Choosing a Moustique as your first indoor model is a very good way to start. It is a fairly simple model, it will teach you all the basic techniques an indoor modeler needs and you can already fly it in competitions. It will do two to three minute flights in a gym hall. At competitions, flights of more than six minutes are not uncommon. Though we tried to make this building instruction as clear and complete as we could, it will be likely that you will encounter some problems. If something is not clear or when you do not succeed in making something, then do not hesitate to ask an indoor flyer for help. They are very friendly people and will certainly help you. After all, they have been beginners too!
When this is your first model airplane you will probably have to learn some new words and terms. Figure 1 shows the main parts of an indoor model. On the drawing there will be more new words. Enlarge the drawing on a copy machine 1,41x.
We need a building board from soft board (in which you can easily stick pins in) of 22x60cm. Tape the plan onto the building board and cover it with clear household foil. This will prevent glue from sticking to the plan.
Ensure that everything is flat and wrinkle-free. We need some other accessories. Cut straight strips from a sheet of 2mm balsa of the following dimensions: 10x250mm (4 each), 10x50mm (2 each) and 10xl6mm (16 each). Glue four layers of 2mm on top of each other and construct the assembly block of figure 2. Try to get the sides and grooves as square as possible.
Figure 3 shows several jigs which you can make from ±6mm thick corrugated cardboard or foam board. As before: cut them as square as you can. Next we make the wing and stabilizer rib templates from thin ply or cardboard (see plan). Finish the curved sides as smooth as possible.
We need two different kinds of glue. For joining wooden parts we use cellulose glue (like UHU-Hart). This glue has to be thinned down about 30% with thinner or acetone. The most handy way to apply the glue is by means of a syringe (needle size ±0,5mm). Stick a piece of wire in the needle to prevent it from clogging up. lndentify the wire with a piece of brightly colored tape so that you find it quickly in the usual mess on your working table!
The other glue we need is contact cement for adhering the covering to the wing and tail frames. This glue also has to be diluted, ratio glue-thinner 1:2. Usually only thinners of the same brand as the glue will work successfully.
For wing spars and wing ribs we need a sheet of 1,5mm middlehard balsa (weight of a 10x100cm sheet 18-27 gram). For tailplane and rudder 1mm is needed, weight of a sheet 10-18 gram. For the fuselage lighter balsa is required: a 4mm sheet of 40-50 gram or a 10x10x1000mm strip of 10-15 gram. In all cases the grain has to straight and regular. For the propellerblades we need a soft sheet of 1mm balsa, preferably quarter grain. This type of grain has more bending stiffness in a direction square to the grain. It is recognizable from its speckled look. We further need a piece of Ø0,4 or 0,5mm steel wire for the propeller shaft and rear motorhook, a piece of 0,5-0,8mm hard aluminium (f.i. from a beer can) for the propeller bearing (bearings are also commercially available) and a piece of Ø2mm I.D. aluminium or plastic tubing for the wing sockets. Wing socket tubes can be made yourselves. This is done by rolling a piece of tissue paper over a piece of Ø2mm O.D. wire, f.i. a drill end, and impregnating this with cement or dope (three windings is sufficient). Pull off the tube before it begins sticking to the wire! For the wing covering we could use lightweight tissue, but only if we cannot obtain one of the many types of lightweight plastic foils that are available. These are called mylar, ultrafilm, microlite, polymicro and the like, and come in weights ranging from 7 to 1,25 grams/m2. We further need teflon washers for the propeller bearing and of course rubber to fly on. Addresses of some suppliers are given at the end of the article.
We start by cutting the ribs and spars. For cutting we preferably use a razor blade. A thicker blade will distort the tiny strips we cut. Cover the other side of the blade that is not used for cutting with a piece of tape or break the blade overlength into two pieces. The ribs are cut in 1,5mm wide strips along the rib template. Make several extra for reserve. The spars are cut along a steel ruler. Cut them 10 to 20mm overlength. Note that the spars of the left wing are longer than those of the right one!
