This is the first build article related to my last article, "Half Sheet No Waste Series Preview". I chose to do the flying wing first because it is a little different from the twin tail boom aircraft that my last build article detailed. Except for the plans and a few details the twin tail boom versions could be built by an experienced builder following the "One Sheet No Waste Twin Tail Boom #3 Build" article. This one is a little different.
Here is a photo of the the latest build with a quick spray can paint job. I have been flying it all summer so it is a little banged up here and there, but it has passed the test of time. See the end of this article for the modifications I ended up with.
First, here are a few photos of the completed prototype:
This one is a little banged up due to a couple of hard nose-first landings while dialing in the aileron reflex setting. I also changed some of the nose, tail and pod details for the second build.
Here are a couple of photos of the completed air frame for this build:
I am waiting for a shipment of motors and servos to complete this one. Therefore some of the running gear photos are from the prototype which is very similar. Differences will be noted.
Here are the "Plans":
Update (9-29-15): I have changed the drawing above to a pdf so you can print a copy and have it on your building table rather than having to reference back to the computer screen for dimensions.
"Plans" is a stretch for this simple pencil sketch. However, all information needed to cut the pieces for this build is shown. In fact many of the details shown would not be needed if you follow this build article step by step.
Here is a detail drawing for the tail fins:
These details will be needed to complete the vertical stabilizer, rudder and tail skid.
So, let's get started.
Layout and cutting parts:
First we measure and cut a full sheet of Dollar Tree Foam Board in half. These sheets are supposed th be 20" x 30" but in reality they vary by about 1/8". The box I am currently working with actually measure 20 1/8" X 29 7/8". Therefore when doing "no waste" builds there have to be some measurements that are shown as "+/-". These are the dimensions that can be adjusted by small amounts without effecting other measurements, how things go together or how the aircraft works. Generally , the length of wings and various other parts can be made slightly larger or smaller with no effect as long as both corresponding parts are the same. In finding the measurement to cut a sheet in half we have to take half of the actual length, in my case 14 15/16" instead of 15".
So, find the center of the sheet and cut it in half:
Put one half aside for your next "Half Sheet" build.
Take the other one and measure 4 1/2" on both sides along the 20"side. Use a straight edge to connect the two marks and cut the 4 1/2" X 15+/- piece off. Take the 4 1/2" piece and measure 6" from one end. Mark both sides and cut the 6" X 4 1/2" piece free. Take the 6" piece and lay out the three pieces shown on the plan and cut them. You should have one piece 3" X 6" and two pieces 1 1/2" X 3". Take the remaining 4 1/2 "X 9" +/- piece and cut it diagonally from corner to corner making two equal triangles. These are the vertical stabilizers. Set them aside.
On the remaining large piece measure 5" to the right from the upper left hand corner. Then measure 5" to the left from the lower left corner. Connect the two marks with a straight edge and cut the two main wing panels. Look at the drawing for the location and cut out the 3" X 4" corner on each wing panel.
When you get done with this you have cut out all of the major pieces. It should look like this:
Scoring and Setting Wing Camber:
Take the two main wing panels and set the other pieces aside.
On the first wing panel measure two spaces of 1 7/8" from the leading edge of the wing root (wider end). Then measure two increments of 1" from the leading edge of the wing tip (narrow end). Like so:
Take the second wing panel and butt the two wing root ends together. Transfer the marks to the second piece. Like so:
Do the same on the tip ends:
Take a straight edge and score cut the 4 wing fold lines using these marks. There will be two long score marks on each wing panel and they will correspond to the broken lines shown on one of the wing panels on the plans. Like this:
Next take a smooth rounded object like a pen cap and deeply indent each of the 4 score lines. This should be done using 3 or 4 firm strokes on each line. The results should be to open the slot all the way to the paper on the other side without damaging the paper. It should look like so:
If you have depressed the foam enough you should be able to bend the wing panel on each of the score marks pretty easily like this:
Take both panels and pre-stress them by over-bending and holding for a minute or so like this:
Next you will need to make two stacks of foam scraps to use for developing the wing camber. One stack should be about 1" X 1 1/2" and 5 pieces high. The other should be about 1" X 3/4" and 3 pieces high. Tape them together with Scotch tape like so:
These will be used, one under each end of the center of the wing, to set the correct wing camber angles.
