60 Model Aviation AUGUS T 2012 www.ModelAviation.com
The red motor case color is appropriate; there
are 200 watts available from this little gem.
Below: Space inside the pod is adequate for power and flight control systems. Note the battery
connection is accessible through the front canopy hatch.
The author completed the Cumulus with these recommended power
system, components, and servos.
outrunner motor, ESC, two small
servos, a receiver, an 850 mAh 3S LiPo
battery, and the CAM unit for ALES
competition. CAM is an altitude-sensing
device used to signal the ESC to shut
off power to the motor when a preset
altitude is reached.
The motor is a High-End Technology
(HET) Typhoon Micro 15-13 900
Kv outrunner. The diameter is 29mm
( 1. 14 inches) and it is 37mm ( 1. 45
inches) long, with a 1/8-inch diameter
shaft. It weighs 74 grams ( 2. 6 ounces).
Maximum rated current is 17 amps and
maximum rated power output is 200
The motor is controlled via a 25-gram
(0.9 ounce) Arrowind Hobby Matrix
25-amp ESC, with built-in BEC that can
provide up to 2 amps and handle 2S to
4S LiPo input. The Arrowind ESC can
be programmed via a built-in function
that requires moving the throttle stick
and listening to the beeps. It can also be
programmed via a stand-alone program
card. At the time of this review, the
program card was unavailable.
Motor current with an Aeronaut
11 x 6 folding propeller is 16. 5 amps
or 204 watts. The battery used is a 70-
gram ( 2. 5 ounces) SiegPower 850 mAh
3S LiPo, also from Arrowind Hobby. It
is rated at 30C discharge rate and 6C
The power and control systems are
laid out with the motor, battery, ESC
and receiver, two servos and the CAM
unit at the rear. The battery is attached
to the fuselage with Velcro tape.
The Cumulus has a hatch to access
the battery so the battery can be
connected at the last moment before
launching without the hassle of taking
the wing off to connect or disconnect
The finished Cumulus weighed 26. 4
ounces. The CG was roughly 87mm
from the LE near the fuselage. The
recommended CG is 90mm, so I added
0.5 ounces of weight near the elevator
to move the CG to 90mm.
The first flight was okay, although
there was a 6 to 8 mph wind. The climb
was good, so I let it all out to climb at a
90° angle to see how the power was. The
Cumulus reached the 200-meter cutoff
altitude in 20 seconds! There is plenty of
power to spare.
The entire flight was slightly edgy.
The dive test indicated that it may be
somewhat tail heavy. The airplane did
not pull out of the dive and it might
have tucked down a tiny bit. I let two
expert pilots fly it and both agreed that
it was slightly tail-heavy.
The second flight was with a fully
charged battery and the tail weight
removed, putting the CG at 87mm.
The climb was as spectacular as the
first one; with a little less wind, the
Cumulus performed noticeably better.
It is easy to control and is without
any bad tendencies. It was in the late
afternoon and there was little thermal
activity around, but the Cumulus stayed
up better than I
A week later, I
asked my old flying
buddy to come out