We start by building the stabilizer. Rub the edges of the four longest assembly strips with a candle wax. This prevents glue from sticking to it. Pin the strips on the building board along the outside of the stabilizer outline (figure 4). Do not cut the strips to length. We need them for the wing also. Position the stabilizer spars along the strips and clamp them against it with the small 10xl6mm pieces of balsa (figure 5).
The spars rest on the building board with their small side, with the thin tapered ends towards the tip of the stabilizer. Never stick a pin through the spar!
The spars have to be glued together in the middle. Glueing is always done in the following manner, called "double glueing". Coat each surface with a thin layer of glue, wait a few seconds, apply glue to one of the surfaces and then join the pieces. This gives the strongest bonds. So for glueing the spars we have to remove them from the building board (setting them up was a useful exercise). Coat the end of one spar and replace it between the clamps, coat the end of the other spar, wait a few seconds, coat again, replace and press the spar against the other and reposition the clamps.
Take one of the ribs and hold it in its position over the plan. Carefully mark both ends to the correct length and cut off. The rib should fit in between the spars such that it is not under any bending stress, but still stays upright in position. Now prepare the next rib. If you cut one too short accidentally, do not worry. It can be used at a position closer towards the tip. When all ribs fit accurately they can be glued. Again: doubly glued. Avoid big blobs of glue.
Leave the stabilizer to dry for half an hour, remove the clamping blocks and carefully lift the frame from the board. If it is stuck to the building board at some place, then loosen it by running a pin underneath. Cut off the extending ends of the spars. Inspect every glue joint closely. Add glue when necessary and remove excess glue with a razor blade. A careful and experienced builder will seldomly have to do this!
The rudder is assembled in the same way as the stabilizer. Position the strips on the board, cut to length, remove, glue and reapply. Note that one end of the sticks is not cut off (figure 6).
The procedure for building the wing is the same as for the stabilizer. Again note the correct position of the spars. The left wing is intentionally longer than the right wing. The middle rib is glued just left of the centerline. You may have noted that the wing tips will be raised to a V-shape. We will do this after covering the wing. So the wing halves are joined in the middle temporarily.
The wood for the fuselage has to be of very good quality. Straight grain and no weak, hard or brittle spots. The motorstick can be tapered towards the ends from 6x4 to 5x3 mm to save some weight. Do the sanding in one direction only. A to-and-fro movement may easily break your carefully selected piece of wood.
For joining the motorstick and tailboom we need the large assembly block. Put cellotape over one of the small sides. Do not fold over the unsticked part, it may be cutted off (figure 7). Pin the block on the building board along the top side of the fuselage at the stick-to-boom joint.
Position motorstick and tailboom on the plan and check whether the joining faces fit accurately (figure 8). Take time to make this fit as good as you can. This joint is a vital one! Glue the pieces together (doubly glued!) and clamp them between the small balsa blocks.
When the glue has dried remove the fuselage from the building board and lay it upside down. Prick a hole with a pin between the motorstick and the tailboom along the glue joint for the rear motor hook. Put glue onto the hook and insert it into the hole. Lay a half knot in a piece of thread, slide the knot over the hook, pull tight and glue each end of the thread downwards along the sides of the motorstick (figure 9). Add a couple of winds after drying, put on extra glue and cut the ends off after drying.
The propeller bearing is tack-glued with cellulose glue. With a piece of wire we adjust the bearing such that it is positioned with 1 to 2° of side-thrust to the left. That is to the right when viewed from the bottom as in figure 10! Let the glue dry thoroughly. It is then secured with thread in the same manner as the rear hook, add several extra winds at the front and the rear of the bearing and glue with a generous amount of glue. You can also use instant glue or epoxy for this purpose. The last thing to add is the little vertical piece of balsa at the end of the tailboom. This piece raises the trailing edge of the stabilizer a little. Practice has shown that the tailboom usually tends to droop downwards instead of upwards. The wing sockets are added later.
