This is the build article ralated to an earlier article "One Sheet No-Waste Twin Tail Boom Series". The basis for the series is to develope several designs all using one full sheet of Dollar Tree foamboard and one 3/16" X 36" dowel cut in half to make a twin tail boom. That article gave an overview of five versions of the concept. I chose #3 for this build article because it has the best over-all flight charactoristics. It is suitable for a pilot with moderate 4 channel experience.
This design has fairly short tapered wings with a long wing chord, large ailerons and generous camber. It is capable of good slow flight charactoristics as well as moderate aerobatics with the right power.
Update 9-30-15: This is a picture of the prototype after a summer of flying. It has spent a lot of hours in the back of a hot pick-up so the paper is a little delaminated in spots but otherwise she has passed the test of time. The orange and yellow are oil based spray paint. The black is colored duct tape.
(end of update)
This picture shows #3 on the left and #4 on the right.
Update 1-10-15: There are two wing options shown on the plans, wing "A" and wing "B". On the left above, #3 is the one featured in this article. It uses wing "A". The one on the right, #4 uses wing "B". They use the same foamboard blank. The difference is whether the taper is on the laeding edge or the trailing edge. As you can see it makes quite a bit of difference in the appearance.
(end of update)
Here are the plans:
This is a pdf. You should be able to click on it and print the full 8 1/2 X 11 drawing so you can work with it on your building board.
I just did a simple pencil sketch on an 8 1/2 X 11 sheet since it is fairly easy to transfer the dimensions to the single sheet of foamboard.
The plan shows two wing details that can be made from the same wing blank. The difference is whether the taper is at the front of the wing or at the back. Design #3 has back taper so we will be making two of Wing "A" for this build.
Note: Foamboard sheets are theoretically 20" X 30" but frequently vary by about 1/8" either way (my current stack measures 20 1/8" X 29 7/8" ) . I have shown some dimensions with "+/-" noted. If the sheets are not exact the discerepancy should be allowed to go into the +/- dimensions.
We will start by marking off the major dimensions along the edges of the sheet. On one 20" side mark the 4 1/2" dimension. The remainder should be 15 1/2 (+/- 1/8"). Next mark off the 7 , 11", 6" and 24" dimensions. There should be 6" (+/- 1/8") left at the bottom for the tail section.
Take a straight edge and cut off the tail section. On tne tail piece measure 4" up from the corner on each 6" (+/-) side and the center of the top edge (10" +/- 1/8"). Cut the two 2"(+/-) X 10"(+/-) tapered pieces off (scrap).
Next mark the 4 1/2" dimension at the bottom LH corner of the remaining big piece for the other end of the wing bottom section. Cut the wing bottom section off. On the wing bottom piece measure 12" on both 24" sides and cut the wing bottom piece into two pieces 4 1/2" X 12". Measure 1 1/4" along the 4 1./2" side on one end of each piece. Use a straight edge alligned with the mark and the corresponding opposite corner to cut off the long tapered piece (scrap) on each.
Then mark the 11", 7' and 6" dimensions on the other side of the wing piece. Using the marks, cut the two wings and pod out. Note that the 11'" and 7" positions are reversed side to side to make the wings taper.
When you get done you have all of the major parts cut out. It should look like this:
Update 12-27-14: Take the 6" X 15 1/2" piece above and cut into two pieces, one 6" X12 1/4" (pod), the other 6" X 3 1/4" (motor mount support. This step was missed in the original article.
Next we will take the two wing panels and stack them. They should be exactly the same, but if not trace the smaller one onto the larger one and trim as needed. Do the same with the wing bottom panels.
Wing fold layout:
Take one of the wing panels and lay it down as shown on the drawing. Measure and mark the two 2 1/4" and two 1 3/8" dimensions. Take the two wing panels and butt the 11" ends together. Transfer the 2 1.2" marks to the second piece. Like so:
Then do the same with the 7" ends. These marks will be used later to score for the wing camber folds. (These look uneven at the leading edge but they are not. One panel is curled up and the other down.) It is important to match up the leading edges exactly.
