4. LESSON 26 - FLYING IN THERMALS
- Always plan ahead
- Enter the thermal with care – look out!
- Turn in the same direction as the glider(s) already flying in the thermal
- Avoid collisions, keep sufficient distance to others
- Stay within sight of other gliders – take the blind spots into account
- Leave before a dangerous situation occurs
- Do not overtake on the inside of the circle
- Take drifting by the wind into account
Flying in thermals is a lot of fun. Try to have a careful look which direction other pilots set off in after they have released from the winch or aerotow and you will better understand where to find them. Your instructor will explain the things you need to pay attention to when flying in thermals. Flying in thermals is a learning process and the goal is to be able to make your own decisions in a safe and responsible manner. It requires a high level of concentration. ‘Centering’ in a thermal is a continuous process. Most thermals are not round and the thermal core may shift all the time. In the meantime, you have to look out for other gliders and stay aware of your position in relation to the airfield.
Like most new things, thermal flying will become easier after practice. During your training, thermal flying will be practiced continually. Here we will only concentrate on the safety aspects of flying in thermals. If you want to improve and perfect your thermal flying technique there are at least twenty books on the subject you could read or you could spend some time eavesdropping at the bar of a random gliding club. Gliders in a thermal seem to attract each other like magnets. Very often several gliders end up flying in the same thermal at the same time, which is called flying in a ‘gaggle’. Here are five important safety rules:
1 TURN IN THE SAME DIRECTION
The first pilot to enter a thermal determines the direction of circling. All those who arrive later adopt the same direction of circling. Sometimes during circling you will see another glider circling nearby – at the same altitude but in a different thermal core. As you climb further you will then notice that the two thermal cores get closer; be careful to keep sufficient distance from the pilot in the other core or change your circle to join him or her.
In general, the rule is that you try not to hinder a glider that is already circling when you join the same circle. Try to stay on the opposite side of their circle and always maintain visual contact. There’s a simple way to let another pilot know that you see him or her: wave! If the other pilot waves back, you know they’ve seen you as well. Try not to stare at your instruments when thermalling but keep looking outside the cockpit for most of the time. Electronic variometers indicate whether you are climbing or descending by high or low beeping noises. There is no need to keep staring at the needles, simply pay attention to the beeps.
2 KEEP YOUR DISTANCE
It is important that you always keep as much distance as possible from all other circling gliders. Especially vertically: a higher pilot cannot see you if you are flying directly below or behind them. And if the lower glider climbs faster than the higher glider a very dangerous situation could arise. Always take a position in a thermal in such a way that all gliders have sufficient space to circle and correct and so that everyone can see everyone else. If you want to leave the thermal core clearly level your wings and fly away in a straight line, having first checked that it is clear to do so. By doing this you show the others that you are leaving. Remember that if you feel uncomfortable or it gets too crowded, it might be better to find a new thermal.
3 DO NOT OVERTAKE ON THE INSIDE OF THE CIRCLE
Efficient thermalling is not easy in the beginning. To achieve the highest climb rate, you will need to adapt your circle continuously. When you are alone, you can do this more easily than when more gliders arrive. In that case, you will have to adjust your bank angle and rate of turn having regard for the other pilots. Don’t overtake someone inside the circle, even if you suspect that you’ll find a better climb there. Very experienced glider pilots have no problem flying with several planes in the same thermal. But if you don’t have this experience or when you notice other pilots not keeping sufficient distance it is better to leave and find another thermal.
When a thermal is still being triggered, or ‘fuelled’ by more hot air, it will travel slower than the speed of the surrounding wind. However, thermals do move downwind!
After releasing from the winch or aerotow try to find thermals in the direction where the wind is coming from (up-wind) and monitor your position frequently as you fly. Do not circle above the winch and keep your distance from other gliders doing a winch launch. Calculate the required height above the ground at a certain distance from the airfield in such a way that you can always reach the circuit safely. At first, your instructor will help you to do this. How much height you need depends on:
- the performance of your glider
- the wind direction and strength
- areas with possible increased sink
- your experience
5 RETURN TO THE AIRFIELD IN AN EFFICIENT MANNER
On your way back to the airfield, you will pass through areas with rising and sinking air. If you fly through sinking air at a higher airspeed, you will pass through it faster and lose less height. The other way around, when you encounter lift, you can stay in the rising air a bit longer and gain some height, or reduce your height loss, by flying slower.
Different aids give guidance for best speeds to fly. Many training gliders are equipped with a McCready ring. The McCready ring is a rotatable ring on your variometer that indicates the best airspeed to fly in sinking and rising air. In modern flight computers the formula behind this ‘ring’ is integrated in the software and when set correctly, it gives you a very accurate optimal speed to fly.