The propellerspar is sanded from middlehard balsa, 12cm long and tapered from Ø3 to Ø2mm towards the ends. The center section is reinforced with a few windings of tissue paper glued onto it. Next the propellerhook is bent and glued squarely in the spar. First bend the rounded hook end, prick a hole fore and aft through the tissue with a pin, push the hook through and bend the end squarely twice. Pull the hook backwards so that the rearward bent wire end sticks into the spar. Check alignment carefully and secure the hook with glue on the front and rear side.
The outline of the propellerblades is transferred to the balsa with carbon paper. It is perhaps better to make a cardboard or ply template of the blade shape and cut the blades along this template. This assures that both blades will be of the same shape. The blade can be sanded thinner towards the edges. Forming the blades into the correct pitch and camber is done in a simple way. For this we need a cylindrical shape, f.i. a paint tin, with a diameter of ±12cm. The blades are wetted in warm water for half an hour. They are then strapped to the cylinder with bandage under an angle as indicated on the plan. By putting both blades on top of each other they will get exactly the same twist. Be sure you have got the direction of the angle right, the propeller will turn to the right (when viewed in flying direction). Let dry thoroughly, a day in the open or 15 minutes in an oven (be careful, lowest temperature setting and leave the lid open). The blades have to be glued to the spar in the correct angle. For this we make a simple jig as in figure 11.
There is no need to cut a groove in the blade. You can glue it to the rear of the spar. Use a non-shrinking glue such as PVA or cellulose glue with some drops of castor oil in it. If you decide to make a groove then take care that the blade fits without distortion. On the other hand avoid any gaps. These take up too much glue, which can lead to distortion of the blade. The last thing to do is to slide two teflon washers over the hook and finished is your propeller!
On an indoor model only the topside of the surfaces is covered. We start with the stabilizer and practice the procedure before we use any glue. Clean up your worktable and spread out a sheet of newspaper. Onto this we lay the sheet of covering material. It can be spread easily by gently blowing it downwards. Pick up the stabilizer in the middle with one hand, curved side downwards, hold it about 2cm above the foil, check that there is at least 2cm of excess foil all around and drop the frame. It is of great importance that this procedure goes successfully at the first try. Because we will use contact cement there is no second try! Practice until you feel confident.
Now for the wet run! Lay the stabilizer - curved side upwards - onto another sheet of newspaper. A glue drop on the covering newspaper sheet will lead to disaster! We can apply the glue with a little stick with a piece of velvet (figure 12). You can also use fine brush.
It is better to have the glue thinned down a bit too much than too little. You can always apply a second layer of glue. The glue is applied only to the topside of the spars and the end ribs. It is not really necessary to do the ribs as well. The glue may hardly be visible, but it should feel tacky when you touch it. If in doubt add a second run. Pick up the frame, turn it over, hold in position over the foil, check that there is excess foil all around, lower the frame and drop it from ±2cm height. Press the middle of the spar nearest to you down onto the film. Press down the left end of this spar, then the right end. Be sure to make vertical movements only. Tap the spar downwards at some places in between. Now press down the middle of the other spar and its ends. Because of the curvature of the ribs the fixed spar will lift a little from the board and the ribs will bend, but the structure is sufficiently flexible to do this without risk of breakage. Now the frame is fixed and there is no danger anymore of shifting. Next go all around the outline cm by cm and press down firmly.
With a bit of experience this method will result in relatively little wrinkling. Do not bother about wrinkles, they hardly have any effect on performance. When you use paper as a covering material these wrinkles are even beneficial. Changes in humidity will less likely cause warping of the structure. Never dope a paper covered indoor model! Instead of contact cement you can also use thinned white glue or a glue stick (like Pritt). The wing and rudder are covered in the same way as the stabilizer.
Take a new sharp razor blade. Lay the stabilizer on the buildingboard, curved side upwards, with one spar just outside the edge of the board. Take one corner of the foil between thumb and forefinger, insert the razor blade and move it to the right (figure 13). It is as if you try to pull the framework off the table with your left hand and are resisting that with the knife. Go all along the outline of wing, stabilizer and rudder. Take care not to cut into the wood. Do not bother too much when you cannot remove the foil close enough to the spar.
