Let i7aUa #lbout Powers _______A ne Deiqri IN THE APRIL 1980 issue MA article entitled Lets Talk About CG discussed subject Static Longitudinal Stability Whether flies models full-size aircraft under standing subject essential satisfactory performanceand safety well An unstable airplane difficult impossible control Thus poses threat bystanders case models can life-threatening pilot full-size plane As time goes new readers seem come up same old questions soit probably appropriate cover sub ject agaln particularly since responses Part 1 group articles indicated lack understanding some readers Part 1 example stated stable airplane normally carries down load horizontal tail up elevator trim airplane reader particular posed condition shown Fig 1 sisting CG location slightly aft AC Aerodynamic Center wing requires up load tail surface looks might right Lets see First lets define AC wing AC point Lift may considered concentrated point little no momentlittle constant case cambered airfoils no moment case symmetrical uncambered airfoils AC point wing Lift acts Before going further lets con sider simple analogy shown Fig 2 place board sawhorse balance brick exerting pressure finger force equal weight brick will result f disregarding weight board total force however sum W ight brick plus load f applied finger total load acts supported sawhorse Now lets get discussion Longitudinal Stability well make additional reference sawhorse brick later Longitudinal Stability tendency airplane recover inadver tent digression its flight path gust causes nose up slow down example instead stalling will nose down speed up resume its original flight attitude speed should nose down will raise its nose slow down again resume original attitude speed must agree very nice trait should nurtured fos LIFTat wing AC L UPload t weight 27% MAC Fig1 L Total W--f FW -] Fig 2 h h varies h MAC Area center AC Fig 3 88 Model Aviation Jliii III El 0 F tered etc Two things determine Longitudinal Sta bility decalage CO location Decalage angular difference setting cidence between forward surface usu ally wing aft surface usually horizontal tail Decalage French word roughly translates mean wedge shaped implying angular dif ference another name longitudi nal dihedral two reasons decalage first forward surface must higher angle attack will stall first thus producing diving mo ment affect recovery stall true types aircrafttailless conventional canard second reason aft surface reason decalage does fact trim ward surface desired angle attack maintain desired speed except case canard forward sur face does trimming need trimming surface discovered back last century Frenchman named Alphonse Penaud early theorist about such things CG location longitudinally stable airplane must have CG ward Aerodynamic Center whole airplane corresponds total W diagram sawhorse brick Aerodynamic Center whole airplane generally referred Neutral Point designated letter N called Neutral Point because CG placed N Can airplane have stable flight up-load horizontal tail Part 3 discusses question other factors affect ing longitudinal stability condition called Neutral Stability prevails shall see distance CG placed ward N called stability margin expressed percentage Mean Aerodynamic Chord MAC MAC chord passes through center area wing panel shown Fig 3 See also Lets Talk About CG May 1980 Model Aviation placed wind tunnel cam bered wing alone wing attached fuselage no tail exhibits increas ing nose-up positive moment angle attack increased shown Fig 4 must countered horizontal tail produces negative div ing moment shown Fig 5 Lift wing acts AC wing 25% MAC Lift horizontal tail acts AC tail although common practice consider tail lift acting elevator hinge line practical reasons AC whole airplane N fore lies somewhat aft wing AC shown Fig 6 stick models fuselages engines etc position N may approximated weighted areas wing tail see April 1980 MA Actually N function moments affecting trim airplane moments change increasing angle attack shown Fig 7 Since moments vary angle attack ie constant must find position N dealing rates change derivatives better yet determine values wind tunnels Thus determination N easily made modeler creating own design Suffice say Neutral Point N Scale-type models lies very close 30% MAC after considering destabilizing effects power high angles attack fuselage nacelles also stabilizing effect extended landing gear produces favorable negative moment Fig 8 show three conditions show stable arrangement b show arrangement neutrally stable c show unstable arrangement stable condition Fig 8a CG shown about 27% MAC / / POSITIVE MOMENT no horizontal tail 4 Fig4 NL her w GATIVE TAIL MOMENT balances positive moment Fig 5 4/ 7 Forces producing Other moments Fig6 December 1984 89 thus 3 o forward Neutral Point may said have Stability Margin 3% MAC satisfactory 5% betterespecially beginners properly designed airplane downwash wing will place sufficient down load tail trim wing angle attack cruising usually about 30 tail set zero incidence zero elevator deflection cruis ing speed down landing speed creasing down-load up elevator re quired raise nose slow down minimum speed condition limits forward position CG keep stick forces pilot com fortable range Thus see CG forward N somewhat aft AC wing alone down load horizontal tail required maintain level flight up-load shown Fig 1 stable airplane time up-load tail required trim pilot wishes drop nose speed up beyond cruising speed As long CG forward N airplane will tend recover stall because negative diving moment pre vails shown Fig 9 due said forward CG location combination moment