Science Olympiad 'Wright Stuff'
Airplane Construction Instructions
This article is intended for those who have never built an indoor rubber powered plane, are somewhat convinced that they can't, but don't realize that with a LITTLE help, THEY CAN. The overall intent is too provide enough information to construct a competitive flying model that meets the latest Science Olympiad Wright Stuff ('Propeller Propulsion') rules.
Note: The information contained herein is a compilation of modeling information from many sources, Principally, I stole most of the format and writing from the introduction to rubber flying (written by George Benson) for the Marin County California Flying Club. A copy of it can be found at Thayer Syme's excellent web site, VISIT IT!
http://www.mindspring.com/~thayer5/modelhp.htmlAdditional information was obtained from those books listed in the recommended reading section.
Where to Start?
I truly believe that if you want to build something right you need the right tools. What you may not realize is that building model airplanes does not take fancy expensive tools. In fact, the best tool is just information - the secrets to successful building - which I hope this compilation provides.
The following list provides an idea of what should be collected prior to starting. It lists the basic building supplies required, supplies required for the airplane will be listed separately later. The following paragraphs describe why the items are used and possible alternatives.
|Building Board||Ceiling Tile||Hardware Store|
|Razor Blade||Single Edge||Hardware Store|
|Number 10 Knife||Xacto type||Hobby Store|
|Pins||Dress Makers||Hobby or Sewing Store|
|Sandpaper||Fingernail file or 200 grit - one sheet||Hardware or Hobby Store|
|Glue||Duco Household cement or Ambroid modeling cement||Drug or Hardware Store|
|Wax Paper||Any type||Grocery Store|
|Poster Board||1/16th Inch thick||Hobby Store|
|Glue Stick||UHU 'purple'||Drug or Hobby Store|
TOOLS and TECHNIQUES
Building Board: A piece of Cellotex or similar wood fiber ceiling material about 12" x 24" from building suppliers makes a good board for construction. Ceiling tiles are an acceptable short term item, generally the unpainted or unfinished side is used as it is smooth. A ceiling tile can be cut in half then used by two builders. The board will support the wing while building it, it's main feature is to assure the airplane components will be built FLAT. It also allows pins to be pushed into it, which are used to hold the components in place. Bulletin boards, soft pine, thick cardboard, or any pinnable flat surface can be used as an alternate construction surface. In a pinch, thick cardboard can be used. Long term builders use luxurious laminated balsa wood building boards.
Cutting: For cutting, use single edge razor blades and/or an Xacto knife with No. 11 blades. Keep sharp and replace blades regularly. To reduce the weight of the plastic airplane propeller used in this project, an Xacto knife with a number 10 blade has proven to be the BEST technique. A plastic cutting pad is a very useful luxury (about $15 when on sale at Micro Mark, cheaper at sewing supply stores) minimizing dull blades. Most will be able to get this airplane built using a thin piece of wood or heavy cardboard to cut parts on.
Hold Down Pins: T pins are available from hobby stores and sewing stores for our building purposes. Regular straight pins work just as well. You probably will not use more than 50 pins for this entire project. These are used to position the balsa wood components prior to gluing. Do not EVER push pins through the airplane wood. Scraps of balsa will be used to clamp the balsa to the building board. Pin clamps are plastic "discs" which slide tightly on to T pins to hold down wood to the building board.
Sandpaper: This should be the most used tool, perhaps after a sharp cutting blade. A single sheet will prove more than enough for this one project. A couple of Emery boards are also adequate. If you continue to construct models, make sure to get a good selection from 100-320 grits. It lasts a long time on balsa wood, and will really make a difference in the quality of your work. Empty oval glue bottles are handy to wrap sandpaper around for shaping concave edges, e.g., wing tips.
Glues: An often debated subject. For this project only two types are recommended. Carpenters Wood Glue, either Elmer's or Titebond, are acceptable. The other choice is Duco Household cement. The wood glue requires a longer drying time, but allows for a much EASIER cleanup. I use wood glue when helping younger modelers because it can be cleaned up. 'Duco' cement is a cheap, easily found glue that is stronger than wood glue. The best reason for choosing it is that WORLD CLASS indoor flyers use Duco because it is good. 'Sigment' from Sig Manufacturing or 'Ambroid' modeling cement are acceptable substitutes but cost more than 'Duco'.
Glues should be applied sparingly. Use just enough to cover the end being glued. Any joint is only as strong as the wood. Additional glue only adds extra weight. One method is to take a piece of modeling clay about half a golf ball in size and flatten it with a depression in the center. Place a disc of waxed paper on the clay and press it down. Pour a little glue on the wax paper and apply the glue to the balsa with a toothpick. If you use any other method to apply glue on this model you will be using too much.
For gluing balsa some modelers use balsa cement, others use white P.V.A. glue and some use CyA. (Krazy Glue, Hot Stuff, Zap, etc.). CyA glues are especially heavy. CyA glues are also potentially dangerous as it instantly sticks fingers together and is hazardous around the eyes. IT is NOT recommended for juniors or the clumsy! However, if CyA is used, the odorless is preferable as, although more expensive, it does not irritate the nose and also is compatible with blue foam.
