A Cute Triangle

[A Cute Triangle]The Triangle is a weird Czech ARF plane.  It's super lightweight, with a 24" wingspan, yet supposedly fully aerobatic.

It has a thick rectangular wing with a fully symmetrical airfoil.  In shape, it's quite a bit like the Lil Hornet, my favorite plane -- a great aerobat while still a slow flier.  My hope for the Triangle is that it will be a miniature Hornet with an IPS-class motor: an aerobat for small spaces.

The control linkage is unusual.  They recommend using only two servos, and connecting the rudder to the aileron servo, so that the rudder is always coordinated with the ailerons.  This means no opposite-rudder maneuvers, of course; but it also means very tight coordinated turns without needing the weight of an extra servo.  I set it up as recommended, to see whether it worked, and it seemed to work quite well.


The kit goes together very easily, though the instructions are very sketchy and the English is poor (in a charming sort of way: "Always mind the safety of yours and your audience!"  The fuselage is a rather nice tapered diameter carbon fibre tube; the wings and tail pieces are pre-covered.  Just join them with hinge tape, slip the wings onto the tube, and glue the tail pieces on.  The instructions gave no clue how to mount the engine (a weird but well made IPS-sized gizmo with a complicated folding prop) or the wheels, so I ended up using strapping tape.  Mounting the servos was a bit challenging, but that's always true when building planes (does that get easier eventually?)  I used two Cirrus 4.4 oz servos, which chatter annoyingly but are very small and light, and a GPS Pico receiver and speed control, and a 700mAh li-po battery.  I wanted to use a smaller battery, but like all planes, the Triangle is set up for much heavier batteries and it's quite tail-heavy even with my 700 battery.  I'm not sure what the total weight is: my hanging postal scale (0-4 oz) says 3.5 oz, the spring postal scale (0-5 lbs) says 5 oz (with battery). 

It's a lovely gossamer thing; it feels like a sharp glance will rip it beyond repair.


First flight: the outfield of a small baseball diamond near home.  I tried to take off from the infield, but the prop is too long for the tiny landing gear.  (This isn't a problem for landing, since the prop can fold when the engine is off.)  So I hand-launched it with much trepedation.

No problem!  It needed no extra trim, and flew beautifully, making very sharp turns and needing very little space.

However, the engine is beyond anemic.  I spent about a minute trying to climb to sufficient altitude to try a loop or a roll, and finally gave up -- I couldn't get the plane higher than about 25' AGL.  It was fun to fly around, and might even be possible indoors (but our local indoor flying venue was impossibly crowded this week, so I didn't get a chance to try), but for outdoor aerobatics, it needs more power.

Second outing (after waiting a week for sufficiently calm winds): I flew a short flight.  Dave said incredulously, "Is that full throttle?"  When I admitted it was, he walked over to his Pico Stick, pulled the IPS off and said "Here, take this.  I'll drive home and grab yours and come right back."

So I taped the IPS-B with the 9070 prop onto the Triangle's stick, pulling the tape hard so the motor wouldn't shift around too much.  The IPS weighs about the same as the weirdo Czech motor, but delivers way more pull.  Flying with the IPS was worlds better than with the original motor!  The Triangle had no trouble climbing at steep angles, and I could fly around at 2/3 throttle and have way more fun than I had with the original motor at full throttle.

The 9x7 prop is way too big for the Triangle's gear, though.  So I got an IPS-1, geared for an 8x6 prop.  I cut a motor mount stick from an old wrecked Pico Stick, and epoxied it into the inside of the Triangle's fuselage tube.  This put the motor slightly farther out (more nose weight), and not only did the motor and prop work fine, but the Triangle flew better.

With the IPS, I could climb to sufficient altitude to try some aerobatics.  Loops are a kick!  This plane specializes in tight loops and tight cropduster-style turns.  Then I flew up higher to try a roll ... and discovered that with a gossamer balsa plane covered in transparent mylar, when you get the plane between you and the tall trees at the other side of the field, it's impossible to tell what it's doing or whether it's inverted or not.  Fortunately, the Triangle's incredible responsiveness makes for some spectacular just-before-it-hits-the-ground heart-pumping saves.

Being more careful about where I flew, I climbed back to altitude and tried some rolls.  Wow!  The Triangle whips around in no time flat with that coordinated aileron and rudder.  Snap rolls and spins are especially fun to watch.  The Triangle dances, it floats, it caprioles.  It's wonderfully fun to fly.  I just wish it wasn't so delicate -- it's hard to transport (I need to make a box for it) and I'm afraid to fly it in wind.

[Triangle, front view]
I have no idea why it's called a Triangle.  But I think mine's a cute Triangle!  (Har.)

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