Is it a bird? Is it a plane? It's a plane


#1

Many moons ago I enjoyed building free-flight rubber-band powered planes and gliders. They were very cheap compared to remote controlled gear, you could build them in a relatively short time - a few hours for a simple model, a few weekends for a moderately involved model - and they were somewhat easy to repair when it all went wrong.[1]

I mostly made “Delta darts” which were constructed from balsa wood and tissue paper and “peanut” scale[2] models. My pride and joy was a peanut-scale WW2 Mitsubishi Zero which flew exactly once before exploding into a soul-destroying mess thanks to a sudden gust. I stopped building them as I found that I was spending more time repairing them than flying them.

When I stumbled on to the design for the tricopter via the FliteTest youtube channel https://www.youtube.com/channel/UC9zTuyWffK9ckEz1216noAw it was hard to miss that they also had a provrbial fleet of aircraft designs and they happened to be built from foamboard - the stuff that artists mount images onto for display. You can buy ‘speed build’ kits from them but they have also continued the open-source movement of model builders by sharing plans. I had a couple of sheets of foamboard lying around so I figured I’d have a bash and see how difficult it was to build a model or two. My aim was to ascertain if the designs were straightforward enough to build with my nephew. I chose two models - the small, slow-flying ‘mini speedster’ and something a bit more flexible - a flying wing. The FliteTest guys have great build videos so check out their youtube channel if you’re interested.

Step 1: Print out the plans - remember if you’re doing this yourself that some parts are in effect replicated by being mirrored. Thus in the case of the flying wing, I was able to get away with only printing about half of the sheets. I printed onto 200gsm thin card as I wanted to be able to reuse the templates. Taping the sheets together isn’t too difficult as long as you remember that some of the overlaps are a bit hard to gauge. I found it best to use a long straight-edge to match the lines running between pages. A preferential method[3] seems to be printing the full scale plans from Adobe Reader and letting it deal with page-spanning automagically.




Step 2: I cut the parts from the template and verified that I had everything I needed. A no. 11 scalpel blade and metal straightedge made this straightforward. Curves are best done with scissors. As you can see there is only four parts per wing.



Step 3: Transfer the designs onto the foamboard. The foamboard is backed with paper on both sides so it takes felt-tip pen very well with no smudging even though the paper is somewhat glossy. Remember to flip the templates over for the other wing. I used just under two A1 sheets for the delta wing. I’m sure I could have optimised the parts positioning a little more but I was satisfied that I’d made the best use of the foamboard I could.



Step 4: Lots of long, gradual cuts with a no-11 and I had my parts. Note that the plans describe ‘50% score cuts’ on the red lines. One doesn’t need to be exact with this but it helps to try and be somewhat consistent when forming the wings later. I marked one of the ‘elevons’ as a seperate piece to make the best use of the foamboard.



Step 5: The FliteTest guys were pretty clever about how the wing construction was planned. In effect the spar is used both to give the wing rigidity and to press the top surface of the wing into shape. Coupled with the back edge spacing it was relatively painless to get two fairly similar wing profiles. Thankfully the designs are supposed to be quite forgiving so small errors in construction don’t seem to have a large effect on the model’s flight characteristics. My earlier comment on 50% score cut consistency was relevent here as a couple of deeper cuts on one wing made it tend to bend more severely on the leading edge.



Step 6: Two finished wings. You might notice some wiring coming from the front-facing surface of the wing-spars… I couldn’t resist installing some LED striplighting. :slight_smile: The foam is translucent so it makes for an excellent flying lantern.



Step 7: Now, at this point I could glue and tape the wings together and call it a day but the FliteTest guys had released plans for a modification - a blunt-nose variant. The benefits are that one does not need to strap everything to the outside of the plane as there is dedicated space for electronics and the battery inside the centre section. I cut it out, matched it to the two wings (with a little coercion) and glued all three parts together.



TODO:

  • Add the electronics, other than two servos I had lying around which are built into the wings.
  • Glue on the winglets.
  • Balance the wing.
  • Test flights.
  • Waterproof the foamboard.
  • Make whoosing noises.

[1] Which it did. Frequently.
[2] Peanut scale models have wingspans of less than 13 inches (imperial units - boo!)
[3] That I’ve read about but not tested!


#2

The mini speedster was a really satisfying build (that I didn’t document, apologies).

As with the flying wing I need to pick up a few bits and pieces to finish it. I’ll keep the thread updated as I progress.


#3

Looking great!

Have you had a chance to play with the “vinyl” cutter yet? It (obv) also works on paper so you could probably export fiddly designs to that and get them cut on slightly higher grade card for the foamboard template. Of course you could also make the case that this is a case for getting a CNC miller … :smile:

For anyone else, here’s the link to the mini speedster plans


#4

I’ve not been in Farset since I was working on the headphone amp so sadly I’ve yet to see the vinyl cutter.

A few years ago I did consider buying a “robotic cutter”, specifically one for papercraft. Can the vinyl cutter cut 200gsm cardstock?


#5

I think so, but I also haven’t been in the space since it arrived so I’m not sure. Website says it does “cardstock” but isn’t specific on weight.


#6

Step 8: Time to make some pusher rods! These translate the rotation of the servo arm to the control surfaces (rudder, elevator, aileron). A bit of stiff wire is commonly used but since I didn’t have any to hand I built mine out of a strong, light, flexible (inexpensive!) bamboo kebab skewer with sections of paperclip attached. I wrapped the bent to shape paperclip hook onto the skewer with nylon thread and sealed it with superglue. Five minutes to make two. :slight_smile:

Step 9: Control horns are required on the control surfaces. The other end of the pusher rod connects to them. I made mine out of a handy plastic card I just happened to have lying around. The upright control horn fits into a rectangular base. This stops the plastic from piercing the relatively soft foam of the control surface and provides a larger gluing surface. Free advertisement for Q-con and DragonSlayers. :wink:

I then punched a hole through the top of each control horn, hot-glued them onto the control surfaces and attached the pusher rods.

Step 10: Quick test to make sure the control surfaces - elevons in this case - were working as intended. Elevons are a combination of elevators and ailerons. Apologies for the poor video.
http://vid41.photobucket.com/albums/e259/Maeglamor/rc_flying_wing/12%20-%20control_surfaces_test.mp4