MOST airplane factories have huge room full engineers Sit big drafting tables design ing landing gears wing ribs engine mounts fuselage bulkheads etc etc Periodically usually day designer approached Weights Engineers job keep track much things weigh go Weights engineers seem have built-in resistance adding anything making changes will add weight also sort sneaky designer wants add bracket support autopilot lets say estimates itto weigh 15 pounds Weights Engineer will probably convince him 2 pounds realistic figure designer later finds can item Weights Engineer will usually begrudgingly give him back pound half Actually course thousands items airplane very close stingy policy regarding weight followed airplane could wind up being seriously disastrously overweight because airplane designed stipulated Gross Weight made up basically two parts Weight Empty Useful Load Since structural performance reasons Gross Weight must held overweight items making up Weight Empty will reduce Useful Load Spruce Goose classic example poor choice material wood large airplane demanded upward revisions original weight estimate finally nothing left Useful Load So weights engineers seem tight fisted have good reason way good way modelers think also John Preston wrote article MA Jan 1978 praising virtues keeping weight down can no valid argument Now lets take look what Weights Engineers up job keep running tab weight equally important keep watch distribution weight sure CG limits exceeded Now can design still paper Fig 1 shows sawhorse supporting teetertotter two pounds butter side balanced pound other Its easy see pound butter will balance two pounds butter placed further support point Ignoring weight teetertotter itself fact product weight times its distance arm~ support point called its Moment because its relative importanceas matter great moment momentous because bears relation moment time basis balance simply moments produced two objects about support balance point must equal Thus 2 lb x foot equals 1 lb x two feet 2 ft-lb equals 2 ft-lb assign positive values moments side support point negative values other side 2 ft-lb t-lb 0 satisfies basic definition Equilibrium sum moments equal zero Now lets put extra pound butter right-hand side see two-pound package must move balance shown Fig 2 Adding extra pound right side moves two packages left side over bit away support knew would can still another way can place sawhorse off side call Reference Line let moments act opposition Up Down shown Fig 3 simply another way expressing 4 4 first two parts trilogy author dis cussed slinky friend CG now piece de resistance Howthe placement items ensure CG will de sired location Brad Powers same set conditions shown Fig 2 Using method can run continuing Weight Balance Summary butter together couple bottles milk plus dozen eggs want fact could keep running balance model airplane way Ill bet Before going further should probably di gress bit philosophical real airplane smallest parts excep tion rivetswhich allowed along paint general way must accounted because total effect impor tant other hand building kit designing scratch unreasonable impractical account maybe hundred small fuselage parts order estimate weight balance fuselage wing tail So following plans items should built rough completion weighed bathroom baby scale balanced finger string find weight CG major items CG item should accurately marked plans real airplanes begin fixed Gross Weight no consequence really quarter-scale Concept Bipe has fuselage weighs few ounces less yours final gross weight quite agreement mentioned instruction book long ballpark want fly End philosophical section So lets say building kit have indicated small pencilled notes crosses CGs fuselage wing tail together weights accurately fore aft directionalong thrust line wish vertical locations arent critical plans show servo receiver locations know wish place battery batteries cameras smoke generators etc course engine landing gear now time weigh items mark weights plan fact atthis point should start Weight Balance Sheet shown Fig 5 order necessary establish arbitrary reference line Fig 3 moment arms items can taken line can center line propeller inch forward Its location has no effect balance keeping once chosen important model like real airplane has both Weight Empty condition full Gross Weight Condition payload consists fuel must placed near CG its depletion will cause serious shift balance equally true course removable