Aero Modeller

lT WAS THOUGHT that a bettersolution than the adnittedly verysimple ofset tow-ring might well liewith a combination of the Russianhook and the 'spring and ring'system, especially after the draw.backs of the former method outlinedin the August issue, and so now wolkbegan along these lines.

I was by now coming to theconclusion that my original prioritieshad been wrong! Positive line lockwas st i l l the prime requirement, but

Fiasr. l0- Author ' ! l . t . r t c i . .o l . r towd.vic. (utilir€t "rprinr :nd rina" ?.1c...)

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good circular tow belraviour wasnow considered to be an attributepreferable to catapult tum. In fact,the latter could be obtained to somedegree by the simple expedient ofsetting up the straight tow with aslight bias in the direction of theglide turn. High-speed releases couldthen result in a useful altitude gain,and lhis in fact can be obtained on aconventional tow-hook system at therisk of some deterioration of theslraight tow properties.

Mdr.r jot D, i l l No,^56.

I . in du,o

w' i) FRAME

OIBCULARTOW - Part3

Elton Drew discusseshis latest devices formodern A/2 g l iders

Thus, it was decided that addi-tional rudder ofset for the circulartow mode should be a feature, andthe hook shown in Fr?rtes 10 and I Iwas prcduced for installation in my'hack' fuselage in place of the'Russian hook' variant. The aim wasto produce a system more versatilethan either the Russian hook(including the Burroughs adaptation)or the offset hook systems, in thatstraight tow should be possible ingusting wind and/or at high speed.In fact, provided that line tension ismaintained, it could be operated asa conventional straight tow nodel ifdesired.

St\tdy of Figure 1l will explain theoperalion of this system - theillustrations show an all-moving finas used on the author's circular towmodels, but obviously the system isapplicable lo the convenlional Iinand rudder arrangement.

858

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859 September 1975

For straight tow the hook pivotsforward against stop A which is usedto adjust th€ rudder strajght towposition. To facilitat€ a catapultreleas€, a slight bias in the directionof the glide tum may prove advan-tageous, mthe. than a dead straighttow settrng,

Stop B efrects both circular towand glide rudder s€ttings - thedifference between glide tum and thetighter circular tow turn is rcgulatedby stop C. In practice, the desiredcircular tow setting i9 first achievedand the glide s€tting adjusted, bymeans of saop C, r€lativ€ to this.

The auto-rudder line adjustmentis a worthwhile 'optional extra'. Itfacilitates both fine tuning of thesystem or can be used with coarspadjustments to effectively move the'hook' position fore or aft. The latteradjustment is, of course, carried outin cotjunction with movement foreand aft of slops A and B.

This hook provcd an immedialesucc€ss. After only s few fli8htsI was sumciently confident to use itin comDetition. the fitst tim€ I hadus€d ciicular tow of any descriptionin actual competition. The weatherappearcd ideal for circular tow -iniaially overcast, later turning todrizzle aDd rain, little drift and lightthermal activity, the latter to con.lirue even duriog the rain but neververy fr€queot, For the frsa fourflights I thought that I had lhecomplete aoslver to the prevailingconditions. It seemed almost tooeasy ! The tactical advantage over theoppositioD, all straight towing, wasenomous. One could use thei.models as cooveltional markers, butin the light lift and with smallnumbers flying positive indicationsby upwind models were few. The

obvious l€chnique was to tow upalongside any likely lookinS model,then go into the circular mode toass€ss th€ ai(. If favourable, onecould catapult otr, gaining a usefulheiSht incrc{se relative to lhe markermodel. If unfavourable, one couldcarry on towing indefinitely untileither lift was sens€d or 3omeoneels€, committed to straight tow,would be obliS€d to run upwind andlaunch arlother 'iodicator' model.

An infallible system - then thhesstart€d going \{rong, as only theycan under contlst conditioN ! Havingpreviously had many flighb trying tol€arn how to release a s€eminglypermalently 6xcd hook, I now,unexpectedly and somewhat per.plexingly, found several ways inwhich to release the modcl unirtten-tionally. The first was to ellow toomuch slapk to develop around me,catch it on a sl€eve button atrd -binSo! - away went the model fromabout halfline heidt. Thc nexlfiasco was attributed to carclcssnessin not followinS my usual practice ofunfurling the pennalt befor€ eachflight. The twisted pennant rolaledon the lioe and the final unfurlingtum suddedy releasing the last twistof line scross the p€nnaot prcvidedan impulse to the spring, and another ,flight spoilt. The final unintentionalreleas€ was thought to be due toallowing the model to get too lowand too far dorrnwind- the lineangle thus becoming very acute,and with the model pointing down.wind there appears to be I po$si-bility that the hook tip foul€d th€fus€lage undelside, thus being pushedf.om lhe riog. Not too likely, butno other exDl.nation could bc fouDd.

