R/C Soaring Digest - Jul 2002

Page 1July 2002

July, 2002Vol. 19, No. 7

U.S.A. $3.50

R/C Soaring DigestPage 2

ABOUT RCSD

R/C Soaring Digest (RCSD) is a reader-written monthly publication for the R/C

sailplane enthusiast and has been publishedsince January, 1984. It is dedicated to sharingtechnical and educational information. Allmaterial contributed must be exclusive andoriginal and not infringe upon the copyrightsof others. It is the policy of RCSD to provideaccurate information. Please let us know ofany error that significantly affects themeaning of a story. Because we encouragenew ideas, the content of all articles, modeldesigns, press & news releases, etc., are theopinion of the author and may notnecessarily reflect those of RCSD. Weencourage anyone who wishes to obtainadditional information to contact the author.RCSD was founded by Jim Gray, lecturerand technical consultant.

RCSD should not be considered to endorseany advertised products or messagespertaining hereto. An advertising rate card isavailable for businesses, and clubs.

Feature ColumnistsBill & Bunny Kuhlman (B2),

Lee Murray, Tom Nagel, Mark Nankivil,Dave Register, Steve Savoie, Jerry Slates,

Greg Smith, Gordy Stahl

ArtworkGene Zika is the graphic artist

who designs the unique ZIKA clip art.

RCSD StaffJerry Slates - Editor/Technical EditorJudy Slates - Managing Editor, SubscriptionsLee Murray - RCSD Index/Database

(available on-line)Bill & Bunny Kuhlman - RCSD Web Masters

PayPal Coordinators

Copyright © 2002 R/C Soaring Digest.All rights reserved.

R/C Soaring Digest556 Funston Drive

Santa Rosa, CA 95407phone: (707) 578-7871

e-mail: [email protected]://www.b2streamlines.com/RCSD.html

OTHER GOOD STUFF

19 Classified Ads - New Products 3 Schedule of Special Events

Monthly Feature Photography & Web Version of the Printed Article (where appropriate)Highlights & Mailing Status of the Current IssueAbout RCSD..................................................................................... Subscription Information...................................................Advertising Rate Card (Adobe Acrobat PDF format).............................................RCSD Feature Columnists, Reporters, and Editors....................... (E-mail/web addresses, plus general information about their areas of interest)"Getting Started in RC Soaring" ........ Getting started guide - Adobe Acrobat PDF formatLinks to Organizations, Special Interest Groups & ClubsOn-Line Articles - Great articles originally written for the printed version of RCSD......................................... "Trimming Your Sailplane for Optimum Performance" by Brian Agnew.................................................................................................. "Flys Faster" by Dr. Michael Selig.............................. "The Square-Cube Law and Scaling for RC Sailplanes" by Dr. Michael Selig.................................. "Modifying & Building the MB Raven (Parts 1-4)" by Bill & Bunny KuhlmanBookshelf Listings - A listing of recently published books of interest to aeromodelers.Complete RCSD Index, 1984-2001

RCSD ON THE WEBhttp://www.b2streamlines.com/RCSD.html

TABLE OF CONTENTS

3 "Soaring Site" ....................................................................................... Judy SlatesEditorial ................................................................................................................. Cartoon Humor

4 "Tech Topics" .................................................................................... Dave RegisterTechnical analysis & Design .......................................... Omen and Omega-E Electric Sailplanes

8 "Have Sailpalne Will Travel!" ................................................................ Tom NagelTravel Sagas .......................................................... Converting a Chrysalis HLG into a Park Flyer.............................................................................................................................The Chrysl-Stick

10 NATS Coverage..................................................................................... Lee Murray.......................................................................................Comments on the 2002 LSF/AMA NATS

13 F3B News .............................................................................................. Glenn Dean...................................................................................................................... A View from Base B:............................................................................................................... The US F3B Team Trials

16 Technical analysis & Design .......................................................... Gregory Ciurpita.......................................................................................................................... Bending-Moments

6 Aerospace Composite Products9 B2 Streamlines6 Cavazos Sailplane Design18 Hobby Club6 R/C Soaring Digest

Special Interest Groups19 Eastern Soaring League (ESL)19 International Scale Soaring Assoc.19 League of Silent Flight19 Sailplane Homebuilders Association19 T.W.I.T.T.19 Vintage Sailplane Association

Advertiser Index

Page 3July 2002

TheSoaring

Site

Happy Flying!Judy Slates

SCHEDULE OF SPECIALEVENTS

October 18-20, 2002Deep South Soaring Championships Houston, TXhttp://home.houston.rr.com/kovacs/hawks/deepsouth.htm

February 1-2, 2003Southwest Classic Phoenix, AZ

Please send in yourscheduled 2003 events

as they become available!

Beautiful in full color, allcover photographs are

available for downloading fromthe RCSD main web page.

Cajon 2002

Dan Sampson’s Sukhoi Su-25Frogfoot tank-killer. Built

from Carl Maas molded fiber-glass fuselage, balsa sheeted foamwings.

Photography by Dave Garwood,New York.

ZIKA

GONE SOARIN’

ZIKA

POW !POW !18

I SEE YOU’VE DECIDED TO TRY

ÒELECTRIC FLIGHT!Ó

Cartoon Humor

Hope all of you enjoy the 'toonsincluded in this issue of RCSD.

Our thanks to the talented Gene Zikaand Phil Bauer!

I'm still having quite a few computerproblems, but neither rain, sleet, snow,or tornados have stopped us fromenjoying this wonderful hobby and,with this issue, it catches us up anothermonth!

Thanks for your patience and under-standing! Enjoy!

And, don't forget that cover photogra-phy is available in full color fordownloading from our web pages.


TECH TOPICS

Dave RegisterBartlesville, Oklahoma

[email protected]

Omen and Omega-EElectric Sailplanes

Over the past year there hasn’t beenmuch time for soaring at the

Register household. When you don’thave a lot of time to spare, HLG/DLGis a great way to get some exercise andstick time without a lot of parapherna-lia. But after you’ve pranged your lastDLG, or you’d like a few long flightsafter work, what’s a soaring pilot todo? I’d highly recommend the newclass of smaller electric sailplanes thatrun on geared Speed 400 motors. Ifyou stick with a 500mAh, 7 or 8 cellpack, the cost is very affordable.

The beauty of these systems is thatthey are compact enough to fly safelyin a decent athletic or soccer field(PLEASE have your AMA insurancejust in case), they’re nimble enough tojog around the occasional tree whenlanding and they’re light enough tonot be a serious threat if somethinggoes awry. In addition, the onboardlaunch equipment and soaring abilityof the more recent designs can giveyou 20 minutes or more of flight time.Since I rarely have more than about an

hour to spare, one or two battery packswill fill the bill nicely.

Which leads us to a review of theOmen and Omega-E designs from Sal’sshop (Northeast Sailplane Products).The way this all started was helping ayoung pilot (Andrew Geibel) puttogether the Omen and then realizingthat this type of ship was a heck of alot of fun to fly!

The Omen uses a geared Speed 400with a 11 x 8 Graupner folding propand a 7 or 8 cell Sanyo pack. A Sun1000 unit provides the BEC/Throttlefunction. The Omen planform ispolyhedral with ailerons and a V-tail.The planetary gearbox on the Speed400 makes for a sleek front end and theoverall performance was impressive.

After getting Andrew up and flying, Ireally wanted to give this a try but Ialso wanted flaperons for camberchanging ability to help with the lowend of the speed envelope. A quicklook through Sal’s website found thatthe Omega-E matched all my require-ments.

