Exotic Rotors Heli

Bearingless main rotor heads LAST MONTHS article examined var- coming technology Air resonance occurs rotor jous rigid hingeless bearingless modelblade lead-lag frequency coalesces rotor head designs RC model Helicop- helicopters intoof fuselage structural frequencies ters month will zoom 6-ft-each oscillatory action excites other dia bearingless rotor currently being used 1 990SThe result Helicopter self-destructs conduct- Ground resonance occurs Heli scientific research purposes ByDesia n i ng andcopter still ground pilot ing wind tunnel tests rotor system pe advance knowledge towardtesting modelrevving up blade blade lead-lag fre goal designing successful bearing-quency coincides natural frequency less rotor future full-size helicopter ap-bearingless rotor isof flexible landing gear machine plicationswill begin rock laterallyand de design emphasis l990s ona critical step thestroyed within few seconds Fortunately development workable bearinglessthe pilot can quickly negate air ground rotor because simplicity sys-development ofresonance problems changing rotor tem has low parts count aerodynam-rpm ically clean has no mechanical compo-functional rotor blades chordwise center nents wear outreliable forof-gravity farther 30% behind lead beauty bearingless rotor sys- ystemsing edge prone aeroelastic insta tem no mechanical bearingsbility chordwise CG slightly hinges Blade flapping lead-lagging orfullsizeward 25% coincide airfoil pitch change feathering accom- heaerodynamic center system likely plished elastically bending twistingbe aeroelastically stable Other design pathe flexible rotor hub flexible part oframeters may induce rotor aeroelastic model Helicopterinstability too-soft rotor flap stiffness hub called flexbeam Bearingless rotors however difficultfraternity benefitsblades torsionally too soft too-soft design properly Avoiding aeroelasticcontrol linkages too much flexibility aeromechanical instability majorfrom what nedcyclic collective control setup too-large challenge Thats such extensive theo-blade radius too-small chord insuffi retical experimental research has goneConclusion twocient blade torsional inertia Helicopter ro development bearingless rotors designers take variables full-size helicopter industry duringpart seriesconsideration ensure given rotor last 10 years ngwill safe through entire flight enve uames IVilope Before look bearingless model ro tor lets disuss aeroelastic aerome chanical instability its impact RC model Helicopters certain flight conditions main ro tor blades may become unstable begin flapping up down wildly called aerodynamic instability pilot doesnt correct instability immediately whole system will quickly disintegrate Aeroelastic stability solely dependent main rotor blade design Aeromechanical stability other hand function blade rotor fuselage interacting whole Air reso nance ground resonance examples iver ryiar nere aeromechanical instability reso-b0.gless model rotor being tested Thisis called closed-return wind tunnel De cause air driven 2000-hp electric motor around circular tunnel seven-bladed nances extremely destructivefan made up cut-down ww II 6-29 propeller blades Windspeeds can reach 100 mph May 1990 83 Design engineers must examine pa rameters carefully hingeless bearingless rotors articulating teetering rotors Since flapping leadlagging feathering actions achieved deforming rotor hub struc ture hingeless bearingless rotors good structural couplings may initiate unwanted control move ments pilot attempting change pitch recent develop ment technology properly analyze such strongly coupled structural system hingeless bearingless rotors have acquired new popularity two categories helicopter rotor blade aeroelastic instability designers must consider divergence flutter Lets examine turn Divergence static instability poorly designed blade divergence can occur flight cause blade snap off creasing torsional stiffness blade system will prevent divergence well correct tendency flutter Since model rotor blades already very rigid tor sional stiffness must increased primarily adding tension control linkage Tightening up control system using stiff pushrods strong bellcranks avoid ing long servo arms builds slight amount friction Friction may bad control crispness its good aeroelastic stabil ity Flutter dynamic aeroelastic instability caused interaction aerodynamics elastic inertial forces selfsustained oscillation driven above three forces its different resonance forced-response oscillations types flutter two important pitch-flap flutter flap-lag flutter Pitch-flap flutter helicopter rotor blades similar airplane wing flutter up-and-down flapping occurs poorly designed wing excited gust As wing blade flaps up leading edge twists upward producing lift mak ing blade want flap up As flaps down leading edge twists down ward lift reduced making blade want flap lower Eventually os cillation amplitude increases point structural failure occursthe wing blade snaps off process may take few seconds Flap-lag flutter peculiar rotor blades condition due blades flap motion lead-lag motion being coupled through Coriolis force ag gravated negative aerodynamic damp ing Coriolis force alaw physics dictates blade flaps up will swing forward lead burn up its extra ro tational energy Conversely