Page 1August 2004

August, 2004Vol. 21, No. 8

R/C Soaring DigestPage 2

Copyright © 2004 R/C Soaring Digest.Published by b2streamlines.com

All rights reserved.

CONTENTS

3 "Soaring Site" ..............................................................Bill and Bunny KuhlmanEditorial ........................................................................................................... Dear RCSD Readers

4 "Tech Topics" ......................................................................................................... Dave RegisterTechnical Analyis & Design .................................................................. V-Tails and Turbulators

8 "On The 'Wing..." ............................................................ Bill & Bunny KuhlmanFlying Wing Design & Analysis .................................................................................Diva, Part 5

12 F3B World Record .............................................................. FAI Announcement........................................................................................................... Distance to Goal and Return

13 Technical Analysis & Design ......................................................... Mark Drela........................................................... Basic Sizing Checks for Homebrew RC Thermal Gliders

16 "Gordy's Travels" .......................................................................... Gordy Stahl................................................................................................................ Anatomy of Task Soaring

18 Tips and Tricks ............................................................................ Bill Swingle......................................................................................................... Taking Care of Foamie Wings

20 Event Report ............................................................................ Mark Nankivil................................................................................................................................ JR Aerotow 2004

RCSD Staff & Feature Columnists

Judy Slates: Managing Editor, Article Submissions“The Soaring Site”

B2 Kuhlman: Publisher, Internet Support, Columnist“On the ‘Wing...”

Dave Register: Video Coordination, Technical Editor, Columnist“Tech Topics”

Lee Murray: Historian - Keeper of the Index, Columnist“The Natural Side of Thermal Soaring”

Jerry Slates: Technical Editor, Columnist“Jer’s Workbench”

Gordy Stahl: Advertising Coordinator, Roving Correspondent“Gordy’s Travels”

Tom Nagel: Travel Saga Correspondent“Have Sailplane Will Travel!”

Mark Nankivil: Columnist“Electric Connection”

Greg Smith: Columnist“The Sloper’s Resource”

Dave Garwood: Photographer, Writer

About RCSD

R/C Soaring Digest (RCSD) isa reader-written monthly

publication for the R/Csailplane enthusiast and hasbeen published since January,1984. It is dedicated to sharingtechnical and educationalinformation. All materialcontributed must be exclusiveand original and not infringeupon the copyrights of others.It is the policy of RCSD toprovide accurate information.Please let us know of any errorthat significantly affects themeaning of a story. Becausewe encourage new ideas, thecontent of all articles are theopinion of the author and maynot necessarily reflect those ofRCSD. We encourage anyonewho wishes to obtain addi-tional information to contactthe author.

August, 2004/Vol. 21 No. 9

Page 3August 2004

TheSoaring

Site

Dear RCSD Readers,

Shortly after the July issue went up on the web site, Judy askedBunny and me to serve as temporary editors for RC Soaring Digest.This is both an honor and a privilege, and we sincerely thank her forasking us to fill in for a while. Her confidence in our abilities isinspiring and we’re going to do our very best to meet the challengeswhich are sure to surface.

Judy has been working with us quite extensively over the past fewweeks in an effort to make the transitions as smooth as possible.Despite everyone’s best efforts, however, we’re sure to hit a fewsnags. Bunny and I very much appreciate constructive feedback, sodon’t be hesitant to let us know if you think of ways to improveRCSD or point out a glaring error in typography, layout orinformation.

RCSD is a “reader written” publication and as such we rely oncontributions which spontaneously arrive in our e-mail andconventional mail boxes. If you have a particular interest or projectwhich you believe other RCSD readers would like to know about,please contact us. Single photos, contest announcements, suggestionsand questions are also welcome. With this in mind, we’ve set up atemporary e-mail box specifically for RC Soaring Digest

RCSDigest@themacisp.net

http://www.b2streamlines.com/RCSD.html

correspondence. The address is <RCSDigest@themacisp.net>, and all contributions should be sentdirectly to that address until further notice. We do have quite a bit of free server space for e-mail, so don’tbe afraid to send large files — up to around 5 MB is OK. If you need to send something larger than 5 MB,please check with us first.

A couple of notes of interest:

• Mark Shryack is looking for an ASW 12 kit, fuselage, plans... well, pretty much anything. He has the3-views from Bob Banka, but is looking for something to really get him started. You can pass oninformation directly to Mark at <tmshryack@aol.com>.

• The CVRC Fall Soaring Festival will be held this year on October 2nd and 3rd. 2004 will mark the 31styear of this annual CVRC contest. There's a limit of 325 entries, and while this sounds like a lot, it mayalready be too late to get a spot. Entry forms are available on the CVRC web site <http://www.cvrcsoaring.com/fall_fest.htm>, and this year entry fees can be forwarded via PayPal.

As you can see from the facing Contents page, this issue of RC Soaring Digest has a wide variety ofmaterial to present, from two technical treatises to a photo essay, with lots of stuff in between. We neededto add four pages to the usual complement in order to get everything to fit!

The September issue of RCSD will be posted to the RCSD web site during the latter part of August. Ifyou’d like to receive e-mail notification when the issue is posted, simply join the RCSoaringDigest groupon Yahoo!

Alyssa and her newlycompleted Diva - painted,covered, and ready to fly! Divahas 1000 square inches of wingarea and a 123 inch span;overall weight is 56 ounces fora wing loading of 8oz./ft2.Despite numerous positivecomments on her good looks,Diva has proven to be a realhandful to control, particularlyin pitch, and flight testingcontinues as this issue ispublished. All the details arelaid out in this month's "On the'Wing..." column!

R/C Soaring DigestPage 4

TECH TOPICS

Dave RegisterBartlesville, OKregdave@aol.com

After a hiatus of several monthsto handle a retirement transition(what day of the week is it,anyway?), I’ve had a bit moretime to get out to the flying fieldlately. One thing is readilyapparent - it takes more than afew sessions to get your timingright. Oh, the basic flying skillsare still there (some mightquestion that!) but the littledetails of approach height, turncoordination, etc. are a bit rusty.Consequently, most of thesessions have been spent relearn-ing the details of launching,landing and trimming a sail-plane.

The equipment I’m using is asport winch and a new, hollowmolded wing (and stab) twometer sailplane. Added to themix is an Eagle Tree Systemsflight data recorder. The latterhas been a great tool for lookingat launch conditions, trim setup,polar evaluation and the generalhealth of the flight pack. We’lldiscuss the results of that analysisin another column.

While trying to trim out the newtwo meter, a number of interest-ing challenges were encounteredand some knowledge gained thatI hope is worth sharing. The firsttopic is V-tail differential; thesecond is a more in-depth look atturbulator strips.