produced hori zontal tail negative moment increases becomes negative angle tack acts sort like spring pitch nose down recover stall deed criterion Longitudinal Sta bility curve Moment versus Angle Attack have negative slope shown Since position N conventional configurations lies ap proximately 30% MAC since 5% stability margin about right customary place CG 25% MAC Since 25% MAC also AC wing aione think causes some con fusion people seem believe CG AC wing no down-load tail have just seen simply case Neutral stability shown b Fig ures 8 9 prevails CG placed N under conditions no trim load tail other downwash much T-Tail configuration tail always loaded course basic up-load shown Fig 5 Lift N Weight pure opposition thus pro ducing no moment means plane will have no automatic recovery stall neither will want stall will very sensitive controls will make delight skilled Pattern flier beginner because unforgiving error control demanding control constantly otherwise going off its own slightest disturbance graph Fig 9 shown zero slope moment curve positive slope moment curve shown Fig 9c bad defines stability occurs CG aft N shown Fig 8c Under conditions airplane becomes less less controllable CG moved aft until completely unmanageable winds up buying farm say nose pitches up example forces play now arranged cause pitch up further thus stall ensues Nevertheless advent com puterized control latest military air craft possible satisfactorily operate aircraft unstable regime because computer can programmed antici pate sudden disaster before occurs correct controls maintain steady flight done super fighters can crab through air sideContinued page 176 N 30% MAC approx a stablecg limits t A25% Forward cg DOWN load tail Fig8a STABILITY N 0 W Fig Bb NEUTRAL STABILITY istability margin produces neg moment -balanced pos L downwash Fig C 0 E 0 N W 8c INSTABILITY Fig 9 unstable c 4 neutral b 0 036912 Angle attack-degrees CC 90 Model Aviation PATTERN SHIP AS GOOD AS YOU ARE. MAYBE BETTER T\DCIk Technician totally functional design combines great flying characteristics ease construc tion goad looks first quality kit throughout FIBERGLASS FUSELAGE FOAM CORES BASIC KIT BASIC HARDWARE PKG BASIC KIT $10795 DELUXE KIT $15995 Add $600 Freight direct shipment DEALER & DISTRIBUTOR INQUIRIES INVITED ALL OF THE ABOVE PLUS ALL REQUIRED BALSAS MOTOR MOUNT AND HARDWARE L&L MODEL MFGBV PRODUCTS 513 385-0912 7342 Applerlde Court CIncInnati Ohio 45247 CG try swapping spinners trim setup use gives better grove improves wind penetration tends dampen effects somewhat shortish nose airplane stands liter ally cockpit stitching rudder above others high angle attack low gross weight gets off rough fields goad order recent local holiday demonstration took Barnstormer out two full days actual barnstorming just like name says wasnt especially trying full pattern flight sometimes just doing big sweeping oldstyle maneuvers show folks what good CL ship can few closing thoughts Barnstorm er game build using oaly Ambroid Testors glue con sidered backed off moment weakness built know Modelers didnt always build oak steel cable ferro concrete present-day modeling counterparts writing advertisers mention read about Model Aviation LIghtweIght Foam WlnglEvans Continued page 85 / capstrip butt against Cut two strips balsa least A-in wider leading edge foam about /2 sheet A-in balsa Glue pin trailing edge again centering allow cap strips After leading trailing edges have dried mark cores 2-in inter vals locate cap strips Mark both top bottom cores top cap strips directly over bot tom cap strips Also mark location 3-in-wide inboard sheeting Place wing core top cradle flat surface place core top cradle bottom side up Cut board sheeting fit glue pin place bottom wing Next cut / x /l6 cap strips fit between leading trailing edges glue pin place Repeat steps other wing panel After bottom cap strips have dried place repeat top wing Again use wing cradles help ke wing free warps After assemblies dry trim ar sand leading trailing edges flu cap strips Mark locations lightening hole cut hole saw Cover wing transparent fil enable full effect work show construction described resulte weight reduction 50ofrom i oz 8 oz strength has moi adequate Airplane DesignlPowes Continued page 90 ways vertically off angle whil maintaining forward speed thus increas ing ability outmaneuver thei adversaries model industr comes out such equipment stability CG location will no longer 1 problems modelers Questions comments may dressed Brad Powers 5470 Castle Hill Dr San Diego CA 92109 Pomlilo PElNoonan Continued oaae 96 leading trailing edges win roots Bamboo 2-in OD aluminur pins about / long act method c indexing wings fuselage center cabane section fit i aluminum tubing fuselage wings important have tub ing exact alignment before cementing place assure accuracy necessary assemble wings th proper dihedral angle temporary ji apply epoxy wing root tubin has index pin place Allow cc ment dry before disassembling eight interplane struts may mad flattened plastic straws cut fror balsa use straw method whic has advantage being virtually destructible will necessary inser bamboo slivers about 1 long cad end strut allowing / pro Super Sport Planes Midwest Send $150 complete Kit Catalog q P Midwest Pmducts Co Inc G 400 5 Indiana St PO Box 564-SP Hobart 1n46342831032 DIVISION OF BAR/RICH SALES Co #2 FAIRWAY HANNIBAL MO 63401 314 221-6803 MANUFACTURERS OF SPORT PATTERNSTINGEI II PEPPERMINT PATTIE -60SPARTAN PEPPERMINT PATTIE 40 SPORT/SCALE PEPPERMINT PATTIE 15 HIPERBIPE 176 Model Aviation DELUXE KIT aster
Edition: Model Aviation - 1984/12