On the prototype I tried to set both angles on each wing at the same time. It was hard to hold the center panel flat on the blocks because of the different angles and therefore amounts of compression between the two folds. On this one I am recommending setting the back angle first, letting the glue set and then doing the front one. That way the pressure of the front angle is not trying to transfer into the rear one.
First do a trial fit. Set the blocks under each end (5 stack under the root end and 3 stack under the tip) and do a trial flex of the wing. You will feel the pressure trying to make the two angles the same. You should be able to control the shape by pushing down on the leading and trailing edges and putting some pressure on the stack blocks at the same time.
Next take the panel and spread a moderate bead of glue in the back joint only. Use the glue gun tip to quickly squeegee the joint to a uniform look. Before the glue sets place the wing panel over the form blocks. Hold pressure on the trailing edge and on the blocks at the same time. The middle section of the wing should lay flat on the blocks. Hold about a minute till set. Use one hand on each end to control. Like so:
Next do the same with the front joint. After spreading the glue place the panel on the blocks again and push the leading edge down to the table surface. Make sure the trailing edge is on the table and the blocks are in place under the center at each end and that the leading edge is down to the table all along. Hold about one minute till set.
You have to be certain to hold the whole length of the leading edge down till the glue sets. It will want to spring back till it is set well. Put another bead on each joint one at a time and spread it about the width of the depressed area. Place over the blocks again till set. Do front and back separately, otherwise the softened glue may let the angles change. After the second step when you take your hands off both leading and trailing edges should be in contact with the table all along and the middle panel should be in contact with the blocks on both ends.
Do the same to the other wing.
Joining Wing Halves:
The next step is to join the two wing halves into a single unit. The way the wings taper in combination with setting the camber creates a natural dihedral angle of about 3 degrees if the two halves are joined without any trimming. You can verify this by holding one half flat on the table and butting the other up to it. They should touch on both corners with a gap in the middle. If you raise one tip the gap will close when the tip is about 1 1/2" above the table. This is the dihedral angle to use for a 4 channel set-up.
Note: If you want to do 3 channel you need the dihedral to be about double that. You would have to trim a little off the center of each wing and use 1 1/2" under each wing tip. The trimming should be done the same amount on each side. It is only at the center of the wing and not the leading or trailing edges. This can be done by standing the wing on end, tipping it toward the top surface and dragging it over 120 grit sand paper. You should also mark but NOT CUT out the 3" X 4" piece on each wing because you would need the trailing edge solid to the back at the wing joint. You would not glue the two 3" parts together but would fit and glue the rest of the wing, then cut the two 3" X 4" pieces out.
Let's proceed assuming 4 channel.
Even with 4 channel there is some disadvantage to having the 3" X 4" pieces missing but it is manageable.
Set the two wing halves on the table butted together. Lift one tip and place a paper towel roller or similar object under the tip. Adjust it till the joint comes together all the way along (should be raised about 1 1/2").
Note: If the joint cannot be made to come together you may have to trim slightly by holding it on end and sanding per the FT method. Glue will fill a slight crack so unless it is pretty rough sanding should not be needed. A piece of 120 grit sand paper flat on the table and a few light strokes should do it . I am just saying,,, just in case.
You may want to put a piece of wax paper down to protect the cutting boad while glueing.
Take the raised panel and spread a moderate bead of glue on the mating surface. Put it back in place and qiuckly match the two halves up as perfety as you can. You should keep the leading edges matched exactly (the trailing edge can be trimmed if needed). Squeegee any excess glue immediately while still holding pressure. You will also need to push down on any edge that is high to try to get everything to match up before the glue sets. I know, it is like having to do 4 things at one time with only two hands. Do the best you can. You can always melt it apart if worse comes to worse but it is much easier to get it right the first time. It should look like so:
This was the dry fit. Pretty good.
Squeegee while the glue is still hot:
I usually go back over the joint and spread glue anywhere there is any gap and then squeegee again.