V-TAIL

Although the technology forproducing hollow molded wingshas made fantastic progress, bothin quality and value, there’s verylittle you can do to modify one ofthese wings if it doesn’t flyexactly the way you’d like. Thelast two planes of this type that Ihave flown are, in my opinion,low in dihedral angle. In onecase, the included dihedral anglewas about 2.5 degrees; thecurrent plane has about 3.5degrees. Experience has told methat I prefer about 5 degrees foran aileron ship and about 10degrees for an RES.

A symptom of insufficientdihedral angle is low spiralstability – the tendency of thenose to fall into the turn once astable bank angle has beenestablished. With a low dihedralwing, you generally have to holda bit of opposite aileron and atitch of up elevator to maintainthe proper bank angle andvelocity. The upside for this extraeffort is very nice roll sensitivitywhen you’re looking for lift; adownside is trying to handle thissame roll sensitivity when you’reflying at the edge of your visualcapability.

Once you have the planetrimmed well, low dihedral ismanageable. However, the

challenge of setting up the properturn coordination for this shipmotivated some reading andexperimenting. An excellent on-line reference for help on thistopic comes from DJ Aerotech’sweb site and the “Ask Joe andDon” column. Joe Hahn and DonStackhouse have generouslyshared a great deal of experienceon their website. It’s one of myfavorite bookmarks wheneverI’m looking for background onmost flying subjects.http://www.djaerotech.com/index.html

The DJ website discussed severalquestions related to V-taildifferential and wing dihedral –all of which fit the types ofbehavior I had been experiencing.

In particular, a good V-tail setupshould not have any significantpitch response when the V’s areused in rudder mode.

When a V-tail is deflected forrudder action, the V-stabs movein opposite directions – i.e. oneside goes up while the other goesdown. See above photo (Picture1). In this way, the pitch directionlift components are nearlycanceled while the yaw directionforces are reinforced. If the pitchcancellation is incomplete, someup or down response will beobserved.

A way to check this out (as perDJ) is to set the plane in a straightand level cruise and then give a

Picture 1

Page 5August 2004

full deflection of the rudder stickand hold that deflection momen-tarily. The initial response shouldbe in the yaw axis only. From adecent launch height, you shouldbe able to execute this maneuverseveral times for both left andright rudder deflection.

In my case, the plane exhibited asignificant pitch up for eitheryaw direction. What this meantwas that the V-tail ‘rudder’deflection was not well balancedin pitch .

This pitch response explainedone of the trim issues. Whenentering a thermal turn the usualcontrol input is to roll the planewith ailerons and then pull itthrough with elevator. For thisship, the low dihedral required asignificant amount of ailerondifferential and rudder couplingto counter adverse yaw. Therudder coupling inadvertentlyprovided an up elevator response– which was fine for initiating theturn.

After the turn was established,opposite aileron was required tohold the turn (due to the lowspiral stability from the lowdihedral angle). This tended tonegate the elevator input andallowed the nose to fall.

Three flights later, all was well.For this ship I actually needed80% up vs. 100% down to takeout the pitch response. Once thatwas done, the tracking in the turnwas much more consistent andthe pitch sensitivity, especiallywhile turning, was very manage-able.

How to setup V-tail differential?Each radio supplier will probablylist different coupling methodson their web sites. I fly a Futaba9C (H) and found the easiest waywas with end point adjustment.

V-tails are normally run onchannels 2 and 4 with a V-tailprogrammable mixer. By limitingthe ‘up’ or ‘down’ travel on yourendpoint menu, you should beable to get whatever differentialyou need. The total throw for theV tail can then be compensated inthe mixing menu once thedifferential is established (nor-mally V-tails require morerudder throw than elevator).

I’m sure other folks have moresophisticated ways of setting up

V-tail differential. Up until thisexperience, I had not useddifferential but had assumed thatif the throws were mechanicallybalanced (same amount of upand down deflection) everythingwas copasetic.

Mechanically yes; aerodynami-cally no. If you haven’t checkedyour V-tail setup lately, try a fewtrim flights to see if it’s workingproperly - and check out Joe andDon’s website – good advice andgood products, too.

TURBULATORS

This topic is more speculative interms of the final outcome but Ithink is worth reviewing. Withthe advent of molded wings andstabilizers, I believe we have thepotential for a problem due to thelow Reynolds number of ourcontrol surfaces and the highquality of the airfoils and sur-faces. Sounds a little counterintuitive so let’s review the shortversion of this issue.

Professor Michael Selig, in aseries of experiments at theUniversity of Illinois (“Summaryof Low-Speed Airfoil Data”,Volumes 1-3), has provided a richsource of information for R/Csailplane enthusiasts. ProfessorMark Drela of MIT, has provideda terrific complementary tool inthe X-Foil program. Both sourceshave highlighted a problem withcertain symmetric airfoils whichare often used for horizontal andvertical stabilizers.

Volume 2 of the UIUC researchsummary defines the topic of‘dead-band’ for thin, symmetricairfoils. ‘Dead band’ is a region offlow in which the change in Cl(and Cd) with angle of attack isnonlinear and may exhibithysteresis. That is, the specific Clobserved at a given angle ofattack depends on whether thatangle of attack is being ap-proached from a lower or ahigher angle. In particular, ProfSelig’s group observed that theNACA 0009 exhibited poor liftlinearity at low angles of attack,typically between -4 and +4degrees (Vol 1).

X-Foil can be run for the NACA0009 and, for low Reynoldsnumbers, clearly shows thepresence of a large separationbubble around + or – 3 degrees

angle of attack for Re of 60,000.The onset of separation occursaround + or – 1 degree andcontinues to about + or – 3.5degrees. Separation is due to anunfavorable pressure distributionwhich does not allow the transi-tion bubble to reattach well overthese angles of attack. Conse-quently, both the lift and dragcoefficients are somewhat erraticin this region.

Now consider the results of apolar analysis of a typical 2 metersailplane – a topic we’ve dis-cussed in this column at somelength. We find that the normalangle of attack for the wing willbe in the range of 3 to 6 degrees.That range spans the MaximumL/D to Minimum Sink range ofthe polar.

The normal decalage for thehorizontal stabilizer is around -1degrees. When the downwashfrom the wing is considered wefind that the most desirable partof the polar curve places thehorizontal stabilizer smack in theworst part of the separationregime. This could be a problem.

Figure 1 shows the X-Foil Cl andCd response vs angle of attack forthe NACA 0009 airfoil at Re =60,000. For this example, thetransition criterion in X-Foil wasset to encourage laminar flowconditions (Ncrit = 12). The resultof the separation bubble in theregion below 4 degrees angle ofattack is apparent.