Page Numbers: 88, 89, 90, 176
Let i7aUa #lbout Powers _______A ne Deiqri IN THE APRIL 1980 issue MA article entitled Lets Talk About CG discussed subject Static Longitudinal Stability Whether flies models full-size aircraft under standing subject essential satisfactory performanceand safety well An unstable airplane difficult impossible control Thus poses threat bystanders case models can life-threatening pilot full-size plane As time goes new readers seem come up same old questions soit probably appropriate cover sub ject agaln particularly since responses Part 1 group articles indicated lack understanding some readers Part 1 example stated stable airplane normally carries down load horizontal tail up elevator trim airplane reader particular posed condition shown Fig 1 sisting CG location slightly aft AC Aerodynamic Center wing requires up load tail surface looks might right Lets see First lets define AC wing AC point Lift may considered concentrated point little no momentlittle constant case cambered airfoils no moment case symmetrical uncambered airfoils AC point wing Lift acts Before going further lets con sider simple analogy shown Fig 2 place board sawhorse balance brick exerting pressure finger force equal weight brick will result f disregarding weight board total force however sum W ight brick plus load f applied finger total load acts supported sawhorse Now lets get discussion Longitudinal Stability well make additional reference sawhorse brick later Longitudinal Stability tendency airplane recover inadver tent digression its flight path gust causes nose up slow down example instead stalling will nose down speed up resume its original flight attitude speed should nose down will raise its nose slow down again resume original attitude speed must agree very nice trait should nurtured fos LIFTat wing AC L UPload t weight 27% MAC Fig1 L Total W--f FW -] Fig 2 h h varies h MAC Area center AC Fig 3 88 Model Aviation Jliii III El 0 F tered etc Two things determine Longitudinal Sta bility decalage CO location Decalage angular difference setting cidence between forward surface usu ally wing aft surface usually horizontal tail Decalage French word roughly translates mean wedge shaped implying angular dif ference another name longitudi nal dihedral two reasons decalage first forward surface must higher angle attack will stall first thus producing diving mo ment affect recovery stall true types aircrafttailless conventional canard second reason aft surface reason decalage does fact trim ward surface desired angle attack maintain desired speed except case canard forward sur face does trimming need trimming surface discovered back last century Frenchman named Alphonse Penaud early theorist about such things CG location longitudinally stable airplane must have CG ward Aerodynamic Center whole airplane corresponds total W diagram sawhorse brick Aerodynamic Center whole airplane generally referred Neutral Point designated letter N called Neutral Point because CG placed N Can airplane have stable flight up-load horizontal tail Part 3 discusses question other factors affect ing longitudinal stability condition called Neutral Stability prevails shall see distance CG placed ward N called stability margin expressed percentage Mean Aerodynamic Chord MAC MAC chord passes through center area wing panel shown Fig 3 See also Lets Talk About CG May 1980 Model Aviation placed wind tunnel cam bered wing alone wing attached fuselage no tail exhibits increas ing nose-up positive moment angle attack increased shown Fig 4 must countered horizontal tail produces negative div ing moment shown Fig 5 Lift wing acts AC wing 25% MAC Lift horizontal tail acts AC tail although common practice consider tail lift acting elevator hinge line practical reasons AC whole airplane N fore lies somewhat aft wing AC shown Fig 6 stick models fuselages engines etc position N may approximated weighted areas wing tail see April 1980 MA Actually N function moments affecting trim airplane moments change increasing angle attack shown Fig 7 Since moments vary angle attack ie constant must find position N dealing rates change derivatives better yet determine values wind tunnels Thus determination N easily made modeler creating own design Suffice say Neutral Point N Scale-type models lies very close 30% MAC after considering destabilizing effects power high angles attack fuselage nacelles also stabilizing effect extended landing gear produces favorable negative moment Fig 8 show three conditions show stable arrangement b show arrangement neutrally stable c show unstable arrangement stable condition Fig 8a CG shown about 27% MAC / / POSITIVE MOMENT no horizontal tail 4 Fig4 NL her w GATIVE TAIL MOMENT balances positive moment Fig 5 4/ 7 Forces producing Other moments Fig6 December 1984 89 thus 3 o forward Neutral Point may said have Stability Margin 3% MAC satisfactory 5% betterespecially beginners properly designed airplane downwash wing will place sufficient down load tail trim wing angle attack cruising usually about 30 tail set zero incidence zero elevator deflection cruis ing speed down landing speed creasing down-load up elevator re quired raise nose slow down minimum speed condition limits forward position CG keep stick forces pilot com fortable range Thus see CG forward N somewhat aft AC wing alone down load horizontal tail required maintain level flight up-load shown Fig 1 stable airplane time up-load tail required trim pilot wishes drop nose speed up beyond cruising speed As long CG forward N airplane will tend recover stall because negative diving moment pre vails shown Fig 9 due said forward CG location