Wax Paper: Used to keep from gluing the airplane to the building board. Simply placed over the model airplane plan. Glue will not stick to it, and the airplane can be removed. Some rub soap or wax over the areas where glue joints occur, but wax paper is superior. Do not use 'Saran' type plastics as they will attach to the balsa wood when the glue dries.
Poster Board: The secret to building successful flying indoor airplanes. The poster board will be cut, to form a template, around which the airplane wing and stabilizer are built. It will also be used to create a cutting template for the wing ribs. A 24" X 18" size should be sufficient.
Glue stick: e.g., Ross Purple Stick, UHU Glue Stick, Kidstick, will be used to adhere the tissue covering to the balsa structure by rubbing the stick over the balsa. No better way exists to introduce tissue covering. Apply the tissue and smooth down with a finger. Any brand of solid glue stick is acceptable. The 'purple' type stays purple till it dries, which can be a help.
Tweezers & Pliers: Tweezers are used often for positioning bits of wood while building. Try finding a pair of "stamp" tweezers with a broad flat blade. This will help prevent crushing the soft wood.
A small selection of pliers for wire bending is necessary. Needle nose pliers are very useful, as are a good pair of round nosed pliers. These are most useful for prop hooks, and can be tough to find. A good pair of diagonal cutters will be appreciated, as music wire can be very hard. Cheap cutters will soon develop notches in the blades.
A full size plan for the suggested flyer is not required. The three view should provide an adequate amount
of information. The design is based off Cezar Banks' successful 1990 novice pennyplane design. The
aircraft was used successfully by a number of Kansas students in 1998 and 1999. A few modifications
were introduced to comply with the 2000 Science Olympiad rules. All dimensions are in centimeters (CM).
The wing and stab dimensions are prior to raising the tip panels (the overall dimensions will then match
NOTE: Change to wing dimensions, center section should be 34 cm, tips 11.3 cm long. This builds a slightly longer flying airplane. Just equally space the ribs to adjust.
What to buy;
2 - 1/16th inch square x 36" balsa sticks
1 - 1/16 x 1/8 x 36 balsa stick
1 - 3/16 x ¼ x 36 balsa stick
1 - 1/32 x 2 x 36 balsa sheet (this is more than 3 people will use - so share)
1 - 9 ½ inch Peck Polymers Plastic prop
1 - 12" length of 1/16th diameter aluminum tube
1 - 1/32 in diameter music wire
1 - sheet of Japanese Tissue or condensor paper
The first two items constitute the bulk of material required for the plane, the rest will provide enough for multiple airplanes, so if buy a couple extra balsa sticks and pieces of tissue you will be able to build many planes. This will allow you to experiment with different designs later.
Where it is used;
Wing & Stab:LE 1/16 square - this stick will be sanded to get a round nose
3/16 x 1/4 - the rear end will be cut to taper to 1/8 square end
9.5" Peck Polymers - which will be cut down to 20 cm
Prop Shaft & hook:
1/32 diameter music wire
1/16" OD aluminum tubing
Many local hobby shops carry a range of supplies suitable for our needs, including many items from the Peck catalog listed below. But, most likely all supplies (especially the tissue) will need to be ordered.
Peck Polymers, P.O. Box 710399, Santee, CA 92072-0399 (619) 448-1818.
Peck carries wood, adhesives, tissue, and a large variety of plastic propellers. They sell a "Slow Flier Designer Kit" specially tailored for Science Olympiad competition. Call for details. Catalog is $4.00, and they take phone orders and accept Amex, MasterCard, & Visa cards. This is quite possibly the best individual supplier for our needs.
E-mail: PPModels @aol.com Web site: http://www.peck-polymers.com/
Indoor Model Supply, Box 2020, Florence, Or 97439, 541-902-8508
Specializing in indoor model supplies. IMS caters to both beginner and veteran indoor fliers, and offers kits, wood, rubber, and lots of other items for this unique niche of aeromodeling. This includes their Sci Oly Wright Stuff model, updated for the new 2002 rules. IMS carries condenser paper, the lightest covering material allowed under the Science Olympiad rules. They sell a good 15:1 rubber winder, plus many non-standard widths of Tan II rubber for indoor flying. Proprietor Lew Gitlow has a new $4.95 book on the Wright Stuff event. He takes phone orders. Catalog is $2.00.
Web site: http://www.indoormodelsupply.com/
Micro-X is another vendor dealing primarily with indoor-oriented products: kits, select quality indoor wood, specialty covering materials (including condenser paper) and accessories, and many sizes of Tan II rubber strip. They carry the Midwest Sorcerer Science Olympiad kit and a new $4.95 book on the event by Lew Gitlow (see IMS). Anyone interested in indoor flying should have their $2.00 catalog.
E-mail: email@example.com No website yet!
Aerodyne and Old Time Model Supply, 17244 Darwin, Unit H, Hesperia, CA 92345, (760) 948-6634. This is the source for lightweight Japanese tissue (white only) or even better condenser paper (brown).