blade flaps down rotational energy falls blade lags back poorly designed blade ag gravates oscillatory motion cer tain flight conditions aerodynamic force blade elastic force inertial force enthus iastically unite break up blade Flutter isnt usually problem RC model Helicopters because rotor blades controls considerably stiffer used full-sized choppers However certain conditions pres ent flutter can occur instability mani fests itself model rotor blades sud denly becoming wildly out track much five six inches Some modelers call phenomenon woof Once perturbation triggers flutter bringing model out critical operat ing sphere wont usually stop wild flap ping flier has two choices can land Helicopter immediatelyor try pick soft crash site What combination factors promotes flutter RC Helicopters High rpm very lightweight blades blade lead-lag too loose flexible control rods using outermost hole servo control arms torsionally soft blades chordwise cen ter-of-gravity forward 20% aft 35% conditions may lead flutter Once have volatile mix ingredi ents flutter may triggered aerody 84 Model Aviation Figure 2 1/8th-scale model future bearingless rotor full-size helicopter appli cations 6-ft-dia model rotor undergoing hover simulation tests 817 rpm deter aeroelastic stability floor panels have removed prevent rotor downwash impinging floor forward flight simulations floor panels replaced Figure 3 Bearingless rotor heads thing iggOs no flap hinges lead-lag hinges feathering bearings Blade motion controlled flexing elastic flex beam shown photo flexbeam machined Torlon synthetic petroleum based material strong steel 100 times costlier flexbeam performs same functions flap hinge lead-lag hinge feathering hinge very stiff fiberglass tube called cuff fits outside flexbeam control pitch angle blade namic perturbations such stalling blades high-G maneuver tight turn unsteadiness caused suddenly changing collective pitch setting maneuver distorts rotor inflow Though av erage flier never encounters flutter should aware does happen best way avoid pitch-flap flaplag aeroelastic instability RC Helicop ter select forward location blade chordwise center-of-gravity 23% 27% ideal prevents flutter pitch divergence hut helps stabilize entire model Other preventive mea sures include decreasing aspect ratio blade shortening rotor diame ter tightening rotor head flap stiffness compressing rubber damper 0ring adding Delta-3 flap hinge offset Delta-3 flap hinge offset discussed article Heli Flap Stabilizing Feed back May 1989 Model Aviation type offset prevents pitch-flap flut ter has greater stabilizing effect blade Helicopter whole X-Cell has Delta-3 flap hinge offset tail rotor reduce excessive tail ro tor flapping forward flight Delta-3 used GMP Legends flybarless main rotor head reduces main rotor blade flapping improves hover forward flight stability gusts Another modification lag-hinge offset known Delta-4 used prevent flaplag flutter full-size helicopters ever since mechanical lead-lag damper usually installed dampen blades leadlag motion Delta-4 often used il lustrated article explaining lag damper appeared June 1989 issue Model Builder RC Helicopters having rotor hubs built-in coning angle may also less prone flap-lag flutter modifica tion would undesirable pilots like fly models inverted Flutter may occur rotor thrust lev el disturbance has observed near 00 collective pitch RC models Nonrotating model Helicopter blades wind tunnel tests have observed stall 00 angle attack could due leading edge air bubble bursting flow separation caused bubble failing re attach separated flow generates un steady aerodynamic forces excite models rotor blades causing flap up down wildly Because small chord low operating tip speed giving lower Reynolds numbers compared full-size helicopter blades seems oc cur model blades weighted blade seems alleviate problem increasing centrifugal force keeping blade taut Roughing up leading edge blade 100-grit coarse sandpaper increases effective Reynolds number helps prevent flow separation 00 angle attack Rounding off leading edge blade also helps reducing blade pitch change sensitivity Similarly sanding leading edge Hiller paddles slightly blunt will desensitize cyclic controls -t6e Hub0 Pitch liiikade Figure 4 Boeing design example proposed bearingless rotor de signs future helicopters BO-108 helicopter introduced Germanys MBB Company 1989 worlds first full-size production helicopter employing bearingless main rotor May 1990 85 Figure 5 objective wind tunnel test determine aeroelastic stability new bearingless rotor design author built set blades improve stall angle Figure 6 set swept-tip blades similar used Apache AH-64 Besides aeroelastic stability tests also interest studying aerodynamic dy namic effects advanced tip designs swept-tip blade employed full-size hel icopters prevent supersonic airflow near blade tip found useless model rotor blade applications since dont rotate anywhere near supersonic speeds bearingless rotor featured arti cle originally designed Boeing Heli copter Company future combat heli copter wind tunnel model exact A-scale replica proposed design Scaling down full-size rotor use aeroelastic research exacting compli cated procedure stiffness mass distri bution inertia rotor blade flexbeam pitch link must scaled