AIRCRAFT BUILDING

BUILDING A COMPOSITEAIRCRAFT

BY RON ALEXANDER

Within the sport aviation world,the term "composite aircraft" is syn-onymous with sleekness of designand speed. These airplanes, com-posed largely of fiberglass, arebecoming more and more popular.Certainly when we attend a large fly-in we see rows and rows of compositeaircraft. To many of us these air-planes are somewhat mysterious.How are they built? What does theword "composite" actually mean?Are they safe? How difficult are theyto build?

Actually, composite aircraft con-struction is not a new idea. Glidershave been constructed using fiberglassfor many years. Throughout aviationhistory, advances in design have beenmade. Beginning with wooden struc-tures that were covered with fabric,technology then advanced to weldedsteel framework and on to aluminum.As each type of construction was in-troduced, design improvements weremade in strength and aircraft perfor-mance. Composite construction is yetanother advancement for the aircraftindustry. Fiberglass construction hasbeen and continues to be used in man-ufacturing a number of parts found onmost airplanes. Of course, we nowsee many airplanes that are con-structed almost exclusively out ofcomposite material. Composite tech-nology has certainly changed theentire aviation industry and in particu-lar sport aviation.

Amateur built composite airplaneswere actually introduced during the1970s when Ken Rand introducedthe KR-1. Burt Rutan also intro-duced the VariViggen that featuredsome composite construction, andthe VariEze in 1976. This airplane92 OCTOBER 1997

RESIN MATRIX REINFORCEMENT FIBERS

FOAM CORE

STRENGTH 1.0WEIGHT 1.0

design included a more comprehen-sive type of composite constructionusing moldless techniques. The termmoldless will be defined later. TheVariEze was very successful inspir-ing Rutan to develop the Long-EZ.During the 1980s, several other de-signs were introduced to sportaviation enthusiasts as popularity ofthis type of construction heightened.It was during this period of time thataircraft "kits" were first introduced.Supply companies began offeringmaterial kits to builders to simplify

the building process. Plans for com-posite airplanes could be purchasedand then materials for each phase ofconstruction could be obtained on anas needed basis. The amount of timeneeded for completion is a factor inbuilding an airplane from a set ofplans. With this in mind, severalcompanies began introducing theirown airplane designs in kit form.The objective was to allow thebuilder to spend less time actuallyconstructing the airplane. A largenumber of parts and pieces were

manufactured by the company andsold to individuals. This concept in-troduced the pre-fabricated kitairplane that is popular today in alltypes of construction.

From the late 1980s through todaywe have seen many composite air-craft kits offered to prospectiveairplane builders. This decade(1990s) has seen a tremendousgrowth in the popularity of amateurbuilt composite airplanes. Higherperformance airplanes with manyvarying appearances are being of-fered by a large number of kitmanufacturers and also by designerswho offer plans. This is truly an ex-citing time for our industry.

Before beginning our discussion ofcomposite construction, let's definethe word "composite." The dictionarydefines a composite as "a complexmaterial such as wood or fiberglass,in which two or more distinct, struc-turally complementary substancescombine to produce structural or func-tional properties not present in anyindividual component." In simpleterms, a composite structure has morestrength than the individual compo-nents that make up the structure itself.For our purposes, the component partscomprising a composite structureconsist of a core material, a reinforc-ing material and a resin binder. Eachof these substances alone has very lit-tle strength but combined properlythey become a composite structurethat is very strong.

To further explain the structure,the core material keeps the rein-forcement fibers separated so theycan be kept in maximum tensile (ten-sion or stretching) strength. Thereinforcement fibers carry the load.They must be properly oriented toachieve their maximum potential.The resin keeps the fibers in place sothey can maintain straightness anddeliver their maximum strength. Theresin also binds the fibers to the core.Therefore, a composite structure isreally a mixture of critical compo-nents. When loads are applied to awing, as an example, the majority ofthe stress occurs at the outer sur-faces. To take advantage of thisprinciple, a sandwich panel is de-signed with two working skins onthe outside that are separated by alightweight core. This type of designconcentrates the strength in the area

of high stress (outer surfaces) whilereducing the weight in the area oflow stress (inside the wing). I willfurther expand on the specific typesof materials used later in the article.

To further complicate the issue,you will hear the words moldlessand molded used in composite con-struction. To define these words asthey apply to us is relatively simple.Moldless construction, as the nameinfers, does not use a mold. Thistechnique allows the builder to con-struct a part by forming a corematerial to a desired shape and thenlaminating the reinforcement mater-ial to the shaped piece to make upthe final part. The core structure,usually a foam like material, allowsthe builder to employ virtually anyshape desired. Original designs suchas the VariEze used moldless typeconstruction. Many airplane designscontinue to use this type of fabrica-tion. Moldless techniques allow thebuilder to produce a safe, superiorairplane without the requirement ofexpensive equipment or extensiveexperience.

In contrast, molded fabricationuses a mold to build the part. A mas-ter mold or "plug" must first be builtin the same manner as you wouldbuild a moldless part. You then con-struct a working mold from themaster and then finally make the ac-tual part from the working mold.Within our industry, molded com-posite construction is very popular.A large majority of kit manufactur-ers use this type of fabr icat ion.Molds are made by the kit manufac-turer who then fabricates the partsfrom the mold. The manufacturerthen supplies you, the builder, withthe parts. As an example, a wing kitmight consist of two wing halves,built from a mold, along with thenecessary ribs. You would then as-semble the wing by bonding the ribsto the wing halves and, of course,bond the halves themselves together.Compare this with moldless in whichyou actually form the wing, comply-ing with a set of plans, out of a foammaterial. You then place several lay-ers of fiberglass on the foam usingresin to bind the two. The end resultwould be very similar. One type ofconstruction (moldless) has a corematerial you have shaped that issolid whereas molded usually has

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thin cores that are sandwiched be-tween skins and you actually assemblethe supplied parts. Building a moldedtype composite kit is very similar toassembling a plastic model airplane.The building of most amateur builtcomposite airplanes will require useof both types of construction.