disposable items have spring-loaded pilot upon command pops out seat way rear makes spectacular parachute jump its just possible airplane will thrown off balance much will make nose-first landing still floating high air So cameras bombs etc either dropped used occasionally should placed CG like fuel possible Otherwise effect CG should determined will discuss further Fig 4 shows Inboard Profile hypo thetical model looks something like Cessna Off left placed zero reference line arbi trarily placed 20 inches forward leading edge wing root Lets assume have carefully figured MAC its location based planform similar Fig 6 Part 2 leading edge MAC Station 2075 aft Reference Line MAC 12 inches long model weigh approximately 20 lbs full fuel movie camera payload have built wing fuselage leaving ourselves room further work way installing radio etc have weighed items installed have indicated drawing plan install prop spinner weigh 4oz Sta 65 engine weighs 88 oz will Sta 10 etc Fig 5 Weight Balance Sheet enables us ascertain final weight well determine Balance weights items Weight Empty Condition add up 270 ounces 16875 pounds Adding 1 pound 54 Model Aviation fuel movie camera complete film 34 ounces brings Gross Weight up 20 pounds 320 ounces Now lets have look airplane balances Being good conscientious designers have honest conservative figures thus assuring believable answers sensible attitude have something weighs 6 ounces thats what its weight allowance sheet must show little allow support wiring etc conservative things will come out pretty well dont make proper allowances both weight space well problems invariably ensue isnt moralize just way works Fig 5 sum moments Weight Empty Condition adds up 6400 oz 6400 Solving arm givesa 2370 distance Weight Empty CG Reference Line express CG terms MAC subtract distance Ref Line LE MAC divide length MAC CG 237Q -2075 _ 295 246% MAC 1212 Since shooting 25% MAC very good indeed No need try improve since well within Stability Limits about 22% forward limit based good control aft limit Stability about 30% Now add fuel movie camera payload CG shouldnt change much since located desired CG location 25% Sta 2375 So Gross Weight adds up 320 oz 20 lbs having total moment 75875 oz As shown gives CG location 2466% essentially same Weight Empty Condition expected So appears good shape wont need add ballast rearrange things suppose balance say 27% acceptable CG locationbut perfectionists want keep good 5% stability margin figure what to bring 2% forward Gross Weight 20 lbs times MAC 12 in. 240 lb work represents 100% CG travel equivalent moving total weight full length MAC percent CG travel percent 240 Hft - -N 21b- -lib Ka b 1 ftj --fib lfb 2 Ibx ftllbxlftllbx2ft b t5ft 21b .Eig3 ret --__- lib- -- -- -_ Weight nt EUi ft1iM Libitt { ftlb lblift-lb 2 lba3ft-Ib 15 ft line in lb 24 lb same 384 oz So 2 percent shift CG amounts 2 x 384 or 768 oz two tail servos M weigh 6 oz support structure will weigh about 2 oz can move about 6 inches forward before get involved solid bulkhead picks up landing gear load So moving servos if405080 IIII MAC 12 2075 - REFERENCE LINE Fig 4 z9 ii Station65 ItemA U - 582615 N0 June 1980 55 20 30 137 C Ib7 1 5E F 2375 265 G25 K H IJ 3437 LM Fig 5 WEIGHT AND BALANCE SUMMARY ITEM AProp Spinner BEngine CNose Gear D4 C Nicads HThrottle Servo FReceiver GFuel Tank HMovie Camera Mount Aileron Servo J Wing K Main Gear L Fuselage M Tail Servos 2 N Horizontal Tail 0 Vertical Tail WEIGHT EMPIY tJWTP.0ZARMINMOMENT OZ-IN 40 880 60 80 30 60 30 30 30 500 100 620 60 100 80 65 100 13 150 157 180 2375 2375 250 250 265 340 370 582 615 2370 CG 2370 — 24 6% MAC 12 USEFUL LOAD Fuel 1 pint Movie Camera GROSS 160 340 WEIGHT3200 CG 2075 orward pick up 6 x 6 z So still need juggling equipment pick up difference 7 68-48 about 29 oz going achieve shift 2% can probably accomplished moving receiver throttle servo forward far possible placing servos forward bulkhead Under no circumstances should move fuel tank camera mount away CG can avoided 2375 1Z5 C 23771 260 8800 824 1200 471 1080 7125 7125 750 12500 2650 21080 2220 5820 6o 3800 2466 % MAC Now lets suppose CG 5% aft hoped would say 30% MAC would require extensive changes almost 200 oz. would cause serious practical problems What we arent too far along construction simplest answer just move wing 5% aft amounts to5% x 12 6 ofan inch cant done say because windshield structure something next best o tion sweep wing such way MAC moved 6 aft Moving