In the early learning stages the instructor normally flies the takeoff to about 500 feet and then hands control to the student for the rest of the aerotow.
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During the aerotow you are effectively flying in tight formation with the tug - the rope is usually 150 metres long. This requires plenty of concentration and good coordinated flying. As the tug pilot is responsible for lookout during the two, you should concentrate on the formation-flying with occasional glances earthwards to check for a suitable field for landing. Photo: aerotow at takeoff from Aboyne (click photo for a larger image) |
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During the aerotow you must always know what to do if it goes wrong. Until you are sure you can get back safely to the airfield, you must have a field in mind in which to land. If there is a problem you will have little time to work out where to go. The usual cause of aerotow trouble is a rope break - but sometimes the tug has a problem like the engine running rough or failing. Inexperienced glider pilots sometimes upset the tow by getting too high - in which case the tug pilot will likely release the glider immediately.
My early aerotows were hard work. With each twitch of the tug I seemed to drift horribly out of position. At the high speed of towing (around 70 knots compared to normal gliding speed of around 45 knots) the controls feel quite different. The ailerons on the wings are much heavier, which can lead to less bank being 'delivered' than desired, which slows the rate of corrective turns to keep the glider in position. At the same time, the elevators in the tailplane are more sensitive, so with barely a nudge on the stick the glider is either rapidly climbing or diving - much faster than you at first expect.
I remembered that the rings at the end of the towrope have weak links in order to make sure the forces on the glider and/or tug are not excessive: Winch launch cables occasionally break as the forces can be very high and increase quickly. Aerotow rope breaks are less common, but turbulence or rope-snatching after getting out of position can jerk the rope sufficiently to sever a weak link or the rope itself. A rope break is also more likely if the rope is worn or has a knot (which roughly halves the strength of a rope).
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As the tug and glider gently climb
together, occasionally turning as the tug seeks out the best bit of sky
to drop you in, at first you have to work hard to keep the glider's
wings level with the wings of the tug. If there is a difference in the
bank angles of the tug and glider, you will soon diverge which can be
dangerous. In order to stay in formation, I soon realised I had to point
the glider's nose a little outside the turn circle as the tug and glider
are flying on different tangents to the turn, aiming at the outside wing
instead of the tail. The steeper the turn, the more I had to point
outside the turn (further along the outside wing). Photo: aerotow departing Aboyne (click for a larger image) |
At one point during an early flight I got rather out of position to one side and the rope began to form a large bow. I was getting worried as the bow approached the tug, follwed by the glider. I levelled the glider to start taking up the slack and then entered a turn to try and get back behind the tug. The instructor then intervened with some useful advice: Do not try to turn back into position - just level the wings with the tug and relax on the controls and the tightening rope will pull the glider back into position behind the tug. I obliged - and lo & behold we started sliding in nicely behind the tug again. Banking towards the desired position can easily result in an overshoot out to the other side.
The main technique in flying the aerotow is to closely match the bank angle of the tug to avoid following a different path, and to hold a vertical position just below the tug's extended centreline - which is just above its slipstream. You get used to the correct view of the tug. In some countries a 'low tow' position is used with the tug below the tug's slipstream. The high tow position is preferred by many pilots (and is routine in the U.K.) as it enables a better view of the ground ahead to keep an eye out for a landing-out field.
If slack develops in the rope you have to take it up gently or there can be a wild jerk which can stress the two aircraft - and cause a weak link or the rope to break. So anticipation is essential - as soon as there is a deviation from this ideal position, a small correction should be made, and it in turn should be stopped quickly to avoid an overcorrection.
At an early stage of learning it is all too easy to get into a positive feedback situation with the glider careering all over the sky. Early in my aerotow experience, just after the release after the ordeal of close formation flying, the instructor suggested that the next time I flew the tow I should use more rudder, as some of the trouble I'd experienced was due to inadequate rudder. This meant that there was some aileron drag; e.g. when I banked left to try and turn left a little, the glider rotated slightly right due to the drag on the right wing (which should be compensated by appropriate left rudder). So at the start of each turn the glider was effectively moving slightly in the opposite sense to my intended control input, leading to some oscillations as I over-corrected. Another example of the importance of stick and rudder coordination.
Patches of turbulence often bounced us around during many of my early tows and I applied rapid corrections (sometimes too much). If you see the tug bouncing around in rough air, you can be sure to follow very soon after. It helps if you let both aircraft ride out the same rough air rather than fighting it. Throughout the tow - and the rest of your flying - you need to try and relax. Easier said than done at first. Precise but gentle control movements should keep you where you want to be. Otherwise it is too easy to get into a pilot induced oscillation, so you are in fact fighting yourself rather than the glider or tug.
On another flight I was introduced to an exercise to help develop aerotow control, called boxing the tow.
After what seems like an eternity, you reach the tow height - normally 2,000 feet - and pull the yellow handle to release the rope. The routine for rope release is to make sure that the glider and tug separate quickly and the rope is removed from the vicinity of the glider as quickly as possible. Once you are sure the rope is indeed gone (try to see it go), the tug dives to the right and you lookout then climb to the left. At this stage you shouldn't relax too soon to admire the view. Once a safe separation is assured you can change course as desired. The climbing turn also converts the excess tow speed into height, perhaps adding another 100 feet or so to the start of the glide and the search for lift. At that point you trim for level flight and make sure you know where the airfield is. If you are 'lost' the best thing to do is to quickly follow the tug which will normally be heading straight back to the airfield.
It is important to know the tug signals in case of a problem or emergency:
Check Airbrakes: If the tug swings its rudder (hence the tail) from side to side you should check if your airbrakes are released. The tug pilot has detected too much drag or can see your extended airbrakes in his/her mirror. Accidental deployment of airbrakes is more common than it should be, more often due to overlooking the pre-flight check ensuring they are locked, although sometimes the lock tension may have a problem.
| Release Imediately! A rapid rolling of the tug means "Release Immediately!". This may be given if the
tug is losing power or has another serious problem. Of course, if there
is no time to lose the tug can release the tow rope at its end and leave
you to it.
NB: If you ever lose sight of the tug - Release Immediately |
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