Hey guys, check out my 4 metre glider project! I like to build things that expand my building skills, and last time (on my balsa baby baron) it was a removable rudder and a two piece wing. This time, it's size. I like motor gliders, so I decided to build a HUGE motor glider! If you're not up for a read, here's a YouTube video I made of the build. Enjoy!
Specs:
Wingspan: 400cm (157.5 in.)
Length: ~170cm (67 in.)
Wing Area: 93dm2 (1441.5 sq. in.)
Aerofoil: SD7037
Estimated Flying Weight: 2000 grams (~71 ounces)
Let's get building!
Fuselage
The first thing I made was the fuselage sides.
To make these, first I cut the front part out of 3mm sheet, then I cut some 3mm by 10mm strips to go down towards the tail. The strips weren't quite long enough, so I had to join them together. I did that by sanding a bevel on both surfaces to give them plenty of gluing surface area, then I glued them together. After that I glued some vertical pieces down the rear section, and side number one is done!
After making the next fuselage side piece, it was time to glue them together with some formers. First, I glued two main formers to one of the sides. One former goes where the leading edge of the wing will be, and the other where the trailing edge will be. Then, I glued the other fuselage side on top of the two formers. After the glue had dried, I glued the firewall on and the fuselage sides together at the tail. I sanded a bevel into the fuselage sides at the tail for more gluing surface area.
Next, I added some 3 x 6mm strips between the fuselage sides down the rear.
My dad was a bit worried about the torsional stiffness, so I glued some diagonal pieces on the top, bottom, and both sides. It felt much better!
Next, I put in some supports in the forward fuselage section,
and sheeted it with some 1/16th inch balsa.
I almost forgot to support the other side so the fuselage sides don't get squeezed together too much. To do that, I cut some pieces of scrap and jammed them between the two fuselage sides.
After the glue dried, I trimmed off the excess balsa and gave it a good sanding.
I'm pretty happy with how it turned out!
Horizontal and Vertical Stabilizers
Next, it was time to build the horizontal stabilizer. I built it just like a wing with ribs and spars,
but with a simple, flat 1/4 inch thick aerofoil.
The leading edge is 1/4 inch long, and the spars and diagonal bracing are 3mm square.
The trailing edge is 10mm long, and the moving elevator part is 30mm long.
Previously I've used covering film for hinges, but sometimes they would peel off at the ends, which really annoyed me. This time I wanted to go with something really robust and reliable, so I went with nylon hinges.
Cutting the hinge slots where probably the trickiest cuts on the whole plane!
The gap caused by the hinge between the horizontal stabilizer and the elevator was enough for plenty of control deflection, so there was no need for bevelling. 
To cut down on drag and reduce the risk of flutter, I'm planning on sealing the hinge gaps with tape.
Next on the build list was the rudder.
It also has a simple, flat aerofoil.
To build it, first I printed out a template I had drawn on CAD.
Then, I put the main parts in place and put some CA glue on each joint. After the glue dried, I cut and glued in the bracing pieces. The main frame is made of 10 x 5mm balsa, and the bracing is 3 x 5mm. It's hinged the same as the elevator.
I won't be attaching the tail surfaces until I've made the wing, but I couldn't wait to see what it looks like!
That's all for part one. I hope you enjoyed this article, and stay tuned for part two where I build the wings.
Happy flying!
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