16 S S A 2007 M e m p h i s C o n v e n t i o nby K e m p t o n I zunoIt may have been a little chilly in the Exhibit Hall, but we all had a hot timelooking at the new sailplanes and accessories. Join us in Memphis with words andpictures!

24 Three M o d e r n Sa i lp lanes

T a k e n f r om SOARING M a g a z i n e , J a n u a r y 1 9 3 7 Recapturethe "Golden Era" of glider flight and design with a reprint from our very firstissue.

28 A South A f r i can G e m — T h e J S 1 Reve la t ion byL e o Bene t t i - Longh in iWe take a quick jump from the 1930's to the present where advanced designtechniques and computer aided manufacturing evoke the true meaning of"modern."

35 A Flight Test Eva lua t ion of the S i n h a W i n g P e r f o r m a n c e E n h a n c i n g Deturbu lators

b y R i c h a r d H . J o h n s o nThe new Sinha Deturbulator could be the first significant drag-reducing aerodynamic invention since laminar-flow airfoils. The wing surface deturbulators aretested at great length at Caddo Mills, Texas.

4 Soaring Mail 51 Affiliates & Divisions8 Soaring News by Pe te r W. Smith

13 C l u b News 53 Soaring Calendarby F r auke E lbe r 57 B a d g e s and R e c o r d s

43 Safety Corner by J u d y Rup rech tby G e o r g e The l en 59 Soaring Classi f ieds

48 2007 Safety Program 68 Clio's Wingsby R i c ha rd Ca r l s on by R a u l B lacks ten

Front Cover: Choosing a cover to commemorate SSA's 75th Anniversary was not easy, but every Societymember will identify with this photograph. Derek Lisoski, of Simi Valley, CA photographed this Black-browed Albatross in Antartica.

Centerspread: As we take a retrospective look at The Soaring Society of America with this Special 75th Anniversary issue, we offera collage of unique and interesting images from our photo archives.

Special 75th Anniversary Edition - May 2007 - SOARING Magazine

A South African Gem —The JS 1 Revelation

by Leo Benetti-Longhini

Introduction

Any mention of South Africa inevitably results in thoughts ofMandela, diamond and gold mines, spectacular wildlife, finewines, pristine beaches and surfing, or maybe even the 2010World Cup of soccer. But the Rainbow Nation's mineral-richinland plateau is also regarded as one of the best places in theworld for cross-country soaring, and many an international pilothas made a pilgrimage to the sun-baked "highveld" in search ofdistance diamonds. Visiting pilots are now also able to discoveranother gem, the JS1 Revelation, a new racer built by JonkerSailplanes (www.jonkersailplancs.co.za) of Potchefstroom, aboutan hour's drive southwest of Johannesburg. The FAI 18-metersailplane has a wing area of 11.25 m2 (121 ft.), aspect ratio of 28.7,VNE, of 290 km/h (157 kts), and published L/D of 53:1.

The JS1 is the creation of the Jonker (pronounced "Yonker")brothers and a dedicated team including Johan Bosman -aerodynamics, Ronald Taljaard - prototyping, and Michael Kahl -quality control. (See the sidebar for some background about thebrothers.) Their sailplane recently caused a buzz inthe soaring community with its notable maiden flight inDecember 2006, followed immediately by an unanticipated winof the South African 18m/Open Class Nationals. As the newestcompetition sailplane on the world scene, questionsunderstandably abound about the racer's origins, designers,construction, and performance. Hence this article aspires to bringreaders up to speed about the steadfast development that has, atleast until now, proceeded relatively unnoticed on the other sideof the equator.

