The first airplane you build is usually the hardest. Experience, and advanced construction techniques actually make more advanced planes easier to build. In this chapter, we will look at what it takes to assemble all of the parts into a working sailplane. The assumption is that you have purchased a traditional wood kit, like the Gentle Lady . If you have purchased an almost-ready- to fly kit, you need only read the sections on covering (if appropriate), final assembly and radio installation.
First, you need to find a suitable area to work. Ideally, you would like a separate room, well ventilated and heated, with plenty of flat workspace, with a variety of power tools and high tech equipment available. In practice, most airplanes are built in the garage or the basement with little more than a bottle of glue and a No 11 X-acto knife. Still, whatever work area you can negotiate from your wife and kids will become your castle for a few weeks, so nurture it and treat it with respect.
Select a location that is out of the way, so the kids, dog and cat won't be walking over your newly constructed wing panel. You want a location where the parts can lay out for several weeks without being destroyed. Try to find an area that is well ventilated. You will be using plenty of glue and possibly some paint, and you don't want to fail a drug test at work because you inhaled too many fumes. No one will believe you were building model sailplanes at the time. Good lighting is important, since you will be trying to align small parts without gluing your fingers together.
A good solid flat work surface, at least four feet long and two feet wide is a must. Sailplane parts are constructed directly over the plans and pinned in place, so you need to have a flat, smooth work surface where parts can dry overnight. An inexpensive solution is to purchase 1/2 sheet of high quality plywood, and lay this over your existing work bench or a table. Choose a piece that is flat, and try to level and support it on your bench the best that you can. If your building board is warped, your wings will also be warped, and your plane will have many undesirable flight characteristics.
Minimal Building Tools
Additional items that are nice to have:
Safety is a prime consideration when using any glues or paints. Most of the glues used in model construction are toxic, and many have toxic fumes. In addition, prolonged exposure to epoxy and other paints and glues has been demonstrated to cause cancer in laboratory animals. The best insurance is to buy a box of throw-away rubber gloves, a mask, and wear long sleeves when working with these hazardous materials. In addition, always work in a well-ventilated area and a clean workbench. Many spills and large area exposures occur accidentally when you are trying to do too many things at one time. Focus on one thing at a time, and try to avoid direct contact with glues and their fumes.
Tip 10: Always work in a well-ventilated area when gluing or painting.
I rarely buy more than a 1oz bottle of CA because it usually either goes bad or the tip gets clogged before I finish larger bottles. The first problem can be mitigated somewhat by storing your CA in the refrigerator. Cold temperature slows down the curing process, so your CA will remain useful longer. The second problem is a tough one. Always try to clear the tip of the bottle after using even a little bit of CA by wiping the excess off it and giving it a squeeze to make sure you don't have drops of CA stuck in the tip. You can also purchase extra CA bottle tips from your hobby store if you have a bottle with a hopelessly jammed tip.
Tip 11: Store your Cyanoacrylate glue in the refrigerator when not in use - this will significantly increase the useful lifetime of the glue.
Medium grade CA, also called "gap-filling", with a 5-15 second bonding time is the grade I use for the bulk of model building. Like many things in modeling, glues are a matter of personal choice. I know many pilots who prefer thin CA over the medium grade. Medium grade CA is thicker than the super-glue most people are familiar with, allowing it to fill wood grain to form a very strong joint. It generally takes at 15-45 seconds for medium grade CA to fully set, which gives you sufficient time to apply the glue, and properly position the pieces being glued. In addition, medium glue can be added to the edge of a joint to fill gaps, making the joint substantially stronger. Use medium grade CA for virtually all of your conventional wood building, including built-up structures such as the tail, most of the wings, and most of the fuselage. Only on places where you need exceptional strength, such as the wing joiners, wing mounts, or motor mounts should you switch to a heavier, stronger glue such as Epoxy.
Thin grade CA is used for special applications. Since thin CA very quickly soaks into wood and dries in place almost instantly, it does not do a great job of filling the grain or gaps in the wood. Use thin CA primarily to saturate or strengthen a joint already made, or possibly to bond two pieces best bonded by a penetrating glue. As a good example, wing joiner boxes are often wrapped with thread (kevlar thread is best). After tightly wrapping the thread, a coating of thin CA over the thread and joiner box will create a very strong wing joiner. For this application, the penetrating thin CA is ideal since it will soak into both the wood and the thread. Thin CA can also be used to strengthen fragile parts. For example, coating the trailing edge of a wing or stabilizer with some thin CA will reduce the risk of bumping and cracking the edge, since the thin CA will penetrate the wood and harden it.
