Transcript Thermaling 101 - University of Rochester
PGC 2003
XC Soaring Lift Sources
Ken Kochanski 2/21/2004
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PGC 2003
Prerequisites
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Skepticism of Weather Forecast(ers)
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Verified TE Compensation
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Audio Variometer - A Must !!!
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Proper CG Location for Thermalling
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Logical neat panel
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Proficient Speed and Bank Control L&R 2
PGC 2003 •
Thermal Formation
Insolation warms surface features
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Sheltered warmed air accumulates
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Inertia/surface tension constrains
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Trigger mechanism releases thermal
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Rises through unstable atmosphere
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Cu form … with sufficient moisture
Reichmann:Cross Country Soaring
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PGC 2003
Thermal Structure
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Strong rising core surrounded by sink
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Narrow, disorganized and weaker low
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Stronger and wider with altitude
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Weaker approaching cloud-base (?)
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600’ - 1000’ diameter at altitude
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Limited lifespan … and steady state
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Multi-core and other Forms
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Rotation (?) 4
PGC 2003
March 30th, 2000 Fire-induced Cumulus Cloud
Tom Warner shot air photo in Northern Nebraska
Lift Cross Section
200 FT 8 KT 6 KT 4 KT 2 KT 0 KT -2 KT 1,000 FT
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PGC 2003
Height/Cu Forecast
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Thermal/Cu Height goes up during day
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Drying air can suppress afternoon cu 60 50 40 30 20 10 0 1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM Knots Height 6
PGC 2003 •
Finding Thermals
When you’re high … fly the sky
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Cu, wisps, haze domes
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Birds, debris, gliders
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When you’re low … look below
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Terrain, junk yards, hay fields, heat source
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Smoke, crop movement, flags, debris
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Spacing is related to convection depth
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Mark and return to excellent thermals
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PGC 2003
Thermal Entry/Exit
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Plan entry at least a mile ahead
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Transition sink at cruise speed
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Trade cruise speed for altitude
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Join gaggle safely
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Occupy visible position
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‘Moffit’ exit through center if safe 8
PGC 2003
Centering Techniques
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Don’t turn too soon
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270 degree correction to search
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Toward lifted wing/yaw string swing
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Tighten in surge
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Minimum smooth control movements
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Search/Adjust constantly
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Can’t climb/center? … you’re not alone 9
PGC 2003
Thermalling Speed/Bank
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Goal: Attain highest climb rate
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Libelle bank/sink/diameter comparison Bank Ang
60 45 40 35
Knots
60 54 52 50
Sink Rate Sink Delta Diameter Time 360
392 234 207 187
158 27 20
415 510 560 630 12 18 20 24 Diagonal Screws Horizontal for 45 Deg. Bank
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PGC 2003
Evaluating Thermals
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Evaluate in every climb from tow
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Identify lift chars and operating band
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Thermal core relative to cloud base
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Ground shadows for size and distance
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Look at Cu size/shape/cycle during cruise
WinPilot PRO -Climb Maximizer Page
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PGC 2003
Speed To Fly
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MacCready sets min. value for next thermal
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Reichmann says set for start/end of climb
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Plus you have to reach next thermal
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70 – 100 mph typical in East (2–4 kts)
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Slow down in lift … Speed up in sink 12
PGC 2003
Optimization
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Correct MacCready value selection
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Stepped MacCready operating bands
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Minimize Thermal Entry/Exit Losses
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Course Deviation
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Dolphin flight 13
Stepped MacCready
Thermal Thermal Probability Table 1 Mile 5 Miles 10 Miles 1 Knot 2 Knots 4 Knots 6 Knots 20% 10% 5% 2% 90% 61% 30% 10% 99% 84% 52% 18% PGC 2003 John Cochrane – Fly A Little Faster Please
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PGC 2003
Entry/Exit Losses
Climb 500' 1000' 2000' 5000'
Effective Climb Rates
1Knot 2 Knots 4 Knots 6 Knots 0.7
0.8
0.9
1.0
1.1
1.4
1.7
1.9
1.5
2.2
2.9
3.4
Based on 4 Circle (2 Min) Centering Time
1.8
2.7
3.8
4.8
John Cochrane – Fly A Little Faster Please
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PGC 2003