To summarize our general discus-sion, composite structures that com-bine the best qualities of diverse mate-rials have opened a new world to theairplane builder. Modern compositeconstruction offers several advantagesover conventional techniques. Whilesafety tolerances for metal structuresare often designed at 1.5 to 1, light-weight reinforced composites allow"overdesign" by factors of severaltimes, increasing both safety and per-formance. These designs also achievebetter aerodynamics by eliminatingjoints and rivets in addition to reduc-ing problems of corrosion. Compositedesign allows an easy way to achieve alow drag airfoil. Composite airplanesare usually faster for a given horse-power than their counterparts becauseof airfoil shape and smoothness. Onecommon misconception that docs existis that composite airplanes alwaysweigh less than metal airplanes. Thisis often not the case. Fiberglass isheavy. If we were to construct an air-plane wing out of solid fiberglass wewould have a very heavy airplane. Re-member though, instead of doing thiswe insert a piece of core material be-tween layers of fiberglass to reduce theweight. Kit airplanes use ribs and morecontemporary types of construction toachieve the high strength with a lowerweight. t , ; •-. v.

J STEPS IN BUILDING A! COMPOSITE AIRPLANEii1 Building a composite airplane en-tails five stages of construction.These five stages are (1) decisionand planning, (2) basic building andassembly, (3) systems installation,(4) filling and finishing, and (5) in-spection, certification, and finalpreflight.

i Decision and PlanningAs we have previously discussed,

this phase of construction is critical toour successful completion of an ama-teur built airplane. You cannot spend94 OCTOBER 1997

Composite workshops attendees

too much time planning. A large partof the planning process is technicalknowledge. Composite construction,like all types of construction, requiresa certain amount of basic knowledge.EAA and SportAir offers a 2-dayworkshop explaining the techniquesof composite construction with timespent actually building airfoil sectionsutilizing this method of construction.More information on these workshopsis presented at the end of the article.

In our discussion on decision andplanning we will look at the types ofmaterials used, tools required andworkshop requirements.

Materials Used inComposite Construction

Core Materials

A word of caution. The specifica-tions for the materials to be used foryour airplane should be stated withinyour plans or provided with your kit.It is important that you conform tothe plans of the designer.

Choosing the proper core materialis critical to the overall composite'sperformance. Note the illustration inFigure 1. The first item is one piece ofmaterial with its respective weightand strength being shown as 1.0.When we insert a core material dou-bling the thickness of the compositenotice that the strength increases to3.5, the stiffness to 7.0 but the weightonly increases by 3%. Further strength

is noted by increasing the thicknessfour times. Observe even in this casethe weight only increases by 6%.

Lightweight core materials in-clude wood, foam and honeycomb.Wood has obviously been around fora long time. It serves as a good corematerial for many composite de-signs. It is stiff, strong and has highshear properties. However, its varia-tions in density and physicalproperties along with the difficultyin fabricating limits its application.

Foam is usually the choice of ma-terial for the custom aircraft builder.Foams are easy to shape and reason-able in cost. Three types of foam aregenerally used within our industry.Polystyrene foam is the first. It isblue in color and is supplied in largebillets. Polystyrene foam is oftenused to construct boat docks. Thistype of foam can be easily shapedusing a "hot-wire" technique de-scribed later in this article.Polystyrene foam is the type used inseveral popular composite airplanesin the wings and control surfaces. Itdoes have the disadvantage of beingsoftened by exposure to gasoline andseveral other solvents. This type offoam cannot be used with polyesteror vinyl ester resins, both of whichwill be discussed later.

Polyurethane foam is basically alow-density insulating type foam alsoused for the construction of surfboards. Polyurethane foams are oftenused within a fuselage structure or for

parts requiring detailed shaping. Thistype of foam is impervious to mostsolvents. Its color is usually tan orgreen. Polyurethane foam has certainhazards. It emits a poisonous gaswhen burned. DO NOT USE A HOTWIRE DEVICE TO CUT POLY-URETHANE FOAMS. You also donot want to burn any scraps of thistype foam. Carving and cuttingshould be accomplished using a knife,saw or other cutting tools.

Polyvinyl chloride foams (PVC)are based on the same chemistryused in common PVC water pipematerial. Divinycell™ and Klege-cell™ are trade names for this typeof foam. Both of these are suited forstructural cores. This material is re-sistant to most solvents and it canwithstand a high temperature.

The last type of core material ishoneycomb. This material has an ap-pearance much as the honeycombfound in a bee hive. The sheet mater-ial used to form honeycomb can bewoven fabric, metal or paper. Honey-comb cores are used very extensively

in the aerospace industry. Varyingthicknesses are available along with awide variety of materials. Honey-comb is usually supplied in four feetby eight feet sheets. Honeycomb ma-terials offer exceptional strength toweight ratios but reliable bonding toouter skins is more difficult toachieve.

Reinforcement Materials

Many types of reinforcement ma-terials are available for aircraft use.Three types are used most often tobuild custom aircraf t . These arefiberglass, carbon fiber and Kevlar®.

Glass fiber or fiberglass is themost widely used reinforcing mater-ial. Fiberglass is manufactured withvarying physical characteristics andcost. One of the most widely used istermed E-glass. This type of glassfiber has the best physical character-istics at the lowest price. One othertype with limited use in our area isS-glass that is about 30% strongerthan E-glass but the cost is often 2-3

times higher. Fiberglass is also of-fered in various weaves. The termsunidirectional and bidirectional areused. Unidirectional simply meansall of the glass fibers are running inone direction lengthwise. They areheld together with threads runningparallel to the glass fibers. Bidirec-tional fabric means the same numberof fibers go across the material asfound lengthwise. The type of weaveis then defined. Several weaves areavailable such as plain, basket, satin,twill, etc. Fiberglass also is availablein varying weights from less thanone ounce per square yard to over 10ounces per square yard.

Carbon fiber or graphite is a verystrong reinforcement material. It isused on sail boat masts, golf clubs,etc. Carbon fibers combine lowweight, high strength and high stiff-ness. In the custom aircraft area,carbon is used in critical areas suchas spars, etc. Working with carbonfiber is somewhat difficult and whenit fails it will snap like a carrot. Ofcourse, the failure point where this

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occurs is extremely high.Kevlar® is a product of the DuPont

Corporation. It is a very tough mater-ial with a high strength and is used inmaking bulletproof vests. Kevlar® isvery effective in applications requir-ing resistance to abrasion andpuncture. However, its use in primarystructures is often limited by the rela-tively low compression strength anddifficulty in handling.