Tip 12: Acrylate based nail polish remover will remove CA glue from your hands and tools.
Thick CA is used primarily to fill very large gaps in joints. I personally don't use thick CA. If I have two parts that fit together so poorly that they need thick CA, then I will simply sand and rework the joint until it does fit properly, and then use medium CA on it. Poor joints can't be fixed by adding glue. A tight fitting joint will always produce a stronger, lighter structure than a poor joint filled with glue. Similarly I don't use CA to fill gouges and holes, but rather have a can of balsa filler for this purpose.
A cautionary note on CA: CA will bond skin instantly . CA was originally developed for surgical purposes to close cuts in the skin quickly. It does this very well, whether there is a cut or not. It's not uncommon to get it on your hands and even glue your hands to your model since CA penetrates small gaps in wood rapidly. Even worse, once it's on your hands, it can end up anywhere -- including your clothes, glasses, eyes, hair, dog, other models, and children. In addition to wearing gloves, you need to have some paper towels and CA solvent handy whenever you work with CA so you can wipe the excess off of your hands and models before it ends up somewhere else.
Tip 13: Vinegar will remove epoxy resin from your hands and tools.
On beginner sailplanes, epoxy should be used whenever major parts of the airplane are joined together. This includes joining wing panels together, bonding wing joiner boxes, attaching wing mounts to the fuselage, and attaching the tail to the fuselage. Using epoxy instead of CA for these applications will significantly increase the strength of these joints. Slow cure epoxy is the primary glue for bonding wood skins to foam wing and stabilizer cores, and adding carbon-fiber reinforcement on more advanced sailplanes. Epoxy is also used to add fiberglass reinforcement to wing panel joints and the fuselage.
I primarily use five minute epoxy, and very strong, slow cure 2-hour or more epoxy. The five minute epoxy is useful when I'm building and want to add just a little more strength to a part. I can mix it up quickly and have enough time to get a moderately complex part in place before it will cure. Since the five minute epoxy cures fast, it is easy to use without disrupting the work currently being done. Five minute epoxy is also very useful for field repairs, since you can mix some up, press the parts together and be flying a short time later. If you need to join a major break, such as a cracked fuselage in the field quickly, you can reinforce the joint with some fiberglass cloth and five minute epoxy for an incredibly strong field fix.
Very slow cure epoxy is used for sheeting foam cores, joining wing panels, applying fiberglass reinforcement, wing joiners, and other applications where extra strength and working time is required. Two hour or more working time is generally the standard, as this epoxy will be several times stronger than five minute epoxy and allows for plenty of time to lay up wing joints or sheeting.
Special low-viscosity epoxy is also available from hobby specialty shops for foam core sheeting. This type of epoxy can be useful, but must often be thickened with micro-balloons or another filler since it is simply too thin to strongly bond foam core skins. Use of low-viscosity epoxy and epoxy fillers is primarily an advanced building technique to create very low weight joints, and not for the beginner.
Since many types of CA are corrosive to foam, and epoxy is relatively heavy, many people use carpenter's glue as to bond edging pieces to the foam wing core. Some people also use thinned carpenter's glue to bond wing sheeting to foam cores, but I do not endorse this practice. Sheeting wings with carpenter's glue is not nearly as strong as epoxy, and can lead to delamination and failure of the wing. I use carpenter's glue primarily to attach non-structural elements like the leading edge, wing tips, and aileron and flap trip strips to wing foam cores.
The basic construction method is the same for all built-up sailplanes. Each major part is built directly over the plans, and shaped after the glue dries. The following outlines the basic procedure for any built-up structure. Typically the spars, leading and trailing edges are cut and pinned first, followed by the ribs and inner structural members.
Tip 14: Always cut pieces of wood 1/16" oversize and sand to an exact fit. Tight joints will result in a much stronger, lighter airplane.
Here's a few tips that apply to any building project.
The rudder, fin, stabilizer, and elevator are built directly over the plans using stick balsa approximately 3/8" thick (sizes vary depending on the plane). Typical construction is a sturdy outline made of heavier balsa, with and internal trusswork of triangles using lighter balsa.
Carefully pin both the plans to your building board, making sure there are no bumps or debris under the plans. Pin wax paper over the rudder and fin plans, again being careful the plans remain flat and free of debris. Next, select the appropriate pieces from your kit from which to cut the outline of the fin and rudder. In some cases, you may also need one or two die cut pieces to form the base and tip of the rudder and fin. Sand the edge of any die cur pieces to assure a square edge. Measure any stick balsa before cutting it to make sure you have the correct pieces. Using the wrong size balsa early in construction can lead to shortages later.
