After a few flights the instructor introduced the details of the ground roll & takeoff. He said a student wouldn't normally attempt a complete takeoff to the tow height until later in the training, perhaps not until a successful landing had been achieved. The main reason is that although the takeoff isn't especially difficult, keeping a safe formation behind the tug once in the air is a tricky technique, and if there is a cable break or another emergency, the situation needs to be sorted out very fast.
On my introductory takeoff the wind was blowing about 45 degrees across the runway from the left (NE), requiring careful attention to avoid us being blown off of the narrow strip. Since the wind was from our left, I assumed that we would need left rudder to counteract it and keep us running straight. In fact, the reverse is true. You need right rudder to counteract a wind from the left. The glider simply reacts to the wind like a weather-cock and turns into it. So if the wind is from the left, the glider swings to the left. This is due to an aircraft's inherent stability - the vertical tail surface endeavours to keep the aircraft pointing into the slipstream - or into the wind before you are airborne. As an aide-memoire, you might need a little corrective rudder input in the same sense as the windsock is pointing: if it points left you need some left rudder.
The Puchacz has three wheels (small nosewheel and tailwheel and large main wheel). So at the start of the ground run the stick should be held well back so that it quickly lifts the nosewheel off the ground, reducing ground drag, making it easier to steer on the main wheel, and increasing the wing angle a little to help increase lift. Once the nosewheel is off the ground you ease the stick forwards again to keep the glider more level - balanced on the main wheel. Then the glider just flies off gently (in theory) without the rapid 'rotation' associated with a powered aircraft. Since the glider leaves the ground before the tug (lower stall speed), you need to fly close to the ground until the tug starts to climb above you. If there is a strong headwind the nose will rise quicker and easier, so you need to start the ground roll with less rearwards stick.
In the Puchacz and many other fibreglass trainers, when you start rolling, the nose and main wheels are on the ground which resists the turning tendency of any crosswind. As you gather speed and lift the nosewheel, you are then only on the main (centre) wheel, so the pivoting tendency is greater. So just at the moment you get the nose up the glider can start rotating into a crosswind. You need to be ready for this.
Some older (e.g. wooden) training gliders have a nose skid instead of a nosewheel, so it is also important to rotate (raise the nose) as soon as possible in the ground roll to get the skid off the ground, easing directional control and minimising skid damage, especially on a concrete runway like at Aboyne. On the other hand, most fibreglass single seaters have no nosewheel so you have to start the ground roll with some forwards stick in order to get the tail wheel off the ground, then accelerate on the main wheel.
While using the rudder to steer on the ground, you use the stick to keep the wings level. Only a slight drop of a wing is required for it to hit the ground, as gliders have no lengthy undercarriage like a powered aircraft. Initially it is hard to sense if a wing is going down as the visual clues are slight. You cannot look sideways at the wingtips as you need to keep your eyes glued to the tug.
At slow speeds almost full control deflection is required to get the aircraft to respond. But as the speed keeps increasing, the control sensitivity also increases. Soon you are passing the normal gliding cruise speed of around 45 knots up to perhaps 75 knots in the tow, by when the controls are much more sensitive than normal flying.
As the ground roll starts, the greater deflection of the stick and rudder, and using them independently, can be confusing at first. During earlier flights you have been working at coordinated use of the controls, stick-and-rudder together in the same sense. But on the ground the rudder steers the aircraft along the runway and the stick is used to operate the ailerons and keep the wings level. This needs a big mental adjustment until the moment you are airborne. And of course the reverse applies when you make a landing.
When airborne you must remember to coordinate the ailerons and rudder together again - but initially there is another concern: If you try to stop any drift and re-align exactly behind the tug by starting a normal banked turn, a wingtip may hit the ground, causing a nasty ground loop accident. You should concentrate on maintaining the correct height relative to the tug and keep the wings level until you are high enough to start any necessary banking.
The worst thing you can do in the early stages of the tow is get above the glider, as it pulls up the tail of the tug which can force it into a dive, at the same time pulling back on it so that it quickly stalls. When the tug pilot is at low altitude there may not be enough time for the tug to abandon the tow and level out. Getting above the tug is a major cause of gliding accidents - although in this case the glider usually comes out fine as it can release the tow rope and land out. But it is important to keep in mind that during the takeoff the glider pilot has his own life and the life of the tug pilot in his hands.
A Puchacz on a winch tow: note the steeper climb angle.
Aerotowing is perhaps less common than winch towing. There are pros and cons to both: a winch launch is cheaper and faster but is usually lower and closer to the airfield than an aerotow. Learning to fly the winch is another skill entirely: a pilot trained for aerotowing has to be trained separately for winching (and vice-versa).
After about ten flights I started to practice the takeoff by aerotow. I well remember my first attempt:
After the usual ritual of the preflight checks, I centred the stick and held it well back and the tug started to move. Very quickly we were accelerating along the runway but weaving and rolling somewhat as I battled with the controls to keep us on the straight and narrow, and to stop a wing-tip from hitting the ground. If that happens at speed, the aircraft can slew violently round in a 'ground roll', usually causing damage. It's especially dangerous during the tow as it can drag the tug out of the sky at the same time.
A Schweizer taking-off from a grass airstrip
Quickly after we had started rolling, the Puchacz leapt into the air - before the tug - and we started to rise steeply. The instructor immediately called for me to get the nose down and I duly pushed on the stick. Not enough. 'Too high !' he yelled, and this time I gave a hard shove and we were diving earthwards again. I quickly levelled us out and we followed the tug as it started to climb away. I was surprised how much forward stick force was required to keep the glider in the correct position, and that almost full forwards trim was still not enough to remove the pressure. As the tug rose above us I entered a gentle climb behind it.
In the early stages, if you are having trouble keeping the glider straight and level, the instructor might take over one control (e.g. stick) while you take the other (e.g. rudder) - and then swap on the next flight until you are comfortable with each one individually.
A few flights later I discovered how hard it is to keep the glider under control in a strong crosswind with some turbulence:
I got us ready to fly and the instructor suggested I take control for the complete takeoff. I noted that there was almost a completely sideways crosswind which was also a bit gusty. I asked for the tow-rope to be attached and a moment later we were rolling. Immediately we started to swing into the wind. Most aircraft quickly rotate like a weather-vane into the wind. I overcorrected and we swung right. All the time we were speeding up and the controls were becoming more sensitive, requiring less input to produce the same result. As I began to get the yaw oscillation under control, the left wing-tip began rising of its own accord - the crosswind was starting to tip us over. I swung the stick left and once again overcorrected - and now we were left wing low but veering to the right. Very disorientating. We were now just airborne and I was starting to get confused with the controls. On the ground the rudder and stick are used independently, but in the air by even an inch they are used together for coordinated turning. It was all happening too fast. I was rolling and yawing all over the place... "I have control" called the instructor - and as if by magic we slid back behind the tug as it accelerated upwards.