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I also learned that a flying wing can have flaps, and very effective ones at that!ended up in the rafters of the garage forfive years! The end of 2007 I had somefree time on my hands and needed aMontana winter project. So I got the foamcores down from the rafters, emailedHerk and started to think about what Ineeded to do to complete this project.Originally I wanted to launch her viaelectric assist and Herk suggested thatI reduce the amount of twist or washoutfrom 8 degrees to 4.5 due to the higherspeed of the model.Well, after five years and just like theweather, I changed my mind about howto launch the model and wanted to usea hi-start and to have a thermal durationmodel, thus I should have used theoriginal amount of twist. This begged thequestion, “How do you determine theproper amount of twist”?This is when I was led to the late Dr.Panknin, who devised a complex butfairly simple formula with the use of acalculator to determine the requiredtwist. I have since taken his work andmade a companion spreadsheet to“Sailplane Calc” called “Flying WingCalc” that will easily calculate the twist.The spreadsheet is available at THE DESIGNHerk wanted a nice flying thermal HLGflying wing and he was successful. Hechose the SD7037 airfoil for the centersection of the wing as this airfoil wasproven to have good characteristics. TheSD8020 was chosen for the outer portionof the wing as it’s a fully symmetricalairfoil and its sole purpose is to act asthe tail of the wing.A flying wing has a tail just like yourtypical tailed model; it’s just that thetail has a very short moment, i.e. thedistance from the wings quarter chordlocation to the tails quarter chordlocation. Remember from your basicaerodynamics class that the horizontaltail is used to counteract the negativepitching moment of the main wing byapplying a down force, thus pitching theleading edge of the wing up.The same thing needs to beaccomplished with a flying wing. In aswept wing this is done by twisting the68 R/C Soaring Digest
Tinamou SpecificationsSpan 95"Chord, rootAirfoil, root17”, not including bat tailSD7037Chord, tip 9.5"Airfoil, tipSweep angleWing AreaTwist (washout)CG locationWeightWing loadingEffective Wing loadingSD802025 degrees at 0.25 chord26.8 degrees at LE1235 in²4.5 degrees13.2" aft root LE,8% static margin77 ounces8.98 oz/ft²11.67 oz/ft²Note: Effective wing loading is 30%greater, as part of the wing is acting asa tail.outer portion of the wings trailing edge up in relation to theleading edge, thus this applies a down balancing force tothe lifting section of the wing.This is different than with a reflexed airfoil that raises thetrailing edge of the airfoil across the entire span, creating avery low negative pitching moment. Very little, if any, twist isrequired if a reflexed airfoil is used.Some may ask why not use a reflexed airfoil over the entirespan. Well, what I’ve learned during this process is that areflexed airfoil will suffer in its thermalling or lifting ability. Ibelieve that reflexed airfoils are suited more to slope soaring,electrics, unswept plank type wings or where higher speedis desired. I was looking for a thermal duration model.Herk then chose a planform, sweepback angle, taper ratioand aspect ratio for his wing. With all of this informationhe was able place this information into Dr. Panknin’sformulas and determine the required twist angle that wasrequired to be built into the wing. It’s important to note thatDr. Panknin’s formulas require a linear twist. The first 10" ofmy wing are pure SD7037 with no transition to the SD8020as I wanted a good lifting section in the center of the wing.One of the many things I enjoy about aviation is that I amalways learning. During this endeavor I learned about airfoilpitching moments, airfoil zero lift angles, the middle effect,the difference between reflexed and non-reflexed airfoils,and how to determine wing twist to longitudinally balance aflying wing. I also learned that a flying wing can have flaps,and very effective ones at that!See the table on the left for Tinamou’s specifications.October 2008 69
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SoaringDigestRadi C ntr lledOctober
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R/C Soaring DigestManaging Editors,
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the towmen and the strength of theh
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October 2008 7
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Tents are a poor description of the
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of the juniors from Seattle so I di
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adrenaline is up in preparation. In
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The WorldChampionshipsThe Team Even
Page 17 and 18: US Junior WC F3J Team: Dave Kalamen
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Page 21 and 22: 2October 2008 214
Page 23 and 24: spin and managed to fly the plane b
Page 25 and 26: Above and clockwise: Junior Team to
Page 27 and 28: Clockwise from above:The Supra wing
Page 29 and 30: Joe Wurts, Manager for Team New Zea
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Page 33 and 34: Above and right: Cody Remington pre
Page 35 and 36: Above: One of the many collisions t
Page 37 and 38: The F3J WorldChampionship Fly-offsT
Page 39 and 40: Ben Clerx’ plane box and travelin
Page 41 and 42: Above: Ordering at McD’s is easy
Page 43 and 44: first became aware of Pitcherons/I
Page 45 and 46: We agreed that Dan would launch for
Page 47 and 48: out light and stiff and looked up t
Page 49 and 50: Uncle Sydney’s gossip columnMiles
Page 51 and 52: quite as grand for this club compet
Page 57 and 58: Rol Klingberg built and flew hang g
Page 59 and 60: The KW 100 awaits another flight. H
Page 63 and 64: Flaps down!October 2008 63
Page 65 and 66: The FerengiRules of SoaringBy Peter
Page 67: Tinamous are strictly neotropical b
Page 71 and 72: The finished tip panel ready for sh
Page 73 and 74: One of the two tow hook blocks inst
Page 75 and 76: in the hatch, thus holding the hatc
Page 77 and 78: in handling, but I’ve since remov
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