BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW
Edition: Model Aviation - 1976/06
Page Numbers: 42, 43, 44, 45, 46, 99, 100
BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW
Edition: Model Aviation - 1976/06
Page Numbers: 42, 43, 44, 45, 46, 99, 100
BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW
Edition: Model Aviation - 1976/06
Page Numbers: 42, 43, 44, 45, 46, 99, 100
BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW
Edition: Model Aviation - 1976/06
Page Numbers: 42, 43, 44, 45, 46, 99, 100
BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW
Edition: Model Aviation - 1976/06
Page Numbers: 42, 43, 44, 45, 46, 99, 100
BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW
Edition: Model Aviation - 1976/06
Page Numbers: 42, 43, 44, 45, 46, 99, 100
BALSA. different beloved hobby-sport would Can imagine cutting wing ribs pine tend think balsa model air craft natural companions wasnt always way sport model aviations earliest daysaround 1910balsa used Models build pine spruce cane bamboo covered varnished silk thin leather 1923 about half structure typi cal contest model become balsa As late mid-thirties rounded wing tips tail surfaces made bamboo often balsa balsa come predominant modeling structural material Balsas dominance model aircraft structures surprising has low est density commercial structural wood world might surprise know balsa classified bot anists lumbering industry hardwood botanical classification woods either hardwoods softwoods nothing actual hardness softness wood Technically hard woods have seeds enclosed acorn oak whereas softwoodsthe cone-bearing trees examplehave seeds exposed Roughly speaking evergreens softwoods deciduous treesthose lose leaves Fallare hardwoods cellular struc tures two kinds woods quite different Softwoods non-porous cells short tubes closed ends Hardwoods porous cells long open ended Balsa ranges Bolivia Mexico few trees have reported far north southern coast Florida balsa attains its best state development principally Ecuador Colombia northern Peru Given plenty sun rain elbow room well-drained bottom land close rivers too high altitude balsa tree attains height 50 60 feet diameter 24 30 in six years about its best age cutting tree branches toward top section below branches commercial value Un der poorer conditions tree grows slowly has too high density commercial value Some balsa has grown plantations bulk com mercial balsa occurs spon taneously second-growth tree Trees felled stripped bark hauled nearest stream bank animal power tied rafts preparatory downstream journey mills might take days weeks mills rafts disassembled logs sawed boards sopping wet boards stacked such way permit air circulation placed kilns according rigid schedule temperature humid ity wood dried over period What Should Know About Balsa addition facts about favorite wood article describes various cuts grains selected different parts models Bob Meuser several days moisture content about 7% Air drying cheaper less successful After sorting grading some additional cutting woodwhich has now become lumber bundled shipped Rays Rings Things look end log say pine redwood see more-or-less con centric rings consisting alternate layers hard soft wood Under condi tions pair such rings represent years growth properly referred annual gro wth rings simply annual rings Somehow literature hobby often becomes distorted annular rings ring would have tough time being anything other annular since annular means ring-like some species balsa particular ly also see lines radiate center log lines actually rows renegade cells grow outward center tree rather direction length tree nice little cells should cells wood strong stiff lengthwise direc tion weak flimsy lateral direction somewhat abnormal radially-oriented sheets cellsor med ullary rays botanists would have itplay important part proper ties balsa also account some folklore mythology associated balsa terms annual rings medul lary rays seem verbose well just call rings rays rings dominate appearance cross section woods rays often scarcely visible balsa however rays dominate appear ance rings appear mere slight dis colorations regions hard soft wood indeed truly annual rings balsa must spaced inch two apart account rate growth dominance appearance rays balsa rather rings woods has apparently caused considerable confusion labeling wood according grain orientation Balsa Grain C model aviation use letter designate angle between rays surface sheet rays A-grain wood perpendicular surface within about 10 degrees C-grain wood quarter-grain wood often called rays parallel surface make angle no 10 degrees surface C-grain easily identified almost iridescent specks streaks exposed rays Bgrain might have guessed half way between two rays make angle roughly 35 55 degrees surface region between A-grain B-grain according folk-jargon hobby often called AR-grain between Bgrain C-grain called BC-grain designations precisely defined fact sheet cut close cen ter tree possible have C-grain edge A-grain other According Frank Zaic ABCgrain designations originated early thirties brother