RADIO CONTROL HELICOPTERS - 2003/06

118 MODEL AVIATION
IT’S ANOTHER GREAT month to be enjoying the sport of Radio
Control (RC) helicopters! I’m going to start out with a discussion
about a new “big block” for our wing-spinning Tim Taylor types to
get excited about.
The newest helicopter engine to ship in any quantity is the latest
offering from one of the oldest and most respected RC-engine
manufacturers: O.S. Engines Mfg. Co. This is actually its second
big-block .91 helicopter engine, and it has the same SX-H
designation as the .91 that came out a year ago.
However, almost everyone will refer to this new .91 as the “CSpec,”
which is the tag that O.S. put on the end of the model name
to differentiate it. Following is a first look at the O.S. .91 SX-H
Ringed C-Spec engine.
If you have been reading this column for the last year, you know
that the original .91 S-XH had a great deal of power but turned out
to be a bit lacking in manners at times. Some (maybe most) would
not run at all well without the addition of a Perry pump, and even
then they were a bit on the rough side in terms of vibration.
They were also a bit difficult to turn over, requiring a goodquality
starter and a fully charged starter battery. The addition of
head shims or the lower-compression Hyper Head alleviated the
starting problem, but the Hyper Head cost $70-90. And nothing we
tried made the engine smooth like the O.S. .50 or the O.S. .70.
Realizing that it had an engine that needed refinement, O.S.
spent time and money working to retain the power and torque of the
.91 while adding manners and smoothness to make the helicopter
crowd happy. The result is the new .91 SX-H C-Spec “Competition
Special” version.
This is still a ringed engine, and it still fits the 61 mounting
dimensions as far as engine mounts and crankshaft. And it’s still .91
cubic-inch displacement. Other than that, you will be hard-pressed
to find any common ground between the original .91 and the CSpec.
The C-Spec comes with a new version of the Hyper Head
installed as stock, with a gold finish. The crankcase has a black
finish. The head and case are treated with Alumite, which is not a
good conductor for your glow-plug battery, so O.S. recommends
using a backplate bolt as the ground-wire-attachment location. The
taller head may cause installation problems in some helicopters,
such as the Raptor 60, and in others you may have to do some
cutting on the fan shroud for clearance.
The major changes to improve smoothness (besides the head)
include a lighter piston, a lighter connecting rod, and a considerably
different balancing on the crankshaft itself.
My greatest excitement about the new engine is that it comes
with the same three-needle carburetor as the O.S. .70 SZ-H: the
60K-C. The O.S. .70 is one of the most perfect helicopter engines I
have ever owned, and a big part of that is the carburetor’s flawless
performance. Idle, transition, and full-power settings are easy to
tune, and there is little fiddling to be done after the initial settings
are established. If the carburetor works as well on the C-Spec as it
does on the .70, there will be many happy pilots.
The C-Spec’s published specifications include a weight of 19.3
ounces and a practical speed range of 2,000-16,000 rpm. Power is
specified as 3.0 horsepower at 15,000 rpm. Thus you will need to
run a lower gear ratio than the standard 60, which is true of all of the
other .80-.91 engines.
Although the muffler-mounting spacing is identical to that of the
O.S. .61, most of the 60-size mufflers lack the area to deal with the
exhaust volume of the .91 engines. You’ll want to make sure that
you have a muffler designed for the bigger engines.
Eric Hawkinson, 319 Yellowstone Ave., Billings MT 59101; E-mail: [email protected]
RADIO CONTROL HELICOPTERS
The newest big block from O.S. Engines: the .91 SX-H C-Spec,
which is a highly modified version of the original .91 SX-H.
At the shop we’ve run three different exhausts that work well on
these large engines. The inexpensive Mavrikk 90 muffler and the
one-piece Hatori 90 muffler run almost identical. The popular
Muscle Pipe II from Curtis Youngblood adds a definite power boost
and fits the O.S. and YS engines, as does the new two-piece tuned
muffler from Hatori.