After the glue has set I use a pie lifter heated with a heat gun to "iron" the joints smooth. There is a cutting edge on one side that can be used hot to remove any big lumps. Get everything as smooth as possible before taping. Here I am using it on another build:
Then tape all joints top and bottom. Tape should be cut on the back wing fold and lapped about 1/2" to prevent wrinkling. Put the back piece on first so the lap is front to back. Cut the tape about an inch long over the front and back. Split it with scissors or knife so it won't wrinkle and wrap over the leading and trailing edges. Start with the bottom tape first for a better finish on top. Like this:
The wing is taped and ready to cut ailerons. Note that each wing tip is about 1" off the table.
Aileron layout and cutting:
The ailerons are laid out on the bottom of the wing since the hinge line will not be cut on top.
Measure 10 1/2" from the wingtip at the trailing edge and as forward as posible.
Line up with the two marks and draw a line 1 1/2" long from the trailing edge. Put a mark at 1 1/2".
Measure and mark 1" from the trailing edge at the wing tip.
Make a cut clear through on the 1 1/2" line, then a second cut at about 1/8" toward the tip. Lastly score cut between the two marks, going about half way through the foam.
Fold the Aileron all the way back against the wing. Cut the 45 degree bevel on the front edge of the aileron and trim out the 1/8" piece to make the wing/aileron gap.
Do everything the same on the other side.
The completed wing, top side.
Fuselage (Pod) construction:
The pod is made from three pieces that were cut in the initial parts cut-out. The two 1 1/2" X 3" pieces make the nose and the 3" X 6" piece makes the hatch. The sides are made from scrap.
Start by taking one of the 1 1/2" X 3" pieces and puting a mark at the center about 1/2" from one edge. Then hold the piece under the leading edge with the mark on the wing joint at the leading edge and the corners even with the leading edge. Trace the leading edge and cut the resulting triangle out. Trial fit the piece against the leading edge. The mark should be back at the center. It should look like this:
There is a little gap but the glue will fill it. (The mark matches the wing center on the bottom side.)
Next join the two 1 1/2" pieces with packing tape on the top side. Back cut both sides of the taped joint a little more than 45 degrees. Do a trial fold. The two edges should be 1" apart on the inside corners after folding. Like so:
Glue the joint and hold against the board (or check with ruler) for the 1" dimension (from inside face to inside face).
Next the angled cut-out on the nose gets glued to the leading edge. Double check the center mark for accuracy and use it to position the nose on the front of the wing. Use a straight edge to keep the nose straight with the wing while the glue sets. Like so:
Fill in fairly heavy beads of glue on the inside joints (where it will not show). Go a little lighter on the outside where it will show.
I trimmed about 3/8" off one end of the 3" X 6" piece to get rid of the dented corner on the lower left. I also made this about a 30 degree back cut to join with the bottom edge of the nose piece where it will hinge from.
The angle is not real clear in the picture but it is there.
I also did a small back-cut on the lower edge of the nose piece so the hatch would fit tightly at the hinge side. This was the trial fit. You also need to have a center mark (1 1/2") on the other end of the hahch cover to make sure the hatch will hit the center properly at the back. I had to trim the front angle a little to get this one to hit right.:
First wrap a piece of tape over the back edge of the nose and another over the front edge of the hatch with half the width of the tape inside and half outside. This will keep the paper from delaminating at the hinge line. You should wrap all four edges of the hatch cover lapping half the width on the outside and half on the inside
Then use two 3"or longer pieces of tape to make the hinge. First attach the tape to the hatch lapping half the width
Then attach it to the nose piece making sure the back is still centered. Cut two more pieces of tape to tripple the hinge. Offset the second piece 1/2" toward the back and the third 1/2" toward he front.
Once the hatch cover is installed make two marks on the bottom of the wing at the back corners on each side. They will be the locations for the pod sides later.
Note: I had not wrapped the edges of the hatch in this picture yet. I did it later. It is easier to do it before doing the hinge.
Making the hatch sides:
First you have to rough cut a piece of scrap to fit the under side of the wing. Make sure it is long enough to go past the front of the nose and the back of the hatch and thick enough to extend below the hatch cover. You may have to trim this a couple of times till it fits right. It should end up as a nice tight fit like this:
Then trace the hatch and nose on the back side.