Resin Matrix

The resin component in a compositeserves to maintain fiber orientation,transfer loads and to protect the struc-ture against the environment. While acomposite's stiffness, flexibility andtensile strength are more affected bythe reinforcement material, its heat re-sistance, shear and compressivestrength are more dependent on theresin system. Three types of resin sys-tems are available: polyesters, vinylesters and epoxies. All three requirethe user to mix a specific amount ofhardener with a base chemical. Thechemicals involved are shipped sepa-rately and combined only when thebuilder is ready to use the resin.

Polyesters are most widely used forindustrial applications and within theboat industry. They are cheap and setup fast. A typical polyester is Bondo.Polyesters are easy to mix with theamount of hardener added only affect-ing the time needed to develop fullstrength. Polyesters are not suitable forapplications requiring high strength.They also will shrink over a period oftime. You may have noticed an auto-mobile fender repair where the paintcracked over a period of time. Chancesare Bondo was used as a filler, andsince it is a polyester, it cracked underthe paint. In a few words, polyestersare the least capable resin for struc-tural aircraft use.

Vinyl esters are used extensivelythroughout our industry. Vinyl estersare a crossbreed between polyestersand epoxies. They are much more ca-pable than polyesters in strength andbonding. Vinyl esters are low in vis-cosity making them easy to use. Thecure time can also be easily affectedby adding more hardener thus speed-ing up the cure time. Despite the curetime, hardened vinyl ester usually ex-hibits consistent properties of strengthand flexibility. Vinyl esters are not96 OCTOBER 1997

Sanding and shaping tools

Filler Material

subject to moisture problems duringapplication and are also lower in pricethan epoxies. One of the disadvan-tages found in using vinyl esters is inthe mixing of the chemicals. Vinylester resin is usually "awakened"from its dormant state with cobaltnapthenate (CONAP) prior to use.Just before using the system dimethylaniline (DMA) is added as an acceler-ator that determines how quickly themix will cure and, in addition, methylethyl keytone peroxide (MEKP) isadded as the hardener that actuallystarts the curing process. Mixing ofthese chemicals can be somewhatcomplicated in addition to being haz-ardous. MEKP mixed directly withDMA or CONAP, apart from the baseresin, can be explosive. Overall, vinyl

esters provide an easy to use, inex-pensive resin system. Proper carecertainly must be taken during themixing process.

Epoxies have come to dominate theaerospace industry and are the basicresins used in most amateur built air-craft. Epoxies differ from polyestersand vinyl esters in that they hardenthrough a process termed "crosslink-ing." Epoxies are essentially longchains of molecules that intertwinewhen hardened to form a strong matrixof crosslinked chains. This provides aninner structural strength to the resin.When combined with the proper rein-forcement material, compositestructures using epoxies are unmatchedin strength and lightness. Epoxies arepackaged in two parts: a resin and a

hardener. Unlike polyesters and vinylesters, the resin to hardener mixturemust be strictly followed. Addingmore hardener will not accelerate thecure time, in fact, it may seriously im-pede the drying and strength of thecured resin. Epoxies are offered withdifferent characteristics includingstrength, curing time, etc. Care mustbe taken to follow the manufacturer'srecommendation regarding the type touse. Most epoxy cures at room temper-ature. Once this is complete additionalstrength is obtainable by raising thetemperature of the epoxy through aprocess called "post curing." Usuallythis involves raising the temperatureabove 140 degrees Fahrenheit for a pe-riod of time. If this has not beenproperly accomplished the heat from aramp on a hot day can "post cure" theepoxy on an airplane. Working timewith epoxies can be much longer thanpolyester and vinyl ester because youcan use specific hardeners that havecustom working times, some as shortas four minutes, others over 24 hoursat 70°. This makes removing excessresin that may accumulate much lessof a problem. Proper skin protection isa must with epoxies due to skin der-matitis which can be caused by thechemicals.

Tools Required ForComposite ConstructionThe tools needed to build a compos-

ite airplane are inexpensive and readilyavailable. The most expensive tool re-quired will be the scales or mixingpump necessary to measure the resinmaterial. A set of postal scales can bepurchased for about $70-$80. This is avery efficient and precise method ofmeasuring epoxies. Special shears tocut fiberglass and other reinforcementmaterials is necessary. Some peoplelike to have a Dremel tool to do shap-ing and cutting. A hot wire device canbe constructed with little cost. Othercutting and sanding tools can be pur-chased at your option. A list of toolsneeded for most composite projects in-cludes:

• Scales or mixing pump• Fabric shears• Band saw (optional)• Utility knife• Rotary pizza cutter• Rubber squeegees• Grooved laminate rollers

• Disposable paint brushes• Sanding blocks• Portable electric sander (op-

tional)• Belt sander (optional)• Charcoal filtered respiratorIn addition, you will need mixing

cups, tongue depressors for stirringand a large supply of latex gloves.

Workshop RequirementsLike most airplane building pro-

jects, if you have a space the size of atwo-car garage, you can begin. Ideallyyou should have a room to do your ac-tual "layup work" and another area orroom in which to sand. You do notwant the sanding particles to floataround your fresh resin on your layersof fiberglass. Good ventilation is nec-essary along with a way to somewhatcontrol the temperature. Resins do notlike cold temperatures. Remember,you will need a workbench in additionto a work table. The work table shouldbe large enough to cut your fiberglassand to assemble component parts. A

table three feet wide by up to 15-20feet long is sometimes recommended.Remember to lay out your tools andyour shop very neatly. This will saveyou a tremendous amount of time dur-ing the building process.

Building a composite airplane canbe a very rewarding experience. Thebasics of composites have been pre-sented in this article. Next month I willexpand on the actual building tech-niques used with this type ofconstruction. I will discuss safety is-sues, cutting and shaping foam, mixingresins, applying layers of fiberglasscloth, post curing, vacuum bagging,bonding and many other compositebuilding procedures.

For additional information on theEAA/SportAir workshops, includingtype of workshops available dates andlocations call 1-800/967-5746 or visitthe website www.sportair.com

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AIRCRAFT BUILDING

COMPOSITE CONSTRUCTIONPartll

BY RON ALEXANDER

L ast month I began a series of ar-t icles int roducing compositeconstruction. As a review, I dis-

cussed the history of composite aircraftwithin the sport aviation field, definedthe term "composite," and listed thestages of building a composite air-plane. The stages of construction arc(1) decision and planning, (2) basic-building and assembly, (3) systems in-stallation, (4) filling and finishing, and(5) inspection, certification, and finalpre-flight. Our discussion this monthwill begin with the basic building andassembly phase.

