1. Thermals.

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3. All diagrams are based on classic ideas. The weather for the day will modify the weather as it pleases. It is your job to predict how the classic structures will be modified on a given day.

4. On each slide we should look as a glider pilot. “What are we going to do.”

5. A classic thermal Core Teasing zone Generally in Blue thermals.

7. Cross section of classic thermal The strong lift is in the core. So stay there. UP DOWN

8. The effect of wind shear, moves the upper part of the thermal down wind. So be prepared to shift the thermal that way at the shear height.

9. The effect of sun shadows. Stay on the “Sunny side of the street”

10. As the sun rises the thermal source becomes blocked so the thermal bends to receive heat energy.

11. Mid day the thermal source is cut off, less predictable thermals.

12. Wind effect on thermal. 8 Kt 2 Kt 4 Kt Wind Direction A thermal bubble rises at an angle proportional to the wind and thermal strength. The result is that the into wind part of the thermal is the strongest.

13. Development of Cumulus Clouds WhispDeveloping Developed Cu with dark concave base Decay and sink.

14. Thunderstorms

15. When the thermal dumps water lift can be found around the edge of the thermal. Be careful.

16. Very Rapid Storm development with Alto Cu. In the morning there is Alto Cu at higher levels, not contactable by gliders, but indicating unstable air in the upper levels. Poor lift at lower levels till later in the morning. MorningAfternoon As heating develops Cu will form at a lower level than the Alto Cu, giving stronger lift for the glider pilot. The cloud reaches freezing level producing heavy rain and sink, lifting dust and creating local squalls, in addition to lift around the edge of the sink. The cloud may rapidly move being steered by the upper level winds. Time to be on the ground and well tied down. As the thermal energy is given to the Alto Cu the Alto Cu builds rapidly in height developing into a Cb. Strong lift for glider pilots. Eventually the Cu rise to meet the Alto Cu adding the thermal energy to the instability of the upper layer of Alto Cu. The cloud grows rapidly being given further heat from all the available heat from the ground, Rain will start to come from corners of the cloud. Strong lift for glider pilots with the possibility of being sucked into the cloud.

17. Once the thermals get established after say approximately 9:30 the day begins to organize itself.

18. How thermals effect one another Why good thermal sources do not always work.

19. As thermals go higher so they go further apart. If you leave the top of a thermal you will pass through about 3 thermals before you have to land, on any given day.

20. After about 2:30 the heating to the ground reduces but the thermal height still goes higher. As there is less energy to go into producing thermals, so they are not produced so often they therefor become further apart.

21. The same theory goes for unsuitable ground, i.e. after previous wetting from rain.

22. The thermal bubble

23. The Hot Layer. Understanding this is critical. RockCropBush

24. Street Development

25. The Bush acts as a reservoir for hot air, increasing in heat and volume to the leeward side. The rock acts as a trigger for the release of the thermal.

26. Thermals continue to stream off Bush. The underside of the thermal bubble is a low pressure and sucks the residue of hot air from the crop. As the thermal bubbles drift down wind they continue sucking from the crop but not with so much strength but certainly enough to help guide you to the source. The upper level of the thermal is still strong and sucking. The lower levels are narrower in all cross sections.

27. See the Movie Thermal Movie

28. Random scatter of Cu on a non wind day, NOT TO SCALE. 200 M max in diameter.

29. Thermals stretched by wind into streets. About 15-30M wide. To the same scale as previous slide. It can be seen that if you travel cross wind on a windy day you will not have to travel very far before finding lift.

30. More realistic streets with Key Holes. Join the thermal by heading into wind Leave the thermal cross wind to find the next thermal.

31. BINGO!

32. Why Large Rocks don’t give lift

33. The novices track around a task.

34. A quicker way around the task. Novice Expert

35. Andrew Repton’s path around a task.

36. Thermalling tips Naturally we need to be able to fly At 45Deg and a constant speed This is for two critical reasons To be able to maintain a constant position in space To be able to stay in the centre of a thermal when you have cored it.

37. Approaching the thermal When we feel the pre thermal turbulence SLOW DOWN ALWAYS. With a thermal diameter of 150m it will take a glider travelling at 120 kts 2.5 seconds to pass through 85 kts 3.5 seconds 60 kts 5 seconds GIVE YOURSELF TIME TO THINK AND SAMPLE.

38. Which Way to turn Still Air Sinking Air Rising Air Pre Thermal Turbulence

39. Three possible ways to approach a thermal.

40. 1kt 2kt 3kt Glider Approaches Thermal Enters Sink Pilot Mentally switches on. Pre Thermal Buffet and SLOWS to 60-65kts Pilot Detects upwards acceleration and lifting of right wing. Acceleration forces stop, pilot using full control movements turns to right. Sink Lift Pilot gets into core of thermal in first turn.

41. 1kt 2kt 3kt Glider Approaches Thermal Enters Sink Pilot Mentally switches on. Pre Thermal Buffet and SLOWS to 60-65kts Pilot Detects Little lift but lifting of right wing so turns to the right. Acceleration forces stop, pilot using full control movements turns to right. Sink Lift Pilot gets into core of thermal in first turn. Pilot Detects acceleration and continues flying straight.

42. 1kt 2kt 3kt Glider Approaches Thermal Enters Sink Pilot Mentally switches on. Pre Thermal Buffet and SLOWS to 60-65kts Pilot Detects upwards acceleration but no wing lift. Acceleration forces stop, pilot using full control movements turns. Sink Lift Pilot maintains a very tight turn for 180 Deg. Pilot opens out turn to 45 Deg and has thermal core in one turn.

43. Turn the wrong way Option 1

44. Turn the wrong way Option 2

45. Staying in the same location in space. Now We Move the Our Centre. We keep in the same location. We now make a new centre Why maintaining VERY accurate angle of bank and speed is important

46. Move Straight or Reduce Bank. Aggressive roll out of turn and fly straight. Or Roll out gradually? If a slow roll out is used you must predict the change in lift in advance. Result

47. When to leave When the thermal strength drops to the same strength as the start of the next thermal you will get to.

48. Look for lift ahead In your climb you should be looking for the next thermalS And assessing wind drift.

49. How long do we have to make decisions? 2.5 seconds to get between the edge of the thermal and the middle Not much time You need it to be instinctive Practice.

50. Practice Technique See how many 1000ft climbs you can do in 2 hours A 2000ft climb counts as one climb! You can go back to the same thermal but you must leave it Compete with friend.

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