Building A Wood Trainer Part Two The Fuselage and Tail

Building A Wood Trainer

Part Two

The Fuselage and Tail

By: Frank Granelli

Part One detailed the wing’s basic assembly. Building the wing rather than assembling an ARF wing allowed for some modifications. The new twin aileron servos will help trim out adverse yaw and permit the ailerons to act as flaperons for some really slow landings. Roll control was improved because the heavier wing ribs were placed closer to the fuselage while the lighter ribs were nearer the wing tips. This will also make lateral balancing easier and will require less tip weight.

The first steps were taken towards using a bolt-on wing rather than employing messy and inaccurate rubber band mounting. This time, the wing will be completed (minus the ailerons) and the fuselage mounting system installed.

Preparing the Firewall

Photo 1

Many wood kits use parts that are stamped out of balsa wood or light weight plywood. This is called “die cut” and once resulted in horrendous fits. But modern die cutting has come far and today’s parts are excellent and fit together well. However, there are some parts that have to be perfect. This is especially true when “box lock” type construction is used (more on this later).

When a perfect fit is required or when a part must be made from standard aircraft plywood (aircraft ply has at least 4-5 layer), modern kits use laser cutting. Four parts had to be perfect in the Kadet kit for reasons that will soon become very clear.

The firewall in photo 1 is made from aircraft plywood. It is 1/4 inch thick and has many layers. It is also a very important part of the fuselage alignment. So are fuselage formers F-2, F-3 and F-6. These four parts form the basis of the fuselage’s locking alignment. They have to be perfect or the fuselage will have a twist. You do not want that. All four parts are laser cut and accurate.

Compare these parts against the plans and mark the top and front side of each. You do not want to accidentally install these parts as there own mirror image. The fuselage might still be straight but the pushrod, engine mount and nose gear bearing mount holes will be reversed. So, mark them now to avoid getting it backwards in the heat of gluing.

Photo 2

Photo 3

The idea is to prepare all the required mounting holes in the firewall before installing it. The first step is to draw a vertical centerline on the firewall. In this instance, the firewall is 3 inches wide so 1.5 inches is the center (photo 2).

Next, measure the engine’s crankcase width with a caliper as in photo 3. Our engine here is the very powerful and, most importantly for a trainer, extremely reliable O.S. Max 46 AX. Its crankcase, measured just under the mounting lugs, is 1.342 inches wide. Half that distance is .671 inches.

Photo 4

Photo 5

Use the caliper’s “inside” measure legs and make some marks that distance from the center line on each side. SIG did much of the work on this for you, but the final mount spacing is up to the builder. Loosely install the four mounting bolts and blind nuts into the two engine mounts. Then align the mounts along the two lines you drew. Make sure the mounts are equally spaced along those lines. The engine should be exactly along the centerline as shown in photo 5.

Photo 6

Photo 7

Tighten the four mounting bolts just a little to temporarily lock them in place and then remove the engine. Place the firewall on your level, flat building surface and check that the mounts are both level and square. The level should fit flatagainst both mounting beams with the bubble centered. Once aligned, tighten the mounting bolts so the blind nuts penetrate fully into the wood.

Test fit the nylon nose wheel bearing in place. Again, only tighten the nuts enough so that the blind nuts just barely penetrate the rear of the firewall. Install the nose gear wire in the bearing and insure it is 90 degrees to the firewall bottom. Then tighten the bolts to fully install the blind nuts. Unbolt and remove the nylon nose gear bearing.

Remove the engine mount bolts. Permanently install the eight blind nuts by applying thin CAA around the nuts from the rear of the firewall. Do not get any adhesive on the interior threads.

Photo 8

Photo 9

After the CAA has dried, re-install the engine mounts. Check again with the level to insure the beams are still square. If the mounts were correctly installed, they should be even with each other. Put the firewall/mount assembly into a vise as shown. Use a drill press vise if you own one as this step is in preparation for using a drill press. I do not have such a vise so I use a small regular one instead.

