Chapter 2

 

Chapter 2

Materials for modelers

The model builder of today is lucky: no need for him to crouch over a candle flame, heating and bending hand-split bamboo strips to form wing tips, or to pare shavings from basswood spars in an effort to lighten a ship powered by sliced inner tube. Old Christmas wrappings are no longer pressed into service as covering material, nor is it necessary to purloin the isinglass from the side-curtains on the flivver to make a windshield. Modern flying fans have at their fingertips - or at least, at the nearest hobby shop - a wealth of superior materials, precisely manufactured and reasonably priced. You won't get the most out of modeling until you know the materials that are available, and what you can do with them.

First, there's balsa wood. It's light, tough, flexible, easily cut and sanded. It takes a smooth finish and holds tight when glued. Moistened, it becomes pliable, and it sets again when dry. And it comes in a wide range of hardnesses and stock sizes.

You'll find balsa sheets in standard widths of 2, 3, and 4 inches, with wider sizes available by special order. Three-inch is the most widely used size; why pay a premium for wider sheets when it is a simple matter to edge-cement to build up whatever width is needed?

Standard lengths are 24 and 36 inches, the latter being most popular. Thicknesses ordinarily available are: 1/32", 1/16", 3/32", 1/8", 3/16, 1/4", and 1/2".

The 1/32" sheet balsa is used for planking, and for ribs and cap strips for small models. It also makes good wings for small gliders and ROG's. Always select hard, straight-grained wood in this thickness.

The 1/16" balsa, commonly called "sixteenth," is used for almost every portion of model structures, including ribs and formers, planking, spars in small models and built-up spars in larger ships, tail surfaces in smaller models, wings for gliders and ROG's, etc. When used for planking, medium 1/16" with straight grain is best; for ribs and formers, medium to hard wood is appropriate, and here's where you can use up the irregular-grained material. Rock-hard 1/16" balsa is fine for spars, keels, and other long stress-bearing members.

The 1/8" sheet balsa is used for much the same purposes as 1/16", but for larger models. It also can be used for fairings, fillets, and filling, since it has sufficient thickness to allow sanding to curved shapes without cutting through.

The thicker sheet sizes are mainly used for building up cowlings, fairings, and other compound curves, or for structural parts on very large ships. Pick the softer grades in thick balsa; the parts made from it are usually non - stress bearing and you need a saw to cut hard material over 1/8" thick.

Balsa strips come in the same lengths and thickness as sheets, and in varying widths. The standard sizes are: 1/16" square, mainly used for fuselage longerons and spacers and as stringers and spars, on small rubber-powered models; 1/16" x 1/8", useful as stringers for larger rubber jobs and small engine-powered ships; 3/32" square, frames for medium-sized rubber and "gas" models; 1/8" square, fuselage frames for large rubber models such as the Wakefield types, and for medium-to-large engine jobs; 1/8" x 1/4", for stress-bearing fuselage members in 1/8" square frames, wing spars for 1/2 A free-flight wings, trailing edges for small rubber models, and fuselages for small stick-fuselage ROG's. The 1/16" square and 1/4" square sizes can be used to build up sturdy box fuselages for large gas models or shaped to form leading edges for small-to-medium wings. All the strip sizes from 1/16" up are used as strip planking on models of appropriate size.

Strip balsa should be individually selected for the purpose for which it is to be used. Pick very hard material for spars and stringers, and medium for leading edges, planking, etc. Very soft strips are useful chiefly for chewing on while pondering the next project or discussing the flaws in the other fellow's model. The hardness oF a strip can easily be determined by pinching its end, in much the same fashion as one selects bananas. Soft balsa squashes flat; medium balsa gives reluctantly; hard balsa makes a depression in the fingers. Be careful to test strips (and sheets) only at the end so as not to ruin the piece if it is softer than you expected.

Balsa blocks can be had in almost any size up to about 2 x 4 inches and up to 3-foot lengths. These should almost invariably be of the softest grade, as they are used to form curved portions of a structure such as the fuselage front end. It is not only hard to carve a tough block, but the added weight of hard wood is undesirable. Styrofoam blocks are sometimes used as a substitute for balsa. When reinforced with a balsa spar or planking, it is strong and lighter than a conventional structure but requires special care in shaping and finishing.

Special formed sections can be purchased also, such as rounded and hollowed leading-edge sections for larger power models, and beveled trailing edges in several sizes.