Next measure 3/16" (thickness of the foam board) in from those marks and make a second set of lines. These are the cut lines. Cut and do a trial fit:
Nice fit. Before glueing it in try it on the other side. If it fits well just trace to make the other side. I had to add a little to the nose and do a little trim at the top on the other side for mine. I just added what was need on the tracing and it fit nicely as well. When you are satisfied with both sides glue them in being careful to keep them flush with the nose and even with the sides of the hatch. Use the marks made earlier for initial positioning. Put glue on all of the mating edges of the side including the nose down to the hinge line. Then carefully line it up with the mark and slide into place. Adjust carefully till it is even with the nose and the closed hatch. When it is set run a light bead on all joints inside and out. Go a little heavier in the inside joints in the nose area. Do the second side the same.
Both sides installed and all glued up.
Wrap the exposed edges of the hatch and pod sides with packing tape. Always start with the exposed side then wrap tightly over the cut edge to the back side. Start in the middle and work out to minimize wrinkles.
First the hatch.
Half on the outside then wrap around to the inside.
All the way around.
Next do the exposed edges of the pod sides.
For the pod sides trim angles on the end of the tape so it does not have to lap onto the wing.
Then cut the tape a little shorter than the length of the sides stopping at the hinge.
Starting with the outside, smooth it down, then wrap around to the inside,
The tape completely seals the exposed bottom edge of the pod sides preventing paper delamination.
Next we have to make the velcro hatch closures. We are going to use 3/4" wide velcro strip to make the closures and at the same time make tabs for pulling it open.
Start by cutting two 2 1/2" strips of velcro loop. Then fold one end over on itself about 3/8" on each strip.
Then attach the remaining sticky side to the inside of the hatch cover about 1/4" from the sides. Leave the doubled part plus 3/16" stick out to the rear. Then roll the doubled end up toward the outside of the closed hatch and let the 3/16" sticky part stick to the back edge of the hatch cover. The two doubled ends will end up sticking straight down at the back edge of the hatch.
Next add a small bead of hot glue between the doubled velcro and the hatch so the adhesive on the end will not come loose. It should look like this:
Finally, place two hook pads on the buttom of the wing aligned with the positions of the loop on the hatch and sticking out about 1/4" past he back of the hatch cover. Before placing them make sure to add a 1" piece of packing tape to seal the exposed paper in each velcro position. You should always have a fairly wide tape base under any velcro.
The pod is done.
Motor Mount Fabrication and Installation:
Next we will construct and install the motor mount support. The completed mount looks like this:
The mount support is the white part.
It is made from a 2" X 4 1/2" scrap. First mark off three incremants of 1 1/2" on each 4 1/2" side. Square the marks across the piece and make two score cuts across. Then lay out two triangles using the dimensions shown below:
Update 1-20-15: I have revised the dimensions in the two pictures below to produce 4 degrees of down thrust to counteract balooning at high throttle.
Cut the excess off leaving the two triangles attached:
Bevel the two score cuts at a little less than 45 degrees on each side. Fold the sides in (a little wider than 90 degrees) and bevel both ends of the middle section to match the angles of the sides. You will also have to trim a little off the inside edges of the 1 1/4" sides so the plywood will lay flat.
When completed ready for glue it should look like this:
(This picture has different dimensions from another build.)
After doing a trial fit spread a generous bead of glue in the two joints and quickly place it on the cutting board holding the spread of the two corners at 2" and the 1 1/2" end centered on the grid. (Same position for trial fit). Like this:
If you do not have a cutting board with a grid simply draw a 2" square on a piece of paper.
After the glue sets run a generous bead on the inside of each joint.
The finished piece should look like this:
Next we will lay out the position for the motor mount on the top trailing edge of the wing.
Make two marks 1/2" from the trailing edge and 1" each from the center line of the wing. Like so:
Put a center mark (3/4" each way) on the front edge of the mount support. Spread a moderate bead on the 3 bottom edges of the mount support. Then place the corners on the two marks with the center mark at the center of the wing. Run a light bead of glue around the outside and a heavier one inside. The installed mount support should look like this:
Next we will make and install the plywood motor mount.