Make sure the beams are level and at 90 degrees to the vise head. Use a small square if you need to. Next, insert the engine into the mount. Position the engine such that the thrust washer, the spinning piece the propeller bolts against, is 4 3/8 inches from the firewall (for this airplane). This allows for propeller clearance from the cowling.

Photo 10

Once the engine is in position, use a Great Planes “Dead Center” Engine Mount Hole Locater (Part No. GPMR8130) to locate one, and only one, engine beam mounting hole into the engine mount (photo 10). After marking, actually a pilot drilling, the hole, remove the engine. Use a drill press. If you do not have one, borrow one or buy an inexpensive one. I bought my $19.95 “cheapie” 40 years ago and it still works fine. It is nearly impossible to drill engine mounting holes correctly without a drill press.

Use a number 37 drill. Do only one hole at a time. The mount is then tapped for a 6-32 socket head bolt one-inch long. SIG provides 6-32 bolts that are slotted. For engine mounting, try to use only socket head bolts as slotted heads cannot be made sufficiently tight and usually do not last. A socket head bolt accepts an Allen Wrench instead of a screw driver.

Photo 11

Tap the hole using a 6-32 tap. Yes, I know that a No. 36 drill is the commonly recommended drill size for a 6-32 tap. If you are using an aluminum mount, then use the no. 36 drill. But this is a fiberglass composite mount and softer than metal. Using the smaller hole extends the mounts life as it better resists vibration with the tighter bolt fit. The tighter fit also resists loosening better. You can not use locking compound on a fiberglass mount as that compound usually damages the mount. Fiberglass “grips” better than metal anyway so even if a locking compound could be used, it would be superfluous.

Photo 12

Drill one hole at a time, removing the engine after marking each new drill spot. It is tempting to mark all three drill spots, drill the holes and tap them at the same time. This sometimes works but usually sends you to the hobby shop for a replacement mount. Go slowly here and you will save much time and gasoline. For reasons unknown, even this precise method still can cause a hole to “wander” just a touch. Maybe it’s my cheapie drill press, who knows? Doing one hole at a time has always worked well. Finally all four holes match and are complete as in photo 12.

Building the Fuselage

Photo 13

Now, after all that hard work, remove the engine and the mounts from the firewall. Put them aside until after the fuselage is ready for hardware installation. The firewall itself is used in the fuselage construction. The fuselage sides are made of 1/8-inch light weight plywood and have a “doubler” or second side that is laminated inside the main fuselage side. Photo 14 shows that the doubler extends from the firewall rearward past the rear of the wing saddle.

Notice in photo 13 how the two fuselage sides and doublers are laid out on the bench. They are positioned as mirror images of each other. This is important. The fuselage sides and doublers are identical until laminated. Then they become very different as one is a left side and one a right. It is important to make one of each, not two left or two right sides. Think that is impossible? How could anyone ever do something that dumb?

I doubt that there is a kit builder with more than a few builds in their experience who has not made, or almost made, that fatal error at least once. Avoid this problem by laying out the sides and doublers as shown. Carefully label all four parts as right and left.

In Part One, the Great Planes metal magnetic building board was used to construct the wing. While this is a great surface for building, not everyone has one of these excellent building aides. The more traditional building surface is the redwood shelf. Redwood is used because, if you locate a straight shelf, it will not warp over time. Redwood also self heals from all the pin holes. It is soft and readily accepts and holds the pin clamps used in this construction method.

Photo 14

The SIG LT-40 has a one-piece fuselage side but also employs a short front fuselage extension. Lay one side out on the building board as shown over a piece of parchment paper that is under the area to be glued. Pin clamp it in place so it lies perfectly flat. Locate the nose extension and test fit it to the fuselage side.

Make sure the parts fit tightly against all the gluing surfaces. This airplane required a very light sanding on the two edges as shown in the photo. (Click on it to enlarge the photo) Once the fit is tight along all edges, it is time to glue the parts together.

I guess that means it is time to discuss adhesives. Remember these are just my opinions but I have built more than a hundred wood kits over the past 40 years. Here are my adhesive recommendations:

ª Use aliphatic resin, wood glues, whenever the adhesive will find its way to an exterior area or must be sanded. CAA adhesives are tough to sand and trying to do so usually results in gouging the surrounding wood.