wing such small amount has very powerful effect balance effect tail arm negligible Sweepback should held minimum however since too much can cause tip stall problems building scale model Jenny Sopwith Camel will certainly have balance problems since proportion ofengine weight total weight model much less real airplanes result because short nose model will tend quite tailheavy faithfully scaled down Since purists can regard lead ballast sacrilegious last resort what can case like First examine details aft CG reduce sand remove oversize redundant whittling sanding etc particularly well aft near tail Second beef up engine mounts real good add reinforcement forward CG isnt enough now time add D cell heat glow plug smoke generator really effective muffler still doesnt try brass boat flywheel under heavy metal spinner Jenny have have spinner starter engage dont worst comes worst get some lead fish weights bury Epoxo ... nobody will find handy kink have found useful place small screw some blocking 25% MAC point bottom wing panel projecting screw head serves guide fingers can lift airplane two points make final balance check airplane remains level supported fashion properly balanced hope series whys wherefores CG has interest would like hear may have some topic would like have try coverif feel qualified Otherwise editor will conjure up subjects seem need some light thrown 56 Model Aviation tions corn ments may addressed author care editor I
Edition: Model Aviation - 1980/06
Page Numbers: 54, 55, 56
MOST airplane factories have huge room full engineers Sit big drafting tables design ing landing gears wing ribs engine mounts fuselage bulkheads etc etc Periodically usually day designer approached Weights Engineers job keep track much things weigh go Weights engineers seem have built-in resistance adding anything making changes will add weight also sort sneaky designer wants add bracket support autopilot lets say estimates itto weigh 15 pounds Weights Engineer will probably convince him 2 pounds realistic figure designer later finds can item Weights Engineer will usually begrudgingly give him back pound half Actually course thousands items airplane very close stingy policy regarding weight followed airplane could wind up being seriously disastrously overweight because airplane designed stipulated Gross Weight made up basically two parts Weight Empty Useful Load Since structural performance reasons Gross Weight must held overweight items making up Weight Empty will reduce Useful Load Spruce Goose classic example poor choice material wood large airplane demanded upward revisions original weight estimate finally nothing left Useful Load So weights engineers seem tight fisted have good reason way good way modelers think also John Preston wrote article MA Jan 1978 praising virtues keeping weight down can no valid argument Now lets take look what Weights Engineers up job keep running tab weight equally important keep watch distribution weight sure CG limits exceeded Now can design still paper Fig 1 shows sawhorse supporting teetertotter two pounds butter side balanced pound other Its easy see pound butter will balance two pounds butter placed further support point Ignoring weight teetertotter itself fact product weight times its distance arm~ support point called its Moment because its relative importanceas matter great moment momentous because bears relation moment time basis balance simply moments produced two objects about support balance point must equal Thus 2 lb x foot equals 1 lb x two feet 2 ft-lb equals 2 ft-lb assign positive values moments side support point negative values other side 2 ft-lb t-lb 0 satisfies basic definition Equilibrium sum moments equal zero Now lets put extra pound butter right-hand side see two-pound package must move balance shown Fig 2 Adding extra pound right side moves two packages left side over bit away support knew would can still another way can place sawhorse off side call Reference Line let moments act opposition Up Down shown Fig 3 simply another way expressing 4 4 first two parts trilogy author dis cussed slinky friend CG now piece de resistance Howthe placement items ensure CG will de sired location Brad Powers same set conditions shown Fig 2 Using method can run continuing Weight Balance Summary butter together couple bottles milk plus dozen eggs want fact could keep running balance model airplane way Ill bet Before going further should probably di gress bit philosophical real