Background: What do you do when a buddy crashes his Formosa, and breaks it in half? Pick up the discarded pieces and make them into a canard style plane! I have had a project like this in mind since I noticed that my eStarter was getting more and more sluggish as I kept adding more and more epoxy to the fuselage. As I practised my landings, I kept cracking the fuselage and regluing. After the third or fourth syringe of epoxy, it flys like a pig. But, the wing is virtually pristine. All the extra weight is in fuselage repairs. When I moved up to my own Formosa, I set the eStarter aside, thinking I might use the wing to make a canard style plane. Opportunity came knocking when a friend was making a low, slow, hands off pass with his Formosa and his receiver glitched him straight into the ground. He had been fighting with the receiver glitching all day, and this crash was the final straw. He gave the plane a kick in the middle, ripped out the electronics and told me I could have the remains. The wing and the tail were in good shape, so I got to thinking that this was a golden opportunity to try my canard plane conversion idea. If it didn't work, no great loss...
Design goals:
My goal was to make a flyable canard plane only with foam from the
Formosa
carcass. How's that for simple. :)
The Canmosa, mark 1:
I had picked up a dozen carbon fiber arrow shafts at a garage sale in
the spring. I cut up a couple and used them for fuselage tubes and a
cross tube for the canard. I milled a chunk of plastic (on my Taig
milling machine) as a nose piece
that holds the fuselage tubes, the canard tube and the steerable nose
gear. I took the elevator flaps from the Formosa and they became the
canard. The main part of the elevator became the main wing stabilizer
winglets. The fuselage tubes are epoxied in holes drilled in the front
of the main wing.
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| Canard stype plane from GWS Formosa parts (Canmosa) mark 1 |
The first test flights did not go well, as I had just estimated
where
the CG seemed like it ought to be. The plane was too nose heavy, and
wouldn't stay in the air.
The Canmosa, mark 2:
I did some calculations and analytically
found where the CG should be, then cut a bunch of material from the
front block and added clay to the motor mount to get the CG right.
Presto! It flew wonderfully! Moving the battery and servos around
allowed me to get the CG right without adding the extra weight of the
clay. The power system is a GWS 350 motor with a C gear ratio, a GWS
1300mAh 2S lipo, and a GWS 9070 prop.
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| Canmosa, mark 2. Battery and ESC moved to the
belly. Servos moved back to the main wing. |
The Canmosa, mark 3:
Next, to increase the canard area... I cut a front extension for
the canard from the sides of the
Formosa fuselage just in front of the tail. The extensions went on the
front of the canard pivot tube, with clear packing tape smoothing over
the bumpy joint. I shifted the battery a half inch foreward figuring
this and the extra weight of the canard extension would put the CG
about right. (You would think I would have learned the first time about
estimating CG location!) Well, it flew horribly. It was extremely
unstable in pitch and wanted to roll hard as well.
Rerunning the CG calculation with the new canard dimensions showed that
the area had gone from 11.3 sq in to 19.25 sq in. This resulted in a
shift in the neutral point of about an inch forward. My actual CG was
about 1.25 inches behind where it was supposed to be, thus the unstable
behavior. So, I moved the battery back up to the nose, and used a bit
of clay to fine tune the CG.
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| Canmosa, mark 3. |
It now flys wonderfully, with enough pitch
authority to do loops on a fresh battery, the same as my Formosa. The
canard still stalls before the main wing, preserving the forgiving
stall behavior. Both my eStarter and my Formosa drop off to one side or
the other when stalling. The canard plane will remain rock steady in
roll, and just drop the nose to gain a little airspeed. It makes
landings a breeze, as the plane just settles to the asphalt. With the
other planes I always had to worry about dropping a wingtip, catching
it, and cartwheeling.
Later that day after 20 more minutes of flight time: I
concluded that looping with authority isn't going to happen
with this plane as is. Rolls, great, flying inverted, great, gliding,
great, stall recovery, great. A dive into a loop gets over the top just
by the skin of its teeth. I've got a double stack outrunner brushless
motor on order.
We'll see if that does the trick....
The Canmosa, mark 4:
Built and installed the brushless motor. This included
fabricating a motor mount and prop saver on my milling machine and
lathe.
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| Motor mount, brushless motor, prop saver. |
This led to a huge jump in power. Here is my after report from
8/21/05:
Previous power system was a GWS 350 motor with a C gear
ratio, a GWS
1300mAh 2S lipo, GWS ICS-300 ESC and a GWS 9070 prop. I upgraded the
power system to a double stack 20 mm brushless motor (made from kit, 16
turns) from customCDR, generic 1800mAh 3S lipo and Tower Pro 15A
brushless ESC from XUShobby, and GWS 9070 prop.
What an amazing differance! The 3S battery pack was so much bigger and
the motor so much lighter that a major shift in the battery pack
location was required. I did a short test flight last night and some
much longer test flights this morning. First, keeping the same 2S
1300mAh battery, with the old motor the throttle would be maxed out
most of the time, and I could get 11-12 minutes of flying if I
stretched it. With the new motor, most of the time I was just above
half throttle (building to full at the end of the flight) and got a
flight time of 21 minutes. Loops with the brushless motor were
absolutely no problem for the first half of the flight. Towards the
end, the voltage dropped and the motor couldn't quite push the plane up
and over the loop.
Second test was with the 3S 1800mAH pack. Unbelievable performance. For
most of the flight, straight and level flight required just over 1/3
throttle. Boosting the throttle just made the plane leap into the sky.
I imagine this is because of the symmetric airfoil on the wing and
canard. Each throttle setting requires different canard trim for level
flight. Loops were unlimited, maxing throttle going up and cutting
throttle coming down. I think the max I did was 6 in a row. Pulling
vertical and maxing throttle would take the plane up until it was just
a speck. I got a kick repeatedly taking it way up, cutting throttle,
and gliding back down in big circuits of the field. I never did find
the limit to the flight time. After about 25 minutes (this is after the
previous 21 minute flight). I was getting a crick in my neck after
doing every maneuver I could think of. I attempted a "field goal" pass
through the goal posts and caught the cross bar. No damage except a
broken horn on the canard.
One interesting quirk of performance displayed itself on the second
flight. On a straight down dive, with slight up canard, the plane shows
a tendancy to suddenly push "down" towards inverted flight. This makes
high looping tricky if you aren't expecting the unexpected push-out. I
haven't yet determined if it is an aero effect or if it is due to the
location of the big 3S battery. The quirky behaviour makes it easier to
do push loops than normal ones. The solution may be a combination of
optimised battery placement and moving the canard servo back to the
front of the plane to stiffen up the linkage.
Further testing revealed the cause of the "push". With the
heavier 3S battery located properly forward for "textbook" balancing,
the slightly undersized canard gives very mushy pitch control.
Moving the battery back improves things, but results in a bit of
down-canard trim for level flight. In loops, pulling up over the
top of the loop hides the trim setting. Heading down the back
side of the loop, if I let the pitch stick go to the neutral, the down
trim kicks in and results in a push-out to inverted flight. I've
experimented with moving the battery placement forward, but really
don't like the pitch mushyness. I've decided to keep the battery
back and deal with the quirky dive behavior. Putting the 2S
battery back on the plane lets me adjust the pitch trim to eliminate
this behavior.
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| Canmosa, mark 4. |
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| Digital video camera on the Canmosa. |
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| Yorktown from the air. |
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| Busted Canmosa. Retired for now. |