3 Preparation
3.1 Wind.
3.2 Laying the rope.
3.3 Briefing the crew.
3.4 Protocol, Signals and Communication
3.4.1 Positioning support vehicles.
3.4.2 Radios.
3.4.3 Positioning the glider.
3.4.4 Using the Over-Run.
3.5 Airport Traffic.
3.6 Launch Procedure.
3.1 Wind
Before you actually lay the rope, assessing the wind direction is a
fine idea. We often think of the wind as being from a certain
direction, but as any sailor can tell you, the wind actually
oscillates through an angle of 45ø to 90ø, and with these directional
oscillations, which have periods of 3 to 12 minutes on the average, it
varies in strength. The gusts are gradient wind brought down from
aloft to displace air lifted from the surface by thermal action or
turbulence, and have the speed and direction of the gradient wind.
The lulls are wind that has been slowed and backed (come from a
compass direction that is counterclockwise or numerically lower than
the gradient wind) in the northern hemisphere.
If there's any choice of runways, studying the wind for fifteen
minutes will resolve these questions. Also consider the weather
forecast. The prognosis for surface winds will tell you want change to
expect during the day. The wind direction will change; the only
question is by how much.
A caveat: if you're near the center of a high, the wind direction may
be highly variable, and the gusts may be both strong and highly
variable in direction if thermal inflow is strong. Localized winds in
any direction of up to thirty miles an hour can accompany dust devils
(thermals), which may not be visible if there's little dust. In this
case, the instantaneous wind direction and velocity may affect when
you launch, but the direction is on such a small scale that it won't
affect the fall of the rope very much.
3.2 Laying the rope
Normally we wind the rope on the spool with the ground launch bridle
on the outside (to permit easy inspection and repair). We first
choose the spot from which the glider is to be launched, and drive to
it with the spool in the box of the pickup. We place the bridle where
we want it, then drive slowly along the route of intended launch,
letting the rope spool out.
Care must be taken not to damage the paint on the box of the pickup as
the rope passes over it (unless the owner doesn't care). It is good
not to pass on the wrong side of a runway light, as during launch, as
we found out, the tow rope will fit under it like a bow string nocked
into an arrow, and when the frangible nut at its base breaks, the
light is launched hundreds of feet into the air, a glass-tipped arrow
that will fall we know not where. When this happened to us, it landed
on the end of the runway, spreading glass explosively over a 100-foot-
diameter area. That's a long time with a broom in the hot sun.
It's important to inspect the rope as it comes off the reel, to make
sure there are no knots. Knots weaken the rope by about 50% and are
impossible to get out after even a single tow. This is also an
opportunity to look for areas of excessive wear.
It's courteous to lay the rope along the side of the runway, in the
grass between the lights and the pavement. This keeps it out of the
way of airplanes who will be using the runway between glider
operations. Fifteen hundred foot long ropes aren't picked up by
props, and we don't operate an airport inhabited by sucking jet
engines, but pilots will catch a glimpse of the rope on the runway and
not know if it's fifteen feet or fifteen hundred, and might worry.
Generally, to lay the rope we simply drive from the chosen launch
position, along the margin of the runway to one side (traditionally
the upwind side), until the end of the rope comes off the reel. Then
we place the reel off to the side, just outside the runway lights, so
that we can find this end easily after each tow (the rope is the same
length after each tow, right?).
3.3 Briefing the crew
OK, I think we're ready. We have the equipment set up, the glider has
been towed out to the launch point, the truck has gas, and the club is
ready to play. Next we have to make sure we're ready to function as a
team, for ground launching is a team sport. Most important is the
coordination between the driver of the tow vehicle and the pilot of
the glider, but the wing runner and the other pilots using the airport
make important contributions to safety, and we can improve efficiency
by delegating many other tasks.
First, we assign roles. We take turns filling these roles, but we
have to agree on who does what, and someone must take the
responsibility for each role. Pilot; driver; wing runner; tow-vehicle
observer; assistants.
It's possible to run a safe and efficient ground launch operation with
only two people, a driver and a pilot. In fact, the two-person
operation, with experienced people, is the most efficient. With
precision landings, no crosswind, no airport traffic, and simple
glides with no thermaling, we are able to launch every six minutes,
ten launches an hour. In a training situation, it's more realistic to
plan on three launches an hour even with no thermaling.
3.4 Protocol, Signals and Communication.
From this point, I'll write material in the sequence in which actions
must occur during launch, with asides, diversions, and interruptions
as necessary.
3.4.1 Positioning support vehicles.
It's important to keep trailers, autos, personnel, and the tow vehicle
out of the way of other airport traffic during ground launch
operations. It's reasonable to ask the airport manager for permission
to drive to the launch site, as this may be more than a mile from the
access point onto the airport. But vehicles and folks should not only
be out of the way, they should appear to be out of the way to any
pilot who might show up to land.