Construction of both the Omen andOmega-E is very similar so I’ll high-light the most recent experience(Omega-E) with notes where there aredifferences.

The fuselage is unpainted fiberglasswith a gelcoated canopy. The trim andfit of the canopy was excellent and thefuselage finish was virtually free of pinholes and surface irregularities. A lightrub down with solvent would prob-ably be sufficient prep for any addi-tional painting.

The push rod jackets are preinstalledand metal pushrods of more thansufficient length are supplied. A beefyplywood servo try is supplied with theaccessories. The wing mounting plateis already installed, drilled and tapped.The Omen used metric nylon bolts, theOmega-E used English (8-32 panhead).I re-drilled and tapped the mountingplate for English 10-32 panhead.

The wings are pre-built and coveredand a suitable length extension cableout to the servo wells is provided. Allconnectors, linkage and hardware aresupplied. The V-tail is glass over foam(built up geodesic balsa in the case ofthe Omen) and uses the upper surfaceglass for the hinge (Omega-E only).This hinge is too brittle and won’tstand up very well, so a strip of clearhinge tape was applied.

The V-tail is sufficiently light that CGbalance is not a problem. For theOmega-E, I had to add weight to thetail to balance it out properly. On the

Page 5July 2002

Omega-E, the rear of the fuselage has amolded in 100 degree slot. The tailsurfaces are beveled so that they gluetogether at that angle with no extrafixtures needed. For the Omen, tubesare pre-drilled across the fuselage toaccept the tail surface mounting rods.Alignment and decalage of the V-tailin both ships is excellent.

The power system (several options arerecommended) is a Speed 400 with aplanetary (in-line) 4.4:1 gear box. Propis a Graupner 11 x 8 folding unit with aspinner. The speed control/BEC is aSun 1000 and provides a JR styleconnector for power and throttle to Ch3 of your receiver. Battery pack is a 7or 8 cell 500 mAh Sanyo with a Deanspower connector.

With all the prebuilt components,these ships should go together veryquickly and they did. The only hiccupwas setting up a template for the 4-hole pattern to mount the motor on theOmega-E. What worked well was tomeasure the mounting diameter andthen set up a template in a CADprogram and print it to size. Then tackthe paper template on the flat at thefront of the fuselage, drill the shafthole and the bolt pattern and you’redone.

Once the motor is mounted, solder onthe speed control connectors (blue andgreen using the European convention)and then solder a capacitor across thepower leads (supplied with the kit). I’dsuggest using some insulation over thecapacitor leads so you don’t shortsomething out by accident. I mountedthe speed control circuit to the bottomof the fuselage with double-sided foamtape. It sits directly under the servos(fuselage depth is pretty good).

On the Omega-E, FMA S-60 servoswere used for the fuselage to save noseweight. After a couple of adventures, Ithink I’d go a little beefier. Say S-90s orHS85s or CS21s. The S60s have plentyof torque but the gears strip easily ifyou tangle up the tail surface. For theOmen, Andrew used standard servoswhich fit in-line behind the battery.This was a bit of a chore to get them inthere so I’d recommend something inthe HS80 or 85 category for easierinstallation.

Aileron or Flaperon servos were S90sor CS21s. The wing wells are plenty

wide and deep enough for the Omenbut they are marginal in depth in theOmega-E. Servo mounting used mystandard practice of wrapping withmasking tape and then using Goopadhesive to glue the servo in place. (Ifyou need to remove the servo, unwrapthe masking tape and lift the servoout.) Then cover the outer surface witha stiff prismatic tape and it’s lockeddown nice and tight.

Connection to the V-tail in both shipsused a Z-bend at the tail surface and astandard clevis at the servo.

Radio set-up

Andrew used his Hitec 5 channel inthe Omen. This allowed the use ofchannels 1 and 5 for ailerons and 2 and4 for the V-tail. Channel 3 was thethrottle control to the BEC.

For the Omega-E, my trusty Futaba7UGFS was used. The complicationhere is that channel 7 is aileron while 5is flap. Since I was using a 5 channelRx (Hitec 535), a little programmingwas in order. In this case, the simplesolution is to use Glid2F with 100%aileron to flap coupling. This has thebenefit of putting camber control in itsnormal position. After some flightexperience, a flap trim value of ~ 20%works well. (Note - since this firstexperience I’ve upgraded to a Futaba9CHF and used the channel 5 option.)

Off to the field

The Omen was finished first so let’sstart here. The CG was set whererecommended. Throws were adjustedto the suggested values. The motorcontrol took a bit to set up on the Hitecnamely because it’s different than onthe Futaba and we didn’t have themanual at the field that day. But wedumb-thumbed our way around untilwe found it and got the reversesettings right.

In a fit of confidence, I decided to tossit and let Andrew see what he coulddo (he had become quite adept withhis Razor). The first toss was supposedto be just a glide test. However, thesetup was so right on the money that Itold him to give it some throttle after ithad cruised out a few dozen yards.And off it went just like that!

After the euphoria of this success wore

off, we started looking more criticallyat the settings. You can get at least 4decent climb-outs with the 7 cell pack.The thrust is adequate but not over-powering enough to haul it into thesky. If the climb angle is too steep, theplane will stall or mush. So you needto use a little down stick under powerto keep the speed up. Flying the climblike this appears to be more efficient onpower and altitude than just bruteforcing it into the clouds.

Dive test showed that the CG couldmove back a bit, but for Andrew it wasfine pretty much at the factory setting.Aileron differential also helps. Thisplane will NOT axial roll so just get thedifferential and rudder coupling whereyou want for coordinated flat turns.Barrel rolls are also a bit dicey unlessyou’ve got lots of altitude. Thermalturns are smooth and tight withoutdropping a tip. The wing loadingcomes in at ~ 11 oz/sq. ft. so you needto allow the plane some decent flyingspeed or you’ll mush it. But it banksand cranks just fine when you core agood thermal.

15 - 20 minute flights are pretty typicalfor a climb and glide flying style withthe Omen. You can zip around somemore under power with a subsequentdrop in flight time. Your choice.

The experience with the Omega-E wassimilar to the Omen. Factory settings,etc., and it climbed out nicely on thefirst flight. About two clicks of up trimwere all that were needed. It becameapparent that the CG was too farforward for me but even at that thefirst flight was 25 minutes.

Next flight looked at the flaperonsetup a little more carefully. Althoughturns were very crisp, there was atendency for the nose to drop into theturn. Loops tracked very well but rollsweren’t very axial at all, again with thenose leading into the roll too hard.After about 22 minutes, it was time tocome in.

Next step was to move the CG backabout 0.5. The rudder coupling waseliminated and flaperon differentialdecreased (about 3:2). Next flightshowed much better glide and turns.Rolls were nearly axial from a modestdive. At these settings the camberchanging capability began to reallypay off. With more sensitive thermal


recognition from the rearward CG,cranking in camber at the first sign oflift really helped this ship take advan-tage of light, small thermals. Flights of35 minutes or more are not hard toachieve!

As with the Omen, powered flight isnot intended to haul this ship vertical.With the 7UGFS (or 9CHF) I’ve beenable to use the Start preset for verynice climb capability. In this case, atouch of down is added and about 10%camber. This gives a little extra lift tothe wing but with enough downelevator compensation to keep it fromporpoising. At least 4 very nice climbouts are typical for the field where Ifly.

Both the Omen and Omega-E haveproven to be really fine designs thatwork well. Each is a bit different inperformance but both provide theirpilots a lot of enjoyment. Each has alsohad reconstruction opportunities.Andrew got a tree shot from a loosebattery connector and I augured ininverted while trying to hot-dogwithout enough mustard. Both shipshave proven to be remarkably robust

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n

Page 7July 2002


HAVE SAILPLANE, WILL TRAVEL!