John John found speckly stuff called C-grain could sliced ribs door models would retain shape Prior discovery ribs steamed shape straight sticks Having no knowledge proper lumbering dustry designations John invented ABC terminology John cut balsa friends New York Aeronuts club later went commercial under name Jasco Junior Aeronautic Supplies Company Frank took over business John went Europe 1932 Both Frank Jasco happy report 42 Model Aviation Piain sawed tangent cut flat grait A-ffrain 4~5 -5rain 800 J5-fjrain qitarter sawed edge 57rain Quartered yrain 2/ II / C-grain zzzzi- d quarter 9ratn ngs domiuiant &a4a 2 Forest products industry terms An9Ie hetueen rays su rface 4-lodel aiation terms alive well Later dis covered lumber industry name speckly stuff term quar ter-grain became synonymous Cgrain modeling lumberman would raise eyebrow two term quarter grain might ask mean quar ter sawed perhaps quarter sawn depending lives lumber mans term quarter-sawed includes what call C-grain quarter-grain wood includes lot too forest-products industry quar tered quarter sawed edge grain mean precisely same thing namely rings make angle 45 degrees surface rays make angle less 45 degrees surface Plainsawed tangent cut flat grain used designate wood has rings make angle less 45 degrees surface Between two sets terms wood tree accounted easy see terms devel oped Quarter-sawed oak once prized its appearance get much good-looking stuff out log pos sible log first sawed quarters sawed boards order have durable wearing surface premium grade softwood flooring selec ted edges hard rings ap pear surface terms quarter sawed edge grain mean precisely same thing wouldnt speak edge-grain oak quarter-sawed fir flooring Sig large balsa manufacturer designates material according its grain orientation Sig has grade called C-grain 8-12 lb balsa Glen Sigafoose tells us grading done eye ballingjudging grain angle appearance surface sheet rather actual measurement angle grain such nonsense eyeballing way Zaic lads did thirties too course will find some C-grain material among Sigs Contest Balsa Very Hard Balsa youll have thumb through stuff local hobby emporium find few cottage-industry manufacturers balsa specifically indoor microfilm models match grain application supply particular grain orientation request Weight Grading Modelers often judge density balsa hefting bending little both length wise crosswise perhaps hobby shop salesman isnt looking gouging thumbnail After weighJune1976 43 A C-grain quarter-grain balsa rayscells grow outward tree centerare paral 161 surface directly across grain Wood stiff cracks easily bent too sharply across grain B Rays 30 deg surface still have mother-of-pearl appearance might called B-C graindesignations precise Compare chart preceding page Know About Balsa ing calculating density piece balsa has come work shop have concluded thumbnail rather poor judge density C-grain wood usually seems dense scale says thin sheet usually seems lower density really critical applications ask hobby shop salesperson can weigh wood before buy tried local hobby shop worked wanted superlight stuff gliders just happy have cull out light stuff customers wanted heavier grades density balsa designated terms such light balsa hard balsa precisely its weight pounds per cubic foot brevity use terms like six-pound balsa whereas six-pound-per-cubic-foot balsa what mean simply too much mouthful Terms such hard balsa soft balsa precisely defined yet general understanding among modelers what terms mean Still possible two identical models built medium balsa differ weight 30% simply cause wide range densities cluded term medium balsa makes communication difficult between author construction article person trying duplicate model pre sented article critical applica tions Tal- better specify density wood used pounds per cubic foot use term such medium balsa spare reader chore calculating density would good idea specify weight particular size sheet strip used following table presents grading system originated AeroModeller magazine included booklet dis tributed Sig called Important Facts About Balsa Wood People Like Know About Everything ask dealer its free Sigs catalog grading system has its deficien cies rather confuse things starting another system hobby would well advised stick inasmuch has already widely distributed C Rays 60 deg surface cause slight mother-of-pearl appearance might designated A-B grain good model ing imperative appropriate grains used various parts plane D Rays A-grain balsa approximately 90 deg surface easily seen wood bends easily across grain Ultra-Light- Me- Me-ExtraLight Gradelightma dium dium- Hard hard diumhard Density 6 6-88-99-1010-121416 lb/cu ft under modelers weigh piece balsa comes workshops mark weight piece Some also calculate density pounds per cu ft mark piece too probably little point doing however unless probability wood will cut strips sanded different thickness tables graphs have appeared various magazines converting weight density simplest kind presented Simply go across line size wood have go down column weight piece read density