airplane smallest parts excep tion rivetswhich allowed along paint general way must accounted because total effect impor tant other hand building kit designing scratch unreasonable impractical account maybe hundred small fuselage parts order estimate weight balance fuselage wing tail So following plans items should built rough completion weighed bathroom baby scale balanced finger string find weight CG major items CG item should accurately marked plans real airplanes begin fixed Gross Weight no consequence really quarter-scale Concept Bipe has fuselage weighs few ounces less yours final gross weight quite agreement mentioned instruction book long ballpark want fly End philosophical section So lets say building kit have indicated small pencilled notes crosses CGs fuselage wing tail together weights accurately fore aft directionalong thrust line wish vertical locations arent critical plans show servo receiver locations know wish place battery batteries cameras smoke generators etc course engine landing gear now time weigh items mark weights plan fact atthis point should start Weight Balance Sheet shown Fig 5 order necessary establish arbitrary reference line Fig 3 moment arms items can taken line can center line propeller inch forward Its location has no effect balance keeping once chosen important model like real airplane has both Weight Empty condition full Gross Weight Condition payload consists fuel must placed near CG its depletion will cause serious shift balance equally true course removable disposable items have spring-loaded pilot upon command pops out seat way rear makes spectacular parachute jump its just possible airplane will thrown off balance much will make nose-first landing still floating high air So cameras bombs etc either dropped used occasionally should placed CG like fuel possible Otherwise effect CG should determined will discuss further Fig 4 shows Inboard Profile hypo thetical model looks something like Cessna Off left placed zero reference line arbi trarily placed 20 inches forward leading edge wing root Lets assume have carefully figured MAC its location based planform similar Fig 6 Part 2 leading edge MAC Station 2075 aft Reference Line MAC 12 inches long model weigh approximately 20 lbs full fuel movie camera payload have built wing fuselage leaving ourselves room further work way installing radio etc have weighed items installed have indicated drawing plan install prop spinner weigh 4oz Sta 65 engine weighs 88 oz will Sta 10 etc Fig 5 Weight Balance Sheet enables us ascertain final weight well determine Balance weights items Weight Empty Condition add up 270 ounces 16875 pounds Adding 1 pound 54 Model Aviation fuel movie camera complete film 34 ounces brings Gross Weight up 20 pounds 320 ounces Now lets have look airplane balances Being good conscientious designers have honest conservative figures thus assuring believable answers sensible attitude have something weighs 6 ounces thats what its weight allowance sheet must show little allow support wiring etc conservative things will come out pretty well dont make proper allowances both weight space well problems invariably ensue isnt moralize just way works Fig 5 sum moments Weight Empty Condition adds up 6400 oz 6400 Solving arm givesa 2370 distance Weight Empty CG Reference Line express CG terms MAC subtract distance Ref Line LE MAC divide length MAC CG 237Q -2075 _ 295 246% MAC 1212 Since shooting 25% MAC very good indeed No need try improve since well within Stability Limits about 22% forward limit based good control aft limit Stability about 30% Now add fuel movie camera payload CG shouldnt change much since located desired CG location 25% Sta 2375 So Gross Weight adds up 320 oz 20 lbs having total moment 75875 oz As shown gives CG location 2466% essentially same Weight Empty Condition expected So appears good shape wont need add ballast rearrange things suppose balance say 27% acceptable CG locationbut perfectionists want keep good 5% stability margin figure what to bring 2% forward Gross Weight 20 lbs times MAC 12 in. 240 lb work represents 100% CG travel equivalent moving total weight full length MAC percent CG travel percent 240 Hft - -N 21b- -lib Ka b 1 ftj --fib lfb 2 Ibx ftllbxlftllbx2ft b t5ft 21b .Eig3 ret --__- lib- -- -- -_ Weight nt EUi ft1iM Libitt { ftlb lblift-lb 2 lba3ft-Ib 15 ft line in lb 24 lb same 384 oz So 2 percent shift CG amounts 2 x 384 or 768 oz two tail servos M weigh 6 oz support structure will weigh