Web site: http://www.freeflightmodels.com/
This is the source for rubber, call to find out sizes (a 3/32 inch wide strip is a good place to start). F.A.I. carries 100+ free flight kits, including the Right Flyer from Midwest Products. This model complies with the 2001 S.O. rules. FAI is the prime supplier of Tan II rubber strip, the performance standard of the hobby, and also stocks tissue, a good 15:1 winder, and many other useful items. Their catalog is $2.00, a must for Science Olympiad competitors.
E-mail: firstname.lastname@example.org Web site: http://www.faimodelsupply.com/
These five suppliers all carry selections of indoor materials and some specialized outdoor supplies, as well as plans and kits. It is well worth sending a couple of dollars for their catalogs.
Draw and cut the wing outline on a piece of poster board. Mark the locations where ribs are to be placed. It will look something like this:
The curvature at the template top is drawn using a compass set for a 12 in radius (24 diameter circle). You can also use a piece of string tied to a pencil to draw the arc. Make two marks on the template. The marks are spaced slightly farther apart than the ends of a completed rib (A plus about 1/8 inch). This template will be used to make wing ribs (the cross pieces in the wing) and stab ribs too. Using the 1/16th sheet rib material, cut a piece as long as the marks. Both ends of this piece must be clean 90 degree cuts. Use a triangle to mark and cut straight ends. (As a weight saving measure, wing ribs can be cut from 1/32" sheet. It will save weight and that's important. It might be best done when you build your second airplane's wing.)
Use the template and a new razor blade to slice ribs of the piece that look like this:
After cutting enough wing ribs for the wing and stab, it is time to begin assembling the wing. Make sure the building board is flat, cover the top with the usual wax paper. Place the wing template on it and pin it securely in place. Using a piece of 1/8" by 1/16" balsa stick, cut a zillion little pieces about 3/16" long. These pieces will be used to hold the wing leading and trailing pieces against the wing template. A properly secured leading edge will look something like this:
With the leading and trailing edges secured to the wing template using pins in the zillion small blocks made earlier, the wing ribs can be fitted. Since the wing ribs were cut slightly larger than the wing cord (dimension A), they will need to be trimmed to get a nice snug fit. Carefully fit each rib in place (they go in the "V" shaped spots cut in the template), carefully trim or sand each end of the rib to create an exact fit. Expect to shorten all the ribs to fit. It does not matter which end is cut off. The curve in the rib is a circle, remember.
Using a toothpick, apply just enough Duco cement to cover each rib end, and place into position.
Do not glue in the wing ribs that are used in the wing joints.
I've noticed that most new modelers have trouble covering the wing after the wing (& stab) center section and the tips have been glued together. Most modelers find that covering the wing is easier if it is flat. To solve the problem, you will need to build the wing in three pieces, a center section and two tips. When assembling the center section, glue all the ribs in (out to the tip section) standing straight up. Allow the ribs to dry. When the ribs have dried remove the wing sections from the pattern. The wing sections should look like this:
The Stabilizer (the smaller wing at the rear of the airplane):
The method for constructing the stab is similar to that used on the wing. Construct a stab template using the dimensions shown on the plan. It is not necessary to allow for leading and trailing edge thickness since it is not as wide as the wing. Follow the wing directions and build it light. Note: that the stab tips are angled at 60 degrees, so glue the joint ribs at a 60 degree angle.
The fuselage is simply a balsa stick with the boom section cut away to remove weight. The fuselage serves as the anchor points for the propeller and rubber motor. The main motor stick uses a piece 3/16" X 1/4" balsa 30 cm long. The boom is formed by cutting away the lower section (tapering). The forward portion of the motor stick remains 3/16 x 14 for the first 30 cm. The boom should be cut to taper to 1/16" at the aft end. Do this by laying a straight edge over the balsa and cutting the lower portion away. Because the stab must sit at a slight angle to allow us to avoid using downthrust, a small block of balsa is glued to the motor stick such that it will tilt the rear edge of the stab up 3/8".
DO NOT GET GLUE INSIDE THE TUBE.
The rear motor hook is constructed from the same 1/32" diameter wire the propeller shaft is made from. Bend a loop into the end of a wire piece about 1 1/2 " long. Push the unbent end of the wire through the motor stick where the boom attaches. Using small pliers bend the end over so that the loop will end up about 1/4 inch below the motor stick. Bend a small right angle to attach trim to shape and glue into position. Add a small piece of scrap motor stick as a gusset to strengthen the wire installation. Your installed motor hook should look something like:
When using a solid motor stick, a small piece of wood must be glued at the end to lift the rear end of the stabilzer when it is attached. Glue a ¼ " long piece of scrap wood on the top of the motor stick at the very end.
An alternate method of fuselage construction is to use a separate stick for the rear portion of the fuselage. A 3/32" square piece of balsa can be glued such that a slight angle is formed (see Dan Benner's model plan at end of this article). This way the extra piece does not have to be used under the stabilizer. The angle should result in the rear being ¼" above the front. By slightly tapering the joint, the stick can be glued on at an angle allowing one to control the size of circular airplane flight.
