Foam Board Rc Trainer Plans Pdf
Jemima Torguson
This is the second build article related to my article tytled "Half Sheet No Waste Series Preview". I showed three variations in the first picture in the article. This is the one in the upper right. I chose it because I have not done a build article for a 3 channel trainer before. Nor have I done a long wing version in either size (half or one sheet). Although many of the details are the same from one of my designs to the other there are some details that change and are critical to the performance of the aircraft. Because of that and the fact that some have not seen any of my articles before I will go through step by step from start to finish. If you follow this article from beginning to end you should have a flyable airplane at the end.
The plans for this build are a simple pencil sketch from which you can take the dimensions and do a layout directly on the foamboard sheet. For these designs which use all straight lines most of which go from edge to edge of the sheet that is actually easier than transferring a drawing.
The first step is to take a sheet of Dollar Tree foamboard and cut it in half. These sheets are theoretically 20" X 30" but they vary by about 1/8". My current box measures 29 7/8" X 20 1/8". So to cut a sheet in half you should take half of the actual measurement instead of just measuring 15". Assuming that we have done that or as in my case we have a half sheet left over from the last 1/2 sheet build, we start with a half sheet.
Note: Your triangular pieces should look narrower. I mistakenly cut these at 1 1/2" and had to remake them. I also revised the length of the 2" by 4 1/2" piece from 3" long earlier so that will look a little diffrerent as well.
Take the two wing panels and stack them. They should be identical. If not, put the smaller one on top and trace it onto the larger one. Take a long straight edge and cut off the excess.
Take a rounded object like the pen tip shown and crease the foam deeply along each score cut. Make 3 or 4 passes so the foam is comperssed clear down to the paper on the other side without damaging the paper. Like so:
Next you will need to fabricate two blocks to set the wing camber. They are made as stacks of scraps of foamboard of the correct thickness. For this build we will need one with two layers 3/4" X 1 1/2" and one with three layers 1 1/4" X 1 1/2". Just cut the pieces to size and either hot glue them or use a wrap of Scotch tape to keep them in a stable stack. I used tape:
Then take one of the wing panels and place it on the building board with the scored side down. Place the larger block under the center panel of the wing at the wider end and the smaller one at the narrower end. The leading and trailing edges should push down to the board easily.
After a trial fit place a moderate bead of glue in the second scored line and place the wing panel over the blocks again. Hold pressure on the trailing edge and the two blocks for a minute or so till the glue sets.
Hold pressure on the leading and trailing edges making sure both are in contact all along for about one minute till the glue sets. When you release pressure both edges should stay down and the centers should be in contact with the bocks.
Place the two wing panels with the two root ends butted together and a 2" support under each wing tip. I used a couple of rolls of Xmas wrap ('Twas the season). You could use a couple of thick books, wing tip gages like are provided in many ot the FT plans or anything else that is 2" thick. Like so:
Update 9-30-15: My original instructions used 1 1/2" under each wing tip for the dihedral setting but I found that to be inadequate. I modified the prototype to a polyhedral with 2 1/4"at the tips and it flies better. I am now instructing to use 2" under each tip which will have the same effect.
Spread a moderate bead of glue on the edge of the foam on one side of the joint and butt them back together. Press down on any high points to get both sides to line up as closely as possible. Immediately squeegee with a scrap of foam board
First measure 3 1/2" in from each end on the straight edge and near the angled edges. Use the cutting board grid or a tri-square to verify that the marks are square to the straight side. Score cut the two resulting lines. Then measure 1/2" from the corner of the straight side along each end and make two marks. Cut from the score line to the 1/2" mark on each end. This makes the back taper on the rudders. It should look like:
The ends should measure 3". Next measure and mark 1 1/2" to the center of each end. Place a long ruler on the two marks and draw a light line across. Then along that line mark 3/4" toward the center and 1/2" toward the tips on each side of each score cut.
