Free Flight Indoor Bud Tenny OUCH Twenty-twenty hindsight After checking what Ive said about prop wobble think need stress point again Indoor props dont wobble because weight im balanceat least reasonable amount static imbalance problem caused structural aerodynamic mismatch between blades reasonable care match blades will pay off because amount energy dissipated prop much greater wobble force caused weight mismatch vivid example Easy B prop blade broken off can static-balance remaining blade wont much wobble Because air loading single blade way demonstrate prop balanced would run vacuum Actually heavier prop relation its size power driving greater effect weight mismatch will exam pie consider amount power dissipated FAI Indoor props Pennyplane props Dennis Jaecks used 18-in diameter 27A-in-pitch props biplane Pennyplanes FAI props go up 22-in diameter pitch rang ing 40 Typically Pennyplane prop weighs three times much FAI prop handles twice peak torque cruises 24 times rpm moderate care Pennyplane prop structure can adequately matched between blades FAI prop harder match prop erly during construction partly because built-up structure stiffness dependent structural matching tight uni form covering neither type prop will suffer equivalent lack balance extra weight does change S Figure 1 Comparison round square prop-spar cross sections 0 Figure 2 Diagonal insertion prop shaft makes spar theoretically stiffer its difficult accurately Prop spar matching obviously important smooth running Two types spars nor mally usedround square Years ago Bill Bigge calculated square balsa spar would lighter round see Figure 1 spar equivalent stiffness Using Chilton sanding guide described June 1986 column square spar easier make Once spar made matched shaft must attached few fliers mount shaft diagonal Figure 2 gain maxi mum stiffness props rotational plane Theoretically minimizes both forward bowing blade sweepback under full-torque stress However shaft precisely aligned spar diagonal some difference stiffness between blades will generated automatically Consequently shaft usually mounted perpendicular face spar Figure 3 course shaft should truly perpendicular side-to-side centering supremely critical End-to-end centering prop shaft quite critical since deflection-testing made matched distances end spar After adding shaft deflection both front side directions should checked again before adding blades spar Built-up prop blades should have ribs made pairs rib station blade Take care match ribs both length cross section ribs should correct curvature contact both building block spar Figure 4 Note rib will touch spar corner Stan Chilton recommends spar corner burnished slightly flat just rib touches gives wider glue surface allows stronger joint ri-i II L1 6 Figure 3 Normal mounting prop shaft perpendicular face spar two planes must just close Jim Clems Novice Pennyplane prop has WIDE blades Since prop diameter limited event high torque rubber motor must absorbed somehow Blade outlines both blades should cut same piece balsa same grain orientation can accomplished putting indelible ink mark across balsa sheet making diagonal cut across its end After stripping outline piece sheet tiny diagonal cut remains strip forming outlines sure diagonal cut ink mark oriented same way both strips Blade outlines should formed around blade-shaped form thick enough two outlines can stacked atop other making identical size curvature Typically outline strips soaked water wrapped around form baked dry Although lot trouble ideal outline Continued page 152 Figure 4 Prop-rIb curvature should allow rib touch both prop block prop spar Burnish flat spot spar allow better glue joint rib 62 Model Aviation Plastic props can converted efficient pushers simple mod Read column structural stiffness Randolphs Cub has light efficient balsa blades glued plastic hub FF Duration/Murphy Continued page 149 have suddenly appeared everywhere again being listed $695but sale $591 mechanism seems somewhat smaller version last saw shelves however spring very strong can rigged up used fuel shutoff very satisfactorily wont attempt explain pet apparatus design harness mechanisms fuel shut-off use seems nearly Gas flier has own patented device conversion no