The propeller for this airplane must be a commercially available plastic type. Unfortunately, you will probably not be able to find an appropriate one. By appropriate, I mean one that is light enough. The best choice is an 8 inch or 9.5 inch plastic propeller made by Peck Polymers (address listed in source section). Either propeller can be trimmed using scissors to the 20 cm size of the rules limit. It can also be scrapped down in thickness to approach a usable weight. I have scrapped down a propeller from a 5.5 gram starting weight to approximately 2 grams.
Starting with a new propeller, the first thing to do is put in a bushing for the motor wire. Since we are using 1/32 diameter wire, a 1/16th aluminum bushing is the right choice. Using a 1/16th in diameter drill, enlarge the hole through the propeller center. You should be able to drill this using your fingers, no need for an electric drill. Keep the drill in line with the existing hole (perpendicular to the blades). Cut a piece of aluminum tubing to length (just longer than the hub hole) and slide it into the propeller hub. Assure that a piece of 1/32 inch diameter wire will slide freely through the tubing.It is now time to lighten the blades. This is best accomplished using an Xacto knife equipped with a number 10 blade. The number ten blade has a curved cutting edge which allows the curved back side of the propellor to be scrapped easily. Place the blade on a protective surface (cutting mat), front side down. (The front side on a plastic propeller has a ramp arrangement on the center of the hub.) With the knife blade pressed hard against the plastic, drag it back and forth. Plastic shavings will start to appear. I have the best luck always drawing the knife towards the propeller center (like the drawing). This will take about 30 minutes to do correctly. It is time consuming AND MESSY. The shavings will stick to everything (electrostatic action) so it is best done outdoors. Stop frequently to collect and throw the shavings away. As you do this it will become more apparent what is being accomplished. Don't hurry, it just takes time. You must scrap evenly across the entire blade. Eventually, the plastic blades will start to thin. You can check on your progress by holding the blade up to a strong light, eventually the light will 'shine' through. A scale is probably the best way to judge how much plastic must be removed, a propeller that weighs half as much as what you started with is a good goal.
Use a compass (or string) to measure out 10 cm from the propellor's center and mark the blade length. At the marks, cut the propeller blades off (straight) using a pair of scissors.
Don't install the propeller until you are ready to test fly (see trimming instructions later). You need to install a couple of small rubber bands on the fuselage to hold the wing assembly on.
The propeller is attached to the motor stick using a piece of 1/32" diameter music wire as the motor shaft. One end of the shaft is first bent to hold the rubber motor. The easiest way to bend the round portion is using a round form. Use another piece of wire (larger diameter) in a vise or round needle-nose pliers. Cut a piece of wire approximately 1.5 inches in length. Bend the round rubber holding end. The shaft is then passed through the motor stick bearing tube through the propeller. A small washer or plastic bead should be used to reduce friction between the prop and fuselage. The last step is to bend the wire over at a 90 degree angle to engage the prop.
The Wing Saddle:
The wing saddle is a simple way to allow you to remove the airplane wing for transport. It also simplifies the task of balancing the airplane prior to flying. It will also serve as the mount for the landing gear since the Science Olympiad requires rise off ground takeoffs. From a piece of 1/16" thick sheet balsa cut a 1/4" wide piece 20 cm long. Pin this to the building board. Above the base arrange a 1/16" square stick so that one end is 3 1/4 inches above the base and the other end is only 3 inches above the base. Pin this piece into position. Glue two 1/16" X 1/8" sticks on top of the two pieces (it will help if you cut these pieces to length - one 3 ¼" long the other 3" long). Position the two uprights so they are exactly 12 cm apart (the same as the wing cord), for the saddle will be glued to the wing. Leave about 4 cm of base in front and behind the uprights. Allow to dry.
When dry, remove the upright assembly from the building board (Did you remember the wax paper?). Cut another piece from the 1/16" sheet making it 1/4" wide and 20 cm long. Glue it to the top edge of the base to form a "L " shape. This edge will sit on top of the fuselage.
Covering The Wing and Stab:
Use only Japanese tissue and not domestic tissue. Japanese tissue is stronger, lighter. Determine which direction the tissue grain runs by tearing a small piece of tissue. The tissue will tear easily in a straight line with the grain. Once the grain direction is determined, make an arrow on a corner of the sheet to remind you.
After cutting the tissue into pieces, wrinkle, crinkle or wad each piece up into the tightest ball that you can. Then carefully smooth each out as best you can using your fingers on a flat surface. This step breaks up the paper fibers to avoid the usual shrinkage problems. As the paper ages, it will tend to shrink. The humidity (water in the air) is absorbed by the paper. As the paper dries, it will pull tighter. This tightening will pull (wrap) your flying surfaces out of shape. They won't be straight. If you don't think you've broken all the paper fibers, roll the pieces up into a ball again and re-spread again. Each piece can be ironed (no steam!) to improve its smoothness if desired.