combination moment produced hori zontal tail negative moment increases becomes negative angle tack acts sort like spring pitch nose down recover stall deed criterion Longitudinal Sta bility curve Moment versus Angle Attack have negative slope shown Since position N conventional configurations lies ap proximately 30% MAC since 5% stability margin about right customary place CG 25% MAC Since 25% MAC also AC wing aione think causes some con fusion people seem believe CG AC wing no down-load tail have just seen simply case Neutral stability shown b Fig ures 8 9 prevails CG placed N under conditions no trim load tail other downwash much T-Tail configuration tail always loaded course basic up-load shown Fig 5 Lift N Weight pure opposition thus pro ducing no moment means plane will have no automatic recovery stall neither will want stall will very sensitive controls will make delight skilled Pattern flier beginner because unforgiving error control demanding control constantly otherwise going off its own slightest disturbance graph Fig 9 shown zero slope moment curve positive slope moment curve shown Fig 9c bad defines stability occurs CG aft N shown Fig 8c Under conditions airplane becomes less less controllable CG moved aft until completely unmanageable winds up buying farm say nose pitches up example forces play now arranged cause pitch up further thus stall ensues Nevertheless advent com puterized control latest military air craft possible satisfactorily operate aircraft unstable regime because computer can programmed antici pate sudden disaster before occurs correct controls maintain steady flight done super fighters can crab through air sideContinued page 176 N 30% MAC approx a stablecg limits t A25% Forward cg DOWN load tail Fig8a STABILITY N 0 W Fig Bb NEUTRAL STABILITY istability margin produces neg moment -balanced pos L downwash Fig C 0 E 0 N W 8c INSTABILITY Fig 9 unstable c 4 neutral b 0 036912 Angle attack-degrees CC 90 Model Aviation PATTERN SHIP AS GOOD AS YOU ARE. MAYBE BETTER T\DCIk Technician totally functional design combines great flying characteristics ease construc tion goad looks first quality kit throughout FIBERGLASS FUSELAGE FOAM CORES BASIC KIT BASIC HARDWARE PKG BASIC KIT $10795 DELUXE KIT $15995 Add $600 Freight direct shipment DEALER & DISTRIBUTOR INQUIRIES INVITED ALL OF THE ABOVE PLUS ALL REQUIRED BALSAS MOTOR MOUNT AND HARDWARE L&L MODEL MFGBV PRODUCTS 513 385-0912 7342 Applerlde Court CIncInnati Ohio 45247 CG try swapping spinners trim setup use gives better grove improves wind penetration tends dampen effects somewhat shortish nose airplane stands liter ally cockpit stitching rudder above others high angle attack low gross weight gets off rough fields goad order recent local holiday demonstration took Barnstormer out two full days actual barnstorming just like name says wasnt especially trying full pattern flight sometimes just doing big sweeping oldstyle maneuvers show folks what good CL ship can few closing thoughts Barnstorm er game build using oaly Ambroid Testors glue con sidered backed off moment weakness built know Modelers didnt always build oak steel cable ferro concrete present-day modeling counterparts writing advertisers mention read about Model Aviation LIghtweIght Foam WlnglEvans Continued page 85 / capstrip butt against Cut two strips balsa least A-in wider leading edge foam about /2 sheet A-in balsa Glue pin trailing edge again centering allow cap strips After leading trailing edges have dried mark cores 2-in inter vals locate cap strips Mark both top bottom cores top cap strips directly over bot tom cap strips Also mark location 3-in-wide inboard sheeting Place wing core top cradle flat surface place core top cradle bottom side up Cut board sheeting fit glue pin place bottom wing Next cut / x /l6 cap strips fit between leading trailing edges glue pin place Repeat steps other wing panel After bottom cap strips have dried place repeat top wing Again use wing cradles help ke wing free warps After assemblies dry trim ar sand leading trailing edges flu cap strips Mark locations lightening hole cut hole saw Cover wing transparent fil enable full effect work show construction described resulte weight reduction 50ofrom i oz 8 oz strength has moi adequate Airplane DesignlPowes Continued page 90 ways vertically off angle whil maintaining forward speed thus increas ing ability outmaneuver thei adversaries model industr comes out such equipment stability CG location will no longer 1 problems modelers Questions comments may dressed Brad Powers 5470 Castle Hill Dr San Diego CA 92109 Pomlilo PElNoonan Continued oaae 96 leading trailing edges win roots Bamboo 2-in OD aluminur pins about / long act method c indexing wings fuselage center cabane section fit i aluminum tubing fuselage wings important have tub ing exact alignment before cementing place assure accuracy necessary assemble wings th proper dihedral angle temporary ji apply epoxy wing root tubin has index pin place Allow cc ment dry before disassembling eight interplane struts may mad flattened plastic straws cut fror balsa use straw method whic has advantage being virtually destructible will necessary inser bamboo slivers about 1 long cad end strut allowing / pro Super Sport Planes Midwest Send $150 complete Kit Catalog q P Midwest Pmducts Co Inc G 400 5 Indiana St PO Box 564-SP Hobart 1n46342831032 DIVISION OF BAR/RICH SALES Co #2 FAIRWAY HANNIBAL MO 63401 314 221-6803 MANUFACTURERS OF SPORT PATTERNSTINGEI II PEPPERMINT PATTIE -60SPARTAN PEPPERMINT PATTIE 40 SPORT/SCALE PEPPERMINT PATTIE 15 HIPERBIPE 176 Model Aviation DELUXE KIT aster
Edition: Model Aviation - 1984/12
