3D Printed & Foam Board Wing

After building several Flite Test RC airplane kits, I wanted to create a way to make a wing out of foam board that didn't have sharp bend angles, like almost all FT planes. I had tried the conventional hot wire cutting method to make a wing before, and the result was less than satisfactory (largely due to my lack of practice). Sanding a wing into its shape took too much time and made too much of a mess. My sights were straight on creating a wing-making method out of foam board that followed a standard airfoil shape, was easy and relatively quick, and had very good strength to weight ratio. With my 3D printing abilities at my tool belt, I got busy.

This particular build is tailored for creating a replacement wing for a HobbyZone Super Cub S, a 3 channel RC trainer that has long since been discontinued. If by some chance this Instructable helps you make a replacement wing for your old HobbyZone Super Cub, that is excellent! Otherwise, this Instructable serves to be a documentation on the build method I used with hopes that it can be implemented with other builds. The end product is a 4ft wingspan, USA-35B airfoil wing that has a chord length of 7in. I chose that particular airfoil because that's the same one used in a full sized Piper Super Cub.

Materials You Will Need:

• Foam Board
  • I started this build using Home Depot foam board, but the adhesive they use between the paper and foam is too strong for what we're using it for, which is to peel off the paper on one side. I later got two sheets of Dollar Tree Foam Board and the paper peels right off. However, it is easier to accidentally cut right through when you're trying to do a score or bevel cut.
• Square Wooden Dowel Rod (3/8in)
• 3D Printing Plastic (I used PETG)
• 9g Servos x2
• Hot Glue
• Box Tape
• 1mm Piano Wire (~6in)

Total Cost: $8-9

Tools You Will Need

• Extendable Knife or Xacto Blade
• Hot Glue Gun
• Pencil
• Ruler or Yard Stick
• Carpenter's Square if Available
• Measuring Tape (if no yard stick)
• 3D Printer
• Cutting Board or Cutting Surface
• Steel Square if Available
• Servo Tester and Power Source (1s LiPos work great)
• Two Needle Nose Pliers or a Z-Bender

To design my wing, I used SolidWorks. I followed this video on importing airfoil coordinates into Solidworks, and went from there. Other CAD programs very likely have similar abilities to create shapes based on imported coordinates, so don't be discouraged if you have to build this wing using Fusion360, for example.

After importing the curve from this airfoil, I created an outer curve that would be the outer layer of the foam board wrapped around the airfoil rib. I spaced the outer and inner curves to be the width of the foam board (3/16in). I specified the overall length I wanted (7in) and added some holes in the rib to decrease weight. I also put a 3/8in square hole that was located 1/4 the length of the chord for the wooden spar to go through. I then extruded the rib out 1/8in. You can see I intended for the top layer of foam to overlap the bottom layer at the trailing edge by 1-1/2in, that way I can use that flap to cut out an aileron later in the build.

After making the design with the foam board thickness included, use the measure tool to find out how long the foam board needs to be to stretch all the way around the ribs. For me, that was 13in.

I made a variation in the rib to have a slot to hold the aileron servo. This wasn't entirely necessary, but will likely help keep the servo from wiggling loose over time.

After you are satisfied with your designs, it's time to get printing! I printed 8 ribs at 100% infill with a few more perimeters than usual. I also printed out two control horns at 100% infill you can find here, as well as a front spacer and rear gap fill part. The front spacer is needed because I made the wing chord slightly too short, and the rear gap fill part fits in underneath the trailing edge where the plane fuselage will meet the wing, and give the foam more support so that the rubber bands that hold the wing on don't push through the foam over time. Both of these parts were printed with 2 perimeters and 15% infill.

Once you figure out the entire length of the foam board that is wrapped around the ribs, simply mark and cut out a square that measures [wrapped around length] X [wing span]. Because my wing span was greater than the longest length of foam, I cut out two wing halves of foam board that were 13x24 inches each. Next, slowly peel off the paper on one side of the foam board.

Mark out the center point in the wooden spar and figure out where you want the wing ribs to be placed. I put two in the center that lined up with the plane's fuselage, two more that held the servos as far away as the wires would stretch, and two at the ends of the wooden spar. The wooden spar didn't span the length of the wing, so I had ribs at the end of the wing as well.

The best way to do this is by lining up the ribs (which is easy now that they're all glued together) on the foam, and press firmly on the ribs, leaving an imprint on the foam. Take the ribs off and apply hot glue to the foam and then press the ribs into the hot glue. In my case, I also glued on the outer rib to the foam that didn't go through the spar. I did one piece of foam then the other.