The next step would be to break out the UHU brand purple glue stick. The wing is covered in sections, the
center first. Give the wing center a glue coat by sliding the UHU along the wing outline sticks as shown.
Remove any of the big glue chunks away with a balsa scrap, and then lay the tissue on the frame. Work it flat by tugging and smoothing. Wait till the glue dries before applying the wing tip covers. If the glue dries on the framework, it can be reactivated with rubbing alcohol. Indeed, some Modelers will put glue on the surface and let it dry. Later, when the tissue is applied, the glue is re-activated by brushing on alcohol.
Another good way to attach tissue is to use UHU gel glue with a small paint brush. You can control the amount of glue you put on the wing a little better this way.
If you can be patient, wait overnight before trimming the excess. That said, I often trim with the glue still wet, and gum up my razor blades and sandpaper. Yup, sandpaper. A few light angled swipes with some 220 grit will cut the tissue right on the edge of the frame. Be careful, though. It is easy to sand through the tissue, and you can unknowingly reshape the wood below it. A new
single edged razor or Xacto blade will trim the tissue nicely, but there are better, and cheaper blades available. Careful dissection of a disposable razor can also yield a suitable blade, but please be careful!
An alternate covering material is condenser paper: This is a very thin paper that used to be used in making electronic components (condensers, I believe!). It is harder to work with than Japanese tissue, but is significantly lighter than Japanese tissue (also more expensive). You may want to build a model with tissue for practice then build another with condensor paper. Apply as you would the Japanese tissue BUT you do NOT wrinkle it up. It can be easily torn.
The wing and stab should be covered now, but still in six pieces.
After the wing ribs have dried, it is time to glue the wing tips on at the proper dihedral angle. Using small blocks, boxes or tin cans, support the wing tips, at a 45 degree angle, at the end of the tip. Using a toothpick to apply glue again, glue the wing tips to the main wing panel. The resulting bends in the wing provide dihedral and that promotes stability while the airplane is flying. Allow the wing to dry.
Assembling The Wing and Saddle:
The wing saddle is glued to the bottom of the wing. NOTE; the saddle is not glued in the center of the wing (see next two figures). The offset provides extra lift to counteract the torque caused by the propeller during flight. This allows you to control the airplane, forcing it to fly in circles. Prop the wing up on edge using balsa blocks and pins as shown. Use additional blocks to locate and raise the saddle so that its top edge is the same height as the wing leading edge. Glue the saddle to the wing leading and trailing edges, keeping the saddle perpendicular to the wing. Pin scrap balsa as clamps to hold the saddle in place. If in doubt use a triangle to assure the 90 degree arrangement. Allow to dry.
Note; the front edge of the wing is located higher above the motor stick than the rear edge. The front of the saddle is taller than the rear. Make sure you don't glue the wing on backwards (though it will fly that way!). After the saddle has dried, bracing sticks can be added to the front and rear wing edges to add strength to the wing saddle joint. Cut 4 1/16th sticks about 1 and a half inches long. Bevel each end at 45 degrees. With the wing still supported, add the braces to each side of the saddle, on the front and back.
HINTS on Materials and Techniques
Light weight is Important! The importance of building light cannot be overstated. This is the key to improved flight times, as a 10% weight reduction results in a 15% improvement in flight times. Additionally, because the plane flies slower, it will be damaged less on impacts. The main factors which influences weight are balsa weight and tissue weight.
Balsa Wood: Long the traditional material for building models, balsa wood is a huge topic that can only be touched upon here. Take a moment to look at the rack of balsa while first browsing your local hobby shop. Selecting wood can be a real science, but for now, notice that some sheets of wood seem much lighter in color, and weight, than others. Hold a few sheets of 1/32" or 1/16" up to a light, and notice the different grain and color banding that can occur. All of these variations help indicate weight and strength. They will become more meaningful as you build models. Balsa can vary in weight from under 4 lbs. per cu. ft. to over 20 lbs., a variation of 5:1. Obviously if weight is important, and it is, care must be made to choose wood that is strong enough for the job, but not too heavy. If you want, buy a couple of sheets of 1/32", 1/16" and 1/8" balsa. Try to choose ones that are in between the extremes of weight available. It isn't critical for now, but a little care will help.
Balsa selection: Balsa can vary in weight from 4 lb per cu. ft. to as high as 22 lb per cu. ft., a variation of over 5:1, so seek out lightweight sticks and sheets using a pocket postal scale to compare stick and sheet weights.
Tissue: Use only Japanese tissue and not domestic tissue. Japanese tissue is stronger and lighter. Trim tissue after covering with a new sharp razor blade. Careful dissection of a disposable razor can also yield a suitable blade, but please be careful!
When tissuing the model, apply in pieces, and run the tissue grain direction in the long dimension of wings, fuselage, stabilizer. Japanese tissue tears more readily in the grain direction so it is easy to establish grain direction.
Music Wire: For our purposes, a piece of 1/32" (.031") wire is required. The .031" diameter wire is used for the propeller shaft and motor hook. Each increase in wire size doubles the wire weight, so be sure you need the larger size as you build.Aluminum Tubing: Tubing is available in 12" lengths. Use 1/16" OD for holding the propeller shaft, which is 1/32 inch diameter music wire.