Measure 5 1/2" from the 11" end of each wing panel along the leading edge and near the trailing edge.
Note: The measurement at the trailing edge is not measured along the taper but square off of the 11" side.
Allign a ruler with the two marks and with zero at the trailing edge. Put a mark at 2 1/4" and draw a line from the mark to the trailing edge. This will be the cut at the inboard end of the aileron. Do the same on the other wing panel. Like so:
Next mark the 1 1/2" dimensions from the trailing edge at each wing tip.
This compeletes the Aileron layout (to be cut later).
Scoring the wing folds:
Use a long straight edge to score the two wing camber fold lines on each wing. You do not need to go very deep, just so you cut through the paperand maybe half way through the foam. Like this:
Then use a rounded object like a pen tip to deeply crease each score line. Go over it two or three times. You should depress the foam all the way to the paper on the other side without damaging the paper. This should be done on a hard surface Like so:
Make sure your creasing device has a smooth, well rounded end and that you are working on a hard surface.
Adding the wing bottom panels:
Lay the two wing panels down with the creased sides down. Allign the wing bottom panels very carefully with the corner of the wing panel. Hold the joint tight and fasten with a short piece of Scotch tape on each end. Then tape the full length of each joint with packing tape. They should look like this:
Note: The two square corners of the bottom panels go toward the wing panel.
Cutting and installing wing spars:
From scrap material cut 4 pieces 11" long that are 3/4" wide at one end and 1/2" wide at the other. Then stack them together to check uniformity. If they are not exactly the same either trim, sand or re-make till they are. Like so:
They do not need to be exactly the same length but they should be the same thickness. If you can see or feel a difference it should be corrected. These are the spacers that define the wing shape and uniformity is important.
Next the spars are glued to the center sections of the wing panels. Hold the ends about 1/8" from the center of the wing and close to the crease lines. Apply a bead of glue to one edge of the spar and then position it, adjusting the position before the glue sets. Run another small bead along one side of each spar. The completed installation should look like this:
The 3/4" ends are toward us which is the center of the wing.
Cut the leading edge bevels:
After the spars are installed (actually can be done before or after) the leading edges need to be back-cut at approximately45 degrees on each panel to allow the leading edge to form properly. This is done per the standard FT method. Pick the wing up and fold the bottom panel completely back against the wing panel. Make a small cut on the wing panel at the end of the botton panel so the bevel cut will stop there. Back cut both edges on both wings like so:
Be careful not to cut the tape. Note the small cut that controls the end of the bevel on the wing panel.
We are now ready to form the wings into their final shape. Start by pre-stressing the folds. Place the wing bottom panel on the table and fold the wing over with steady even pressure till both spars are in contact with the bottom panel. Hold even pressure to allow the wing to take it's final shape. Like this:
Unfold the wing and apply an even bead of glue to the two wing fold creases (only). The amount of glue should fill the cut portion of the crease with a little overflow, not the entire depressed area. Do not apply glue to the leading edges or spars yet. Quickly re-fold the wing to it's final position and hold for about a minute till the glue sets. Unfold. I t should retain the upper wing surface shape like this:
Note that the ailerons are still not cut yet because the trailing edge needs to be firm during this process.
Next apply a generous bead of glue to the leading edge and along the edges of both spars. Work quickly so the glue stays hot. Quickly fold the wing back to the final position. Hold firm presssure for at least a minute with two hands to assure that both spars remain in contact with the bottom panel till the glue sets.
This process has formed a box spar which is very strong. From the end it should look like this:
There should not be any gaps beteween the spars and the top or bottom wing surfaces anywhere along the length of the wing. If there are gaps you can put a bead on the last two inches or so of a skewer and reach in to fill the gap. Hold pressure till it sets.
Complete this entire process on both wings.
If the wing cuts and assembly were done carefully the joining should be very easy. The process of folding the top siurface should have made a natural angle that will produce about 3 degrees of dihedral angle without any trimming. To check this we will do a trial fit.