ª Use wood glue on parts that need time to be properly aligned.

ª Use medium CAA on parts that can be locked in place and then have the adhesive applied, such as wing ribs and fuselage sides to formers.

ª Use epoxy in areas requiring high strength such as firewall mounting, stabilizer/fin installation and wing mounting systems. Medium CAA does not sink far enough into the wood to provide maximum strength in such high stress areas.

Well, those are my ideas. SIG recommends using medium CAA on everything so we do differ. If you do use only CAA, avoid getting any on the surface areas. Also, when installing the bolt-on wing mounting system, use only 12-minute epoxy as using CAA here will result in two pieces, the wing and the fuselage, landing separately.

Apply wood glue to both fuselage side pieces and pin clamp the extension in place as shown. After about 20 minutes, remove only those pin clamps that are in the areas that will be covered by the doubler. Leave the remaining clamps in place.

Photo 15

Lay one doubler over the corresponding fuselage side. Use the wing mounting dowels as alignment guides as shown. Draw in the areas that will not be covered by the doubler. Insert some pin clamps in only those areas to hold the fuselage side tightly against the building board.

Photo 16

Mix up some 12-minute epoxy in a measuring cup (available at hobby shops or saved from old NyQuil® bottles; they are identical) and place the mixed epoxy in the ice bath as shown. Epoxy set times are somewhat dependent upon heat. When mixed in larger quantities, epoxy often heats up and sets far more quickly than its labeled time. Avoid this by using the ice bath to extend the set time.

You could use a slower epoxy, such as 30- or 2-hour epoxies, but their cure times can sometimes be overnight. That is too long for just laminating a doubler to its fuselage side.

Photo 17

Use an epoxy brush and brush the adhesive over the correct doubler side. Notice how the side being laminated is still oriented against the remaining un-worked side in the photo. This is to avoid making the same fuselage side twice. Align the doubler, the wing dowels help here, and then laminate the doubler using pin clamps as shown. Once the pin clamps are in place, remove the dowels to insure that they are not accidently epoxied in place.

Photo 18

Photo 19

Once both sides are made, lay them on top of each other with the interior sides facing inwards. Use some combination squares to align the sides. Then tape the rear together (photo 19). The masking tape is nearly the same color as the wood so there are a few pen lines drawn on the tape for better photo visibility.

The next steps apply only to box lock type constructions. The idea here is to assemble the entire fuselage, hold it together with rubber bands, and then glue it all together.

Photo 20

The sides and formers have plywood tabs that lock the fuselage parts into a straight, cohesive unit that can then be quickly glued into place using medium CAA. Start by inserting the firewall and fuselage formers 2 and 3 between the fuselage sides. Then hold this assembly in place with several #64 rubber bands. Make sure that the formers are correctly oriented. That is why you labeled them as directed so long ago. Get it right or the pushrod holes will not align.

Use the wing dowels once again to help with the alignment and to hold the sides in place while you install the formers and the rubber bands.

Photo 21

Now install the remaining formers. Use the plans to identify which one is placed where. If you ever have any questions, always refer back to the plans. One rubber band note here: Make sure that the rubber bands are flat, not twisted, across the bottom of the fuselage assembly. If they are twisted, this could cause a slight misalignment.

Photo 21A

Cut the rear tape and insert the stabilizer platform. This part is necessary for alignment but will not yet be glued in place. The same is true for the windshield, the gear mounting block, the rear wing saddle brace and the fuel tank floor. Install them now but do not glue them in place. Hold the fuselage rear together using rubber bands.

Photo 22

Photo 23

Make sure the gear block fits tightly in place, and then remove it for now. Insure all the tabs are locked in place. Position the fuselage on the building board and check it for straightness and alignment. This airplane was perfect.

With everything in its place, lay the fuselage on its side against the building board, the dowels will move upwards and out of the way, so that the interior is facing you. Press straight downwards on the top fuselage side at the F-2 former location. The entire fuselage will lock into place. While still holding the fuselage pressure, apply some medium CAA to the middle of the F-2 bottom fuselage side joint and let dry.