Rubber and WindingRubber: F.A.I. Tan II is the most popular rubber, and available in widths of 1/16", 3/32", 1/8" and 1/4". The Science Olympiad Flyer will use 1/16" to 1/8" wide rubber depending on the flying site. I have found that 3/32" wide strip is just about perfect. Determination of the "best" rubber size is an acquired skill but more experienced modelers or the books listed later can provide guidance.
Rubber is supplied in long strips. A portion of which is used to rubber loops for powering model airplanes. For the Science Olympiad contest the rubber will be around 3/32" wide. Rubber of other widths will work. Smaller size rubber will provide less power but provide longer flights because it allows more turns to be put into it. Your first loop of rubber should be about 10" long and 1/8" wide. Rubber is purchased in long strips. It must be tied to form a loop.
All sizes of rubber can be tied using the methods shown in the figures below. Tie an overhand knot first then tie a square knot pulled up tight against the overhand knot. Be very careful that the second knot is a square knot and NOT a granny knot as the granny knot will not hold. The rubber should be WET when tying the knots. Placing the strands in your mouth and wetting the rubber with saliva works fine. After pulling the knots tight, trim off the rubber ends to no longer than ¼" of shorter than the width of the rubber.
Getting rubber in sizes other than 1/16 ", 3/32 " and 1/8" requires a rubber stripper. These devices allow larger rubber widths to be cut into exceedingly smaller widths. Rubber strippers are available ($150+) to strip 1/4" rubber into any width. These are certainly a "luxury tool which can well wait until the modeling bug really bites. Many experienced modelers have them and can be quite generous with their use at a flying session. Keep an eye on the Gizmo Geezer's website (http://www.gizmogeezer.com/free.htm), as they are developing a low cost rubber stripper.
Lubricating the motor allows a much larger number of turns to be applied before failure. The motor will also unwind more easily, as the strands can easily slide against each other. Both of these factors will increase duration, and altitude of a flying model.
Rubber lubrication is important. Use Armor All or Son-of-a-Gun vinyl restorer. Tie the rubber knot before lubricating. A common way to lube a motor, is to put some of the lube in a plastic sandwich bag. The bag helps keep the lube off your hands. Smear it around a bit, then add the motor. Rub this all around in your hands and then remove and install the motor. You're ready to go! Needless to say, a bit of experimentation will quickly reveal the benefits of winding a well lubed motor.
Stretching the motor while winding will also increase the number of turns it will safely accept. Most modelers will stretch a motor to 2 or more times its relaxed length while winding. After about half of the total turns are wound, the modeler slowly walks towards the model while finishing winding. How is the model held? Either line up a friend to hold it for you, or use a mechanical device called a stooge that holds the rubber band while winding. It is then transferred to the airplane. To aid the transfer, adding two little o-rings to the motor before tying it provides hooks.
Winding Stooge: When winding, it is customary to use a holder or "stooge" to hold the fuselage securely. This allows stretch winding without assistance, and will increase flight times dramatically. This can be as simple as a nail in a board, which is C-clamped to the edge of a table.
Winders: To wind the rubber, mechanical winders with ratios of 5 to 1, 10 to 1, or 15 to 1 are readily available. Prices go up from about $10 with expensive ones incorporating a torque meter to provide an indication of the "power" of the rubber when winding. Counters are frequently incorporated into a winder.
A hand drill can be used to make a winder though the ratio is rather low for small rubber. If you decide to go this route, securely fit a hook by removing the chuck and drilling through the side of the shaft. A wire hook can be fixed in this hole and will not pull free while winding.
Experienced help will save a lot of frustration. A comprehensive 10 step flying and trimming guide is presented below. Study it!! This is a topic that gets beaten to death and I'm sure that the method presented here will open up a flood of comments. It can be used for any type of model from No-Cal to Jumbo Scale. The important thing to remember is not to skip any steps and to follow them carefully and patiently. Do not go onto the next step until you have met the requirements of that step. THERE ARE NO SHORTCUTS BUT THIS METHOD DOES WORK!
There are two concerns with trimming that must be satisfied; Center of Gravity location (CG) and thrustline. The CG of the model must be located at the right location to provide stable flight and provide maximum aerodynamic efficiency. A CG that's too far forward spells loss of aerodynamic efficiency. A CG that's too far back spells stability problems. The thrustline determines how the model is pulled (or pushed) through the air. Many modelers try to juggle each of these two problems at the same time causing unnecessary trimming confusion. The trimming procedure presented separates the two variables and treats them individually. You first get the most efficient "glider" you can with compromises allowed for free flight stability then power the "glider" and adjust the thrust line.
We will assume that your model has been built straight and true. Take the time to check this. I won't go into details on how to do this but make sure you have no warps. This method of trimming also assumes the model has the right amount of dihedral and that all flying surfaces are adequate size but does have some leeway to compensate for this since it checks stability. Your model will also need a way to adjust stab incidence (on this model that's the size of the block under the rear of the stab.) Here are the steps for trimming. Each will be discussed in the text that follows.