First lay the two wings flat on the table right side up with the 11" ends touching. The bottom surface should touch for it's entire length. The top surfaces shold touch at the leading and trailing edges. The center of the top surfaces should be gapped about 1/8" or a little less. It should look like so:
If this looks OK try raising one wing till the center gap just closes. The tip should be about 1 1/2"above the table. You can use a paper towel roller or something similar to hold it up while you check.
If the gap is not uniform or the bottom does not come together you can trim by standing it on end and running it over a piece of 120 grit sand paper till it does. Take a little off of each side till the fit and angle are good.
When the fit is good turn the wing panels over and tape the bottom joint. Allign the leading edges carefully and use Scotch to hold the joint tight. Then apply packaging tape over the whole joint. Do not let it wrap around the leading edge (yet). Turn the wing over and unfold it to about 90 degrees. Quickly apply a moderate bead of glue to all mating surfaces and fold the wing back together. Use the roller again to support the raised tip and keep pressure on the top joint till the glue sets. Immediately squeegee the top surface with a scrap of foam. Push and pull the top surfaces slightly as needed to get them to allign as perfectly as possible.
Note: I use a heat gun and small pie lifter to "iron" my glue joints before appying tape. It is not necessary if you squeegee well but it does make smoother joints. Like this:
You may also have to smooth the rear part of the bottom side of the wing since glue will push out both sides.
Next apply two layers of tape over the joints top and bottom. Allow the tape to extend over front and back about 1", split it with a knife so it will not wrinkle and fold it over the other side. If you do this you will have 4 layers at the leading and trailing edges. Very strong.
The wing after joining:
Next we have to cut the ailerons. Turn the wing over. The layout is already done. Use a straight edge to cut the 2 1/4" lines all the way through.
Move about 1/8" or a little less away from center and make a second cut parallel to the first to produce the aileron to wing gap. Then do the score cut from the 1 1/4 " mark to the 2 1/4" mark. This cut should be at least 1/2 way through the foam but not through the paper on the other side. Like so:
Fold the aileron all the way back and trim the 1/8" piece out. Then do a 45 degree back cut on the front edge of the aileron.
Check the movement of the aileron. It should swing down about 30 degrees with little or no resistance.
Repeat this process on the other side.
The completed wing:
Take the tail section blank and measure a pair of marks 5 " in from each end, one near the leading edge and one at the trailing edge. Make score cuts on each pair of marks. This is the dividing line between the horizontal stabilizer and the vertical stabilizers.
You can measure 5" at two spots and connect the dots...
...or you can use the grid markings from the cutting board. Just line the piece up with the grid, count squares and line the straight edge up with the grid. This method is very good for keepig everything straight and square.
Measure 1/2" from each corner at each end:
Cut from the 5" score marks to the 1/2" marks on all four corners to make the tapers on the vertical stabilizers and rudders. It should look like this:
The tip of each rudder should measure 3". Find the center and mark 1 1/2" on both
Use a straight edge between the two 1/1/2" marks to draw a short line about 1" each side of both of the scored lines. This will be the limits for the rudder and elevator clearance cuts:
Make two pairs of reference marks at 1/2" toward the tips and 3/4" toward the center
Make two pairs of double cuts all the way through, one on the two reference marks and one about 1/8" away from the scored lines each way. This is showing the right side with the 1/2" marks for the rudder to the right and 3/4" marks for thre elevator on the left:
Use a striaght edge to score the two rudder hinge lines
Note: This is from a previous build with the bevels already cut at the score lines.
Flip it over and make two 2" marks for the elevator score line (opposite side from rudder hinge score cuts).
Then score the elevator hinge line from one clearance cut to the other (still opposite side from the rudder score cuts:
With all the score cuts done it is time to cut the bevels. First do a double bevel at the first two score cuts (separating horizontal and vertical stabilizers). Then do singal bevels on the front edges of the elevetor and rudders. The piece ready to fold should look like this:
Note: This is from a previous build where I made the elevator hinge cut on the top. It's not a big deal but it should be on the bottom for appearance sake.
