PGC 20031

XC Soaring Lift Sources

Ken Kochanski2/21/2004

PGC 20032

Prerequisites• Skepticism of Weather Forecast(ers)• Verified TE Compensation• Audio Variometer - A Must !!!• Proper CG Location for Thermalling• Logical neat panel• Proficient Speed and Bank Control L&R

PGC 20033

Thermal Formation• Insolation warms surface features• Sheltered warmed air accumulates• Inertia/surface tension constrains• Trigger mechanism releases thermal • Rises through unstable atmosphere • Cu form … with sufficient moisture

Reichmann:Cross Country Soaring

PGC 20034

Thermal Structure• Strong rising core surrounded by sink • Narrow, disorganized and weaker low• Stronger and wider with altitude • Weaker approaching cloud-base (?)• 600’ - 1000’ diameter at altitude • Limited lifespan … and steady state• Multi-core and other Forms• Rotation (?)

PGC 20035

Lift Cross Section

0 KT

4 KT

8 KT

1,000 FT

200 FT

6 KT

2 KT

-2 KT

March 30th, 2000 Fire-induced Cumulus CloudTom Warner shot air photo in Northern Nebraska

PGC 20036

Height/Cu Forecast• Thermal/Cu Height goes up during day • Drying air can suppress afternoon cu

0

10

20

30

40

50

60

1:00PM

2:00PM

3:00PM

4:00PM

5:00PM

KnotsHeight

PGC 20037

Finding Thermals• When you’re high … fly the sky • Cu, wisps, haze domes • Birds, debris, gliders• When you’re low … look below • Terrain, junk yards, hay fields, heat source• Smoke, crop movement, flags, debris• Spacing is related to convection depth• Mark and return to excellent thermals

PGC 20038

Thermal Entry/Exit• Plan entry at least a mile ahead • Transition sink at cruise speed• Trade cruise speed for altitude• Join gaggle safely• Occupy visible position• ‘Moffit’ exit through center if safe

PGC 20039

Centering Techniques• Don’t turn too soon• 270 degree correction to search • Toward lifted wing/yaw string swing• Tighten in surge• Minimum smooth control movements• Search/Adjust constantly • Can’t climb/center? … you’re not alone

PGC 200310

Thermalling Speed/Bank• Goal: Attain highest climb rate• Libelle bank/sink/diameter comparison

Bank Ang Knots Sink Rate Sink Delta Diameter Time 36060 60 392 415 1245 54 234 158 510 1840 52 207 27 560 2035 50 187 20 630 24

Diagonal Screws Horizontal for 45 Deg. Bank

PGC 200311

Evaluating Thermals• Evaluate in every climb from tow • Identify lift chars and operating band• Thermal core relative to cloud base• Ground shadows for size and distance• Look at Cu size/shape/cycle during cruise

WinPilot PRO -Climb Maximizer Page

PGC 200312

Speed To Fly• MacCready sets min. value for next thermal• Reichmann says set for start/end of climb• Plus you have to reach next thermal• 70 – 100 mph typical in East (2–4 kts)• Slow down in lift … Speed up in sink

PGC 200313

Optimization• Correct MacCready value selection• Stepped MacCready operating bands• Minimize Thermal Entry/Exit Losses• Course Deviation• Dolphin flight

PGC 200314

Stepped MacCready Thermal 1 Mile 5 Miles 10 Miles1 Knot 20% 90% 99%

2 Knots 10% 61% 84%4 Knots 5% 30% 52%6 Knots 2% 10% 18%

Thermal Probability Table

John Cochrane – Fly A Little Faster Please

PGC 200315

Entry/Exit Losses

John Cochrane – Fly A Little Faster Please

Climb 1Knot 2 Knots 4 Knots 6 Knots

500' 0.7 1.1 1.5 1.81000' 0.8 1.4 2.2 2.72000' 0.9 1.7 2.9 3.85000' 1.0 1.9 3.4 4.8

Effective Climb Rates

Based on 4 Circle (2 Min) Centering Time

PGC 200316

Course Deviations• 30 Degree Deviation = 15% Distance Increase

• A 3 Mile 30 Deg. Deviation @ 80 Kts ‘costs’ 20 seconds

• At MacCready 3 … this is an even trade if you gain 100’

PGC 200317

Cruise/Dolphin Flight• Netto Variometer helpful• Slow up to low cruise speed range• S-turn to explore• Thermal … or accelerate in lift • Course deviations to lift• Cloud shadows for bearing/distance

PGC 200318

DIY Climb/Speed Calcs• 150 Mile Course = 5 Mile Climb @ 30:1• 5 x 5280’ = 26,000’ – 5,000’ AGL Start• 20,000’ climb @ 200 fpm = 100 Minutes• 150 miles @ 70 mph = 130 Minutes• 3:50 for 150 Miles = 40 MPH • Use SeeYou for analysis of your flight

0

10

20

30

40

50

60

1:00PM

2:00PM

3:00PM

4:00PM

5:00PM

KnotsHeight

PGC 200319

Cloud Streets• Wind > 15 knots + stable cap layer• Excellent lift … and awful sink • Spacing 3x Convection Depth• Potential Lee Waves over top• 30 degree course deviation OK• 90 degree transition between streets• Use ‘blue’ extension of street• Turn-point access/exit strategy

Drawing: A Met Guide For Beginners – Tom Bradbury

PGC 200320

Blue Days• Stable or dry/drying air• Thermals as frequent and as strong• Follow terrain - high, dry, sun-facing • Turn crosswind in heavy sink • More dependence on gaggles• Haze domes may appear in afternoon

PGC 200321

Shifting Gears• Has the air changed in the last 10 minutes?• Shift down (or up) for declining conditions• Up-shift in improving air or after trouble • Can’t climb/center? … you’re not alone

PGC 200322

Low Altitude Saves• Field selected and appraised • Radio volume down/off • Additional airspeed• Turn immediately in lift• Don’t leave below 2000 feet AGL• 600 FPM down = 200 feet in 20 seconds

PGC 200323

Ridge Running • Ridge sites/camps best initial experience• Wind Speed and Direction Important• Ridge Shapes/Orientation/Gaps• Wave and Thermal Suppression• Crotch Strap and No-Hands “P” System

PGC 200324

Ridge Thermals• Favor Upwind side of ridge• Often rough/strong … with small cores• Initial turns always away from ridge – 8’s• Circle when > 200 feet above ridge top• 1000 FPM down = 330 feet in 20 seconds • Ridge thermal can suppress weak ridge• Have a field or retreat plan

PGC 200325

Wave/Rotor • Typically After Cold Front – U/S/U• Lennies … Rotor Clouds … or None• Terrain or atmospheric generators• Parallel to Ridge – 1st, 2nd, N Cycles• Interference Patterns – Peaks/Nulls• Inter-day Wavelength Changes• Rotor/Thermal Entry

PGC 200326

Wave Entry/Flying• Wave Induced Cumulus • Climb upwind side of rotor• Transition through windows• Fly directly upwind … or crab • Cold, O2, Visibility Issues

PGC 200327

Other Lift Sources • Sea Breeze Fronts• Temp or Moisture Frontal Systems• Thunderstorms/Dust Devil • Gap Roll/Obstruction Waves• Magic Lift

PGC 200328

Reading/Research • Moffat – Winning on The Wind• Reichmann – XC Soaring• Knauff/Wander/Bradbury• Internet – Many Resources

PGC 200329

Mark … Good Finish !!!

Ken Kochanski