Balsa Workbench Primary Trainer Step 2: Fuselage

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Now that we have the wing panels built, we can move on to the fuselage.  It uses 1/16″ balsa sheet left over from building the wing.


Step 2:  Fuselage Construction

We’ll start with something easy.  The front hatch is a piece of 1/8″ balsa with a 1/64″ plywood doubler on the bottom to keep it from splintering.  Put a piece of plastic on your building table to keep the airplane parts from sticking.  I use the backing from covering film.


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We’ll laminate these two pieces to make a strong hatch lid.  There are a few different types of adhesive that can be used for this operation.  A lot of guys use 3M 77 spray, or regular contact cement.  Or you can use Gorilla Glue, epoxy, or medium or thick CA.  Just don’t use a water based adhesive when laminating wood parts.  White glue, Titebond, or other wood glues are great for balsa, but they will cause sheets to warp.  I chose to use 6 minute epoxy on my hatch.


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I like to mix my epoxy directly on the part to be laminated, so I don’t have to pick it up and put it there after mixing.  Use your wife’s credit card, a balsa stick, or similar tool to spread it evenly.


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Now put something flat on it and weigh it down to hold it in place.  At the bottom of this tower you can see the laminated parts being pressed.


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Now that you got that easy step done, we can move on to the fuselage sides.  There are two very important details.  First, you have to make sure the doubler lines up accurately on the fuselage side.  These parts have holes for wing dowels, which provide the best way to align the parts to be laminated.   Even more importantly, you have to make one left and one right side.


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Once again, you can use any adhesive you want as long as it’s not water based.  I decided to use medium CA glue, so I can press it with my hands rather than stacking books on top of it.  The only liability is that you get one chance with CA glue.  Keep your eye on the dowel holes to keep the parts aligned.  You may find it easier to actually stick dowels through the holes, then push the doubler down on to the fuselage side with the dowels in place.


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Note how much glue I used.  Don’t put it right next to the edges or load up with tons of glue because you don’t want extra glue squeezing out.

 

The next step is to add the bulkheads to one fuselage side.  You’ll notice that the bulkheads fit easily and accurately into the slots in the doubler.  Keep the bulkhead at 90 degrees while gluing so you don’t have to fix it later.


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Now hold the square and the bulkhead with one hand, and glue it with the other hand, using thin CA glue.  Note that the bulkhead has a hole in it for the push rods.  Turn the bulkhead so the hole is toward the bottom of the plane.  Don’t glue your tools to the airplane.


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Add the other bulkhead at the front of the cabin.  Note that the hard plywood bulkhead goes at the front of the wing.  The end that is V-shaped to match the wing dihedral goes at the top.

When you get these bulkheads in place on one fuselage side, lay the other fuselage side on the table and place the first side on top of it.


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Keep everything square, and use thin CA glue to attach the second side. Now add the firewall.  Note that the width of this plane is constant from the firewall to the trailing edge of the wing, so you don’t have to worry about warping the nose of the plane.


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After you add the firewall, this is what the plane should look like.


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Make sure the fuselage is square by comparing the diagonal dimensions of the cabin area.  From front left to rear right should be the same length as from front right to left rear.


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My fuselage is nice and square, so it’s time to add some 1/16″ sheeting on the bottom of the cabin.  Once you glue this on, the fuselage will stay square.  Use a piece of medium hard sheeting for this job, and attach it so the grain runs crosswise to the fuselage.  If your fuselage wasn’t square, glue the balsa to the rear bulkhead, then squeeze the fuselage to make it square while gluing the balsa sheet to the fuselage sides.  Also, note that if it isn’t 100% square, it’s not the end of the world.  This just means you’ll have to line up the tail later to make it straight, and possibly shim your engine to make everything line up.  Try to make it square, and if it’s not, you can deal with it later.


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Now you’ll need your landing gear.  This is made from 3/32″ music wire.  It has a 90 degree bend in the middle, 4.5″ legs, and 1″ axles.  Note that the axles are angled slightly to create toe-in on the wheels.  3/32″ wire is easy to bend by hand, without a special wire bender.  I like to hold the wire in the jaws of a crescent wrench while I bend the end of it with my fingers.  Note that when bending the axle, it is better to hold the axle with the tool and bend the leg with your hand.  This way you will have a straight axle.  Use an abrasive wheel to cut the wire.

Note the angle of my axles.  You want the wheels to toe in a little bit if possible, but if the axles are straight, that’s good as well.


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Make small notches in the bottom of the doublers to accommodate the landing gear legs.


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Your kit comes with three little triangles of 1/8″ plywood.  These are placed around the landing gear on the front of the plywood bulkhead, and the rectangular bulkhead doubler is placed over the landing gear and the triangular spacers.  On this prototype model I chose to stitch the landing gear onto the bulkhead with copper wire and seal it with epoxy.  But I decided that the other method was better for a beginner.  Your kit will have better looking parts, but I’ve demonstrated the construction here with pieces of balsa wood.  Try to imagine that the copper wire is not there and that those triangles are made of laser cut plywood.


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Place the triangles and the landing gear in position, and cover with the plywood cover plate.