By Tom H. Nagel904 Neil Ave.

Columbus, OH [email protected]

Converting a ChrysalisHLG into a Park Flyer –

The Chrysl-Stick

Don Stackhouse and Joe Hahn arebuddies of mine. They have been

making world class sailplanes sincebefore I ever stripped my first servo. Afew years ago they introduced theChrysalis HLG, intended to be anentry level, all-wood, easy to build,good performing HLG. That wasbefore discus launch had ever beenheard of, and back when I had ashoulder that could marginally launcha HLG.

Neither the Chrysalis HLG nor myshoulder are even marginally competi-tive anymore. The Chrysalis is still onthe market and easy to build. Thisarticle explains how you can use leftover Pico Stick parts to convert aChrysalis to a ROG Park Flyer, inabout twenty minutes.

This project started when one of myson’s buddies stuffed our GWS PicoStick in a thoroughly convincingmanner, fracturing the woodenfuselage stick, cracking the wings andleaving me with a GWS motor, prop,flight pack and speed control, and ahandful of styrofoam parts. I decidedto find out if the little Pico Stick motorwould fly a 60" HLG.

I consulted with my friend BillHoelcher who had been flying someelectrics. He recommended usingabout 5 degrees of down thrust and acouple of degrees of left thrust on themotor mount. Then I consulted the DJAerotech plans for the Chrysalis HLGto find out where the center of gravitywas supposed to be. That was theextent of my design work.

Step A:

Cut a piece of thick balsa sheet (1/4" ifyou have any) into a long thin triangle,with the skinny angle 5 degrees; and aright angle for the second corner(which mathematically leaves the thirdangle at 85 degrees). The short side ofthe triangle needs to be about _ inchlong, which is the distance from yourworkbench surface to the center of theChrysalis nose, when the fuse is on thebench. This is the guide for drillingholes in the nose block of the Chysalisfor the motor mounting stick.

Step B:

Tape the triangle to the workbench,with the skinny angle at the edge ofthe bench, and tape the Chrysalisfuselage to the workbench right behindit. Using a long drill bit, drill a holethrough the nose block of the Chrysa-lis, just a smidge off center. Move thefuse over one smidge, and drill a

second hole parallel to the first. Thediameter of the drill bit isn’t toocritical, as long as it is less than 3/16".Use a file and create a rectangular holethrough the nose block, sized to accepta left over piece of Pico Stick fuselagestick. (Even after a thorough stuffing, Ihad a few pieces three or four incheslong. The Pico Stick fuse stick is metricsized, but approx. 5/16 by 3/16". Youcan cut and sand one to fit the hole inthe Pico Stick motor if you have to.)The Pico Stick motor sticks on thismotor stick. I put it on so the motorwas below the stick, and I used a clip-on aluminum heat sink, which hadbeen on the Pico Stick.

Step C:

Drill a 3/16" hole (or thereabouts)through the plywood bottom of thefuse, right behind the nose block. Use asmall file to open it up into an oval.The Pico Stick motor wire and plug gothrough this hole into the cockpit area,and connect to the speed control.

Step D:

Find a piece of threaded rod about 1 1/2" long; drill a hole the diameter of therod through the plywood floor of thefuselage, just about a half inch in frontof the first former (at the back end ofthe cockpit area, on the center line). Iused a small piece of formica sample

Page 9July 2002

(free samples from Home Depot leftover from building RDS pockets) andglued a piece inside and outside thefuse, and drilled through that. Thishole and threaded rod is the landinggear mount. Use a nut or two on theinside; slide the Pico Stick landing gearwire over the rod outside the fuse, andclamp it down with a small piece ofthin ply, or formica or a big washer. Iset mine up so the gear trailed behindthe threaded rod, but it works OKeither way.

Step E:

Stick a piece of velcro on the bottom ofthe fuselage behind the first former(under the wing). Initially I used anicad 150mah seven cell pack, and got8 minute flights in dead air. Whateverpack you use, velcro it down under thewing so that the CG is correct. (I flymine with the CG almost three inchesfrom the leading edge of the wing.)The battery connector can stick out onthe front side of the former so you can

re-charge without having to take thewing off.

That’s it. Done. You got a Chrysl-Stick.And while it is not a Speed 400, thelittle Pico Stick motor has plenty ofpower to fly the Chrysalis airframe.

Using the stock Pico Stick motor, GWS

receiver, landing gear and speedcontrol, you should be able to ROGand fly long, high semi-thermal flights.If you use a GWS 0806 prop, you willbe able to stop the motor and have theprop spin down to a stop while flying,so you can thermal; and you will haveplenty of airspeed at full throttle to doloops. ROG takes a smooth surface anda 30 to 50 foot run, but is totallyreliable. I eventually bought a 650 mahNIMH pack, a sort of carrot shapedthing with 4 cells and 3 cells attached

end to end – it fit nicely between theChrysl-Stick pushrods, under thewing, and I have had a couple of 20 +minute flights so far, without runningout of power.

The conversion is about 99% revers-ible. Unbolt the landing gear, plug uptwo holes, and you are back to HLG.(As if.) I fly the Chrysl-Stick a wholelot more as a park flyer than I ever didas a HLG.

n

ZIKA

GONE SOARIN’


Jon Stone’sAddiction fuse

and MH-32 wing(custom).

Ben Roberto & Stingray 7.

James Beck &Ernest

Schlumberg’sEminar 100’s.

Lenny Keer’s Escape,convertable sailplane.

Lenny Keer’sEscape w/

sailplane nose.

Don Woelfel’sEdge. “GravitySucks” on left

wing...

After an 8-year absence, I returnedto the NATS. One thing that was

the same was the oppressive heat andhumidity. Some of the things that Ifound different, I think readers willalso find interesting. I’m not going tocover what you can download fromthe AMA site because much of that isexcellent in coverage. The NATSresults can be obtained at: http://www.modelaircraft.org/Comp/2002Natsfront.htm\.

I arrived Wednesday afternoon and,after unpacking, I headed out to seeHand Launch Golf at Cardinal HillsGolf Club. I shot some nice video onthe 9th hole capturing the entire flightsfrom tee to green. Seeing the discuslaunches was new to me. I wouldnever have imagined that launches likethat were possible by athletes and oldtimers alike. With some coaching onthe green, modelers landed theirmodels very close to the cup in a singleflight. Following the golf task therewas the task of knocking a plasticbottle off an inverted paper cupwithout knocking over the cup. Severalpeople were able to do it and one evenhand caught the model after beingsuccessful at the task.

Thursday was the start of the Unlim-ited event. The number of moldedairplanes being entered surprised me:Edges, Icons, Emeralds plus somestrange looking sailplanes, Mantises.These were long poles with a verysmall pod on the front for the electron-ics and the wing on tall pylons. A highpercentage of the radio transmitterswere computerized. I took a snapshotsurvey of what brands of radios werebeing used. This was during the

contest so some were out and in use.The photograph of the transmittersbeing used in RES showed a muchdifferent distribution of older andlower cost radios.

Radios used forUnlimited Class:Airtronics 32JR 24Futaba 10Multiplex 5Hitec 2

Some of the more artistic models areshown in the photographs. Jon Stoneof Madison, Alabama designed hisown. Jon said he used a number ofprograms including PC-Soar (myfavorite design program - ljm).

