part 37 DUE TO THE amount material will presented article divided three parts months installment deals foam material types foam chemical characteristics compatible sol vents glues etc Part two will deal methods techniques cutting foam cutting bows power supply safety etc Part three deals covering skinning cements construction finishing first installment seems excessively detailed because need supply comprehensive reference will found useful later date Foam Pros Cons Construction Speed work impor tant advantage Once master tech niques cutting foam wing cores can ready cover wing minutes after get two rib templates made takes little longer make extra wing youre foam does break can often epoxy together back air leaving flying field instance Silent Squire flown post 40 mph hitting wing about 15 root putting -in deep dent wing built-up wing would have sheared two foam wing back tow line after merely covering damaged portion few strips masking tape What Foam plastics can produced foam adding chemicals called foam ing agents gases generate gases heating cause plastic assume cellular structure open cells absorb liquids closed cells generally absorb very little liquid Foam plastics produced rigid semi-rigid flexible form Several closed cell rigid plastic foams have used successfully wings fuselages model aircraft Polystyrene Expanded Bead Foam Poly styrene expanded bead foam often called quality foam approximately same density density foam affects strength properly made foam shown comparative strength tables StyrofoamExtruded Polystyrene Foam Styrofoam Dow trademark name polystyrene foam made same basic raw material polystyrene dif ferent process exact process secret generally follows Poly styrene liquid form pumped pro cessing equipment heated foaming agents introduced extruded continuous sheets material has continuous matrix relatively uniform bubbles gas trapped Freon gases used being large molecule does gradu ally escape pentane gas does expanded bead type foam Due solid matrix between bubbles styro foam generally has minimum density 17 pcf lbs/cu ft opposed 08 pcf expanded bead term styrofoam widely used describe polysty rene foams distinction made between expanded-bead type Foam Techniques Ease accuracy construction two big advantages get true airfoil easy get graduated washout root tip covering material follows exact plotted airfoil rather flattening out between ribs Only root tip ribs need plotted tapered wing eliminating plotting stack cutting remaining ribs built-up wing inherent accuracy also makes foam ideal modern scale models few disadvantages Poly styrene expanded bead foam attacked wide variety solvents core can easily ruined dont know what doing major purpose article help avoid such pitfalls take maximum advantage good properties foam Flight Characteristics accuracy airfoil ability build graduated washout high strength no weight penalty offer significant advantages well supported domination foam wings Formula racers pattern ships Its use types gliders well established spreading Moreover foam wings provide shock absorbing character istics have saved ship bead board popular pro duced expanding polystyrene beads usually contain pentane gas expanding foaming agent Foam Made Polystyrene beads appropriate grade bead size fed steam vacuum pre-expander expanded cell size required desired product density expanded beads dried aged six hours common molding sys tem arethen fed preheated molds steam applied heat beads point will complete expan sion fuse together mold cooled molded foam removed number variables affect final product Some design variables such bead size high low volatility beads resin compounds resin quality Some processing equipment varia bles several alternative processes pre-expanding molding beads also number operator controlled variables above affect characteristic finished product either design circumstance fore some variation will encountered extruded Styrofoam brand foam modelers think Styrofoam relatively light brittle DB decorator board type widely used florists Styrofoam type used aircraft modelers light solid blue color has fine texture like sandpaper called SM sheathing material usually about 18 pcf about 80% heavier 10 pcf expanded-type foam generally used Styrofoam advantageous un skinned wings due its greater strength finer grain Expanded bead foam preferred weight factor wing skinned provides ample strength rigidity example typical 60-in Styrofoam wing core could 4 5 oz heavier cut expanded bead foam Chemical Properties Solvents Polystyrene expanded bead foam especially sensitive attack due thin cell walls same solvents also attack Styrofoam Fast Acting Solvents following type solvents dissolve foam quickly Aromatic hydrocarbons like benzene chlorinated hydrocarbons like