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- Tow line cutting device immediately at the towing power source.
- Weak link that enables separation of a glider from the source of power.
- Release - device that enables pilot to drop the towline in any moment.
- Constant towline tension.
- Drogue chute (must be used if the tow line is steel cable).
- Reliable communications by radio or visual signals.
- Quality education of pilots and system operator.
TOWING SYSTEMS
Of all possible towing types from
hand towing to aEUR towing we will point up the main ones with reference
to systems that are in manufacturing programme of our company.
Basicaly we can divide towing systems depending
on wheather source of towing power is moving during towing procedure or
not. Accordingly the system is mobile or stationery.
MOBILE SYSTEMS
1. STATIC TOWING
In this type of towing the towline
does not change its lenght from launching to releasing – it stays static
(no reeling). Consequently the source of towing power must be moving;
usually that source is a car.
Towline has to be stretchable to
certain percentage to annule or reduce the effect of thermic or wind gusts
on glider and so enable precise tow force regulation. Tow force is regulated
by changing the speed of vehicle used for towing which basicaly depends
on wind speed and is rarely more than 40 km/h (back wind). Precision of
regulation depends on driver’s expertise and there is no option of automatic
tow force regulation. Basic variant of this towing system is the simplest
there is; equipment is simple and consists of towing vehicle and tensiometer
which can be in different variants but we prefere hydraulic. All other
parts are similar as in other systems (towline, release on pilot and towing
vehicle, weak link, sometimes drogue chute and other equipment).
Altitude that can be achieved with
this system depends of course on available towpath and towline lenght.
Approximately estimated, from the towpath lenght of 1000 m we can achieve
at least 200 m, with no wind.
In most cases towline lenght is about
40 % of towpath lenght. The lenght of the towline can be changed according
to wind, so the longer towline may be used in stronger winds and accordingly
glider can achieve higher altitude on the same towpath lenght. Besides
there is an option of pulley towing, which is anchored on one side of
towing path and towline is laid along the whole towpath lenght; pilot
is on one side of towpath and vehicle and pulley on the other. In the
course of towing the vehicle is moving towards pilot and towline is going
through pulley. This is yet another possibility of using maximal potential
of wind and in some conditions this method can mean safer towing procedure.
2. PAYOUT TOWING
We could define this category of towing as towing with controlled reeling
of towline drum, and it can also be used as static towing.
Essential parts are braking drum
and tensiometer which are attached to towing vehicle.
Towline is reeled off for some 50
m from vehicle. Pilot attaches to towline and vehicle begins moving and
maintains constant speed while operator regulates force by braking reeling
off drum. After pilot releases towline is reeled up manualy or electrically.
This system is regularly used for
"boat towing" on water.
3. WATER TOWING - BOAT TOWING
Towing system that is practically
the same as payout winch. The only difference is that towing takes place
on water. (It is not recommended to use it as static towing for launching
from the coast because water produces great amount of drogue on towline.
Consequently precise tow force regulation is not easy).
Launching can be done in two ways:
- From the shore – where the right wind direction towards shore is needed.
- From the boat platform – it is convenient because all wind directions
can be used.
In any case very interesting way
of towing which has so many advantages that occasionally getting wet pays
off J .
Here are some of the advantages:
Enables using of all wind directions.
Favourable alternative for dusty and hot towing sites on land.
As a rule there are no obstacles.
Very long towing paths.
Possibility of achieving very high altitudes.
Enables avoiding different restrictions (agricultural activities are not
as popular as on the continent J etc.).
No joke; be aware of other flight
activities, especially in tourist season
Don’t forget that additional equipment and for PG pilot life jacket are
needed.
STATIONARY TOWING
In 80's, after expansion of payout
system, boat towing, and static line systems which are most popular ways
of towing, stationary winch that was used a lot in Europe, draws more
and more attention in EUR and Canada.
For many years stationary winches
were only used for towing sailplanes, where great powers and speed are
needed. After appearence of some sophisticated elements, especially on
field of electronic and hydraulic and dropping of prices of sometimes
enormly expensive parts, interest for using it in paragliding and hanggliding
is growing.
And now about the towing:
In stationary towing power source
does not move and stays stationary during entire towing procedure. Winch
is often on a trailer so it can be used on almost any terrain.
Most often winches have one or two
drums, sometimes even four. More drums mean more capacity of the winch
or more launches in time unit.
Basic parts of these systems are:
running engine, driving mechanysm (hydraulic or mechanic), drum, towline
(most often steel cable 1.6-2 mm in diameter) and safety elements that
every towing system must have.
At the start of towing procedure
towline can be reeled off as much as pilot requires, respective of course
to towing site environment. Pilot attaches to towline and after the start
procedure (which is often performed by radio because of a long distance
from pilot to winch), winch operator begins with towing by reeling up
the towline with certain tow force. After the pilot releases the rest
of the towline is controllably reeled up with great speed (up to 80 km/h),
and drogue chute keeps it off the ground.