RES and Nostalgia were flown onSaturday with alternating rounds.These events were more relaxing forthe competitors. Several were heard tosay, “The pressure is off.” One reasonmay have been that the landing task

By Lee MurrayAppleton, [email protected]

Comments on the 2002 LSF/AMA NATS

Page 11July 2002

Mark’s Esprit, Nostalgia.

RES radio sample.

Gerry & Jim Marcicki w/Edge.was modified to increase the distancebetween the landing circle and thesafety line. I believe it was doubledfrom 8 to 16. While I didn’t violate thesafety line, several people did includ-ing one LSF official who will remainnameless. Only one person in 2M andUNL (4 days of flying) was able to geta 100 point landing. The 100 pointlanding was earned by landing on a 4"disc. That would be about 1 perfect for2000 tries. Some competitors felt likethe landing circle met the goal ofeliminating fly offs. Others felt likelandings were too difficult and had away of ruining an otherwise goodperformance, especially if you slid pastthe safety line. There was a suggestionthat a plastic snow fence be providednext year to protect fliers and timersbut end the problem of sliding past thesafety line.

Many RES and Nostalgia models wereoverstressed on the launch equipment.It was possible to launch models safelybut I believe many people just were

not expecting the power that thesewinches were capable of producing.Utilizing the capability of the winchesin zoom launching was very spectacu-lar and I suspect was an important partin winning the UNL event if you had aheavy ship or needed more time tofind some lift. People who couldmaximize the launch were 1/3 higher

than those who had more conservativelaunching methods perhaps dictatedby the durability of their models.

The LSF was balloting for 4 options forfuture NATS event schedules. Someevents attract only a few competitorswhile others fill up. There is somepressure to give more time to RES andF3J. It is not clear how much supportthe new class will receive in registrants


and volunteers to run it. President JackStrother and the LSF crew did a greatjob of running the contest, communi-cating the goals of the LSF and plan-ning for future NATS.

During the lunch break, there was ademonstration of a rocket-poweredmodel glider. The model, a Stingrayseries 7, was designed to compete inthe S8E FAI event, which includes adeclared duration and a precisionlanding. The Stingray series was firstdesigned by Kevin McKiou of Chicago.Versions 5, 6 and 7 had the additionaldesign support of George Riebesehland Ben Roberto. Ben is pictured in thephoto holding the Stingray. Phil Barnswas the pilot.

Three demonstration flights wereperformed with three sizes of motors.FAI motor limit for Impulse is 40Newton-sec.; a combination of forceproduced and burn time. The rulebooksays you’re allowed +10% more powerthan the 40 N-sec, hence the 44 N-secmotor. The English equivalent of 40 N-sec would be 9.0 lbsec.

Phil demonstrated that the modelcould be pointed straight down toreturn it to earth without a problem. Inthe boost phase, the model wasactually flying faster. Good engineer-ing and a strong lightweight model areobvious essentials. Even with the allthese requirements, the model wouldslow down for hand catches.

Ben describes the model’s constructionas follows:

The Stingray series of rocketgliders was designed by KevinMcKiou ([email protected],[email protected]) up here inChicago. George Riebesehl andmyself teamed up with Kevin todevelop Stingrays 5, 6, with 7being my notes for the nextversion. The Stingrays up to #6featured parabolic dihedralscheme like the Hobie Hawk. Thiswas done by bagging the wingwhile on a curved bed. The lay-up,from top to bottom: top core bed/wing lay-up, pink foam core/Mylars/ vacuum bag/bottom corebed/curved bed.

Stingray 6 was a team effort of 12models for the 98 World Champi-onship. Kevin did the aero work

including coming up with thewing and tail airfoil and cut thecores. George shaped the coreleading edges and cut the fiber-glass and carbon pieces. And I didthe rest of the molding and bag-ging work including the fuselageplug.

Stingray 7 featured a more conven-tional dihedral scheme with a flatcenter section to accommodate afull-span center section landingflap for the new precision durationrules. Stingray 7 also had a largerinverted v-tail tail. The originalformula for the v-tail was based onprojected area. The newer one tookinto account the v-tail angle as perMark Drelawww.charlesriverrc.org).

Phil built several Stingray 7 usingmy notes and plans. He usedKevlar for the wing skins insteadof 0.75 oz. glass and Japanesetissue as we used on #6. The samecarbon spar was used. Phil alsoused my original fuselage plug/mold combination for the pods.For the pods, I used 2 layers of 1.5oz. Kevlar. Phil chose to use thehybrid Kevlar/carbon fabric. Thetail boom is an Avia G-ForceStandard Ultra-Light.

Ben says that the 2002 World Champi-onship event is now a precisionduration event with a 6 minute taskonto a landing strip scored man-on-man. The landing strip is 50 meterslong to accommodate up to 5 pilots.Landing within 0.5 meters on eitherside gives you 100 points, 1 meter oneither side gives you 50 points any-thing outside of that but within anoverall landing boundary gives you 25points. (A big contrast to the 4" 100point circle of this year’s NATS - ljm.)Ben believes that the working time is12 minutes to get your transmitter andmake a flight. The Spacemodelingorganizers will probably adopt theprocedures used for F3B or F3J dura-tion, but still limit it to 3 mandatoryrounds, and 2 flyoff rounds. At theWorld Championships Phil will use

Aerotech E6 expendable/40N-secignited by an electrical system. Detailsof available systems can be seen athttp://www.aerotech-rocketry.com/.

A full size ASW-27 glider was as-sembled in the parking lot and wasadmired by all. The detail on the fullsize glider was very impressive. Amodeler or two was commandeered tohelp set up the glider.

Saturday evening, the night before theelectric competition, I watched some ofthe competitors limbering up withpark fliers. Even these flights wereimpressive for the length of time in theair and the variety of aerobaticsperformed. In another field the freeflight modelers were making testflights of their limited motor runmodels, towline gliders, and handlaunch gliders.

On Sunday morning I went out to thefield to scavenge information from theClass A and 1/2 -A electric competi-tors. Lenny Keer showed me hismolded Escape sailplane. Somemodelers feel that this may be the bestfiberglass fit and finish of all themolded ships. The model was quiteversatile. That one could change powerplants by exchanging nosepieces. Evena glider nosepiece was an option.Lenny was partial to Hacker motorsbecause he felt they gave the bestperformance for the dollar. I sawmodels where the pilots would notspend all their motor run time at thestart of a flight for visibility reasons. Iwas also impressed with James Beckand Ernest Schlumbergs “Eminar” 100for limited motor runs. They each hada one-piece 100" wing that theyvacuum bagged. They were generousin giving me information about lowcost - good performing systems. BeforeI left I saw an official Class A electricflight that was very impressive. I’mthinking that I have some work to doin matching my components to get thatkind of performance.

n

Motor Used Energy Estimated Altitude Reached

Aerotech D7 re-load 20 Newton-sec 500-600 FeetAerotech E6 re-load 40 1200Aerotech E6 expendable 44 1300-1400 ~limit of visibility

Page 13July 2002

by Glenn [email protected]

Decatur, Georgia

(Originally appearing on RCSE, reprintedwith Glenn’s kind permission.)

The US F3B Team Selection Trialscontinued today with 15 of the

hottest soaring pilots in the US com-peting for the three coveted slots on“TEAM USA”. Five rounds are com-plete; rounds six and seven are ex-pected to finish Monday and we willname the team for next year’s worldchampionships.

The day’s flying started before 8 AMwith challenging conditions. Pilotsflew two rounds of duration first,under heavily overcast skies andtemperatures in the low-to-mid 60s.Lift was sparse, and many pilotsscratched their flights out betweentreetop height and launch level. Windsall day were about 8 knots out of theeast, with little slope lift to be found onthe tree lines. Still, the skills of our bestpilots showed — they still maxed theirtimes, even with heavy F3B planes inconditions that would have youraverage thermal pilot on the ground inunder 3 minutes.