carbon tetrachloride 26 Model Aviation ketones like acetone MEK Methyl Ethyl Ketone esters like polyester resins essential oils high terpene content like oil lemon orange turpentine Slower Acting Solvents aromatic hydrocarbon portion gasoline solvent naptha common paint solvent thinner fuel oil mineral oil exert solvent action polystyrene Higher alcohols ether alcohols glaciel alcohol acetic acid some unsaturated hydrocarbons coal-tar pitch cut-back asphalt essential oils low terpene content cause relatively slower softening swelling Polystyrene has relatively good resis tance weak acids caustics salt water bleach alcohol-based paints waterbased paints cements asphalt paraffin wax lubricating oils Whenever possibility chemical used polystyrene may dissolve test apiece ofscrap Adhesives Polystyrene Foam As general rule avoid coatings adhesives direct application foam contain solvents such AcetoneMEKStyrene glues casein animal etc Some specific products known authors satisfactory contact cements Light Dex Carl Goldbergs Blue Goo Core Grip Southern Sorghum 3M 77 Scotch Grip slow drying adhesives Kwick Tak Wil hold Glu Saver paints Foam Luster Perfect Paint Styromate no doubt other good products have mentioned have opportunity try test Test adhesives scrap first sure Emulsion Solvent Asphalt Asphalt Inorganic Inorganic Resin* Resin* Rubber** Rubber** Silicone Silicone Reactivewhich thickens hardens due chemical reaction between two com ponents both remain joint Hot Meltwhich composed solids become fluid heated return solid state joint cool principle solid components drying-type adhesives used listed under three basic types liquid carriers follows pressure sensitive silicone also used wide variety adhesives have used successfully Water sure way test suitability spe cific adhesive Test scraps foam Natural using Because formu lations testing way sure unless adhesive specifically labeled use polystyrene foam has Rubber** structions application drying type generally work best solvent escapes thoroughly open assembly time before two pieces joined Coatings Polystyrene foam damaged exposure ultraviolet rays sun light plan cover balsa cardboard plywood etc should Casein animal glue etc Inorganic *Typical resins Polyvinyl Acetate Polyvinyl Chloride Polystyrene Natural Polymer principal components reac tive-type adhesives used Cement. Epoxy InorganiceMortare Resourcinal Although foam-core construction dates back 15 years commonplace kits modelers hesitate use scratch-build basis spite its obvious advantages definitive series articles covers subject Zthe material cutting skinning U Bill Evans Max Lester Butanone Esters Ketones Naptha Nitrocellulose Petroleum Distillates Toluol Turpentine Xylol AdhesiVes often contain solvents include Model jewelry cements contact cements butyrals general purpose cements Some spe cific examples Ambroid modeling glue Hot Stuff Superpoxy Coatings category include Air plane dope lacquer oil-base paints poly ester resin spray paints acrylic epoxy synthetic base ure thane types some adhesives coatings list polystyrene foam materials can used may prove disastrous foam wings cases materials containing some solvents may work applied very thin coats solvents allowed largely evaporate before assembly As general rule following adhe sives coatings can safely applied directly polystyrene foam White glues usually must dry tacky before assembly water-base contact cements epoxies mixed user watch out spray cans silicone adhesives natural SiliconeUrea principal compo nents Hot Melt type used Polymide Polyethylene following information based principally technical manual Adhe sives Coatings Used Foamed Dy lite Polystyrene published Sinclair Koppers Co Three basic types adhesives used Dryingwhich contain liquid evaporates solid remains joint painted suitable material Latex paints work well some lacquers en amels varnishes can used two prime coats shellac applied first Epoxy paint probably best protective coating material going used solvent polystyrene foam epoxy least two coats should applied due tendency coat ings form pinholes applied foam Other commercial resins can also used depending solvent Again Continued page 90 COMPARATIVE STRENGTH TADI Density Compressive Strength Tensile Strength grain Shear Strength Flexural Strength grain Balsa Expanded Bead Polystyrene 102030 15 35 60 21 55 90 pcf80 psi 150 psi 100 psi2000 psi psi 200 psi3000 Styrofoam 20 30 45 140 70 200 1935604575 229014595150 Data Modern Plastics magazine technical publications ARCO/Polymers Inc DOW Chemical USA Differences noted between sources shown range some cases range valid due variations foam table provides useful compar ison what appeared average strengths January 1978 27 cated compressed air rather usual freon because tests run