Also in Figure 1, the X-Foil resultfor Cl and Cd at Re = 60,000 isshown for Ncrit =1, whichencourages early transition of theflow. As can be seen, the transi-tion problem is essentiallyeliminated. A closer examinationof the pressure distributions forthe Ncrit =12 case shows theonset of the transition at around40% of the chord. This unfavor-able pressure distribution iseliminated for Ncrit = 1.

Figure 2 shows a screen captureof X-Foil output for this case.Note that the flow attachment, asseen in the pressure distribution,is much better for the turbulentcase (Ncrit=1). Note also that Clis increased by almost 2x whileCd is reduced significantly.

Although laminar flow is favor-able for lower drag, that result isonly obtained when the flow

R/C Soaring DigestPage 6

stays attached. For every airfoil,there will be a region of laminarflow near the leading edge.However, at the Reynoldsnumbers for normal R/C sail-planes (> 50,000), it is difficult tomaintain laminar attachmentacross the entire chord. Thus,management of the transition toturbulent flow and reattachmentof the ‘bubble’ is critical for goodairfoil performance. The oldersymmetric sections often used forstabilizers were not designed tooperate efficiently in the low Reregime.

Prof. Selig’s solution to thisproblem was to redesign thestabilizer airfoil to give bettercontrol of the low angle of attacktransition region. One such airfoilis the S8025 and it appears to bevery successful at handling thisproblem.

However, what if we suspect thestab has a separation problemand it’s a hollow core molded tailsurface? How would this affectthe flight characteristics? Whatwould one do to solve theproblem?

A potential flight response to the‘dead band’ problem might bethe tendency for the plane tohave poor pitch tracking, espe-cially at slower flight speeds.Slower speeds are achieved nearminimum sink and higher anglesof attack. Under these conditions,the Reynolds number is low andthe stabilizer angle of attack is inthe region we’ve highlighted.

At a slow enough speed, thehorizontal stab loses efficiency. Ifno stabilizer control input ismade, the nose of the plane willdrop, speed will increase and thestab airflow will reattach. Oncethe stabilizer establishes goodairflow, its effectiveness increasesand the nose rises again.

Unfortunately, this ‘scalloping’type of flight may be difficult todistinguish from a bad CG /decalage combination. It’s veryimportant to be sure both of thoseare correct before assumingthere’s a problem with thestabilizer – that’s why we wrotethose articles about the CG andIncidence meters a few monthsago!

Probably the most distinguishingcharacteristic I’ve found is thetendency for the plane to ‘hunt’

Figure 1

Figure 2

Figure 3

Page 7August 2004

in pitch, especially when tryingto fly at or near minimum sink. Inthis case, the plane does notactually stall but requires manysmall elevator corrections tomaintain level flight. Since this isa subtle observation, the cure - ifit works - will give a subtle (andprobably subjective) result.

How to ‘fix’ this problem? Sincewe want to encourage reattach-ment of the transition bubble, a‘trip’, or turbulator strip, seems tobe the best answer. Fortunately,Volume 3 of the UIUC study alsoprovides some excellent summa-ries on trips. I encourage you tostudy the details of Chapter 6 ofVolume 3 of Prof. Selig’s work. Inthis section, a detailed analysisand measurement program wasundertaken. For applicationpurposes, I’ll give a brief sum-mary here.

Both 2-D (linear) and 3-D (zigzag)trips of various dimensions andlocations were evaluated in theUIUC study. The width of thetrips did not seem to be critical.The thickness was important andis most efficacious at around0.005” to 0.015”. Position on thewing should depend on thelocation of the transition bubblebut appeared to be highlyeffective (for the airfoil studied)at anywhere from about 15% to50% of the chord.

No dramatic difference was seenbetween 2-D and 3-D trips.However, for all the cases stud-ied, a noticeable reduction indrag was experimentally ob-served when a trip was used. The

effect is more pronounced at lowRe and is less noticeable forairfoils that are designed for goodtransition control. The E374, forinstance, benefited significantlyfrom a trip while the SD7037 didnot.

For my purposes, a zigzag (3-D)trip of 3/16” nominal width and0.010” height was used. It wasplaced at the 25% position onboth the upper and lower surfaceof the horizontal stabilizer. Thisturbulator can be seen in Picture1.

Picture 2 shows a very simpleway to make this device. A pieceof wood is first covered withmasking tape. The width of theturbulator strips are marked onthe masking tape followed bytwo layers of clear wing tape.Most wing tapes are about 0.005”thick so two strips will give thedesired thickness.

Once this layout has been pre-pared, a rolling Olfa pinkingcutter is run along the marks. Besure that the flutes of each cutstart at the same location. Onceall the strips have been cut, theycan be lifted off the masking tapeand attached to the appropriatelocation on the wing. After layingdown the trips, the tape is rolleddown with a small paint roller(seen in the picture).

Off to the field for flying evalua-tions. Since the original observa-tion was somewhat subjective, I’llallow that the final result mayalso be subject to interpretation.However, it seemed apparent to

me that the pitch problem(‘hunting’) had been eliminated.Slower, more stable flight wasroutinely achieved without anyapparent loss of efficiency.

As partial verification of thisoutcome, the flight speed of thisplane was measured with theflight data recorder. Typicalvelocity vs. time samples fromflights before and after installingthe turbulator are shown inFigure 3. Note that the ‘before’trace (18-Jul) shows a characteris-tic oscillation of the velocity(‘hunting’). That effect is almostcompletely eliminated in the‘after’ data (21-Jul).

Admittedly, this result is subjectto some interpretation. However,it does appear that near mini-mum sink, our horizontal stabi-lizers are flying in an unfavorableoperating regime. It is myopinion that the irregularitiesinherent to built-up stabilizershave probably masked this issue.Spars, longerons, leading edgetape and Monokote seams can allbe effective triggers for flowtransition.

Although this topic is a some-what obscure area of study, itmay be an important point forderiving the best overall perfor-mance from the improvedcapabilities of molded, highquality R/C sailplanes. As wemove to more affordable moldedsailplanes, careful selection of thestabilizer airfoil should beconsidered so as to derive thebest benefit from this technology.

Picture 2: Making turbulator strips with an Olfa rotary pinking cutter

R/C Soaring DigestPage 8

DIVA, PART 5

Diva is complete and has beenflown somewhat

successfully! This column isdevoted to covering and paintingthe airframe and descriptions ofinitial test flights. Contrary toplan, however, it will not be thelast article in the series, as westill have some adjustments andmodifications to accomplish andwhich need to be related to thosewishing to build their ownrendition. Read on!

