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Heinz McArthurNorth Carolina Soaring Association

July 26, 2008

Speed to FlyFly faster, turn tighter

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Agenda

• Glider polars, best L/D, minimum sink• MacCready theory• Reichman approach• John Cochrane: “Just a Little More Speed”• Wil Schuemann: “The Price You Pay for

MacCready Speeds”• Final glides• P1 notes

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Polars

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MacCready Theory

Goal: maximize average cross-country speed using optimal inter-thermal cruising speed

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MacCready Theory

• MacCready speeds based on:– Glider performance– Sink rate between thermals– Expected average strength of next thermal

• MacCready setting = Expected average strength of next thermal

• MacCready setting = Minimum acceptable thermal strength

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MacCready speedsThen

Now

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Reichman update

• Thermals tend to be stronger in the center– Weaker at the bottom and the top

• MacCready setting– final climb = speed setting = initial climb

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John Cochrane• During flight figure out/adjust the right level of confidence

– “How much higher would I have to be in order to finish a minute sooner?”

– This is the MacCready value• Take any thermal greater than the MacCready value; leave any

thermal below the MacCready value.• Fly the speed ring setting corresponding to the current MacCready

value.• MacCready value is the weakest thermal you would take for one

circle. It is substantially less than the peak climb in the best thermal of the day.

• As you get lower, take weaker thermals and fly slower. • As you get higher, leave weak thermals, stop only for stronger ones,

and fly faster.

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John Cochrane

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John Cochrane

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Wil Schuemann

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Wil Schuemann

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• Schuemann’s conclusions– Moderate speed with little variation costs very

little XC speed– Reducing MacCready intensity yields more

time to think!!! And look outside– Increasing range may improve thermal

selection– Slower flight makes air easier to assess

Wil Schuemann

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Final Glide -- DJ Notes• Leave the last thermal

– When you can fly the MacCready speed and reach the goal

– Plus a safety margin• MacCready setting = Average of the last thermal

– The one you’re in• Wind now a factor

– Glide angle over the ground– Flatter with a tailwind– Steeper with a headwind

• As is wing loading and bugs– Set your calculator accurately– Which requires practice

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Final Glide -- DJ NotesPsychological Pressures

• Glide angle visually flat in modern glas

• Excessive sink might be encountered

• Flying fast, loud, low– And the turbulence gets rougher lower– And the pilot’s IQ starts to fade

• Tunnel vision/narrowed focus dangerous

• Must fly the airplane to a safe landing, not just a good finish

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Final Glide -- DJ Notes

• Soaring accidents on final glide

• Waiting too long to thermal

• Relying on Zero MacCready to ‘make it’

• Off-landing without preparation, from low altitude

• Analyze fields near the airport

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Final Glide – J7 Notes• Start shifting mentally to ‘final glide mode’ as early as

possible• Watch cloud picture as you go into final TP to decide

which way to run home• Try a 1 McCready setting to decide when to go on final

glide• On some days it makes sense to start below glide path if

cloud picture indicates you can work your way up to glide path while mostly sinking!

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Final Glide – J7 Notes

• When on glide path, turn up McCready setting until you maintain glide path, fly as fast (slow) as you are directed

• Connect with lift sources, cloud picture on course, pull up in lift

• Overly aggressive flying puts you in a field!• Set your arrival altitude to 700-800’ above home

field elevation, go much later to 500’. • Allow for another margin if you are not sure of your

final glide/wind calculations• Be prepared to see the goal airport at a very shallow

angle, it looks as if you won’t make it

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Final Glide -- XM Notes

• Set MacCready 3

• Leave last thermal when final glide altitude achieved

• On glide slope, continue MC speed

• Under glide slope, slow down

• Over glide slope, speed up

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P1 notes

• Shifting gears– Sam Giltner and the blue hole at Winter Haven

• Speed-to-fly vs thermal heights

• Do you pull up in lift, speed up in sink?

• Do you follow the push-pull indicator?

• Do you set the MacCready “ring”? When?

• When do you start final glide? What speed?

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Wrap up

“Deciding when to stop and when to leave, and achieving the best average climb rate, are the most important determinants of cross-country speed.”

-- John Cochrane

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References• Cross-Country Soaring: Helmut Reichmann• Cruising for Speed: Sam Zimmerman presentation, 2007 Perry

Cross Country Racing Camp• Final Glides: Doug Jacobs presentation, 2007 Perry Cross Country

Racing Camp• Glider Polars and Speed-To-Fly: Bob Wander• Just A Little Faster Please: John Cochrane

http://faculty.chicagogsb.edu/john.cochrane/research/Papers/#maccready

• Preparation for Contest Flying: Herbert Killian, Chicago Glider Club presentation http://groups.yahoo.com/group/NCSoaring/files/Presentations/Preparation_for_Contest_Flying-Killian-c.ppt

• The Price You Pay For MacCready Speeds: Wil Schuemann http://www.betsybyars.com/guy/soaring_symposia/72price.html

• Training for Cross-Country: Article by Helmut Reichmann

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Glider Polars