The mount is made from a 2" X 1 1/2" piece of 1/16" (in picture) or 1/8" plywood (holds screws better). Place the blank in position and trace tha shape of the mount support. Like so:
Cut off the excess. Spread a moderate bead of glue on the back edges of the mount support and press the plywood into place. Immediately squeegee any excess with a foamboard scrap. Then spread a generous bead of glue at the bottom of the plywoood filling in the gap between it and the wing surface. Finish it off with an even bead smoothed by the glue gun tip.
The finished mount:
Elevator Installation (optional but used in this build):
Note: For a more conventional flying wing set-up you can eliminate this step and eliminate the rudder cuts on the vertical stabilizers. You would then have a 3 channel set-up with only two servos. The ailerons would become elevons using the elevon function in your radio settings.
The CG would move forward 3/8" to 1 3/8" from the leading edge at 9" from the wingtip.
(End of update)
Note: The elevator on this aircraft is optional. If you do not have a radio with servo mixing or "elevon" functions you will need to use conventional ailerons and this elevator for three or 4 channel operation. If you have "elevon" function you can control with just the elevons and would not even need to install an elevator. In that case I would recommend installing it in a fixed position just to complete the wing area which is figured in the CG calculations. Theoretically (and in my experience) this plane would fly fine without it if the CG is moved forward the corresponding amount. I have not calculater that CG. We are proceeding based on the assumption of a functional elevator.
The horizotal stabilizer and elevator are made from the two 3" X 4" cut-outs from the wing panels.
First they need to be made into one piece. Simply butt the two best 3" sides together and tape with two small pieces of Scotch tape to control the allignment. Then tape the joint with packing tape. Turn it over and open the joint about 90 degrees. Spread a modest bead of adhesive on the foam on one side and fold it back to a flat butted condition. Lay it down on a flat surface quickly and squeegee any excess glue from the joint. You can iron the joint with the pie lifter if needed. Then apply tape to the second side. You should have a solid piece 3" X 8". Like this:
Mine was a little uneven and had a bad factory edge so I trimmed one 8" side just enough to straighten it (about 1/8").
Next measure 1 3/4" along the 3" side on both ends.
Make sure to measure from the same 8" side. If there is a bad corner put it on the 1 3/4" side because those corners will be trimmed off at an angle to allow rudder swing. Using a straight edge, do a score cut from mark to mark. Use a little more pressure if needed at the glue joint to get most of the way throught the glue. Bend it at the score cut to "break" the joint.
On the 1 3/4" side measure and mark 1/2" from each corner along the 8" side. Use a straight edge alligned with the score cut and the 1/2" mark on each end to cut off the corner. This is to allow swing room for the rudders. Like so:
The angled wider part is the elevator. The narrower part is the horizontal stabilizer. This is the bottom.
Fold the elevator completely back onto the horizontal stabilizer and trim the front edge of the elevator with a 45 degree back-cut. Like so:
After making the back cut the elevator should be able to flex down about 30 degrees with little resistance.
Fit the vertical stabilizer between the two trailing edges behind the motor cut-out. The elevator hinge should align with the wing's trailing edges. The back edge of the vertical stabilizer aligns top and bottom with the wing but the leading edge is offset down the thicknesss of the foam. The top surface of the vertical stabilizer is aligned with the bottom surface of the wing. Like so:
Put generous amounts of glue on both the top and bottom of each of these joints. First put a light bead and let it set. Then put a heavier pass over each and smooth it with a wet finger. You want to pretty much fill the corner in, Like so.
The way the horizontal stabilizer was installed aligns it with the bottom of the wing rather than the top surface. This will help produce a downward force (considering the down-wash over the wing) that will help to keep the wing in a positive angle of attack. This tendancy can be adjusted more or less with elevator trim.
Next we will fabricate and install the tail fins (vertical stabilizer and rudder). They are made from the two remaining large triangles from the original parts cut-out.
First lay out the positions on the wing.
The vertical stabilizers are set at about 1/4" toward center from the end of the aileron on each side. Measure 4 3/4" from the center line at the trailing edge and at the front wing bend (where the front of the vertical stabilizer stops). These marks will be the outside side of the vert. stab.