Basic building starts with safety. Safetyconsiderations are of the utmost impor-tance as you begin the actual constructionof your composite airplane. Working withcomposites can be hazardous if properprecautions are not taken.

SAFETY ISSUES

All resins, hardeners, catalysts, sol-vents . . . in short, all chemicals usedin composite construction should beconsidered hazardous. Some of theseare more hazardous than others but allpose a potential health problem. Ab-sorption of these chemicals throughthe skin is a major hazard. Epoxies canbe absorbed through skin contact andthe effects are cumulative with ex-tended use. You may use a certainepoxy for years with no adverse skinreaction and then you suddenly be-come sensitized and develop a painfulrash or other problem. A wide varianceof opinion exists among professionalsconcerning the best way to protectyour skin (hands in particular). It isimpossible to make an emphatic state-ment concerning how to protect yourhands. It's impossible because thereare individual physiological differ-ences. The bottom line is some people96 NOVEMBER 1997

1T3> -i» i & a

Template for hot wiring.

Hot wire device and polystyrene foam.

are much more sensitive than others. Ifyou are just beginning to work withresins and your chance of contactingthe chemicals is minimal, you can useInvisible Gloves, a skin barrier cream.The key to using Invisible Gloves is torecoat at least every hour. Barriercreams provide adequate protectionwhen you have limited exposure. La-tex gloves also offer protection and arewidely used. Some people will useboth Invisible Gloves followed by la-

tex gloves. Sweating of the hands of-ten contributes to an allergic reaction.To preclude this many people will usecotton glove liners followed by vinylor butyl gloves. Overall, butyl glovesoffer the best possible protection butthey are expensive. You will need todecide which method works best foryou. Avoid skin contact with epox-ies. There are no safe epoxies.

Wear long sleeve shirts to protectyour arms. Never wash your hands with

solvents after you have been workingwith resins. Use only soap and water. Agood cleaner for composite tools is or-dinary apple cider vinegar. Denaturedalcohol also works well. There is reallyno reason to use solvents with compos-ite construction. Do not breathe thevapors emitted when using resins. En-sure that you are in a very wellventilated area and use a charcoal fil-tered respirator as an added precaution.

An additional hazard involved withusing resins is the exothermic reactionthat results from the curing process. Arapid increase in temperature resultswhen the curing process of the resinsystem begins. Mixing large quantitiesof resins should be avoided. Often alarge quantity of resins will exotherm tothe point that the heat can potentiallyreach a temperature that wi l l ignite afire. To avoid this problem mix smallquantities, no more than one quart.

Vinyl ester resins pose another typeof problem. Skin sensitivity is oftennot as pronounced as with epoxies.However, vinyl esters must be cat-alyzed using M E K P (methyl e thylketone peroxide). This chemical isvery hazardous if it contacts your eye.Be sure to wear eye protection if youare using a v iny l ester. Addi t iona lproblems can be encountered if youare promoting vinyl esters. Usually avinyl ester has been promoted whenyou receive it.

As I discussed last month, cuttingthe core materials can pose a safetyproblem. The only core material that

we cut using a hot-wire device is poly-styrene. All other foams emit apoisonous gas when burning. Theymust be cut using a saw or knife. Re-member, do not burn the excess scrapsof urethane foam. The gas emitted iscyanide. When cutting using a saw besure to wear a dust mask to preventbreathing of the particles.

Sanding of reinforcement materialswill release small airborne fibers intothe air. To protect your lungs fromthese particles you should wear a dustmask or a respirator. Also, protectyour skin from these small particles ofglass. Mixing microballoons (smallglass spheres) emits the spheres intothe air. Do not breathe these glassspheres. Milled glass, Cab-O-Sil, andcotton flox also present the same prob-lem. Do not breathe these particles orallow them onto your skin. Eye protec-tion should also be used to prevent theparticles from reaching your eyes.

Composite construction does havecertain hazards. However, with everytype of construction we are confrontedwith different types of safety problems.Proper knowledge and adequate prepara-tion wi l l protect you from the risksinvolved in building a composite aircraft.

BASIC BUILDINGTECHNIQUES

A brief outline of each step involvedin composite construction follows.This discussion is introductory in na-ture providing an overview. The actual

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steps involved require a more detailedanalysis than space permits.

Cutting Foam Cores

If you are building an airplane froma set of plans you will be cutting thefoam cores into the shape of an airfoil.Many kit airplanes come with premadeparts precluding the necessity of learn-ing how to shape a section of theairplane. Assuming you will need tocut the foam core, I will briefly outlinethe procedure.

You will need a large work table onwhich to lay your foam pieces for shap-ing. If we are using polystyrene foamwe will make a template the shape ofour airfoil from our plans using ma-sonite or aluminum as a backing.Duplex nails are used to secure the tem-plate to the foam. Notice that the

Postal scale to weigh resins for mixing.

template has numbers on one side.These numbers are used to ensure uni-form cutting by the two peoplenecessary to hot wire the foam. Oneperson calls the number where the ac-tual wire is located and the otherensures that the hot wire on their side ison the corresponding number. Our hotwire device is nothing more than an in-conel wire mounted between two postswith a source of electricity providingcurrent through the wire. The wire be-comes hot and actually melts its waythrough the foam forming a verysmooth, even surface. Hot wire devicescan be up to about 60" wide. Anythinglonger than that is difficult to handle.

As you may ascertain, severalpieces of foam will need to be cut andshaped then glued together to form acomplete airfoil such as a wing. Finalshaping of the piece is usually done by

sanding. Once each piecehas been properly shaped,all pieces are then gluedtogether using a resinmixture. This completesthe airfoil section. Usu-ally additional shaping isnecessary after the partsare glued. The entire foamstructure is then preparedto accept the reinforce-ment material.Polystyrene foam haslarge cells that must bef i l led. If these cells arenot filled the resin matrixwill be absorbed into thefoam through these cells.This will result in excessresin being used which

Marking fiberglass for cutting.

adds to the overall weight. In addition,a poor bond with the reinforcementmaterial may result due to voids thatmay be present. These cells are filledusing a filler material. This can be amixture of resin and microballoonsmixed to the consistency of a thickgravy. Another filler often used forthis process is SuperFil that is a light-weight, premixed material manu-factured by Poly-fiber. A thin layer ofthe filler is then placed on the core ma-terial using a rubber squeegee.Urethane and PVC foams usually re-quire a different viscosity of mic-roslurry because their cells are verysmall.

