Temporarily put the bottom wing retaining dowels in place in the fuselage and attach the bottom wing. Also attach the top wing with rubber bands. Look at the plane from the tail forward to make sure the two wings are parallel. If they’re not, do a little bit of trimming and sanding to make the wings sit straight. If your top wing wobbles, or if it slants way down on one side you may want to add a little bit of 1/16″ balsa sheet to the top of the wing saddle on one side. The great thing about building with balsa is that you can add a layer of balsa and sand it back off if you want to.

Once the wings are straight, hold the horizontal stabilizer on the stabilizer saddle and look at the plane from the tail again. The stabilizer and both wings should look parallel. Here’s a photo with the plane already covered with film, but yours isn’t covered yet.

If your tail slants, gently sand the stabilizer saddle to make the tail sit parallel with the wings. The saddle is cut to a specific angle, so try not to alter the pitch. It’s not the end of the world if you can’t help changing it a little bit, but try not to.

Dry fit the stabilizer and head rest, making sure the head rest doesn’t hang over the end of the stabilizer at the tail post. If it does, trim and sand it to fit.

Cover the entire aircraft and control surfaces with film, or if you’re really ambitious you can apply a fancy old fashioned dope finish or paint. I have a series of articles on this website about covering, or you can get advice from friends or an online chat group. I’m won’t go into detail here about covering with film, but I will give you two pieces of advice.

Cover the plane before installing the wing rubber band dowels.

And most importantly, when you’re covering the tail you need to leave bare wood where it attaches to the fuselage and the fairing, but DO NOT USE A BLADE TO CUT THE COVERING AWAY FROM THE TAIL! If you cover the whole piece and THEN cut the film away from the contact area you will cut the wood inadvertently and create a stress concentration point which may cause the tail to fail under stress. The correct way to do it is to trim the film before ironing it on, so you leave a bare spot for gluing.

The Simpleton is generally an easy plane to cover, but the cabane struts may give you a little bit of trouble. You should cover the bottom of the plane first and work your way up, so this area is done last. When you finally get to it, here’s the easy way to do it. In the following photos, the front of the plane is to your right.

Starting at the rear of the top deck, above the dashboard, cut a piece of film to fit between the rear struts, with extra area at the rear to allow you to heat and stretch it around the corners.

After you stretch the corners, trim the edges and iron them down:

Cut the next piece to overlap the first one about a quarter inch and extend forward to the rear edge of the front struts.

Iron the piece into place, trim the edges, and iron them down.

Cut another piece to overlap 1/4 inch, with some extra area in the front.

Iron the main piece on, trim the edges, and iron about 1/8 to 1/4 inch of of film to the ceiling inside the fuel tank compartment.

Trim the film away from the holes in the fuselage where the wing dowels are to be installed. Your dowels should be 5 1/2 inches long. Round off the sharp edges on each end with sand paper. If you’re making your trim black, this is a good time to color the dowels with a black marker.

Center the dowels in the holes so the length is equal on both sides.

If you’re using a glow engine, fuel proof the inside of the firewall, the fuel tank compartment, the strut assembly, and the wing dowels. You can use dope, epoxy thinned with denatured alcohol, or fuel proof paint. Don’t do the wing dowels or struts first, because that would cause you to get gunk all over your hand when you do the tank compartment. So start with the compartment. When you coat the inside of the firewall, be sure the inside of the fuel line holes are thoroughly soaked. It’s difficult to thoroughly coat the ceiling in the fuel tank compartment, but that’s not really a place where fuel and oil tend to collect anyway, so don’t worry about it too much.

If necessary, lengthen the brush to reach the bottom. The standard brush for this application is a cheap acid brush with a tubular handle. A balsa stick can be crammed into the handle to make the brush longer.

It’s also a good idea to coat the insides of the lower wing saddles to prevent oil intrusion.