about 2 oz can move about 6 inches forward before get involved solid bulkhead picks up landing gear load So moving servos if405080 IIII MAC 12 2075 - REFERENCE LINE Fig 4 z9 ii Station65 ItemA U - 582615 N0 June 1980 55 20 30 137 C Ib7 1 5E F 2375 265 G25 K H IJ 3437 LM Fig 5 WEIGHT AND BALANCE SUMMARY ITEM AProp Spinner BEngine CNose Gear D4 C Nicads HThrottle Servo FReceiver GFuel Tank HMovie Camera Mount Aileron Servo J Wing K Main Gear L Fuselage M Tail Servos 2 N Horizontal Tail 0 Vertical Tail WEIGHT EMPIY tJWTP.0ZARMINMOMENT OZ-IN 40 880 60 80 30 60 30 30 30 500 100 620 60 100 80 65 100 13 150 157 180 2375 2375 250 250 265 340 370 582 615 2370 CG 2370 — 24 6% MAC 12 USEFUL LOAD Fuel 1 pint Movie Camera GROSS 160 340 WEIGHT3200 CG 2075 orward pick up 6 x 6 z So still need juggling equipment pick up difference 7 68-48 about 29 oz going achieve shift 2% can probably accomplished moving receiver throttle servo forward far possible placing servos forward bulkhead Under no circumstances should move fuel tank camera mount away CG can avoided 2375 1Z5 C 23771 260 8800 824 1200 471 1080 7125 7125 750 12500 2650 21080 2220 5820 6o 3800 2466 % MAC Now lets suppose CG 5% aft hoped would say 30% MAC would require extensive changes almost 200 oz. would cause serious practical problems What we arent too far along construction simplest answer just move wing 5% aft amounts to5% x 12 6 ofan inch cant done say because windshield structure something next best o tion sweep wing such way MAC moved 6 aft Moving wing such small amount has very powerful effect balance effect tail arm negligible Sweepback should held minimum however since too much can cause tip stall problems building scale model Jenny Sopwith Camel will certainly have balance problems since proportion ofengine weight total weight model much less real airplanes result because short nose model will tend quite tailheavy faithfully scaled down Since purists can regard lead ballast sacrilegious last resort what can case like First examine details aft CG reduce sand remove oversize redundant whittling sanding etc particularly well aft near tail Second beef up engine mounts real good add reinforcement forward CG isnt enough now time add D cell heat glow plug smoke generator really effective muffler still doesnt try brass boat flywheel under heavy metal spinner Jenny have have spinner starter engage dont worst comes worst get some lead fish weights bury Epoxo ... nobody will find handy kink have found useful place small screw some blocking 25% MAC point bottom wing panel projecting screw head serves guide fingers can lift airplane two points make final balance check airplane remains level supported fashion properly balanced hope series whys wherefores CG has interest would like hear may have some topic would like have try coverif feel qualified Otherwise editor will conjure up subjects seem need some light thrown 56 Model Aviation tions corn ments may addressed author care editor I
Edition: Model Aviation - 1980/06
Page Numbers: 54, 55, 56
MOST airplane factories have huge room full engineers Sit big drafting tables design ing landing gears wing ribs engine mounts fuselage bulkheads etc etc Periodically usually day designer approached Weights Engineers job keep track much things weigh go Weights engineers seem have built-in resistance adding anything making changes will add weight also sort sneaky designer wants add bracket support autopilot lets say estimates itto weigh 15 pounds Weights Engineer will probably convince him 2 pounds realistic figure designer later finds can item Weights Engineer will usually begrudgingly give him back pound half Actually course thousands items airplane very close stingy policy regarding weight followed airplane could wind up being seriously disastrously overweight because airplane designed stipulated Gross Weight made up basically two parts Weight Empty Useful Load Since structural performance reasons Gross Weight must held overweight items making up Weight Empty will reduce Useful Load Spruce Goose classic example poor choice material wood large airplane demanded upward revisions original weight estimate finally nothing left Useful Load So weights engineers seem tight fisted have good reason way good way modelers think also John Preston wrote article MA Jan 1978 praising virtues keeping weight down can no valid argument Now lets take look what Weights Engineers up job keep running tab weight equally important keep watch distribution