Application ofReinforcement Material

Recalling our composite structure,we have basically three materials. Oneis the core (usually foam), the secondis the reinforcement material (usuallyfiberglass), and the third is the resinmatrix (usually epoxy) which bindsthe materials. The three together forma very strong part.

After the foam has been properlysealed, we now are ready to "lay-up" thelayers of reinforcement material. Thetype of material and the number of lay-ers are determined by the aircraftdesigner. Be sure to follow the manu-facturer or designer's plans. Thefiberglass is usually placed on the foamin layers with the strength required de-termining the number of layers.

The work area should be clean withthe ideal temperature being 70° to 80°F.Cut your pieces of fiberglass usingshears designed for cutting this type ofmaterial. Keep the pieces clean. As agoal to minimize the overall weight ofthe airplane, the weight of the resinshould equal or be slightly less than theweight of the fiberglass you are layingup. If you strive for 50-50 weight dis-tributed between the resin and the glassyou will usually achieve your objective.It is essential that you wet out the fabricthoroughly while being careful not touse too much resin. Excess resin iswasted and simply adds additionalweight. So, weigh the fiberglass or ma-terial you are bonding and mix thatamount of resin material. The most ac-curate way to mix resins is with asimple postal scale. These scales arefairly inexpensive and they provideboth ounces and grams as units of mea-

98 NOVEMBER 1997

BAGGING FILM

SEALING TAPE

CONNECTORVALVE

BLEEDER PLY

PART BEING"BAGGED"

PERFORATEDRELEASE SHEET

PEEL PLYFABRIC FIGURE 1

surement. Prepare yourself for mixingresins by protecting your skin. Using ameasuring cup weigh the properamounts of resin and hardener as notedon the container. Mix the two togetherby stirring with a mixing stick for a pe-riod of at least two minutes to ensureadequate blending. At a temperature of70° you will usually have a workingtime of about 45 minutes, depending onthe resin system used. Place the fiber-glass on the foam surface orienting thefibers according to the design and thenpour a small amount of resin on thefiberglass. Use the rubber squeegee tospread the resin onto the glass. Brushesand grooved laminate rollers are oftenused in the laminate process Be sure tocover the glass uniformly with the resinmixture. Clean up your tools using ap-ple cider vinegar. Points to remember— proper mixing of the resin is essen-tial to ensure adequate bondingstrength, mix small amounts to avoidthe exotherm problem, thoroughly wetthe fabric without using excess resin,and don't forget to protect your skin.

Use of Peel PlyPeel ply is a nylon or polyester fab-

ric (similar to the fabric used onairplanes) which is used after a layuphas been completed to remove excessresin and to ensure an adequate bondbetween layers of glass. This material isplaced on the resin before it has cured.It is squeegeed into place actually wick-ing up resin from underneath the peelply itself. The resin is then allowed tocure and then the peel ply is removedfrom the laminate. The result is a verysmooth surface, derived without sand-

ing, which will result in greater adhe-sion of subsequent layers of material.The use of peel ply on laminates (lay-ers) of material has the followingadvantages: (1) peel ply causes thefibers to lay flat, (2) it reduces theamount of sanding necessary, (3) peelply increases the adhesion in subse-quent bonding and the adhesion of

primers, and (4) it reduces the amountof resin used on the structure.

Vacuum Bagging

The term is fami l iar to manybui lders but often not understood.Vacuum bagging, very simply, is amore sophisticated method used to re-move excess resin and to improvelaminate quality. Vacuum bagging is aprocess us ing a vacuum pump to"draw" a vacuum on several parts of alaminate. This draws the parts veryt ight ly together forcing out all voidsand excess resin. The process alsoserves to hold reinforcements, resins,and core materials in close conformityto complex shapes. Without a doubt,vacuum bagging increases the timeand materials cost of a laminate. How-ever, it offers significant advantageswhen optimum strength to weight isessential. While specific materials mayvary depending on the particular appli-cation, the basic components of avacuum bag assembly include lami-nate (layer of glass), peel ply, bleeder

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Basic lay-up.

Clean up items.

ply, bagging film, sealant, connectorand vacuum pump (see Figure 1).

As noted, peel ply is also used withthis application. The vacuum pump isattached through the connector valveinto the bagging film. The bagging filmcontains the vacuum and applies pres-sure to the laminate. It must be able tostretch and conform without rupturing.Bleeder ply absorbs the excess resinand communicates the vacuum evenlyover the entire surface. A perforated re-lease sheet allows excess resin totransfer from the part being bagged tothe bleeder ply. Peel ply separates thecured laminate from the bag assemblyallowing removal after curing. The re-moval of the peel ply is usually notdone until the surface is ready for paint-ing or secondary bonding. Keeping it inplace will protect the laminate surfacefrom dirt and oil. A tremendous amountof pressure can be applied using thisprocess. As an example, a vacuum of100 NOVEMBER 1997

15 inches of mercury will produce aforce exceeding 1000 pounds per squareinch. As you can see, this is a very effi-cient means of removing excess resinand eliminating voids.

Post Curing

Post curing is a process used to ob-tain maximum strength from a resin. Tounderstand post curing it is necessary todefine the term Glass Transition Tem-perature or Tg. The transitiontemperature of a resin from a hard glassystate to a soft rubbery state is called itsTg. At the Tg the tensile strength, chem-ical resistance, and hardness aresignificantly reduced while the flexibil-ity is increased. Post curing is performedby raising the temperature of the lami-nate above standard room curetemperature. Most resin systems willnot reach their full strength unless theyare cured at a temperature considerably

above room temperature. Usually thistemperature is about 40°F below the Tgspecified for the resin. The post curetemperature should never surpass anymaximum temperature of another mate-rial in the laminate such as the foam.Without post curing the Tg will only beapproximately 40°F above the tempera-ture at which the resin was cured. On ahot day the temperature of a structurecan exceed the Tg which could causethe entire matrix to soften. This soften-ing can result in the matrix of the heatedportion being softened and pulling away.The once smooth surface now exposesthe weave of the fabric. Structural in-tegrity can also be affected by hightemperatures in structures that have notbeen post cured.

With this in mind, it is important thatyou follow a post curing procedure. Youcan do this yourself by introducing theproper amount of heat into a fireprooftent-like structure containing your partor the entire airplane. Introduce the heatgradually to the temperature specifiedby the resin manufacturer. Usually thiswill be between 140° to 180° F. Again,care must be taken to not exceed thebreakdown temperature of other compo-nents such as the foam.