You can make extremely tough light-weight load-bearing members (particularly wing spars, fuselage keels, etc.) by laminating balsa with other materials. Two pieces of hard 1/16" sheet balsa with a piece of celluloid cemented between them have at least twice the strength of the balsa alone, with little increase in weight. Tough brown paper is another excellent laminating material, and is easy to use since it can be obtained in the form of gummed tape, ready for application. Silk and nylon can be used between thin balsa layers, or applied to the outside, as on landing-gear fairings and scale wing-struts.

Solid or laminated hardwoods (in modeling, all woods other than balsa are hardwoods), either plywood or veneer, are indispensable materials, used for firewalls, bulkheads to which landing gears or wing mountings are attached, spar reinforcements, etc. Plywood, consisting of at least three layers of wood with the grain alternating at right angles, is obtainable in thicknesses of 1/32" and up. The more layers the plywood has, the tougher it is. A good 1/8" plywood will have about five laminations; this is tough enough for a firewall on even the largest model, if properly supported. Light-weight, three-ply mahogany or other relatively soft wood, from 1/16" to 3/16" thick is easily worked and strong enough for most applications. Four-or five-ply birch is stronger and heavier, and should be used where heavy shocks are taken, as on a landing-gear bulkhead in an R/C job. Hobby shops and most lumber yards carry plywoods and veneers in useful thin sheets. Veneers generally have only one layer of 1/28" thick hardwood, such as walnut, applied to a core of basswood or poplar. This material is subject to warping, and is both heavier and weaker than plywood, but it can be used successfully if not too much is expected of it.

Bamboo, once a standard modeler's material, has faded from the scene in recent years; however, it is still a light, tough wood, which has the virtue of splitting easily into extremely narrow strips for small stringers. It is a flexible wood, which can be curved sharply without breaking, and makes excellent wing struts, since it will give and spring back in a hard landing, unlike balsa or hardwood when trimmed to a small cross-section.

Tough hardwoods, such as oak, ash, and hickory, are useful in modeling chiefly as motor mounts for beam-mounted engines. Softer or brittle hardwoods like mahogany or fir won't last. A lemonwood bow stave, purchased from an archery supply house, will make a vast number of really indestructible motor mounts at small cost.

Model builders' cement is the universal adhesive for assembling balsa parts (as well as repairing broken dishes, loose shoe-soles and other errata, which the modeler must accept gracefully as the price of family indulgence of his aeronautical noises, stinks, and stains). In addition to regular fast-drying cement, extra-fast cement is also available for quick field repairs. Fuelproof glue for use with glow-plug engines is also obtainable in several speeds. Also fuelproof, and incredibly strong, is epoxy glue, which will bond anything to anything. It requires a modest extra effort in mixing a resin and a hardener, but impatient modelers have even been known to epoxy an engine direct to a firewall.

Ordinary mucilage is useful to the modeler in covering, since it dries slowly and is sticky from the word go, unlike cement, which sometimes refuses to hold the paper in place, right up to the moment it hardens.

For joining hardwood parts, as when motor mounts are glued against plywood bulkheads, a glue such as Weldwood is best. White liquid polyphenyl resin glues are also acceptable for this purpose, and while not as strong, they dry more quickly and are easier to use. You can strengthen cemented joints with crinoline.

Metals are joined with solder (all except aluminum); a plain solder used with an acid-type flux is most satisfactory, except in electrical work; here resin-core solder should be used.

After a frame has been built, it is usually necessary to cover it. For this purpose, various grades of paper are commonly used. Japanese tissue, which comes in many colors, is feather-light, tough, and long-lasting. It is used for the smallest built-up ROG models and other rubber jobs, and for small F/F ships.

A heavier paper called Silkspan, available in several weights, is very widely used for covering power models from about 30-inch span up to the largest sizes. A still heavier paper made from bamboo can be used for extra-large ships, or where great strength is needed, as on R/C models.

The plastics industry has contributed a number of new covering materials, including Monokote, a self-adhesive film with a plasticized finish, requiring no doping for a high gloss. This is an exceedingly tough covering, and can be heat-shrunk to a taut surface equal in appearance to a hand-rubbed 20-coat paint job. It comes in a variety of colors. A similar product is Shrink-Tight, available only in white, but of even greater strength. In fact, the process of heat-shrinking must be done with care or the structure will collapse under the pressures created. Any of the above may be applied over sheet balsa planking for an improved finish.

Silk and nylon are more expensive, trickier to apply, and require more dope for sealing, but have the advantages of tremendous strength and very long life, as well as good looks.