Glenn L Martin wind tunnel testing down using special law physics called conducted Its called closed-return Froude Scale Since RC model Helicop- wind tunnel because air driven around ter blades actually much stiffer circular tunnel 2000-hp electric motor what Froude Scale dictates models seven-bladed fan fan about 15 capable performing incredible anti- ft diameter blades cut-down gravity stunts arent possible World War II B-29 bomber propellers full-size counterparts test section wind velocity can reach 300 Figure 1 depicts floor plan mph Continued page 19] Left Figure 7 technician left adjusting rotor blade pitch angle achieve proper tracking helper blade wood block attached mounted electronic inclinometer used electronically Right Figure 8 Close-up beefy swashplate scissor unit makes inner swashplate turn LIIdI black cylinders hydraulic servo actuators control pitch cyclic roll cyclic collective Collective pitch corILIuIu jui X-Cell RC Helicopters sliding swashplate up down solid 4 x 4-in steel block lower right-hand corner actually six-component balance measures thrust drag force side force torque pitching moment rolling moment main rotor Left Figure 9 wind tunnel control room During testing seats occupied operators captain sits cente ls out test sequence computer left operator calculates rotor lead-lag damping control wild blade lea television monitor hanging ceiling displays rotor during tests Right Figure 10 rotor control console operatol six knobs console control collective longitudinal cyclic lateral cyclic main rotor shaft fore/aft tilt angle rotoi .. 86 Model Aviation Left Figure 11 An array data gathering monitoring instrumentation signal conditioners instrument amplifiers frequency counters computer interface strip chart recorder Right Figure 12 rats nest wires plugs cables behind instrumentation Figure 2 shows model bearingless ro tor undergoing hover tests determine aeroelastic stability new design floor panels removed prevent rotor down-wash impinging floor forward flight simulations floor panels replaced Figure 3 shows excellent flexibility elastic flexbeam Machined syn thetic petroleum material called Torlon flexbeam acts like flap hinge lead-lag hinge feathering hinge very stiff fi berglass tube called cuff fits out side flexbeam control pitch gle blade pitch link attached cuff Figure 4 illustration rotor hub Figure 5 shows special set blades built improving stall angle Fig ure 6 shows set swept-tip blades similar used Apache AH-64 type sweptback tip used full-size hel icopters prevent supersonic flow near blade tip just sweeping wings back jet aircraft will delay supersonic flow Since rotor tips RC Helicopters dont approach supersonic speeds swept tips useless Measuring blade pitch angle $100000 rotor model like being tested ought get rather fancyand does individual right Figure 7 holding wooden airfoil template Attached electronic inclinometer mea sures tilt angle blade Figure 8 shows beefy swashplate three hydraulic servo actuators con trol pitch cyclic roll cyclic collective Collective pitch controlled just GMP X-Cell RC Helicopters sliding swashplate up down three control actuators driven hydraulic fluid pumping fluid either end moves piston inside actu ator pneumatic retractable landing gear systems RC model airplanes work similar principle solid 4 x 4-in steel block lower right-hand corner actu ally six-component balance measures thrust drag force side force torque pitching moment rolling moment main rotor balance alone costs approx imately $20000 Figure 9 shows control room computer console seen left oper ator calculates rotor lead-lag damping ensure blades wont lead-lag wildly television monitor ceiling displays rotor during tests anything goes wrong tunnel air velocity shut down immediately rotor stopped case rotor should fail during wind tunnel tests glass window covered A-in steel plate mounted h-in-thick plywood board safety barrier can seen Figures 9 10 model rotor tested 817 rpm Most RC model Helicopter rotors turn 1500 rpm higher pilot usually stands within five 15 ft protec tion scares lot wind tunnel en gineer friends bank data gathering recording devices shown righthand side Figure 9 Figure 10 shows control console Theres no joystick fly bearingless ro tor operator pilot uses five knobs THIRTY-SIXTH ANNUAL RADIO CONTROL EXPOSITION APRIL 6 7 8 1990 FRIDAY9am to6pm SATURDAY9am to6pm SUNDAY9 am 430 pm TOLEDO SPORTS ARENA ONE MAIN STREET TOLEDO OHIO TICKETS can purchased door ADVANCE sending self-addressed stamped business size 41/ex91h envelope TICKETS 38235 Castle Romulus Ml 48174 orders above 10 tickets must include double postage US orders must include 25 cents per order handling charge foreign orders must include 50 cents per order handling charge need send addressed envelope will provide necessary postage NOTE Registered Express Type Mail Orders Will Accepted! Include check money order US funds made payable Weak Signals R/C Club Ticket prices $400 per day adults $100 per dayfor children 12 under Please specify number Deadline ticket orders March 30 1990 sales final non-refundable Hotel info map area may obtained sending stamped self-addressed envelope ticket address above Any other Exposition information avail able contacting Wayne Veager co director ticket address phone 313941-6661 We Will