To set this narrative in context: In mid-2006, while on a

return visit to South Africa, a friend and national team member,Dolf Pretorius, shared his contagious excitement about the JS1.My interest grew rapidly, and, after establishing contact with theJonker brothers, I made another southbound trip in late December,during which I was privileged to test fly the prototype. Myimpressions of the sailplane and team were very positive and itclearly made sense for me to work towards a representationagreement for North America (recently finalized). Because of theestablished affiliation that now exists, my commentary on theflight characteristics has intentionally been excluded from thisarticle. Flight reports will have to wait until the first JS1Revelation delivered to the US can be placed intothe hands of independent SOARING contributors so that it can beobjectively evaluated.

WingThe JS 1 has a polyhedral wing with removable 1.5-meter tips.

The wing loading ranges from 31.2 kg/m2 (6.5 lbs/ft2) to aballasted maximum of 53.3 kg/m2 (10.9 lbs/ft'). The wing sparsjoin via the classic tongue and fork method secured by two mainpins. The connection between the fuselage and wing is viabushings at the fuselage compression tubes and shear pins at theroot ribs, keeping pins from protruding to each side of thefuselage. As expected, the controls all hook up automatically.The spars of the 1.5m tip extensions have a cleverly simple pinsystem and aileron connection.

The wing design uses a series of six profiles derived from theT12 airfoil of 12.7% relative thickness developed by company

28 May 2007 - SOARING Magazine - Special 75th Anniversary Edition

aerodynamicist, Johan Bosman. Each is tailored to the specificReynolds number requirements at various spanwise locations. Forinstance, the airfoil at the tip was modified to stall at a greaterangle of attack and have a higher capable lift coefficient than thebaseline T12 airfoil. It also has less profile drag at lowerReynolds numbers than the parent airfoil. The TI2 was based onan earlier Bosman section called the JJB44 that in turn has itsorigins in a profile designed by Attie Jonker. The airfoil and thewing were refined and finalized by Bosman at the Delft TechnicalUniversity in the Netherlands while studying under the tutelage ofProf Loek Boermans.

The lower surface of the wing has a double row of holes, onelocated just upstream of the flaperon seal (at 71%) and onedownstream of the flaperon seal (at 93%). The aft row providesblowing at all flap settings. In the prototype's currentconfiguration, the forward row provides blowing at low speeds (to transition the laminar boundary layer directly to attachedturbulent flow and preemptively avoid flow separation) and isclosed off at high speeds. However, the unique characteristic isthe intended future implementation of suction (used with all flapsettings) at the forward row. Blowing is retained at the aft row.Wind-tunnel tests have shown that the addition of suctionstabilizes the flow across the flaperon gap, reduces the boundarylayer growth, eliminates sensitivity to the Mylar seal, and lowersdrag. The surprising difference, when compared with the muchexperimented upper-surface suction systems, is that very littlesuction energy is needed, and thus, theoretically, powerrequirements are low. The method appears to have the potentialof being a practical boundary layer suction system.

At the time of this writing,the blowing/suction systemtheoretical calculationswere finished, wind-tunneltests were complete, theuniversity-held technicalpatent was pending, andflight tests to optimize thefree-flow condition werescheduled. On the technicalside, the main unknowncontinues to be the source ofsuction energy; while on theregulation side it is IGCapproval (the endorsementlikely being dependent onthe energy method). Until these are decided upon, the JS factoryremains understandably non-committal about implementation.When pressed for quantitative expectations, factory managerUys (pronounced "Ace") Jonker divulged an expected gain of acouple of percent (a slight, yet meaningful number in the contestenvironment). Whether executed or not, the airfoil with bothrows blowing already seems to be performing as intended, soany success with the suction system will be a pleasant bonus.

The airbrakes are placed far aft on the thin wings to maximizethe laminar flow distance. With the thickness being only 12.7%of chord length, the available depth restricts the airbrake bladeheight: therefore triple-blade airbrakes were necessary in order tomeet the CS-22 area requirements. The rear of the airbrake capsopen first, the same method as used on some other sailplanes.This allows the brakes to be cracked without being sucked open.One practical benefit is that launching with the airbrakesinadvertently unlatched does not become an emergency. Full afttravel of the airbrake handle activates a heavy-duty hydraulic discbrake from Parker Aerospace (Cleveland).