Two rounds of distance followedunder the same conditions — ex-tremely difficult with lift spotty oncourse, but the occasional thermaldrifted through to make things excit-ing. About noon the skies cleared tobright blue with cumulus clouds, andconditions became strongly cycling,and a third round of distance (the fifthfor the weekend) was flown afterlunch. Gavin Botha put up the high lapcount for the weekend with 25 laps.

Two rounds of speed followed.Slightly variable winds and cyclingconditions on course caused manypilots to elect to relaunch to try andmaximize their conditions. Times weregenerally in the 18-22 second range,with the fast time of the contest thusfar set by Darrell Zaballos on Saturdaywith 16.9 seconds. Despite the close-intree lines providing a psychologicalhazard for the pilots, everyone finishedspeed without incident.

We flew two more rounds of durationafter speed, starting round six with thelast duration task. Lift cycles had

evened out some, and several flightgroups had very light and spotty lift,resulting in some very impressive andtactical flying. Round 6 speed anddistance will be flown in the morning,followed by round 7 and then the finalresults and identification of TeamUSA.

Lessons Learned

I’ve had the distinct pleasure asserving as an official timer and punch-ing laps down at Base B in the hotGeorgia sun, and have seen a lot of theaction. So what did an average thermalflier learn from watching F3B? Well,like one of our club members BuddyRoos said, it’s like getting free sail-plane lessons all day long. It’s notevery day you can watch the best ofthe best compete up close. Here’s someof the general things I observed:

1. It’s all about TEAM.

I was surprised to see how much agreat team makes or breaks a pilot. Thewhole group has to be functioningflawlessly to put a good round to-gether, and the winch guys are reallyhumping, especially when they areswitching drums, changing lines, andrunning back and forth for multiplereflights. West coast team Botha/Zaballos/Jennings, and East coastteam Lachowski/Kiesling/Lawlessseemed to have particularly well-practiced techniques and procedures.It may be individuals who get selectedfor Team USA, but these guys areknocking themselves out to make eachothers’ flights the best they can be.

2. Ya gotta be smooth.

Smooth, consistent flying is the nameof the game. Inconsistent fliers will putup one hot flight only to bomb thenext, and low-level pilot-inducedoscillation cost more seconds on speedruns than any bad launch (AKA tooLOW too FAST). One of the mostmemorable speed runs, for me, wasflown by Gordon Jennings. It wasn’tthe fastest, but the plane looked like itwas on rails from the start of thelaunch to the end of the speed run —smooth, steady, consistent.

3. Know your limits — and use‘em.

These guys know exactly what theirairplane is capable of, and fly right upto the outer limits. They aren’t extremeplanes — they’re actually quite pre-dictable. The pilot has to know exactlyhow much to expect from a launch, orhow far he can search under whatconditions, in case he has to bail acrossa field of sink to find the one patch ofrising air on the field.

4. Check small things.

Attention to detail is where it’s at. TheF3B guys here obsess over the exact fitand finish of their airplanes, and havethem trimmed to perfection. They haveintricate systems to keep track of whatwinches and batteries have launchedhow many times, with what line, sothey know when to change out a linethat’s about to go. All those littlethings add up to a big increase inperformance.

5. Know when t’ hold ‘em; knowwhen t’ fold ‘em.

The best teams/fliers have figured outtheir go/no go criteria before theylaunch, and talk about it during flight.“Past relight point, fly what you got,”you hear. If conditions don’t meet theircriteria, they come down NOW,decisively. Indecision on relaunchloses precious seconds that you maynot have. I saw teams relaunch threetimes during a speed round — threelaunches in under four minutes! — toget what they wanted. That wholeteam had to move like clockwork tomake that happen.

6. Good enough is all you need.

I noticed this watching some of theless-experienced F3B hands. Somepilots will bail from lift that is weak —but will get them their 10 minutes — togo after something that looks stronger,only to have it fall apart on them.Other relighted after an OK — but notballistic — launch, only to get a launchthat was worse than the first, or getsink on course.

7. CONFIDENCE, BABY!

The fliers who grabbed victory fromthe jaws of defeat in marginal lift on along flight stayed confident the wholetime, and their crews were alwayspositive. I won’t say they made theirown lift — but the mental edge had tohelp. I know I’ve been more often

A View from Base B: The US F3B Team Trials


defeated by sinking feelings thansinking air, myself.

What were the hot planes?

The ones flown by the hot pilots, ofcourse! Heck, from Base B I can tellyou there were 14 V-tails and onecruciform tail — what more do youneed?

OK, there were a few planes thatcaught my eye among the Ellipses,Cobras, and Tragis.

- The “SP1”, an original designflown by Botha and Zaballos.

From down at the turnaround, itlooked like these planes were consis-tently outlaunching the rest of thefield. Of course, I’m sure the pilotshelped, as did the unique super-special construction winches with thedouble-bearing extra-long drums.These planes seemed to range well,hang well, go fast, and go slow. Theplanform looks unique, probablyspecially tailored. Gavin said the planewas designed specifically to launchwell, and that it definitely does.

- The Icon.

Of course it stood out; it was the onlyconventional-tailed airplane on thefield. It’s a BIG plane, and flew like itwas on rails. Its pilot (Jennings, Ithink) put up some very consistentflying.

- The Caracho (sp?).

Lachowski & Kiesling flew this design,and possibly some others. Has a prettyunique look — pylon mounted wing,unique planform, wide-chord ailerons& flaps. These seemed very fast &maneuverable — quite impressive inspeed & distance.

- Brian Agnew’s plane — a Warp(I think).

Clean lines, nice handling — a lot ofpotential there. Someone told meAgnew hadn’t flown much F3B — youcould have fooled me!

Day 3 ...

Flying began just after 8 am today afterthe mist lifted, revealing clear, cloud-less skies and virtually dead calmconditions. We flew round 6 Speed in

almost completely dead air, with thehigh times in the 19 second range.Light thermals began to cycle onto thecourse by 0930 as we started round 7speed, and course times improved to afast time of just over 17 seconds, notquite beating the course record set onSaturday. We lost one plane — whichfortunately was not severely damaged— to a radio failure during one speedrun, when the radio shut off just as thedive onto course began. The planepulled out, circled, and landed all onits own with some minor cracks and adelam. Oleg Golovidov finished thecontest flying his backup Stratos.

Following speed we flew round 6 and7 distance. Lift conditions continued toimprove with cumulus formationsover the field, leading to strong cyclesof lift and sink. Several flight groupswere able to turn in fast courses withstrong thermals on course -- high lapcount set at around 24 laps. Severalother flight groups were treated toheavy sink, and rushed to relaunchinto better air.

Following the two distance rounds anda lunch break, we flew round 7duration, which saw two flight groupslaunch into booming thermals, and theother two flight groups launch intomarginal lift that resulted in scratchingto make times. One pilot fought for airtime at treetop height way downwind,and clipped a tree, luckily recoveringjust above the ground and recoveringthe plane back to the field.

Despite a few thought of putting inround eight, we ended the contestafter round seven, at about 1300, andhad the field cleared by 1530.

The combination of good conditions,thorough preparation, herculean workby the CD and his assistants, greatclub support, and outstanding flyingand cooperation by the attendingpilots and crews combined to makethis a great event.

I’m glad I came and helped out. I had alot of fun, and learned a lot watching alot of great fliers.