Page Numbers: 88, 89, 90, 176
Let i7aUa #lbout Powers _______A ne Deiqri IN THE APRIL 1980 issue MA article entitled Lets Talk About CG discussed subject Static Longitudinal Stability Whether flies models full-size aircraft under standing subject essential satisfactory performanceand safety well An unstable airplane difficult impossible control Thus poses threat bystanders case models can life-threatening pilot full-size plane As time goes new readers seem come up same old questions soit probably appropriate cover sub ject agaln particularly since responses Part 1 group articles indicated lack understanding some readers Part 1 example stated stable airplane normally carries down load horizontal tail up elevator trim airplane reader particular posed condition shown Fig 1 sisting CG location slightly aft AC Aerodynamic Center wing requires up load tail surface looks might right Lets see First lets define AC wing AC point Lift may considered concentrated point little no momentlittle constant case cambered airfoils no moment case symmetrical uncambered airfoils AC point wing Lift acts Before going further lets con sider simple analogy shown Fig 2 place board sawhorse balance brick exerting pressure finger force equal weight brick will result f disregarding weight board total force however sum W ight brick plus load f applied finger total load acts supported sawhorse Now lets get discussion Longitudinal Stability well make additional reference sawhorse brick later Longitudinal Stability tendency airplane recover inadver tent digression its flight path gust causes nose up slow down example instead stalling will nose down speed up resume its original flight attitude speed should nose down will raise its nose slow down again resume original attitude speed must agree very nice trait should nurtured fos LIFTat wing AC L UPload t weight 27% MAC Fig1 L Total W--f FW -] Fig 2 h h varies h MAC Area center AC Fig 3 88 Model Aviation Jliii III El 0 F tered etc Two things determine Longitudinal Sta bility decalage CO location Decalage angular difference setting cidence between forward surface usu ally wing aft surface usually horizontal tail Decalage French word roughly translates mean wedge shaped implying angular dif ference another name longitudi nal dihedral two reasons decalage first forward surface must higher angle attack will stall first thus producing diving mo ment affect recovery stall true types aircrafttailless conventional canard second reason aft surface reason decalage does fact trim ward surface desired angle attack maintain desired speed except case canard forward sur face does trimming need trimming surface discovered back last century Frenchman named Alphonse Penaud early theorist about such things CG location longitudinally stable airplane must have CG ward Aerodynamic Center whole airplane corresponds total W diagram sawhorse brick Aerodynamic Center whole airplane generally referred Neutral Point designated letter N called Neutral Point because CG placed N Can airplane have stable flight up-load horizontal tail Part 3 discusses question other factors affect ing longitudinal stability condition called Neutral Stability prevails shall see distance CG placed ward N called stability margin expressed percentage Mean Aerodynamic Chord MAC MAC chord passes through center area wing panel shown Fig 3 See also Lets Talk About CG May 1980 Model Aviation placed wind tunnel cam bered wing alone wing attached fuselage no tail exhibits increas ing nose-up positive moment angle attack increased shown Fig 4 must countered horizontal tail produces negative div ing moment shown Fig 5 Lift wing acts AC wing 25% MAC Lift horizontal tail acts AC tail although common practice consider tail lift acting elevator hinge line practical reasons AC whole airplane N fore lies somewhat aft wing AC shown Fig 6 stick models fuselages engines etc position N may approximated weighted areas wing tail see April 1980 MA Actually N function moments affecting trim airplane moments change increasing angle attack shown Fig 7 Since moments vary angle attack ie constant must find position N dealing rates change derivatives better yet determine values wind tunnels Thus determination N easily made modeler creating own design Suffice say Neutral Point N Scale-type models lies very close 30% MAC after considering destabilizing effects power high angles attack fuselage nacelles also stabilizing effect extended landing gear produces favorable negative moment Fig 8 show three conditions show stable arrangement b show arrangement neutrally stable c show unstable arrangement stable condition Fig 8a CG shown about 27% MAC / / POSITIVE MOMENT no horizontal tail 4 Fig4 NL her w GATIVE TAIL MOMENT balances positive moment Fig 5 4/ 7 Forces producing Other moments Fig6 December 1984 89 thus 3 o forward Neutral Point may said have Stability Margin 3% MAC satisfactory 5% betterespecially beginners properly designed airplane downwash wing will place sufficient down load tail trim wing angle attack cruising usually about 30 tail set zero incidence zero elevator deflection cruis ing speed down landing speed creasing down-load up elevator re quired raise nose slow down minimum speed condition limits forward position CG keep stick forces pilot com fortable range Thus see CG forward N somewhat aft AC wing alone down load horizontal tail required maintain level flight up-load shown Fig 1 stable airplane time up-load tail required trim pilot wishes drop nose speed up beyond cruising speed As long CG forward N airplane will tend recover stall because negative diving moment pre vails shown Fig 9 due said forward