Making the rudder folds:
First do a trial fold to verify that they wil go to 90 degrees. Trim if needed. Then spread a thin bead of glue in the bottom of the "V" and a generous bead along one side. Fold to 90 degrees and hold with a triangle or square cut scrap of foam. Immediately squeegee any excess glue. Hold about a minute till set:
Same thing for the second side:
Run a small bead of glue in each fold crease and squeegee again if needed. I usually just use the gun tip to smooth it out and leave it at that.
The tail is ready now for assembly.
Fuselage (Pod) Construction:
Take the 6" X 12" "Pod" piece and mark 2" increments on both 6" ends. Then mark 3/16" toward the middle from each 2" mark. Score all 4 lines. Remove the 3/16" strips. It should look like this:
The middle strip measures 1 5/8" and the two sides are 2" each.
Use a scrap to make a template matching the leading edge of the wing. Do a rough cut and trim as needed till it fits tight at 1" from the wing joint. Measure 1" in each way from the corners of the 6" side on each end. Hold a ruler on ona pair of marks with zero at one end and draw a 4 1/4" line. Also make a mark about 1/4" long at 4 1/4" point going away from the center strip. Line the template up with the 1" line with the rounded end at the 4 1/4" mark. Trace the rest of the wing profile as shown below. Do the same on the opposite side:
Then measure the 3/4" and 1 1/2"dimensions on trhe corners on the other end. Cut off the triangles and cut the wing notches; The piece ready to fold should look like this:
Next do the folds. This is just like doing a FT power pod with a "B" fold. The sides are beside the bottom plate. Use a triangle or square scrap to hold the sides square.
Check the two angles to be sure they are parallel. You can do this by sight or use a flat scrap of foam. Trim or sand if needed.
We are ready to make the nose:
First cut a blank 2" X 4" from scrap. Measure and trim 3/16" corner lap from 3 sides like so:
Fit the trimmed end into the nose end of the pod and mark the first corner.
Score the back on the marks and do a double bevel back-cut. These will be less than 45 degrees due to the nose angle. Reinsert and mark the second angle. Score and back-cut it as well to fit the second angle. The remaining piece should be about 7/8" and remains untrimmed. It will lay on top of the open side of the pod and be the point where the hatch will hinge.. Make sure everything fits well. Then go throgh the same sequence glueing one section at a time. You should put a light bead onn the foam and press the paper in using the table or a flat piece of foam so the paper stays flat. Glue the inside joints including the angles as you go. You will not be able to reach them easily later.
Ready to glue:
Glued: Note some loose edges of paper. No big deal. The taping of the nose will take care of that
I like to wrap the nose with two layers of tape to help it resist damage from nose bumps. This must be done in sections. I start by cutting a piece about 1 1/2" long and wrapping the back edge of the nose piece inside and outside. The hatch will be attached here later and it needs the reinforcement. Then cut pieces about 6" long and starting from the same edge lay them across the top, split the ends at the bends and fold them down over the sides. Some corners will lap onto the bottom helping to reinforce it as well. The narrow pieces will overlap on the sides due to the angle. Overlap about 1/2" on each piece. Go across the bottom to the back of the nose as well. These pieces should be long enough to cover the whole sides and can betrimmed at the top corner. Finish off with another layer on the top
I like to wrap a piece of tape over the top edges of the open sides from the nose back to the wing. Half the width goes outside and half inside. Start with the outside to avoid wrinkles there. These will be exopsed and take a lot of wear and tear. The tape will keep the paper from coming loose. You should also line the entire inside with tape to allow for Velcro attachments later. The hatch will be added later since it has to be fit to the wing.
The first step in assembly is attaching the booms to the tail. First cut the 3/16" X 36" dowel into two equal lengths. If they end up a little different trim the longer one to match:
Update 12-27-14: Dowel size originally listed as 3/8" above corrected to 3/16".
Check the dowels for straight. They usually have a small amount of curve in one direction. Put a small dot on the inside of the curve on one end.