means unique have something little different surefire functional would certainly interested relaying design readers Well its about time disappear two months well So see ya downwind Harry Murphy 3824 Oakwood Blvd Ander son IN 46011 FF Indoor/Tenny Continued page 62 form twisted like prop blade will fit flat prop block Thus out line formed already properly curved twisted done outline should fitted block during construction moistened relieve stress twisting glued ribs spar after drying Note outline moistened after being tached ribs spar wood will ex pand stress whole structure Prop covering Prop blades should covered prop block possible Otherwise water saliva used adhesive cover trim prop return prop block until moisture has evaporated Also prop covered prop block film must slack enough blade lie film distortion blade twist - can changed during covering film will too tight let blade resume normal twist stress Another important tactic sure film attached both outline ribs accomplishes three things First mois ture used adhesive entire blade ex pands evenly minimizing stress Second individual panels film small enough stiffen blade Finally damage film single section wont spread other sections Dont worry about wrinkles appear blades dry out simple operation will remove Use very fine artist brush moistened water work out wrinkles Stroke brush along wrinkle will pull up level film around After wrinkles treated let whole assembly dry again Finally store prop holder keeps blades touching anything Prop InnovatIons number different plastic props available photos shows convert efficient pusher operation Peanut Scale models free wheeling ratchet front trimmed flat make bearing surface shaft pro jected through hub bent over push against blade Al Backstrom flew setup Bedford Boys Ranch Bedford TX Another photo shows same basic prop hub Photo 1 case small plastic blades removed much larger balsa blades substituted model Profile Scale model flown Randy Randolph again Bedford Boys Ranch Novice Pennyplane has rule limiting prop diameter handle power three-gram model needs Jim Clem trying very wide blades 2Y-in wide blade six inches long shaft tip Ill report performance soon can get some numbers Next time prop blocks prop-covering techniques Bud Tenny Box 545 Richardson TX 75080 Dawnwalker/Oldenkafl1P Continued page 67 maintain rigidity aft motor peg form mount DT tube platforms etc True up main joint slide boom over aft motor hard collar glue works together white glue CyA Eyeball everything good symmetry Sand whole fuselage including down right thrust Add platforms front edge strapping tape reinforcement CyA glue wicks well stufi make up pylons pins wing plat form etc Sand wing mounting unit contour glue yet Make drill nose plug may want spray IN STOCK FOR IMMEDIATE SHIPMENT NEW AH 6237 Cu in$19995 NewOoedre40CDII3-bOeniflgI$12995 Reg 0040 40 912266 Bnighelle flywheel 014295 Reg Ooede 40 Power Aeoenrbly Only$7195 OUAORA REPAIR81000 plo pertol Jin Me. ERCOUPEPLANS $2300 SEMI-KIT 99995 Jim Moeger TOMAHAWK PLANS $2290 SEMI-KIT $9996 Jin Menor6BALLTRPLANS $2395 SEMI-KIT$9995 Ji Meceer ACROBATPLANS 91996 SEMI-KIT $6996 MALONEY 100912996ZONOAH 939 $12995 SACHS-DOLMAR ai CDI 9637 CDI 96 FLOATS 49 114 onclc $2190 co,rplnte kit $4796 19WWIWHEELS 92696 PlKSpningStenton92490 PLANS SUPER STEARMAN 114 IGodfreyl$2999 113 TAYLORCRAFT 0112 CUB Nelite92995 Volkoplco 113 Chicken Charliol$2395 Servo H366 42 no $1296 Wonld 516 9 Ing wodele 93696 PROPS loll aicee Anger Top Flit Oynethnool 20% OFF US Onedre FUEL TANKS160066992300 9796 FIBERGLASS ARROW SHAFTS 911$ 023 long6/61196 24 Hoe Se.4nc 5250 penEege Seed Meek Cheek en Meey 0-do JIM MESSERS QUALITY MODEL PRODUCTS Valey View Dr Box 43 eany NY 14706 PRODUCTS Complete Line Exhaust Systems o Tuned Pipes0 Muffled Tuned Pipes o Headers * Venturi Mufflers o Expansion Mufflers 0 Helicopter Ball Mufflers ialized Exhaust Systems UnsurpaSJ WANNA RACE N RTH AST AREA BEGINNER RACES 0 nFORM-1 oFAI E Instructions Club Programs Information Contact NORTH EAST PYLON RACING ORGANIZATION m 119 DEAN AVE FRANKLIN MASS 02038 Tel 617 528-4043 203 673-2000 152 Model Aviation MODEL PRODUCTS CORP BOX 314 Pompton Plains NJ 07444 available write direct add S200 $500 outside US
Edition: Model Aviation - 1986/08