Tip 15: If building the fin and rudder simultaneously, be careful to avoid gluing the fin and rudder together.
Cut the outline pieces of the fin and rudder approximately 1/16" oversize. Use either your razor saw or your x-acto knife, and attempt to make each cut as close to square as you possibly can. When using a razor saw, a small miter box can help to make square cuts. Sand each piece to size using your sanding block and medium to fine sanding paper. Check fit each piece periodically while sanding to assure the correct angle and a tight fit. This is more time consuming than simply filling bad joints with glue, but will result in a stronger lighter tail. Tight joints on the outline are very important, since these form the strength for the entire fin and rudder structures. Once you have achieved a tight fit for the entire outline and it matches the plans, carefully glue and pin each piece in place over the plans, being sure to tightly pin pieces flat on the board. If you do not tightly pin each piece flat on the board, you will have misaligned joints which will create bumps in the finished tail.
After completing the outline pieces, select and cut the inner trusswork. Again, cut each piece slightly oversize at the appropriate angle, then sand each to fit precisely. When creating a triangular truss, try to tightly fit each cross piece both in the outline, and against adjoining trusses. Any pieces that are cut too short or fit poorly should be replaced. If necessary, you can obtain additional balsa stick from your local hobby shop to replace miscut pieces. Once you have a tight fitting trusswork, glue each piece into place with thick CA glue. Unless you are using slow dry glues, it is usually not necessary to pin the inner pieces in place.
Wait a few hours for the glue to completely set, and remove the completed rudder and fin structures from the wax paper. Some wax paper will often stick to the balsa, particularly at the glue joints. Lift the structure slowly to separate the wax paper from the wood. Any excess wax or glue can be easily removed by sanding both sides so they are flat. Give the entire structure a quick pass with medium grit sandpaper to remove any large glue bumps or imperfections. It is important that the tail surfaces be free of warps or asymmetries. Carefully inspect both the rudder and fin to be sure both are straight. Replace any warped or misaligned parts before proceeding. A plane with a warped tail will not fly well. Parts to build a new rudder and fin from scratch will only cost a few dollars from the local shop if you find you've made a serious error. Just measure the sheet and stick pieces needed and purchase them from your local shop.
The elevator and stabilizer are built using the same method as the rudder and fin. Place wax paper over the plans, carefully cut and glue the outline, and then fill in the trusswork. Many beginner planes use a single solid piece of wood for the elevator, rather than a built up structure. When the elevator and stabilizer are complete, sand them flat and check for warps and misaligned pieces. Replace any parts to obtain a flat stabilizer and elevator before proceeding.
Assuming you now have a flat, warp free tailpieces, you can now shape the edges of each surface. The proper shapes for the rudder and elevator assemblies are shown in figure 3. The leading edge of the fin and horizontal stabilizer are rounded, and the trailing edge of the fin and horizontal stabilizer are left square. The leading edge of the rudder and elevators are sharply beveled to allow these control surfaces to move properly. The trailing edge of the rudder and elevator are tapered to a thin edge. The tips of all surfaces are also generally tapered.
The best method for trimming the edges of all surfaces is to start by marking with a pencil or pen the center of each edge. These marks can be used while sanding to assure that each side is rounded or tapered equally. Next, use your razor plane to rough cut each of the edges, being careful not to cut past the centerline on any edge. For the round leading edges, hold the plane at a 45 degree angle. For the tapered edges, make a more shallow cut. After roughing, finish using a sanding block. I find it easiest to place each piece flat at the edge of my building board when sanding, since this produces a more even edge. Don't attempt to hold the pieces in your hand while sanding edges, because the edge will flex as you sand it, creating an uneven edge. Try to make each edge as symmetric as possible, and be patient when sanding. It takes a lot of time and patience to properly taper and sand each edge to perfection, but the proper shape will improve the performance and controllability of your sailplane.
If you are using traditional slotted hinges for the rudder and elevator, it is a good idea to cut the slots at this time. Carefully mark the location of the hinges on both sides of the control surface, so that the hinges will align each surface properly. Cut a slot near your marks as close to the center of the surface edge as possible. If you make a mistake and split the edge, consider moving the hinge to another location and sealing the damaged area completely. Do not actually glue the hinges in place until you have covered the plane. You might want to consider using iron-on cloth hinges rather than traditional slot hinges. The iron-on hinges come in a strip that you literally apply with a covering iron before covering the control surfaces. The main advantage of an iron-on hinge is that it seals the gap between the control surfaces completely, which will improve the efficiency of the surfaces, and reduce control surface flutter at high speed. I believe iron-on hinges also provide a more secure hinge with less control surface play.