The above discussion will provideyou with a basic understanding of com-posite construction. Most composite kitaircraft do not require shaping the airfoilsection from foam. Instead, you are pro-vided sections of the airplane that haveto be bonded together. Next month Iwill conclude the discussion of compos-ite construction by presentinginformation concerning bonding tech-niques and finishing composite surfaces.Hopefully, at the conclusion of these ar-ticles you will have a basicunderstanding of composite airplanesand how they are assembled. At thatpoint you will be prepared to decidewhich airplane you want to build.

The author may be reached at ralexan-der@sportair.com. Diagram furnishedby Richard Kunc.

The schedule for EAA/SportAirworkshops is as follows:

November 1-2 Chino, CANovember 22-23 Atlanta, GADecember 6-7 Griffin, GA

For information on available work-shops, prices, curriculum, etc., call1-800/967-5746 or visit web sitewww.sportair.com +

AIRCRAFT BUILDING

COMPOSITE CONSTRUCTIONConclusion

BY RON ALEXANDER

This article concludes the series on composite construction. The two previous articlesdefined the word "composite," discussed safety issues, listed the stages of building acomposite airplane, and presented the basic composite construction techniques.

Again, the five stages of compositeconstruction are: (1) decision andplanning, (2) basic building and as-sembly, (3) systems installation, (4)filling and finishing, (5) inspection,certification, and final pre-flight. Lastmonth's article concluded with a pre-sentation of most of the building andassembly steps. In this issue I willcomplete the discussion of buildingsteps and then review the steps of sys-tems installation and finishing. Theinspection, certification, and final pre-flight procedures were discussed in theJune issue of Sport Aviation.

The majority of plans-built aircraftrequire the builder to completely formthe entire structure using the hot-wireand foam cutting techniques previouslypresented. Some of the kit aircraft alsouse this building procedure for certainportions of their design. Usually, how-ever, a kit aircraft will only demand asmall amount of shaping and forming.Composite kit airplanes are often soldwith pre-molded parts that need only tobe assembled — not unlike a model air-plane. This, of course, reduces theamount of construction time consider-ably. The kit manufacturer assumes theresponsibility for a properly shapedwing or fuselage. Molds are constructedby the manufacturer and the parts of theairplane actually built within the molds.You then receive the various compo-nents and bond (glue) them together toassemble the airplane. This also allowsthe kit manufacturer to ensure thequality of construction, i.e., theproper mixing of resins, orientationof fiberglass, etc. The number of90 DECEMBER 1997

Sanding prior to bonding.

parts pre-molded and supplied to thebuilder vary from one kit to another.Often, a kit manufacturer will design anairplane to use a combination of bothpre-molded parts and moldless (thebuilder forms the piece) construction.

So, instead of having a foam corewing, as an example, a kit manufac-turer wi l l supply us with a hollowwing. With this type of constructionthe strength of the wing is found insome type of spar system similar to awood or metal wing. A wood or metalwing uses a spar and wing rib combi-nation to support the aluminum skin.

The number and spacing of ribs, thesize of spars, etc., determine thestrength of the wing. The same appliesto composite construction. The advan-tage of a pre-molded composite wingis found in the sandwich type con-struction that is used. Recall the term"sandwich construction" that meanswe are using a foam core, reinforce-ment material and resin together toform our structure. A pre-molded wingwill use the sandwich type construc-tion on the wing skin only. Obviously,the wing skin will only utilize a thinlayer of foam or core material instead

of the entire wing being constructed inthe sandwich manner. The pre-moldedwing is curved which also providesstrength and the wing is held togetherwith ribs just like conventional con-s t ruc t ion . Spars constructed fromcomposite materials and ribs are thenused in a similar manner to a conven-tional airplane. These spars and ribsare often supplied by the manufac-turer. This type of construction allowsthe wing to be assembled using a mini-mum amount of ribs versus a metalairplane that may require considerablymore ribs to acquire the same strength.

With this type of composite con-struction all of these parts must beproperly glued (bonded) together. It isessential tha t the bonding be com-pleted properly.

Bonding

Bonding is not a new process in air-craft building. In fact, bonding has beenused in aircraft construction since thevery beginning. The technique of glu-ing wood structures together has beenused for years. Many of the same glu-ing elements found in wood are alsofound in composites. The term bonding,as applied to composites, is used to de-scribe a common method for joiningcomposite structures. Bonding is theprocess in which previously manufac-tured component parts are attachedtogether during assembly of the air-plane. Bonding composites can also becompared to welding metal. It is de-signed to be a permanent joining

method. Several important points mustbe considered in bonding. We mustknow how much strength is needed inthe joint, the bonding area required,what type of material must be used toprovide the adhesion, and the procedureused to apply the bonding mater ia l .Preparing the surfaces that are to bebonded together is also crucial.

The first method of bonding used inamateur-built aircraft involves a fourstep process. The first step is to cutand trim the component parts to get theproper shape and fit. The second stepis to position the two pieces together.This can be accomplished by usingtemporary jigs or by temporarily glu-ing them together with a non-structuraladhesive. Third, we must fill any gapsthat may exist as a result of butt ingtwo pieces together. The f ina l stepconsists of actually creating the struc-tural joint using wet (resin laden) stripsof reinforcement material (usuallyfiberglass) bonded over the area con-necting the two components together(see Figure 1). The example in Figure1 represents a typical fuselage withtwo pre-molded halves being bondedtogether by the builder. If we are bond-ing toge ther two pieces tha t areperpendicular to each other as in Fig-ure 2, then we must create a fillet onceagain using wet lay-ups of reinforce-ment material. An example of this typeof construction would be in mating awing rib to the wing skin.

The strength of a joint that is joinedby a f i l l e t is derived from the rein-forcement material and not the fillet

itself. The fillet is only needed to pre-vent the reinforcement fibers frommaking a direct 90° bend without anyradius. Composite materials must havea bending radius just like sheet metal.The number of strips of reinforcementmaterial laid down over the fillet de-termines the strength of the bond.