Have TraditionalSwap Shop Saturday Night Auction COMPETITION CLASSES NON-MILITARY SPORT SCALE PLANE AMA Rules MILITARY SPORT SCALE PLANE AMA Rules PRECISION SCALE PLANE AMA Rules PATTERN PLANE No Jets SPORT MONO-PLANE non-scale models SPORT BI-PLANE non-scale models OLD TIMER FREE FLIGHT R/C ASSIST R/C SAILPLANE non-scale models No Engines HELICOPTER R/C CAR COMPETITION BOAT MILITARY SCALE BOAT PLEASURE POWER BOAT WORKING VESSEL-UNARMED presented Weak Signals R/C Club Toledo Ohio May1990 191 later Happy Landings Hell Rotors/Wang Continued page 86 1t US RIC Flight School Stop Crashing Start Learning CLASSES FILLING FAST Info pack $300 1st US RIC FLIGHT SCHOOL 521 S Sawyer. Shawano WI 541N d7lRl K2A-0ftR Rubber ft Onglne Power Free Flight Display control LIne ElectrIc Power RJC Airplanes new Illustrated 32 page tabloId size catalog us & canada *ia@ Forelgh *300 Penn Valley Hobby center 837A W Main St Lansdala PA 19440 2153684770 -uEEEEEEEEEmEEE U mum mu mm umm U mum BIG GLOW FUEL MANUFACTURED WITH THE PUREST FINEST QUALITY INGREDIENTS AVAILABLE * *I * * *at * U U U U U U U U S I] Superior Igniters Improve starting idle acceleration Youll notice power bargain fuels Special Detergents Promote clean burning prevent residue buildup Rust Inhibitors Protect engines corrosion After run oil needed engines Film Strength Additives Increase lubricity provide extra lean run protection Anti-Wear Additives Help keep engines running peak performance longer Satisfaction Guaranteed FREE SHIPPING ON ORDERS OVER $1500 SIG CHAMPION 2-STROKE FUEL P4NT 9UART GALLON 0%Nitrontetftne$10 75 5%Nitroithane$65$525$1275 10%Nitro~i$4 15~4Q$1475 15%Nltrom~han$43O$6~$1675 25%Nitrom1I34$21 95 35%Nitromethane$595$925$2695 SIGPREMIUM 4-STROKE FUEL 10% Nitromethane$1425 15% Nitromethane$1625 THE CHOICE OF CHAMPION FLYERS U aver 20 years SIG has blending finest quality model engine fuel available using finest quality ingredients instance Methanol use 995% pure very best grade money can buy also use real 100% pure U Nitromethane get full measure youve paid based honest percentage-of-volume I method percentage weight SIG fuels contam 50-50 blend Bakers purest AA Castor Oil new improved Klotz Techniplate Synthetic Racing Oil U for maximum engine lubrication protection Based experience sincerely believe finest quality fuel can made price dont take word try some judge yourself Pcos sobiod obonge wthoot ,otice See dealer first available order direct Call LZJ 800-247-5008 toll free orders Latest Catalog $300 MANUFACTURING CO Montezuma IA 50171 Dynamic Duo Durability Stand Ready Help Take Encounters Planet Earth scuffle ground isnt some thing should have face own may have gotten own dont think model should stand After two team So join up airplanes thatll stick through thick thin Dumcmft Inc 71007 Qdwd Grove Orwe Royai Oak NI 48067 DuraPlane II 25-size 3-channel basic flight trainer DuraBat 40-size 4-channel aerobatic trainer U U I U U U i I U U U I I U U set rotors collective pitch longitudinal cyclic lateral cyclic main rotor fore/aft shaft tilt angle rpm Figure 11 shows signal processing equipment signal conditioners instrument amplifiers frequency counters computer interface strip chart recorder sig nals monitored include flapping angle lead-lag angle pitch angle four blades flexheams bending twisting strain rotors pitching roll ing moments thrust drag forces flap bending moment blade number rpm plotted continuously strip chart recorder Figure 12 gives some idea nest wires behind instrumentation valuable data collected phenom ena being observed wind tunnel tests bring us nearer goal better safer helicopter 21st century Ligeti Stratos Continued page 100 time George Sauers called tell gained access CADCAM machine plugged models dimensions come up new computer-generated balance point computer agreed calculations within 4 reweighed nose wheel came out weighing 3/2 lb like wheel changes original shroud re moved close attaining flight speed time absolutely knew Stratos would fly next time out after Ed showed off around town club meeting folks still convinced wouldnt fly day flew things just felt right very tense excited weather forecast called 5-15-mph winds out north right down runwaya downhill run north wind summer God side course arrived field wind stronger shifted east-northeast much takeoff room direction grass hadnt mowed So before could attempt fly mow grass devil time getting mower started finally succeeded sec ond pass wind increased temperature dropped fourth pass getting rained jaw muscles set mind clicked lock Reason no longer functioned going fly airplane today moment Bob Terhune showed up saw look face jumped other mower Just quickly rain sub sided George showed up ran model through series taxi tests looked con vincing Other people began showing up hanging around picnic table knew figured airplane went hogwild started attacking everybody theyd just duck under wind dropped dead calm conver sation stopped Stratos started down runway its first takeoff attempt Speed gathered slowly first faster faster Lift-off still get goose bumps just thinking about longawaited moment George Sauers sticks Just after lift off wing dropped dangerously corrected instantly smoothed Out headed out over Continued page 196 192 Model Aviation U U U U U U U U U U i U U U U U U I I U U E ER K EUUEUUUUU