Thus, tliis first cont€ot outio&whilst not entirely succesful, had

Th. .{.o .odd.r ll.. 'tot.b!.k|.' dlc-t.r t rilon.d trom . lOlA rcr.i .ndbr|! tsb. - a .how. In th. chn vi.r olth. .ll.movi.t fin dEw. i. Flrur. ll .tritha.

shown the enormous possibilities andscope of the system - and, pelhapsmore important, it had highlightedsome pitfalls. It did also indicatethat the latter were perhaps mainlydu€ to lack of familiarity wilh thesystem and that lhey could beov€rcome with more pmctice.

Results were sumciently encourag.ing to irnmediately re-equip LeadingLady with a similar device in plac€of the Russian type hook origirEllyinstalled.

(To be conlinued)

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Part 4 - concluding EltonDrew's fascinating insight tomodern A/2 glider flying, witha close look at his special ly

LDADING LADY by Elton DrewFtor cenrre ponels a circular tow derivative of 'Lavoly Lady'

THE ORTGINAL Leadins Ladrdesign was cen(red speci6cally arounda Russian-type towhook installationand intended principally for us€ in'calmish' air. It was not intended asa purely slill-air machine, but it wasto be as aerodynamically clean aspossible if only for 'design exercisesatisfaction' rather than for anypractical advantages. Thus, the de-siSn requirement was to produce amachine having a high 'still-air time'potential without any undue con-cessions being made to stability,rel iabi l i ty and'thermalabi l i ty ' and,ofcourse, able to take fulladvantage

feature the hook mounted in theconfines of a very small pylon, andthus virlually fixed in position.I wanled lo be sure that the positionchos€n would be right first time, andreference to a known layout was theeasiest means lo ensure this.

Apart from the obviously com-pletely different fuselage and all-moving fin, the only fundamentalchangc from Lively LadJ is Iherevised posilion of the dihedralbreaks and the adootion of a flatcentre section. These changes, whichresult in a slightly different wingplalform as the tips are tapered fromthe dihedral breaks, arc inler-related. The inlention was to incrqrsetorsional rigidity of the wing tocombat the possibility of flutteroccurring under high-sp€ed catapultrelease conditions. Accordiogly, the

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centre panels fcaturc a torsion box,achieved by lhe addit ion of /oin.sheet between lhe' l ' beam spars. Tokeep the moment of inert ia as low aspossible with this heavier forn o[construction. lhe inboard Danelswhere reduced in length. B€ndingstrenglh was also increased wilh theaddilion of tapcred spruce fillets tothe front spar over lhe inboard ribbays. This was only a precautionarymeasure, as the Llfelr,l,a./.t structurehas nevet given cause for concernin bending, although f lul ler doesoccur quile readily, thouglr this, too,has never produced problenrs, lnorder to ut i l ise my standard wing.bui lding board, with f ixed dihedralangle incorporated, it was decidedto us€ t ip dihedral only, lhe longertip panels giving lhe same totaldihedral for the fixed wing dihedralbreak anglc. The flat centre sectionalso fitled in conveniently with thepylon wing attachment methodchos€n. This was to bc a spring-loaded knock-off device inspired byThoman's famous ,{qrrila design, but

adapted to suit a srral l airfoi l-sectioned pylon. A vcry low dragwing mounting resul lcd, relainingmost ol the resihence and knock-olfabi l i ty of a conventional rubb€r-bandattachmenl wilh a positive locationthe latter achieved by use of an 8BAnylon screw shear pin. This ade-quately holds the wing for normalflying and landing loads, but shearsreadily on an impact.

The hearl of thc model is a nylon'plug' inserted in lhe pylon lop andattached by lhrec l0BA countersunkscrews. Sec lhe explodcd view inFigwe 12. This plug carr ies thewing l ixings and the main towhookpivot, thereby transferr ing al l towingloads directly from wing to towline.The original Russian-type hook waslater replaced by the'spring and r ing'adaplalion of the type illustrated anddescribed earlier ( FErrr? ,/0).

The 20swg duIal pylon is slotledand epoxied into the lin. diameterdural lube front fus€lage. Thishous€s thc Seelig timer, access towhich is gained by sliding lhe whole

nose ofl forward of the pylon (seephotograph). Thc tiner is activateddirectly from lhe hook lalch mecha-nisnr on release of tlre towline. Therear fuselage is a glassfibre boomspecial ly produccd by Lauric Bur-roughs, and is an cxtendcd versionof his standard Wakelield boom.This, dcspi lc i ts largcr front enddiamcter, is considerably l ighter thana convcntional A/2 glassfibre rodithe larger dianrcter pcrmitting athinner wall thickncss. This boom isattached by tlrree l0BA countersunkscrews, being rcmovablc to providcaccess 1o the'works'.

