How choose suitable airfoils for tailless models advent latest Northrop flying wing B-2 Stealth bomber expect will revival interest flying wings tailless airplanes Unfortunately also expect 40year-old mistakes repeated people attempt rediscover design flying wings have developing campaigning tailless models years now competitive superior conventional models class flying wing configuration well worth investigating important right people discuss flying wings lot ballyhoo about concept stable airfoils Reflexed airfoils discussed later usually held up examples magic stable airfoils no such thing stable airfoil Nor such thing unstable airfoil matter stability airplane depends relative positions center gravity aerodynamic center dependent shape airfoil notion stable airfoil misconceptions caused use archaic notion airfoil center pressure Noted aerodynamicist lrv Culver last word antiquated idea stated concept center pressure invented manufacturers oxcarts prevent manufacture aircraft kernel truth notion stable airfoils stable unswept tailless airplane must have airfoil positive pitching moment trim out nose-down moment produced putting center gravity ahead aerodynamic center required stability Although stable airfoil myth difference between types airfoils suitable tailless conventional airplanes very common mistake among designers tailless models use unsuitable airfoils An airfoil appropriate conventional airplane tail will right flying wing Pitching Moment addition producing lift drag airfoil generates torque pitching moment twists leading edge up down moment positive acts raise leading edge negative acts lower leading edge vital differences between tailless airplanes conventional airplanes pitching moment characteristics wing airfoil far important flying wing stable U Barnaby Wainfan September 1994 19 airplane trim airplane whole must have positive aerodynamic pitching moment about its aerodynamic center conventional airplanes moment provided tail tailless airplanes wing must produce necessary moment trim airplane welt providing lift support pitching moment generated airfoil called pitching moment about aerodynamic center zero-4ft pitching moment can nondimensionaiized same way lift drag reduced C1 Cd form pitching moment coefficient Cmx Cm0 pitching moment about aerodynamic center does change angle attack airfoil changes long airfoil stalled aerodynamic center located very near quarter-chord airfoil simplify things during discussion will simply refer pitching moment about aerodynamic center pitching moment Effect Camber Pitching Moment pitching moment generated airfoil determined almost entirely camber airfoil Both amount camber distribution camber have effect general camber airfoil has negative its pitching moment will symmetrical airfoil has no camber has zero Cm0 generates no pitching moment An airfoil negative inverted camber will generate positive nose up pitching moment distribution camber airfoil has dramatic effect its pitching moment Adding same amount camber different points airfoil affects pitching moment less depending chord camber added aft position camber larger its effect mo will figure shows primary reason aerodynamic center airfoil near 25% chord position lever arm leading edge aerodynamic center 25% chord lever arm trailing edge 75% chord other words camber change near leading edge will have Y3 lever arm camber change near trailing edge Because change aft camber roughiy three times effective changing pitching moment change camber near nose airfoil advanced airfoils general aviation have appeared last 5-10 years have featured large amounts aft camber Such airfoils also showing up some RC gliders Unfortunately aft-cambered airfoils also generate large negative pitching moments make entirely unsuitable tailless airplanes same true thin highly undercambered airfoils used free flight rubber models flat-bottomed airfoils like old reliable Clark Y produce some negative pitching moment result using negative-pitching-moment airfoil flying wing poor performance difficult trimming airplane must either have lots sweep washout large up-deflected tabs both have positive pitching moment required trim airplane flight Both approaches trimming can produce high drag poor performance also difficult get amount twist and/or tab deflection right first time flying wing models particularly free flight models damaged before can successfully trimmed Low-Moment Airfoils As reader may have already inferred above discussion vast majority airfoils produce negative nose down pitching moment surprising since airfoils have positive camber types airplane moderate amount negative pitching moment acceptable tail canard can easily generate enough pitching moment trim airplane 20 Model Aviation aby Wainfan launches Cyrano II Mile Square Park Los Angeles area Don Larsen photo authors Pee Wee-30 Successful competition models airfoil has less camber reflex Cyrano TD-020-powered model has won Northrop Flying Wing contest points way high-performance flying-wing models Unlike other airplane types tailless airplanes flying wings have separate surfaces such tails canards generate