Oct - Rcsoaring.com

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