The'al l-noving' f in fol lows apractise I have used from linle totimc ovcr reccnt ycars. My interestwas aroused by an articlc by GeorgeXenakis in the American NclrbrrlFree Flight Socicty Digcst, pointil\gout that such a fin would be lesss€nsilive to airspced changes in thatthe lifi generaled by a synrmetricalseclion would not increase at thesame rate as lhat due to the sectionpresentcd by a conventional fin andrudder, which is in eflect a flappedsection. Thus. such a fin should beless l ikely to promote a spiral dive,the bane ofmost A/2 flyers from limeto l ime. Furthcr, a symmetricalsection has lcss drag than a flappedone. Small , but perhaps signiJicantadvantages. However, lhe mainattract ion lor mc was thcir simplici tyof construclion and ready inler-changeabifily if required (see Figtre1J).Th. ....mbl.d onit (d..wn oppo.itc)in...ll.d i. 'L..di.r l.dy'. Nor. rhc.diu.tm.nt .toD. .nrl th. hol. for th€.p?inr.ompr. . .or tool , Al .o v i . ib l . i ton. of thG tOlA.ount.r .unk.Gr.v.which r.t.inr th. ...r a1... fibr. boomonto th. du..l .ub.. Th. timcr i. hiddcnf.om vi.r b.hind th. d.t.Gfi.bl. tront

One frequenlly expressed cotnmentis lhal such fins must be more critrcalto adjuslment lhan the conventionalfin and rudder. In fact, I have foundthe rcverse lo be true and have be€nrather surprisc\i irt lhe large olTs€tsrequired wilh al l-moving f ins, andtheir doci l i ly.

Despite being completed in early1972, the modcl has not t tccn l lowne\tensively to date. l t is und('ubtedlyaerodynamical ly very clean. anddespite ils closc relationship to astandard a,e/,y ,Ld.t shows verydifferent flight characteristics. Inparticular, evcn lhough sections andCG posilion are idcntical, the flyingspeed is definitely faster. With thel imited f l ying undertaken, assessmentof st i l lair ' potential is di l l iculr, butindications are that i l is sl ighl lyhighcr than a srandard Lhely Lalyeven without lhe catanult heighladvantage. Whether the additionalconplexity of the model, as apractical conlcst machine, is worth-while is certainly open to question.I nrust admit, I became intr igued withthe challenge prcsented as a designexercise with regard to the installationof thc hooks and the hook-activaled

927

timer start mechanism, together withthe wing attachmcnt Delhod, etc.,and I do regard il as a very rewarding,shal l we say, diversion front lharaspect atone.

To l inish, and to cnable thisdesign lo be viewed in its correctperspective, perhaps it should bestated that it was never intended as acomplete substitute for my conven-lional A/2s, rather to supplementthem, particularly in circumslanceswhen a specialised circular towmachine can be used to advanlage.

In producing and f lying i t , I havelearnt a lot - nol al l of which is of apositive nature. However. olten'negalive' lessons are thc nlostvaluablc.

End pieceIt is hopcd and, indccd, intcnded -that lhis series o[ articles has pro-vided sonre food for thought rcgard-ing lhe use of circular k)w dcvices.

October 1975

One feels that Brilish A/2 flyers, inthe main, are too conservalive intheir approach to lhe game - it is allloo easy ro dismiss anyrhing otherthan slraightforward lactrcal ly based'flying as bcing unnecessary andunrewarding, arguing lhat lhe simpledirect approach is lhe right one forour condil ions and conlest 'scenc'.Many adopt the at l i tude that theBritish contest calendar providesnumerous gl,der evenls and lhus. i lcondi l ions on any part ic lar day donot lend thenrselves to tact ical f lying,Ihcn the clrances arc lhat those of lhenext weekend wil l . [ t is an undoubtedfact thal thc contest days which areideal ly suited lo a special isedapproach, be it a spccial still-airdesign, circular tow techniquc orwhatever, are l inr i ted.

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Aero Modellsr

However, the author feels thatwith our rather insular tendancy toignore, or too readily dismiss, suchdevelopments as circular tow, we arein danger of lalling way behind inA/2 technology. lt is my opinionthat we should give more attentionto such techniques, and not onlyadopt them but, more importantly,adapt them to suit our particularrequirements. This is surely the wayto improve the breed, not only withreeard to A/2 flying in Britain, bulalso to improve our relative standingalongside A/2 flyers internationally.Both A/2 flying technique and modeld€sign has tended to become verystereotyped in this country ovcrrecent years. This must restrict theinterest, and indeed challenge, ofer-ed by this class of model. The

928

adaptation ofdevices such as circulartow can provide a vital stimulus indesign, conslruct ion and operationof a gl ider and the polenl lal benefi lsare enormous.

Study of various foreign nraga-zines and newsletters over recentmonths indicates the developmentand usage of circular tow is givenmuch more attention than in GreatBritain. As a final point, I wouldmention that at the 1973 WorldChampionships circular tow wasemployed by many conrpetitors, notleast of all by Ekhtenkov, theRussian winner, and the runner-up,Krejcirik from Czechoslovakia, bothfrom countries where the systen hasbeen largely pioneered and isextensively used.

We can be certain that Ekheten-

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kov's world Championship vicrorywil l not be lhe last to be gained usingctrcular tow-