Take one of the triangles and hold it over the marks with the tip at the front wing bend. Mark the positions of the second wing bend and the trailing edge.
Then make the layouts shown on the sample below:
Cut the section out with the 1/4"dimensoin so the the vert. stab. will fit over the wing bend. Cut the small triangle off the bottom left corner ( for ground clearance) and save it for landing skids to be insalled later. Score on the line marked. Make a 45 degree bevel cut on the front edge of the rudder. This is for the left side.
Note: If you want a more conventional flying wing set-up with elevons only eliminate the rudder score cuts. The vertical fins would be vertical stabilizers only. The CG then moves 3/8" forward or 1 3/8" from the leading edge at 9" from the wingtip.
(End of update)
Trace this onto the second piece. Make all the same cuts but with the score cut on the opposite side. The second one is for the right side.
Do a trial fit on both sides. The front tip should be on the front wing bend. The rudder hinge should align with the wing's trailing edge. The pencil marks on the wing should be on the side toward the wing tip. If there is any gap under the piece it should be very small. Trim for a close fit if the gap is too big.
To install run a moderate bead of glue on the bottom edge from the rudder hinge to the front tip. Set it in place aligned as it was for the trial fit. Make minor adjustments quickly. Hold the piece at 90 degrees from the wing surface using a tri-square or square cut foamboard scrap. Hold a minute or so till the glue sets. Run a small uniform bead along both sides using the glue gun tip to squeegee it to a uniform shape.
The completed tail fin installation:
Next we will install landing skids. The purpose of these is to prevent impact damage to the faomboard parts while landing.
The finished skids will look like this:
The front skid is a simple piece of flexible cutting board material cut 1" X 3" and glued to the bottom of the nose just in front of the hatch hinge. It is let hang down about 3/8" so it will hit the ground instead of the corner with the hinge hitting. To install, spread a generous amount of hot glue on the skid leaving about 3/8" along one side bare. Then press it against the lower part of the nose letting it extend about 3/8" below the hinge. The goal is to get as close to 100% coverage with the glue as possible. You can see the glue in the picture above. Nip the exposed corners with a pair of scissors.
The rear skids are only a bit more complicated. The two triangles cut from the bottoms of the rudders are glued directly below the vertical stabilizers with the back corner matching the trailing edge of the wing. A bent flag wire skid is then glued into prepared holes and slots.
First glue the two skids in place. They can be aligned with the vert. stab. visually or you can do a simple layout.
Next measure 3/4" from the back corner of the skid and use a skewer point to pierce a hole at least 1/2" deep at 90 degrees to the bottom surface of the skid. Take the tip of your glue gun and melt a slot about 1/8" deep from the hole to the back of the skid. It should be just the foam and not the paper.
Then take two pieces of flag wire 2" long and make 90 degree bends 1/2" from one end. After that leave 3/4" straight. The last 3/4" needs to be bent in a gentle arch in the same direction as the 90 degree bend with several slight bends totaling about 30 degrees. They should lay flat and look like this:
The 90 degree bend goes into the pierced hole and the straight part goes into the slot with the arched part trailing out to the rear.
To install first fill the pierced hole and slot with a generous bead of glue. Then insert the 1/2" bent end into the pierced hole and press the straight part into the guled slot all the way down to the foam. Glue will squeeze up on either side. Wet a finger and smooth it down over the wire. Add another bead of glue over that and smooth it down as well. The completed installation should look like this:
Next we will install the wingtip launcher. This is a short dowel at the wing tip that lets you hand launch easily without assistance. It should be on the left wingtip for right handed flyers. It looks like this:
First cut a square of cutting board 1" X 1". Drill a 3/16 hole about 3/8" from one edge. Trim one corner so it will lay flat at the wing tip with one side even with the tip. Spread a generous amount of glue on the back of the reinforcer and press it onto the bottom of the wing as shown.
Next take a skewer and pierce through the hole in the reinforcer till it just pierces the upper paper. Then go from the top to complete the hole, working it around to enlarge the hole to match the one in the reinforcer.
