In my last post I waxed lyrical about the good old days of 3D profile foam models. I decided to see if I could build one to rekindle some of that line-of-sight fun. Well, there’s no time like the present…

Setting some parameters

The first thing I did was to sit down with a pen and paper and write a list of what I wanted this model to be. Here’s what I came up with:

  • A target wingspan of 600-800mm
  • Use a KFm2 airfoil if possible
  • Have the facility to add side-force generators (i.e. flat wingtips) if desired
  • Be simple to draw and cut
  • Constructed using foam board
  • Must have simple undercarriage

With these points in mind, I went off in search of some design inspiration…

Choosing the design

If you follow the simply “cruciform” flat plate design it is really easy to come up with something as all aircraft have a profile and a plan view that can be used as a template or inspiration. There are loads of models already out there and I thought for a while about just drawing a shape and having done with it, but then I remembered a plane that I’ve been wanting to build again for ever – the Terzi T-30 Katana.

The Katana is a single seat aerobatic aircraft that first flew in 1991. Despite being a competent and agile flyer, it never really caught on with full-size pilots. The same cannot be said for the RC hobby though and many scale and inspired designs have flown over the years. My first big 3D aerobat was the Hangar 9 Funtana S40 and I flew it until it fell apart.

A quick search on the internet fashioned me with a useable 3-view drawing on the Katana so I fired up Sketchup to see what I could come up with.

Actually drawing the plans was surprisingly easy. I simply imported the 3-view image into SU, scaled it to an 800mm wingspan and then traced over the outline with the pen tool!

The beauty of the Katana is that those massive wing fairings give a huge amount of lifting surface above and beyond the core wing area. For this reason I chose to stick with the scale outline and not enlarge anything (for now). I added some KFm2 steps at 50% of the wing chord and recessed the motor mount into the nose but, with the exception of a couple of servo holes at the back of the canopy, that was really all I did.

For the motor mount and undercarriage I drew up a few 3D structures and printed them on the trusty FlashForge. Hopefully they will be strong enough. If they are I may even change the filament for something that isn’t fluorescent green!

Next time…

I’ve rattled on far too long now. Next article I’ll post some photos of the build and then hopefully we’ll get to see if it flies.