winter temperatures down 15 degrees F Some interesting facts useful model ers gleaned paper proper rotation lift-off main gear centers must /4 3/ behind CG ground angle attack should set two degrees nose-up ease lift-off protection nose gear Gear collapses caused shattering four sets hand-carved maple props half lefthand requiring 40 minutes carving time two engineers flew Piper model well quali fied recreational radio-control model fliers speed characteristics model new experience gained needed familiarity heavy plane progressively adding weight practice plastic-and-foam ARF until loaded up 2 times its design weight Some useful hints twin-engine flying included notes Asymmetrical power during spins throttle open wider caused autorotation rates twice normal spin rate results flat spin rate descent reduced spins can induced unequal throttle settings idle retreating engine tends quit due reverse air flow over prop twin-engine plane spins after failure engine close other throttle quickly open again after recovery dive plane has retracted landing gear dont extend until near touchdown reduce drag modelers would perform intentional spins twin accidental spin twin last Lake Charles Nats concluded crash could possibly have avoided Bob Wischer Rt 1 S-221 Lapham Peak Rd Delafield W1S3018 Foam/Evans/Lester continued page 27 adhesives first test coating foam scraps Sources Foam Expanded Bead Polystyrene FoamGen eral Sources independent manufacturers some will sell directly club purchase suffi cient quantity Otherwise can direct dealers sell foam density interested typically 1-1 cu ft Both manufacturers retailers may found yellow pages under PlasticsFoam Beadboard insulation common forms usable modeler typically available 1 lb/cu ft density thicknesses 2 some times 3 building materials sup pliers carry material also widely used aquatic applications typic ally molded 15 pcf density name nearest supplier can obtained writing Arco Polymers Inc Philadel phiaPA 19101 Custom cutting cores done some hobbyists local RC club good place start looking Styrofoam Extruded Polystyrene Foam styrofoam manufactured Dow Chemical Company its licensees Styro foam SM Sheathing Material widely available type suitable air craft modelers ranges 18 20 pcf available through building material suppliers 4X8-ft sheets thicknesses 1 1 2 sometimes 3 Look Dow Chemical yel low pages under Plastics write Dow Chemical USA Midland MI 48640 continued First Last/Aycock continued page 31 ing P-47 Thunderbolt will finished same flew Europe capable design work can attested author has flown original bipe very fine performer fighter Bills comment need trainer want looks like airplane atti tude outlook man first American Ace World War II Acknowledgment The author would like thank Lt Col Dunn assist ance supplying records photographs 90 Model Aviation GEE BEE RACER 1/32 SCALE PLASTIC MODEL KIT CONSTRUCT R-1 OR 1-2 ALSO SEPARATELY WASP SEND 5Ot FOR COMPLETE ILLUSTRATED CATALOG DEPT MA PAWNEE ST SAN MARCOS CA 9 Another Sport Scale entry Riverside David Lovitts Blackburn Land-Sea Monoplane Note laminated prop Covered Coverite powered K&B 40 Slim Line muffler
Edition: Model Aviation - 1978/01
Page Numbers: 26, 27, 90
part 37 DUE TO THE amount material will presented article divided three parts months installment deals foam material types foam chemical characteristics compatible sol vents glues etc Part two will deal methods techniques cutting foam cutting bows power supply safety etc Part three deals covering skinning cements construction finishing first installment seems excessively detailed because need supply comprehensive reference will found useful later date Foam Pros Cons Construction Speed work impor tant advantage Once master tech niques cutting foam wing cores can ready cover wing minutes after get two rib templates made takes little longer make extra wing youre foam does break can often epoxy together back air leaving flying field instance Silent Squire flown post 40 mph hitting wing about 15 root putting -in deep dent wing built-up wing would have sheared two foam wing back tow line after merely covering damaged portion few strips masking tape What Foam plastics can produced foam adding chemicals called foam ing agents gases generate gases heating cause plastic assume cellular structure open cells absorb liquids closed cells generally absorb very little liquid Foam plastics produced rigid semi-rigid flexible form Several closed cell rigid plastic foams have used successfully wings fuselages model aircraft Polystyrene Expanded Bead Foam Poly styrene expanded bead foam often called quality foam approximately same density density foam affects strength properly made foam shown comparative strength tables StyrofoamExtruded Polystyrene Foam Styrofoam Dow