There will probably always be ongoing discussion in thesailplane community about wing skin shrinkage and spar bumpsshowing through laminar wing surfaces. I found the procedurestaken by the JS factory to avoid skin shrinkage commendable.Specifically, the spar caps are bonded wet-on-wet directly to theskins during the initial lay-up in the molds (no doubt alsonecessary to maximize spar depth of the thin wings). Thiseliminates a thick structural filler bond between spar caps andthe skins, considered to be a main source of shrinkage. The shearweb, looking much like an I-beam with flanges just as wide asthe spar caps, is first placed into one mold half and the structuralbond completed. This step is relatively straightforward due to fullaccessibility.

Bonding of the second flange is necessarily performed blindduring union of the two wing halves. The application techniqueused by JS to ensure adequate bonding is both creative andpractical. The exposed spar cap surface is first mapped, as is theun-bonded flange of the shear web, and all the values enteredinto a spreadsheet. Values for resin weight for defined sectionsof spar are then automatically generated, and the thickenedstructural resin applied accordingly between the cap and webflange. The factory reports that the mapping method is

Special 75th Anniversary Edition - May 2007 - SOARING Magazine 29

extremely accurate and the squeeze-out consistency attainedalong the length of the spar is impossible to attain by eyeballalone. I considered it noteworthy and reassuring that, in spite ofthe high confidence with the technique, a post-closureinspection is still performed with a borescope camera to verifyall bonds. In addition, the shear web bonding area has a safetyfactor of 2.

FuselageThe Revelation's fuselage geometry is visibly quite conventional,

yet I discovered that beneath the surface it was structurallyadvanced. The brothers, being enamored with the shape and linesof the ASH-26, approached the Alexander Schleicher factory in2001 for a fuselage shell, intending to mate to it the pair of yet-to-be-built wings. Schleicher provided willing support and sold theman unfinished fuselage; work then began on integrating the newwing design plus the multitude of subsystems. But, asforeshadowed by experiences in their youth, the pair encounteredthe domino effect of interrelated parts affecting neighboringcomponents and recognized that very little could be reused. TheASH-26 fuselage was put aside, and work essentially began overwith a plug that retained the graceful look

of the fuselagethat they soadmired. Onthe engineeringside, cockpitsafety andcrashworthinesswere extensivelyoptimized. Thecockpit structuredesign wasrefined using finite-element analysis (FEA) modeling methods,resulting in a lightweight hybrid-composite structure of carbon,aramid (Kevlar), and glass fibers. (The fuselage shell fromSchleicher ultimately made its way through the composites repairshop and, with the addition of donor wings from an insurancewrite-off plus many new parts from the Schleicher factory,eventually took to the air.)

As fit of a modern racer, the JS I cockpit layout andergonomics are refined. I found the controls placed whereexpected and easy to reach and operate. The attention to detailwas surprising for a pre-production prototype. This was mostevident in the canopy frame. The handles were completely flushand all latching mechanisms neatly hidden within the hollowstructure of the frame - quite elegant. The canopy transparencywas by Plexiweiss of Germany and the optics were flawless. Atinted transparency is an available option. I found the integrationof the instrument panel and the canopy to be well-designed. Therouting of cables and tubing was particularly clean via a flexiblespiral wrap conduit near the hinge point. All pressure tubing wascolor coded for easy identification. A tubular O2 tank holderwith MH bracket is standard, as is a holder for a Camelbakdrinking reservoir. The tow-rope release handle was nicelyintegrated into the center console.