Page Numbers: 62, 152
Free Flight Indoor Bud Tenny OUCH Twenty-twenty hindsight After checking what Ive said about prop wobble think need stress point again Indoor props dont wobble because weight im balanceat least reasonable amount static imbalance problem caused structural aerodynamic mismatch between blades reasonable care match blades will pay off because amount energy dissipated prop much greater wobble force caused weight mismatch vivid example Easy B prop blade broken off can static-balance remaining blade wont much wobble Because air loading single blade way demonstrate prop balanced would run vacuum Actually heavier prop relation its size power driving greater effect weight mismatch will exam pie consider amount power dissipated FAI Indoor props Pennyplane props Dennis Jaecks used 18-in diameter 27A-in-pitch props biplane Pennyplanes FAI props go up 22-in diameter pitch rang ing 40 Typically Pennyplane prop weighs three times much FAI prop handles twice peak torque cruises 24 times rpm moderate care Pennyplane prop structure can adequately matched between blades FAI prop harder match prop erly during construction partly because built-up structure stiffness dependent structural matching tight uni form covering neither type prop will suffer equivalent lack balance extra weight does change S Figure 1 Comparison round square prop-spar cross sections 0 Figure 2 Diagonal insertion prop shaft makes spar theoretically stiffer its difficult accurately Prop spar matching obviously important smooth running Two types spars nor mally usedround square Years ago Bill Bigge calculated square balsa spar would lighter round see Figure 1 spar equivalent stiffness Using Chilton sanding guide described June 1986 column square spar easier make Once spar made matched shaft must attached few fliers mount shaft diagonal Figure 2 gain maxi mum stiffness props rotational plane Theoretically minimizes both forward bowing blade sweepback under full-torque stress However shaft precisely aligned spar diagonal some difference stiffness between blades will generated automatically Consequently shaft usually mounted perpendicular face spar Figure 3 course shaft should truly perpendicular side-to-side centering supremely critical End-to-end centering prop shaft quite critical since deflection-testing made matched distances end spar After adding shaft deflection both front side directions should checked again before adding blades spar Built-up prop blades should have ribs made pairs rib station blade Take care match ribs both length cross section ribs should correct curvature contact both building block spar Figure 4 Note rib will touch spar corner Stan Chilton recommends spar corner burnished slightly flat just rib touches gives wider glue surface allows stronger joint ri-i II L1 6 Figure 3 Normal mounting prop shaft perpendicular face spar two planes must just close Jim Clems Novice Pennyplane prop has WIDE blades Since prop diameter limited event high torque rubber motor must absorbed somehow Blade outlines both blades should cut same piece balsa same grain orientation can accomplished putting indelible ink mark across balsa sheet making diagonal cut across its end After stripping outline piece sheet tiny diagonal cut remains strip forming outlines sure diagonal cut ink mark oriented same way both strips Blade outlines should formed around blade-shaped form thick enough two outlines can stacked atop other making identical size curvature Typically outline strips soaked water wrapped around form baked dry Although lot trouble ideal outline Continued page 152 Figure 4 Prop-rIb curvature should allow rib touch both prop block prop spar Burnish flat spot spar allow better glue joint rib 62 Model Aviation Plastic props can converted efficient pushers simple mod Read column structural stiffness Randolphs Cub has light efficient balsa blades glued plastic hub FF Duration/Murphy Continued page 149 have suddenly appeared everywhere again being listed $695but sale $591 mechanism seems somewhat smaller version last saw shelves however spring very strong can rigged up used fuel shutoff very satisfactorily wont attempt explain pet apparatus design harness mechanisms fuel shut-off use seems nearly Gas flier has own