1. Collision Avoidance
Thermalling
See and be seen
A wave is nice!

2. To Avoid overtaking anything it is a normal reaction to slow down and turn away.
Does this work when both gliders are thermalling?

3. Dynamics of see and be seen
Turning away, he can no longer see me!

4. About to Turn right!
Turning towards – can he safely?

5. In a thermal, higher performance will not save you
In a thermal, higher performance will not save you. These older gliders turn like birds!

6. K 18 on a better line turning towards you and you have approached ‘stealthily’ from his blind spot.

7. Speed Verses Angle of Bank Turn Radius Achieved in MetreS BANK = SPEED
AOB
40 kts
45 kts
50 kts
55kts
60 kts
65 kts 35
61.7
78.1
96.4
116.6
138.8
162.9 40
51.5
65.2
80.4
97.3
115.8
136.0 45
43.2
54.7
67.5
81.7
97.2
114.1 50
36.3
45.9
56.6
68.5
81.6
95.7

8. Effect of Reducing speed
Turn radius reduces and rate of turn increases
AOB
40 kts
45 kts
50 kts
55kts
60 kts
65 kts 35
61.7
78.1
96.4
116.6
138.8
162.9 40
51.5
65.2
Rot 20.3
80.4
97.3
115.8
136.0 45
43.2
54.7
67.5
81.7
97.2
114.1 50
36.3
45.9
Rot 28.9
56.6
68.5
Rot 23.6
81.6
95.7

9. Effect of Increasing Bank
Again turn radius reduces and rate of turn increases
AOB
40 kts
45 kts
50 kts
55kts
60 kts
65 kts 35
61.7
78.1
96.4
116.6
138.8
162.9 40
51.5
65.2
Rot 20.3
80.4
Rot 18.3
97.3
115.8
136.0 45
43.2
54.7
67.5
81.7
97.2
114.1 50
36.3
45.9
Rot 28.9
56.6
Rot 26.0
68.5
Rot 23.6
81.6
95.7

10. If your nose is tracking ahead of the glider in front you are ‘leading’. If you are flying on the inside at the same speed and angle of bank you will overtake or hit the glider ahead.

11. If your nose is tracking ahead of the glider in front you are ‘leading’. If you are flying on the inside and either slow down or/and increase your angle of bank, you will overtake the glider ahead.

12. Regardless of speed and/or angle of bank, to escape you must track you nose behind the glider ahead. (lag)

13. These dynamics occur even if there is vertical displacement
Blind spot
Are they catching?
Unlikely because their nose is pointing behind my tail

14. And if I were to recentre now!

15. Soon this glider will not be on the same circle
This glider has tightened his turn
AoB increased

16. This is YOUR BEST visual clue.
If your nose is ever tracking ahead of the glider in front, you are ‘leading’
This is YOUR BEST visual clue.
If you increase bank, the rate of overtake only gets worse.

17. Fine IF they know you are following behind

18. Is this a
problem?

19. Lookout may involve moving your head or your wing!
Could be a problem!

20. A well disciplined gaggle. Are you sure!
Leaches

21. Anticipate when dangerous situations might be developing

22. Just like stalling or spinning, thermalling with other gliders is not dangerous, but it should be clear that it is simple to generate a dangerous situation.
It is easy to get into a position where one cannot see the other. The ‘blind’ pilot therefore does not know what you are doing or where you are. In this situation they must be given absolute freedom of manoeuvre.
Even when you can both see each other it is easy to get into a challenging situation if you concentrate and adjust on the thermal centre unaware that you are generating a lead on the adjacent glider/s.
In these situations it is often the case that one glider is the leader, dictating where the gaggle goes and the others just follow.