Who made the team?

Congratulations to: Gavin Botha, MikeLachowski, Darrell Zaballos, and TomKeisling (alt) for their great flying.

These pilots will be representing the

USA at the World’s in Germany nextyear. GO TEAM USA!

Here are the final scores, afterthrowout. The closeness of the scoreswill give you the idea of the kind offlying we saw over seven rounds:

1. Gavin Botha 176522. Mike Lachowski 175663. Darrell Zaballos 175454. Tom Keisling 174375. Gordon Jennings 169486. Ben Lawless 168987. Rich Burnoski 167608. Phil Renaud 166329. Brian Agnew 1640010. Dennis Phelan 1635511. Oleg Golovidov 1611412. Jeff Stiefel 1533213. Mike Leal 1506414. Don Sciegel 1464215. Bill Wingstedt 14244

Flying Technique Observations

What follows are the specific observa-tions about flying techniques that Ifound from watching pilots at the F3Bfinals. For those familiar with F3B, thisis probably old hat, but I find that evenreinforcing things I know can beuseful.

1. Launching

If there is one absolutely critical must-have skill for F3B, it seems to belaunching. Heck, that’s probably trueof any sailplane flying — barring goodair, you only have the energy you putinto the plane at launch, so you’dbetter make the most of it.

I saw a lot of different launchingtechniques and styles at the finals. Thehighest, most consistent launchersseemed to have the following incommon:

- They know their equipment. Theplane is trimmed for a hard pull andquick rotation on launch — a carefullytuned mix of CG, hook position, flapsettings, and elevator preset. Theyknow what their winches are capableof, and adjust both line and drums tosuit conditions. Teams were runningmono as narrow as 1.05 mm and 1.11mm, changing out entire spools asneeded if the line got nicked or over-stressed. They had those proceduresdown, and had their winch-area set upjust so, to maximize their launcheffectiveness — marking winches and

Page 15July 2002

batteries based on number of launches,keeping equipment clear in case of awinch backlash, and that sort of thing.

- The whole team drilled the sametechnique over and over, and thelaunch was a team event. Pilot checksairplane; winch master confirmscorrect winch is selected and winch ison. Timer indicates ready. Spotterchecks the air, and confirms the pilot’sflight plan. Pilot tells launcher when togo (on the horn, or wait). Pilot:“Ready.” Launcher: “Set,” braces, andgets arm back into throwing position.Pilot: “Go.” — Launcher (orwinchmaster) stands on the pedal,building tension until the winch startsto stall. Then the launcher leans backand throws the plane for all he’sworth. The well set up planes areflying the second they leave thelauncher’s hands, already rotated formaximum climb. Less proficient crewshad a jerk or waggle as the planestalled on launch, losing some poten-tial as the plane got back to flyingspeed.

- The launch is consistent. I saw anumber of pilots that circle-towed,doing big S-turns on the line to buildline tension before climbing andzooming. Except in the cases wherethey used this for a slight adjustmentto get into the wind, though, I neversaw this pay off. The highest launchesall seemed to come from pilots whoclimbed straight and smooth into thewind with minimal heading correctionbefore the zoom. Of course, they alsogot the best setup, tension, and throw,too.

- Zooms. That monofilament zoom isamazing. The consistent teams wouldhave a signal when the line was at maxtension, and would tell the pilot whento zoom. This wasn’t really that far upthe climb — maybe 60-70 degrees upfrom the turnaround, no where near asfar as we tend to do on braided linewith thermal winches. They didn’tdive too deep to start the zoom, andimmediately rotated smoothly andpinged off into a climb. I saw all sortsof climbs, from shallow to vertical, andeven past vertical. I guess in theoryvertical is probably best, but the bestzooms seemed to come from about a70-degree climb. Too many of the fliersdoing vertical climbs pulled pastvertical, climbing inverted, or pushed/rolled out too late, losing altitude atthe top because they had no airspeed.

- The pilots immediately started toexecute the task at hand. They had aplan beforehand — if they were goingto abort based on the launch, theyaborted right then, otherwise theywent into their plan. You could tell theindecisive pilots — they would kind offloat around a bit off of launch, losingaltitude without accomplishinganything.

2. Landing

- Unlike TD, F3B is not a landingcontest — or else it is, and everyone isjust too good at it. It’s a big spot, 1meter per 5 points, and I saw very fewlandings under 95 points. Crewshelped by laying the tape out into thewind, and counting down time untilthe plane was right close to the end ofthe tape.

- Also unlike a TD contest — whereyou see every kind of landing tech-nique imaginable, from the wallow-stall-splat to the speed-dork-spike —everyone used a very similar tech-nique. They used their flaps early inthe approach, to get down to oneapproach speed — fast for control, butnot too fast. Then (unlike me) theycame in with a clean airplane on asteady glide path (about two spans upat 15 seconds and 75m out), applyingflaps right at the end to stop the planeover the spot, either settling in or witha slight nose push to stop the plane onthe spot. I didn’t see too many AMA“spikes”.

3. Duration

- Not too much different here, exceptthat F3B guys fly heavy airplanes for10 minute tasks every round, and we’drather have our 3-5-7 landing contestwith 57 oz. airplanes. The pilots had agood plan at launch, adjusted for theconditions, and weren’t afraid to bailto cross the field or run way down-wind if necessary. They turnedperfectly smooth, whether it was aslow, wide, 10 degree bank circle, or atight, spinning 45 degree bank circle.And they weren’t afraid to circle attreetop level a quarter mile downwindif that’s where the lift was. Know youairplane is the name of the game here.

- A good team helps here — the bestwere giving constant, positive feed-back about where the lift was, how toadjust the thermal circle, when to stickwith it, and when to bail. I found

myself thinking: “Where are the guyslike this when I need a timer?”

4. Distance

- I thought this was the best event.(Partly because I got to fly a lot of itleading up to the event when we weretraining the officials. It’s a LOT harderthan it looks!) It’s not as pure-adrena-line ballistic as speed; it’s much moretactical, combining good air readingskills with good turning and racingskills. Except for the number of peopleneeded to run it, it would be a greatevent all by itself.

- These guys know a lot about ballast,and have tried all different settings atall different conditions. They’reconstantly adjusting to suit conditions,and comparing notes with each otherabout how much lead they’re adding.

- It’s tactical flying. Sometimes its bestto cover the top guy in the group,flying in his air, so at worst he beatsyou by a lap or so. Other times, yourread on the air is best — we had acouple of rounds where there was oneguy on one side of the course, and theother three on the other. Sometimesthe lone wolf buried everyone; some-times he got buried; once it evenlooked like the lone wolf was in worseair but tricked the other three intocoming down and relaunching into hisair. Definitely a thinking man’s game.

- Smooth flying pays. The high lapcounts not only usually had good air,but every turn looked the same. Knowwhen to speed up, and when to slowdown. Denis Phelan was explaininghow to get consistent — by timingevery lap until you get each two-lapupwind/downwind combo to thesame rhythm. It looked like the teamhelped out here, too — the turnindication system worked on bothlight and audio signal, but since whenseveral planes turned at once the audiocould get slightly delayed, the guysturning on the light wasted less timethan those turning on audio only.

- Have your relight drill down. ‘Nuffsaid.

5. Speed

- You’ve got to be ready. The start ofyour working time is no time to findout that something on your plane

...continued on page 18


Bending-Moments

Greg CiurpitaSomerset, New Jersey

http://ciurpita.tripod.com/rc

Ithink most wings are over-built. Thisdoesn’t mean that they can’t be

broken, just that they are built toostrong where they don’t need to be,and not strong enough where theycould be. Rather than guess, a modelerneeds to know how strong the wingneeds to be, and where that strength isneeded. The simple answer is they canbe weak at the tip, and strong at theroot. The more complete answer ishow much stronger.

