, the start must be aborted by notching or cutting the rope to avoid an accident.

Load in the winch launch

When the winch takes off, the attachment of the tow coupling and the wing root are mainly stressed. Overloading is particularly relevant at the second point.

The wing is not loaded by its own mass because it is distributed similarly to the lift distribution. During normal unaccelerated flight, it is mainly stressed by the non-load-bearing parts. In order to calculate an equivalent load, the maximum rope load with an almost vertical rope must be added to the mass of the non-load-bearing parts (hull and load plus water ballast). With conventional glider types, the equivalent load at the wing root calculated in this way is 2-3 g. In the extreme case, the ASK 13 can be taken as an example: With a maximum weight of the non-load-bearing parts of 320 kg and a permissible predetermined breaking point of 1070 daN, the equivalent load is 4.3 g.

Permissible speeds and predetermined breaking points with modern take-off winches

Experience has shown that overloads in the winch start rarely occur, even if the maximum speed is exceeded and the predetermined breaking points are too strong. Aborted take-offs, on the other hand, were more common.

The predetermined breaking points and maximum speeds specified by the aircraft manufacturers come in some cases from times when there were no strong enough winds to test high loads. As an example, the Grob G 103 Twin Astir can be mentioned, which according to the flight manual is approved with a 600 daN predetermined breaking point (blue), but due to the 650 kg permissible take-off weight, it is usually started with significantly stronger predetermined breaking points (in contrast, the similarly heavy ASK 21 and even the significantly lighter ASK 13, an approval for 1000 daN predetermined breaking points).

Taking into account the rope loads customary today, the minimum speed in winch start should be around 1.3-1.7 times higher than the minimum speed in free flight Vs1, the maximum speed should increase by up to 80% of the maneuvering speed. This minimum speed is often close to or even above the maximum speed specified in the manual. Correspondingly stronger predetermined breaking points are often used despite the information in the flight manual and some studies on winch launching indicate that they ensure greater safety.

literature

Chapter start. In: Winfried Kassera: Flug ohne Motor: Das Lehrbuch für Segelflieger , Motorbuch Verlag, 22nd updated edition from 2016, ISBN 978-3-613-03946-9 , pp. 105 ff
Lars Reinhold: Free start! (about take-off types) In: aerokurier , No. 2/2019, pp. 10–12 (in the special section for gliding)
Chapter start. In: A. Willberg: Gliding for Beginners , Motorbuch Verlag, Stuttgart 2014, ISBN 978-3-613-03658-1 , p. 69 ff

Web links

Commons : Winch launch - collection of images, videos and audio files

The Skylaunch winch album , collection of various winches
Winch towing and UL towing , paragliding and hang gliding in Germany, Deutscher Hängegleiterverband e. V.

Individual evidence

↑ ^a ^b ^c Start winch driver regulations, DAeC, January 2017, accessed on October 6, 2019 .

↑ Ad Kennes: Lierstart in de sneeuw tot FL50 KAC (Winchlaunch in snow. Up to FL50 or 1550 m. KAC (B)) youtube.com, January 30, 2010, published February 1, 2010, accessed on November 7, 2013. - Video 7:08, rolling off to releasing takes 1:55, take-off is at Weelde military airfield , Belgium, just a little above sea level.

↑ German Aeroclub e. V .: Gliding Operations Regulations (pdf)

↑ Winch launch communication by radio in France

↑ C. Santel: Numeric Simulation of a Glider Winch Launch, student thesis, Chair for Flight Dynamics, RWTH Aachen University (2008).

^ C. Santel: Numeric Simulation of Glider Winch Launches , German Aerospace Congress 2009, Aachen (2009).

^ A. Gäb and C. Santel: Simulation of Glider Winch Launches, Technical Soaring 35 (3), pp. 78-84, (2011).

↑ C. Santel: An Investigation of Glider Winch Launch Accidents Utilizing Multipoint Aerodynamics Models in Flight Simulation, diploma thesis, Institute for Flight System Dynamics, RWTH Aachen (2010).