Color scheme

Despite spending substantialtime looking over the paintschemes in Hot Rod magazine,Alyssa did not find any whichshe thought appropriate forDiva. Skulls, flames, colorfulgeometric shapes and 3-Dshading were all cast aside infavor of a more simplecovering theme which wouldbe easy to apply over thesheeted areas of the wing andvertical stabilizer.

As we had two full rollsalready, we had agreed aheadof time to cover the entirebottom of the wing withmetallic charcoal, a CGUltracote Plus color. Ultracotetends to feel a bit thicker thanconventional Monokote, andin our experience remains“softer” and a more pliableafter shrinking. This makes itideal for a wing lower surfacewhere the covering must beresilient to puncturing forcesfrom grass, and small sticksand rocks.

At the hobby shop, Alyssabecame enthralled with theMonokote pearl colors. She

finally settled on pearl red andgreen with pearl white as themain color. Pearl purplebecame the trim color aftergoing through and discardinga couple of yellows.

The choice of covering colorspretty much dictated thefuselage be painted white, sowe looked for white dope,finally digging our waythrough two baskets filledwith cans and jars of variouscolors. We finally foundseveral one ounce glass bottlesof AeroGloss semigloss Swiftwhite. We collected six with alarge amount of diligence, andpurchased all of them.

Using several copies of theDiva 3-view publishedpreviously, a large number ofcolor designs were drawn outusing crayons and coloredpencils. Alyssa looked overthe more than dozenpossibilities and settled on theone most simple — thecolored portions would belong and narrow, and allplaced over sheeted areas. Redat the leading edge, greenbehind, with the purple trimused to separate the colors.

Painting

The entire fuselage and wingfillet combination had alreadyhad a number of coats ofAeroGloss clear applied.Sanding between each coatenabled the clear dope to fillthe weave of the fiberglassand provide a smooth surfacefor the color coats. We didn’tbother with any sort of primer.As all of the fiberglass weave

was filled, we startedbrushing on thin coats ofwhite directly over theexisting substrate of ’glass andclear dope. Four coats wereneeded to completely coverthe wood color which camethrough the clear layers. Acouple extra coats wereapplied to the lower front endof the fuselage, as that areatends to get a lot of abrasion.

Covering

We started by covering thebottom of the wing with theUltracote metallic charcoal.While we were very pleasedwith the red Ultracotecovering applied to our largecross-country Blackbird, thismetallic charcoal was muchmore difficult to work with,especially when it came timeto bond the covering to thebalsa. Ultracote requires thecovering and balsa both beheated, and a cool cloth thenapplied to press the coveringto the balsa while everythingcools. This must be doneslowly and carefully or thecovering will not stick to thebalsa. Rather, it tends to growbubbles across huge areasover a period of days. Afterseveral weeks, we still findourselves reapplying thecovering in some areas.

We also had problems withthe Monokote pearl colors.The pearl white was appliedfirst, and it went on veryeasily. This color is not asopaque as we had anticipated,and in certain lightingconditions the interior of thewing can be discerned. This isOK, but not what we hadanticipated. As well, the pearlred and pearl green wereextremely difficult to applywhen used over othercovering. These colors were adelight to apply over balsa(the entire structure had beendried out with a heat gunbefore covering commenced),but the number of smallbubbles formed overpreviously covered areas wasno less than astounding. Weresorted to using an extremely

Page 9August 2004

fine pin to puncture one sideof each bubble, and thencarefully manipulating thebubble with the covering ironto expel the trapped air. Thisworked well, but wasextremely time consuming.

Preliminary balancing

As the leading edge of thewing forms a straight line, themean aerodynamic chord canbe determined quite easily.The span without the fuselageis 120 inches and the totalwing area is 1000 squareinches. The MAC, therefore,has a chord of 8.33 inches, sothe MAC quarter chord pointis 2.08 inches behind the

leading edge. We marked theneutral point and 2.5% and 5%static margin points on thefillet stubs for future reference.It should be noted that thesepoints are roughly 3/16"apart, so balance is critical. Weinitially set the static margin at5%, with the CG 0.4 inchesahead of the neutral point.Since we’re using the BW 0502 09 section, we alsopredicted the CG wouldeventually be located back atthe 2.5% static margin point.

Test flying, Part 1

Hand launching a taillessaircraft of this size (123 inchwing span) is alwaysproblematic. The hope is that

the aircraft can be thrownwith enough force that flightspeed can be approximated,yet with force insufficient tocreate a severe nose upmoment which would cause astall and unrecoverable dive tothe ground. But with the staticmargin at 5% and a smallamount of up elevator trim,we felt confident Diva wouldmanage to glide at leastsomewhat smoothly to theground. That was not to be.

Rick Helgeson, fellow SASSmember and an experiencedpilot, volunteered to handlethe transmitter for the handlaunches. The first twolaunches ended abruptly withDiva nosing into the ground.Quite a bit of weight wasremoved from the front endover several more tenuous butmore successful glides.Because of its high aspect ratioand accompanying lowinertia, Diva is very quick inpitch once the CG is movedback, so from there it becameincreasingly difficult todetermine when increasedsensitivity was in reality lossof control.

Flight distance kept increasingwith each hand launch, but itbecame easier to over controlas the CG moved rearward, soelevator deflection wasswitched down to 40% ofnormal. Despite thisadjustment, the last flight ofthe day was actually more likea semi-controlled crash, withDiva touching the groundwith left yaw and the sub-finsplitting open in the areawhere contact was made.

Rick, feeling he was guilty ofbreaking a perfectly goodairplane, apologizedprofusely. We countered noapology was necessary fromour point of view — we seeRick as a much better pilotthan ourselves — we hadsimply removed too muchnose weight at one time,leading to rapid changes inpitch which no pilot couldfollow and correct, especially

R/C Soaring DigestPage 10

with so little height available.Additionally, the damage wasbarely more than superficialand easily repaired.

Test flying, Part 2

We needed a relatively lowbut steep slope to continueflight testing. One of the localschools has two fields, eachabout the size of a footballfield, oriented in an L shapewith a 16 foot high 40 degreeslope separating them. Theslope is filled with ScotchBroom, a rather dense woodyand firm thornless plant, atthis time of the year. Weconsidered this an ideal slopefor our purposes. Before thefirst launch we added somenose weight, hoping to have

the same balance point as thelast successful flight.

As the wind was comingacross the slope at an angle,the first launch was slightlycanted into the prevailing airmovement. Good thing theScotch Broom was thick, as thefirst launch ended with Divadiving into the thick of it. Theelevator was not sensitive atall, and in fact was barelysufficient to change the pitchattitude before the aircraft washeld firmly by the shrubbery.