It should be obvious that a littleupward force near the wingtip createsa much larger force near the root if thefuselage is held still. This force iscalled a bending moment. It is actuallytrying to pull the bottom spar cap,putting it in tension, and is compressingthe upper spar cap. Both of these forcesare greatest near the top and bottom,and decrease to zero near the middleof the spar.

The bending moment at any point iscalculated by multiplying a force bythe distance between that point andthe force. Figure-1 shows these forceson a wing where the tip is on the left,and the root on the right. The 3 ounceforce at the tip is shown with theupward arrow. The moment arm is40". The bending-moment is shownwith the clockwise arc on the right,and is 120 oz-in.

The same force produces a bending-moment all along the wing. Figure-2shows the bending-moment due to thesame 3 oz. force at a point closer to thetip. In this case, it produces a bending-moment of only 90 oz-in, 30" from thetip. Any force on the wing contributesto the bending-moment at all locationsfrom the point of the force toward theroot. Similarly, the bending moment atany point on the wing is due to all theforces outward of that location on thewing.

While a wing is generating lift, there isnot a single force near the tip, but anupward force distributed all along thewing. The bending-moment at the rootis due to the entire force on thehalfspan. If the lift is (unrealistically)assumed to be evenly distributed

(constant) across a rectangular wing,then the entire force of each halfspancan be approximated by a single forcemidway between the root and tip. Fora plane with a 200" wingspan andweighing 4 pounds, each halfspan is100" and supports 2 pounds. Thisresults in a bending moment of 100pound-inches (lb-in) at the root. Seefigure-3.

Another way to come to the sameresult is to split each half-span, witheach quarter-span supporting onequarter the weight of the plane, 1 lb.The inner quarter supports 1 lb. at itsmidpoint which is 25" from the root,producing a moment of 25 lb-in.Likewise, the outer quarter supports 1

lb. at its midpoint which is 75" fromthe root, producing a moment of 75 lb-in. The combined moment for thehalfspan is still 100 lb-in. (See Figure-4.)

This example emphasizes how muchmore the outer portions of the wingcontribute to the total bending momentat the root. It also seems to suggesthow the moment may be calculated formultiple tapered wings by multiplyingthe force generated by each section bythe distance from the root to wherethat force is effectively centered. Butthese examples assumed a uniform liftdistribution.

To precisely determine the bending

Page 17July 2002

moment, requires an accurate liftdistribution for the planform beingconsidered. Even a rectangular plan-form has a more elliptical than uniformlift distribution. This means that thewing loading across the span varieswith span location for all but trulyelliptical planforms. Accurate bendingmoment calculations not only require

how little variation there actually isbetween the too extremes, a rectangu-lar wing with uniform lift distribution,and a triangular planform.

Figure-5 shows the bending momentsfrom root to tip for several representa-tive wing planforms. While we’ve onlydiscussed the total bending moment atthe root, it’s important to know thetotal bending moment at each locationon the wing to properly design thespar at that location.

There are two plots for a rectangularwing. The 1st and uppermost plot, is aplot assuming a constant lift distribu-tion across the entire span, from root totip. This is the same as the exampleillustrated by figure-3. The 2nd is arectangular wing using a more realisticlift distribution. The 3rd is an ellipticalwing with an ideal elliptical liftdistribution. The 4th, and bottom-mostplot is for a triangular wing with asomewhat realistic lift distribution.The rectangular and triangular wingsrepresent the two extremes. Any otherwing planform should be somewherebetween the two.

All of the plots are for wings of thesame area generating the same amountof lift, but because of their shape, thecenter of lift may be closer to the root.The rectangular wing has the center ofits lift force furthest from the root atmidspan, and therefore has the highestbending-moment. The triangularplanform has the center of its liftclosest to the root, and therefore thesmallest bending moment.

The most important thing to see inthese plots is that the bending momentdecreases very quickly. For the rectan-gular planform, it is has decreased25%, roughly 1/8 of the distance fromthe root to the tip. It is nearly half atapproximately 1/3 the distance to thetip. And is approximately a 1/4 at 1/2the distance to the root. From a differ-ent perspective, a wing needs to betwice as strong at the root as it is at 1/3the distance from root to tip. The outerhalf need only be half as strong as it isat 1/3 the halfspan. And these ratiosare basically the same for all plan-forms.

The bending moment at the root is fourtimes greater than at midspan. Makingthe wing twice as strong at the rootthan at midspan is not enough. It will

an accurate lift distribution, but moremethodical accounting by dividing thewing into many small sections. This ismore easily accomplished today thanwhen Martin Simons discussedbending moments in a short series ofarticles entitled Elementary Stress, inthe Nov-Dec 1996 issues of RC SoaringDigest. But you might be surprised


doesn’t work. (Finding out when youenter the course is even worse!)

- The consistent runs started at thelaunch. The speed run really started atthe push -over from the zoom, with asteady dive toward base A followed bya quick vertical dive and smooth pullinto the course. The guys who“floated” off the line generally seemedto lose more altitude and start withless speed than those who wereaggressive at entry. The initial diveonto the course looked really hard tojudge — a perfect dive meant comingon course at maximum velocity. Divetoo short, and you lose velocity pullingout; dive too long, and you wastealtitude without gaining any morespeed. The fastest had a fairly constantaltitude usage through the first threelaps of the course, with of courseextremely smooth consistent turns.

- A few pilots did split-S’s mid course,instead of the tight pylon turns most ofthe others did. I never figured out ifthis was better — it looked like theynot only bled off speed turning, butsacrificed altitude in the process. Idon’t recall a run where it looked likethis tactic paid off.

- It’s not for the faint of heart. Anyaltitude left at the end of the run iswasted, and we saw a lot of potentiallyreally fast runs blown in the last lapbecause there was altitude that wasn’tused; or there was altitude wastedearly on in the run; or because theelevator was over-controlled and theplane bled off a good bunch of air-speed.

My hat’s off to the guys that fly F3B.I’m really impressed with their pilot-ing skills, and the amount of thingsthey have to master to fly one round —let alone fly well and be competitive.Even if you never want to be any morethan a run-of-the-mill TD pilot, if youget a chance to go sit and guard aturnaround for a day at an F3B contestyou should jump at it. It will give youa lot to think about.

Congrats again to the winners; I’mglad I got to help out. It was definitelyworth my time! Good luck at theWorld’s! (And to the rest of the world... Watch out for those Americans ...They can launch!)

n

...continued from page 15still break at the root, before it breaksat midspan. While adding weight inthe wings doesn’t make the problemany worse, it does make the planeheavier, and adding weight to theouter parts of the wings makes it moredifficult to roll the plane, and lesssensitive to thermals. While bendingmoments are an important consider-ation in designing wing spars, shearstrength is another.

Shear affects wings in the verticaldirection, and is simply the strengthneeded to support the load on thewings. The bending-moment causeshorizontal forces putting the lowerspar in tension and the upper spar incompression. Shear force affects theentire spar from top to bottom, unlikethe bending-moment which hasmaximum affect on the top and bottomof the spar and zero affect in themiddle. Webbing can significantlyincrease the shear strength of the spar.Like the bending-moment, shearstrength is maximum at the root,where the entire lift generated by thewing supports the plane, and is zero atthe tip.