Coat the struts next, and let the paint/epoxy get into the joint between the struts and the covering film. If you coat the inside edges of the struts before you start on the outsides you’ll be less likely to get stuff on your hands. I think the best sequence is to coat all inward facing surfaces, then do the bottom of both wing saddles. When that’s finished, do all forward facing surfaces, then all backward facing surfaces, then the top, then finally the outward facing surfaces. If you do approach it systematically you are more likely to coat all surfaces without forgetting any. If you just sort of start somewhere and keep going around corners randomly, you’ll get it all over your hands and probably miss a spot. Once the struts are done, coat the bottom wing dowels, making sure to get epoxy in the crack where the dowel goes through the fuselage side.

Set the fuselage aside to let it cure.

Check to see if you have epoxy or paint running down from the struts and puddling on the covering film, or from the lower wing dowels and collecting under the bottom of the plane. If this is a problem, clean it up with a paper towel and alcohol to prevent the plane sticking to the table. It’s probably a good idea to set it on a piece of plastic.

After your coating cures, cut the film away from the holes for the fuel lines, engine mount screws, and throttle cable. You can run a drill through the fuel line holes again to make them smooth if necessary.

If your runway is paved, mount the landing gear so the legs slant backwards, and install whatever size wheels you like. If you fly from grass, mount it so the legs slant forwards, and you probably want 3″ wheels, or 3.25 depending on the condition of the runway. When you decide which side of your landing gear is in front, use a crescent wrench to twist the axle mounting area to provide about 2 degrees of toe-in per side.

Assemble the axles in the wheels. If the bolt doesn’t fit through the wheel hub or if the wheel binds, you’ll have to enlarge the hole slightly to allow the wheel to spin freely. It’s best to use a drill bit that’s not really big enough, and wobble it a little bit to munch the plastic slightly, rather than use an oversize bit. The wheel goes between the bolt head and the first nut. Put the end of the bolt through the hole in the landing gear, and hold it in place with the second nut.

If epoxy/paint got in the threads of the mounting holes for the landing gear or engine mount, use a tap to clean the threads. (A screw with flutes cut into the sides with a Dremel cutoff wheel is good enough to clean epoxy out of threads.)

Put the tail and head rest in place on the plane and mark the fuselage top at the front of the head rest. Find the center line and mark the top of the fuselage to remove a strip of film 7/16″ wide. Make sure the strip isn’t too long. The goal is to have the bare wood entirely covered by the head rest, so the area should be a little smaller than the footprint of the head rest.

Use a fresh blade to cut out the film. You may remember that you’re not supposed to cut film from the horizontal stabilizer this way, but this area isn’t subjected to flight loads. Don’t cut through the wood, but don’t worry about it too much.

Hold the horizontal stabilizer in place and line it up with the lines you made before covering.

If your film placement was slightly inaccurate and you see some bare wood, you can add a little strip of film to cover it up. Or you can ignore it. If you have a choice between aligning your film cut-out or making the tail straight, make the tail straight.

Check the fit on top.

Glue the horizontal stabilizer in place using CA, epoxy or Titebond. It really doesn’t matter because all of these adhesives are stronger than balsa, so do whatever floats your boat. (When a plane crashes, usually the tail doesn’t come off, no matter what you glue it with. When it does come off, usually the rest of the plane is destroyed.)

Put the head rest in place and center it over the centerline on the stabilizer, and the center line you drew on the fuselage top.

Glue the head rest in place with medium CA glue. While you’re gluing it, it may help to insert a stick of 3/16″ balsa in the slot to hold it in the right place for the vertical stabilizer later. Just don’t glue the spacer in accidentally. (If you do glue a guide stick in accidentally, you can dig it out with a utility knife. It’s not the end of the world.)

Use medium CA to attach the vertical stabilizer. Use the included mini square to make sure it stands up straight.

When you’re placing the vertical fin, the idea is that the trailing edge is supposed to be in line with the fuselage tail post.