In-between values can determined well enough estimation closer work sizes listed expensive four-function pocket calculator will make quick work simply matter multiplying weight grams value K particular size wood listed last column table know density want divide K get weight look weight-grading stack wood same size use calculator con stant mode sizes listed value K can calculated formula given bottom table Stress Strength Such cell walls woods made roughly same stuff balsa cells relatively large thin walled accounts its low density sur prising density balsa increases its mechanical properties ap proach lighter structural softwoods spruce pine fir some woods cells partially filled resins other materials add weight contribute little strength such materials absent balsa infer strength stiffness other mechanical properties vary exact proportion its density would mistake mechanical properties highdensity balsa generally superior relation its weight lighter wood before go too far better define some terms well need Stress does relate properties wood rather load applied it force divided area over force applied stress may directtension compression shear best illustrated sketches strength material its ability resist stress failure Failure can mean several things failure taken mean actual separation col lapse material corresponding strength referred ultimate strength failure taken mean *Emzzi 4 1LLzz4 -r Bending cau3es. __ TOr6 ion causes. 17 Thn5de ct Compress i# 6hear __ sses tensile -I stresies ofan shears/rsse material gives will return its original size shape load removed corresponding strength called yield strength Stiffness quite different thing strength re lation between stress deflection dis tortion material stiffness relation direct stress called mod ulus elasticity Youngs modulus stiffness relation shear stress called modulus rigidity shear modujus sorts other kinds strength mentioned such cleavage strength bending strength etc fundamental kinds strength look tiny piece spar being bent would find that piece acted upon simple direct shear stresses combinations thoseturn page s/i ca r stresses June1976 45 Stresses Above Forces acting upon wood used model vary greatly hence need proper selection Below Very soft balsa top photo snaps across grain bent Hard balsa breaks easy-to-repair jagged tear 1 Know About Balsa /4 Balsa classified hard wood believe what structure hard wood looks likeif want technical about 1 cross sectional face 2 radial face 3 tangential face 4 annual ring 5 earlywood 6 latewood 7 wood ray 8 vessel 9 perforation plate Courtesy US Forest Products Labora tory BALSA DENSITY TABLE sheets 3 x 36 strips 36 long Table gives weight grams SheetsDensity lb/cu-ft thickness4567810121416K 1/32354443532620709886106124142113 1/16709886943124142177213248284564 3/32106133159186213266319372425376 1/8142177213248284354425496567282 3/16213266319372425532638744851188 1/4284354425496567709851992113.141 3/8425532638744851106128149170.094 1/2567709851992113142170198227.071 Strip Noof sizestrips 1/16x 1/16 16 1/16x 1/88 236295354413473591709827945169 116x144 3/32x 3/328 2 66332399465532664797930106150 3/32x3/16 4 1/8x 1/88 1/8x1/44473591709827945118142165189847 18x122 3/16x3/164s32664797930106133159186213752 3/16x3/82 1/4 xl/44 1/4x1/22945118142165189236284331378424 1/4xl1 closer work sizes listed Density lb/cu-ft ht grams x K Weight grams ity lb/cu-ft / K K appears right column table sizes listed K may calculated formula 381 K Lx W x Tx N L W T length width thickness inches N number pieces Now have learned modulus refers stiffness material its strength let throw mod ulus rupture term used express strength beamsspars usof rectangular cross section long thin beam principal states stress ten sion surface varying compression opposite surface because peculiar properties wood bending strength beam related tensile compressive strength material simple way Since bend ing strength wood important structural application wood modulus rupture important property just wish invented less confusing namefor guess name justified inasmuch modulus simply means measure Besides strength stiffness other properties wood importance especially important toughness Toughness ability absorb energy fracturing Gen erally speaking brittle materialsthose snaphave low toughness stretch give lot before finally let gowe would call ductile talking about metalshave high toughness expense possibly ruining day must mention another kind fail ure important Consider very straight piece 1/8-in sq balsa 24 long Put between two pointing fingers push two toward other some point stick will sudden ly start bend sideways though pushing stick lengthwise buckling failure say stick has failednot sense has broken rather sense can no longer resist load elastic insta bility kind failure has nothing whatsoever strength material depends entirely stiff nessthe elastic modulusof material dimensions member Which Grain Best great deal folk lore witchcraft has developed around application various grain orientations specific parts model hand some mod elers use C-grain material everything C-grain available