Assemble the cardboard jigs Ll, M2 and R3 on the working table as in figure 14. The big assembly block is pinned to the building board. Place the fuselage against the block and clamp it between the little balsa blocks. Check that the fuselage is aligned squarely with regard to the stabilizer. If the end of the tailboom does not touch jig 2 put something under the jigs to raise them. Place the stabilizer in position (figure 15). When all is properly aligned glue the stabilizer at the indicated spots. Let it dry for at least 15 minutes. From now on you will have to handle your model with extra care: a sudden movement can easily lead to damage. The best way to hold the model is at the nose between thumb and forefinger.
Lay the fuselage with stabilizer upside down. Hold the rudder in its correct position. Note that that the rear is offset to the left 8mm (figure 16). Put glue on the rudder as indicated, hold it in position and keep it there for a few seconds. It will stay upright. Leave it to dry further.
First we exercise in making a half-knot (figure 17). Take both ends of the rubber (1), cross the ends (2), pass one end underneath the other (3) and pull lightly (4).
Now we make a complete motor (figure 18):
It is possible that the knot gets loose when you tied it too loosely. When the motor is lubricated (later more about that) then remove the lubricant as far as possible, tie again with the same type knot but now an extra half- knot is put on top of that (7). This knot usually holds. If not then a small drop of instant glue between the loose ends will help.
The wing posts are cut from relatively hard balsa. The ends are sanded round such that they fit precisely in the wing sockets. The fit must be such that no real force is required to insert them, but on the other hand they may not slide too easily. The front post is 60mm long, the rear 55mm.
The exact position of the sockets on the fuselage is determined as follows: hook the propeller into the bearing. Slide one of the rings of the rubbermotor over the propellerhook and the other ring over the rear hook. Support the motorstick with a little stick en shift the fuselage till it balances horizontally (figure 19).
Mark this position on the motorstick with a fine pencil. Set other marks at 105mm forward and 45mm aft of this mark. These indicate the positions of the front and rear wing post.
Take the building board with the big assembly block and pin it down as indicated in figure 20. Lay the fuselage parallel to but not against the block. Leave about 1,5cm between so that the fuselage can be clamped with the little blocks. The lengthwise position should be such that the front and rear wing post marks align with the grooves in the assembly block. Slide a socket over each of the wing posts and lay them in the grooves (figure 21).
Let the sockets stick out over the motorstick equally at both sides. View the posts along the fuselage direction to be sure that they are aligned in the same plane. Glue the sockets to the motorstick sparely. Do not let any glue get onto the posts themselves! Let dry for 15 minutes. Add an extra layer of glue. Only after everything has dried completely you can pull out the posts from the sockets.
The next step is to make dihedral in the wing and mount it to the wing posts. For this we have to set up a jig as in figure 22. Pin the cardboard jigs 4 and 5 vertically on the building board and jigs L6 and R7 against them with the 125mm side forward. Note that L6 and R7 are not exactly equal. The rear side of L6 is shorter than the rear side of R7. This guarantees that the wing halves will be glued together with the right warps built in. The left wing gets a positive warp of 6mm. Pin the large assembly block on the building board with two pieces of balsa underneath to raise it about 2mm.
Insert the longest wing post in the front wing socket and the shortest in the rear socket. Clamp the fuselage against the assembly block as in figure 23. The tail of the model will stick out beside the table, so be careful not to hit it or the building board accidentally. Take the wing and lay it upside down. Make a half cut where you joined the wing spars. Gently break the joint further till you get the required dihedral amount. Handle the wing with care to prevent tearing of the covering and lay it on the jig (figure 24). Be sure that the leading edge is forward. The left wing is longer than the right. Position the wing break on top of or just between the wing posts and glue firmly.
You will notice that a big wrinkle has developed in the middle of the wing. It may not look nice but it will not influence the flying capabilities of your model. Add the four struts and let dry for half an hour. Remove the model from the jig and admire your model for a moment. It is finished!
