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

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.

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

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

 Tree lines  Buildings  Ridges  Turkey nest dams  Creek/ river lines  Tractors Thermal Triggers

Stages of a thermal

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”

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

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

Thermal Entering Feel the rising wing and decide whether to turn, when to turn, and then which way to turn. Reduce speed in rough air, not too slow Keep momentum through sink Pull up in lift Avoid strong pull-ups, push overs  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

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

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

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

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

Thermalling Safety Assume that all other aircraft have not seen you.Assume that all other aircraft have not seen you. Always be aware of what is happening around you.Always be aware of what is happening around you. Always keep other sailplanes in sight and ensure that you can be seen.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.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.The first sailplane in the thermal has the right of way. Join the thermal to turn in the same direction.Join the thermal to turn in the same direction. When joining ensure that other sailplanes do not have to manoeuvre to avoid you.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.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 or dive sharply in the thermal. Do not pull up in front of another sailplane.Do not pull up in front of another sailplane. Be Predictable

Enjoy !