Turn the fuselage over with the side you just glued facing upwards. Apply the same pressure to this side and glue that side of F-2 to the side. Apply pressure to the fuselage side at F-3 and also glue in place. Turn the fuselage over and glue the other side of F-3 in the same way.

Turn the fuselage upright on the building board. Make sure the fuselage is still straight and then glue in the bottom of the remaining rear formers while holding the fuselage against the building board. (Now you know why the rubber bands can’t be twisted on the bottom.) Apply medium CAA to all the rear former joints. Remember, do not glue in the stabilizer deck.

Photo 24

The firewall is installed next using 12-minute epoxy. Mark where the fuselage sides meet the firewall (photo 24). Spread the sides slightly and remove the firewall.

Photo 25

Apply the epoxy to both fuselage sides and the fuselage bottom. Install the firewall checking its alignment. Once properly aligned, clamp the fuselage against the firewall as shown. The weight insures that the fuselage stays square against the building board.

Before the epoxy hardens, use a hobby chisel blade to remove any excess epoxy from the joints. For extra strength, triangle stock will be epoxied in place later to firmly lock the firewall against the sides and bottom. The triangle stock supplies extra gluing area for increased strength in this critical area.

Once the epoxy cures, remove the clamps and the fuel tank floor. This allows access to the front sides/bottom joints. Hold the fuselage against the board and glue the bottom to the both sides. Make sure the rear formers are glued to the fuselage top. Remove the rear wing saddle brace and glue all those areas.

Caution: If you are installing the bolt-on wing system, do not apply any CAA to the top one inch of the front of F-3 nor to either side of the top one inch of F-2. Triangle stock and other structures will be built in these positions.

Bolt-On Wing Mounting

Photo 26

Draw a center line on the top of F-2 as shown. Do the same for F-3.

Photo 27

Place a piece of 4-inch wide nylon reinforcing tape along the wing saddle as shown. This tape is part of the wing reinforcing system and will be applied later to the wing center section. But allowances for its thickness must be made now.

Photo 28

Lay the wing in position, making sure the tape remains in place. Align the wing’s center joints with the fuselage center marks. This centers the wing on the airplane. The final alignment will be checked later. For now, make sure the front wing joint is aligned with the fuselage center mark. Hole the wing firmly in place and use a pin vise to drill a 1/16-inch hole through F-2 and into the wing center as far as possible.

Photo 29

Remove the wing and gradually increase the F-2 hole’s diameter using successively larger drill bits. Wear an old pair of gloves and rotate each drill bit by hand to prevent damaging F-2. Continue the process until the hole is a tight fit for a 5/16-inch hardwood dowel.

Photo 30

Use a 1/8-inch ball drill bit on a high speed rotary tool and drill out the hole you made in the wing’s leading edge. Make sure the ball bit follows the 1/16-inch hole you drilled.

Photo 31

Use the same process of hand drilling with successively larger drill bits and drill out the center ribs. Continue until the hole is at least 1 and 1/4-inch deep and is a tight fit for the dowel.

Photo 32

Using some of the scrap light plywood, this kit provides a lot of scrap light plywood, trace the front of rib W-1 from the plans and make two front rib copies. Note that the inside of the new front ribs, called “false” ribs, have been relieved slightly to make room for the dowel. Do this with the ball cutter on your high speed rotary drill. Only relieve as much wood as is required to clear the dowel. Try not to totally remove the inside layer.

Photo 33

Photo 34

Test-fit the wing to the fuselage and push in the dowel from F-2. Remember to position the reinforcing cloth. The wing should still lie flat against the saddle and be exactly centered. If not, make the necessary corrections.

Remove the wing and epoxy the two false ribs in place using 5-minute epoxy. Clamp in place until the epoxy cures. While the epoxy is curing, slide the dowel into the center hole and insure that it penetrates all the way. Then remove the dowel to prevent epoxying it in place now. That comes much later. Doing this removes any epoxy that might have entered into the dowel hole.