trademark name polystyrene foam made same basic raw material polystyrene dif ferent process exact process secret generally follows Poly styrene liquid form pumped pro cessing equipment heated foaming agents introduced extruded continuous sheets material has continuous matrix relatively uniform bubbles gas trapped Freon gases used being large molecule does gradu ally escape pentane gas does expanded bead type foam Due solid matrix between bubbles styro foam generally has minimum density 17 pcf lbs/cu ft opposed 08 pcf expanded bead term styrofoam widely used describe polysty rene foams distinction made between expanded-bead type Foam Techniques Ease accuracy construction two big advantages get true airfoil easy get graduated washout root tip covering material follows exact plotted airfoil rather flattening out between ribs Only root tip ribs need plotted tapered wing eliminating plotting stack cutting remaining ribs built-up wing inherent accuracy also makes foam ideal modern scale models few disadvantages Poly styrene expanded bead foam attacked wide variety solvents core can easily ruined dont know what doing major purpose article help avoid such pitfalls take maximum advantage good properties foam Flight Characteristics accuracy airfoil ability build graduated washout high strength no weight penalty offer significant advantages well supported domination foam wings Formula racers pattern ships Its use types gliders well established spreading Moreover foam wings provide shock absorbing character istics have saved ship bead board popular pro duced expanding polystyrene beads usually contain pentane gas expanding foaming agent Foam Made Polystyrene beads appropriate grade bead size fed steam vacuum pre-expander expanded cell size required desired product density expanded beads dried aged six hours common molding sys tem arethen fed preheated molds steam applied heat beads point will complete expan sion fuse together mold cooled molded foam removed number variables affect final product Some design variables such bead size high low volatility beads resin compounds resin quality Some processing equipment varia bles several alternative processes pre-expanding molding beads also number operator controlled variables above affect characteristic finished product either design circumstance fore some variation will encountered extruded Styrofoam brand foam modelers think Styrofoam relatively light brittle DB decorator board type widely used florists Styrofoam type used aircraft modelers light solid blue color has fine texture like sandpaper called SM sheathing material usually about 18 pcf about 80% heavier 10 pcf expanded-type foam generally used Styrofoam advantageous un skinned wings due its greater strength finer grain Expanded bead foam preferred weight factor wing skinned provides ample strength rigidity example typical 60-in Styrofoam wing core could 4 5 oz heavier cut expanded bead foam Chemical Properties Solvents Polystyrene expanded bead foam especially sensitive attack due thin cell walls same solvents also attack Styrofoam Fast Acting Solvents following type solvents dissolve foam quickly Aromatic hydrocarbons like benzene chlorinated hydrocarbons like carbon tetrachloride 26 Model Aviation ketones like acetone MEK Methyl Ethyl Ketone esters like polyester resins essential oils high terpene content like oil lemon orange turpentine Slower Acting Solvents aromatic hydrocarbon portion gasoline solvent naptha common paint solvent thinner fuel oil mineral oil exert solvent action polystyrene Higher alcohols ether alcohols glaciel alcohol acetic acid some unsaturated hydrocarbons coal-tar pitch cut-back asphalt essential oils low terpene content cause relatively slower softening swelling Polystyrene has relatively good resis tance weak acids caustics salt water bleach alcohol-based paints waterbased paints cements asphalt paraffin wax lubricating oils Whenever possibility chemical used polystyrene may dissolve test apiece ofscrap Adhesives Polystyrene Foam As general rule avoid coatings adhesives direct application foam contain solvents such AcetoneMEKStyrene glues casein animal etc Some specific products known authors satisfactory contact cements Light Dex Carl Goldbergs Blue Goo Core Grip Southern Sorghum 3M 77 Scotch Grip slow drying adhesives Kwick Tak Wil hold Glu Saver paints Foam Luster Perfect Paint Styromate no doubt other good products have mentioned have opportunity try test Test adhesives scrap first sure Emulsion Solvent Asphalt Asphalt Inorganic Inorganic Resin* Resin* Rubber** Rubber** Silicone Silicone Reactivewhich thickens hardens due chemical reaction between two com ponents both remain joint Hot Meltwhich composed solids become fluid heated return solid state joint cool principle solid