CG location combination moment produced hori zontal tail negative moment increases becomes negative angle tack acts sort like spring pitch nose down recover stall deed criterion Longitudinal Sta bility curve Moment versus Angle Attack have negative slope shown Since position N conventional configurations lies ap proximately 30% MAC since 5% stability margin about right customary place CG 25% MAC Since 25% MAC also AC wing aione think causes some con fusion people seem believe CG AC wing no down-load tail have just seen simply case Neutral stability shown b Fig ures 8 9 prevails CG placed N under conditions no trim load tail other downwash much T-Tail configuration tail always loaded course basic up-load shown Fig 5 Lift N Weight pure opposition thus pro ducing no moment means plane will have no automatic recovery stall neither will want stall will very sensitive controls will make delight skilled Pattern flier beginner because unforgiving error control demanding control constantly otherwise going off its own slightest disturbance graph Fig 9 shown zero slope moment curve positive slope moment curve shown Fig 9c bad defines stability occurs CG aft N shown Fig 8c Under conditions airplane becomes less less controllable CG moved aft until completely unmanageable winds up buying farm say nose pitches up example forces play now arranged cause pitch up further thus stall ensues Nevertheless advent com puterized control latest military air craft possible satisfactorily operate aircraft unstable regime because computer can programmed antici pate sudden disaster before occurs correct controls maintain steady flight done super fighters can crab through air sideContinued page 176 N 30% MAC approx a stablecg limits t A25% Forward cg DOWN load tail Fig8a STABILITY N 0 W Fig Bb NEUTRAL STABILITY istability margin produces neg moment -balanced pos L downwash Fig C 0 E 0 N W 8c INSTABILITY Fig 9 unstable c 4 neutral b 0 036912 Angle attack-degrees CC 90 Model Aviation PATTERN SHIP AS GOOD AS YOU ARE. MAYBE BETTER T\DCIk Technician totally functional design combines great flying characteristics ease construc tion goad looks first quality kit throughout FIBERGLASS FUSELAGE FOAM CORES BASIC KIT BASIC HARDWARE PKG BASIC KIT $10795 DELUXE KIT $15995 Add $600 Freight direct shipment DEALER & DISTRIBUTOR INQUIRIES INVITED ALL OF THE ABOVE PLUS ALL REQUIRED BALSAS MOTOR MOUNT AND HARDWARE L&L MODEL MFGBV PRODUCTS 513 385-0912 7342 Applerlde Court CIncInnati Ohio 45247 CG try swapping spinners trim setup use gives better grove improves wind penetration tends dampen effects somewhat shortish nose airplane stands liter ally cockpit stitching rudder above others high angle attack low gross weight gets off rough fields goad order recent local holiday demonstration took Barnstormer out two full days actual barnstorming just like name says wasnt especially trying full pattern flight sometimes just doing big sweeping oldstyle maneuvers show folks what good CL ship can few closing thoughts Barnstorm er game build using oaly Ambroid Testors glue con sidered backed off moment weakness built know Modelers didnt always build oak steel cable ferro concrete present-day modeling counterparts writing advertisers mention read about Model Aviation LIghtweIght Foam WlnglEvans Continued page 85 / capstrip butt against Cut two strips balsa least A-in wider leading edge foam about /2 sheet A-in balsa Glue pin trailing edge again centering allow cap strips After leading trailing edges have dried mark cores 2-in inter vals locate cap strips Mark both top bottom cores top cap strips directly over bot tom cap strips Also mark location 3-in-wide inboard sheeting Place wing core top cradle flat surface place core top cradle bottom side up Cut board sheeting fit glue pin place bottom wing Next cut / x /l6 cap strips fit between leading trailing edges glue pin place Repeat steps other wing panel After bottom cap strips have dried place repeat top wing Again use wing cradles help ke wing free warps After assemblies dry trim ar sand leading trailing edges flu cap strips Mark locations lightening hole cut hole saw Cover wing transparent fil enable full effect work show construction described resulte weight reduction 50ofrom i oz 8 oz strength has moi adequate Airplane DesignlPowes Continued page 90 ways vertically off angle whil maintaining forward speed thus increas ing ability outmaneuver thei adversaries model industr comes out such equipment stability CG location will no longer 1 problems modelers Questions comments may dressed Brad Powers 5470 Castle Hill Dr San Diego CA 92109 Pomlilo PElNoonan Continued oaae 96 leading trailing edges win roots Bamboo 2-in OD aluminur pins about / long act method c indexing wings fuselage center cabane section fit i aluminum tubing fuselage wings important have tub ing exact alignment before cementing place assure accuracy necessary assemble wings th proper dihedral angle temporary ji apply epoxy wing root tubin has index pin place Allow cc ment dry before disassembling eight interplane struts may mad flattened plastic straws cut fror balsa use straw method whic has advantage being virtually destructible will necessary inser bamboo slivers about 1 long cad end strut allowing / pro Super Sport Planes Midwest Send $150 complete Kit Catalog q P Midwest Pmducts Co Inc G 400 5 Indiana St PO Box 564-SP Hobart 1n46342831032 DIVISION OF BAR/RICH SALES Co #2 FAIRWAY HANNIBAL MO 63401 314 221-6803 MANUFACTURERS OF SPORT PATTERNSTINGEI II PEPPERMINT PATTIE -60SPARTAN PEPPERMINT PATTIE 40 SPORT/SCALE PEPPERMINT PATTIE 15 HIPERBIPE 176 Model Aviation DELUXE KIT aster