Then cut a piece of 3/16" dowel 1 1/8" long. Use a sanding block to taper both ends slightly. Insert the dowel from the top with a twisting motion till it just comes through the reinforcer on the bottom. Then put a ring of glue all the way around the dowel above the wing by twisting the dowel as you apply the glue. Continue to twist the dowel and push it down till the same amount is above and below. Then apply a ring of glue around the dowel at the bottom. Smooth the glue top and bottom with a wet finger if needed. The top glue can come out as a neat ring without smoothing if applied evenly and rotated till a nice ring forms.
This completes the airframe.
Marking the CG pioint:
The CG is 1 3/4" back from the leading edge at 9" from the wing tip. I mark mine with a spot of glue which can be found by feel for balance checks. See the picture below.
Note: For elevons only the horizontal stabilizer and rudder are eliminated and the CG moves 3/8" forward. The CG in that case would be at 1 3/8" from the leading edge at 9" from the wingtip.
(End of update)
Installing Servos, Control Horns and Push Rods:
The first step is to make control horns. I make mine from flexible cutting board material. The sequence is as follows:
1. Cut a 1" strip from a sheet of cutting board with a straight edge and hobby knife
2. Cut two 1" squares from the 1" strip with hobby knife or scissors.
3. Cut each 1" square diagonally into two equal triangles with scissors.
4. Cut two corners off one triangle with scissors as shown.
5. Use the first triangle as a pattern to cut the corners off the remaining triangles.
6. Drill holes: Use vice grips to stack and hold the 4 resulting control horns. Carefullly align the edges that will be drilled and the ones that will be embedded. Drill 3 uniformly spaced 1/16" holes as shown in the picture;
You will end up with 4 control horns that look like the last step in the picture below:
Six horns were made from the pieces shown in various stages above. Here they are stacked for drilling:
Here is the stack of 6 drilled and ready to install:
The exact size and shape of these is not as important as that the holes and mounting edges ( down and to the right in this picture) are uniform.
The next step is to use a straight edge to establish the positions of the servos and control horns.
A ruler was used to mark servo and horn positions prior to installing the aileron horn. The servo (horn) position is on the right.
A flag wire was used to mark the positions of this servo and control horn because the wire must pass through the motor slot and there is not room for a ruler. It was done prior to installing the rudder horn. The position of the servo horn is marked on the right.
The same procedures were use to establish the other servo and control horn positions. In general the control rod should be parallel to the line of flight as much as possible. On this build the rudder push rod needs to be on a slight angle because of passing through the motor slot.
Insalling control horns:
After laying out positions we follow these steps:
1. Make a knife cut on the pencil line.
2. Widen the slot with a cheap plastic mechanical pencil tip (lead retracted). Make sure to get down to the paper in the other side.
3. Trial fit. The holes should be directly above the hinge line.
4. Fill the slot with hot glue.
5. Insert the horn and quickly align the holes with the hinge line. Make sure the inserted part is down to the paper but not pushing the paper out on the back side.
6. Put a light pass of glue on each side of the horn.
Here is a picture of a completed installation:
The servos are simply glued to the bottom side of the wing close to the CG line with the control horn on the pencil line. Remove the sticker and rough-up the glue side of the servo with a knife tip prior to glueing. The wires are run as straight as possible and run through a small hole in the side of the pod near the bottom of the wing. Secure the wires with packing tape. They should look like this:
Note the CG point marked in the foreground.
Installing push rods:
Push rods are made from flag wire. They are installed with the servo centered (radio on, control stick centered and trim centered). The control surface should be in it's anticipated neutral or take-off position. On this build the ailerons should be about 15 degrees positive (flying wing reflex). The rudders and elevator should be neutral (straight). The radio gear should be installed and switched on so the servo horns are in their flying positions.
The push rods use a "Z" bend at the servo and a modified "Z" bend at the control horn. This combination allows the push rods to be twisted and snapper into place and prevents them from slipping loose.
There is also a "V" bend in the middle or closer to the control horn to allow for slight length adjustments and to use as a handle to twist the push rods into place.
The steps are as follows:
1. Make the "Z" bend and install it on the servo. You will have to drill the servo arm holes out to 1/16" and ream a little. I usually skip the end one and then drill every other one.