pitching moment trim stable airplane trim complete airplane configuration must generate positive aerodynamic pitching moment about aerodynamic center no tail canard wing must have positive pitching moment two ways create positive-pitching-moment wing first use combination sweepback washout zero total wing lift tips pushing down root lifting up second use airfoil has positive Cm0 use sweep twist limited several factors cannot produce very large pitching moment can enough trim airplane airfoil has little no negative pitching moment Unswept flying plank tailless airplanes must have positivepitching-moment airfoils order trim Airfoil Shapes Low Positive Pitching Moment camber low-pitching-moment airfoil suitable flying wings different camber conventional airfoils possible choice symmetrical airfoil disadvantage symmetrical sections have minimum drag zero lift wing symmetrical airfoil will have drag could airfoil properly cambered match cruise lift coefficient model Symmetrical sections have relatively low maximum lift coefficients can lead high stall speeds poor glide performance drawbacks problem RC models intended sport flying aerobatics fact symmetrical airfoil combined elevons pitch roll control good choice type model although airplane will always require smail trailing-edge-up deflection elevons fly level gliders free flight models must fly efficiently right-side up disadvantages symmetrical airfoils severe better solution required Negative-camber airfoils produce positive pitching moment therefore might considered suitable flying wings Unfortunately negative camber does work very well airfoil must generate positive lift negative-camber airfoil has its minimum drag negative lift coefficient very useful wants fly upright second problem negative camber causes maximum lift coefficient quite low fact negative-camber airfoil worse symmetrical airfoil negative-camber airfoil does seem very attractive solution problem designing efficient flying wing So far have seen two ways produce low-pitching-moment airfoils has limited usefulness would like retain lift drag advantages normal positive-camber airfoil airfoil positive zero pitching moment Reflex goal high-performance positive-pitching-moment airfoil can achieved using two facts about camber affects airfoil characteristics 1 Camber near trailing edge has much effect pitching moment camber near leading edge 2 Camber forward portion airfoil can have large Aft portion camber line concave up Forward position camber line concave down Reflexed airfoil has positive pitching moment Aft camber has effect pitching moment nose camber September 1994 21 22 Model Aviation tive effect maximum lift airfoil can move minimum drag positive lift coefficient Using two concepts arrive proper camber distribution highperformance positive zero-pitching-moment airfoil suitable use flying wing airfoil should have positive camber over its forward portion provide good lift drag characteristics negative camber over its aft portion control its pitching moment Note forward portion camber line airfoil concave downward aft portion camber line concave upward mathematical term curvature reversal type reflex type airfoil said have reflex camber Usuaily just called reflexed airfoil term reflex used describe amount upsweep aft portion airfoil amount reflex required determined desired pitching moment amount positive camber forward portion airfoil Reflexed airfoils can have positive pitching moments good lift drag characteristics general still tend have somewhat lower maximum lift coefficients conventionally cambered airfoils low render unacceptable Some Good Flying Wing Airfoils 1 Cyrano II P-30 airfoil constant-chord plank tailless P-30 model prototype won Open P-30 1984 Reno Nats plans published December 1986 Model Aviation still available Cyrano airfoil good all-around free flight flying wing airfoil have used successfully rubber models gas models Electrics has also used 48-inchspan RC HLG model thermals beautifully does penetrate well 2 Airfoil used Pee Wee 30 airfoil used Pee Wee 30 gas model won 1987 Orbiteers Annual model certainly competitive conventional models may well superior airfoil nearly flat-bottomed intended fastclimbing gas models burst-climber rubber models think would also work well RCHLG 3 Swallow P-30 Airfoil airfoil has lot camber other two excellent slow floaters have used successfully cruise-climbing rubber models towline gliders appropriate gas models because large undercamber forward will hurt climb performance airfoil gives best glide performance three presented 4 Airfoils Tailless RIC Sailplanes An excellent series airfoils RC glider flying wings developed Dave Jones Western Plan Service Coordinates available along plans Daves excellent Raven other flying wing models Western Plan Service 5621 Michelle Drive Torrance CA 90503 LmSH 710 Pkg 24- $295 2Satisfaction Guaranteed Ill L THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges e apply few drops favorite CA glue youre donei SUPER FAST SUPER EASY SUPER STRONG MFG CO INC.401-7 So Front St.Montezuma IA 50171 623-5154
Edition: Model Aviation - 1994/09