Edition: Model Aviation - 1984/12
Page Numbers: 88, 89, 90, 176
Let i7aUa #lbout Powers _______A ne Deiqri IN THE APRIL 1980 issue MA article entitled Lets Talk About CG discussed subject Static Longitudinal Stability Whether flies models full-size aircraft under standing subject essential satisfactory performanceand safety well An unstable airplane difficult impossible control Thus poses threat bystanders case models can life-threatening pilot full-size plane As time goes new readers seem come up same old questions soit probably appropriate cover sub ject agaln particularly since responses Part 1 group articles indicated lack understanding some readers Part 1 example stated stable airplane normally carries down load horizontal tail up elevator trim airplane reader particular posed condition shown Fig 1 sisting CG location slightly aft AC Aerodynamic Center wing requires up load tail surface looks might right Lets see First lets define AC wing AC point Lift may considered concentrated point little no momentlittle constant case cambered airfoils no moment case symmetrical uncambered airfoils AC point wing Lift acts Before going further lets con sider simple analogy shown Fig 2 place board sawhorse balance brick exerting pressure finger force equal weight brick will result f disregarding weight board total force however sum W ight brick plus load f applied finger total load acts supported sawhorse Now lets get discussion Longitudinal Stability well make additional reference sawhorse brick later Longitudinal Stability tendency airplane recover inadver tent digression its flight path gust causes nose up slow down example instead stalling will nose down speed up resume its original flight attitude speed should nose down will raise its nose slow down again resume original attitude speed must agree very nice trait should nurtured fos LIFTat wing AC L UPload t weight 27% MAC Fig1 L Total W--f FW -] Fig 2 h h varies h MAC Area center AC Fig 3 88 Model Aviation Jliii III El 0 F tered etc Two things determine Longitudinal Sta bility decalage CO location Decalage angular difference setting cidence between forward surface usu ally wing aft surface usually horizontal tail Decalage French word roughly translates mean wedge shaped implying angular dif ference another name longitudi nal dihedral two reasons decalage first forward surface must higher angle attack will stall first thus producing diving mo ment affect recovery stall true types aircrafttailless conventional canard second reason aft surface reason decalage does fact trim ward surface desired angle attack maintain desired speed except case canard forward sur face does trimming need trimming surface discovered back last century Frenchman named Alphonse Penaud early theorist about such things CG location longitudinally stable airplane must have CG ward Aerodynamic Center whole airplane corresponds total W diagram sawhorse brick Aerodynamic Center whole airplane generally referred Neutral Point designated letter N called Neutral Point because CG placed N Can airplane have stable flight up-load horizontal tail Part 3 discusses question other factors affect ing longitudinal stability condition called Neutral Stability prevails shall see distance CG placed ward N called stability margin expressed percentage Mean Aerodynamic Chord MAC MAC chord passes through center area wing panel shown Fig 3 See also Lets Talk About CG May 1980 Model Aviation placed wind tunnel cam bered wing alone wing attached fuselage no tail exhibits increas ing nose-up positive moment angle attack increased shown Fig 4 must countered horizontal tail produces negative div ing moment shown Fig 5 Lift wing acts AC wing 25% MAC Lift horizontal tail acts AC tail although common practice consider tail lift acting elevator hinge line practical reasons AC whole airplane N fore lies somewhat aft wing AC shown Fig 6 stick models fuselages engines etc position N may approximated weighted areas wing tail see April 1980 MA Actually N function moments affecting trim airplane moments change increasing angle attack shown Fig 7 Since moments vary angle attack ie constant must find position N dealing rates change derivatives better yet determine values wind tunnels Thus determination N easily made modeler creating own design Suffice say Neutral Point N Scale-type models lies very close 30% MAC after considering destabilizing effects power high angles attack fuselage nacelles also stabilizing effect extended landing gear produces favorable negative moment Fig 8 show three conditions show stable arrangement b show arrangement neutrally stable c show unstable arrangement stable condition Fig 8a CG shown about 27% MAC / / POSITIVE MOMENT no horizontal tail 4 Fig4 NL her w GATIVE TAIL MOMENT balances positive moment Fig 5 4/ 7 Forces producing Other moments Fig6 December 1984 89 thus 3 o forward Neutral Point may said have Stability Margin 3% MAC satisfactory 5% betterespecially beginners properly designed airplane downwash wing will place sufficient down load tail trim wing angle attack cruising usually about 30 tail set zero incidence zero elevator deflection cruis ing speed down landing speed creasing down-load up elevator re quired raise nose slow down minimum speed condition limits forward position CG keep stick forces pilot com fortable range Thus see CG forward N somewhat aft AC wing alone down load horizontal tail required maintain level flight up-load shown Fig 1 stable airplane time up-load tail required trim pilot wishes drop nose speed up beyond cruising speed As long CG forward N airplane will tend recover stall because negative diving moment pre vails shown Fig 9 