Thursday, 3 September 2015

Materials and Hardware used for RC Modelling Part 1 - Construction Materials

1. Construction Materials.
Materials Used for Construction of RC-Aircrafts
  1. Balsa Wood
  2. HD Form
  3. Depron Foam
  4. Coroplast Sheets
  5. EPP form
  6. Aircraft grade Ply Wood
  7. Carbon and Glass Fiber
  1. Balsa Wood
  • Model airplanes are no different than any other type of flying machine, large or small - THE LIGHTER IT IS BUILT, THE BETTER IT WILL FLY!
  • Keep it in mind, then it is easy to understand why balsa wood has been the standard material for model airplane construction since it first became readily available in the U.S. in the late 1920s.
  • Its outstanding strength-to-weight ratio enables RC hobbyists to construct durable models that fly as of real aircrafts.
  • Balsa also absorbs shock and vibration well and can be easily cut, shaped, and glued with simple hand tools.
  • Balsa trees grow naturally in the humid rain forests of Central and South America.
  • Its natural range extends south from Guatemala, through Central America, to the north and west coast of South America as far as Bolivia.
  • The small country of Ecquador on the western coast of South America, is the primary source of model aircraft grade blasa in the world.
  • Balsa needs a warm climate with plenty of rainfall and good drainage.
  • For that reason, the best of balsa usually appear on the high ground between tropical rivers.
  • Ecquador has the ideal geography and climate for growing balsa trees.
  • The scientific name for balsa wood is ochroma lagopus.
  • The word balsa itself is Spanish meaning raft, in reference to its excellent floating qualities.
  • In Ecquador it is known as Boya, meaning buoy.
  • Many hobby shops supply balsa sheets, sticks, and blocks that you can choose from if you are going to build a model airplane from scratch.
  • Because of the nature of balsa, the actual weight of each piece of wood of the same size can vary slightly.
  • Remember this when you select the pieces you want to buy you should keep their final use also in mind.
  • Logically one should select the lightest grades for the lightly stressed model parts (nose blocks, wingtip blocks, fill-ins, etc.) and the heavier grades for important load bearing parts of the structure (spars, fuselage stringers, etc.).
  • Balsa is a very "friendly" wood to work with - so light, so soft, so easily can work into so many shapes.
  • You don't need heavy-duty power saws and sanders for working on balsa,  like working with a hardwood.
  • The professional model builders rely simply on 4 or 5 simple hand tools for the majority of their work.
  • If you are just starting out in the model airplane hobby, here are some tools that they recommend you to get.
  • A good Hobby Knife with changeable blades for general cutting.
  • A good knife with sharp blade for carving.
  • Razor saw for cutting thick sizes of wood.
  • Razor plane for shaping.
  • A knife or razor blade will work well for cutting balsa sheets and sticks up to 3/16".
  • Always keep replacement blades on hand - blades do wear out and a dull blade can make it impossible to do a good job.
  • Good quality paper cutter is a good choice.

  • In addition to the cutting tools, you will need different size sanding blocks.
  • These are indispensable tools for model construction.
  • You can buy ready-made sanding blocks or make your own.( making our own blocks as per requirement is a better choice).
  • The most often used general-purpose sanding block can be made by simply by wrapping a sand paper sheet around a hardwood or plywood block.
  • Use some screws or glue along one edge to hold the overlapped ends of the sandpaper in place.
  • Use rough sandpaper on the block during general construction.
  • Another handy sanding block can be made by gluing sandpaper onto a 24" or 36" long piece of aluminum channel stock.
  • Most hardware stores carry a rack of aluminum in various sizes and shapes.
  • This long sanding block is very helpful for shaping leading and trailing edges, and other large pieces, accurately.
  • Then glue sandpaper onto different sizes of scrap plywood sticks and round hardwood dowels.
  • These are handy for working in tight places and for careful shaping where a big sanding block is too hard to control.

  • In selecting balsa sheets for use in your model, it is important to understand the way the grain runs through the sheet as well as the weight of the sheet.
  • The grain direction actually controls the rigidity or flexibility of a balsa sheet more than the density does.
  • For example, if the sheet is cut from the log so that the tree's annular rings run across the thickness of the sheet (A-grain, tangent cut), then the sheet will be fairly flexible edge to edge. 
  • In fact, after soaking in water some tangent cut sheets can be completely rolled into a tube shape without splitting.
  • If on the other hand the sheet is cut with the annular rings running through the thickness of the sheet (C-grain, quarter grain), the sheet will be very rigid in edge to edge and cannot be bent without splitting.
  • When the grain direction is less clearly defined (B-grain, random cut), the sheet will have most intermediate properties between A and C grain.