Once you have the final edge on all of the parts, carefully give each piece a final sanding with very fine sandpaper to achieve a nice smooth finish. This final sanding will produce a smooth finish once you cover the tail. Set the parts in a safe place away from your building board so they are not damaged accidentally while you complete the remainder of your plane.
Tip 16: As you complete each part, place them in a safe location away from your building board to avoid damage.
On most beginner planes, you have one or more options to choose when constructing the wing. First, you often have a choice of building a single piece wing or the wing in multiple pieces. A single piece wing is stronger, but also hard to transport. If you have a small car, you may not be able to put a 2 meter wing into the car. Even with a large car, your 2 meter wing will be more likely to be damaged in transport. I personally prefer either a two or three piece wing, since it will easily fit into the trunk and is less likely to be damaged in transport. You can lay the whole plane in the trunk or on the back seat.
Build a spoiler option in your wings if it is available. Even if you don't have the extra servo or inclination to install the spoilers at this time, you should at least cut out the spoiler bays and install any cable tubes in the wings when you build them. As you get more experienced with your plane, you will want to have spoilers on it for precision landings and getting you out of killer thermals. If you have a kit like the Gentle Lady which doesn't have a spoiler option, try to get someone from your local club to show you how to add them. It will only cost you a few dollars and a few minutes extra time, but you will be happy that you did it in the long run.
The following are the general steps for building conventional built-up wings:
Tip 17: It's a good idea to wrap your wing joiner boxes tightly with strong thread, and then soak the thread with thin CA. This will significantly increase the strength of the wing joints.
If you built your tail surfaces first, you should have no problem with the steps outlined above. Focus on obtaining a tight fit between pieces with no gaps, for a strong wing. Strength is more important than weight on a beginner plane, so don't be afraid to beef-up any weak joints with small balsa triangles (gussets) to assure a strong bond. Lay the finished wings aside in a safe place where they won't be broken.
Tip 18: Use a square, yardstick and the plans to make sure your fuselage is straight and square during every step of the construction process.
Always follow the instructions provided with your kit. Construction of a wooden fuselage generally proceeds along the following steps:
Tip 19: Buy or borrow a modeling iron to apply covering. Don't use a clothes iron!
There are two major types of covering -- low-temperature and normal. Low temperature coverings are used over foam and foam-core wings. They adhere and shrink at lower temperatures, so the foam does not melt. Ultracote is a good general low-temperature covering, and Monokote is the most popular high-temperature covering. Both are available at around $11 to $16 per six foot roll, and it will take two rolls to cover a 2-meter trainer. You might want to order an extra roll for repairs and inevitable mistakes. Again, an experienced builder can save you money and wasted covering by showing you how to cover your plane.
The selection colors is important for visibility, and visibility really matters when the plane is a mile or more away in a gray sky. It is hard to imagine that a 6-10 foot wingspan plane can get far enough away to lose sight of, but it does. It's happened personally to me on two occasions, and I've had many more close encounters. The problem is one of contrast. While a dark plane may do great against a light blue sky, the same plane will completely fade on a dark gray day. Similarly a white or day-glow yellow plane might look great on a dark day, and completely fade in a sunny blue sky. If you mix too many colors on a wing, things actually get worse, since you can usually see only one of the colors well, and that color may be only a fraction of the wing area. The most common compromise today is to use a dark color on the bottom of the plane, and light color on the top, with the fuselage dark. Since you will most likely be circling in a thermal when you lose sight, both the light and dark color will be exposed as the planes turn.
Tip 20: The best color scheme is lighter colors on the top and darker colors on the bottom of the plane.
Which colors work best? I personally like dark red and white, with red on the bottom/fuselage and white on the top. Other good bottom colors include dark blue, transparent blue or red, and very dark green. I personally don't like black - it's a little too dark to contrast well in dark skies. Other colors for the top are yellow and light orange. Stay away from excessive use of light and florescent colors because they tend to fade badly on sunny days. If you are going to cover the whole plane in one color, choose a dark color. Dark colors will do OK on cloudy days, but light ones are lousy on sunny days. If you use a two color scheme, always put the darker color on the bottom.
For added visibility, I put a six-inch contrast stripe, swapping top and bottom colors, diagonally on one wing. This helps a bit with orientation in close-in maneuvers, though it tends to fade out at long distance. Other good schemes include reversing colors on the wings, and placing high contrast stripes in patterns on the wing. Avoid placing really light colors on the leading edge because the plane will disappear when you are trying to fly it towards you from great distances. I had an Aquila with the classic white swish across the leading edge, and it became virtually invisible when I tried to pull it back from any distance.