3.4.2 Radios
Portable radios should be used in vehicles when transiting the airport
grounds. While I am opposed to broadcasting every movement of a
vehicle on the airport, it is important to announce runway and taxiway
incursions. The amount of communication should be reasonable and
reflect the traffic. My judgment is that vehicles should be on the
runway only when the pattern is clear of all traffic and should move
quickly to get off it. Normally it is perfectly safe, unless there is
mud, to stay on the grass margins of the airfield and off the paved
surfaces.
3.4.3 Positioning the glider
Gliders get in the way of powered aircraft, and their pilots express
frustration in various ways. Never mind right of way rules; no one
likes the inconvenience of giving way. Use your rights judiciously,
and remember to be polite. Do be gently assertive about your own need
not to be grossly inconvenienced by other pilots. The pilot who
announces, "Cloudfire seven two xray on eight mile final for runway
two three, Pilots' Paradise," is a nuisance and a danger, and must be
dealt with for everyone's sake. Meanwhile, he's in everyone's way.
It will probably be necessary to taxi the glider with a vehicle to the
staging location. This may be a mile to a mile and a half at some
airports, and must be done at a walk. The fifteen minute treck down
the center of runway one seven to its downwind end might just possibly
be seen as frustrating to the pilot wanting to practice touch and
goes. On the other hand, towing through the grass at the side is
bumpy and it's harder walking. You mom can help you figure out how to
handle this one.
3.4.4 Using the Over-Run
One strong reason to use the grass over-run, if it's long enough, for
the staging area and takeoff site is that the glider is therefore not
parked on the approach end of the runway for minutes at a time while
the rope is readied, communications among the launch crew are
completed, and the tow vehicle journeys to the far end of the rope and
hooks up. To use the over-run inconveniences other traffic minimally.
But it is more hazardous.
Another reason is to save wear on the tow vehicle, something that
interests its owner. Bumping off the runway lip at 40 miles an hour
at the end of the tow probably stresses the CV joints and shock
absorbers more than usual.
Reasons not to use this area for takeoff is that the end of the runway
is bordered by lights on two-foot-high stalks and that there's always
a lip at the edge of the pavement. In the past five years we have
often used our own 500 foot long overrun for both takeoffs and
landings, but two landing lights have been lost and the runway lip
damaged the tailwheel when proper procedures were not followed. It is
my judgment that this should not be done in training situations, and
is defensible only when the PIC is financially prepared to purchase
landing lights and glider parts and to pay for their installation.
In any case, the runway end-marker lights are at risk even if the
glider is staged on the runway, as a gust of wind may turn the glider,
pushing some part of it against a light and knocking it over. These
things break off pretty easily, so the damage, except for a small ding
or scratch, is all to the light and to the pilot's pocketbook.
If the glider is staged in the grass overrun, meticulous care is
necessary to ensure that the rope is run through the middle of the
end-marker lights and to manage the takeoff such that the glider is
under full aerodynamic control before it passes the lights. It is
easy to taxi through them; level wings clear the lights easily.
Normally the glider should be aloft and climbing well before the
lights are reached.
3.5 Airport Traffic
Conflicts with other traffic are inevitable. It's ideal to ask the
airport manager to issue a NOTAM for those days on which glider ground
launch operations will occur. Unfortunately, VFR pilots flying
locally seldom check NOTAMs. Use of radios is very helpful. Usually
other pilots are understanding; many will use the cross-wind runway to
avoid conflict. Others barge around with no consideration at all,
making themselves dangerous as well as inconvenient. Our memory is
vivid of the visiting pilot doing touch and goes for an hour, who all
the while kept a running commentary going on our unicom frequency
about a glider that kept showing up in the pattern. He didn't respond
to any transmissions, and continually interfered with our operation
and other traffic. Finally one of our pilots stood in the middle of
his runway, flagged him to a stop, and asked him to plug in his
headphones.
The safest rule is to launch when no aircraft is in the pattern. With
experience and understanding among pilots, this rule can be bent
cooperatively. But it's well for the glider crew to consider that the
power pilot unfamiliar with ground launching will have no idea
whatever of their needs or of the actual hazards, and so they will
either be excessively cautious or ignorantly dangerous. In either
situation they will resent you intruding into their airspace.
3.6 Launch Procedure
I will assume that preflight inspection of the glider is complete at
this point.
1. Review and rehearse signals before the day's first launch, and
every time folks change roles unless you have reason to know the
person is up to speed on the signals. When to give each signal
is as important as its meaning.
The first action is to confirm who will play what role in the
launch, and the scheme for rotating jobs.
2. The tow driver and the pilot must agree on tow speeds, relative
to the winds and the climbing style of the pilot.