Course Deviations
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30 Degree Deviation = 15% Distance Increase
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A 3 Mile 30 Deg. Deviation @ 80 Kts ‘costs’ 20 seconds
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At MacCready 3 … this is an even trade if you gain 100’ 16
PGC 2003
Cruise/Dolphin Flight
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Netto Variometer helpful
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Slow up to low cruise speed range
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S-turn to explore
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Thermal … or accelerate in lift
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Course deviations to lift
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Cloud shadows for bearing/distance 17
PGC 2003
DIY Climb/Speed Calcs
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150 Mile Course = 5 Mile Climb @ 30:1
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5 x 5280’ = 26,000’ – 5,000’ AGL Start
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20,000’ climb @ 200 fpm = 100 Minutes
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150 miles @ 70 mph = 130 Minutes
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3:50 for 150 Miles = 40 MPH
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Use SeeYou for analysis of your flight 60 50 40 30 20 10 0 1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM Knots Height 18
PGC 2003
Cloud Streets
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Wind > 15 knots + stable cap layer
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Excellent lift … and awful sink
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Spacing 3x Convection Depth
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Potential Lee Waves over top
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30 degree course deviation OK
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90 degree transition between streets
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Use ‘blue’ extension of street
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Turn-point access/exit strategy
Drawing: A Met Guide For Beginners – Tom Bradbury
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PGC 2003
Blue Days
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Stable or dry/drying air
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Thermals as frequent and as strong
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Follow terrain - high, dry, sun-facing
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Turn crosswind in heavy sink
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More dependence on gaggles
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Haze domes may appear in afternoon 20
PGC 2003
Shifting Gears
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Has the air changed in the last 10 minutes?
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Shift down (or up) for declining conditions
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Up-shift in improving air or after trouble
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Can’t climb/center? … you’re not alone 21
PGC 2003
Low Altitude Saves
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Field selected and appraised
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Radio volume down/off
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Additional airspeed
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Turn immediately in lift
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Don’t leave below 2000 feet AGL
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600 FPM down = 200 feet in 20 seconds 22
PGC 2003
Ridge Running
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Ridge sites/camps best initial experience
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Wind Speed and Direction Important
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Ridge Shapes/Orientation/Gaps
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Wave and Thermal Suppression
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Crotch Strap and No Hands “P” System 23
PGC 2003
Ridge Thermals
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Favor Upwind side of ridge
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Often rough/strong … with small cores
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Initial turns always away from ridge – 8’s
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Circle when > 200 feet above ridge top
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1000 FPM down = 330 feet in 20 seconds
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Ridge thermal can suppress weak ridge
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Have a field or retreat plan 24
PGC 2003
Wave/Rotor
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Typically After Cold Front – U/S/U
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Lennies … Rotor Clouds … or None
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Terrain or atmospheric generators
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Parallel to Ridge – 1 st , 2 nd , N Cycles
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Interference Patterns – Peaks/Nulls
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Inter-day Wavelength Changes
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Rotor/Thermal Entry 25
PGC 2003
Wave Entry/Flying
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Wave Induced Cumulus
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Climb upwind side of rotor
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Transition through windows
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Fly directly upwind … or crab
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Cold, O2, Visibility Issues 26
PGC 2003
Other Lift Sources
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Sea Breeze Fronts
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Temp or Moisture Frontal Systems
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Thunderstorms/Dust Devil
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Gap Roll/Obstruction Waves
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Magic Lift 27
PGC 2003
Reading/Research
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Moffat – Winning on The Wind
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Reichmann – XC Soaring
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Knauff/Wander/Bradbury
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Internet – Many Resources 28
PGC 2003
Mark … Good Finish !!!
Ken Kochanski
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