  • Normally, B-grain is the most common and is suitable for most jobs.
  • The point remember is that whenever you come across pure A-grain or C-grain sheets, learn where to use them to take best advantage of their special characteristics.
  • A-grain sheet balsa has long fibers that show up as long grain lines.
  • It is very flexible across the sheet and bends around curves easily, also warps easily. 
  • Sometimes called "tangent cut."
  • Use it for sheet covering rounded fuselages and wing leading edges, planking fuselages, forming tubes, strong flexible spars, HL glider fuselages.
  • DO NOT use for wings or tail surfaces, flat fuselage sides, ribs, or formers.
  • B-grain sheet balsa has some of the qualities of both type A and type C.
  • Grain lines are shorter than type A, and it feels stiffer across the sheet.
  • It is a general purpose sheet and can be used for many jobs. Sometimes called "random cut."
  • DO use for flat fuselage sides, trailing edges, wing ribs, formers, planking gradual curves, wing leading edge sheeting.
  • DO NOT use where type A or type C will do a significantly better job.
  • C-grain sheet balsa has a beautiful mottled appearance.
  • It is very stiff across the sheet and spits easily.
  • When used properly, it helps to build the lightest, strongest models.
  • Most warp resistant type. Sometimes called "quarter grain." 
  • DO use for sheet balsa wings and tails, flat fuselage sides, wing ribs, formers, trailing edges.
  • Best type for HL glider wings and tails. DON'T use for curved planking, rounded fuselages, round tubes, HL glider fuselages, or wing spars.
2. HD Form
  • Thermocol is a commercial name.
  • In 1951 the researchers of a German company named BASF successfully restructured chemical bonding of polystyrene (a synthetic petroleum product) molecules and developed a substance named stretch polystyrene.
  • This substance was named Thermocol, which nowadays is manufactured through a simple process.
  • Thermoplastic granules are expanded through application of steam and air.
  • Expanded granules become much larger in size but remain very light.
  • Thermocol is a good resister of cold and heat but since it is a petroleum product it dissolves in any solvent of petroleum.
  • Polystyrene (PS) is a synthetic aromatic polymer made from the monomer styrene.
  • Polystyrene can be solid or foamed.
  • General purpose polystyrene is clear, hard, and rather brittle.
  • It is an inexpensive resin per unit weight.
  • It is a rather poor barrier to oxygen and water vapor and has a relatively low melting point.
  • Polystyrene is one of the most widely used plastics, the scale of its production being several billion kilograms per year.
  • Polystyrene can be naturally transparent, but can be colored with colorants.
  • Uses include protective packaging (such as packing peanuts and CD and DVD cases), containers (such as "clamshells"), lids, bottles, trays, tumblers, and disposable cutlery.
  • As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about 100 °C, its glass transition temperature.
  • It becomes rigid again when cooled.
  • This temperature behavior is exploited for extrusion, and also for molding and vacuum forming, since it can be cast into molds with fine detail.
  • Polystyrene is very slow to biodegrade and is therefore a focus of controversy.
  • It is often abundant as a form of litter in the outdoor environment, particularly along shores and waterways, especially in its foam form.
  • So I do not advice you to use it extensively for your models.
  • We can make use of thrown away packing pieces for some parts of our aircraft, thus helping our environment.
3. Depron Foam
  • Depron is a closed cell  styrofoam foam in sheet form, it is a fantastic medium for building model aircraft, and also a popular medium for architectural model building, as well as model boats and prototype design.
  • Light and strong enough for light electric motor battery set ups, the secret to strengthening depron is carbon and light wood rods and strips, light weight push rods & horns are now available.
  • Depron is very good to construct ultra lightweight flying model aircraft.
  • The only limit is your imagination.
  • Developed primarily for use as thermal and sound insulation.
  • Depron is very common medium for use in the food industry.
  • Food trays are quite useful if you can find large unused ones to make light weight model parts from.
  • Depron is actually polystyrene (EPS/XPS) plastic and the (EPS) means expanded while (XPS) means extruded.
  • For our purposes, we’re only interested in the stronger, denser XPS Depron which also happens to be closed-cell foam.
  • Open or Closed cell refers to its structure and because open cell (sponge type) foam soaks up all fluids (water & glue) it’s just not suitable for a model plane.
  • The superior closed cell foam takes much less glue and is easier to waterproof.
  • Its sealed surface adds considerable strength as well as making it very easy to apply non-solvent depron friendly paint or ink finishes.
  • You don't have to worry about grain direction and splitting like with balsa wood, although depron can show a sort of grain on the surface, this is not consistent as this forms as the styrene cures in the manufacturing process, within the core of the sheet the cell formation is consistent.