Page Numbers: 19, 20, 21, 22
How choose suitable airfoils for tailless models advent latest Northrop flying wing B-2 Stealth bomber expect will revival interest flying wings tailless airplanes Unfortunately also expect 40year-old mistakes repeated people attempt rediscover design flying wings have developing campaigning tailless models years now competitive superior conventional models class flying wing configuration well worth investigating important right people discuss flying wings lot ballyhoo about concept stable airfoils Reflexed airfoils discussed later usually held up examples magic stable airfoils no such thing stable airfoil Nor such thing unstable airfoil matter stability airplane depends relative positions center gravity aerodynamic center dependent shape airfoil notion stable airfoil misconceptions caused use archaic notion airfoil center pressure Noted aerodynamicist lrv Culver last word antiquated idea stated concept center pressure invented manufacturers oxcarts prevent manufacture aircraft kernel truth notion stable airfoils stable unswept tailless airplane must have airfoil positive pitching moment trim out nose-down moment produced putting center gravity ahead aerodynamic center required stability Although stable airfoil myth difference between types airfoils suitable tailless conventional airplanes very common mistake among designers tailless models use unsuitable airfoils An airfoil appropriate conventional airplane tail will right flying wing Pitching Moment addition producing lift drag airfoil generates torque pitching moment twists leading edge up down moment positive acts raise leading edge negative acts lower leading edge vital differences between tailless airplanes conventional airplanes pitching moment characteristics wing airfoil far important flying wing stable U Barnaby Wainfan September 1994 19 airplane trim airplane whole must have positive aerodynamic pitching moment about its aerodynamic center conventional airplanes moment provided tail tailless airplanes wing must produce necessary moment trim airplane welt providing lift support pitching moment generated airfoil called pitching moment about aerodynamic center zero-4ft pitching moment can nondimensionaiized same way lift drag reduced C1 Cd form pitching moment coefficient Cmx Cm0 pitching moment about aerodynamic center does change angle attack airfoil changes long airfoil stalled aerodynamic center located very near quarter-chord airfoil simplify things during discussion will simply refer pitching moment about aerodynamic center pitching moment Effect Camber Pitching Moment pitching moment generated airfoil determined almost entirely camber airfoil Both amount camber distribution camber have effect general camber airfoil has negative its pitching moment will symmetrical airfoil has no camber has zero Cm0 generates no pitching moment An airfoil negative inverted camber will generate positive nose up pitching moment distribution camber airfoil has dramatic effect its pitching moment Adding same amount camber different points airfoil affects pitching moment less depending chord camber added aft position camber larger its effect mo will figure shows primary reason aerodynamic center airfoil near 25% chord position lever arm leading edge aerodynamic center 25% chord lever arm trailing edge 75% chord other words camber change near leading edge will have Y3 lever arm camber change near trailing edge Because change aft camber roughiy three times effective changing pitching moment change camber near nose airfoil advanced airfoils general aviation have appeared last 5-10 years have featured large amounts aft camber Such airfoils also showing up some RC gliders Unfortunately aft-cambered airfoils also generate large negative pitching moments make entirely unsuitable tailless airplanes same true thin highly undercambered airfoils used free flight rubber models flat-bottomed airfoils like old reliable Clark Y produce some negative pitching moment result using negative-pitching-moment airfoil flying wing poor performance difficult trimming airplane must either have lots sweep washout large up-deflected tabs both have positive pitching moment required trim airplane flight Both approaches trimming can produce high drag poor performance also difficult get amount twist and/or tab deflection right first time flying wing models particularly free flight models damaged before can successfully trimmed Low-Moment Airfoils As reader may have already inferred above discussion vast majority airfoils produce negative nose down pitching moment surprising since airfoils have positive camber types airplane moderate amount negative pitching moment acceptable tail canard can easily generate enough pitching moment trim airplane 20 Model Aviation aby Wainfan launches Cyrano II Mile Square Park Los Angeles area Don Larsen photo authors Pee Wee-30 Successful competition models airfoil has less camber reflex Cyrano TD-020-powered model has won Northrop Flying Wing contest points way high-performance flying-wing models Unlike other airplane types tailless airplanes flying wings have separate surfaces such tails