other hand some modelers wont use C-grain anything can avoided Some claim C-grain brittle shatters easily whereas A-grain tougher tears rather shatters some applications undoubtedly true general state ment makes little sense inasmuch grain C-grain same wood merely cut differently Further case piece square stock no difference between C grain continued page 99 46 Model Aviation just depends upon surface look insofar bending across grain concerned can no question Cgrain stiffer A-grain roll ing sheet balsa tubethe tailboom Nordic glider perhapsthen A-grain stuff use want sure wont split being rolled goal maximum stiffness against lateral crushing after made C-grain stuff difficult understand consider basic structure wood stresses acting tempts bend cells wood form tiny thin-walled tubes strong stiff longitu dinal direction like tube weak lateral direction bend sheet cross-wise wood inside bend subjected compressive stress es oriented across grain wood outside curve acted upon tensile stresses directed across grain A-grain material no cells oriented same direction stresses bending sheet simply causes round cell tubes distort ellipses C-grain material some cellsthose make up raysare oriented direction stresses direction strong stiff Rolled balsa tubes find application phases free-flight modeling both Indoor Outdoor motor sticks tailbooms rubber-power duration models tailbooms towline gliders power models C-grain wood results tube has great resistance cross-wise crushing turn gives greater resistance collapse under tension torque fully wound rubber motor wood likely split rolled tube first place Indoor modelers soak wood water roll along piece tissue paper around man drel tends keep wood under compression cross-wise direction being rolled inhibits splitting Using technique able roll 020-thick C-grain wood around 1/4 form Scale up try roll 1/16 C-grain sheet around 3/4-in mandrel likely disappointed best course treading unknown ground try rolling short section material would like use splits youll simply have use material closer A-grain side sheets sheet-covered fuse lages C-grain wood stiff wont dimple inward under tension doped tissue covering readily A-grain can important appearance lightweight scale model likely split model squeezed hand launching FF gas model covering leading-edge portions wings C-grain logical choice provided curvature isnt great wood cracks curved shape thin wide trailing edges highly undercambered wing such Nordic towline glider C-grain logical choice C-grain wood withstands cross-wise bending forces due tension covering better A-grain say warps less wings tails hand-launch gliders particularly indoor models using very light wood C-grain warps less across grain A-grain glider certainly dont want undercamber appear stabilizer simply because put little dope bottom top C-grain cracks easily surfaces must bent proc ess adjusting model Some builders prefer use AB-grain wood wings rather pure C-grain meticulous builder might orient sheet pure C-grain near leading edge BC-grain wood toward trailing edge adjustments made ribs indoor microfilm models sliced progressively moving template across sheet after cut C-grain choice wing spars tips opinions vary spars usually set edge wide dimension oriented vertically sliced sheet having thick ness equal narrow dimension spar Some modelers claim spars made C-grain wood tend curl Conquest Engines thL ted engines Cox 15 AMA FAI FF above FAI Combat Scale Racing Speed $5595 15 RC Quarter Midget Sport Perry carburetor $5995 40 $6595 FF CL Rat Speed Formula 1 low $7995 RC 40 Perry carbu retor Sport Pattern Now available hobby shop Cox Hobbies 1525 E Warner Ave. Santa Ana CA 92702 June 1976 99 Kraftsmanship kit processed AAMCO GOLD BALSAThis Trainer will blow apart hits ground Price $3495 kit per dollar bar em Support AMA U GREATEST R/C BASIC TRAINER Design & Kit ALL TIME JIUJ Ask over 25000 satisfied builders H-RAY dealers sold themSHALL WE SAY MORE Assdrewo Aircraft Model Co Inc US Ete 1& North St Topsfield Mass 01983 887-8541 Know About Balsa/Meuser continued page 46 gsroductrevieworsducsrevgeworsducsroviewnroductreviaw producsresiewproducsreviewproducsrasiewproducsresjew Balsa continued wood cut also tend warp after wing constructed Others say grain orientation makes no difference probably best play safe use Agrain wood spars available Consider spar simple single-spar wing spar set edge wide dimension vertical Some modelers will swear C-grain spar such appli cation stronger stiffer Agrain spar also brittle tends fracture across grain ratherthan fracturing jagged tear pure nonsense spar bends material spar subjected length wise tension compression stresses Re gardless grain orientation rays 90 degrees stresses grain orientation simply makes no differ ence simply theory Ive cut sets spars both A-grain C-grain same plank checked carefully make sure dimensions densi ties identical tested no significant difference stiff ness strength appearance fracture Thin Hard Thick Soft rib made 1/16 material having density 12 lb/cu ft weighs same made 1/8 material having density 6 lb/cu ft Which best