Use the marks to make 4 cuts all trhe way through. Make a second cut all the way through at 1/8"or less from the first cut on the side away from the score line. You should end up with 8 cuts that look like this":
Then flip the piece over. The elevator hinge cut will be on the other side. Measure 1 1/2" on each tip again and use a straight edge set on the marks to score cut between the two inner sets of double cuts. It should look like this:
Next we need to make the bevel cuts. The first two score cuts separating the horizontal stabilizer from the two vertical stabilizers will get double 45 degree cuts. The leading edges of the elevator and rudders will get single 45 degree cuts. Like this:
After sanding and verifying the 90 degree fit, spread a small bead of glue right in the center of the joint and then a moderate to generous bead on one side of the foam. Fold it up and hold at 90 degrees using a tri-square or a square cut scrap of foam to hold square. Immediately squeegee any excess adhesive from the joint. Hold for about a minute till the glue sets. Do the same on the other side.
Spread a small bead of glue in the joints of the rudders and elevator. Use a scrap of foam or the tp of the gun to remove all excess. If you are using the gun you have to be careful not to melt too much foam. The goal is to have the tip rub the paper and slightly melt the foam on each side while pushing the glue into the foam. If you have not done this before try practicing on a scrap. If in doubt the foamboard scrap method is safer. The goal is to get the glue thin enough so that the joint moves freely.
Note: You need to get the heavier skewers that are available. The ones I am using come from Wal-Mart 100 to a pack for $2 or $3. I tried to look them up but they are listed as "store information". They should measure 1/8" diameter and about 11 5/8" long. After trimming the point off they should be 11" long. If in doubt you can use 1/8" dowel but I think the boaboo is stronger.
There will be some in the pack that seem really round and hard. Some will seem splintery, like the bark is separating. Let Mom use the splitty ones for shish-ka-bobs. Pick the firm round ones for this.
Some skewers in a pack will be fairly straight but most will be bowed slightly. Lay the skewers on the work table. They will naturally settle with the straightest side down. You should be able to tell which side is bowed in. You want to find and mark that side with a dot on one end. When you lay them on the table the mark should be on the side, not top or bottom, but right on the side. If you hold them with the dot up and hold them down in the middle both ends should be off the table and you should be able to line them up with a straight line. Some are just too twisty to use,
Now stand it up on end with one rudder on the table. Align one skewer with the 3" mark and the dot up. You want all the curvature to go toward the enter of the aircraft. Hold the skewer in place with your thumb while spreading a bead of glue about 1" long on one end.
Let it set till firm then remove your thumb and complete the bead to the end. Use a pen or something similar to hold the skewer in place till the glue is set, Then run a bead of glue on the other side. After both sides are set I like to put a second light pass on the first side and use the gun tip to smooth it out. A little extra weight is worth it here for the extra strength.
First we have to do the layout. Measure across the tail from outside to outside of the two skewers. The theoretical number is 8" but the folds tend to add a little. Mine measures 8 1/16. We have to measure half of that number or 4 1/32 each way from center at the front and back of the bottom side of the wing.
Cut the piece out and check the fit. Make any small adjustments needed so it fits flush to the bottom of the wing and tight to the under side of the wing surface. MIf something does not fit make a replacement from scrap if necessary. Once you have a good fit on the first side try it in the second. If the wings are uniform it should fit both places. If so, trace it to the second triangle and cut the second rib. Glue both in holding the marks on the wing on the wingtip side of the rib. Spread a small bead of glue on thehe edge of the rib and position it. Then run a nice filling bead on both sides. Keep it fairly small but use enough to fill in any small gaps between the rib and wing.
On one side spread a moderate to genrerous bead of glue on the bottom of the rib from the mark to the trailing edge of the wing. Set the skewer into the glue with the mark on the skewer at the trailing edge. The other skewer should be touching the wing near the other rib but do not wory about alignment of the second side at this time. Immediately use a wet finger to smooth the glue on each side of the skewer. Keep the dowel in the center of the rib and hold till set.
The second side will be off by however much the skewers were bowed. Spread glue on the second side and align that skewer with the rib the same way. You are straightening both skewers in the process. If everything is straight the two skewers should be parallel as you sight scross and the tail shuld be parallel with the wing viewed from center front.
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