patented device conversion no means unique have something little different surefire functional would certainly interested relaying design readers Well its about time disappear two months well So see ya downwind Harry Murphy 3824 Oakwood Blvd Ander son IN 46011 FF Indoor/Tenny Continued page 62 form twisted like prop blade will fit flat prop block Thus out line formed already properly curved twisted done outline should fitted block during construction moistened relieve stress twisting glued ribs spar after drying Note outline moistened after being tached ribs spar wood will ex pand stress whole structure Prop covering Prop blades should covered prop block possible Otherwise water saliva used adhesive cover trim prop return prop block until moisture has evaporated Also prop covered prop block film must slack enough blade lie film distortion blade twist - can changed during covering film will too tight let blade resume normal twist stress Another important tactic sure film attached both outline ribs accomplishes three things First mois ture used adhesive entire blade ex pands evenly minimizing stress Second individual panels film small enough stiffen blade Finally damage film single section wont spread other sections Dont worry about wrinkles appear blades dry out simple operation will remove Use very fine artist brush moistened water work out wrinkles Stroke brush along wrinkle will pull up level film around After wrinkles treated let whole assembly dry again Finally store prop holder keeps blades touching anything Prop InnovatIons number different plastic props available photos shows convert efficient pusher operation Peanut Scale models free wheeling ratchet front trimmed flat make bearing surface shaft pro jected through hub bent over push against blade Al Backstrom flew setup Bedford Boys Ranch Bedford TX Another photo shows same basic prop hub Photo 1 case small plastic blades removed much larger balsa blades substituted model Profile Scale model flown Randy Randolph again Bedford Boys Ranch Novice Pennyplane has rule limiting prop diameter handle power three-gram model needs Jim Clem trying very wide blades 2Y-in wide blade six inches long shaft tip Ill report performance soon can get some numbers Next time prop blocks prop-covering techniques Bud Tenny Box 545 Richardson TX 75080 Dawnwalker/Oldenkafl1P Continued page 67 maintain rigidity aft motor peg form mount DT tube platforms etc True up main joint slide boom over aft motor hard collar glue works together white glue CyA Eyeball everything good symmetry Sand whole fuselage including down right thrust Add platforms front edge strapping tape reinforcement CyA glue wicks well stufi make up pylons pins wing plat form etc Sand wing mounting unit contour glue yet Make drill nose plug may want spray IN STOCK FOR IMMEDIATE SHIPMENT NEW AH 6237 Cu in$19995 NewOoedre40CDII3-bOeniflgI$12995 Reg 0040 40 912266 Bnighelle flywheel 014295 Reg Ooede 40 Power Aeoenrbly Only$7195 OUAORA REPAIR81000 plo pertol Jin Me. ERCOUPEPLANS $2300 SEMI-KIT 99995 Jim Moeger TOMAHAWK PLANS $2290 SEMI-KIT $9996 Jin Menor6BALLTRPLANS $2395 SEMI-KIT$9995 Ji Meceer ACROBATPLANS 91996 SEMI-KIT $6996 MALONEY 100912996ZONOAH 939 $12995 SACHS-DOLMAR ai CDI 9637 CDI 96 FLOATS 49 114 onclc $2190 co,rplnte kit $4796 19WWIWHEELS 92696 PlKSpningStenton92490 PLANS SUPER STEARMAN 114 IGodfreyl$2999 113 TAYLORCRAFT 0112 CUB Nelite92995 Volkoplco 113 Chicken Charliol$2395 Servo H366 42 no $1296 Wonld 516 9 Ing wodele 93696 PROPS loll aicee Anger Top Flit Oynethnool 20% OFF US Onedre FUEL TANKS160066992300 9796 FIBERGLASS ARROW SHAFTS 911$ 023 long6/61196 24 Hoe Se.4nc 5250 penEege Seed Meek Cheek en Meey 0-do JIM MESSERS QUALITY MODEL PRODUCTS Valey View Dr Box 43 eany NY 14706 PRODUCTS Complete Line Exhaust Systems o Tuned Pipes0 Muffled Tuned Pipes o Headers * Venturi Mufflers o Expansion Mufflers 0 Helicopter Ball Mufflers ialized Exhaust Systems UnsurpaSJ WANNA RACE N RTH AST AREA BEGINNER RACES 0 nFORM-1 oFAI E Instructions Club Programs Information Contact NORTH EAST PYLON RACING ORGANIZATION m 119 DEAN AVE FRANKLIN MASS 02038 Tel 617 528-4043 203 673-2000 152 Model Aviation MODEL PRODUCTS CORP BOX 314 Pompton Plains NJ 07444 available write direct add S200 $500 outside US