Some models are wholly or partially covered with balsa wood, particularly where a smooth surface is desired for the sake of scale appearance or where extra stiffness and rigidity is needed. Sheet balsa is used for flat or simply curved surfaces, and strip balsa for compound curves.

Open areas such as cabin windows are usually covered with sheet plastic or celluloid. These materials can be purchased in all thicknesses from paper-thin to board-thick, and are very strong and durable. Some plastics such as celluloid are soluble in model cement; these are easy to glue. Others are impervious to cement, and so are difficult to attach, but have the advantage of not being susceptible to damage from cement, dope fumes, or overflow. Model shops carry small-sized sheets; large sheets can be bought at lumber yards and paint stores.

Microfilm is a special covering material used for the most delicate and fragile of all models, the indoor endurance job. It is a liquid which is poured over a pan of water to form a thin film, which is then lifted on a wire loop and applied to a spider-light frame.

For the finishing of models, the special light-weight paint known as "dope" is universally used. The term, which includes regular dope and several types of fuel-proof dope, clear and in dozens of colors, is a lacquer which dries quickly to a glossy surface, forming a tough film which helps consolidate the structure and adds to its strength. For the special fuelproof dopes, special thinners are required, and the different types cannot be mixed. Paint in spray cans is available in exotic colors such as Tahitian Orange and Candy Oriental Purple; it is more expensive but easier to apply than the brush-on product. The builder who has a high rate of production will find it economical to purchase pint or quart cans of red, yellow, blue, black, white, and silver dopes and mix his own colors. Regular dope is cheaper, and can be fuel-proofed by a coat of a clear material such as Humbrol fuelproofer.

Epoxy paints are also available, requiring mixing before application. Two coats of epoxy equal several dozen coats of ordinary dope, but the penalty is paid in the form of extra weight. Still, epoxy makes an impressive finish for models where high performance isn't vital.

A fifty-fifty mixture of dope and cement (be sure to use the same type to be certain they'll mix) makes an excellent material for coating a frame before covering, for added strength. It can also be used to dope a loose section of paper covering which has resisted the shrinking effects of water and plain dope.

On wood surfaces, a filler should be used before doping to fill the open pores. A good filler can be made by adding talcum powder or cornstarch to clear dope. Lacquer-base auto body putty can be thinned and applied with a brush when a hard metallic surface is needed, as on a scale model of a metal-surfaced ship. Again, be sure to use a dope which will not dissolve the filler, or bubbling will occur.

After a model is fully doped, added decorative touches can be achieved by the use of decals. Standard designs such as military insignia can be had at a hobby shop; the modeler can make his own designs by using sheet decal material in various colors. Numerals, scallops, stripes, etc., can be drawn on the back of the decal material and cut out, then transferred to the model. Clear dope or fuelproofer should be painted over the decal to seal it to the surface and prevent fuel damage.

For forming cowlings, wheel pants, fillets, etc., there are several useful materials. Carve a wooden form, dope and wax it, and over it build up fiberglass or papier-mache, which can be sanded to exact shape when dry. Fiberglass can also be molded over a wire screen form for large shapes. Some modelers form whole fuselages, especially for C/L ships in this way.

If trim is to be painted on the ship, either by brush or spray, masking tape can be used to good advantage to cover the areas which are not to receive paint. If a light coat of clear dope is applied over the edges of the tape, seepage under the tape will be prevented. Tape should be carefully stripped after the paint is dry to prevent damage to the covering or finish.

Rubber is one of the modeler's most useful materials. Flat rubber from an old inner tube can be used to cushion engine mounts and L.G. installations. Sponge rubber serves to absorb vibration around a radio installation. Rubber bands of all sizes are a must for holding knock-off flying surfaces in place, actuating various mechanisms, etc. And, of course, rubber is an important power source for models.

Flight rubber for motive power comes in flat strips approximately 1/32" thick, in widths of 1/16", 1/8", 3/16" and 1/4". A model may carry from one strand of the smallest size to several dozen of the largest. Rubber should be stored in total darkness when not in use, preferably in a tight tin can, and sprinkled with talcum to help keep it in condition. When installed in a model, lubricate it with glycerin, liquid soap, or special rubber lube to cut down friction.

The same rubber is used in many R/C jobs to operate the escapement.

