Presentation on theme: "TECHNIQUES FOR EFFICIENT INTERTHERMAL SOARING"— Presentation transcript:
1 TECHNIQUES FOR EFFICIENT INTERTHERMAL SOARING CRUISING FOR SPEEDTECHNIQUES FOR EFFICIENT INTERTHERMAL SOARING
2 INTRODUCTION CRUISING = 60%-80% OF FLIGHT HOW FAST TO FLY BETWEEN THERMALS?MACREADY STILL RULES – BUT WITH NUANCES WORTH UNDERSTANDINGOUT MACREADYING MACREADY – FOLLOW THAT ENERGY PATH!SeeYou L/DDB’s flight
3 PROGRAM PLAN REVIEW CLASSIC MACREADY THEORY WIL SCHUEMANN’S PAPER The Price You Pay For Macready SpeedsJOHN COCHRANE’S PAPERJust A Little Faster PleaseTECHNIQUES FOR SPECIFIC SITUATIONSThe implications of these papers in our evolving use of MacCready theory
4 Classic Macready Theory AssumptionsAll thermals same strength at all altitudesStrength of next thermal is knownInterthermal sink/lift is assumed constantThree PilotsHair on fire Pilot CNamby pamby Pilot BOllie Optimal Pilot A1938 Polish pilots began “best speeds’ curves—lost in war1948 Karl Nickel published tangential construct1948 Macready published speed ring design
6 Classic Macready Theory Optimal inter-thermal speed for maximum average cross country speed can be calculated
7 Effect of inter-thermal sink/lift– essentially subtracts from/adds to achieved climb rate Effect of Headwind/Tailwind--none except on final glideWater ballast-- shifts polar down to rightPut in an anticipated thermal strength, a polar and a wing loading to the on-board computer and a speed to fly emerges as a tone and needle indication
8 PROBLEMS WITH MACREADY Don’t know next climb rateClimb rate varies with altitudeAnd time to center the climb – achieved climb rateDon’t know sink/lift between thermals– varies constantly
9 Wil Schuemann- renaissance soaring man Total energy compensation boxWater ballastWingletsDiscus plan-formSeminal paper on modified MacCready flightSoaring symposia—1972– see referencesThe ASW-12 experimental platform
10 The Price You Pay For Macready Speeds by Wil Schuemann
11 Cruise speed vs. achieved Average speed minimal difference +/- 8 to10 knotsBig difference at best L/DEffect on range – does slower speed increase range? Yes with respect to airmass- more range, larger chance to find special thermal (Remember Pilot B?)
12 Who would you rather be if you don’t know where the next thermal is? PilotsBAC
13 Flying MaCready accurately ain’t easy What is the next (achieved) thermal strength??Chasing the needle may do more damage than goodControl dragNon-optimal G loadingDamp out airframe responsesScare the s--- out of fellow pilotsDistracts from other tasks
14 Lessons learnedSpeed variations 8-10 knots from ideal Macready minimal impact on ave. x/c speedSpeeding in sink gains littleRange gained with slowingBut perfect speed adherence would give slightly higher speeds.
15 Schuemann’s conclusions A moderate speed with little variation costs very little speedReducing MacCready intensity yields more time to think!!! And look outsideIncreasing range may improve thermal selectionSlower flight makes air easier to assess
16 John Cochrane PHD economics, U. of Chicago dept. Finance Highly successful competition pilotRegular contributor to Soaring magazine
17 Just A Little Faster Please John Cochrane Speed and modern MacCready theory-observationsMacCready still key to in-flight speed decisionsMacCready determines cruise speed--- the mathematical solution is still validBut what is the correct MacCready value?Reichmann’s elliptical thermal lift concept- bottom and top are usually less than mid-level climb rateLikelihood of finding best thermals goes down with altitude
18 Random lift distribution curve plotted against altitude Assumes thermals vary in strength quite a bitThere are many weak thermals to use to save a flight lowThere are a few really good thermalsSeems to fit with pilots’ real world observations
19 Proper MacCready setting drifts down as glider gets lower
20 CENTERING TIME-AT THERMAL ENTRY John Cochrane (cont.)CENTERING TIME-AT THERMAL ENTRYOften several circlesDilutes average rate of climbMakes stopping for short climbs less efficientLonger down low and on windy daysEffect larger for strong thermalsSupports trying to pick easily centered thermals
21 Implications for Flying Tactics Recognize that thermals are variableSteadily reduce MacCready as altitude lowerLeave weak thermals to search as get higherAverage MacCready much lower than best seenAlways adjust MacCready to expected future—save altitude now!!!