components drying-type adhesives used listed under three basic types liquid carriers follows pressure sensitive silicone also used wide variety adhesives have used successfully Water sure way test suitability spe cific adhesive Test scraps foam Natural using Because formu lations testing way sure unless adhesive specifically labeled use polystyrene foam has Rubber** structions application drying type generally work best solvent escapes thoroughly open assembly time before two pieces joined Coatings Polystyrene foam damaged exposure ultraviolet rays sun light plan cover balsa cardboard plywood etc should Casein animal glue etc Inorganic *Typical resins Polyvinyl Acetate Polyvinyl Chloride Polystyrene Natural Polymer principal components reac tive-type adhesives used Cement. Epoxy InorganiceMortare Resourcinal Although foam-core construction dates back 15 years commonplace kits modelers hesitate use scratch-build basis spite its obvious advantages definitive series articles covers subject Zthe material cutting skinning U Bill Evans Max Lester Butanone Esters Ketones Naptha Nitrocellulose Petroleum Distillates Toluol Turpentine Xylol AdhesiVes often contain solvents include Model jewelry cements contact cements butyrals general purpose cements Some spe cific examples Ambroid modeling glue Hot Stuff Superpoxy Coatings category include Air plane dope lacquer oil-base paints poly ester resin spray paints acrylic epoxy synthetic base ure thane types some adhesives coatings list polystyrene foam materials can used may prove disastrous foam wings cases materials containing some solvents may work applied very thin coats solvents allowed largely evaporate before assembly As general rule following adhe sives coatings can safely applied directly polystyrene foam White glues usually must dry tacky before assembly water-base contact cements epoxies mixed user watch out spray cans silicone adhesives natural SiliconeUrea principal compo nents Hot Melt type used Polymide Polyethylene following information based principally technical manual Adhe sives Coatings Used Foamed Dy lite Polystyrene published Sinclair Koppers Co Three basic types adhesives used Dryingwhich contain liquid evaporates solid remains joint painted suitable material Latex paints work well some lacquers en amels varnishes can used two prime coats shellac applied first Epoxy paint probably best protective coating material going used solvent polystyrene foam epoxy least two coats should applied due tendency coat ings form pinholes applied foam Other commercial resins can also used depending solvent Again Continued page 90 COMPARATIVE STRENGTH TADI Density Compressive Strength Tensile Strength grain Shear Strength Flexural Strength grain Balsa Expanded Bead Polystyrene 102030 15 35 60 21 55 90 pcf80 psi 150 psi 100 psi2000 psi psi 200 psi3000 Styrofoam 20 30 45 140 70 200 1935604575 229014595150 Data Modern Plastics magazine technical publications ARCO/Polymers Inc DOW Chemical USA Differences noted between sources shown range some cases range valid due variations foam table provides useful compar ison what appeared average strengths January 1978 27 cated compressed air rather usual freon because tests run winter temperatures down 15 degrees F Some interesting facts useful model ers gleaned paper proper rotation lift-off main gear centers must /4 3/ behind CG ground angle attack should set two degrees nose-up ease lift-off protection nose gear Gear collapses caused shattering four sets hand-carved maple props half lefthand requiring 40 minutes carving time two engineers flew Piper model well quali fied recreational radio-control model fliers speed characteristics model new experience gained needed familiarity heavy plane progressively adding weight practice plastic-and-foam ARF until loaded up 2 times its design weight Some useful hints twin-engine flying included notes Asymmetrical power during spins throttle open wider caused autorotation rates twice normal spin rate results flat spin rate descent reduced spins can induced unequal throttle settings idle retreating engine tends quit due reverse air flow over prop twin-engine plane spins after failure engine close other throttle quickly open again after recovery dive plane has retracted landing gear dont extend until near touchdown reduce drag modelers would perform intentional spins twin accidental spin twin last Lake Charles Nats concluded crash could possibly have avoided Bob Wischer Rt 1 S-221 Lapham Peak Rd Delafield W1S3018 Foam/Evans/Lester continued page 27 adhesives first test coating foam scraps Sources Foam Expanded Bead Polystyrene FoamGen eral Sources independent manufacturers some will sell directly club purchase suffi cient quantity Otherwise can direct dealers sell foam density interested