A small portion of the weightwhich had just been addedwas taken out and anotherlaunch attempted. The initialdive was immediatelycounteracted with up elevator,but not before Diva grazed the

top of one Scotch Broom andperformed a flat spin into theoutstretched limbs of a largercompanion plant.

A third attempt, initiated afteranother small amount ofweight was removed from thenose, was successful. Divatraveled 70 paces across thelower field before touchingdown. Elevator authority wasgood, but not overly sensitive,so more weight was removedfrom the nose.

Several more successful testflights were then made, withsmaller amounts of weightremoved with each success.This process extended theflight distance each time, andthe elevator becameincreasingly sensitive, asexpected.

When evidence of pilotinduced oscillation wasobserved, we replaced theweight just removed andperformed one last test flight.This flight covered 150 paces,more than double the distanceof the first flight.

Once home, we put Diva onour balance stand. The CGwas exactly on the pointmarking the 2.5% staticmargin!

Test flying, Part 3

While we were fairlycomfortable with the CGlocation and elevatorauthority, thoughts of a winch

Page 11August 2004

launch produced a lot ofanxiety. We needed someheight to get Diva trimmedout, and the only way to dothat was through a winchlaunch; but just the thought ofbuilding line tension andreleasing the aircraft to thewilds produced an acceleratedheartbeat.

After arriving early at 60Acres, we immediately setupon putting Diva together.Safety being a concern, wewanted the first winch launchto be with as few people onthe field as possible.

We should not have been soanxious regarding winchingDiva into the sky, as uponrelease she climbed outstraight and steep with notendency at all to veer offcourse. Rather than stressingthe airframe, we let Diva slideoff the line from a moderateheight. The initial 90 degreeturn to the left was verysmooth, and it was evident theaileron differential and ruddermixing was very close tobeing right on the mark.

The straight glide to the eaststarted getting steeper, so asmall amount of back stickwas applied. This leveled theflight path, but as soon as theelevator was neutralized theglide again became moresteep. Despite the first signs ofpanic, we managed anotherleft turn.

This time the bank got steep

quickly, but at least the aircraftwas not plummeting to theground on a wing tip, andopposite aileron rapidly rolledher out of the turn andheading away from the field,completing a 480 degree turn.But she was diving again. Theelevator was overcontrolled,Diva pitched up, then fell nosedown, and recovery was into a360 degree right turn. Theground was closer now andpanic was indeed beginning totake over. Luckily, Diva wasflying toward the main fieldand over the area with tallgrass, and we managed to gether level and see a relativelysmooth flat landing well out.

Exploring the problems

Once safely on the ground, weimmediately began thinkingabout the reason(s) for theflight behavior. Diva is basedon Dieter Paff’s PN9f design, amodel of a potential full sizesailplane. We knew from theoriginal White Sheet articlethat three of Dieter’s modelswere lost during testing due toelevator blow-down.

As the PN9f used circa 1980servos with around 42 ouncesof torque, we felt a Hitec HS-605BB with 76 ounces oftorque would be up to thetask, eliminating the elevatorblow-down problem. But intesting at home, we found theservo arm could be movedabout 1/32 inch each side ofneutral through the pushrod

before any significantresistance could be felt. Someof this came from the servoitself, but most of the playcame from the rubbergrommet mounting system.

Moving to the rear of thefuselage, the end the elevatorcontrol arm could be movedup and down more than 1/16th inch from neutral withthe same seeming lack ofresistance. This translates tonearly 1/8th inch at theelevator trailing edge. Thisadditional play came from theelevator pushrod, a segmentof #505/506 blue/goldSullivan Gold-N-Rod. Whilethese assemblies are rated as“semiflexible” rather than“flexible” (red/yellow set), themounting method of the outertube has a greater effect onsystem rigidity than we at firstthought.

Although we initially resistedacknowledging ourconclusions, we eventuallycame to realize a lack of rigidelevator control was at theroot of the flight controlproblem. Although the servoand pushrod are inherentcontributors to this problem,as outlined above, the flightbehavior indicated the airfoilis a major contributor as well,and elevator deflection insidethe limits of play is speeddependent.

As we are currently workingon modifications to two of thethree above noted

R/C Soaring DigestPage 12

components, we’ll have to end this month’s column with “To be continued...” Next month we’llexplain in detail what was going on in flight, as well as the effectiveness of our hardware andairframe modifications.

“On the ’Wing...” News

• The recent “On the ’Wing...” poll on the RCSoaringDigest Yahoo! group resulted in anoverwhelming 50% of the votes going to a scale project. Our preliminary choice is the AkafliegBerlin B-11, a beautiful tailless Unlimited Class glider of the early 1960’s with high aspect ratiowings swept forward at 18 degrees. This configuration will offer several challenges so far asspar and wing joiner materials and construction methods, along with other items. Although thefull size aircraft never flew, we’re pretty excited about producing a quarter scale (4.3 meterspan) model, suitable for aerotow, and have finally arranged to communicate with aknowledgeable archivist at Akaflieg Berlin.

• Followers of this column will be happy to hear “On the ’Wing... the book,” the first volume,is now available in its entirety (52 articles) in PDF format through the B2Streamlines web site<http://www.b2streamlines.com/OTW.html>. The volume can be downloaded as either asingle document of 13.7 MB, or as a series of individual PDFs which dramatically vary in size.Volumes 2 and 3 are also available, along with articles from Volume 4 as they appear in RCSD.

• While we do have a reservoir of topics for future “On the ’Wing...” columns, we are alwaysappreciative of suggestions from readers. Aerodynamics, structures, model reviews andcomputer programs are just a few of the areas this column covers.

RCSD readers can always contact us at P.O. Box 975, Olalla WA 98359-0975, or at<bsquared@appleisp.net>.

FAI has received the following Class F (Model Aircraft) record claim :

================================================================Claim number : 9643

Sub-class F3B (Glider)F3: Radio controlled flight Category

Type of record : N°158: Distance to goal and returnCourse/location : St Vincent les Forts (France)

Performance : 7.14 kmPilot : Frédéric JACQUES, Thierry REGIS (Monaco)

Date: 17.07.2004

Current record : 1.90 km (27.05.2003 - David L. HALL, USA)===============================================================

The details shown above are provisional. When all the evidencerequired has been received and checked, the exact figures will be

established and the record ratified (if appropriate).