22 DJ Practical Observations In a modern glass shipFly knots if nervousFly 80 knots if feels OKFly knots if great dayMaCready on 2 and leave it aloneNo zoomies - gentle pull-ups and pushovers to feel the airConcentrate instead on following the max energy pathOther observations???
28 Cruising techniques Cruising with cumulus clouds Classic Streets Speed to fly– MacCready still appliesAltitude-- higher better but need to seeDeviation angles up to 30 degrees, occ. moreBridging to next streetOften best speed will cause falling away from clouds“End of street” planningGet high
29 Cruising techniques “Make your owns” Even a random pattern of dots can be connectedOptimize the time spent “in the shade”Fully utilize the clouds you have
30 Departing the CloudWhen the lift drops off, not necessarily at cloudbase!Want to maximize average climbplan ahead – while you’re topping outspeed choices – maximize the weak liftuse the rest of the cloudlook for bridges to next energy path stepIdeally should have idea where next stop will be
31 When to stop in general Long cruise legs reduce centering loss No point in stopping high – centering time lossSet a height band floor—usually ~ top % of thermal–Below 50%, lift begins to disconnect from cloudsTry to end streets highUnderstand the thermal strength profile for the day- changes with height
32 Big Blue Holes Assess– why blue?? Get high and try to stay high Lake/sea shadow?Airmass changeWave influenceHigh wind streetingGet high and try to stay highGo slow until you’ve had time for assessment –may be good but dry– or not!!!Look for gliders- good thermal markers
33 Blue thermal cruising Read the ground Streeting prominent on blue days Wind direction key!!!Wind arrow on Ilec or GNII, etcStreets almost always on the windFeel for the lines of lift and do this continuouslyDeviate onto the lines of lift (energy paths)
34 Blue thermal cruising Go slower?– greater range when weak and blue Practice centering lines of lift on blue daysFeel for asymmetric lift, and make small turns into itTry to sustain reduced sink – can augment achieved L/D substantially, extend range, lead to a thermal
35 Weak blue day strategyGreater uncertainty warrants more conservative MacCreadyFind some company 3-5 gliders not 20Spread out when cruising with other gliders—don’t hide behindLift asymmetries and lift lines –lead to thermalRead the ground
36 When to slow up (changing gears) Cochrane’s theory– progressiveWhen going from cu to blueApproaching overdeveloped areaCirrus overcast aheadKnown or visible wet area ahead—lake, known shower history, standing water,Multiple low gliders aheadLots of whining on the radio“No see-um’s” ahead
37 Low saves Go slow for max range Look for birds, other gliders, dust devilsridges, rock piles, fire, smoke, edge of lake or woodsTake anything and work its edges, especially up-wind-- be patientQuit at a safe altitude– know your limits
38 Water ballast Adjustable wing-loading Slows climb directly, increased circle speed and diameter (farther away from core)Improves glide performance-greater range, ave. speedRule of thumb-keep water if ave. lift 350 ft./min or moreEspecially helpful on long streets, ridges
39 Water ballast use (cont.) Don’t dump too soonMay need to dump a portionLow savesThermals generally small in diameterDon’t dump in gaggle thermals
40 Water ballast (cont.) Check your system Practice before you go to a contestLoading’s a hassleFlies differentlyAdds an interesting element of complexity
41 What we really do Conservative MacCready dictates ave. Speed Plan ahead, WAY AHEADNot a lot of zooming—gentle speed changesSlower with lower highly variableMajor emphasis on best track (thus improved L/D)Extreme emphasis on finding best thermalsLeave mediocre thermals as soon as safe
42 What we do (cont.) Major deviations are the norm Do what it takes to avoid out-landingsRemember the sky usually is not fallingHave fun, don’t obsess about falling behindEverybody has a bad day sometimePractice, practice, practiceFly for speed every time you flyGet better!!!
43 Recommended reading Cross-Country Soaring: Helmut Reichmann Introduction To Cross-Country Soaring: Kai GertsonThe Price You Pay For MacCready Speeds: Wil Schuemann
44 Just A Little Faster Please: john Cochrane http://faculty. chicagogsb
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