typically 1-1 cu ft Both manufacturers retailers may found yellow pages under PlasticsFoam Beadboard insulation common forms usable modeler typically available 1 lb/cu ft density thicknesses 2 some times 3 building materials sup pliers carry material also widely used aquatic applications typic ally molded 15 pcf density name nearest supplier can obtained writing Arco Polymers Inc Philadel phiaPA 19101 Custom cutting cores done some hobbyists local RC club good place start looking Styrofoam Extruded Polystyrene Foam styrofoam manufactured Dow Chemical Company its licensees Styro foam SM Sheathing Material widely available type suitable air craft modelers ranges 18 20 pcf available through building material suppliers 4X8-ft sheets thicknesses 1 1 2 sometimes 3 Look Dow Chemical yel low pages under Plastics write Dow Chemical USA Midland MI 48640 continued First Last/Aycock continued page 31 ing P-47 Thunderbolt will finished same flew Europe capable design work can attested author has flown original bipe very fine performer fighter Bills comment need trainer want looks like airplane atti tude outlook man first American Ace World War II Acknowledgment The author would like thank Lt Col Dunn assist ance supplying records photographs 90 Model Aviation GEE BEE RACER 1/32 SCALE PLASTIC MODEL KIT CONSTRUCT R-1 OR 1-2 ALSO SEPARATELY WASP SEND 5Ot FOR COMPLETE ILLUSTRATED CATALOG DEPT MA PAWNEE ST SAN MARCOS CA 9 Another Sport Scale entry Riverside David Lovitts Blackburn Land-Sea Monoplane Note laminated prop Covered Coverite powered K&B 40 Slim Line muffler
Edition: Model Aviation - 1978/01
Page Numbers: 26, 27, 90
part 37 DUE TO THE amount material will presented article divided three parts months installment deals foam material types foam chemical characteristics compatible sol vents glues etc Part two will deal methods techniques cutting foam cutting bows power supply safety etc Part three deals covering skinning cements construction finishing first installment seems excessively detailed because need supply comprehensive reference will found useful later date Foam Pros Cons Construction Speed work impor tant advantage Once master tech niques cutting foam wing cores can ready cover wing minutes after get two rib templates made takes little longer make extra wing youre foam does break can often epoxy together back air leaving flying field instance Silent Squire flown post 40 mph hitting wing about 15 root putting -in deep dent wing built-up wing would have sheared two foam wing back tow line after merely covering damaged portion few strips masking tape What Foam plastics can produced foam adding chemicals called foam ing agents gases generate gases heating cause plastic assume cellular structure open cells absorb liquids closed cells generally absorb very little liquid Foam plastics produced rigid semi-rigid flexible form Several closed cell rigid plastic foams have used successfully wings fuselages model aircraft Polystyrene Expanded Bead Foam Poly styrene expanded bead foam often called quality foam approximately same density density foam affects strength properly made foam shown comparative strength tables StyrofoamExtruded Polystyrene Foam Styrofoam Dow trademark name polystyrene foam made same basic raw material polystyrene dif ferent process exact process secret generally follows Poly styrene liquid form pumped pro cessing equipment heated foaming agents introduced extruded continuous sheets material has continuous matrix relatively uniform bubbles gas trapped Freon gases used being large molecule does gradu ally escape pentane gas does expanded bead type foam Due solid matrix between bubbles styro foam generally has minimum density 17 pcf lbs/cu ft opposed 08 pcf expanded bead term styrofoam widely used describe polysty rene foams distinction made between expanded-bead type Foam Techniques Ease accuracy construction two big advantages get true airfoil easy get graduated washout root tip covering material follows exact plotted airfoil rather flattening out between ribs Only root tip ribs need plotted tapered wing eliminating plotting stack cutting remaining ribs built-up wing inherent accuracy also makes foam ideal modern scale models few disadvantages Poly styrene expanded bead foam attacked wide variety solvents core can easily ruined dont know what doing major purpose article help avoid such pitfalls take maximum advantage good properties foam Flight Characteristics accuracy airfoil ability build graduated washout high strength no weight penalty offer significant advantages well supported domination foam wings Formula racers pattern ships Its use types gliders well established spreading Moreover foam wings provide shock absorbing character istics have saved ship bead board popular pro duced expanding