56 MODEL AVIATION
BY JERRY SMITH
Plane Talk: Kangke USA Dragon 90 ARF
THE DRAGON 90 is another in a long
line of ARFs that Kangke Industrial USA,
Inc. has manufactured to attract the wannabe
and experienced 3-D pilot. It is not a
trainer, but a true aerobatic aircraft that
was purposely designed to fulfill the needs
of those craving fun and excitement while
showing their skills to the crowd.
RC airplanes is a wide-ranging field
that engenders passion in its practitioners,
and like all great forms of expression it
creates skills and provides fun and
excitement.
Looking at the Dragon, the first thing I
noticed was that fat constant-chord wing.
The airfoil was fully symmetrical and its
high point was well forward toward the
LE. Its chord thickness was approximately
3 inches. The 31/2-inch-wide ailerons were
flat and extremely effective when it came
to roll rate.
The tail group looked rather small
compared to the wing but had generous
elevator and rudder area. The fuselage was
a plain box, keeping things simple, with
the engine completely uncowled and
utilitarian for any adjustment needs. This
was a simple airplane indeed.
The UltraCote covering was expertly
applied. The enormous supplied graphics
The Dragon can be set up as a sport
or 3-D trainer. It’s best at Harrier
and hovering maneuvers.
Removing the necessary covering from the
stabilizer and fin I glued the parts in place
with 30-minute epoxy, wiping off the
excess with alcohol and a paper towel. I
mounted the control horn on the stabilizer
and hinged it in place.
I installed the tail wheel and then
hinged the rudder, capturing the tiller on
the tail-wheel strut. I affixed the wheels to
the landing-gear struts and fastened the
landing gear in place with the supplied
bolts.
I mounted the servos in the laser-cut
holes in the servo tray with servo mounting
screws and then assembled the pushrods. I
found that the rudder pushrod was roughly
2 inches too long (better too long than too
short). I cut it off and made a new hole and
groove for the wire. Do not make the final
bend in the wire at the servo arm
beforehand.
Pushrod installation is completed by
hooking up the clevis at the control
surface. Make sure the surface is neutral
and that the servo is centered. Lay the wire
on the servo arm and mark the point for the
bend in relation to the servo-arm hole. Put
in the bend and secure the wire with a
keeper.
After marking the holes in the firewall
and drilling them, it was time to install the
blind nuts to retain the engine mounts. I
found this to be next to impossible; my
big, fat hand would not fit in the fuel-tank
opening to position the nut when I
attempted to insert a bolt from the opposite
side to thread it onto.
I changed the blind nuts to 8-32 US
thread. I soldered a piece of thin cable to
the end of a short length of soft steel
threaded rod. Passing the rod through the
hole, I installed a nut on it, grabbed the
cable, and pulled the nut into the hole.
How easy! Then I put a washer and nut on
looked outstanding on the huge wing,
from tip to tip.
When I opened the box I found a wellpackaged
Dragon 90. All the major
airframe parts were in plastic slips. Other
items included an engine mount, wheels,
formed landing gear, fuel tank, control
horns, pushrods, general hardware, servo
plate, decal sheets, and a 12-page
assembly manual.
Construction: Putting the Dragon 90
together was a no-brainer. I installed the
servos in the wing, pulling the leads
through the tubes to the center. They
barely made it, so you will need a couple
6-inch extensions.
I installed the large ailerons with the
provided cyanoacrylate hinges and fixed
them in place with thin cyanoacrylate. After
installing the control horns I hooked the
linkage to the servos, and
the wing was
complete.
This simple sport
model will add fire
to 3-D flight
10sig2.QXD 8/23/07 10:31 AM Page 56
October 2007 57
Photos by the author
Tail weight had to be added to balance
the Dragon. The correct balance point is
at 30% of the wing chord.
A Du-Bro Exhaust Diverter is a must to keep residue from the SK .90 engine off the
wing. Tru-Turn’s latest anodized spinner helped promote ease of starting.
The neat and clean pushrod-exit,
stabilizer, and fin slots are arranged to
accommodate the best configuration.
The Dragon 90 is built with
quality laser-cut parts that fit
together seamlessly.
The Dragon’s minimal parts count means quick assembly. Slots for cyanoacrylate
hinges are premade. Tall landing gear makes it suitable for electric conversion.
There is plenty of room in the radio compartment. The
receiver and battery fit best up front, behind the tank.
Four bolts hold the landing gear in place.
The Dragon 90 assembles fast. Consider
using Loctite on these bolts.
Hardware supplied for mounting the
wheels is great; it’s not just a threaded
bolt for an axle, as is seen so often.