The second method of compositebonding is termed "adhesive bond-ing." Adhesive bonding involvesassembling component parts togetherusing a structural adhesive. Structuraladhesives range from pre-formulated,two part mix tu res tha t are in pasteform to structural laminating resinsthat are mixed with flocked cotton ormiller fiber to provide the necessarystrength. The first method of bondingdiscussed used laminating resins andreinforcement material to create abonding overlap. Adhesive bondingrequires a bonding area to be formedinto the part when it is molded. Thisis usually accomplished by loweringone side of a part and raising a side ofthe second part. This allows the twopieces that will be bonded to slideover each other providing a precisefit. The joint that is formed when thepieces are joined in this manner is re-ferred to as a "joggle" (see Figure 3).With this type of overlap the builderis only required to lay down the struc-t u r a l adhes ive and apply someclamping pressure. Figure 4 showsadhesively bonded joints similar tothe wet lay-up joints in Figure 1.

Some kit manufacturers prefer tocombine both bonding methods to

Figure 2

Figure 4

^Adhesive-

J L

SPORT AVIATION 91

achieve the greatest possible strength.The key to achieving strength in anyjoint is to properly prepare the surfacesthat will be joined. The laminatingresin or structural adhesive must bondwell to the surfaces. The surfacesshould be cleaned properly and sanded.

The main alternative to bonding ismechanical fastening using rivets,screws, bolts, etc. Metal aircraft typi-cally use mechanical fastenersexclusively. Composite aircraft usemechanical fasteners in areas whereparts will be disassembled for mainte-nance or inspection. These areasinclude cowlings, fairings, inspectionopenings, etc.

Bonding composite pieces togetherhas an added benefit over mechanicalfastening in that a bond is created alongthe entire surface of the joined parts in-stead of only where fasteners areinstalled. A bonded joint will be asstrong as or often stronger than a me-chanically fastened joint as long as thebonding is properly done. As a review,to accomplish a proper bond the surfacesmust be properly prepared, an adequatebonding area presented, and the appro-priate adhesive material applied.

Cleaning prior to bonding.

SYSTEMS INSTALLATIONInstalling the various systems in a

composite airplane will consume ap-proximately 1/3 of the building time.Typically, the time required to build acomposite airplane will consume ap-proximately 1/3 of the building time.Typically, the time required to build a

composite airplane will consist of 1/3spent in basic building, 1/3 in systemsinstallation, and 1/3 in finishing. Thesystems installation varies consider-ably depending upon the actualairplane you are building and howmuch has been completed by the man-ufacturer. Installation of systems iscomposed of control surface tubes or

Vacuum bagging92 DECEMBER 1997

cables, engine installation, engine andpropeller controls, instruments, seatbelts, landing gear and brakes, etc. Asyou build and assemble the airplaneyou wi l l install the various systems.Your plans will specify when to in-stall or fabricate each system. Systeminsta l la t ion is an ongoing process.The bu i lder can also legally h i r esomeone else to assist wi th certainsystems installation. An example ofthis would be in engine installation orinstalling avionics. Advisory Circular20-139 explains in detail what you asthe builder are allowed to contract outcommercially without jeopardizingthe major portion rule.

FILLING AND FINISHINGAs previously mentioned, finishing

a composite airplane consumes fully1/3 of the total building time. Obvi-ously, th i s stage of construction isvery important to the builder becauseit determines the final look of the air-plane. Two choices are ava i lab leregarding when to finish a compositeairplane. You can fill and finish com-ponent parts prior to assembly. Thisrequires even more time because youare assembling the airplane then dis-assembling it to complete thefinishing process. Then the completedparts are joined together. Most peopleprefer to finish the airplane after it hasbeen assembled. In both cases the fi-nal painting is usually accomplishedafter the airplane has been test flown.

Why is finishing necessary? A com-pleted composite part wi l l exhibi t arough look. The weave of the rein-forcement mater ia l w i l l be veryapparent. Filling is usually required asthe first step to a smooth finish. Wehave all seen the extremely smoothsurfaces found on composite aircraft.That finish is the result of a lot of hardwork. There are many rough imperfec-tions that exist before the f i l l ing andfinish process. It is also interesting thatmost composite aircraft are paintedwhite or a light color. This is neces-sary because of the heat build-up whenthe airplane is in the sun that creates ahigh skin temperature. This is detri-mental for two reasons: (1 ) it causesepoxy to shrink more than normal, and(2) it will overheat and damage foamcores. In 90° ambient temperatureswhite paint has a skin temperature of140°F and black painted skin can reach

210°F. You have two choices — eitherfly only at night or paint the airplanewhite or a light color.

F i l l ing and finishing does a lotmore than simply creating an awardw i n n i n g look. Composite a i rcraf thave about a twenty-year track recordwhich can be examined. There havebeen a lot of composite airplanes builtsince the KR series and the Kutan rev-olution that began in the 1970s. Hereare some observations regarding fin-ishing that have surfaced as a result ofthis history.

First of all, many builders haveused too much filler on their airplanes.Too much f i l ler of any sort is badnews in high flex areas or on leadingedges. Fillers are to be used for fillingand not for building. Several of thesefillers have been made from polyesterresins. In previous art icles I havestated that polyester should not beused for aircraft application. The rea-son — it cracks and peels off insheets. That is beginning to occur inseveral composite airplanes that havebeen flying for a number of years.

Secondly, polyester surfaceprimers have been used on a numberof airplanes. Same problem! Mostpaint cracking is caused by heavy ap-plication of these primers that w i l lresult in shr inkage over the years.When it shrinks it takes the topcoatwith it, even high-dollar polyurcthanepaints . There arc a number of air-planes being repainted today becausetoo much polyester primer was used.

Thirdly, th ick coats of high buildautomotive polyurethane wi l l alsocrack. Most two-part polyurethanewill flex very well as topcoat paintsbut t h i ck coats of the product wi l lthen quit. The quest for the perfectfinish should be done with sandpaper,not the spray gun. Professionalpainters realize that surface prepara-tion is 90% of the job.

Lastly, epoxies must be protectedfrom UV radiation. Epoxy resins aresubject to deterioration when exposedto sunlight. One resin manufacturercautions that their highest grade epoxycan totally break down in 15 monthsif not protected from the sun. This is

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Adhesive bonding.

true of all epoxies. The symptom ischalkiness followed by delamination.The best way to protect epoxy is touse a primer that will block sunlight.When paint manufacturers state thattheir products have 100% UV pro-tection, they are talking about thepaint or primer that is being pro-tected from UV radiation and not thesubstrate they are covering. Primersthat totally block the sunlight aresimple insurance policies.