In addition, there is an option of
pulley towing where pilot's start position is next to the winch, which
enables winch operator to more precisely control launching.
Stationary winches can be divided
in two categories regarding to driving mechanysm: hydraulic and mechanic
winches.
HYDRAULIC DRIVE WINCH
Basic running drive is heat engine (often reparated car engine) with power
of 15KW or more. Power of the engine is determined by conception of the
winch (solo or tandem version). Engine runs hydraulic pump and hydraulic
motor which transmits force to towline drum.
Role of hydraulic is great and enables
"soft" towing in all conditions (termic or wind gusts etc.).
We can say that this system presents
all systems in one, and besides it enables "step towing" where
high altitudes can be achieved without long towing paths. Since up to
3000 m of the towline can be reeled up on drum, altitudes of 2500 m above
the ground are registered.
Our hydraulic system has an excelent
tow force control and safety valves which automaticaly amortize all eventual
sudden changes while towing, so between other it is ideal for educating
new pilots.
MECHANICAL DRIVE WINCH
As a rule the concept of these winches
is very similar to hydraulic winches, except that driving mechanism is
direct (engine – drum) or contains build in hydraulic elements between
engine and drum.
Scooter winches are popular as well,
but also car winches and other various mechanic winches are used.
Between other methods of towing our company quite often uses step
tow, especially on short terrains. On a terrain of 500 meters
in lenght it is possible to achieve the same height or even more.
The step tow method
Here is a description of the method:
Once the glider has reached the end of the tow, tensions
are dropped and the glider turns downwind and pulls the towline behind
it. After flying above the original launch point or beyond, the glider
turns back into the wind. Tow tensions are reapplied and ghe glider is
pulled again to climb higher. The glider's altitude ratchets up in sequential
steps with each cycle.
Since the climb rate on a winch
tow slows down the closer you get to the wind, the second climb should
stop short of the winch. Each subsequent climb should stop shorter still,
and continue further downwind, even past the limits of the field (if safe
clearance is maintained). This procedure will get you the highest in the
shortest lenght of time. Step towing should not be practiced
by inexperienced tow pilots.
Communication and coordination between
the winch operator and pilot are extremely critical for the preservation
of safety. We believe reliable radios are an absolute requirement for
step towing. When the pilot turns back upwind, the glider
is generally much too distant for visual inspection of the line by the
winch operator. A glider pointed back towards the winch does not indicate
a safe condition to resume towing. A radio transmission
from the pilot is required to confirm that.
Step tow procedures – stationary winch
With the stationary winch,
when the pilot has reached the end of the tow, he commands "drop
tension" rather than releasing. The winch operator should drop the
tension immediately. A few pounds (1 or 2 kg) of tension or drag are desirable
to prevent freewheeling of the drum and spinning off excess line. It also
serves to keep the line off the ground to minimize snagging. Radio back,
"drop tension confirmed". The pilot now knows he can safely
turn 180 degrees and head downwind trailing the line. This phase of the
tow is critical. The line must be dispensed smoothly with no jerks or
snags. A superior level-wind system is essential for obtaining the tight
clean wraps required for this activity.
The pilot must not get too low before
turning back into the wind nor the line over any obstacle that could snag
the line. If winds are significant, do not forget to account for drift
and begin a turn early.
A hang glider pilot
must be especially careful when making the turn. The line will extend
failry horizontally towards the winch. If the pilot rolls too aggressively
while making the turn, the wing will pass below the towline and loop it
over the wind. This is a very precarious situation. Keep the turn very
shallow. The towline must be kept in sight during the whole turn. If you
lose sight of it, promptly level out and reestablish its position.
The paraglider pilot
must make a decision when turning downwind. When the turn away from the
winch is made, the line can be routed around his side and back to the
winch, or he can lift a leg over the line and pull it back between his
legs. The seat of the harness generally prevents any crotch discomfort
from the line. When turning back towards the winch to resume the tow,
if the line is wrapped by his side, the pilot must turn in the opposite
direction of the previous turn. In other words if he turned right to head
downwind, he must turn left to turn back upwind. Otherwise the line will
wrap completely around him. If the line routes between his legs, he must
lift his inside leg way up to clear the line. This action can interfere
with weight shift control of the paraglider. Because of the risk of not
getting a leg up and over the line and compromise to the weight shift
control during the turn, we suggest pulling the line by your side.
When the glider is oriented back
into the wind and aligned with the winch, radio, "resume tension".
The winch operator should smoothly reapply tension.
HOW TO CHOOSE A TOWING SYSTEM,
WHAT ARE THE ADVANTAGES AND POSSIBLE DISADVANTAGES?
T A B L E S O F C
O M P A R I S O N
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