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Old Jan 05, 2013, 03:42 PM
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Simple airfoiled wing

I thought I would share the way i build bluecore foam wings. This is one of the simplest ones I build. This one is 7.5X 48". The attached pictures detail the wing panel build.

The panel is 48X 12.25. Folded it is 6X 48. the ailerons are simply taped on to the top wing skin making it 7.5" chord.

Step one is to cut off a piece of the bluecore. I just cut off a panel in the crease which gives me a 24"X 48" piece. After cutting it, I square up the sides of the sheet with a straight edge and hobby knife. I us a 1/4" X 1" X 48" piece of flat bar as a straight edge. If you don't square it up your wing will come out crooked.

Now that the panel is straight I mark my leading edge, spar and top panel cut lines and draw these onto the side of the foam with no film on it. The film side is the outside part of the wing.

I think the pictures should detail the rest. Hot glue is only used to glue the foam spar to the bottom skin and to glue the CF rod to the bottom skin and foam spar.

Polyglue and water mist are used on the top of the spar and the trailing edge.

Ask questions if its not clear!
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Old Jan 06, 2013, 02:02 PM
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Garland, Tx.
Joined Mar 2002
1,095 Posts
Thanks for this. Nice build and documentation. How about a little text description to go along with it. This is much like a wing that I have drawn up but not yet built.

Do you really need the carbon tube spar in this wing? I would think that just the foam skins with the 3/4" shear web would make a pretty strong wing.

J.P.
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Old Jan 07, 2013, 07:34 AM
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I will type up some instructions later. At work now.

There is a weight limit to the foam only wing. I am not sure what it is. I have not had any of the wings fold up but I have had them start to crease a bit near the wing root which causes them to start flexing too much. Models under 16 ounces flying weight have worked well without the CF spar.

The taller the spar the more weight they can carry. The wing in this build can use a 1/2" tall spar for a thinner profile.

A 12" cf tube glued at the root would probably work well and save some weight.
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Old Jan 07, 2013, 01:39 PM
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Wing design basics for scaling. Wing thickness should be 10 to 15% of the chord. Ailerons should be about 18.75% of the wing area for general flying. Bluecore is about 3/16” thick so you would add the skin thickness of .375 to the spar height. The spar line should be marked 25 to 28% behind the leading edge of the wing. The spar is set right behind this line.

A good heavy straight edge like a piece of 1/4"X1" X48" aluminum flat bar is really necessary as it makes this much easier to build. A thin flimsy one will cause problems.

Step one is to cut off a 24”X48” panel of blue core foam and square off the bottom and side corners using a straight edge and knife. A 90 degree angle helps too.

Step two is to mark all lines on the bare side of the foam panel. This will be your spar line, leading edge line and top panel cut line. For the wing in the pictures, the leading edge line is 6” the spar line is 1.75” behind the leading edge line and the top panel cut line is 12.25 inches from the bottom of the sheet. The .25 is added because the wide crease the screwdriver makes shortens the top panel and the wing will not fold symmetrically in half. So the entire wing panel is 12.25” X 48”.

Step three is to lay the straight edge along the back side of the leading edge fold line and weight it down and drag the screwdriver back and forth at an angle down the straight edge until you have a nice indention like in the picture.

Step four turn the wing panel over so the filmed side is facing up and bend the wing just a little bit so you can see the leading edge line. Now weight the panel down and run one line of packing tape down the filmed side of the leading edge. Try to center the tape on the line. Once taped, fold the wing in half and weight it down to see that it folds symmetrical. Sometimes one side is a little longer. If so, trim the excess off so both sides are the same when folded. Note the skin side is on the outside.

Step five is to cut out your foam wing spar. I chose to build this wing 15% thick so I went with a ¾” tall spar. I marked the spar on the end of the left over piece of foam I cut the wing panel from. The piece was already squared up and the right length for the spar. Once marked, align and weight down the straight edge and cut the spar out.

Step six is to weight down your straight edge on the wing panel so that the spar sits right behind the spar line. Now take your hot glue gun and apply glue to about 6 inches of the spar at a time and glue the spar down the wing panel. So glue 6 inches let it set then glue 6 more until done. I like to add a little more glue around the center of the wing. Do not drown the spar in glue just a thin line.

Step seven Glue the Carbon fiber tube to the bottom wing skin and to the back of the spar. On this wing, I used a 40 inch long .210 diameter CF tube. The tube is only glued in 5 places. The last 4 to 6 inches of the CF tube on both ends, the center 6 or so inches and 1 inch section midway of both wing halves.

You can use a smaller CF tube of even CF flats. On lighter planes under 16 ounces you may not need any CF supports.

Step eight. Now that the spar is glued in place, it is time to close up the wing. Apply a medium thin line of poly glue to the top of the foam spar and the edge of the lower wing panel’s trailing edge. See the pics of the glue applied. Take a water spray bottle and spray down the top skin. Now lay your straight edge across the edge of the top wing panel and fold it down over the wing spar and on down to the bottom skin so both panels meet. Make sure the trailing edges meet up in line with each other. If you did step four the wing should fold perfectly. Now add weights on top of the straight edge to hold the wing panels together as they dry. I us four 5 pound weights. Sometimes a 15 pound boat anchor is needed in addition to the weights . You need enough weight to keep the edges together firmly. Sometimes the straight edge will bow a little in the middle. In this case the skins will not be pushed together. This is when you need more weight in the center.

Step nine wait 45 minutes to one hour for the poly glue to set. Now your wing panel is ready for ailerons and servos. With this wing the ailerons will be 1.5 inches wide. Cut a 1.5” strip form the left over foam you just cut your foam wing spar from. I usually cut two 22” ailerons for 4 foot wings. It really depends on how wide your fuselage is. I use a band saw to cut a 45 degree angle along the ailerons and then I simply attached them to the top wing skin using packing tape. Bevel side is down. A hobby knife works well for the bevel if you don’t have a band saw.

Step ten installing the servos is simple. I like using 2 servos. I determine where I want the servos by making sure the wire can reach the middle of the wing will a little slack. I mark the servo position so it is just behind the wing spar and then I trace the servo onto the wing. Cut to the inside of the traced lines and test fit. Once you have a snug fit, cut a hole in the center of the wing big enough for the servo leads to be pulled out and shake the wing until you get the leads out of the hole. Tape the wire so it doesn’t fall back in. Now simply lift up the servo a little and lay a thick bead of hot glue under each servo mounting tab and push the servo back down in the wing. The glue will mash out and bond the servo. Aileron control horns are cut from PVC gutter pipe like SPAD airplanes. I uses 2/56 pushrods and clevises. A 1/16 bit makes the right sized holes in the horn. I just hot glue them on. Add a servo screw and back plate for security if you like. Just hot glue has not failed me yet.

There you have it a 10 step airfoiled foamy wing!
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