Photo 35

Photo 36

Now that the front wing mounting dowel is positioned, the top wing sheeting can be installed. For me, sheeting a wing using CAA is always difficult. There are many opportunities to misalign the sheeting or to have parts of it raise away from the ribs. I always seem to take advantage of these opportunities and usually ruin the sheeting job.

So I use wood glue instead. Apply some wood glue to the top rear of the leading edge and to the ribs. Pin clamp the sheeting front in place as shown. Work backwards pressing the sheeting firmly against the ribs and pinning in place. The finished job should look like photo 36 as the glue begins to dry.

Photo 37

Purchase two maple blocks, 1 x 3 inches, at your hobby shop. The blocks are usually used for engine mounts. If you can’t find the precut blocks, buy a 12-inch piece and cut to length. Epoxy the blocks to the top rear of the fuselage as shown. The blocks must be level with the slot for the rear wing saddle brace as this part will cover the blocks. Use 12-minute epoxy. Clamp the blocks in place.

While waiting for the epoxy to cure, carefully turn the fuselage over and scrape away any excess epoxy from the contact areas. These areas will be braced with hardwood and so must be able to fit squarely into the joint areas.

Photo 38

Photo 39

Once the epoxy cures, remove the clamps. Working from underneath and through the top, epoxy a piece of 1/4-inch spruce hardwood as shown against the bottom of the blocks where they join F-3.

It is getting difficult to find hardwood triangle stock so I cut mine from short lengths of 3/8-inch square hardwood. These brace the block/ fuselage side joints as shown and are glued in place with epoxy. You can use the square 3/8-inch spruce if you wish.

Photo 40

Photo 41

The final brace is the stock wing saddle brace. Install it using 12-minute epoxy and weight it in place until the epoxy cures. There is no flight stress sufficiently strong to pull those blocks out of the fuselage. Each is epoxy-braced top, rear, side and bottom.

Photo 42

Mark the inside block edges on the top of the fuselage by the rear wing saddle. The mounting hole will be drilled in the center of the distance from this mark to the fuselage side.

Photo 43

Photo 44

Position the wing in place and transfer those marks to its rear top. Then, move the mark forward to the rear spar. The drill point is in the middle of the spar at this mark. Don’t worry about the hole’s weakening the spar as this installation actually strengthens it. Drill the hole to tightly fit the outside of a 1/4-inch fiberglass pushrod (hobby shop again). The inside dimension should be 1/4-inch which is the size of the 1/4 x 20 nylon bolts used to bolt the wing in place. The outside dimension is usually 0.3 inches.

Gradually enlarge the hole through the soft balsa as was done on F-2. Stop when the arrow shaft just fits. The hole should be at a slight forward angle to the wing to allow the bolt heads to fit flush against the wing top. Slip a bolt into the hole now and make sure it is flat against the wing top. If not, remove the arrow shaft and adjust the hole until it is.

Make a 1-inch or so plate from scrap light plywood and drill it out to accommodate the arrow shaft. Slide the plate over the arrow shaft and against the wing. Draw around the plate and then remove the assembly.

Photo 45

Photo 46

Use a cutting bit to remove a little balsa from the plate area to a depth of 1/8 inches. This allows the ply plate to be countersunk into the wing so it becomes invisible after being covered. Do not remove too much balsa or the area will have to be filled. The top of the plate should be level with the top of the wing skin. Test fit that the dowel fits through the hole.

Photo 47

Do the same for the other side of the wing top. A suggestion: If I had it to do over again, I would have continued the plywood plates all the way into the wing center section. This used to be my standard procedure and should have been done here. But I claim a senior moment here as I forgot my usual practice. I don’t know why as it has only been six years since I last did this modification. Regardless, continue your plywood plates all the way to wing center.

Once the plates are installed, cut two arrow shaft pieces to fit using a hobby razor saw. The ends should be flush with the top and bottom of the wing. Glue in place with medium CAA.

