Efficient Thermalling: Finding, Centering and Leaving Thermals

1. Thermalling The importance of efficient thermalling How thermals are formed Finding thermals Thermal selection Centering Staying centred Leaving Mike Codling May 2008

2. Efficient Thermalling – why ? • X-country speed = 0 while thermalling • 3hr flight, difference between 4 knot av. and 4.5 kn av. is approx 32 secs/ thermal or 10mins 40 seconds for flight. • Better speed, further difference, best use of day.

3. How thermals are formed • Parcel of air warmer than the surrounding air • Source • Trigger What things come to mind that effect thermal generation? • Sunlight • Wind • Slope • Soil Type • Shadow lines • Moisture level • Inversions • Vegetation • Time of day • High level cloud

4. Thermal Sources • Dark ploughed paddocks • Red soil paddocks • Vegetation – evening • Gullies in the sun • Quarries, mines • Fires • Power stations, industry • Rock faces

5. Thermal Triggers • Tree lines • Buildings • Ridges • Turkey nest dams • Creek/ river lines • Tractors

7. Stages of a thermal

8. Finding Thermals – blue days • Know the wind direction • Look for sources • Look for triggers • Account for wind, slope, sun angle • Dust Devils “In order to find a thermal, I think like one”

9. Finding Thermals – CU days • Look for CUs ;-) • Note cycle timing • Account for wind, sun angle • Check for dark, flat bottoms or concave • Check for swirls, wisps • Avoid “hanging” remnants • Avoid clouds lower than others nearby • If in doubt fly to centre whilst high • If low treat as blue day

10. Thermal Selection • Look for correct timing of cycle • Look for energy lines, streets and future options • Check out the other gliders for bank angle • Modify selection strategy for time of day Plan on for every 1000ft of convection, 1 knot of climb rate

11. Thermal Entering Feel the rising wing and decide whether to turn, when to turn, and then which way to turn. • Never fly through the same patch of bad air twice. • Always shift towards the stronger part of the thermal • Air is smooth in the core • Feel will always precede the vario • Reduce speed in rough air, not too slow • Keep momentum through sink • Pull up in lift • Avoid strong pull-ups, push overs

12. R = 149 m 25 degr. bank angle R = 85 m 45 degr. bank angle Turning • Maintain attitude A.R.E. • Adjust once per turn and wait to note effect • Good angle of bank (45deg in Aust) Use wires, straws, or instrument screws to determine 45 degree bank

13. Thermal Centering – simple method A-B turning into lift. B-C steep angle of bank due to weakening lift. C-D shallow angle of bank due to strengthening lift. D maintain normal 45 degree angle of bank while in steady lift

14. Worst Heading Centering Method When vario is weakest (A) roll out (B), wait for 2 seconds as vario rises, roll back in (C) Good for low hours as low workload

15. Leaving • Use McCready rule for leaving • current climb = expected next climb • Decide exit strategy well below cloudbase • Build speed during last turn or … • Turn across the centre ( not when sharing a thermal) • Exit upwind or downwind to avoid sink • Have cruise speed before sink

16. Thermalling Safety • Assume that all other aircraft have not seen you. • Always be aware of what is happening around you. • Always keep other sailplanes in sight and ensure that you can be seen. • A sailplane that remains stationary in the canopy and is growing larger, is going to hit you unless you take avoiding action. • The first sailplane in the thermal has the right of way. • Join the thermal to turn in the same direction. • When joining ensure that other sailplanes do not have to manoeuvre to avoid you. • If there is more than one sailplane thermalling in different directions turn in the same direction as the one at your height. • Do not pull up or dive sharply in the thermal. • Do not pull up in front of another sailplane. Be Predictable

17. Enjoy !