Use CA hinges to attach the elevator. Sometimes it helps to trim the end of the hinge to make it pointy, so it will go into the slit more easily. Use two hinges per elevator half.

Glue the hinges with a drop of thin CA. It’s tempting to put lots of glue on these things, but any more than a drop will run along the hinge line, and when it gets to the end it will drip on your pants.

Move the elevator up and down. If the elevator joiner bumps into the tail post or the vertical stabilizer, you can trim those parts for clearance. You want the elevator joiner to move freely without hitting anything.

After the elevator is installed, install the rudder. If it interferes with the elevator joiner, trim out a little notch for clearance.

Install the rudder, using two hinges above the horizontal stabilizer and one below.

Here’s what it looks like with all the tail surfaces installed. Note that the vertical fin has been trimmed slightly to make room for the elevator joiner. The fuselage tail post was also trimmed, but you can’t see it in this photo.

Install the ailerons, using three hinges per aileron. Align the tips to make a smooth line from wing to aileron.

The next step is to install all equipment that goes in a specific place. After it’s all there you can figure out where to put the battery and the servos.

Cut the film out of the servo holes in the bottom wing. Make sure the film is ironed down firmly all around the hole first.

Tie a small nut to one end of a piece of sewing thread, and tie the other end to the plug on the end of your wing servo cable. Tie it so pulling the thread will pull the plug straight ahead of the wire. You don’t want the plug to bend over when you pull it.

Hold the wing up vertically and drop the nut through the holes. Fish it out of the hole at the wing root. Mount the servo with screws and remove the thread. Repeat with the other servo.

The holes in your control horn, where the clevis attaches, should be in line with the hinge line. In other words, don’t mount the control horn so the part with the holes hangs over the surface of the wing, and don’t mount it behind the hinge line so the holes are over the aileron. Standard practice is for the holes to be right at the hinge line.

When you set up your radio for flight, don’t make the bottom surface of the aileron flat to the bottom of the wing, nor the top surface flat to the top of the wing. When your stick is centered, the ailerons should be straight back from the trailing edge as shown on the plan and in the following photo. You’ll see a concave angle when viewing the wing from the top and from the bottom.

It’s always a good idea to secure your clevis with a small piece of silicone fuel line or heat shrink tubing.

Install the rudder and elevator control horns, with the rudder horn at the same level as the push rod slot on the fuselage side. The higher slot is for the elevator push rod, and the lower slot is for the rudder.

The next step is the tail wheel assembly. Here’s a generic assembly.

On the plan, the steering axis is placed ahead of the rudder hinge line. When the plane is sitting on the ground, the wire bears against the bottom of the fuselage and does not stress the rudder hinges. The tiller arm is padded with a piece of fuel line and attached to the rudder via a plastic strap made from a milk jug or soda bottle, held in place with a 2-56 screw and nut, which are included in the kit. Tighten the screw and rough up the threads on the bolt with a pair of pliers to prevent the nut backing off, or secure the nut with a drop of thin CA.

Another way to do it is to use leftover push rod material bent to look like a lollipop, with the stem inserted into a hole drilled in the bottom of the rudder and hardened with thin CA. The stem is about an inch an a half tall.

You can also use any upgrade tail wheel assembly you prefer, and install it to manufacturer’s specs.

Install your engine and throttle cable. Install the propeller and spinner so you can calculate the center of gravity.

Put your fuel tank in the tank compartment and install the hatch.

Attach the wings with a few rubber bands. Set the servos, battery, receiver, switch, and any other radio accessories on top of the fuselage. Lift the plane with your fingers under the top wing saddle. The specified center of gravity is at the #2 bulkhead, and there is a little bump on the underside of the top wing saddles so you can hold the plane up with your fingers and feel the bump. Move the battery and servos around if necessary so it hangs level or very slightly nose down with your fingers at the indicated center of gravity. Please note that this plane flies very badly if the center of gravity is a quarter inch too far back. If your plane flies badly, put weight in the nose.