2. Insert the "Z" bend into the servo horn. Place the wire in it's approximate location and mark the desired location of the "V" bend. These should be at about the front edge of the motor slot. They should all point down or away fom the wing. Make the "V" bend trying to keep the two ends of the wire in alignment.
3. With the control surface in it's neutral position mark the position of the hole in the control horn. Make the modified "Z" bend with the last bend pointing away from the control surface.
4. Grip the "V" bend and twist the rod 1/4 turn to insert it into the horn. You can also flex the horn in the right direction to help it go in. Once it is inserted let go of the "V" bend and it should snap into place. Make any fine adjustments needed by adjusting the "V" bend. You will usually have to adjust all three bends, first the middle one to adjust the length and then the other two for straightness.
Note: If properly made the tip of the wire at the servo should point straight ahead. The tip of the wire at the control horn should point sideways and away from the control surface.
Here is a picture of the completed push rods on the prototype (the layout is slightly different for this build):
This picture is from the prototype. On that build the rudder horn was below the elevator so the push rod was below as well. On this build the rod will pass through the motor slot because the horn is above the elevator. Ther elevator servo and control horn will be able to be placed closer to the aileron servo because the elevator was made longer. That will let the motor slot be more unobstructed.
This is a typical push rod. Note the directions of the bends.
Installing the rudder tie rod:
The rudder tie rod is made with two "Z" bends and two tabs made from cutting board material. Both wire ends point out. It looks like this:
The rod has to be made carefully to length so the rudders are parallel when it is installed. Make a trial fit before glueing. The tabs are inserted into two holes in the back of the rudders made using the pointed end of a skewer at 1/2" from the bottoms of the rudders. The first tab is glued in and then the rod is inserted. The second side tab has to be put on the rod before it is inserted. Fill the second hole with hot melt glue and insert the second tab.
The tabs are made from cutting board in the following sequence:
1. Cut the tapered piece from a 1" strip of cutting board with scissors. The thick end is about 3/16" wide.
2. Drill a 1/16" hole in the wider end.
3. Nip the corners with scissors for a rounded effect.
Motor installation: This is a Turnigy Park 250 motor selected for it's light weight . It iscentered on the plywood both ways. Note the wires passing through the motor mount.
A hole about 1/2" X 1/2" needs to be cut in the wing below the motor mount for the motor wires to pass through and into the pod..
This is the runnung gear in the pod:
The battery and receiver are pushed as far forward as they will go in the pod for balance. The ESC wires are soldered directly to the motor leads to minimize weight. If you want to use connectors they should be small (2 mm).
Motor: Turnigy Park 250 (make sure to use Locktite on the set screws)
ESC: 10A with UBEC
Servos: Hextronik HXT500 5g
Battery: 800mah 2S
Let me know if you find any inconsistencies or missing information.
If you have any questions or comments please respond in the article comment section so that everyone gets the benefit of the questions and answers.
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Well, that's everything for now. Good luck with your build.
This is the third build or this plane and I have made a few modifications.
Here is a picture of the latest bottom side:
1. Based on a FT article showing that rudders are not effective on flying wings I eliminated rudder and elevator controls and set up elevons instead. It is now bank and yank. It is also a lot lighter. I never did fly it with the rudders and elevator.
2. The former rudders are set with two or three degrees of out angle each to help stabilize yaw. I think it helps.
3. The former elevator is set with a permament positive angle of 20 degrees as measured from the top rear wing surface. This provides some permanent reflex.
4. The elevons are set at 15 degrees positive. The strongly undercambered wings need a lot of reflex.
5. I have removed the original cutting board nose skid plate and added flag wire landing skids instead. The skid plate resulted in frequent power pod damage. No major damage since the change.
6. I widened the power pod from 3" to 3 1/2" to allow a 1000 3S battery.
7. I changed to wire tail skids instead of the skewers shown in the original construction. They just hold up better.
8. I changed radios from FlySky FS-T6 which had only single antenna receivers to a FlySky FS-i6 which has all double antennae. It made all the difference in the world. I had a lot of lost signal crashes before the change and none since. Note the two antennae set at 90 degrees to each other.
Otherwise it is pretty much exactly the same :).