Next we will glue one dowel to the bottom of each side of the tail, making sure that any curve is toward the center (Up as we glue). Start by placing the tail on end with one of the rudders on the table. You can put a weight on it if you like. Then place one of the dowels even with the back edge if the tail and tight to the table wirth the dot up. Put glue on one side and allow it to set. Pick it up and put a bead in the other side. Each side should have a full bead the full length of the dowel. I use the glue gun tip to form a nice bead:
Note a thin bead of glue filling the gap on the outd=side ofthe upper dowel. There is room ror a heavier bead on the inside. If you sight across the two dowels they should line up, not one up and the other down.
Next we have to attach the dowels to the wing.
First measure the distansce from out to out on the dowels at the tail. Mine usually end up at 10 1/8" due to the vertical stabiliizer folds. Take half of this measurement and put marks at the leading edge, near the back edge of the wing bottom and at the trailing edge of the wing. Hold a ruler on the two marks on the wing bottom with zero at the leading edge. Make a mark at 2 3/8" and a light line from there to the back edge of the wing bottom panel. The mark will be the forward end of the dowel (also the CG) and the line will be the outside side of the dowel.
Starting with one side, hold the dowel on line and the mark on the trailing edge with the tip on the 2 3/8" mark. Put enough glue to hold at the trailing edge and at the wing bottom. Hold till it sets. Place the dowels on the marks on the other side and glue them as well. Fill in continuous beads under the wing and a genreuos dollup al he trailing edge.
They should come out like this. They are parallel to the wing center joint and stop 2" before the leading edge of the wing.
Next take a couple of scraps and trace the triangle between the dowel and twing top panel. Cut the filler a little bigger than the tracing which tends to get small because of the limited space. Trial fit and adjust as needed for a snug fit. Glue the edge that touches the dowel and carefully install, rolling it into place. USe a wet finged to smoth the glue on each side. Then run a small bead in each side where it contacts the wing. This really helps to stiffen the dowel and about doubles the mounting strength.
The tail should be parallel to the wing like this.
Next we have to install the the pod. Start by making 4 marks on the wing bottom. Two at the leading edge and two at the back of the bottom panel. They should all be 1" from the wing joint. Slip the pod over the wing and allign with the four marks. Check the gaps all around. Trim if you need to to get a reasonably tight fit. If it looks good put small dabs of glue in the 4 corners and let it set. Check allignment again and if all is good run continuous beads of glue wherever you can access.
This shows the dry fit ready to glue.
The plane has now taken shape:
Next we have to add the hatch, motor mount and tail skids shown in this picture:
Ther hatch cover is a simple rectangular piece of foamboard with one tapered end. The width is 1/16" less than the pod opening. That may vary slightly depending on your folds so just measure and deduct 1/16". The length can also be measured directly from the pod. Cut the blank at about 1/2" longer than the measurement and make the sharp taper on one end. The taper should approximately match the slope of the front of the wing. Pick the best side of the blank and place it down on tne table. Mark a line at 1/2" from the good end of the back side of the blank. Then barely cut through the paper. Finally, use the cut to help guide the knife to make the long taper cut just missing the paper on the far side. Like so:
These cheap break-away knives are pretty handy for the longer cuts like this.
Next fit the tapered end to the wing and mark the length, deducting 1/16". Make a good square cut on the mark. Do a trial fit. It should be a little loose but not sloppy.
After cutting to length completely wrap the piece with packing tape. Start by wrapping a short piece over each end placing about half of the width top and bottom. Then use two longer pieces to cover end to end. Start on the top to avoid wrinkles where they will show. Let the two pieces overlap about 1/4" at the center. Wrap it tightly over the edge and around to the botton surface. The two should overlap agaain on the bottom side. Split corners as needed for a smooth finish at the tapered end.
Use a short piece of packing tape to attach the hatch cover and act as a hinge at the front end. Double it for better strength:
Here is the first hinge layer going on,
Cut a piece of 1/8" or 1/16" plywood about 3/4" wide and cut to fit for width between sides to back up the hinge joint. Glue it to the bottom side of the nose piece.
