Page 18 - MFW Dec 2024

had one available. However the short wheelbase was
struggling with the bumps in the grass strip and more flip-
related blade catastrophes followed. I’d aimed to keep the
model as scale as possible but now it was time to face
reality and refine the design. I spent more time on the
computer experimenting with ways to lengthen the
wheelbase without changing the appearance too
radically. I lengthened the front keel and reduced the
castor of the front spring to move the wheel 65mm
forward, then moved the main wheel front wishbone
mounting point forwards to disguise the longer keel. I
shortened the mast to
lower the rotor a little
and moved the rotor
head rearwards to
adjust the c-of-g, which
meant redesigning the
rudder top mount too. I Ready to go again. Most noticeable of many changes are longer front keel,
also found the motor wheelbase, and new main wheels
t h r u s t l i n e w a s knew I was getting closer at last. I made some transmitter
misaligned, so I raised adjustments and waited for the new prop to arrive.
the front of the engine
mount to correct it. Success!
While I was at it I found After more trials the blades subsequently got longer again,
some new wheels to the alloy extrusion was replaced with music wire to
replace the wonky old simplify manufacturing and give more flexibility and the
Tundra ones I’d used to printed parts got more sophisticated. With blade set no. 13
reduce weight. The I finally got it into the air. The elation was short-lived as it
Rotor blades improved with every set.
result was different but did a beautiful climbing roll before hitting the deck in a
still recognisable as a Dominator and if that was what it tangle of thrashing rotor blades. Never-the-less a ragged
took to make a functional model I reluctantly decided I cheer erupted around the flying field! At this point I was
could live with it. creating a video of crashes to amuse my flying mates but it
developed a life of its own and ended up as a bit of a
Not content with re-designing the aircraft, I decided to re- p r o d u c t i o n ! Y o u c a n w a t c h i t h e r e :
think my rotor manufacturing process yet again. I’d https://youtu.be/BdubjmBXpww It gives a good overview
noticed the airfoil shape of the last set wasn’t accurate and of my rotor blade manufacturing setup if you’re interested.
it took a while to identify that the 3D printed sanding blocks
I’d made were collapsing slightly under pressure. Subsequent improvements
Although CAD modelled as solid parts, printed parts are I added a rotor tachometer with telemetry to my transmitter
normally thin skins with the internal space made up of a to give me some indication of when I could safely add full
lattice or grid in order to save filament and hours of printing power; it helped a little but wasn’t the full answer. The
time. I added handles to make them easier to use without video features an awful lot of crashes resulting from what
blistering my palms and reset the print parameters to beef look like the same control reactions on repeat and it finally
them up. Along with a few other refinements, blade set no. dawned that the pilot was the problem. A live pilot
8 were finally what I’d aimed for but not quite achieved on instinctively reacts if the nosewheel lifts by moving the
the previous seven sets. stick forward to level the rotor, but when bumps in the
grass runway bounced the model nosewheel up Jimmy
Re-maiden time again Too just sat there with his inscrutable expression and did
I was finally ready to try again. The first taxiing run proved nothing! I added a gyro stabiliser to compensate. (See
the wheelbase and geometry changes gave a lot more more about this in the sidebar.) With these mods finally got
stability and the latest rotor blades would spin up in a it into the air and under control. It flew beautifully, looking
breeze when hand-started. Within a couple of runs I could and sounding just like the real thing. A proper cheer
see the front wheel lifting as it should and I now had time to erupted this time, perhaps more from relief than anything
correct it with the controls. The next run was getting more else!
serious. I gave it more throttle and when the wheel lifted I
controlled it, but not before a bump knocked the gyro off Unfortunately I think Murphy must have been present
line. With low airspeed and the wheel in the air there was because my main videographer’s phone timed out just as I
little steering so it couldn’t be straightened until the wheel started and another mate couldn’t follow the model in his
landed, whereupon it started to correct before the wheel phone screen after take-off so the only real record was in
lifted again and it toppled over. Unfortunately one rotor the audio. The final insult came when I went to turn for a
blade broke away and was hit by the prop which pass closer to the runway and the DomiNiner stopped
disintegrated as it cut almost through the full chord of the responding. We all had to watch helplessly as it fell out of
blade. A pity, as it was the last of my spare props… the sky and destroyed itself in the neighbouring paddock!
Despite the damage I was very happy with the trial as I It transpired that one cell in my transmitter battery had
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