REICHARD MODEL SPORT CUMULUS - 2012/08

Reichard Modelsport, in the
Czech Republic, manufactures
the Cumulus. It is sold through
Hobby Club in San Clemente, California,
which also supplies the power system
components. The Cumulus, designed for
FAI F5J competition, is also suitable for
Altitude Limited Electric Soaring (ALES)
contests in the US.
The Cumulus has a fi berglass/carbonfi
ber pod and a carbon-fi ber boom.
The wing is balsa-covered foam and
fi nished with Oracover (UltraCote). The
stabilizer and fi n are built up with balsa
and covered with Oracover, and the
control surfaces are prehinged. There are
only a few small steps to assemble the
airplane. Only the servo tray needs to be
constructed, for which all the parts are
provided.
The instruction manual is brief, with a
few photographs to fi ll in for the lack of
text. The accessory pack is complete—
from pushrods to servo linkages.
Following is a brief overview for
assembling the model:
1. Install the mounting plate for the
horizontal stabilizer.
2. Attach the top and bottom vertical
stabilizers to the boom, making sure
they are perpendicular to the horizontal
stabilizer. A hole is predrilled to install the
carbon-fi ber rod joining the upper and
lower fi n to provide more strength.
3. Mount the wing to the fuselage and
use the wing to align the tail group when
gluing the tailboom to the pod. Use care
to ensure proper alignment.
4. Install the pushrod housings in the
boom. A slot needs to be cut in front of
the fi n for the rudder pushrod to exit the
boom. The slot should be reinforced by
wrapping it with Kevlar thread. The front
end of the boom was also wrapped with
Kevlar thread. The thread is not provided
in the kit.
5. Install the fi rewall to the pod. The
front of the pod is factory cut to provide
the proper downthrust and right thrust.
6. Install the mounting hardware for
the canopy. Two pieces of magnet were
provided to secure the canopy to the
fuselage.
The pod of the Cumulus is small for
an airplane with a 2.5-meter wingspan.
It has enough room to house a brushless 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
watts.
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
charge rate.
Prefl ight
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 battery.
Test Flight
The fi nished 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 fi rst fl ight 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 fl ight 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 fl y it and both agreed that
it was slightly tail-heavy.
The second fl ight was with a fully
charged battery and the tail weight
removed, putting the CG at 87mm.
The climb was as spectacular as the
fi rst 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
expected.
A week later, I
asked my old fl ying
buddy to come out to help me fl y and take the obligatory
photographs for the review. The wind—
10 to 12 mph—was slightly stronger
than I preferred. I launched the Cumulus
with my buddy on the camera clicking
away. I asked him to time the climb, and
the Cumulus reached the cutoff altitude
(200 meters) in 25 seconds. The wind
felt much stronger at 200 meters than
near the ground.
I proceeded to push the airplane
harder to see how it handled the wind.
It was no problem at all, and easy to
read when lift was detected. A couple
of “high-altitude” landings later, I
felt comfortable enough to drive the
Cumulus to a real “contest” landing.
With maximum fl aps and appropriate
down compensation (3/8 inch down)
on the elevator, the model came in at
approximately 30° nose-down attitude
with no increase in speed. Landing was
easy, even with the wind blowing at 8
to 10 mph. With practice, landings with
top marks can be easily achieved.
Post-Flight Comments
I glued a piece of sandpaper on both
sides of the fuselage to create a better
grip for launching the airplane.
I do not like to use an outrunner
motor for glider power, because the
spinning case can snag wires or lose
parts in the fuselage, but in this case,
the fuselage has so little space that an
inrunner with a gearbox is out of the
question. The wires from the motor are
taped down to the side of the fuselage to prevent accidental snagging.
I added a piece of G-10 fiberglass
board to the front of the battery, to
make sure if the battery slid forward, the
motor’s spinning case would not damage
the battery’s insulation.
The firewall angle is spot-on from the
factory. In level flight, there was no pitch
change with the motor turned on and
off. The contest-type launch will require
a nose-high launch and some up-elevator
to quickly get to altitude.
Because of the small size of the
Cumulus airframe components—pod,
boom, narrow-chord wing—I had
trouble seeing it at distances of more
than 1,000 feet. The dark-colored
bottom helped, but at a distance, it
was hard to see the airplane. Although
the shiny LEs helped, some optical
enhancements could improve visibility.
One can’t always count on having a
timer/spotter who has better eyes than
the pilot.