Kwatz (oz15163)

About this Plan

Kwatz. Radio control sport fun-fly model, for .40 engines.

Quote: "It's small, it's light, and it loops in its own length. John Rutter slaps the face of convention with his latest little tailless trickster. Kwatz.

With 1999 drawing to a close, I found myself mysteriously doodling so-called 'fun-fly' designs on bits of scrap paper. (Personally, I find the term 'fun-fly' rather strange because, to my mind, all model aeroplanes should be fun to fly'. Typically for me, the design had to be a bit different, and since I was thinking of bolting an OS 26FS up front, it had to be light, too.

My last couple of models used an old control-line stunt type rib construction, which provided very strong and stiff wings, with very little weight; a well proven concept, and I decided to use it once again. Previous attempts at fun-fly models with parallel chord wings had displayed a less than perfect roll rate, so a tapered wing was called for in order to speed things up a bit.

Most regular fun-fly types use very simple, built-up flat plate section tail and control surfaces, that seem to work well at low speeds. They also avoid flutter, so if it's good enough for them... As various bits of the puzzle fell into place, I realised that my design was beginning to look a little like all the others. Then, with a flash of inspiration, I came up with a good way to save a few ounces. Leave the tail off! Hmm... One less servo, a lot less building, and a probable saving of 4 - 5 ounces in total. Oh, and it looked different, too!

The final piece of the jigsaw, and one that put the proverbial seal on my design spec, arrived when a friend showed me his Just Engines newsletter. There, I found an article promoting the Leo range, which includes their 'thirty-seven' - a near 40, producing (apparently) 1.2 hp from its shoe-horned, 25-sized crankcase. Great! And, it's reasonably cheap into the bargain.

On reflection, I reasoned that this would give far more power than the four-stroke. Since I can't resist a bargain, I ordered one straight away, and began building.

I started by constructing the fin and rudder. Both are built over the plan from strip balsa, with a solid sheet sub fin; the latter is designed to accept a tail skid, and forms the major joint between the fin and fuselage sides. I suppose, if you really wanted to save the last fractions of an ounce, this could possibly be lightened further between the fuselage sides.

As you'll doubtless notice from my photos, the rudder has a vee-shaped chamfered leading edge for hinging (with Mylar strips added later on), whilst the front of the fin is rounded off to make it look nice. Simple, eh?

Next, the fuselage. Cut a pair of sides from medium 1/8 (or 3/16 if you want the model to be a little stronger) balsa, and glue your 1/32 ply reinforcements in with impact glue (remember to make a handed pair!). I taped mine together at this point and smoothed them on a disc sander; unfortunately, I got a bit over-enthusiastic, and the tank bay shrank a bit..."

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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