Photo 48

Converting a rubber band mount to bolt-on has one advantage. The rubber mount system can be used to hold the wing’s position during the alignment and drilling procedures. Slide the two dowels in place and mount the wing onto the fuselage.

Photo 49

Photo 50

Align the wing center in the rear with the F-3 center mark. Insert the dowel through F-2 and all the way into the wing. Make sure the wing center is aligned with the F-2 center mark.

Photo 51

Photo 52

Install a large building pin in the middle of the fuselage rear as shown. Then measure from that pin to the inside of the outside wing rib. Now, measure the other side. The two measurements should be identical. Both distances were 43 and 3/8 inches. So far, the fuselage seems to have been built straight. When the center mark alignment matches the actual wing alignment measurements, it is usually a very good thing. For added alignment security, pin the wing’s trailing edge in place.

Photo 53

Photo 54

The 1/4-inch outside diameter brass tubing has the perfect inside diameter to match the No. 7 drill bit normally used for a 1/4-20 tap hole. Slide the tubing into the arrow shaft just enough to be firm. It is a tight fit and it is not a good idea to pull the arrow shaft out of the wood when trying to remove the brass drill guide.

Photo 55

Drill one hole through the guide and into the maple mounting plate. Make sure not to move the wing and spoil the alignment. Remove the drill and, with the wing still in place, tap the hole for the bolt. Then screw the bolt in place. Do only one bolt at a time to best preserve the alignment. Then repeat for the other side.

Photo 56

If you are careful, the wing will be aligned as shown in photo 55. This process is easier than it sounds and is good experience when re-aligning a damaged ARF wing.

Photo 57

Photo 58

Cut two pieces of scrap light plywood to fit between the fuselage sides at F-2 and to extend down to the former’s fuel tank opening. Epoxy them together. Drill a hole to match the one in F-2. Epoxy these braces to the front of F-2 as shown. Pass the dowel through the hole to make sure the pieces are well aligned.

Photo 59

Cut a short piece of the stock wing dowel and fill the two front wing dowel holes. Both the interior and exterior dowel edges must be flush or slightly recessed into the fuselage sides.

Photo 60

Epoxy two short lengths of 3/8-inch hardwood triangle stock (made as described previously) in place as shown. Make sure that these pieces are mounted low enough and do not interfere with mounting the windshield. Do the same on the other side of F-2. Again, do not interfere with the wing’s seating on the fuselage.

For extra insurance, cut a small piece of 3/6-inch regular aircraft plywood, drill the hole and epoxy it in place as shown. The small missing light plywood pieces will be replaced with epoxy and micro balloons when the windshield is installed. Sand the small plywood piece so that the windshield will fit as designed. I added this small reinforcing piece because the dowel hole in F-2 is more toward the top than I would have preferred since the airplane was not designed for this type of mounting system.

Here is some philosophy. If this article were not designed for first-time builders, I would have made a replacement F-2 out of 3/16-inch aircraft plywood. Replacing parts with lighter or stronger ones that the builder produces is one of kit building’s greatest advantages. However, this aircraft uses locking type construction and all the alignment is based off of the F-2 former. Therefore, the new F-2 must be an exact replica and that could be difficult even for experienced builders to replicate so perfectly. So, I reinforced the stock F-2 instead.

Photo 61

Photo 62

This airplane used the locking construction to insure a straight fuselage. It is a fast and accurate system. But most aircraft kits and all the older kits you might want to try building, do not. How are these fuselages assembled?

The more traditional fuselage construction strongly resembles how the wing was built in Part One. Lay the top view fuselage plans on the building board and cover them with parchment paper. Use a straight edge and extend the former positions out past the fuselage bottom (photo 62.

Photo 63

Photo 64

Position the fuselage floor over the plans and pin clamp it in place. Using the marks you made on the plan, draw the former positions on the bottom piece. Layout both fuselage sides, one at a time, next to the fuselage bottom and mark the former position on them to match the marks you made on the bottom. Use a “T” square and continue those lines all the way up the fuselage sides.

Photo 65

Put the sides aside for now. If the fuselage sides are located on top of the bottom, make two small false fuselage sides from balsa the same thickness as the side; about 3 inches square. If the sides just butt up against the outside of the bottom then forget this step.