Find a box in which you can store and carry your model. The dimensions should be 56x34x14cm minimum. Construct the flaps of the box such that they cannot fall into the box and damage your model (figure 25). The fuselage is fixed with the motorstick slid into two foam rubber blocks. Cut a slit in each block and glue to the bottom of the box. The wing is mounted in the same way as it is fixed to the fuselage. Glue wing socket tubes to a piece of balsa and glue this in the box. Also in this case the sockets have to be aligned properly to prevent warps from developing in the wing.
For winding the rubber motor we need a winder with a gear ratio of about 1:10. You can make one yourselves from an old hand drill, alarm-clock or Meccano gears. They are also commercially available.
For our first trim flight we need a draft-free space with a floor space of 10x10m minimum (a gym hall, cantine, hangar, church). Because an indoor model airways flies powered by its propeller and not as a glider we will trim it directly as a powered airplane. Remember that the safest way to hold your model is at the nose between thumb and forefinger. This way you also hold the propeller. Force yourself to slow down, make gentle movements. When you run with the model in your hand all that will be left is the motorstick and remnants of wing and tail will flutter behind you.
Insert the propeller into the bearing and attach the rubber motor (knot at the rear!). Check that:
Take the model at the nose with your left hand and turn the propeller with your right hand 200 turns to the right. Now switch over the model such that you hold it with your left hand from the front at the bearing also keeping the propeller from rotating. Take the model with your right hand at the motorstick under the wing and release the propeller. Let the propeller turn for a few seconds and release the model with a gentle movement. Do not throw it! The model will turn to the left if everything is right. Do not panic when it hits the wall. Just let it happen and pick it up when it has slid down. Also when it risks to collide with a person say to him to stand still, freeze and let the model hit and slide down. The model flies so slowly and is so flexible that hardly any damage will result.
The model should not dive nor climb. When it tries to climb you will notice that it looses velocity, stalls and dives to pick up speed again (figure 27). When it stalls the front wing post has to be lowered in the socket. Do this in small steps of ± 1 mm. When it dives the rear post has to be lowered. When the model flies a neat and level left turn you can increase the number of turns. From now on we do not do this by hand any more as you can easily damage your model. We use the winder. The motor now always has to be lubricated with castor oil or another type of lubricant. Only then will the motor unwind smoothly and have a longer life. Hold the model between thumb and forefinger at the front so that you also hold the propeller. The rubber is hooked up at the propeller (knot at the rear!). Ask a friend to wind ±500 turns in the motor. Take of the motor from the winder grabbing it firmly just before the 0-ring and hook it up to the rear hook. The winding is best done by stretching the rubber about 4 times its original length. In this position wind in about half the number of turns. The other turns are wound while gradually approaching the model till it matches the length of the motorstick. With this procedure, which can be refined a lot, you will get much more turns in the motor and it will last longer!
When the model flies level cut off the end of the wing post that extends below the wingsocket. This ensures that you will allways mount the wing onto the fuselage with the correct incidence angle. Always slide the wing posts into the sockets till they are aligned with the underside of the sockets.
You can now further increase turns till the model approaches the ceiling. When the ceiling is flat and smooth you can even allow it to hit the ceiling. When your winding technique has become optimum you can get up to 1600 turns into the motor. In large halls times of almost 10 minutes can be flown! But in a gym hall flights 5 minutes are very well possible. It is all a matter of clever experimenting with longer, shorter, thicker or thinner rubber, a larger propeller, more pitch, other blade shape or whatever design change you can think of!
That depends on you. Building or flying this model may not have been as satisfying as you expected or you have had some bad luck. We do not think that that is too bad. You have tried something and gained new experience. But you also may have become curious to what this model really can, and that is quite a bit. It requires further experimenting with rubber sizes. A lot can be told about winding technique. There are many, many other more challenging designs. Remember this: when you fail at something, or have something to ask, call or write one of the other indoor fliers. They will be glad to help you!