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When you get your landing gear and spacers set up so they all fit and everything looks straight, use a generous amount of epoxy to attach everything, and clamp it together with clothes pins or clamp-type paper clips until it sets.  When your landing gear is finished, complete the bottom cabin sheeting with 1/16″ balsa, and then glue the ventilated 1/16″ plywood chin plate into place. Note that it has little notches for the landing gear legs.  You may have to enlarge these notches to prevent binding and allow the plate to sit flat on the bottom of the fuselage.


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Now add some strength to all of your joints by applying a glue fillet to all joints that you have made inside the fuselage so far.  Once again, you can use thick or medium CA, Titebond, white glue, or epoxy.  The obvious choice, and the one I always use, is medium CA followed by a shot of accelerator.  Apply it around the landing gear assembly, on the vertical bulkhead joints, between the fuselage sides and the floor, and between the fuselage sides and the firewall.  My lighting and photography may not be the best, but I hope you can see the fillets on all of these joints.


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Now we’re in the home stretch.  The basic fuselage is built, and all we have to do is close everything.  Glue a piece of 1/8″ x 1/4″ balsa stick to the front of the forward bulkhead (the one at the leading edge of the wing).


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Sand this stick flush with the fuselage sides where the windshield attaches.


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Do the same on the back side of the bulkhead behind the wing.

 

Select a piece of 1/8″ balsa for the windshield.  It should be medium hard.  It doesn’t have to be rock solid, but make sure it’s not super light and fluffy.  Sand the edge to a 45 degree angle.


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Now when you put it in place the bottom edge should match the top of the fuselage nose.


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When it fits correctly, glue it into place.

Next, cut two pieces of 1/8″ x 1/4″ balsa stick 3.75 inches long.  Glue them to the inside of the fuselage sides, at the top, in the rear.


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These sticks will provide extra gluing area when you attach the horizontal stabilizer, but there’s just one problem.  They don’t allow the tail to come together.


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Trim and sand the inside edges of these two sticks so they will allow the tail of the fuselage to come together at the rear.  Glue the tail end together.


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Attach 1/16″ balsa sheet to the bottom of the aft fuselage, with the grain running crosswise.  Be careful how you hold the fuselage while gluing the sheeting, because if you warp the sides and glue the sheeting, the warp will be permanent.  If you make sure it’s straight when you glue the sheeting, it will be permanently straight.  This sheeting should be medium weight, but you should use the hardest sheet you have for the last 1/2″ at the rear for durability.


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If you plan to use tube-type push rods in this plane, install them now.  Refer to my article on this site to learn how to do this.  If you want to use stick-type push rods, which is what I’m doing with the prototype, we can move on to the next section, which is the top sheeting.

Use your 1/8″ x 1/4″ balsa stick to make some interior reinforcements where the back window meets the aft fuselage.  Put one at the bottom of the window and one at the front of the aft fuselage.


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Put another piece in the top of the aft fuselage, at the front edge of the stabilizer.  This piece is 3.75″ in front of the tail end of the fuselage.


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Don’t forget to put a stick in the top of the back window, on the back side of the bulkhead.  I mentioned that when we were doing the one at the top of the windshield, but I didn’t get a photo of it.

Now attach 1/16″ medium balsa sheeting to the top of the aft fuselage.  Leave the last 3.75 inches of the top open, where the stabilizer will attach later.


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Don’t worry about those rough edges.  We’ll sand all of that off later.  Now let’s move on to the front hatch.  If you’re building this plane for glow fuel, this hatch can be glued into place, or used as a removable hatch without the air scoop.  Any way you want to build it, the first thing to do is to bevel the rear edge to fit on the windshield.


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For electric power, add the air scoop.  Insert the two sides and glue into place.


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Now select a piece of 1/16″ balsa wood that you can bend easily around a curve without cracking it.  Cut a strip 1″ wide and roll it around the top of the scoop, and glue it into place.  Note the direction of the grain in the photo.  Don’t worry about the edges hanging over.  We’ll sand those off later.


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The hatch needs a little scrap of wood glued to the underside to hold it in place under the windshield.


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Put the hatch in place and glue a strip of 1/8″ wood in front of it, on top of the firewall.


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After that strip is glued in place, give the inside edge of it the same treatment as the rest of the inside of the plane.  Put a glue fillet along the inside edge where it meets the firewall.

Make sure the hatch fits correctly and can be removed and replaced easily.  If it binds, do a little bit of sanding to the edges of the hatch.


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Using a sanding block (with fresh sand paper) sand the nose of the plane flat.


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The last fuselage item is the cowl cheeks.  If you want your plane to be flat-nosed, all you need to do is sand and cover.  But if you want to dress it up a little bit, install the cowl cheeks.  There should be four pieces. Laminate them together using your favorite method.  I used CA glue.


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Keep the parts lined up and join them.


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Now give the straight edge of the cowl cheeks a light touch with the sanding block to make sure it’s straight and flat, and glue them onto the front of the airplane.  You’ll need to decide if you want your cowl cheeks to lean in to make a narrower nose, or if you want them to point straight ahead.  When you figure it out, glue them on.


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This fuselage is all built.  For the next step, go to the menu at the top and find the Sanding and Assembly instructions.