due said forward CG location combination moment produced hori zontal tail negative moment increases becomes negative angle tack acts sort like spring pitch nose down recover stall deed criterion Longitudinal Sta bility curve Moment versus Angle Attack have negative slope shown Since position N conventional configurations lies ap proximately 30% MAC since 5% stability margin about right customary place CG 25% MAC Since 25% MAC also AC wing aione think causes some con fusion people seem believe CG AC wing no down-load tail have just seen simply case Neutral stability shown b Fig ures 8 9 prevails CG placed N under conditions no trim load tail other downwash much T-Tail configuration tail always loaded course basic up-load shown Fig 5 Lift N Weight pure opposition thus pro ducing no moment means plane will have no automatic recovery stall neither will want stall will very sensitive controls will make delight skilled Pattern flier beginner because unforgiving error control demanding control constantly otherwise going off its own slightest disturbance graph Fig 9 shown zero slope moment curve positive slope moment curve shown Fig 9c bad defines stability occurs CG aft N shown Fig 8c Under conditions airplane becomes less less controllable CG moved aft until completely unmanageable winds up buying farm say nose pitches up example forces play now arranged cause pitch up further thus stall ensues Nevertheless advent com puterized control latest military air craft possible satisfactorily operate aircraft unstable regime because computer can programmed antici pate sudden disaster before occurs correct controls maintain steady flight done super fighters can crab through air sideContinued page 176 N 30% MAC approx a stablecg limits t A25% Forward cg DOWN load tail Fig8a STABILITY N 0 W Fig Bb NEUTRAL STABILITY istability margin produces neg moment -balanced pos L downwash Fig C 0 E 0 N W 8c INSTABILITY Fig 9 unstable c 4 neutral b 0 036912 Angle attack-degrees CC 90 Model Aviation PATTERN SHIP AS GOOD AS YOU ARE. MAYBE BETTER T\DCIk Technician totally functional design combines great flying characteristics ease construc tion goad looks first quality kit throughout FIBERGLASS FUSELAGE FOAM CORES BASIC KIT BASIC HARDWARE PKG BASIC KIT $10795 DELUXE KIT $15995 Add $600 Freight direct shipment DEALER & DISTRIBUTOR INQUIRIES INVITED ALL OF THE ABOVE PLUS ALL REQUIRED BALSAS MOTOR MOUNT AND HARDWARE L&L MODEL MFGBV PRODUCTS 513 385-0912 7342 Applerlde Court CIncInnati Ohio 45247 CG try swapping spinners trim setup use gives better grove improves wind penetration tends dampen effects somewhat shortish nose airplane stands liter ally cockpit stitching rudder above others high angle attack low gross weight gets off rough fields goad order recent local holiday demonstration took Barnstormer out two full days actual barnstorming just like name says wasnt especially trying full pattern flight sometimes just doing big sweeping oldstyle maneuvers show folks what good CL ship can few closing thoughts Barnstorm er game build using oaly Ambroid Testors glue con sidered backed off moment weakness built know Modelers didnt always build oak steel cable ferro concrete present-day modeling counterparts writing advertisers mention read about Model Aviation LIghtweIght Foam WlnglEvans Continued page 85 / capstrip butt against Cut two strips balsa least A-in wider leading edge foam about /2 sheet A-in balsa Glue pin trailing edge again centering allow cap strips After leading trailing edges have dried mark cores 2-in inter vals locate cap strips Mark both top bottom cores top cap strips directly over bot tom cap strips Also mark location 3-in-wide inboard sheeting Place wing core top cradle flat surface place core top cradle bottom side up Cut board sheeting fit glue pin place bottom wing Next cut / x /l6 cap strips fit between leading trailing edges glue pin place Repeat steps other wing panel After bottom cap strips have dried place repeat top wing Again use wing cradles help ke wing free warps After assemblies dry trim ar sand leading trailing edges flu cap strips Mark locations lightening hole cut hole saw Cover wing transparent fil enable full effect work show construction described resulte weight reduction 50ofrom i oz 8 oz strength has moi adequate Airplane DesignlPowes Continued page 90 ways vertically off angle whil maintaining forward speed thus increas ing ability outmaneuver thei adversaries model industr comes out such equipment stability CG location will no longer 1 problems modelers Questions comments may dressed Brad Powers 5470 Castle Hill Dr San Diego CA 92109 Pomlilo PElNoonan Continued oaae 96 leading trailing edges win roots Bamboo 2-in OD aluminur pins about / long act method c indexing wings fuselage center cabane section fit i aluminum tubing fuselage wings important have tub ing exact alignment before cementing place assure accuracy necessary assemble wings th proper dihedral angle temporary ji apply epoxy wing root tubin has index pin place Allow cc ment dry before disassembling eight interplane struts may mad flattened plastic straws cut fror balsa use straw method whic has advantage being virtually destructible will necessary inser bamboo slivers about 1 long cad end strut allowing / pro Super Sport Planes Midwest Send $150 complete Kit Catalog q P Midwest Pmducts Co Inc G 400 5 Indiana St PO Box 564-SP Hobart 1n46342831032 DIVISION OF BAR/RICH SALES Co #2 FAIRWAY HANNIBAL MO 63401 314 221-6803 MANUFACTURERS OF SPORT PATTERNSTINGEI II PEPPERMINT PATTIE -60SPARTAN PEPPERMINT PATTIE 40 SPORT/SCALE PEPPERMINT PATTIE 15 HIPERBIPE 176 Model Aviation DELUXE KIT aster