Page 13August 2004

Basic sizing checksfor homebrew RC thermal gliders

by Mark Drela

If you do a lot of homebrews, it really pays to do some simple sizing checks forvertical tail, horizontal tail, and Equivalent Dihedral Angle (EDA). It can save a huge

amount of aggravation and possibly unwarranted disappointment with a new design.

Specifically, you should always calculate the following three quantities:

Vh = (hor_tail_area/wing_area) x (hor_tail_arm/mean_wing_chord)Vv = (ver_tail_area/wing_area) x (ver_tail_arm/span)B = EDA x (ver_tail_arm/span) / CL_therm

where EDA is in degrees, and CLtherm is the typical CL during slow thermalling.

It's OK to just assume CLtherm=0.7 for big gliders and CLtherm=0.6 for HLGs. For a V-tail, first compute the equivalent hor_tail_area and ver_tail_area, as described in<http://www.charlesriverrc.org/articles/design/markdrela_vtailsizing.htm>

Vh = horizontal tail volume, indicates mainly pitch stability.Vv = vertical tail volume, indicates mainly yaw damping and rudder power.B = Blaine Rawdon's parameter, indicates spiral stability...

B > 5 spirally stableB = 5 spirally neutralB < 5 spirally unstable

B also approximately indicates the degree of roll power available to a poly glider,provided Vv is reasonable.

For a good-handling poly glider you want to be in these ranges:

Vh = 0.3 - 0.6 (I like 0.4 - 0.45)Vv = 0.02 - 0.04 (I like at least 0.03)B = 4.0 - 6.0 (I like 5.0 - 5.5)

For an aileron TD glider you want to have:

Vh = 0.3 - 0.6Vv = 0.015 - 0.025 (I like at least 0.025)B = 2.0 - 5.0 (I like at least 3.0 )

A DLG wants a huge amount of yaw damping:

Vv = 0.05 - 0.06 is not out of line.

Having said all that, it should be mentioned that moments of inertia influence thechoices for the Vh and Vv values. A glider with an unusually small pitch inertia becauseof a very light tail unit can get away with using a smaller stab (smaller Vh to be moreprecise). Similarly, a glider with exceptionally light wing tips will have small yawinertia and can get away with a smaller than usual. And of course gliders with largerthan normal inertias will require larger than normal Vj and Vv values.

Comment: The Allegro-Lite seems to have a fairly modest tail sizes.

R/C Soaring DigestPage 14

There are no universal values for Vh and Vv which will work well for all aircraftconfigurations. This is because the Vh and Vv definitions do not account for all factorswhich influence tail sizing.

First of all, we should state the standard Vh and Vv definitions:

Vh = (hori_tail_area/wing_area) * (tail_length/wing_chord)Vv = (vert_tail_area/wing_area) * (tail_length/wing_span )

What do these definitions ignore? First let's look at Vh...

Vh ignores the destabilizing influence of the wing's flowfield on the effective angle seenby the stab. This influence is a complicated function of the tail length, since there's a tip-vortex downwash part which increases slowly with distance, and a bound-vortex partwhich decreases rapidly with distance. The net effect usually decreases withdownstream distance. So longer tails require smaller Vh values for the same stabilizingeffect.

Vh also ignores the issue of tail aspect ratio and tail airfoil quality, both of which affectthe dCL/da lift curve slope of the tail. Increasing the tail's aspect ratio and switchingfrom a slab airfoil to a good (non-deadband!) airfoil will allow a slightly smaller Vh forthe same real stabilizing power. The Allegro-Lite has a high aspect ratio stab with agood airfoil immune to low-Re effects. So it can get by with a smaller than usual Vh.

Finally, Vh also ignores the effect on pitch damping, which depends on tail_length2. Butpitch damping is usually adequate for any reasonable tail size, so this is a minorconsideration in horizontal tail sizing.

Now let's look at Vv...

Yaw damping is the main issue in vertical tail sizing, especially on a rudder/elevatorglider. Since Vv is not a measure of damping power, it is simply not a good indicator ofvertical tail size. A much better definition which quantifies yaw damping would be

Vv' = (vert_tail_area/wing_area)*(tail_length2*mass/yaw_inertia)

It's less convenient to use since yaw inertia is not easily computed. But Vv' can beestimated in terms of the “radius of gyration”

rg = √(yaw_inertia/mass)

which has the units of length and is typically some fraction of the wing span. A uniformplank flying wing has

rg = √(1/12)*wing_span = 0.289*wing_span (flying plank)

For normal gliders the rg is somewhat less than this formula indicates since they havemore stuff concentrated near the center of mass. For the unballasted Allegro-Lite it is

rg = 0.2*wing_span (Allegro-Lite)

and for a highly-ballasted AL it can be as small as 0.1*wing_span.

Equivalent expressions for the yaw damping parameter Vv' are then

Vv' = (vert_tail_area/wing_area)*(tail_length/rg)2

Vv' = Vv * tail_length * wing_span / rg2

Page 15August 2004

In any case, increasing the tail length clearly allows smaller Vv for the same Vv' (whichis what really matters). Reducing yaw inertia or adding central ballast, both of whichreduce rg, also allows smaller Vv for the same Vv'.

So to get to the original question, the AL with its long tail and very light tips and tail(low yaw inertia) has in fact a quite large Vv' compared to other gliders. This isapparent in its rather nice yaw damping characteristics, especially when ballasted. TheSpirit 2m which was mentioned, has a short tail and broad (heavy) tips, and is verywobbly by comparison.

One other issue which often arises in vertical tail sizing is spiral stability.Increasing the tail size tends to worsen spiral instability on most aircraft.

But on r/c gliders with generous dihedral it has a much lesser effect.

For large EDA values it has in fact little or no effect on spiral stability. According toBlaine Rawdon's approximate criterion, we get spiral stability if

EDA * (tail_length/wing_span) / CL > 5.0

This favors a longer tail length, but vertical tail area doesn't enter in.

Another obscure fact is that a spirally-stable glider can become spirally unstable above acertain bank angle in a steady turn. It will hold trim in a shallow banked turn, but willbecome unstable and try to spiral in above a critical bank angle. The larger vertical tailthe larger this critical angle is. The AL has a critical bank angle of about 50 degrees.

For more pictures from the JR Aerotow 2004,see Mark Nankivil's photo essay starting on page 20.

Randy Martin’s 1/3.5 scale DG-1000 with its canopy ajar on final.From the EMS kit, this model spans 5.3 meters and weighs approximately 22 lbs.

R/C Soaring DigestPage 16

GORDY’S TRAVELS

Gordy StahlLouisville, KentuckyGordySoar@aol.com

“Your job, should you choose to accept it...”