weight sure CG limits exceeded Now can design still paper Fig 1 shows sawhorse supporting teetertotter two pounds butter side balanced pound other Its easy see pound butter will balance two pounds butter placed further support point Ignoring weight teetertotter itself fact product weight times its distance arm~ support point called its Moment because its relative importanceas matter great moment momentous because bears relation moment time basis balance simply moments produced two objects about support balance point must equal Thus 2 lb x foot equals 1 lb x two feet 2 ft-lb equals 2 ft-lb assign positive values moments side support point negative values other side 2 ft-lb t-lb 0 satisfies basic definition Equilibrium sum moments equal zero Now lets put extra pound butter right-hand side see two-pound package must move balance shown Fig 2 Adding extra pound right side moves two packages left side over bit away support knew would can still another way can place sawhorse off side call Reference Line let moments act opposition Up Down shown Fig 3 simply another way expressing 4 4 first two parts trilogy author dis cussed slinky friend CG now piece de resistance Howthe placement items ensure CG will de sired location Brad Powers same set conditions shown Fig 2 Using method can run continuing Weight Balance Summary butter together couple bottles milk plus dozen eggs want fact could keep running balance model airplane way Ill bet Before going further should probably di gress bit philosophical real airplane smallest parts excep tion rivetswhich allowed along paint general way must accounted because total effect impor tant other hand building kit designing scratch unreasonable impractical account maybe hundred small fuselage parts order estimate weight balance fuselage wing tail So following plans items should built rough completion weighed bathroom baby scale balanced finger string find weight CG major items CG item should accurately marked plans real airplanes begin fixed Gross Weight no consequence really quarter-scale Concept Bipe has fuselage weighs few ounces less yours final gross weight quite agreement mentioned instruction book long ballpark want fly End philosophical section So lets say building kit have indicated small pencilled notes crosses CGs fuselage wing tail together weights accurately fore aft directionalong thrust line wish vertical locations arent critical plans show servo receiver locations know wish place battery batteries cameras smoke generators etc course engine landing gear now time weigh items mark weights plan fact atthis point should start Weight Balance Sheet shown Fig 5 order necessary establish arbitrary reference line Fig 3 moment arms items can taken line can center line propeller inch forward Its location has no effect balance keeping once chosen important model like real airplane has both Weight Empty condition full Gross Weight Condition payload consists fuel must placed near CG its depletion will cause serious shift balance equally true course removable disposable items have spring-loaded pilot upon command pops out seat way rear makes spectacular parachute jump its just possible airplane will thrown off balance much will make nose-first landing still floating high air So cameras bombs etc either dropped used occasionally should placed CG like fuel possible Otherwise effect CG should determined will discuss further Fig 4 shows Inboard Profile hypo thetical model looks something like Cessna Off left placed zero reference line arbi trarily placed 20 inches forward leading edge wing root Lets assume have carefully figured MAC its location based planform similar Fig 6 Part 2 leading edge MAC Station 2075 aft Reference Line MAC 12 inches long model weigh approximately 20 lbs full fuel movie camera payload have built wing fuselage leaving ourselves room further work way installing radio etc have weighed items installed have indicated drawing plan install prop spinner weigh 4oz Sta 65 engine weighs 88 oz will Sta 10 etc Fig 5 Weight Balance Sheet enables us ascertain final weight well determine Balance weights items Weight Empty Condition add up 270 ounces 16875 pounds Adding 1 pound 54 Model Aviation fuel movie camera complete film 34 ounces brings Gross Weight up 20 pounds 320 ounces Now lets have look airplane balances Being good conscientious designers have honest conservative figures thus assuring believable answers sensible attitude have something weighs 6 ounces thats what its