factors affect such choice goal course get greatest strength durability least weight regardless whether model indoor microfilm plane RC pattern machine other factors affect choice too modeling applications very light woodthat below 5 lb/cu ftis bummer has low toughness relative its weight tends snap shatter straight across cells whereas break higher-density wood takes form ragged tear Further strength very light wood highly variable whereas strength heavier wood predict able Very light wood especially subject compression failures caused wind tree standing perhaps caused tree felled appear lines across grain often almost invisible very light wood indispensable some applications wing indoor hand-launch glider example wood half dense can twice thick twice thick its bending strength would twice great provided wood same strength-to-weight ratio So thick wing will stronger despite lower strength-to-weight ratio softer wood thicker wing can have better airfoil section too same reasoning applies trailing edges Lighter material permits piece wider thicker hence stronger soft material subject dents nicks reasonable dura bility edging strip hard balsa spruce often used seems trend Nordic glider design use very hard balsa trailing edges back strip spruce keep weight such trailing edges within reason must rather narrow turn makes life dif ficult ribs Only time will tell wheth er trend fad about ribs lighter-the-thickerthe-stronger argument applies sideways bending rib sideways bending strength usually important survival rib adequate strength provided wing covering provided takes trouble dope covering rib So harder material logical choice except material too hard difficult cut simple rectangular spars harder wood logical choice spars cap-strip-and-web variety strips flush top bottom surfaces act flanges I-beam use hard material especially important strength depends distance tween centers strips thin strips hard material will farther apart surprising Nordic gliders airfoil sections thin yet wings must withstand punishment zoom launches still light spruce spars usually used parts subject localized impact leading edges examplethere little question small cross sections dense material result durable structure Hard balsa simply has greater energy absorbing capability its weight bounce ounce soft balsa light free-flight models though sometimes wants large piece lumber front order get desired airfoil section popular solutionbut requires bit work use lami nated leading edge spruce backed up soft balsa Veteran free-fighter Charlie Sotich recently built Nordic glider using bamboo wing-tip outline similar way models frequently built twenties thirties reports wings survive encounters con crete runways better modern construction avoided appearance factor joints hard soft woods come together hard ribs soft trailing used example might difficult sand ribs flush tendency undercut soft trailing edge un sightly covering job result Also soft materials used better off using ordinary cellulose model airplane cement stronger harder glues such aliphatic resins careful block sanding difficult sand hard glue joint flush indoor microfilm models very light wood must used wire-braced wing spars under compression subject buckling failure Light wood permits use relatively large cross section gives greater resistance buckling though stiffness Youngs modulus rememberof material its weight bit lower soft material Needless say selection wood indoor models fine art time balsa cut sheets few thousandths thick price up almost $1000000 per thousand board feet No kidding piece 008 X 1-3/16 X 18 goes close $100 nowadays Sal Taibis original Starduster 900 built 8 lb/cu-ft wood survived ten continuous years rigorous competition built 6 lb/cu-ft material another modeler barely made through season comparison completely valid because two models did weigh same Nevertheless seems clear except very specialized applications hand-launch glider wings planked sheet covered surfaces models must extremely lightthe harder grades balsa best choice provided thick nesses reduced avoid excessive weight competition free flight weight all-important seems trend direction wish thank Glen Sigafoose Sig Manufacturing Co Sal Taibi Competi tion Models Frank Zaic Model Aeronau tic Publications Jasco Peter Mont gomery Solarbo Ltd Gerald Skrjanc Micro-X Indoor Model Supplies Norman Boyer Belcobalsa Division Baltec Corp others pestered help information supplied addition Sig booklet mentioned article suggest following book further reading Balsa Wood Its Properties John F Dreisbach pub lished Columbia Graphs Columbia CT 06237 out print li brary might have able get 100 Model Aviation r~isirtrnviewproductreviewproductreview andle New comfortable grip sturdy handle features easy line adjustment 3-inch leadout spacing thumb screw makes adjustment simple easy manu facturer considers closer leadout spacing desirable reduces sensitivity turn improves beginners chance suc cessful flight well improving smooth ness expert Price $395 Fox Manu facturing Co 5305 Towson Ave Fort Smith Arkansas 72901 productreviewproductreviewpiOdUCtreViOW