Using a few combination squares, position and glue each former in its place on the bottom. Use the false sides to indent the formers the correct amount if the sides are designed to glue on top of the bottom. Once the formers are firm, install one side making sure that the formers are vertical, use those squares, and aligned with the marks you made in the previous step.

Remember, glue or epoxy all the formers on the bottom first, then assemble each side with adhesive. Don’t forget to apply glue to the side/bottom joints. Once the fuselage is assembled, do not add the top until all the pushrods are installed.

This airplane’s locking construction made it impossible to illustrate much of this more traditional construction as the protruding tabs always got in the way. The tabs had to remain so the locking construction could be used. Locking construction is a big improvement and if you can use it, by all means do so. It is faster and superior to the more traditional construction method.

Building the Tail Feathers

Photo 66

Photo 67

The mission is to turn the sticks in photo 66 into the stabilizer and vertical fin in photo 67. This is a far easier task than these photos lead you to believe. The only tools needed are a razor saw, a matching miter box, a sharp hobby razor knife, wood glue, parchment paper and a legion or two of pin clamps.

Photo 68

Photo 69

Layout the stabilizer plans on the building board. Cover them with parchment paper as usual. The stabilizer’s trailing edge is always the most critical. Pin it in position first using the trailing edge line on the plans. Make sure you have it perfectly straight using a metal straight edge (photo 68).

The next most critical piece is the front angle piece. Pin it in position as shown. Use two long sticks on the front to check the alignment. After the front is pinned in place, butt the sticks against the piece’s leading edges. Both sticks should follow the plan all the way to the plan’s ends. If they do not, reposition the front piece until they do. Then firmly pin clamp the front piece in place.

Photo 70

Then install the middle piece. I used wood glue here since the finished stabilizer needs to be sanded. If medium CAA was used as directed, sanding will leave many flat spots and ridges. First, fit the center piece in position. You may have to lightly sand one edge to get a good but tight fit.

Once the fit is confirmed, apply the wood glue to the piece ends and to the trailing edge and front piece. Wait about a minute for the glue to sink into the wood pieces. Then position and pin clamp the middle piece in place. Wipe off any excess glue from the top.

Photo 71

Position the first 5/16 x 1/2 inch leading edge stick, with glue in the appropriate places, in place against the front piece. Pin clamp it along its length and use the razor saw to cut it to length. Mark the front angle as shown and cut it using a very sharp hobby razor knife. We’ll worry about sanding the front tip flat when the stabilizer is being installed. Repeat for the other side.

Photo 72

Photo 73

There are two ways to cut the sticks and their angles. For the wider sticks, the outside edges, I prefer to lay the razor saw against one piece already in position and cut the new angle. For smaller pieces, the interior sticks, I mark the position and then cut slightly outside my mark. Then I fit the interior piece using light sanding as necessary. Pin and glue all the exterior pieces in place.

All of the interior gluing will be to end grain balsa wood. There is a gluing technique for this. Apply a little glue to the end grain first. Wait a minute or so for it to sink into the balsa. The wood glue will turn a darker color. Then wipe off the glue you just applied and apply another dose. Now pin clamp the piece in position.

The first glue application penetrated into the wood grain. The second glue application rewets the now penetrated glue and bonds the whole assembly. This bond is much stronger than just a butt gluing.

Glue in each stick until the stabilizer is completed. This is a faster operation than it appears. Allow the assembly to dry for a few hours and then remove it from the plans.

Photo 74

Photo 75

Photo 76

Photo 77

Building the vertical fin follows the exact same procedure. Photos 74 through 77 illustrate some of those building steps. Always remember, start with the exterior pieces first and then add the interior ones.

Do not worry about fitting the rudder and elevator at this point. Before they can be matched and hinged, the stabilizer and vertical fin will need to be filled and sanded to “covering condition” and that will be covered in the next installment. Part Three will cover finish sanding the airplane and installing the hardware. Part four will cover the covering task and final assembly. See you then.