  • Like balsa wood the inertia effect is quite low and at only 20 grams per square foot, it is considerably lighter than the equivalent 95g psf of balsa.
  • You can paint your depron masterpiece with foam friendly water colour paints, or non-solvent marker pens, always do a test on a scrap piece before committing to your model.
  • With depron the name of the game is experimentation, build yourself established designs, or reach out with your own designs and above all enjoy your modelling. 
  • Almost all the tools used for balsa wood can be used with depron foam.
  • Most important is that it is made out of recycled plastics.
  • By using depron sheets we can support our theme "RECYCLING" and protect trees.
4. Coroplast Sheets (Sun Board or Flute Board or PP Plate Sheet)
  • Coroplast is a brand name of corrugated plastic and a registered trademark of Coroplast, LLC, a member of the Inteplast Group of companies.
  • Because of the success of this brand, it has become a generically used tradename and many people in North America today refer to all corrugated plastic as "coroplast".
  • A similar product is marketed in Australia under the brand name Corflute.
  • Coroplast, also called pp plate sheet ("Fluted Polypropylene Sheet"), is a lightweight (hollow structure), non-toxic, waterproof, shockproof, long lifespan, corrosion preventive material.
  • Compared with cardboard, Coroplast has the advantages of waterproof, colorfast and corrosion preventive.
  • Coroplast Applications.
  • Coroplast is sturdy, light, resilient, and inexpensive, making it ideal for indoor/outdoor signage, electronics, packaging, machinery, light industry, postal services, food, pharmaceuticals, pesticides, household appliances, advertising, decoration, stationery, magneto-optical technology, bio-engineering and other medical and health industries.
  • Coroplast is widely used in advertising background, stationery materials, industrial packaging products, shock, etc.
  • The most common are crates, detachable combination boxes, product packaging boxes and boxes in the partition and so on.
  • Currently widely used international plastic materials. It is also used for some animal cages.
  • Coroplast received worldwide attention when the material was used to make an extremely light, folding kayak (Oru Folding Kayak).
  • Because of Coroplast's durability and weather resistant properties it is commonly used for outdoor advertising, billboards, and signage.
  • All these advantages of coroplast can be used for our RC model aircraft.
  • It is cheap and locally avialiable.
  • Only one drawback is the increase in model weight when comparing with other materials used in RC modelling, but a lot of money saving!!
5. EPP form
EPS or EPP: Which Foam is Best?
  • EPS - Expanded Polystyrene
  • Which foam will work best for your project depends on several factors.
  • Low cost
  • Rigid Foam (High Structural Strength)
  • Cover with Balsa Sheeting, Fiberglass or Carbon cloth, Color tape, or Low Temp coverings
  • Works well for small or large wings
  • Compatible with Epoxy or Polyurethane Glue
  • Not compatible with CA or Goop Glues
  • Can be Vacuum Bagged
EPP - Expanded Polypropylene
  • High cost
  • Impact resistant
  • Low Structural Strength
  • Reinforcement required for most wings
  • Cover with Shipping Tape or Low Temp coverings
  • Works well for small wings
  • Does not scale up well
  • Compatible with Epoxy, CA or Goop Glues
  • Not Compatible with Vacuum Bag methods
6. Aircraft grade Ply Wood
  • No matter the size of your home built or experimental aircraft, in many places we have to use plywood.
  • We requires some plywood to be used for fuselage construction, aircraft spars and aircraft wing spars.
  • Some times to make aircraft T-stringers, corner blocking, cap strips etc..
  • It is better to use special plywood to get better results, but as it is difficult to get we can do with light weight normal plywood which you will get from local shops.
7. Carbon and Glass Fiber 
Carbon-fiber-reinforced polymer
  • Carbon fiber–reinforced polymer, carbon fiber–reinforced plastic or carbon fiber–reinforced thermoplastic (CFRP, CRP, CFRTP or often simply carbon fiber, or even carbon), is an extremely strong and light fiber-reinforced plastic which contains carbon fibers. 
  • CFRPs can be expensive to produce but are commonly used wherever high strength-to-weight ratio and rigidity are required, such as aerospace, automotive and civil engineering, sports goods and an increasing number of other consumer and technical applications.
  • Specialist aircraft designer and manufacturer Scaled Composites have made extensive use of CFRP throughout their design range including the first private manned spacecraft Spaceship One.
  • CFRP is widely used in micro air vehicles (MAVs) because of its high strength to weight ratio.
  • Ultralight aircraft (see SSDR) such as the E-Go, rely heavily on CFRP in order to meet the category weight compliance requirement.
  • Carbon fiber tubes, rods and plates are widely used in RC-Aircrafts for strengthening.
  • It is a must when you are doing construction with HD Foam, Depron and EPP foam.