polystyrene beads usually contain pentane gas expanding foaming agent Foam Made Polystyrene beads appropriate grade bead size fed steam vacuum pre-expander expanded cell size required desired product density expanded beads dried aged six hours common molding sys tem arethen fed preheated molds steam applied heat beads point will complete expan sion fuse together mold cooled molded foam removed number variables affect final product Some design variables such bead size high low volatility beads resin compounds resin quality Some processing equipment varia bles several alternative processes pre-expanding molding beads also number operator controlled variables above affect characteristic finished product either design circumstance fore some variation will encountered extruded Styrofoam brand foam modelers think Styrofoam relatively light brittle DB decorator board type widely used florists Styrofoam type used aircraft modelers light solid blue color has fine texture like sandpaper called SM sheathing material usually about 18 pcf about 80% heavier 10 pcf expanded-type foam generally used Styrofoam advantageous un skinned wings due its greater strength finer grain Expanded bead foam preferred weight factor wing skinned provides ample strength rigidity example typical 60-in Styrofoam wing core could 4 5 oz heavier cut expanded bead foam Chemical Properties Solvents Polystyrene expanded bead foam especially sensitive attack due thin cell walls same solvents also attack Styrofoam Fast Acting Solvents following type solvents dissolve foam quickly Aromatic hydrocarbons like benzene chlorinated hydrocarbons like carbon tetrachloride 26 Model Aviation ketones like acetone MEK Methyl Ethyl Ketone esters like polyester resins essential oils high terpene content like oil lemon orange turpentine Slower Acting Solvents aromatic hydrocarbon portion gasoline solvent naptha common paint solvent thinner fuel oil mineral oil exert solvent action polystyrene Higher alcohols ether alcohols glaciel alcohol acetic acid some unsaturated hydrocarbons coal-tar pitch cut-back asphalt essential oils low terpene content cause relatively slower softening swelling Polystyrene has relatively good resis tance weak acids caustics salt water bleach alcohol-based paints waterbased paints cements asphalt paraffin wax lubricating oils Whenever possibility chemical used polystyrene may dissolve test apiece ofscrap Adhesives Polystyrene Foam As general rule avoid coatings adhesives direct application foam contain solvents such AcetoneMEKStyrene glues casein animal etc Some specific products known authors satisfactory contact cements Light Dex Carl Goldbergs Blue Goo Core Grip Southern Sorghum 3M 77 Scotch Grip slow drying adhesives Kwick Tak Wil hold Glu Saver paints Foam Luster Perfect Paint Styromate no doubt other good products have mentioned have opportunity try test Test adhesives scrap first sure Emulsion Solvent Asphalt Asphalt Inorganic Inorganic Resin* Resin* Rubber** Rubber** Silicone Silicone Reactivewhich thickens hardens due chemical reaction between two com ponents both remain joint Hot Meltwhich composed solids become fluid heated return solid state joint cool principle solid components drying-type adhesives used listed under three basic types liquid carriers follows pressure sensitive silicone also used wide variety adhesives have used successfully Water sure way test suitability spe cific adhesive Test scraps foam Natural using Because formu lations testing way sure unless adhesive specifically labeled use polystyrene foam has Rubber** structions application drying type generally work best solvent escapes thoroughly open assembly time before two pieces joined Coatings Polystyrene foam damaged exposure ultraviolet rays sun light plan cover balsa cardboard plywood etc should Casein animal glue etc Inorganic *Typical resins Polyvinyl Acetate Polyvinyl Chloride Polystyrene Natural Polymer principal components reac tive-type adhesives used Cement. Epoxy InorganiceMortare Resourcinal Although foam-core construction dates back 15 years commonplace kits modelers hesitate use scratch-build basis spite its obvious advantages definitive series articles covers subject Zthe material cutting skinning U Bill Evans Max Lester Butanone Esters Ketones Naptha Nitrocellulose Petroleum Distillates Toluol Turpentine Xylol AdhesiVes often contain solvents include Model jewelry cements contact cements butyrals general purpose cements Some spe cific examples Ambroid modeling glue Hot Stuff Superpoxy Coatings category include Air plane dope lacquer oil-base paints poly ester resin spray paints acrylic epoxy synthetic base ure thane types some adhesives coatings list polystyrene foam materials can used may prove disastrous foam wings cases materials