Want to get into wing racing, but want to do so as cheap as possible? That was my goal when I started building the Foamboard Spec Wing.
In January of 2017, Alex Greves announced the open-source plans of the FPVWRA (rc groups post) Spec Wing. Along with the plans, a specific set of hardware was announced to create a spec class for wing racing and make a level playing field with a low cost of entry.
However, I'm a cheapskate! I had only been flying RC for about 9 months and fixed-wings for only about 6 months. So when I found a local group that was going to be racing spec wings, I was excited but hesitant to buy an $60 wing plus $100 in electronics as a new pilot who was unsure if I would even enjoy racing. Therefore, I set out to build a wing that met the specs using simple foamboard construction and budget parts. In the end, I ended up with with a total price tag of less than $90! You can find a complete list of the parts I used at the end of the article, but I wanted to share the plans and build process for the foamboard spec wing.
First, cut out all the parts for the spec wing. You should have:
- 2 wing (right and left)
- 3 nose reinforcements (small triangle)
- 8 spars (long strips)
- 1 power pod mount (not included on plans: this piece is simply a piece of foamboard folded to fit tightly around the mini power pod)
You will also need:
- 1 mini firewall
- 1 mini power pod (no thrust angles)
- 2 servo horns
Next, prepare the wings by using standard FliteTest methods:
- Cut a single bevel cut on each elevon
- Cut a double bevel cut along each leading edge
- Score cut along the three lines on each wing and lightly open them with a skewer or other object.
After all the pieces are cut out, beveled, and scored, we will build the spars and nose reinforcements. This is a simple matter of gluing the spars, one on top of the other with 4 spars to a stack. You will end up with 2 spars that are 4 layers of foam thick. Once the spares are glued, move on to the nose reinforcements. These also get glued into a simple stack, becoming 3 layers of foam thick. Finally, we are going to prepare the wing by gluing the two halves together. Just as with many FliteTest designs, first place a piece of packing tape along the bottom side of the wing, in the center. Then, fold open the hinge you created with the tape, squeeze a bead of hot glue along the edge of the foam, and hold it flat on the table to bond the bottom edge of the wing.
Before proceeding to folding and gluing the wing you will need to decide how you wish to run your electronics. While you could run all your servo, power, and video leads on the top surface of the wing, I chose to hide all of my wiring inside the wing. If you choose to do this, you will need to determine where you wish to mount you servos, receiver, video transmitter, and camera. Keep in mind we will be cutting a recess for the battery at the end, so be careful to keep any wiring away from the center of the wing where our battery will sit.you servos, receiver, video transmitter, and camera. Keep in mind we will be cutting a recess for the battery at the end, so be careful to keep any wiring away from the center of the wing where our battery will sit.
With any internal wiring complete, we are now ready to fold the wing. This is the most challenging step due to the symmetrical airfoil of the FPVWRA Spec Wing. In order to get a proper airfoil, first test fold the wings to give a nice, even curve to both the top and bottom of the wing. Next, align your spars just behind the score cut closest to the leading edge. The spares will stand on edge, with the paper sides of the foamboard facing forward and backward. Place glue on the bottom side of the first spar and hold it firmly against the wing. Now, trim the end of the spar straight across the line between the two wing halves. Do the same for the second spar and test its fit before gluing it in place the same way. The nose reinforcement should be glued to the bottom of the wing now. It fits back against the spars, leaving plenty of room along the front edge for the wing to fold on the double bevel.
Now, the wings are ready to be folded. Test fit each wing, aligning the back edges and maintaining a uniform and symmetrical airfoil on the top and bottom. Once you are comfortable with the fit, place glue in the leading edge, along the top of the spar, on top of the nose reinforcement, and along the trailing edge of one wing half. Fold the wing and hold everything tight and straight until dry. Repeat with the other wing half, making sure to also glue along the join between the two wing halves. Now you just need to square up the wing tips. Note that the plans make the wing quite a bit wider than the specified 36" wingspan of the Spec Wing, so you will need to cut them down to meet the spec.
You now have a wing! The final steps are fairly straightforward.
- Cut out an opening in the nose to fit your FPV camera
- Cut out a recess in the center to fit your battery. A normal 2200 3s will sink 90% in and still leave plenty of foam to maintain strength
- Mount motor using mini power pod and mini firewall.
- Install servos, camera, vtx, rx, control horns, and control rods.
- Cut out two winglets to your liking and add them to the ends of each wing.
And there you have it! a foamboard spec wing! In developing these plans, I went through several revisions trying to for a symmetrical wing that fits the specified standard. In the end, the simple method of scoring the wing, just like on the flite test planes, worked the best. Finally, here are a few tips from my several attempts at this build:
- The water-resistant foamboard is far superior and much more durable!
- Using the water-resistant foamboard, you can peel the paper off and laminate it over various pieces. Specifically, I lined the battery cutout with it to add reinforcement, make it easier to put the battery in and out, and adds water-resistance to these exposed layers of foam
My parts list:
- EMAX - BLHeli Series 40A ESC
- DYS 2826 2200kv Motor
- EMAX ES08MA II 12g Metal Gear Servos
- FrSky X4R Receiver
- Eachine 1000TVL 1/3 CCD Camera
- Eachine ET200R VTX
- China Hobby Line 2200mah 3s 55C LiPo(s)