To power your engines, you can get commercial fuels tailored to each particular power plant. There are 1/2 A fuels, speed fuels, fuels for engines with piston rings, glow fuels, and diesel fuels. You can get it in 1/2-pint cans or 55-gallon drums, depending on how much you fly. Or you can make your own by mixing (for glow engines) castor oil and alcohol, 1:2; (for diesels) ether, kerosene, and mineral oil, 1:1:1. Test your mixture in your engine and vary it until you get the best results. Commercial fuels contain potent additives which make them hotter and easier-starting; but for sport flying, home-brew is fine - and cheap.

Plastic tubing for fuel lines comes in several sizes and also makes good bushings, spacers, insulators, etc.

For making accessories and fittings for model planes, everything from empty tin cans to burned-out flashlight bulbs is useful. The practiced modeler never lets a good defunct alarm clock get away, or a dead radio chassis. Such odd-and-end materials can be grouped under several headings, along with standard modelers' items.

A basic material is wire, which appears in a multitude of forms. Tough, springy, steel piano wire is sold by hobby shops in several diameters, in 3-foot lengths. The 1/32" piano wire is used for propeller shafts (prop hooks) and landing gears for small rubber models, lead-out wires for C/L jobs of all sizes, tail skids, wing hold-down hooks, etc. It is easily bent to various

shapes, and adds little weight, but is not stiff enough for C/L pushrods or landing gears for any but the smallest craft. The 3/64" piano wire makes an excellent pushrod for small C/L models, and wing hold-downs, etc., for big ships. The 1/16" size is widely used for L.G. struts for 1/2 A sport models, pushrods in bigger ships, shafts for all sorts of installed mechanisms, and many other things. The 3/32" wire makes a sturdy L.G. for medium-sized, powered ships, and 1/8" is super tough (and heavy) for the big ones. Fisherman's leader wire is useful for small items, on all kinds of models.

Softer wires are also useful. Fine copper wire is used to wrap joints to be soldered; a larger size can be bent into tiny circles and pounded flat to make small washers; soft paper-clip stock can be bent to form such items as pendulum arms and other lightly stressed mechanisms. Insulation slipped from heavy wire doubles as fuel tubing, or can be cut in short sections as spacers in various gadgets. Fine steel wire or stranded cable is used for control lines for heavy ships. Number 30 linen thread does fine for the small ones.

Metal tubing, of brass, aluminum, or copper, is another basic gadgeteer's item. Brass tubing makes good bushings for folding landing gears and other operating parts, as well as outlets for special homemade fuel tanks. Exhaust stacks of soft aluminum tubing help keep engines clean and quiet, and keep dirt out of the ports. Special tools for reaching hard-to-get-to spots can be improvised from tubing, and a sharpened length of the right size is an excellent hole-cutter.

Sheet metal often comes in handy. Aluminum sheet, being light and easy to cut, is most useful, and makes motor mounts, L.G. retaining plates, and special fittings of all sorts, including gear boxes. Brass is heavier but has the advantage of soldering easily, and is used, along with tin-can stock, for making fuel tanks, engine mounting-nut retainers, etc. Extra-strong dural can be used for "Cessna-type" landing gears and other load-bearing items.

Sheet lead is a useful form of the metal commonly used as weight to trim a model for flight or as a pendulum bob.

Gears salvaged from clockwork mechanisms are indispensable for putting together fascinating things like retractable landing gear installations and other automatic or semi-automatic devices. Springs of all kinds are also useful here as well as on shock-absorbing L.G.'s.

Never throw away a small nut, bolt, or washer. A small can or jar filled with these odds and ends will be one of the most used items in the modeler's shop, for mounting engines, landing gears, gear boxes, etc. In fact, any small metal object should be saved in a gadget box; old cartridge cases, empty aluminum cigar containers, ball-point pen cartridges - all of them come in handy at one time or another. Many items manufactured for other uses have been taken over by the modeler for his own purposes. Fishline swivels work fine to clip models on to control lines; sandpaper makes realistic scale wing-walks; tiny oiler cups made for heavy machines make good fuel filler-caps with automatically closing covers; glass beads are dandy thrust bearings for dinky rubber models; dress snaps hold down cowlings. A modeler soon develops an alert eye for spotting the potentially useful.

The real key to resourcefulness in modeling is a little of everything. A piece of stiff cardboard for patterns; white paper for fillets; gauze or crinoline for hinges; a scrap of tracing cloth for reinforcements, a piece of inner tube for shock absorption; formica, felt, wire screen, all have their moments. The bottom taken from an old kitchen strainer makes a perfect radiator bug screen for a scale job; a toy aluminum pot makes a metal engine cowling; and imitation rubies and emeralds become scale navigation lights. It is up to the modeler to accumulate a trove against the hour of need.

 
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