containing some solvents may work applied very thin coats solvents allowed largely evaporate before assembly As general rule following adhe sives coatings can safely applied directly polystyrene foam White glues usually must dry tacky before assembly water-base contact cements epoxies mixed user watch out spray cans silicone adhesives natural SiliconeUrea principal compo nents Hot Melt type used Polymide Polyethylene following information based principally technical manual Adhe sives Coatings Used Foamed Dy lite Polystyrene published Sinclair Koppers Co Three basic types adhesives used Dryingwhich contain liquid evaporates solid remains joint painted suitable material Latex paints work well some lacquers en amels varnishes can used two prime coats shellac applied first Epoxy paint probably best protective coating material going used solvent polystyrene foam epoxy least two coats should applied due tendency coat ings form pinholes applied foam Other commercial resins can also used depending solvent Again Continued page 90 COMPARATIVE STRENGTH TADI Density Compressive Strength Tensile Strength grain Shear Strength Flexural Strength grain Balsa Expanded Bead Polystyrene 102030 15 35 60 21 55 90 pcf80 psi 150 psi 100 psi2000 psi psi 200 psi3000 Styrofoam 20 30 45 140 70 200 1935604575 229014595150 Data Modern Plastics magazine technical publications ARCO/Polymers Inc DOW Chemical USA Differences noted between sources shown range some cases range valid due variations foam table provides useful compar ison what appeared average strengths January 1978 27 cated compressed air rather usual freon because tests run winter temperatures down 15 degrees F Some interesting facts useful model ers gleaned paper proper rotation lift-off main gear centers must /4 3/ behind CG ground angle attack should set two degrees nose-up ease lift-off protection nose gear Gear collapses caused shattering four sets hand-carved maple props half lefthand requiring 40 minutes carving time two engineers flew Piper model well quali fied recreational radio-control model fliers speed characteristics model new experience gained needed familiarity heavy plane progressively adding weight practice plastic-and-foam ARF until loaded up 2 times its design weight Some useful hints twin-engine flying included notes Asymmetrical power during spins throttle open wider caused autorotation rates twice normal spin rate results flat spin rate descent reduced spins can induced unequal throttle settings idle retreating engine tends quit due reverse air flow over prop twin-engine plane spins after failure engine close other throttle quickly open again after recovery dive plane has retracted landing gear dont extend until near touchdown reduce drag modelers would perform intentional spins twin accidental spin twin last Lake Charles Nats concluded crash could possibly have avoided Bob Wischer Rt 1 S-221 Lapham Peak Rd Delafield W1S3018 Foam/Evans/Lester continued page 27 adhesives first test coating foam scraps Sources Foam Expanded Bead Polystyrene FoamGen eral Sources independent manufacturers some will sell directly club purchase suffi cient quantity Otherwise can direct dealers sell foam density interested typically 1-1 cu ft Both manufacturers retailers may found yellow pages under PlasticsFoam Beadboard insulation common forms usable modeler typically available 1 lb/cu ft density thicknesses 2 some times 3 building materials sup pliers carry material also widely used aquatic applications typic ally molded 15 pcf density name nearest supplier can obtained writing Arco Polymers Inc Philadel phiaPA 19101 Custom cutting cores done some hobbyists local RC club good place start looking Styrofoam Extruded Polystyrene Foam styrofoam manufactured Dow Chemical Company its licensees Styro foam SM Sheathing Material widely available type suitable air craft modelers ranges 18 20 pcf available through building material suppliers 4X8-ft sheets thicknesses 1 1 2 sometimes 3 Look Dow Chemical yel low pages under Plastics write Dow Chemical USA Midland MI 48640 continued First Last/Aycock continued page 31 ing P-47 Thunderbolt will finished same flew Europe capable design work can attested author has flown original bipe very fine performer fighter Bills comment need trainer want looks like airplane atti tude outlook man first American Ace World War II Acknowledgment The author would like thank Lt Col Dunn assist ance supplying records photographs 90 Model Aviation GEE BEE RACER 1/32 SCALE PLASTIC MODEL KIT CONSTRUCT R-1 OR 1-2 ALSO SEPARATELY WASP SEND 5Ot FOR COMPLETE ILLUSTRATED CATALOG DEPT MA PAWNEE ST SAN MARCOS CA 9 Another Sport Scale entry Riverside David Lovitts Blackburn Land-Sea Monoplane Note laminated prop Covered Coverite powered K&B 40 Slim Line muffler