Put a small dab of glue on each end and squeegee it tight to secure the ends to the sides of the pod.
Next we will install a plastic lifting tab made from flexible cutting board on the tapered end of the hatch..
Cut a piece 1" X 3/8" and trim one end to a taper:
Use a pair of needle nose pliers to bend about 3/8" of the square end up:
Use needle nose pliers to bend the end up for a tab about 3/8" long
Curt a slot in the tapered end of the hatchwith a hobby knife, being careful not to damage the top side:
Put hot glue in the slot and insert the tapered end so the tab is even with the end and pointing up:
The finished hatch and lifting tab.
Next we take two pieces of skewer and glue one on each side as shown to stiffen the hatch. Just be sure to make them short enough to miss the plywood and wing. I was able to make both pieces out of one skewer with the tip cut off and then cut in half. Then put velcro in the right positions to hold the hatch closed without having it stick up. You may have to reposition a time or two till it is right. Obviously the velcro needs to be short enough to fit between the skewers.
Update 12-27-14: The description below was revised to use a piece from the plans rather than a scrap.
The motor mount is made from a piece 3 1/4" by 6" left over from cutting the pod piece to 12 1/4" long. Next measure 2 1/4" and 3 3/4" along each 6" side. Score cut the two lines that result. Measure the dimensions shown in the photo to establish the two side triangles. Cut the excess off, leaving the two triangles attached to the sides of the middle 1 1/2" piece. It should look like this:
Here is the same piece after beveling the joints and edges:
When you fold it together nothing should stick out. The scored joint is beveled a little less than 45 degrees on each side. The two 1 1/2" ends are beveled to match the side angles. The 1 7/8" edges are beveled slightly so the inside edges do not stick out when folded.
The cutting board can help with alignment when gluing the angles:
Spread a generous bead of glue in both joints. Hold it on the board so the two sides are spread 2" and the other end is centered on the grid till the glue sets. Run an extra bead on the insides of the joints. It shold ook like this:
Layout and installing the motor mount:
Put a center mark on the 1 1/2" end of the mount. On the wing measure 1" from the center line and 1" forward from the trailing edges on both sides. Put a mark on each side at the intersection of those marks. The back corners of the motor mount will hit the two marks. The center mark on the front will align with the wing joint. Make sure all of the bevels allow the piece to lie flat. Spread glue on the bottom edges and put it on the marks. Make any adjustments quickly. Run an extra bead of glue around the outside and heavier ones where you can reach on the inside.
Cut a piece of 1/8"plywood 2" X 2". Hold it against the back of the mount and trace. Cut it so it will fit flush all the way around. Spread a moderate bead of glue on the edged of the mount. Put the plywood piece on the back and quickly remove any excess glue with a faom scrap squeegee. Run a bead of glue along the bottom of the plywood. It should look like this:
Start by installing two skewer dowels in the bottom of the pod to attach the gear.
Measure 2" and 4" from the leading edge of the wing on the bottom of the pod.
Square the marks across.
Pierce through the bottom faomboard on the marks going half way from each side with a twisting motion till they meet in the middle then push all the way through.
Cut two skewers 2 3/4" long and round the ends slightly with a sanding block.
Insert a squeeze of hot glue into each hole (one at a time) and insert the dowel with a twisting motion till it comes out the other side. Quickly adjust so the same amount is on each side and squeegee the excess glue from the end of the dowel. You only have afew seconds to work. Installing the dowels through the bottom foam is stronger and it leaves the inside of the pod free of any obstructions for velcro and gear.