The flight controls and the retractable landing gear are alldriven by push-pull linkages. Having some personalspecialization in kinematics, I just couldn't stay away from theingenious flaperon control mixer and landing gear mechanisms;

the design methods employed are the subjectof a technical paper presented at the 5thSouth African Conference on AppliedMechanics (SACAM) in 2006. The desiredkinematic motion and resultant loads wereoptimized using parametric spreadsheetmodels that stretch the capabilities of Excelspreadsheets to levels rarely seen in thetechnical world. As a result, no cams wererequired to achieve the proportional outputmotion of the flaperon mixer. Also, I foundthe landing gear actuation loads were tunedand well balanced.

Tooling and MaterialsProduction of the wing molds started with

the use of an in-house multi-axis CNCmilling machine. Johan Bosman developed aprogram to convert the CAD models into

30 May 2007 - SOARING Magazine - Spec ia l 751/, Anniversary Edition

accurate G-codes for the milling procedure. The method provedto be more accurate than available codes at the time. Accordingto Johan, it took around two years to cut all the mold sectionsnecessary for the wings, elevator, and flaperons. During the lastfew years of building the prototype, many of the small molds (ribs, bulkheads, etc) were also cut with the CNC machine. Thecomputer numeric control milling machine was also used to cutpositioning jigs used to locate parts. This effort in accuracyproved to be most successful, resulting in perfectly matched partsand much time saved.

Materials are all industry standard resins, fabrics, fibers, andcoatings. The same can be said for tubing and hardware. It wasevident the brothers had been in the sailplane repair business forsignificant time and that they identified with the importance ofmaking sure that any repair shop around the world could work onthe Revelation.

FactoryA multi-day factory visit goes a long way toward understanding

a company's culture, dedication, capabilities, and professionalism.Prior to the visit I admittedly held preconceived ideas about whatmight be found: certainly a well-crafted

prototype, talented team, and passion for the project; but I alsoexpected that key background tasks might be lagging. Instead, Isatisfyingly discovered that design documentation, calculations,tests, cost analyses, and inventory planning were largely in placeand the somewhat anticipated "cart-before-the-horse" scenariowas absent. As an example, Attie Jonker modestly pulled out twothick binders of engineering drawings (380 sheets in all) thatwere, in my scrutinizing opinion, of impressive quality. Alldrawing sheets were generated from 3D CAD model data. (It isthe factory's intent to make PDF versions available on an as-needed basis; the future usefulness to owners and repair facilitiescannot be ignored.) Similar careful preparation was apparentelsewhere. The factory has amassed a huge database of well-documented calculations and tests, all performed in accordancewith CS-22 requirements. In addition to destructive tests ofvarious structures, material coupons (tensile, shear, andcompression) were regularly tested throughout development andin Attie's words, "Correspondence with finite element analysis (FEA) models was spot on." I believe this should greatly facilitatethe certification process. The Jonker Sailplanes business plan andfinancing documentation were also robust. Unquestionably, themagnitude of work remaining is substantial, but any warning flagsindicating unreasonable risk or concern with the new companywere simply not present.

FutureThe latter half-decade of the JS1's development has seen much

tangible progress, culminating in the recent milestones of amaiden flight on Dec. 12, 2006, the public debut to an impressedaudience on Dec. 15, and a cautious entry for comparisonpurposes in the 18m/Open Class Nationals the week afterChristmas, which led to the historic first contest win that grabbedthe attention of the soaring community worldwide (see the March2007 press release in SOARING Magazine). The next phase ofthe saga is now in full swing. As of this writing, the pre-production Revelation is undergoing fine tuning and being putthrough the rigors of flutter and certification testing (asimultaneous certification plan for South Africa and other

Special 75th Anniversary Edition - May 2007 - SOARING Magazine 31

BROTHERS IN AVIATION

The story of brothers in aviation is not unknown in thehistory of aircraft design and manufacture. We all recognizesurnames like those of the Montgolfier, Wright, Granville,Bell, Taylor, and Schweizer brothers. So what about the Jonkerbrothers? Their story is surely unique because of their remotelocation, yet pleasantly familiar through that shared passion forthings flying.