Bearingless main rotor heads LAST MONTHS article examined var- coming technology Air resonance occurs rotor jous rigid hingeless bearingless modelblade lead-lag frequency coalesces rotor head designs RC model Helicop- helicopters intoof fuselage structural frequencies ters month will zoom 6-ft-each oscillatory action excites other dia bearingless rotor currently being used 1 990SThe result Helicopter self-destructs conduct- Ground resonance occurs Heli scientific research purposes ByDesia n i ng andcopter still ground pilot ing wind tunnel tests rotor system pe advance knowledge towardtesting modelrevving up blade blade lead-lag fre goal designing successful bearing-quency coincides natural frequency less rotor future full-size helicopter ap-bearingless rotor isof flexible landing gear machine plicationswill begin rock laterallyand de design emphasis l990s ona critical step thestroyed within few seconds Fortunately development workable bearinglessthe pilot can quickly negate air ground rotor because simplicity sys-development ofresonance problems changing rotor tem has low parts count aerodynam-rpm ically clean has no mechanical compo-functional rotor blades chordwise center nents wear outreliable forof-gravity farther 30% behind lead beauty bearingless rotor sys- ystemsing edge prone aeroelastic insta tem no mechanical bearingsbility chordwise CG slightly hinges Blade flapping lead-lagging orfullsizeward 25% coincide airfoil pitch change feathering accom- heaerodynamic center system likely plished elastically bending twistingbe aeroelastically stable Other design pathe flexible rotor hub flexible part oframeters may induce rotor aeroelastic model Helicopterinstability too-soft rotor flap stiffness hub called flexbeam Bearingless rotors however difficultfraternity benefitsblades torsionally too soft too-soft design properly Avoiding aeroelasticcontrol linkages too much flexibility aeromechanical instability majorfrom what nedcyclic collective control setup too-large challenge Thats such extensive theo-blade radius too-small chord insuffi retical experimental research has goneConclusion twocient blade torsional inertia Helicopter ro development bearingless rotors designers take variables full-size helicopter industry duringpart seriesconsideration ensure given rotor last 10 years ngwill safe through entire flight enve uames IVilope Before look bearingless model ro tor lets disuss aeroelastic aerome chanical instability its impact RC model Helicopters certain flight conditions main ro tor blades may become unstable begin flapping up down wildly called aerodynamic instability pilot doesnt correct instability immediately whole system will quickly disintegrate Aeroelastic stability solely dependent main rotor blade design Aeromechanical stability other hand function blade rotor fuselage interacting whole Air reso nance ground resonance examples iver ryiar nere aeromechanical instability reso-b0.gless model rotor being tested Thisis called closed-return wind tunnel De cause air driven 2000-hp electric motor around circular tunnel seven-bladed nances extremely destructivefan made up cut-down ww II 6-29 propeller blades Windspeeds can reach 100 mph May 1990 83 Design engineers must examine pa rameters carefully hingeless bearingless rotors articulating teetering rotors Since flapping leadlagging feathering actions achieved deforming rotor hub struc ture hingeless bearingless rotors good structural couplings may initiate unwanted control move ments pilot attempting change pitch recent develop ment technology properly analyze such strongly coupled structural system hingeless bearingless rotors have acquired new popularity two categories helicopter rotor blade aeroelastic instability designers must consider divergence flutter Lets examine turn Divergence static instability poorly designed blade divergence can occur flight cause blade snap off creasing torsional stiffness blade system will prevent divergence well correct tendency flutter Since model rotor blades already very rigid tor sional stiffness must increased primarily adding tension control linkage Tightening up control system using stiff pushrods strong bellcranks avoid ing long servo arms builds slight amount friction Friction may bad control crispness its good aeroelastic stabil ity Flutter dynamic aeroelastic instability caused interaction aerodynamics elastic inertial forces selfsustained oscillation driven above three forces its different resonance forced-response oscillations types flutter two important pitch-flap flutter flap-lag flutter Pitch-flap flutter helicopter rotor blades similar airplane wing flutter up-and-down flapping occurs poorly designed wing excited gust As wing blade flaps up leading edge twists upward producing lift mak ing blade want flap up As flaps down leading edge twists down ward lift reduced making blade want flap lower Eventually os cillation amplitude increases point structural failure occursthe wing blade snaps off process may take few seconds Flap-lag flutter peculiar rotor blades condition due blades flap motion lead-lag motion being coupled through Coriolis force ag gravated negative aerodynamic damp ing Coriolis force alaw physics dictates blade flaps up will swing forward lead burn up its extra ro tational energy Conversely blade