The process can be summarized as follows:
Here are some general tips and problems to watch out for:
The process above may sound simple, but it is a difficult skill to master. The first plane you cover need not be perfect, especially since you will likely be repairing it soon. Try to avoid large wrinkles and do the best you can. As you gain in experience, covering planes will become much easier.
The four basic steps are:
Slit the covering in your hinge locations, and test-fit your hinges before gluing. It is critical to minimize the gap in the hinge. A properly installed hinge will leave only a 1/16"-1/32" gap between the surfaces. If you have too large of a gap, the control surface will tend to flutter at high speed, which can be disastrous. You may need to cut away some balsa and covering to seat the hinge.
Next, check the movement in the hinge. Make sure that the surface can move at least 30 degrees in both directions without binding. Once you have everything perfect, carefully glue the hinges in place. Be extremely careful to keep glue out of the hinge itself, or your control surfaces will not move at all. Place glue on the flange only, far away from the hinge. I recommend using slow drying glue for hinges -- this will give you extra time to properly align everything.
First, be sure to tape both sides of the hinge of the tail surface you are installing so the surface cannot move. This will give you a flat surface for sighting alignment. Next, make sure covering is removed from the mating surfaces. You want to glue wood to wood, not monokote to monokote.
Trial fit the stabilizer in place. Use pins to securely hold the stabilizer on the fuselage. Using a square, check that the stabilizer is square to both sides of the fuselage. If one side is too high, carefully sand the fuselage to bring the stabilizer into a perfect horizontal alignment. Hold the model straight in front of you and sight down the fuselage from the nose to tail. Sight to a plain white well-lit background, and try to get your light source behind you. Lights from above will tend to cast shadows that may destroy your sighting. Move the nose up and down to see the stabilizer from several angles. You should get an even sight picture from all angles. In addition to checking the horizontal alignment, make sure that the stabilizer is not twisted on the fuselage. Repeatedly sand, shim and adjust the fitting until it is completely level and not twisted.
Next, measure the distance on the front and back of the stabilizer from the fuselage to both tips. You want to center the stabilizer on the fuselage. The right and left measurements should match in front and in back if you have it perfectly centered. Once the stabilizer is centered and pinned, mark the position on the bottom of the stab so you can reposition it when gluing. Take one final sighting of the stab, checking from several angles. Glue the stabilizer on using a moderate amount of 30-minute epoxy. Pin the stabilizer in place and check alignment and measurements one more time before the glue dries.
Installing the fin-rudder assembly is largely the same as installing the stabilizer. Test fit the piece, and check alignment several times before marking your final position with a pen. Be particularly aware of twist, because it is very easy to install the fin perfectly vertically but twisted in the yaw direction. Use a square to make sure that the rudder is perpendicular to the stabilizer. Use slow-setting epoxy, and check alignment several times while the glue is setting.
Before installing your wings, perform some simple checks to make sure they are ready for mounting. The following checklist can be used.
Once the wings have been checked the next step is to check the alignment of the wing in the wing saddle. First, trial fit the wings using some rubber bands to hold them in place. Look at the wings from the front of the fuselage to ensure that the wing saddle is even. If properly aligned, the wings should form the same angle on both sides of the fuselage. The wings should also align horizontally with the stabilizer. If one side appears higher than the other, you can either sand or shim the wing saddle to seat the wing properly. Also look for twists in the saddle that might result in one wing being at a higher angle of attack. Slowly tilt the nose upward and ensure that the same amount of wing is visible from the nose of the airplane on both sides. After the wing saddle is perfect you can apply weather stripping to it (if desired) to hold the wing in place. Foam weather stripping tape, used to insulate around doors and windows, provides a great base to keep the wings from slipping. This is particularly an issue if the wings are held only by rubber bands.
Tip 21: Some foam weather stripping tape applied to the wing saddle will keep rubber band wings from moving accidentally during launch.
The final step is to precisely align the wings and either mark the wing or drill wing mounting holes. Again, temporarily attach the wing to the fuselage using rubber bands. Measure the distance from the fuselage to the first panel break on both sides of the wing to center the wing. Perform this check on both the leading and trailing edge of the wing. Next, measure the distance from each wing tip to the tip of the stabilizer. Carefully adjust the wing position to center it. Finally, check the distance from the nose of the plane to each wingtip. When all measurements are as perfect as possible, place aligning marks on the fuselage and wing so you can precisely place the wing. If you are using a bolt-on wing you can mark, drill and tap the wing mount bolt-holes at this time. Have a friend help you hold the wing precisely in place while you drill the holes.