Dubbed the “Todd Bennett Special,” the new Hatori SB-16 is
designed to be smooth and quiet while allowing more power than a
standard muffler. The SB-16 uses the stub header with O-rings
sealing the joint and requires that you mount the muffler body to the
helicopter frame.
If the weather cooperates, I’ll have some time on the C-Spec
within a month or so, and I’ll let you know what I find out.
Now I’ll return to the flying-site discussion I started two issues
ago. You may remember me mentioning that you should not expect
to be welcome if you plan to take your new helicopter out to the
airplane field on a busy weekend and fly your first five tanks of fuel
trying to hover in the middle of the runway. Blocking the runway
(effectively closing it to use for all of the airplanes) to practice with
the only type of aircraft that doesn’t have the slightest need for a
runway will not make helicopters welcome.
Nor will most clubs be happy about your model flying around
behind their backs. If your club has a good working arrangement, by
122 MODEL AVIATION
all means fly there. Otherwise, proceed with caution and respect
for your clubmates.
Since you don’t need a runway to fly a helicopter, you may
decide to fly somewhere other than the local airplane field. When
we talk to RC airplane fliers at the shop, many of them want to
get into helicopters because of the ability to operate at places
other than a prepared landing strip.
Often these pilots own, or have a friend who owns, a pasture
or undeveloped field somewhere that would be perfect for
helicopter flying. But we also hear plans to fly at other locations
that make me a bit nervous. The least comforting thing I hear is
someone talking about flying at a local park or school yard.
Sometimes these places work out fine for helicopter flying, but
there are usually serious safety issues involved.
The obvious problem is that many other people—who have
no particular knowledge of RC helicopters and the potential
dangers they pose—use these places. This is especially true of
the younger crowd, who are the natural inhabitants of any school
yard. And even if the area is vacant when you arrive, don’t
expect that it will stay that way for the duration of your flight.
While they are flying, our helicopters hold an almost
universal attraction for people of all ages who happen to be in
the area or passing by. A few years ago some of us local RC
helicopter pilots started flying at a partially finished soccer
complex in the winter months. It seemed like a great place to fly,
with paved parking and more than 80
acres with minimal obstructions.
There was seldom anybody else
there—that is, until we would start flying!
Suddenly there would be anywhere from
two to two dozen spectators of all ages
surrounding us, sometimes parking
directly below the airspace in which we
were flying. Other times they would park
behind us then walk out beside—or even
in front of—where we were standing!
We kept flying there for a while, but
only when there were two or three of us so
that someone could keep the spectators out
of the flying area. This was better than
having no place to fly, but was not a great
arrangement. We were uncomfortable
“bossing” people around, even though it Hatori’s newest product: the SB-16 tuned muffler for the O.S. .91 and YS 91.
was obviously for their own safety. And since there was no
formal flying site, some people occasionally grumped about us
telling them they couldn’t walk out on “their” park property.
Add to that the fact that many city and county parks actually
have rules prohibiting operation of any motorized vehicles, and
you can see that there are many possible obstacles to being able to
fly safely in these areas.
One thing that airplane pilots occasionally don’t realize when
transitioning to helicopters is that just because the helicopter can
hover in a small area doesn’t mean that it will! I advise new
helicopter pilots not to try to do any flying in the back yard.
First, an RC helicopter accelerates much faster than most
people expect when it transitions into flight, so that big back yard
gets small quickly. Second, yards tend to have far too many
obstacles: fences, trees, houses, garages, decks, and power lines.
There are two reasons why these things are bad. The obvious
one is that your helicopter can hit something and explode. The
other reason is that if something goes wrong and your helicopter
misses all of the obstacles and heads for you, those same
obstacles can impede your ability to move out of the way. I don’t
know if it’s ever wise to operate an RC helicopter in your
average-size yard, but I am certain that it is a bad idea for your
first attempts.
Until next time, fly safely and happy rotoring! MA