Next, flip over the wing and apply some box tape on the gap in-between the two foam boards. Leave 2-3 inches of tape hanging off each side. Flip the wing over again and fill the other side of the gap with hot glue. Grab the tape that is hanging and wrap it on top of the hot glued gap.

At this point, it's a good idea to do a test bend on the foam that will be the top camber of the wing.

In order to have the size of aileron I wanted, there had to be a gap at the part where the ends of the foam meet at the trailing edge. I needed to glue the ends of the foam together, so I had to put in some spacing foam to touch the two ends. To do this, cut the spacing foam out so that it fits in-between the wing ribs, then glue them onto the wing foam. The gap in my design ended up being too small for a single layer of foam, so I got to practice on my bevel cuts for a bit.

First, cut the holes out for the servos. Pop the servos in and glue in place. Thread the wires through one of the holes in the ribs towards the center of the wing. Cut a hole in the center of the wing for the servo wires to pass through, insert them through the hole, then seal with hot glue with the wires snug.

This is the tricky part. It's best to do this with a friend if possible, especially if you have a large wing.

Bend the bottom part of the wing on top of the top foam on a table, ending when the two ends of the foam meet up at the trailing edge. Press hard enough to make an indent in the top foam. Unbend the foam, apply hot glue where the indents are for the length of the wing, and then refold the wing over and hold until the glue dries. If you don't have someone help you, get a heavy object before hand to press on the part of the wing that you can't put reach.

Once it's dried, make sure to take a breath!

Apply hot glue where the trailing edge foam meets section by section. Hold until it dries for each section until the whole wing is done.

Again, I added the front spacer because my wing ended up being shorter than it should have been, you might not have to add that. I recommend putting in the rear gap fill part where the wing meets the fuselage of the plane as stated before.

Ailerons can be a little tricky, but they're a piece of cake once you do them once. Mark out where you want the ailerons to be relative to the fuselage. Sketch them in on the foam then making the cuts. Cut out a little space where the aileron might rub on the wing. Do not cut all the way though the foam where the aileron will hinge. You only need to score that line and then bend it all the way open, careful not to cut the paper on the other side.

After they are cut, fold the aileron all the way around and make a beveled cut, being careful not to cut into the paper again. Resort to any Flite Test build video that has a bevel cut for a control surface to learn how to do it if it's your first time. I recommend reinforcing the aileron hinge by putting box tape on the paper

Position the control horn so that the holes on the control horn line up with the aileron's hinge. Press the control horn onto the foam, making an indent. Hold back the control horn and apply hot glue, then put the control horn onto the glue and hold until dry. Make a z-bend in an end of the piano wire using either two pliers or an actual z-bender, and pull the z-bend through the control horn. Use the servo tester and make sure the servo is in it's centered position. Cut the piano wire to length and create another z-bend in the other end. Remove the servo's control arm and slide the wire through it. Screw back on the servo control arm with the aileron centered. Repeat for the other servo.

Not entirely necessary, but it will increase the performance. To make a simple winglet, hold the end of the wing on some foam board and sketch out the wing shape. Put the wing away and sketch out a winglet shape. Cut the winglet out and lay flat on the foam board and trace around the winglet. Cut out the trace and glue the two winglets onto the ends of the wing, keeping them straight until the glue dries.

Now you're done! Slap that wing the fuselage and connect the servo leads to the receiver. Do a controls check and adjust any sub trim needed. I configured my plane to have flaperons, making landings and takeoffs easier. At the time of writing this, I have yet to do a test flight. However, after doing some high speed taxiing, I can tell it really wants to hop off the ground!

Total weight: 266g

I hope this Instructable helps in creating your wings and enhancing builds. Happy flying!

Flight Test Update: I successfully flew the HobbyZone Super Cub with this wing, however the plane had some unforeseen tail heaviness likely due to swapping several of the key electrical components. Always check the center of gravity on an unfamiliar plane before takeoff!! The plane and wing experienced immediate unscheduled landings (crashes) three times. Amazingly, the wing held up through all three unscheduled landings, while the fuselage cracked on the last one, ending my day at the field. I made repairs, added a bunch of weight to the nose of the plane, and returned to the field. The plane flew much better but still crashed twice, entering into tip stalls from a much higher altitude. The wing only sustained minor damage on the winglets while the fuselage was cracked again. More hot glue!