Aircraft composite filling and fin-ishing has taken most of itstechnology from the automotive in-dustry. The reason for this is becauseautomotive technology has beenavailable and people are familiarwith it. The problem is airplanes flexmore than cars. Again, this can resultin a cracking problem if the wrongtype of filler or primer is used. Auto-motive products are usually polyesteror lacquer. Polyester has been dis-cussed. Lacquer products are alsosubject to the same cracking prob-lem. We have all seen lacqueredfurniture that is crazed.

5 Finishing Steps

Step One — FillingComposite structures usually have

two major areas that need rough fill-ing: depressions caused by seams orjoints and the weave pattern of the

reinforcing material (usually fiber-glass) used in the lay-up. Therougher the fabric the more fillingrequired. Molded kit airplane partsare usually fairly smooth when theycome out of the mold. These partsrequire little or no weave filling butwhere these parts are joined (bonded)together there are troughs andcrevices. Rough filling in these areasis inescapable.

The classic method of fillingrough areas or weave patterns is touse a homemade "micro or slurry," amix of epoxy with microballoons.Remember, microballoons are smallbubbles or miniature balls made ofglass or plastic. The idea behind thisis to offset the epoxy resin with alighter material. You add microbal-loons to epoxy until you get aconsistency like peanut butter. Youthen trowel or squeegee the mixtureinto the area you want to fill.

Many people have used Bondo inplace of micro. Recall our earlierdiscussion considering polyesters.Bondo is a polyester and will shrinkwith time. It is also heavier than ourmixture. I do not recommend the useof Bondo on an airplane unless youwant to repaint it after a few years.

Another product that is now avail-able is called SuperFil . Thiscommercially formulated product is apre-mixed epoxy filler. It eliminatesthe guess work necessary in mixing

your own micro. It is made in a high-shear mixer that allows more filler tobe used. When mixing your own mi-cro, if you add too little f i l ler themixture is difficult to sand and if ithas too much filler it will becomeweaker in shear. Many builders arenow using SuperFil instead of mixingtheir own slurry. Of course, weight isimportant when we are filling. Ourown mixture of micro can weigh aslittle as 6 pounds per gallon com-pared to Bondo that weighs about 12pounds per gallon. SuperFil weighs inat 3-1/2 pounds per gallon. The bot-tom line with fillers is use only anepoxy filler or a polyurethane fillersuch as PPG's Rage.

The filler is mixed by weight andthen spread onto the area to be filled.You must be careful not to put toomuch filler on the surface. Too muchfiller of any sort has the potential ofcracking over the years. You startwith very thin coats of filler forcedhard into the surface. Technique be-comes very important in thisapplication and will be discussed in afuture article devoted entirely tocomposite finishing.

After application of the filler ma-terial our soon-to-be favorite activityof sanding begins. Hand sanding ispreferred over machine sanding. Useof high quality sandpaper is also es-sential. There is also a new line oftools available for sanding manufac-tured by the Perma-Grit Company.Be aware that you may have to applyseveral layers of filler to get the de-sired final result.

Step Two — PrimingActually, priming a composite air-

plane usually consists of a smallamount of filling. The filling stepcompletes 90% of the needed surfacepreparation. The remainder is usu-ally accomplished using a fi l ler/primer. Several primer/fillers areavailable on the market. FeatherCoat, Feather Fill, and Smooth Primeare examples. The objective of afiller/primer is to fill small imperfec-tions left from the major filler and tofill all pinholes. Filler/primers areusually sprayed on the surface. Afterabout the second coat those dreadedpinholes (every composite builders'curse) appear. Several coats offiller/primer will be needed to fill

94 DECEMBER 1997

these pinholes. A new product thathas just appeared on the market willactually fill pinholes. The name ofthat product is Smooth Prime. It isalso a water based primer that is partof an entire water based compositefinishing system called Flight Gloss.It is a Poly-Fiber product availablethrough major suppl ie rs . Manyfiller/primers only bridge pinholeswhich means they reappear aftereach sanding.

The actual primer designed for aspecific topcoat paint will do littlefi l l ing. A topcoat primer is definedas a coating that is used to ensure thesubsurface does not deteriorate andto provide a base for the topcoat. Incomposite applications, this typeprimer is usually not necessary if afiller/primer has been used. Remem-ber, most primers wi l l not protectresins from the UV rays of the sunand there are no corrosion issueswith composites. If you are going touse a pr imer use the one recom-mended by the topcoat manufacturer.

Concerning UV protection, theFlight Gloss composite f inishingsystem has a step to block the UV ra-diation. The product name is SilverShield and it contains mica that is aknown blocker of UV rays. It is awater borne product that is sprayedon over the filler/primer and it wil lprotect the epoxy resin.

Step Three — Final TopcoatThe topcoat is one of your choice

as long as it is light in color — usu-al ly white. There are a number ofexcellent topcoats on the market.Most of them are polyurethane paintsand you need to be aware of thehealth hazards involved if you arespraying them. A forced air breath-ing system must be used such as theone manufactured by HobbyAir. Usethe product as directed by the manu-facturer.

This concludes our discussion ofcomposite aircraft building. I hopeyou will consider the pleasures andbenefits to be derived in building acomposite a i rplane. The choicesavailable for composite airplanes arealmost un l imi ted . Composite con-struction is the leading technology inthe aviation industry today. Ama-teur-built aircraft designers have

certainly contributed to the overalldevelopment of composite technol-ogy. Composite airplanes arc sleek,efficient, lightweight and extremelystrong. Bui ld ing a composite air-plane is a very rewarding experience.I would recommend the workshoppresented by the EAA and SportAiron composite construction. This two-day course is available in variouslocations around the country. I want

to acknowledge the fo l lowingSportAir instructors for their input tothis article: Jeff Russell Acrocad,Inc., Greg Kress — Kress PrecisionComposites, and Jon Goldenbaum— PolyFiber, Inc. Other referencesinclude Basic Composites by AndrewMarshall, Composite Construction byJack Lambie, and Understanding Air-craft Composite Const ruct ion byZeke Smith. *

EAA/SportAir Workshop ScheduleDecember 6-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Griffin, GAJanuary 16-17, 1998 . . . . . . . . . . . . . . . . . . . . . . . . . Sebring, FLFebruary 7-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Griffin, GAFebruary 2 1 - 2 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chino, CAMarch 21 -22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Denton, TXApril 4-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minneapolis, MN

Information on these workshops can be obtained by calling 1-800/967-5746 or contacting the website at www.sportair.com. The author can beemailed at ralexander@sportair.com

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