NO NONSENSE TRIMMING
1. Locate the Center of Gravity (CG).
2. Balance model W/O prop and motor to located a CG.
3. Glide model.
4. Adjust stab for smooth glide.
5. Check stability by launching into slight dive and slight climb.
6. Readjust CG for stability if necessary.
7. Mark location of new CG (if changed in step 6).
8. Install prop/motor and rebalance to established CG.
9. Test fly under power.
10. Adjust flight pattern with thrust line.
1. Locate CG
Assemble the model using two little rubber bands to hold the wing approximately as shown in the three view. The wing saddle allows you to move the wing along the fuselage to fine tune balance without adding extra weight. With out the prop some weight will be needed (not much). The model built here balances with the center of gravity about 1/4 inch ahead of the rear wing edge.
What?! Without the prop? You gotta be kidding! Nope. Leave the prop off! Have you ever seen people trying to test glide a ship the prop on? One toss goes into a stall, one toss goes into a dive, next toss looks OK. The problem is that it's difficult to get a free wheeler up to a consistent speed that would be similar to when the model is flying at a consistent glide speed. One toss may not have enough RPM and will provide additional drag and stall the model. Another toss might have too much RPMs which means the ship is being launched at too great a speed to give realistic, usable results. The model will be much easier to test glide without the prop. Oh, I hear you theorists out there, the spinning freewheeling prop contributes to drag so will effect the glide. Waa, waa, waa. DON'T WORRY ABOUT IT! Glide the ship at best L/D and when the prop is added it will bring the ship into the best sink rate portion of the polar curve! (that was for all you theorists, the rest of you who just want to get your models to fly just ignore it). So leave the prop off for now so we can establish CG/decalage. Remember? One thing at a time!
3. Glide model
Of course this is the easy part. Now you have a glider, so glide it! Launch (with this model, a launch is just a flip of the wrist!!) the model smoothly towards an imaginary spot somewhere out in front of you on the floor. If you're working on a small, light model such as this, it can be done right in your living room (if your mother will allow it...and you don't hit the dog). The trick is to launch the model at it's glide speed. Do it a number of times to get the hang of it and to get some usable information on the gliding flight characteristics. If the model is turning then you have a warp! A slight amount of turn is OK but hard turns must be tracked back to a warp and eliminated.
At this point the glide is adjusted using only the stab. DO NOT CHANGE THE CG BY ADDING OR REMOVING CLAY! The most efficient method for stab adjustment is to re-glue the stab with positive or negative incidence. Cement-type glues work great for this since the joint can be unglued with solvent and re-glued. Adjustable elevators can be used but produce more drag and risk being bumped out of adjustment. Take your time to obtain a smooth but not to floaty glide (best L/D not best sink rate theorists)
5. Check stability by launching into a slight dive and slight climb
6. Readjust CG location for stability if necessary
For a model that seems to stay in a dive add nose weight and negative stab incidence (leading edge lower). For a model that acts like a falling leaf or is overly stable (pulls out hard from a dive) remove nose weight and add positive stab incidence (leading edge higher). Continue gliding and adjusting until satisfactory results are obtained. Avoid TOO MUCH stability.
7. Mark location of new CG (if changed in step 6)
Easy enough. This is your permanent CG for your model! From this point on you will not change this!
8. Install prop/motor and rebalance to established CG
9. Test fly under power
10. Adjust flight pattern with thrust line
Adjust powered flight through the following adjustments:
stalling - add down thrust
diving - add up thrust
excessive right turn* - try small amounts of left thrust otherwise go back to step 3 and glide to adjust for left turn
excessive left turn* - try right thrust otherwise go back to step 3 and glide model for right turn
*these may also require modification of model fin area.
Phew! So there you have it. Please give this a try with your next model or it you have one of those pesky models that just doesn't seem to want to fly take it back to Step One. THIS DOES WORK and really is a simple method for successful trimming. I don't consider it a cure-all but you'll be pleasantly surprised at the results.
What is a torque meter and how is it used to help indoor model builders? A torque meter is a device to measure torque (power) in a rubber motor at any number of turns. It assists the modeler in improving duration and/or altitude of a model plane. With most ceiling heights of available flying sites between 20 to 60 feet high, you must control your model from climbing too fast and too high. A torque meter is a winding stooge with a hook attached to a short piece of music wire with a numbered gauge and a needle attached to a winding hook. As you put winds into your rubber motor, you read the increasing torque.
The use of the torque meter is simple. As an example, lets take a loop of rubber motor for your model. Assuming your model is adjusted, put 1000 turns in your motor, and carefully observe the torque meter reading. Say your torque meter reading for 1000 turns was 2.5. Record the data such as the rubber size, the torque meter reading, and the number of turns on your flight chart (see chart, which follows the torque meter drawing). Fly the model and record the time. Let's say your model climbed half-way to the ceiling (or your desired safe altitude) and landed with a time of 1 minute. The rubber had 500 turns left. Try another fIight of 1200 turns and a torque meter reading of 3.0. If the time did not increase, and your climb was slightly higher than the first fIight, record the data on your fIight chart and determine what to do next. I would suggest to either increase the size of your motor or reduce the length of your original motor.