Anatomy of ‘Task Soaring’

S ince last season I havebeen WORKING, not only

at my full time job but athoning my task flying skills.For those of you who don’tunderstand ‘task soaring,’those of us who have decidedthat we want to improve ourair reading skills and ourability to achieve precisioncontrol of our sailplane’sactions, we attend ThermalDuration (TD) contests.

When we show up at an event,the Contest Director (CD) isthe boss, and he assigns the‘tasks’ for the day of soaring,much like showing up to workand the boss telling you whatis expected that day.

Do the task well and getrewarded with a trophy andthe admiration of fellowsoaring enthusiasts, do it sortof well and learn specificallywhere you need to work inorder to improve your soaringskills. Do it poorly and likelyif you have the right attitude,have a wonderful day ofsoaring and learning aboutsoaring.

TD contest formats vary inmany ways. Some are set upto provide an opportunity todraw soaring enthusiasts andfriends together for anorganized day of soaring…this is usually designated asan “Open Winch” contest.With this format, the CDannounces the tasks for theday, say rounds beginningwith a three minute, fiveminute, seven minute, andnine minute flight task and a50’ landing circle.

A piece of nylon tape isanchored in the center of thelanding zone with graduationsdrawn on it to indicatelanding points, usuallystarting at 100 points. Thetape can be swung around thecircumference till some part ofit touches the sailplane’s nose.That corresponding numberindicates the landing pointsearned. Sometimes the CDwill call rounds as the entiregroups of pilots havecompleted the each round.Sometimes the CD willannounce that pilots can flyany round at anytime as longas all the rounds arecompleted by the end of the

contest. With this system ifyou hook a great thermal earlyyou can elect to fly out thenine minutes, or if you getskunked with a down cycle,you can shoot for the threeminutes.

The opposite of the OpenWinch event is Man On Man(MOM). In this format,groups are randomlyassembled for the first task.Usually the task will be tenminutes. Six winches are usedand the pilots launch in aconsecutive shotgun release.The idea being that thosepilots are a mini contest, withall the pilots flying in the sameair. Those pilots get to testtheir strategy, air reading andlanding skills against theothers in that launch group.

If for instance the air is alldown, and the best score istwo minutes, then that pilotwould get 1,000 points sameas if he had flown for the tenminutes. If the next round airis all up and everyone getstheir ten minutes, they wouldstill be measured only againstthe pilots in that launchgroup.

MOM erases ‘luck’ from thesoaring part of the task… as inone group launches in an upcycle and gets ten minutes andthe next in a down cycle, onlythe first group would have achances at glory, even thoughpilots in the first group werefar more skilled and practiced.

The standings of each firstround flight group are thengrouped in the order theyfinished against pilots who

Page 17August 2004

finished in the same orderfrom the other groups. Thispits equal pilots against equalpilots (for the most part)against each other all daylong. It is easily the fairestvariant going. Instead ofnewer pilots against the mostexperienced pilots, at the endof the day each pilot can seehow his practice andexperience stacks up againstpilots of similar experience.

Landing tasks can vary basedon how many pilots have tomove through the event. Forinstance, if there are 200 pilotsat an event, taking time towait for swinging tapes andthe straightening them againcan burn up the day.

They also vary depending onthe mood of the CD! At largeevents such as the Fall Festivalin Visalia, California, wherearguably the best of the bestcome to have fun and to testtheir skills, ‘gymnastic’landing targets, say in theshape of Pac Man (who’smouth is a zero and body is 6’diameter), or a shuffle boardwedge shape with the apexbeing 100 points!

These landing tasks really testthe pilot’s ability to control hissailplane’s speed, altitude andtiming... but mostly allow forimmediate recognition by thelanding judge, and to clear thelanding area quickly.

The most common landingtargets are the circle tape (alsoused in the rest of the world asthe official landing task), orthe runway tape. This is apiece of tape anchored on bothends with the tape being 100points and every inch away oneither side of that tape a lossof a point. Again measured

from the tape to the sailplane’snose, usually done with lengthof plastic pipe with incrementsmarked along its length.

Task flying is the most fun!Not that just soaring aroundfor a day isn’t, but task flyinggives soaring a point! TheLeague of Silent Flight (LSF)has an achievement programset up to provide various skillimprovement tasks. The LSFLevel 1 task sets a task ofmaking a small number offairly generous measuredlandings, the LSF levels are alldesigned to soar a RCsailplane pilot along the skillsof RC soaring.

LSF Level 5 is the ultimateachievement including aneight hour continuous flightand a multi-mile flight fromone point to another alongsome roads (the pilotlaunches, gains good altitude,and then climbs into the backof a pickup and flies hissailplane the distance andback!).

Improved skills means morefun and a lot lessopportunities to dig yoursailplane out of the ground orout a tree!

There are many variations oftask soaring, some involvespeed, distance, soaring timeand landing skills. Regardlessof the variant, task flyingturns our sailplanes fromsoaring machines into ‘toolsfor a task’ and turns soaringinto a challenge.

It’s NOT about ‘beating’ someother pilots, since that’s notpossible. The best you can dois to do the task …perfectly.

The only person you can beatis yourself… or your last bestperformance.

Task flying, or flying contestsis really about sharing thechallenge and the day withfriends of like interests. Istarted this columnmentioning that I had beenWORKING over the lastcouple of years at honing mysoaring skills. That meanspracticing, not just going outand floating around for hourson end, but setting a timegoal, flying with a talkingcountdown stopwatch andalways having a landing spotto attempt to place the nose ofmy sailplane.

Remember, its about precisioncontrol of your sailplane andfinding thermals or flyingsmoothly to get exactly theamount of time (not onesecond more or less) of tasktime... so aimless soaring andlanding prepares you for –aimless soaring.

The result of all that taskpractice? Consecutive wins orplacements in the last 20+events I have flown! Think itwas ‘fun’? You bet! I didn’t‘beat’ a single friend, but I didmanage to get better resultsand some pretty awesometrophies from Australia,Washington, Tennessee, Ohio,Indiana, Missouri, Texas,Indiana, Canada... a bunch offun places!

Give task flying a chance, ifyou haven’t been followingmy columns in the recent pastyear and a half or so, go backand check them out. There area lot of tips and secrets toimproving your skills andgetting your ‘tool’ tuned upfor the ‘job’.

See you on my next trip!

R/C Soaring DigestPage 18

Foamie flying wings have itrough. What other planes get

intentionally flown into solidobjects? We routinely smack theminto other planes, pilots and theground. It’s a tough life indeed.Yet, sadly, most put only aminimum of effort intoconstructing and maintainingthem. Whether your foamie istailless or convention, here are afew suggestions for treating itright.