flaps down rotational energy falls blade lags back poorly designed blade ag gravates oscillatory motion cer tain flight conditions aerodynamic force blade elastic force inertial force enthus iastically unite break up blade Flutter isnt usually problem RC model Helicopters because rotor blades controls considerably stiffer used full-sized choppers However certain conditions pres ent flutter can occur instability mani fests itself model rotor blades sud denly becoming wildly out track much five six inches Some modelers call phenomenon woof Once perturbation triggers flutter bringing model out critical operat ing sphere wont usually stop wild flap ping flier has two choices can land Helicopter immediatelyor try pick soft crash site What combination factors promotes flutter RC Helicopters High rpm very lightweight blades blade lead-lag too loose flexible control rods using outermost hole servo control arms torsionally soft blades chordwise cen ter-of-gravity forward 20% aft 35% conditions may lead flutter Once have volatile mix ingredi ents flutter may triggered aerody 84 Model Aviation Figure 2 1/8th-scale model future bearingless rotor full-size helicopter appli cations 6-ft-dia model rotor undergoing hover simulation tests 817 rpm deter aeroelastic stability floor panels have removed prevent rotor downwash impinging floor forward flight simulations floor panels replaced Figure 3 Bearingless rotor heads thing iggOs no flap hinges lead-lag hinges feathering bearings Blade motion controlled flexing elastic flex beam shown photo flexbeam machined Torlon synthetic petroleum based material strong steel 100 times costlier flexbeam performs same functions flap hinge lead-lag hinge feathering hinge very stiff fiberglass tube called cuff fits outside flexbeam control pitch angle blade namic perturbations such stalling blades high-G maneuver tight turn unsteadiness caused suddenly changing collective pitch setting maneuver distorts rotor inflow Though av erage flier never encounters flutter should aware does happen best way avoid pitch-flap flaplag aeroelastic instability RC Helicop ter select forward location blade chordwise center-of-gravity 23% 27% ideal prevents flutter pitch divergence hut helps stabilize entire model Other preventive mea sures include decreasing aspect ratio blade shortening rotor diame ter tightening rotor head flap stiffness compressing rubber damper 0ring adding Delta-3 flap hinge offset Delta-3 flap hinge offset discussed article Heli Flap Stabilizing Feed back May 1989 Model Aviation type offset prevents pitch-flap flut ter has greater stabilizing effect blade Helicopter whole X-Cell has Delta-3 flap hinge offset tail rotor reduce excessive tail ro tor flapping forward flight Delta-3 used GMP Legends flybarless main rotor head reduces main rotor blade flapping improves hover forward flight stability gusts Another modification lag-hinge offset known Delta-4 used prevent flaplag flutter full-size helicopters ever since mechanical lead-lag damper usually installed dampen blades leadlag motion Delta-4 often used il lustrated article explaining lag damper appeared June 1989 issue Model Builder RC Helicopters having rotor hubs built-in coning angle may also less prone flap-lag flutter modifica tion would undesirable pilots like fly models inverted Flutter may occur rotor thrust lev el disturbance has observed near 00 collective pitch RC models Nonrotating model Helicopter blades wind tunnel tests have observed stall 00 angle attack could due leading edge air bubble bursting flow separation caused bubble failing re attach separated flow generates un steady aerodynamic forces excite models rotor blades causing flap up down wildly Because small chord low operating tip speed giving lower Reynolds numbers compared full-size helicopter blades seems oc cur model blades weighted blade seems alleviate problem increasing centrifugal force keeping blade taut Roughing up leading edge blade 100-grit coarse sandpaper increases effective Reynolds number helps prevent flow separation 00 angle attack Rounding off leading edge blade also helps reducing blade pitch change sensitivity Similarly sanding leading edge Hiller paddles slightly blunt will desensitize cyclic controls -t6e Hub0 Pitch liiikade Figure 4 Boeing design example proposed bearingless rotor de signs future helicopters BO-108 helicopter introduced Germanys MBB Company 1989 worlds first full-size production helicopter employing bearingless main rotor May 1990 85 Figure 5 objective wind tunnel test determine aeroelastic stability new bearingless rotor design author built set blades improve stall angle Figure 6 set swept-tip blades similar used Apache AH-64 Besides aeroelastic stability tests also interest studying aerodynamic dy namic effects advanced tip designs swept-tip blade employed full-size hel icopters prevent supersonic airflow near blade tip found useless model rotor blade applications since dont rotate anywhere near supersonic speeds bearingless rotor featured arti cle originally designed Boeing Heli copter Company future combat heli copter wind tunnel model exact A-scale replica proposed design Scaling down full-size rotor use aeroelastic research exacting compli cated procedure stiffness mass distri bution inertia rotor blade flexbeam pitch link must scaled Glenn