This requires consideration of density altitude, wind speed and
direction (remember that, as sailors know, gusts oscillate
predictably in direction and speed), and wind gradient. Often
there is marked wind shear, usually of wind speed rather than
direction, at 300 to 600 feet AGL, that is undetectable until it
is encountered. Both pilot and driver need to be aware this may
exist. We have seen shear of 10 - 15 knots across a very narrow
altitude boundary that required discontinuing the climb in order
to avoid exceeding ground launch redline.
The pilot should be debriefed after each flight regarding the
suitability of the tow speeds. (The initial speed is greater
than the final tow speed, and either may need to be varied.)
3. The next action completes the preflight inspection of the
glider: Hook up the tow rope and test the release action, both
normal action and back-release.
Then the passenger and pilot enter the glider. The PIC is
responsible to ensure that the passenger is properly buckled
in,and should do this personally or delegate it to someone able
to take this responsibility.
(I don't mean to make a rule here; it can be done either way.
The rule, "don't hook up the tow rope unless someone is at the
controls of the glider with the yellow handle in hand" is a very
safe one, but this part of the checklist is presuming the tow
vehicle is not yet attached to the nether end of the rope.)
4. The tow vehicle now may hook up the rope and make preparations
to check the pattern and to determine whether the glider is ready.
"Take up slack" does not apply to ground launching. There
should be a pre-arranged amount of slack in the rope when the
tow vehicle hooks up, and this is used to aid the initial
acceleration.
5. Pattern clear? The pilot and the driver of the tow vehicle
should have radios and listen for calls; however, at
uncontrolled fields (which we presume you'll be operating from),
unannounced aircraft may enter the pattern. The glider pilot is
least able to check behind the glider to see if anyone is on
final, the most hazardous position for both ships. Whether
there is a wing runner or not, the tow vehicle driver should
also watch both the pattern and the ground environment, and
should simply defer the tow, no matter what the wing runner or
glider pilot signal, if there is any hint of conflict. The
driver of the tow vehicle, being the only participant with a
motor, must be in command of the launch until the glider is in
motion.
Communication between the wing runner and the pilot should be
verbal at this point. By our own convention we close the canopy
only when we have "pattern clear," but this must vary from ship
to ship.
6. Ready to launch. This is a thumbs-up signal from the pilot to
the wing runner. At our field we have a strict rule that one
wingtip of the glider is to be down at all times, and that when
the wing runner picks up the wing and holds it level, the glider
is ready for launch. This is the only signal that is
absolutely, reliably, seen by the tow driver. Remember that the
glider is at least 1500 feet away from the tow vehicle. Small
objects such as wing runners can't be seen well. The
traditional rudder waggle cannot be seen at all in some lighting
conditions, and is difficult to discern at all times.
It is safe practice for the driver and pilot to both have radios, and
to confirm the "ready to launch" signal with a radio call. In a two-
person operation (only driver and pilot), we sometimes provide the
driver with opera glasses, and require that he see the canopy being
closed and a rudder waggle before commencing tow.
Some clubs use a very large flag, and use the "take up slack" signal
when ready to launch and wave the flag in a circle when the slack is
out. We have found the wings-level signal not to require any
accessories, to be more visible, and to be clear and reliable. In
particular, we find that the taking up of slack is integral to the
launch, and that there's no purpose in the wing runner trying to
communicate to the driver that slack is out: the driver can hardly see
the wing runner, the driver should be paying attention to the glider
and to the course of the tow vehicle, and to look for the tiny wing
runner is merely a distraction. Also, it is perfectly obvious to the
driver (and riding observer, if any) from their end of the rope when
the slack is out: the rope, which has been in the grass at the side
of the runway, gets pulled out onto the runway. (The slack is out
well before the rope is straight and taught; slack is out as soon as
the tension begins to straighten it.)
So there is no need for the wing runner to signal that slack is out.
This may be useful to assure the driver or observer that the launch is
going well, but is very hard to see and hence is unreliable. I have
concluded that the safest protocol is for the driver and the pilot to
be disciplined: the pilot must pull the release if anything begins to
go wrong or if the truck begins the tow when the pilot is not fully
ready; the driver must abandon the tow if the glider is not seen to
lift off by the time the truck reaches about 30 mph or if the glider
is in any abnormal attitude.
The rope is taught; the wing runner is alert, the launch is beginning.
The glider is off the ground after a ground roll of usually less than a
hundred feet. The slice of light grey at the left margin is the near
end of the paved runway. Note that the glider's pitch angle is safe;
if a rope break occurred, a slight nose-down pitch would bring a safe
landing a few hundred feet down the runway.
Copyright © 2000, 2002 Daniel L. Johnson; all rights reserved.