Construction

1. Build it FLAT. Build it on thewing beds or at least a flatsurface. Don’t tension the tapewhen applying. Use therecommended taping pattern onboth sides. Many other patternsare fine too if you’re familiar withthe concept. Tensioned orwrinkled tape will causeproblems later by leading tostress and temperature variances.

2. CG can be deceptive on aflying wing but the commonmethods of setting apply. Theonly things to remember are bevery precise when doing so anddon’t be fooled by "sort of OK"results. Meaning watch fordeceptive results. I had a wing ofmy own design that I just didn’tlike. I thought it was setup asgood as possible but 1/2 anounce on the nose turned it into agreat plane. I had the nose weightWRONG by 1/2 an ounce anddidn’t realize it. It took a friend tosee the problem and fix it.

Precision is also important. I hada wing where 1/8th inchdifference of CG location madeall the difference betweenaverage and best plane I’ve everowned. Yet, a world class pilotfriend of mine built the same

plane and thought it was junk.Setup was critical on that one. Igot lucky and learned a lesson.

3. Make sure the control throwsare equal. Once built use a rulerto measure the control throws upand down. They should be thesame. Otherwise you get a pitchinput every time you roll. This issimple but most don’t worryabout it.

4. Equal twist on each half of thewing. Different wing twistsbetween sides really hurtsperformance. Different planes usedifferent amounts of twist andsome have their own personalpreferences. Regardless, keep thesides the same.

5. Control throw magnitude isobviously a personal preference.But, with foamies I’ll often seethrows that are quite excessive.Personally, I like to limit maxthrow to just less than what willcause the plane to snap. Then, ifneeded, use expo to soften it nearcenter.

Maintenance

Though durable, a foamie willstill require some maintenance.Here are the items to remember:

1. Store the plane flat. Warps in aflying wing can strongly degradeperformance. Poor storage canmess up a good plane whileproper storage keeps warps tothe minimum. Personally, I storemy flying wings in their wingbeds on a flat surface.

2. Dents and warps happen.Combat can, surprise, bedestructive. After a combatsession, examine the plane. Fixanything that’s broken. Patchholes and tears in the covering.Remove any warps with thejudicious application of heat andforce. Check the wing twist andkeep both sides equal.

3. Look for damaged foam.Noses are a primary location fordamage, of course. A crinklednose can be fixed several times byadding/removing the coveringover the area and applying heat.

Taking care of foamie wingsBill Swingle

Janesville, CA

Use a ruler to to measure control throws up and down.

Page 19August 2004

Once your results aren’t able toimprove the area very much, usestronger methods. Namely foamreplacement. The damaged foamcan be simply cut away (I like mybandsaw) and the hole refilledwith a new portion of foam. Thensand to the needed shape withsome course sanding paper.

Foamies flying wings have to be:

1. made properly,

2. cared for properly, and

3. stored properly,

just like ANY OTHER plane.

Abuse them and they’ll flypoorly; no surprise.

Abuse them but fix them andthey’ll last a long time but stilleventually fly like dirt and haveto be replaced.

The objective is keep them flyingwell over the course of their lifeand to make that life a long one.

I store my flying wings in their wing beds on a flat surface.

All nested to prevent warps and damage.

And it makes transportation easier, too!

R/C Soaring DigestPage 20

The beginning of June here in theMidwest means that the JRAerotow is nearly upon us whichfor me brings on a level ofexcitement and anticipation forthe drive up to Monticello,Illinois.

Located just a few miles west ofChampaign-Urbana in centralIllinois, Monticello is surroundedby beautiful farm land and hasplenty of shops and eateries tokeep the whole family happywhile you’re out at the localairport enjoying the thermals andgreat flying conditions.

The event is held on the town’sairport which is located on thesouth side of Monticello. Theairport is also home to the IlliniGlider Club so the mix of fullscale and large scale sailplanesadds even more “flavor” to thisevent. This year’s event wassponsored by JR, Horizon, Eflite,Hobby Zone, Park Zone, HobbyLobby, Endless Mountain

JR Aerotow 2004June 11th thru 13th Monticello, Illinois

Models and Futaba.. The CD forthe Aerotow was the affable PeterGoldsmith ably assisted by hiswife Caroline along with many ofthe Horizon Hobby team. Thisyear saw 52 entrants whobrought along 134 sailplanes.

I’ll let the photos and captionsspeak for themselves. Make sure

by Mark Nankivil

you set aside a weekend in June,2005 and make the trek toMonticello for a wonderfulweekend of flying andfriendship! Details on the eventwill be posted to R/C SoaringDigest as soon as they areavailable.

Good Health and Good Lift!

Above: The pits - plenty of fine large scale sailplanes to look over.

Page 21: (Top) Dan Troxell brought along this beautiful EMS Mininoawhich flies quite well at 18 lbs. (Middle upper) A shot of John Derstine’sSZD50 Puchacz. (Middle lower) Peter Goldsmith’s Bruckmann PiperPawnee towplane on final - the JR team, along with Johnny Berlin, werekept busy towing sailplanes throughout the weekend. (Bottom) RickBriggs 1/3rd scale ASH-26 on final.

Page 22: (Top) Toby Graither’s DG-800 leaps off on tow. (Middle) PeterGoldsmith’s 1/3 scale Super Cub heads in to pick another tow - a DA-100pulls it along. (Bottom) What scale aerotowing is all about... Dan Troxell’s1/3rd scale Schweizer.

Page 23: (Top) Tim Lavender's Harbinger flies over on final. (Middle)Here’s a close up of the scale finger type spoilers used on this model.(Bottom) One of the many tows heads off on Saturday.

Page 24: (Top) Rusty Rood holding his Ka6. (Middle) Dan Troxell broughtthis 1/4 scale, 18 pound EMS Minimoa. (Bottom) A close-up of theinterior of Rick Briggs' Brequet Choucas, a 6 meter, 27 pound modelscratchbuilt by Arnold Hoffman.

Page 21August 2004

T: Don Troxell' Minimoa

Mu: John Derstine's SZD50

Ml: Peter Goldsmith's Piper Pawnee

B: Rick Briggs' ASH-26

R/C Soaring DigestPage 22

T: Toby Graither’s DG-800

M: Peter Goldsmith’s Super Cub

B: Dan Troxell’s Schweizer

Page 23August 2004 Page 23August 2004

T: Tim Lavender's Harbinger

M: Harbinger spoilers

B: Saturday tow.

R/C Soaring DigestPage 24

T: Rusty Rood's Ka6

M: Dan Troxell's Minimoa.

B: Rick Briggs' Brequet Choucas, builtby Arnold Hoffman.