L Martin wind tunnel testing down using special law physics called conducted Its called closed-return Froude Scale Since RC model Helicop- wind tunnel because air driven around ter blades actually much stiffer circular tunnel 2000-hp electric motor what Froude Scale dictates models seven-bladed fan fan about 15 capable performing incredible anti- ft diameter blades cut-down gravity stunts arent possible World War II B-29 bomber propellers full-size counterparts test section wind velocity can reach 300 Figure 1 depicts floor plan mph Continued page 19] Left Figure 7 technician left adjusting rotor blade pitch angle achieve proper tracking helper blade wood block attached mounted electronic inclinometer used electronically Right Figure 8 Close-up beefy swashplate scissor unit makes inner swashplate turn LIIdI black cylinders hydraulic servo actuators control pitch cyclic roll cyclic collective Collective pitch corILIuIu jui X-Cell RC Helicopters sliding swashplate up down solid 4 x 4-in steel block lower right-hand corner actually six-component balance measures thrust drag force side force torque pitching moment rolling moment main rotor Left Figure 9 wind tunnel control room During testing seats occupied operators captain sits cente ls out test sequence computer left operator calculates rotor lead-lag damping control wild blade lea television monitor hanging ceiling displays rotor during tests Right Figure 10 rotor control console operatol six knobs console control collective longitudinal cyclic lateral cyclic main rotor shaft fore/aft tilt angle rotoi .. 86 Model Aviation Left Figure 11 An array data gathering monitoring instrumentation signal conditioners instrument amplifiers frequency counters computer interface strip chart recorder Right Figure 12 rats nest wires plugs cables behind instrumentation Figure 2 shows model bearingless ro tor undergoing hover tests determine aeroelastic stability new design floor panels removed prevent rotor down-wash impinging floor forward flight simulations floor panels replaced Figure 3 shows excellent flexibility elastic flexbeam Machined syn thetic petroleum material called Torlon flexbeam acts like flap hinge lead-lag hinge feathering hinge very stiff fi berglass tube called cuff fits out side flexbeam control pitch gle blade pitch link attached cuff Figure 4 illustration rotor hub Figure 5 shows special set blades built improving stall angle Fig ure 6 shows set swept-tip blades similar used Apache AH-64 type sweptback tip used full-size hel icopters prevent supersonic flow near blade tip just sweeping wings back jet aircraft will delay supersonic flow Since rotor tips RC Helicopters dont approach supersonic speeds swept tips useless Measuring blade pitch angle $100000 rotor model like being tested ought get rather fancyand does individual right Figure 7 holding wooden airfoil template Attached electronic inclinometer mea sures tilt angle blade Figure 8 shows beefy swashplate three hydraulic servo actuators con trol pitch cyclic roll cyclic collective Collective pitch controlled just GMP X-Cell RC Helicopters sliding swashplate up down three control actuators driven hydraulic fluid pumping fluid either end moves piston inside actu ator pneumatic retractable landing gear systems RC model airplanes work similar principle solid 4 x 4-in steel block lower right-hand corner actu ally six-component balance measures thrust drag force side force torque pitching moment rolling moment main rotor balance alone costs approx imately $20000 Figure 9 shows control room computer console seen left oper ator calculates rotor lead-lag damping ensure blades wont lead-lag wildly television monitor ceiling displays rotor during tests anything goes wrong tunnel air velocity shut down immediately rotor stopped case rotor should fail during wind tunnel tests glass window covered A-in steel plate mounted h-in-thick plywood board safety barrier can seen Figures 9 10 model rotor tested 817 rpm Most RC model Helicopter rotors turn 1500 rpm higher pilot usually stands within five 15 ft protec tion scares lot wind tunnel en gineer friends bank data gathering recording devices shown righthand side Figure 9 Figure 10 shows control console Theres no joystick fly bearingless ro tor operator pilot uses five knobs THIRTY-SIXTH ANNUAL RADIO CONTROL EXPOSITION APRIL 6 7 8 1990 FRIDAY9am to6pm SATURDAY9am to6pm SUNDAY9 am 430 pm TOLEDO SPORTS ARENA ONE MAIN STREET TOLEDO OHIO TICKETS can purchased door ADVANCE sending self-addressed stamped business size 41/ex91h envelope TICKETS 38235 Castle Romulus Ml 48174 orders above 10 tickets must include double postage US orders must include 25 cents per order handling charge foreign orders must include 50 cents per order handling charge need send addressed envelope will provide necessary postage NOTE Registered Express Type Mail Orders Will Accepted! Include check money order US funds made payable Weak Signals R/C Club Ticket prices $400 per day adults $100 per dayfor children 12 under Please specify number Deadline ticket orders March 30 1990 sales final non-refundable Hotel info map area may obtained sending stamped self-addressed envelope ticket address above Any other Exposition information avail able contacting Wayne Veager co director ticket address phone 313941-6661 We Will Have