The Simpleton is designed with the assumption that the throttle servo will go in first and be mounted on the smaller servo rails just under the top deck, but you can put it somewhere else if you need to. I think the instrument panel is a great place to mount the radio switch. It reminds me of the earliest biplanes with very simple instrument panels. Just one big switch. These two components are very close to the designated center of gravity, so they’re not going to cause a huge problem.

Install the radio components according to your findings. You can attach the plywood servo mounting planks to the mounting rails with medium CA or with the #4 sheet metal screws included in the kit. Here’s the throttle servo in place, with glue holding the planks.

The prototype model balanced with the receiver next to the throttle servo. It was wrapped in foam rubber and tucked under the servo planks. The battery was under the fuel tank, and the tail servos were placed as seen in the photo.

Dubro EZ Connectors are a very handy way to attach the push rods to the servos, but don’t use the nylon keepers under the servo arms. They are prone to failure eventually. Use the metal locks. When your servos are in place, attached to the push rods, use some leftover pieces of 1/8″ balsa to brace the front end of the nylon push rod guide tubes at F2. If you cut the strips about 1/4″ wide, you can put one stick above the tubes and one below, then use little short pieces of stick on each side of each tube to keep them from moving horizontally.

Elevator travel should be about 3/8″ up and down.

Aileron travel should be about 3/8″ to 1/2″ up and about 1/4″ to 3/8″ down. It’s easy to program aileron differential with a fancy radio, but if you are doing it the old fashioned way set your servos up so the pushrod attachment point is ahead of center at neutral. This will make the ailerons travel more up than down, which is what you want.

Rudder travel can be around an inch each way.

Because this kit is intended for experienced pilots learning to build, it is assumed that you probably know how to set up and test fly an airplane, so I will give only minimal advice. The main thing is that if your plane flies badly, there are two very likely reasons. Center of gravity may be too far aft. Even just a quarter inch too far back makes the Simpleton 40 fly like a piece of junk. Pitch trim is hard to set, and the plane is constantly wallowing and wandering, all the way to the landing. Another potential cause for poor performance is setting your ailerons up with too much droop. They should go straight back from the wing as shown on the plan. When you look at the hinge line you should see a concave angle when viewed from the top and from the bottom. Do not be tempted to set the ailerons flush with the top or the bottom of the wing. If they have too much droop the plane will wallow and wander, it won’t trim, and generally it will be no fun.

For right thrust, see the article on this site about flight trimming an airplane, and use shims behind the engine mount if necessary. The prototype that flew with the Enya 46 4C benefited from a 1/16″ plywood shim behind the left side of the mount.

The prototypes were flown with the following engines:

Enya 46 4C

OS 40 FP

OS 46 SF

Thunder Tiger GP 42

Performance was very good with all engines, but the two lighter engines required a big 2 ounce brass nut on the crankshaft to keep the center of gravity far enough forward. It should be repeated that a too-far aft center of gravity produces terrible flight performance, so if you need weight, add weight.

It’s common knowledge that OS deliberately detuned the 40 FP to encourage beginners to buy a more powerful 40 size engine later, but in spite of this fact the Simpleton has quite brisk performance with the 40 FP and 10×5 propeller due to light wing loading. Speed, climb, and landing are quite satisfactory, and turning radius is very tight.

The OS 46 provided unlimited vertical performance. If speed is your thing, this one is a good choice. Roll response was good in all cases, but it was fastest with the hot 46.

The Thunder Tiger 42 is not quite as powerful as the OS 46 but it’s close, and it’s very close to the same weight as the 40 FP. This engine would be my top pick if you can get your hands on one, although I also really liked the Enya 46 because the big low pitch propeller allowed more sudden acceleration and deceleration.

If you want to use electric power, knock yourself out. I will not comment on it because I know nothing about it.