weight allowance sheet must show little allow support wiring etc conservative things will come out pretty well dont make proper allowances both weight space well problems invariably ensue isnt moralize just way works Fig 5 sum moments Weight Empty Condition adds up 6400 oz 6400 Solving arm givesa 2370 distance Weight Empty CG Reference Line express CG terms MAC subtract distance Ref Line LE MAC divide length MAC CG 237Q -2075 _ 295 246% MAC 1212 Since shooting 25% MAC very good indeed No need try improve since well within Stability Limits about 22% forward limit based good control aft limit Stability about 30% Now add fuel movie camera payload CG shouldnt change much since located desired CG location 25% Sta 2375 So Gross Weight adds up 320 oz 20 lbs having total moment 75875 oz As shown gives CG location 2466% essentially same Weight Empty Condition expected So appears good shape wont need add ballast rearrange things suppose balance say 27% acceptable CG locationbut perfectionists want keep good 5% stability margin figure what to bring 2% forward Gross Weight 20 lbs times MAC 12 in. 240 lb work represents 100% CG travel equivalent moving total weight full length MAC percent CG travel percent 240 Hft - -N 21b- -lib Ka b 1 ftj --fib lfb 2 Ibx ftllbxlftllbx2ft b t5ft 21b .Eig3 ret --__- lib- -- -- -_ Weight nt EUi ft1iM Libitt { ftlb lblift-lb 2 lba3ft-Ib 15 ft line in lb 24 lb same 384 oz So 2 percent shift CG amounts 2 x 384 or 768 oz two tail servos M weigh 6 oz support structure will weigh about 2 oz can move about 6 inches forward before get involved solid bulkhead picks up landing gear load So moving servos if405080 IIII MAC 12 2075 - REFERENCE LINE Fig 4 z9 ii Station65 ItemA U - 582615 N0 June 1980 55 20 30 137 C Ib7 1 5E F 2375 265 G25 K H IJ 3437 LM Fig 5 WEIGHT AND BALANCE SUMMARY ITEM AProp Spinner BEngine CNose Gear D4 C Nicads HThrottle Servo FReceiver GFuel Tank HMovie Camera Mount Aileron Servo J Wing K Main Gear L Fuselage M Tail Servos 2 N Horizontal Tail 0 Vertical Tail WEIGHT EMPIY tJWTP.0ZARMINMOMENT OZ-IN 40 880 60 80 30 60 30 30 30 500 100 620 60 100 80 65 100 13 150 157 180 2375 2375 250 250 265 340 370 582 615 2370 CG 2370 — 24 6% MAC 12 USEFUL LOAD Fuel 1 pint Movie Camera GROSS 160 340 WEIGHT3200 CG 2075 orward pick up 6 x 6 z So still need juggling equipment pick up difference 7 68-48 about 29 oz going achieve shift 2% can probably accomplished moving receiver throttle servo forward far possible placing servos forward bulkhead Under no circumstances should move fuel tank camera mount away CG can avoided 2375 1Z5 C 23771 260 8800 824 1200 471 1080 7125 7125 750 12500 2650 21080 2220 5820 6o 3800 2466 % MAC Now lets suppose CG 5% aft hoped would say 30% MAC would require extensive changes almost 200 oz. would cause serious practical problems What we arent too far along construction simplest answer just move wing 5% aft amounts to5% x 12 6 ofan inch cant done say because windshield structure something next best o tion sweep wing such way MAC moved 6 aft Moving wing such small amount has very powerful effect balance effect tail arm negligible Sweepback should held minimum however since too much can cause tip stall problems building scale model Jenny Sopwith Camel will certainly have balance problems since proportion ofengine weight total weight model much less real airplanes result because short nose model will tend quite tailheavy faithfully scaled down Since purists can regard lead ballast sacrilegious last resort what can case like First examine details aft CG reduce sand remove oversize redundant whittling sanding etc particularly well aft near tail Second beef up engine mounts real good add reinforcement forward CG isnt enough now time add D cell heat glow plug smoke generator really effective muffler still doesnt try brass boat flywheel under heavy metal spinner Jenny have have spinner starter engage dont worst comes worst get some lead fish weights bury Epoxo ... nobody will find handy kink have found useful place small screw some blocking 25% MAC point bottom wing panel projecting screw head serves guide fingers can lift airplane two points make final balance check airplane remains level supported fashion properly balanced hope series whys wherefores CG has interest would like hear may have some topic would like have try coverif feel qualified Otherwise editor will conjure up subjects seem need some light thrown 56 Model Aviation tions corn ments may addressed author care editor I