Last time I decided that the Terzi Katana would be my design of choice and quickly threw some lines together in CAD. Now it’s time to cut some foam and plug in the glue gun…
Building Flite Test style foam board models is always a quick and painless endeavour. With the plans printed out onto A4 paper and taped together I transferred all the shapes onto a large sheet of 5mm foam board using the tried and tested pin method. The only extra work required was to cut some bevels on the control surfaces with a sharp blade and sand them smooth.
Hot glue guns are awesome (and painful at times), and they can’t be beat for this type of build. It took me around 20 minutes to put the whole thing together. In fact so quick that I forgot to take any pictures during the process! The only real thing to be mindful of here is to keep everything square. This is actually pretty easy to do with the wing if you stick the KFm2 steps on first and then slot the horizontal fuselage plate into place after.
The horizontal tail is a bit of a pain. I quickly realised (before applying glue fortunately) that you need to slip the elevator through the slot first before gluing the stab. I guess you could use something like toothpick struts to keep it level but with some care and nice glue fillets I haven’t found it necessary so far.
Also, one nice thing about foam board is the strength compared to Depron. I haven’t added any spars and didn’t even add any reinforcement to the centre of the elevator and it seems plenty strong enough.
The leading edge of the wing needs to be rounded off and to do this I bevelled the edges top and bottom then rounded off with a sanding block. You could always add some tape for strength if you wanted to but I reckon the life expectancy of these models doesn’t warrant it!
The motor mount is a work of art! The position fits the motor I used perfectly but you might want to check the length of your motor and adjust the depth of the recess to suit. The undercarriage worked nicely as well. The little 3D printed parts fit the 2mm fiberglass rod perfectly and by passing them through the fuselage and anchoring into the lower surface of wing they are nice and strong. Just use plenty of hot glue around the crossover to keep it solid. Also, I found I had to offset the wing anchor points for these struts to keep the wheels level and pointing in the same direction.
Everything else is pretty standard foamy construction. The servos are glued in place and my little CNC horns came in handy (I only have a plastic one on the elevator because I fitted it, didn’t like it, then couldn’t get the screws out!). All the control surfaces are taped on top with a smear of glue beneath with the exception of the rudder. I just couldn’t get it to stay put so I double bevelled the hinge line and used laminating film to make traditional hinges.
The CG sits at around 30% of the wing chord – just about bang on the aileron servo horns
Slots were cut for the aileron servo wires to run through and then taped over (you could put them underneath the step if you planned ahead!), All the other wires and receiver were run beneath a foam fillet on the side of the fuselage.
I couldn’t decide where to put the battery initially but after checking the CG I went for the slot and horizontal mounting. I added a strip of fiberglass to the top for strength and some foam block behind. The fit is so good I don’t even think the battery needs to be strapped in place (famous last words…).
Covered in stickers and ready to fly she comes in at around 400g. That’s heavy for a Shockflyer but remember, this isn’t for indoors – it’s for our horribly windy marine climate. A quick power check with the Emax CF2822, 9047 slow-fly prop and 1000mah 3S LiPo suggest it will go vertical on around 75% throttle.
We seem to be experiencing the tail end of Cyclone Gita at the moment so the maiden flight will have to wait a bit. Warm up those glue guns because next time we’ll see how it flies and put some finishing touches to the plans.