canards generate pitching moment trim stable airplane trim complete airplane configuration must generate positive aerodynamic pitching moment about aerodynamic center no tail canard wing must have positive pitching moment two ways create positive-pitching-moment wing first use combination sweepback washout zero total wing lift tips pushing down root lifting up second use airfoil has positive Cm0 use sweep twist limited several factors cannot produce very large pitching moment can enough trim airplane airfoil has little no negative pitching moment Unswept flying plank tailless airplanes must have positivepitching-moment airfoils order trim Airfoil Shapes Low Positive Pitching Moment camber low-pitching-moment airfoil suitable flying wings different camber conventional airfoils possible choice symmetrical airfoil disadvantage symmetrical sections have minimum drag zero lift wing symmetrical airfoil will have drag could airfoil properly cambered match cruise lift coefficient model Symmetrical sections have relatively low maximum lift coefficients can lead high stall speeds poor glide performance drawbacks problem RC models intended sport flying aerobatics fact symmetrical airfoil combined elevons pitch roll control good choice type model although airplane will always require smail trailing-edge-up deflection elevons fly level gliders free flight models must fly efficiently right-side up disadvantages symmetrical airfoils severe better solution required Negative-camber airfoils produce positive pitching moment therefore might considered suitable flying wings Unfortunately negative camber does work very well airfoil must generate positive lift negative-camber airfoil has its minimum drag negative lift coefficient very useful wants fly upright second problem negative camber causes maximum lift coefficient quite low fact negative-camber airfoil worse symmetrical airfoil negative-camber airfoil does seem very attractive solution problem designing efficient flying wing So far have seen two ways produce low-pitching-moment airfoils has limited usefulness would like retain lift drag advantages normal positive-camber airfoil airfoil positive zero pitching moment Reflex goal high-performance positive-pitching-moment airfoil can achieved using two facts about camber affects airfoil characteristics 1 Camber near trailing edge has much effect pitching moment camber near leading edge 2 Camber forward portion airfoil can have large Aft portion camber line concave up Forward position camber line concave down Reflexed airfoil has positive pitching moment Aft camber has effect pitching moment nose camber September 1994 21 22 Model Aviation tive effect maximum lift airfoil can move minimum drag positive lift coefficient Using two concepts arrive proper camber distribution highperformance positive zero-pitching-moment airfoil suitable use flying wing airfoil should have positive camber over its forward portion provide good lift drag characteristics negative camber over its aft portion control its pitching moment Note forward portion camber line airfoil concave downward aft portion camber line concave upward mathematical term curvature reversal type reflex type airfoil said have reflex camber Usuaily just called reflexed airfoil term reflex used describe amount upsweep aft portion airfoil amount reflex required determined desired pitching moment amount positive camber forward portion airfoil Reflexed airfoils can have positive pitching moments good lift drag characteristics general still tend have somewhat lower maximum lift coefficients conventionally cambered airfoils low render unacceptable Some Good Flying Wing Airfoils 1 Cyrano II P-30 airfoil constant-chord plank tailless P-30 model prototype won Open P-30 1984 Reno Nats plans published December 1986 Model Aviation still available Cyrano airfoil good all-around free flight flying wing airfoil have used successfully rubber models gas models Electrics has also used 48-inchspan RC HLG model thermals beautifully does penetrate well 2 Airfoil used Pee Wee 30 airfoil used Pee Wee 30 gas model won 1987 Orbiteers Annual model certainly competitive conventional models may well superior airfoil nearly flat-bottomed intended fastclimbing gas models burst-climber rubber models think would also work well RCHLG 3 Swallow P-30 Airfoil airfoil has lot camber other two excellent slow floaters have used successfully cruise-climbing rubber models towline gliders appropriate gas models because large undercamber forward will hurt climb performance airfoil gives best glide performance three presented 4 Airfoils Tailless RIC Sailplanes An excellent series airfoils RC glider flying wings developed Dave Jones Western Plan Service Coordinates available along plans Daves excellent Raven other flying wing models Western Plan Service 5621 Michelle Drive Torrance CA 90503 LmSH 710 Pkg 24- $295 2Satisfaction Guaranteed Ill L THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges e apply few drops favorite CA glue youre donei SUPER FAST SUPER EASY SUPER STRONG MFG CO INC.401-7 So Front St.Montezuma IA 50171 623-5154
Edition: Model Aviation - 1994/09
Page Numbers: 19, 20, 21, 22
How choose suitable airfoils for tailless models advent latest Northrop flying wing B-2 Stealth bomber expect will revival interest flying wings tailless airplanes Unfortunately also expect 40year-old mistakes repeated people attempt rediscover design flying wings have developing campaigning tailless models years now competitive superior conventional models class flying wing configuration well worth investigating important right people discuss flying wings lot ballyhoo about concept stable airfoils Reflexed airfoils discussed later usually held up examples magic stable airfoils no such thing stable airfoil Nor such thing unstable airfoil matter stability airplane depends relative positions center gravity aerodynamic center dependent shape airfoil notion stable airfoil misconceptions caused use archaic notion airfoil center pressure Noted aerodynamicist lrv Culver last word antiquated idea stated concept center pressure invented manufacturers oxcarts prevent manufacture aircraft kernel truth notion stable airfoils stable unswept tailless airplane must have airfoil positive pitching moment trim out nose-down moment produced putting center gravity ahead aerodynamic center required stability Although stable airfoil myth difference between types airfoils suitable tailless conventional airplanes very common mistake among designers tailless models use unsuitable airfoils An airfoil appropriate conventional airplane tail will right flying wing Pitching Moment addition producing lift drag airfoil generates torque pitching moment twists leading edge up down moment positive acts raise leading edge negative acts lower leading edge vital differences between tailless airplanes conventional airplanes pitching moment characteristics wing airfoil far important flying wing stable U Barnaby Wainfan September 1994 19 airplane trim airplane whole must have positive aerodynamic pitching moment about its aerodynamic center conventional airplanes moment provided tail tailless airplanes wing must produce necessary moment trim airplane welt providing lift support pitching moment generated airfoil called pitching moment about aerodynamic center zero-4ft pitching moment can nondimensionaiized same way lift drag reduced C1 Cd form pitching moment coefficient Cmx Cm0 pitching moment about aerodynamic center does change angle attack airfoil changes long airfoil stalled aerodynamic center located very near quarter-chord airfoil simplify things during discussion will simply refer pitching moment about aerodynamic center pitching moment Effect Camber Pitching Moment pitching moment generated airfoil determined almost entirely camber airfoil Both amount camber distribution camber have effect general camber airfoil has negative its pitching moment will symmetrical airfoil has no camber has zero Cm0 generates no pitching moment An airfoil negative inverted camber will generate positive nose up pitching moment distribution camber airfoil has dramatic effect its pitching moment Adding same amount camber different points airfoil affects pitching moment less depending chord camber added aft position camber larger its effect mo will figure shows primary reason aerodynamic center airfoil near 25% chord position lever arm leading edge aerodynamic center 25% chord lever arm trailing edge 75% chord other words camber change near leading edge will have Y3 lever arm camber change near trailing edge Because change aft camber roughiy three times effective changing pitching moment change camber near nose airfoil advanced airfoils general aviation have appeared last 5-10 years have featured large amounts aft camber Such airfoils also showing up some RC gliders Unfortunately aft-cambered airfoils also generate large negative pitching moments make entirely unsuitable tailless airplanes same true thin highly undercambered airfoils used free flight rubber models flat-bottomed airfoils like old reliable Clark Y produce some negative pitching moment result using negative-pitching-moment airfoil flying wing poor performance difficult trimming airplane must either have lots sweep washout large up-deflected tabs both have positive pitching moment required trim airplane flight Both approaches trimming can produce high drag poor performance also difficult get amount twist and/or tab deflection right first time flying wing models particularly free flight models damaged before can successfully trimmed Low-Moment Airfoils As reader may have already inferred above discussion vast majority airfoils produce negative nose down pitching moment surprising since airfoils have positive camber types airplane moderate amount negative pitching moment acceptable tail canard can easily generate enough pitching moment trim airplane 20 Model Aviation aby Wainfan launches Cyrano II Mile Square Park Los Angeles area Don Larsen photo authors Pee Wee-30 Successful competition models airfoil has less camber reflex Cyrano TD-020-powered model has won Northrop Flying Wing contest points way high-performance flying-wing models Unlike other airplane types tailless airplanes flying wings have separate surfaces such tails canards generate pitching moment trim stable airplane trim complete airplane configuration must generate positive aerodynamic pitching moment about aerodynamic center no tail canard wing must have positive pitching moment two ways create positive-pitching-moment wing first use combination sweepback washout zero total wing lift tips pushing down root lifting up second use airfoil has positive Cm0 use sweep twist limited several factors cannot produce very large pitching moment can enough trim airplane airfoil has little no negative pitching moment Unswept flying plank tailless airplanes must have positivepitching-moment airfoils order trim Airfoil Shapes Low Positive Pitching Moment camber low-pitching-moment airfoil suitable flying wings different camber conventional airfoils possible choice symmetrical airfoil disadvantage symmetrical sections have minimum drag zero lift wing symmetrical airfoil will have drag could airfoil properly cambered match cruise lift coefficient model Symmetrical sections have relatively low maximum lift coefficients can lead high stall speeds poor glide performance drawbacks problem RC models intended sport flying aerobatics fact symmetrical airfoil combined elevons pitch roll control good choice type model although airplane will always require smail trailing-edge-up deflection elevons fly level gliders free flight models must fly efficiently right-side up disadvantages symmetrical airfoils severe better solution required Negative-camber airfoils produce positive pitching moment therefore might considered suitable flying wings Unfortunately negative camber does work very well airfoil must generate positive lift negative-camber airfoil has its minimum drag negative lift coefficient very useful wants fly upright second problem negative camber causes maximum lift coefficient quite low fact negative-camber airfoil worse symmetrical airfoil negative-camber airfoil does seem very attractive solution problem designing efficient flying wing So far have seen two ways produce low-pitching-moment airfoils has limited usefulness would like retain lift drag advantages normal positive-camber airfoil airfoil positive zero pitching moment Reflex goal high-performance positive-pitching-moment airfoil can achieved using two facts about camber affects airfoil characteristics 1 Camber near trailing edge has much effect pitching moment camber near leading edge 2 Camber forward portion airfoil can have large Aft portion camber line concave up Forward position camber line concave down Reflexed airfoil has positive pitching moment Aft camber has effect pitching moment nose camber September 1994 21 22 Model Aviation tive effect maximum lift airfoil can move minimum drag positive lift coefficient Using two concepts arrive proper camber distribution highperformance positive zero-pitching-moment airfoil suitable use flying wing airfoil should have positive camber over its forward portion provide good lift drag characteristics negative camber over its aft portion control its pitching moment Note forward portion camber line airfoil concave downward aft portion camber line concave upward mathematical term curvature reversal type reflex type airfoil said have reflex camber Usuaily just called reflexed airfoil term reflex used describe amount upsweep aft portion airfoil amount reflex required determined desired pitching moment amount positive camber forward portion airfoil Reflexed airfoils can have positive pitching moments good lift drag characteristics general still tend have somewhat lower maximum lift coefficients conventionally cambered airfoils low render unacceptable Some Good Flying Wing Airfoils 1 Cyrano II P-30 airfoil constant-chord plank tailless P-30 model prototype won Open P-30 1984 Reno Nats plans published December 1986 Model Aviation still available Cyrano airfoil good all-around free flight flying wing airfoil have used successfully rubber models gas models Electrics has also used 48-inchspan RC HLG model thermals beautifully does penetrate well 2 Airfoil used Pee Wee 30 airfoil used Pee Wee 30 gas model won 1987 Orbiteers Annual model certainly competitive conventional models may well superior airfoil nearly flat-bottomed intended fastclimbing gas models burst-climber rubber models think would also work well RCHLG 3 Swallow P-30 Airfoil airfoil has lot camber other two excellent slow floaters have used successfully cruise-climbing rubber models towline gliders appropriate gas models because large undercamber forward will hurt climb performance airfoil gives best glide performance three presented 4 Airfoils Tailless RIC Sailplanes An excellent series airfoils RC glider flying wings developed Dave Jones Western Plan Service Coordinates available along plans Daves excellent Raven other flying wing models Western Plan Service 5621 Michelle Drive Torrance CA 90503 LmSH 710 Pkg 24- $295 2Satisfaction Guaranteed Ill L THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges e apply few drops favorite CA glue youre donei SUPER FAST SUPER EASY SUPER STRONG MFG CO INC.401-7 So Front St.Montezuma IA 50171 623-5154
Edition: Model Aviation - 1994/09
Page Numbers: 19, 20, 21, 22
How choose suitable airfoils for tailless models advent latest Northrop flying wing B-2 Stealth bomber expect will revival interest flying wings tailless airplanes Unfortunately also expect 40year-old mistakes repeated people attempt rediscover design flying wings have developing campaigning tailless models years now competitive superior conventional models class flying wing configuration well worth investigating important right people discuss flying wings lot ballyhoo about concept stable airfoils Reflexed airfoils discussed later usually held up examples magic stable airfoils no such thing stable airfoil Nor such thing unstable airfoil matter stability airplane depends relative positions center gravity aerodynamic center dependent shape airfoil notion stable airfoil misconceptions caused use archaic notion airfoil center pressure Noted aerodynamicist lrv Culver last word antiquated idea stated concept center pressure invented manufacturers oxcarts prevent manufacture aircraft kernel truth notion stable airfoils stable unswept tailless airplane must have airfoil positive pitching moment trim out nose-down moment produced putting center gravity ahead aerodynamic center required stability Although stable airfoil myth difference between types airfoils suitable tailless conventional airplanes very common mistake among designers tailless models use unsuitable airfoils An airfoil appropriate conventional airplane tail will right flying wing Pitching Moment addition producing lift drag airfoil generates torque pitching moment twists leading edge up down moment positive acts raise leading edge negative acts lower leading edge vital differences between tailless airplanes conventional airplanes pitching moment characteristics wing airfoil far important flying wing stable U Barnaby Wainfan September 1994 19 airplane trim airplane whole must have positive aerodynamic pitching moment about its aerodynamic center conventional airplanes moment provided tail tailless airplanes wing must produce necessary moment trim airplane welt providing lift support pitching moment generated airfoil called pitching moment about aerodynamic center zero-4ft pitching moment can nondimensionaiized same way lift drag reduced C1 Cd form pitching moment coefficient Cmx Cm0 pitching moment about aerodynamic center does change angle attack airfoil changes long airfoil stalled aerodynamic center located very near quarter-chord airfoil simplify things during discussion will simply refer pitching moment about aerodynamic center pitching moment Effect Camber Pitching Moment pitching moment generated airfoil determined almost entirely camber airfoil Both amount camber distribution camber have effect general camber airfoil has negative its pitching moment will symmetrical airfoil has no camber has zero Cm0 generates no pitching moment An airfoil negative inverted camber will generate positive nose up pitching moment distribution camber airfoil has dramatic effect its pitching moment Adding same amount camber different points airfoil affects pitching moment less depending chord camber added aft position camber larger its effect mo will figure shows primary reason aerodynamic center airfoil near 25% chord position lever arm leading edge aerodynamic center 25% chord lever arm trailing edge 75% chord other words camber change near leading edge will have Y3 lever arm camber change near trailing edge Because change aft camber roughiy three times effective changing pitching moment change camber near nose airfoil advanced airfoils general aviation have appeared last 5-10 years have featured large amounts aft camber Such airfoils also showing up some RC gliders Unfortunately aft-cambered airfoils also generate large negative pitching moments make entirely unsuitable tailless airplanes same true thin highly undercambered airfoils used free flight rubber models flat-bottomed airfoils like old reliable Clark Y produce some negative pitching moment result using negative-pitching-moment airfoil flying wing poor performance difficult trimming airplane must either have lots sweep washout large up-deflected tabs both have positive pitching moment required trim airplane flight Both approaches trimming can produce high drag poor performance also difficult get amount twist and/or tab deflection right first time flying wing models particularly free flight models damaged before can successfully trimmed Low-Moment Airfoils As reader may have already inferred above discussion vast majority airfoils produce negative nose down pitching moment surprising since airfoils have positive camber types airplane moderate amount negative pitching moment acceptable tail canard can easily generate enough pitching moment trim airplane 20 Model Aviation aby Wainfan launches Cyrano II Mile Square Park Los Angeles area Don Larsen photo authors Pee Wee-30 Successful competition models airfoil has less camber reflex Cyrano TD-020-powered model has won Northrop Flying Wing contest points way high-performance flying-wing models Unlike other airplane types tailless airplanes flying wings have separate surfaces such tails canards generate pitching moment trim stable airplane trim complete airplane configuration must generate positive aerodynamic pitching moment about aerodynamic center no tail canard wing must have positive pitching moment two ways create positive-pitching-moment wing first use combination sweepback washout zero total wing lift tips pushing down root lifting up second use airfoil has positive Cm0 use sweep twist limited several factors cannot produce very large pitching moment can enough trim airplane airfoil has little no negative pitching moment Unswept flying plank tailless airplanes must have positivepitching-moment airfoils order trim Airfoil Shapes Low Positive Pitching Moment camber low-pitching-moment airfoil suitable flying wings different camber conventional airfoils possible choice symmetrical airfoil disadvantage symmetrical sections have minimum drag zero lift wing symmetrical airfoil will have drag could airfoil properly cambered match cruise lift coefficient model Symmetrical sections have relatively low maximum lift coefficients can lead high stall speeds poor glide performance drawbacks problem RC models intended sport flying aerobatics fact symmetrical airfoil combined elevons pitch roll control good choice type model although airplane will always require smail trailing-edge-up deflection elevons fly level gliders free flight models must fly efficiently right-side up disadvantages symmetrical airfoils severe better solution required Negative-camber airfoils produce positive pitching moment therefore might considered suitable flying wings Unfortunately negative camber does work very well airfoil must generate positive lift negative-camber airfoil has its minimum drag negative lift coefficient very useful wants fly upright second problem negative camber causes maximum lift coefficient quite low fact negative-camber airfoil worse symmetrical airfoil negative-camber airfoil does seem very attractive solution problem designing efficient flying wing So far have seen two ways produce low-pitching-moment airfoils has limited usefulness would like retain lift drag advantages normal positive-camber airfoil airfoil positive zero pitching moment Reflex goal high-performance positive-pitching-moment airfoil can achieved using two facts about camber affects airfoil characteristics 1 Camber near trailing edge has much effect pitching moment camber near leading edge 2 Camber forward portion airfoil can have large Aft portion camber line concave up Forward position camber line concave down Reflexed airfoil has positive pitching moment Aft camber has effect pitching moment nose camber September 1994 21 22 Model Aviation tive effect maximum lift airfoil can move minimum drag positive lift coefficient Using two concepts arrive proper camber distribution highperformance positive zero-pitching-moment airfoil suitable use flying wing airfoil should have positive camber over its forward portion provide good lift drag characteristics negative camber over its aft portion control its pitching moment Note forward portion camber line airfoil concave downward aft portion camber line concave upward mathematical term curvature reversal type reflex type airfoil said have reflex camber Usuaily just called reflexed airfoil term reflex used describe amount upsweep aft portion airfoil amount reflex required determined desired pitching moment amount positive camber forward portion airfoil Reflexed airfoils can have positive pitching moments good lift drag characteristics general still tend have somewhat lower maximum lift coefficients conventionally cambered airfoils low render unacceptable Some Good Flying Wing Airfoils 1 Cyrano II P-30 airfoil constant-chord plank tailless P-30 model prototype won Open P-30 1984 Reno Nats plans published December 1986 Model Aviation still available Cyrano airfoil good all-around free flight flying wing airfoil have used successfully rubber models gas models Electrics has also used 48-inchspan RC HLG model thermals beautifully does penetrate well 2 Airfoil used Pee Wee 30 airfoil used Pee Wee 30 gas model won 1987 Orbiteers Annual model certainly competitive conventional models may well superior airfoil nearly flat-bottomed intended fastclimbing gas models burst-climber rubber models think would also work well RCHLG 3 Swallow P-30 Airfoil airfoil has lot camber other two excellent slow floaters have used successfully cruise-climbing rubber models towline gliders appropriate gas models because large undercamber forward will hurt climb performance airfoil gives best glide performance three presented 4 Airfoils Tailless RIC Sailplanes An excellent series airfoils RC glider flying wings developed Dave Jones Western Plan Service Coordinates available along plans Daves excellent Raven other flying wing models Western Plan Service 5621 Michelle Drive Torrance CA 90503 LmSH 710 Pkg 24- $295 2Satisfaction Guaranteed Ill L THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges e apply few drops favorite CA glue youre donei SUPER FAST SUPER EASY SUPER STRONG MFG CO INC.401-7 So Front St.Montezuma IA 50171 623-5154