10sig2.QXD 8/23/07 10:40 AM Page 57
58 MODEL AVIATION
Kangke SK
.90AR Engine
The SK .90AR is
new in the line of
engines that Kangke
Industries is marketing.
In addition to it are
the SK .50A, SK .70A,
and SK .80AR twostrokes.
The .50 and
.70 are aluminum/
brass/chrome, while
the .80 and .90 are
ringed.
The .90AR’s casting is well finished with a clean, crisp
appearance. The machining has a smooth finish and adds
much to the power plant.
All engines have Schnuerle porting to boost
performance while delivering exceptional fuel economy.
The balanced crankshaft is supported at both ends by ball
bearings for even, friction-free performance. Carburetors
have high- and low-speed mixture adjustments and are
designed to operate on muffler pressure.
Power output, expected life span, handling, and fuel
consumption are basically the same for all the engines. The
SK .90AR comes with a muffler, a remote needle valve,
and a two-year warranty.
The SK .90AR has a displacement of 14.9cc, the bore is
28.12mm, and the stroke is 24mm. It has a practical range
of 2,300-10,400 rpm and weighs 25.96 ounces.
The online manual recommends a break-in period on a
13 x 8 propeller and then a 14 x 8 to 15 x 6. After running
a half gallon of 15% fuel through it, I found the SK .90AR
to be easy to start and found that it performed within the
limits specified in the manual with the recommended
propeller sizes. MA
—Jerry Smith
Left: The graphics provided for the
Dragon 90 are outstanding. It’s best if
they are applied wet with soapy water.
Below: The large control surfaces can be
deflected 30°-40°. Its structure is very
strong.
The airfoil on the Dragon 90 is almost 3 inches thick with a
high point that is well forward. Landings are comfortable.
the threaded rod, on the far side, using a wrench to pull it in
place.
Don’t get frustrated; do as I did. The how-to article explaining
this technique was published in the March 2007 MA.
After assembling the fuel tank I found that the hole in the
firewall was too small for the stopper. Using a motor tool I
enlarged the opening, allowing the fuel tank to fit properly in the
hole.
Assembling the Dragon was straightforward except for the
few problems I mentioned.
Flying: Before flying the Dragon it was crucial that I check the
CG. I never take for granted that the numbers the manufacturers
throw out are accurate; I like to know, for my own satisfaction,
what they represent in the way of chord percentage. The Dragon
was inherently nose-heavy!
The manual instructed to balance the Dragon at 4-43/4 inches
(231/2%-28% of the wing chord) from the wing LE. For a
constant-chord aerobatic sport model such as this, I generally
start with a CG that is at the 30% point with the intention of
moving it back from there.
To achieve the aft CG location I had to add 5 ounces of
weight to the tail on the bottom of the fuselage just ahead of the
fin. This affected the overall weight, causing the model to exceed
the 7-pound maximum by 2 ounces.
The Dragon flew great at the 30% CG setting—not a bit tailheavy
or unstable. Little down-elevator was needed to hold the
model level when flown inverted, telling me it was close to
neutral.
10sig2.QXD 8/23/07 10:44 AM Page 58
The SK .90 engine had enough power
to haul the Dragon straight up and pull
out of hovers. You can perform most 3-D
maneuvers, from mild to wild, with this
aircraft if you have the skills. It is stable
and goes where you point it; it’s easy to
fly.
Most of the time I flew the Dragon at
half throttle. I used full throttle only
when going vertical and low idle when
heading for earth.
The first few flights were with an
APC 15 x 6 propeller. Then I switched to
a 14 x 6, and the SK .90 seemed to run
happier but may have needed more breakin
time.
I installed one of Tru-Turn’s latest
anodized spinners to facilitate starting.
Don’t they look cool? However, the
engine did perform when told to, and
that’s what counts.
I mounted the engine upright, which
gave the muffler exhaust an issue with
the wing. I installed a Du-Bro exhaust
deflector (item 697) and that did the trick,
leaving just a bit of exhaust residue on
the stabilizer to wipe off.
If you are an intermediate or expert pilot
who is looking to improve your skills or
you just like to bum around the sky, the
Dragon 90 will give you your RC fix in
no time. Paired with a good, strong
engine it will satisfy you with any 3-D
maneuvers you have in mind.
This model is low in cost, high in
pleasure, and simple to maintain. You won’t
go wrong with one in your hangar. MA
Jerry Smith
[email protected]
Manufacturer/Distributor:
Kangke Industrial USA
65 East Jefryn Blvd.
Deer Park NY 11729
(631) 274-3058
[email protected]
www.kangkeusa.com
Sources: