Building a 4 Metre Balsa Wing

Hey guys, this is the part 2 article of my 4 meter balsa glider build. In this article I will be building the wing. I also made a YouTube video of the wing construction, if you want to check it out. If you enjoy the video, please consider subscribing. I plan to post many more interesting builds on my channel in the future!

Here's a link to the part 1 article if you missed it or you want to read it again. Let's get started!

                                                            Wing Center Section

  First, I cut out the ribs, spars, LE’s, and TE’s (leading and trailing edges) for the centre section. 

 Then, I laid the lower main spar on the table and glued all the ribs on except the outer two on each side. When that dried, I glued on the top spar.

  After that, I glued in the outer ribs.

  The reason the outer ribs are in two pieces is so that I can fit a wing joiner through them later.

  Next I glued in a 5x5mm piece of balsa halfway between the spar and the TE. It doesn't add much strength, but I think balsa wings look much better when there is something between the spar and the TE.

 The shear webbing supports the spars and is very crucial to the structure. It prevents the upper and lower spars from buckling under load or twisting. I'm using 1/16th balsa with the grain vertical.

I used 1/16th balsa for the sheeting. I have never sheeted a wing before, but with some very helpful advice from the people on the forums, I think it turned out quite well for my first try. My balsa supplier sells the balsa in 915mm lengths, so I had to sheet the centre panel in sections. Because the stress on the wing gets higher the closer to the root you go, I decided to centre the sheet on the wing panel to keep the sheeting joints away from the maximum stress point.

After the sheeting was done, I glued on some 1/16^th balsa to the outside of the wing with a vertical grain. The vertical grain combined with the rib's horizontal grain creates a ply effect, making it resistant to splitting.Then, I sanded it down and re-opened the hole for the wing joiner.

                                                            Outer Wing panels

   Time to cut out some more ribs.

 Once the ribs were cut out, I glued together the main structure of the first outer pieces.

More sheeting!Somehow I forgot to do the shear webbing, so I had to cut a hole in the sheeting to get to the forward side of the spar.Shear webbing glued in and sheeting fixed! It’s a little messy, but at least it’s on the underside of the wing. No one will ever know :)Time to start the next wing panels. These panels taper from a 25cm chord to 23cm.

Finished the other side!

Time to start the next pair of wing panels.

More of the usual.Hmmm, I think I did something wrong… I built two left wings!I decided to pull one apart and re-glue it instead of cutting out a whole new set of ribs, spars, LE's and TE's.

Commencing reconstruction.Finished!

The little sub-spar between the main spar and the LE is to try and maintain the aerofoil shape, as there is no sheeting on this panel. In hindsight it probably wasn't worth it, but I did it anyway. 

After all the wing panels were constructed, it was time to glue the corresponding wing panels together. I cut some angled pieces out of a hardwood plywood.

Then, I glued some foamboard, 2 of the plywood parts, and 2 balsa pieces all together to make the panel joint piece. 

The wing joiners are made from 2 pieces of 1/8th inch thick aluminium sandwiched between balsa. Then, I glued some more balsa on the outside so I could sand the joiner down to a snug fit in the wing.

They turned out to be about 125 grams each. They're much heavier than a carbon fibre equivalent, but aluminium is so much cheaper, and you can get it pretty much anywhere. Now that the joiners are done, I can finally put all the wing panels together and get an idea for it's size.

"Rockyboy" on the FT forum suggested that some carbon fibre tow on the top and bottom spars would be a good addition to increase the strength. I had no idea how to use it, but the people on the forums chimed in and helped me find some carbon and explained how to put it on the wing. Thanks guys! I only put carbon fibre on the centre panel because that's where the most intense load is, and the outer sections of the wing don't really need it. I doubled up with the carbon fibre on the centre 60cm or so of the panel to really beef up the high load area.

The total weight of the carbon fibre on the top and bottom is 21 grams. That's a pretty small weight penalty for a 4m glider, considering the extra strength you get.

And that's how you build a 4 metre balsa wing! Stay tuned for the next article where I do all the finishing touches like covering, installing electronics, and the like.

Until the next one,

Happy Flying!