For the example in figure-4, with arectangular wing having a constant liftdistribution, the shear strength at theroot is 2 lb. At midspan, it is half, or 1lb. At 25" from the tip, it is 1/2 lb. It issimply the total lift from the tip to thatpoint on the span. With an accurate liftdistribution, the shear strength acrossthe span can be accurately determinedusing the same methods used tocalculate bending-moment. Figure-6shows the shear strengths for the wingplanforms shown in figure-5.

To simplify construction, it seemscommon to use the same spar design

(dimensions and material) for largeportions of the wing. This note showsthat the bending moment decreasesrapidly. If the wing fails, it will mostlikely fail for a given spar design at thepoint closest to the root. If a wing doesfail away from the root, most likely itwill fail where the spar design changes(e.g. no webbing). Since the bendingmoment reduces quickly, even somemoderate strengthening near the rootcan help tremendously. But it’s alsoimportant to recognize that materialand weight can be removed from thespar further from the root. While thisdoes weaken the spar where it doesn’tneed to be as strong, it makes the winglighter and more sensitive to lift.

It is very important to recognize thatthe numbers used in this note are forillustration only. A 200" sailplanesupporting only 4 lb. has both ahalfspan and bending moment of 100which is easy to discuss in terms ofpercentages. However, it’s not weightbut maximum load that must beconsidered, and this typically occursduring a winch launch. The breakingstrength of the winch line is oftenused, and values of 180 to 220 lb. arenot unusual.

Knowing the bending moment andshear strength, and how they varyacross the span, are important in wingspar design. Spar design is a lengthydiscussion and whole books have beenwritten on the subject (Strojnik, Alex,Low Power Laminar Aircraft Struc-tures, 1984). Spar design has alsobecome very sophisticated with the useof various composite materials andstructures. And of course, MarkDrela’s Allegro is an excellent example.Thanks Ollie for all your help.

n

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Page 19July 2002

T.W.I.T.T.(The Wing Is The Thing)T.W.I.T.T. is a non-profit organization whosemembership seeks to promote the researchand development of flying wings and othertailless aircraft by providing a forum for theexchange of ideas and experiences on aninternational basis. T.W.I.T.T. is affiliatedwith The Hunsaker Foundation which isdedicated to furthering education andresearch in a variety of disciplines. Fullinformation package including one back issueof newsletter is $2.50 US ($3.00 foreign).Subscription rates are $20.00 (US) or $30.00(Foreign) per year for 12 issues.

T.W.I.T.T., P.O. Box 20430El Cajon, CA 92021

The Eastern Soaring League (ESL) is a confederation of Soaring Clubs, spread across the Mid-Atlantic and New England areas, committed to high-quality R/C Soaring competition.AMA Sanctioned soaring competitions provide the basis for ESL contests. Further guidelines arecontinuously developed and applied in a drive to achieve the highest quality competitionspossible.Typical ESL competition weekends feature 7, or more, rounds per day with separate contests onSaturday and Sunday. Year-end champions are crowned in a two-class pilot skill structureproviding competition opportunities for a large spectrum of pilots. Additionally, the ESL offers aRookie Of The Year program for introduction of new flyers to the joys of R/C Soaring competition.Continuing with the 20+ year tradition of extremely enjoyable flying, the 1999 season will include14 weekend competitions in HLG, 2-M, F3J, F3B, and Unlimited soaring events. Come on out andtry the ESL, make some new friends and enjoy camaraderie that can only be found amongst R/CSoaring enthusiasts!

ESL Web Site: http://www.e-s-l.orgESL President (99-00): Tom Kiesling (814) 255-7418 or [email protected]

The League of Silent Flight (LSF) is an internationalfraternity of RC Soaring pilots who have earned theright to become members by achieving specificgoals in soaring flight. There are no dues. Once youqualify for membership you are in for life.The LSF program consists of five “AchievementLevels”. These levels contain specific soaring tasksto be completed prior to advancement to the nextlevel.Send for your aspirant form, today:

League of Silent Flightc/o AMA

P.O. Box 3028Muncie, IN 47302-1028 U.S.A.

http://www.silentflight.org

SailplaneHomebuilders

Association (SHA)

A Division of the SoaringSociety of America

The purpose of theSailplane HomebuildersAssociation is to stimulate interest in full-sizesailplane design and construction byhomebuilders. To establish classes,standards, categories, where applicable. Todesiminate information relating to constructiontechniques, materials, theory and relatedtopics. To give recognition for noteworthydesigns and accomplishments.SHA publishes the bi-monthly SailplaneBuilder newsletter. Membership cost: $15U.S. Student (3rd Class Mail), $21 U.S. RegularMembership (3rd Class Mail), $30 U.S. RegularMembership (1st Class Mail), $29 for All OtherCountries (Surface Mail).Sailplane Homebuilders Association

Dan Armstrong, Sec./Treas.21100 Angel Street

Tehachapi, CA 93561 U.S.A.

Classified Advertising PolicyClassified ads are free of charge to subscribersprovided the ad is personal in nature and does notrefer to a business enterprise. Classified ads thatrefer to a business enterprise are charged $5.00/month and are limited to a maximum of 40 words.RCSD has neither the facilities or the staff to inves-tigate advertising claims. However, please notifyRCSD if any misrepresentation occurs. Personalads are run for one month and are then deletedautomatically. If you have items that might be hardto sell, you may run the ad for 2-3 months.

For Sale - Business

PARACHUTES: $12.50 (includes S&H U.S.A.)Send check or money order to Dale King, 1111Highridge Drive, Wylie, TX 75098; (972) 475-8093.

Summary of Low-Speed Airfoil Data - Volume 3 is reallytwo volumes in one book. Michael Selig and his studentscouldn’t complete the book on series 3 before series 4was well along, so decided to combine the two series ina single volume of 444 pages. This issue contains muchthat is new and interesting. The wind tunnel has beenimproved significantly and pitching moment measure-ment was added to its capability. 37 airfoils were tested.Many had multiple tests with flaps or turbulation ofvarious configurations. All now have the tested pitchingmoment data included. Vol 3 is available for $35. Ship-ping in the USA add $6 for the postage and packagingcosts. The international postal surcharge is $8 for surfacemail to anywhere, air mail to Europe $20, Asia/Africa$25, and the Pacific Rim $27. Volumes 1 (1995) and 2(1996) are also available, as are computer disks contain-ing the tabulated data from each test series. For moreinformation contact: SoarTech, Herk Stokely, 1504N. Horseshoe Circle, Virginia Beach, VA 23451 U.S.A.,phone (757) 428-8064, e-mail <[email protected]>.

Reference Material

BBS/Internet

Internet soaring mailing listserve linking hundreds ofsoaring pilots worldwide. Send msg. containing theword "subscribe" to [email protected]. The"digestified" version that combines all msgs. each dayinto one msg. is recommended for dial-up users on theInternet, AOL, CIS, etc. Subscribe using [email protected]. Post msgs. [email protected]. For more info., contact MichaelLachowski at [email protected].

Books by Martin Simons: "World's VintageSailplanes, 1908-45", "Slingsby Sailplanes","German Air Attaché", "Sailplanes bySchweizer". Send inquiries to: Raul Blacksten,P.O. Box 307, Maywood, CA 90270,<[email protected]>. To view summary ofbook info.: http://home.earthlink.net/~raulb

There is a growing interest in scale soaring inthe U.S. We are dedicated to all aspects ofscale soaring. Scale soaring festivals andcompetitions all year. Source for informationon plans, kits, accessories and other peopleinterested in scale. For more information:

web site: www.soaringissa.org

InternationalScale SoaringAssociat ion


Documents

R/C Soaring Digest - Jul 2002