Next fabricate the main gear skids:
The main gear is designed to let the aircraft settle onto grass without flipping over and with no foamboard damage. In the air it is barely noticable and has low wind resistance. The wire is also very light at 8 grams (.25 oz.). It looks like this:
The gear is made using a 21" long flag wire. Find the center and make a sharp bend (tighter than 90 degrees). The angle should fit into a 2" square like so:
Next measure 2 3/8" on each side and make a 90 degree bend angling outward about 30 degrees on each side. Like this:
Then on each side start about 3/4" from the bend and make a series of slight bends to make an arch that makes a total of 90 degrees in about half of the remaining length. Finish off with the two bends shown. The first is bent upward and is 1/2" long. The second bends back down and is about 1/4" long. These bends will let the gear insert into the sockets in the wing under spring tension to stiffen the gear.
Making the arch bends. Note the slightly segmented look.
Check for uniformity. Hand bend till it is even.
Install it in this position with a rubber band.
The ends of the gear are inserted into two sockets in the winges that are reinforced with triangles of flexible cutting board (thanks Honey). First cut a 1" square, then cut it on the diagonal to make two equal triangles. Drill a 5/64" (or reamed 1/16") hole in the center. Measure out two inches from the sides of the pod and 1/2" back from the leading edge and make two dots. Hot glue the triangles with the holes lined up with the dots then drill through the foam. Test fit the tips of the gear to the holes in the cutting board first to estimate the angle to drill. Then insert the ends of the gear into the triangles. Done. It should look like so:
You will probably have to do some hand shaping to get a uniform appearance.
The tail skids are made with a simple tiangle of foam 1 1/4" X 3" and a piece of flag wire 3 1/2" long for each side.
The triangle is glued to the bottom of the horizontal stabilizer and the side of the tail boom dowel even with the back. Measure 1 1/2" from the back corner and pierce the foam at 90 degrees to the bottom edge of the triangle. Take the tip of yuor glue gun and melt a slot in the faom for the glue and wire to lie in.
Make a 90 degree bend 1/2 " from one end of the 3 1/2" flag wire. Leave 1 1/2" straight and then make a gentle bend as show on the last 1 1/2" of the wire. Like so:
Do a trial fit. The wire bend should fit into the pierced hole and lay into the slot. If all is good fill the hole and slot with glue and reinstall the wire. Use a wet finger or scrap of foam to smooth the glue that pushes up around the wire. Run another bead over the wire and smooth that down as well. You want the entire wire to be embedded in glue to the back of the skid.
The Launching Dowel:
Here are a coule pictured of the launching dowel. It goes on the left wing tip for right handed pilots:
The dowel is 3/16 X 1". The reinforcement is cutting board 1 1/8" X 1 1/8" with a 3/16" hole at 3/8 from one edge. The reinforcement is drilled before glueing. Install the reinforcement plate using a generous amount of glue. Use a skewer through the hole and just pierce the top paper, then push it through from the top. Push the dowel through from the top as well till it is just through the reinforcement. Put a ring of glue around the dowel by twisting it. Continue twisting and push down till it is equal above and below the wing. Put a ring of glue around the dowel on the bottom. Smooth the bottom around with a wet finger. Hopefully the top is pretty uniform due to the twisting but if not smooth it as well.
We are now done with the air frame.
Here is a picture showing the motor, push rods and servos in place:
The servos are mounted in the gap between the wing spars. Their positions are determined by positioning the servo control horn straight forward from the control surface control horn.
This is the servo and push rod installation on the right wing.
First a ruler is used to establish the positions of the control horns.
The servo is placed in the middle of the wing spar with the horn on the line and traced.
Cut out the outline. Insert the servo with the bottom flush and the top just high enough so a screw driver can get to the screw (minimizes drag). Use 3 or 4 small dabs of glue to secure. Like so:
The horns can be made from gift card or cutting board material per the merhods described in the related article below.
Push rods can also be made per the methods described in that related article below.
Here is a view from the back (different build) showing a push rod brace and the motor installation:
There is a hole about 1/2"square where the motor leads pass through the wing under the motor mount. I made up about 4" long motor lead extensions so the ESC can be placed just ahead of the wing. There is also a good view of the push rod brace. These push rods are about 16" long and would likely flutter without it.
The servo wires can be slotted through the rear spar and run along the back of the spar to the back end of the pod (different build shown here so the pod extends back more). Extensions are required to reach the receiver in front of the wing. Note the CG glue dot to the right of the dowel.