Step back to the mid-70's. The two young siblings, Attie andUys, were blessed to have a father (a very warm andpersonable Mr. Tienie Jonker) interested in gliders. But at thistime in South Africa, access to hard currency was difficult atbest, and importing a glider was wishful thinking on a teacher'ssalary. Mr. Jonker decided to build a Tern, an American plans-built wood and fiberglass glider of 15-meter wingspan designedby Terry Miller. The fascinated young boys were soonengrossed in the project, which saw completion at the turn ofthe decade.

By the mid-80's the teenaged boys were flying woodengliders under their father's tutelage, soloing shortly after theirsixteenth birthdays (the earliest age South African studentglider pilots can solo), but they yearned for betterperformance. Attie even tinkered with streamlining the boxycockpit of the Tern, only to discover the interrelationship ofadjacent components, and that cleaning things up requiredmore than mere cosmetic change. In the early 90's while atuniversity, the brothers competed at the national level in theClub Class with the beloved Tern and a Standard Austriarebuilt from a wreck. But performance was still paramount tothe boys and, with sleek composite sailplanes simply out offinancial reach, competition soaring was put on the shelf forseveral years while they completed engineering degrees. By themid 90's Uys was working for Denel Aviation (South Africa'smilitary aircraft manufacturer), and Attie was lecturing full-time at the university.

Toward the end of the decade Uys had also taken a lecturer'sposition at the university and the brothers were back in thecompetition arena, flying a pair of Cirrus sailplanes rebuilt in

their now highly-regarded sailplane repair facility. In additionto the composites shop, they also grew a successful wind-turbine blade manufacturing business (fertile ground fornurturing skilled composites workers) and were instrumentalin the creation of the local AkaVlieg Potch (AVP) that hasallowed many university students and several JS staff membersto become glider pilots. The AVP (www.potchgliding.co.za)has the distinction of being the training ground for the country'sfirst licensed black South African glider pilot, Lucky Kokwe,a young technician at the Jonker Sailplanes factory.

They made the national team flying the Cirruses, but withthe persistent call for higher performance, the idea of buildingan uncompromised racing sailplane started to sprout roots.Attie began design work on a high performance airfoil basedon Prof Loek Boermans' design methods, and subsequent windtunnel tests showed good agreement with XFoil. Further workon the all-important airfoil was then delegated to a promisingyoung graduate student by the name of Johan Bosman.

Within the first few years of the new millennium, the projectbegan to transition from theoretical design into more tangibleprogress. As with all projects of humble beginnings and scarceresources, many hours of weekend and evening work wereaccumulated. Resources from the sailplane repair and wind-turbine manufacturing shops were gradually introduced to theRevelation project. Growing outside interest and demand alsodictated that Uys resign his university position to manage thebusiness full-time, while Attie has retained his lecturer'sposition to ensure that the mutually beneficial link between thebusiness and the university remained strong. All told, thesynergies between the university environment, the compositesrepair shop, the turbine blade manufacturing business, and thelocal akaflieg have tied together and allowed the brothers tobuild a talented team.

countries is being followed), manuals are being finalized, andadditional buildings are being added to the facility to allowbetter workflow. A jet-sustainer version is in the works, and apropeller-driven self-launch version is planned. The orderbacklog is healthy, with production for 2007 intentionallylimited to half a dozen aircraft, then conservatively expanding tobetween 12 and 18 aircraft for 2008. What started out as a wayfor each of the siblings to have his own high-performancesailplane has blossomed into a business that will likely put SouthAfrica on the map as a premier supplier of competitionsailplanes. It's fair to say the brothers and their team are off toone of the most interesting production starts the soaring worldhas seen in quite a while.

About the author: Leo Benetti-Longhini resides in the wind-tunnel capitol of Tullahoma, Tennessee. He holds an advancedengineering degree, has extensive machine-design, composites,mechanisms, & wind-tunnel engineering experience. He is aworld record holder, towpilot, and CFIG.

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