Here is where your torque meter is worth its' cost. When you wind again, put in 1000 turns. You will notice the torque meter will be over the 2.5 that you recorded on the first flight if you changed only the rubber. You should unwind until the torque meter reads 2.5. This will enable the model to again climb to the same height, but the model will fly longer and land with fewer turns. Again record all this data on your flight chart and then analyze your results. After a few flights you can determine the amount of turns, the torque meter reading you need for best results, and also develop a good concept regarding the potential of your modeI in any flying site.
It is important to remember two facts;
1--Whenever you change the prop diameter and/or pitch, you must start over with your testing
2--As you buy or cut rubber you wiII find variances in turns and torque meter readings with each
motor of the same size.
It is also important to remember that you must give your motor a chance to rest after each flight.
Flying Site Etiquette
Do not talk to a flier who is winding a motor!!! To see a motor blow (BREAK) as a result of losing count is not a pretty sight.
After launching indoors, immediately step off to the side of the floor so as not to impede planes or fliers waiting to launch.
If in doubt, or seeking guidance on building or flying, please ask for advice. Modelers enjoy our hobby and are eager to help, so don't be shy. Remember, there are no stupid questions, only stupid answers!!
"Rubber Powered Model Aeroplanes" by Don Ross. About $25. A good overall guide to building and flying a wide range of models. Don has also published a follow-up volume, "Flying Models, Rubber, CO2, Electric & Micro Radio Control". This is also highly recommended.
"Hey Kid Ya Wanna Build A Model Aeroplane?" by Bill Warner. A detailed guide to building, trimming and flying two simple rubber powered models available as kits. Two other books follow in the series and cover the Sky Bunny and Flying Aces Moth. While now out of print, they are often seen in local libraries.
"Indoor Scale Model Flying" by Fred Hall is a concise guide to many areas of concern, i.e., model selection, construction, propellers, rubber choice and trimming. About $20.
"Building and Flying Indoor Model Aeroplanes" by Ron Williams is an excellent book, though now long out of print. It is mentioned here in case your local library has a copy. It is well worth reading, despite being dedicated to lightweight duration models.
"Indoor Flying Models" by Lew Gitlow is a worthy substitute for the Williams book above. Contact Indoor Model Supplies or Hannan's Runway . About $20.
These, and other books are available from Hannan's Runway, P.O. Box 210, Magalia, CA 95954. Their telephone number is (916)-873-6421. They also have a web site (http://www.hrunway.com/) with secure online ordering. Bill Hannan has authored a series of excellent books emphasizing "Peanut" class 13" span scale models.
Plans and Kits
When you visit your local hobby shop, you might find many kits for scale models. Generally these are not recommended when starting model flying. More simple models are suggested for getting your start, including designs like the Jetco ROG, and Dick Baxter's Pussycat and his low wing Akro. All three of these are available as free online plans.
A good start is the very simple precut model such as the Sleek Streak sheet balsa model available in hobby shops, toy stores and larger drug stores. This provides a good way to learn the rudiments of trimming to control turning and climbing and the effects of changes in rubber size. Surprising performance can be had with these simple models.
Selection of your first scale model design is very important to avoid discouragement as many full size planes make very poor flying scale models. As a general guide, select a high wing monoplane with a long nose (for better balance) and a minimum of struts and complex landing gear. Planes such as the Nesmith Cougar, Lacey, Fike or early Cessnas can be built from plans or kits.
There are many resources of online information for Free Flight modelers. Surf some of the sites of the Free Flight web ring. Many of them contain Event and Contest information.
Locally, check in at the neighborhood hobby shop, and ask for Free Flight contacts. As Free Flight modeling doesn't have the economic visibility or momentum of radio control, they might not be able to help, but don't be discouraged. There are likely modelers in your area that can help. If not, fall back on Internet resources for help.
A couple of additional model Science Olympiad eligible and simple Pennyplane designs are attached to the end of this article. Some of these airplanes will require you to change the sizes to meet the requirements of the Science Olympiad Competition. But, they could give you some ideas if you want to design your own airplane. Reading through this article should give you a good idea on how to build them.
The information contained in this article is in no way attributable to me alone. It, like my own modeling knowledge, is a compilation of modeling information from many sources, notably those books listed in the recommended reading section. Principally, I stole most of the format and writing from the introduction to rubber flying (written by George Benson) for the Marin County California Flying Club. A copy of it can be found at Thayer Syme's excellent web site, VISIT IT! Thayer's very active site is full of ever-growing amounts of information, tips, plans, and model photos. There's Science Olympiad information too, including model plans and a national listing of volunteer mentors. This site is highly recommended, and has links to many other useful free flight sites.
I've had fun teaching others to fly in this event, I just intended to compile enough information here to allow you to construct a flyable model, I hope I've succeeded!