This is the shorter Aileron push rod. Note the directions of the bends. The one at the servo is a a standard "Z" bend but the one at the aileron is a modified "Z"with the tip pointing up. The opposing bends help the rod snap in and stay in place. The "V" bend allows the push rod length to be adjusted without removing it and without threaded fittings.
Here is the running gear packed into the pod (nose left). The 1250 3S battery is pushed all the way to the nose for balance.
This is the flag wire tie rod that connects the two rudders. Both ends have standard "Z" bends.
These tabs made from cutting board to anchor the two ends of the rudder tie rod. Just cut with scissors as shown and drill a 1/16" hole. Use a skewer to make the hole in the faomboard.
Note the 3 stages of fabrication. The first one can be glued in before the rod is inserted. The rod and tabs have to be joined before gluing the second side.
The horns are glued into a slot similar th the FT wooden ones. The slots can be widened using a cheap plastic mechanical pencil tip. The foam needs to be cleared to the paper on the other side.
The only change I would suggest from the layout above is moving the elevator servo a little to the left to provide better prop clearance. I had to bend it and made a wire support to take the flex out.
The servo leads are slotted through the rear spar and along the gap beween the wing panels, then into the pod and forward with extensions. Put a dab of glue on a couple of spots to secure.
You have to cut a rectangular hole in the wing under the mount to get the motor leads through.
I made extensions for the motor leads about 4" long to get the ESC to the front of the wing.
In my build a 1250 3s fit all the way forward in the nose to balance.
Look at the referenced articles listed below on "Adjustable Wire Push Rods" and "Control Horns from Gift Cards" for some pointers. Those are the techniques I used in this build (well, actually all of them).
The CG is 2 3/8" back from the leading edge and can be established with a couple of small dots of glue. It also matches the front end of the tail boom dowels.
I do not have any angle in the thrust and have only made a couple of short flights so there may be some room for changes there. It could be done with washers if needed. It seems OK without however.
The ailenos are pretty large so they only need 3/8' to 1/2" throw. I am using 30% dual and 65% exponential and it is still reasponsive. I tried 65% on both and it was very touchy.
This design can be made 3 channel by simlpy increasing dihedral to 6 degrees (1 1/2" under both tips when joining the wings. Additonal trimming / sanding at the wing joint will be needed. Then just do not cut the ailerons and eliminate those two servos.
You can make this design as easily with swept wings. Just use wing "B"instead of wing "A". The CG will still be at 2 3/8" from the leading edge but needs to be measured at the MAC (mean aerodynamic chord) which is at 8 1/2" from the wing tips.
Running Gear Suggestions:
Motor: Turnigy 2822-14 1450 kv (anything in the 150 watt / 500 g pull range will do)
Avoid motors with lower kv numbers requiring bigger than 7" propellers.
Propeller: 7038 , 6045 Note: 7" max (coordinare with motor)
Battery: 1250 3S (adjust size / location for balance)
Radio: 4 Channel (with dual rates & exponential if avaialble)
A moderately experienced builder should be able to take it from here...
Please contact me if you are interested in building and have any questions or suggestions.
Please look at my other articles. I think my best is the 4 sheet 80" wing referenced below. It is a quick build despite the size and flies very well.
Thanks for looking here and GOOD LUCK!
Update 12-14-14: I have added a couple of related articles.
The first is "1.3M twin boom pusher" which features a similar design. I did not see this article until the author commented on mine but it goes to show that there is not really anything new in the world.
The second is "Discus Launch Glider". This is an FT article featuring the wing tip grip launching method which was the inspiration for my similar launching method. The difference is that my models are powered so you do not have to do the 360 degree rotation. I simply rotate about 90 degrees without moving my feet and release level. The motor power takes it from there. The powered airplane pretty much pulls itself off your fingers and takes it from there. You do not really throw it so much as gently guide it into level flight and then get out of the way.. If your airplane is trimmed for level flight you will have time to get to the radio.