TraditionalSwap Shop Saturday Night Auction COMPETITION CLASSES NON-MILITARY SPORT SCALE PLANE AMA Rules MILITARY SPORT SCALE PLANE AMA Rules PRECISION SCALE PLANE AMA Rules PATTERN PLANE No Jets SPORT MONO-PLANE non-scale models SPORT BI-PLANE non-scale models OLD TIMER FREE FLIGHT R/C ASSIST R/C SAILPLANE non-scale models No Engines HELICOPTER R/C CAR COMPETITION BOAT MILITARY SCALE BOAT PLEASURE POWER BOAT WORKING VESSEL-UNARMED presented Weak Signals R/C Club Toledo Ohio May1990 191 later Happy Landings Hell Rotors/Wang Continued page 86 1t US RIC Flight School Stop Crashing Start Learning CLASSES FILLING FAST Info pack $300 1st US RIC FLIGHT SCHOOL 521 S Sawyer. Shawano WI 541N d7lRl K2A-0ftR Rubber ft Onglne Power Free Flight Display control LIne ElectrIc Power RJC Airplanes new Illustrated 32 page tabloId size catalog us & canada *ia@ Forelgh *300 Penn Valley Hobby center 837A W Main St Lansdala PA 19440 2153684770 -uEEEEEEEEEmEEE U mum mu mm umm U mum BIG GLOW FUEL MANUFACTURED WITH THE PUREST FINEST QUALITY INGREDIENTS AVAILABLE * *I * * *at * U U U U U U U U S I] Superior Igniters Improve starting idle acceleration Youll notice power bargain fuels Special Detergents Promote clean burning prevent residue buildup Rust Inhibitors Protect engines corrosion After run oil needed engines Film Strength Additives Increase lubricity provide extra lean run protection Anti-Wear Additives Help keep engines running peak performance longer Satisfaction Guaranteed FREE SHIPPING ON ORDERS OVER $1500 SIG CHAMPION 2-STROKE FUEL P4NT 9UART GALLON 0%Nitrontetftne$10 75 5%Nitroithane$65$525$1275 10%Nitro~i$4 15~4Q$1475 15%Nltrom~han$43O$6~$1675 25%Nitrom1I34$21 95 35%Nitromethane$595$925$2695 SIGPREMIUM 4-STROKE FUEL 10% Nitromethane$1425 15% Nitromethane$1625 THE CHOICE OF CHAMPION FLYERS U aver 20 years SIG has blending finest quality model engine fuel available using finest quality ingredients instance Methanol use 995% pure very best grade money can buy also use real 100% pure U Nitromethane get full measure youve paid based honest percentage-of-volume I method percentage weight SIG fuels contam 50-50 blend Bakers purest AA Castor Oil new improved Klotz Techniplate Synthetic Racing Oil U for maximum engine lubrication protection Based experience sincerely believe finest quality fuel can made price dont take word try some judge yourself Pcos sobiod obonge wthoot ,otice See dealer first available order direct Call LZJ 800-247-5008 toll free orders Latest Catalog $300 MANUFACTURING CO Montezuma IA 50171 Dynamic Duo Durability Stand Ready Help Take Encounters Planet Earth scuffle ground isnt some thing should have face own may have gotten own dont think model should stand After two team So join up airplanes thatll stick through thick thin Dumcmft Inc 71007 Qdwd Grove Orwe Royai Oak NI 48067 DuraPlane II 25-size 3-channel basic flight trainer DuraBat 40-size 4-channel aerobatic trainer U U I U U U i I U U U I I U U set rotors collective pitch longitudinal cyclic lateral cyclic main rotor fore/aft shaft tilt angle rpm Figure 11 shows signal processing equipment signal conditioners instrument amplifiers frequency counters computer interface strip chart recorder sig nals monitored include flapping angle lead-lag angle pitch angle four blades flexheams bending twisting strain rotors pitching roll ing moments thrust drag forces flap bending moment blade number rpm plotted continuously strip chart recorder Figure 12 gives some idea nest wires behind instrumentation valuable data collected phenom ena being observed wind tunnel tests bring us nearer goal better safer helicopter 21st century Ligeti Stratos Continued page 100 time George Sauers called tell gained access CADCAM machine plugged models dimensions come up new computer-generated balance point computer agreed calculations within 4 reweighed nose wheel came out weighing 3/2 lb like wheel changes original shroud re moved close attaining flight speed time absolutely knew Stratos would fly next time out after Ed showed off around town club meeting folks still convinced wouldnt fly day flew things just felt right very tense excited weather forecast called 5-15-mph winds out north right down runwaya downhill run north wind summer God side course arrived field wind stronger shifted east-northeast much takeoff room direction grass hadnt mowed So before could attempt fly mow grass devil time getting mower started finally succeeded sec ond pass wind increased temperature dropped fourth pass getting rained jaw muscles set mind clicked lock Reason no longer functioned going fly airplane today moment Bob Terhune showed up saw look face jumped other mower Just quickly rain sub sided George showed up ran model through series taxi tests looked con vincing Other people began showing up hanging around picnic table knew figured airplane went hogwild started attacking everybody theyd just duck under wind dropped dead calm conver sation stopped Stratos started down runway its first takeoff attempt Speed gathered slowly first faster faster Lift-off still get goose bumps just thinking about longawaited moment George Sauers sticks Just after lift off wing dropped dangerously corrected instantly smoothed Out headed out over Continued page 196 192 Model Aviation U U U U U U U U U U i U U U U U U I I U U E ER K EUUEUUUUU