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If you ever had any doubt whether Bill Winter was one of the model airplane hobby's earliest and
most prolific contributors, check out this article that appeared in the January 1955 edition of
Popular Electronics. Radio control systems were just beginning to be commercialized and priced at
a point where a lot of the public could afford it. Quirks and high unreliability that plagued early
systems had become less of an issue so that airplane and power plant design efforts could take priority
with aeromodelers. In this article, Bill addresses setting proper wing incidence and engine thrust
angles for good, repeatable, stable flight.
Adjusting the Power R/C Plane
By William Winter, Editor, "Model Airplane News"
You can avoid a lot of grief and lost airplanes if you will follow the practical hints
for adjusting and flying your R/C plane given here.
launching their powered airplane models on their first flights make two mistakes. One is to use
too much or too little power, and the other, often the fatal one, is to use too much fuel or too
long an engine run.
It is possible for the plane to fly erratically and finally, uncontrollably, on an early test
flight, and still remain in the air to drift away and be lost. Test flights should be short. The
amount of power is most easily controlled by opening up the needle valve for a rich mixture, recognized
by a smoky exhaust. This assumes that the engine uses a glow plug. If it is a diesel engine, back
off the head to obtain a rich mixture; for ignition engines, retard the spark. It is hard to say
exactly what power would be required but, if one had to guess, about two-thirds would be best under
Another possibility is to place the propeller on backwards, letting the engine "rev up." This
cuts effective thrust by a third or more.
Before attempting to fly the plane, run off a measured amount of fuel and time the engine run.
You don't want more than a minute, and remember, if you decide to lean out the needle valve the
same amount of fuel may double the engine run. A fuel shut-off device is desirable for first tests;
back up the device with a limited amount of fuel.
There are many pros and cons as to whether
the radio should be operative on a beginner's first test flight. Chances are the radio will be a
We'll assume that you have made the necessary ground checks, flight checks, etc. Holding the
plane as described in last month's article, run at a moderate speed (a very slow run if the plane
is light and there is any wind) into the wind. When lift is felt, push the plane forward as you
release it, with the nose ever so slightly above the horizon. You should follow through and use
a smooth technique, the same as you would in golf.
While it is essential to handle glide and power-on adjustments separately, it is not always possible
to distinguish between the two in a short first test flight, especially under exciting circumstances.
However, if the plane is high enough to glide when the engine stops, try to remember whether it
glides too slowly, stalling or appearing to "mush" or falter; or whether it seems to dive ever so
slightly. Did it want to turn of its own accord?
Continue to refine the adjustments begun in the hand glide tests, described in last month's article.
It is essential to work out glide trim first, if at all possible. If the plane was not in danger
of cracking up or getting out of control under power, ignore, for the time being, the power-on adjustments
and perfect the glide trim. But if the ship was in danger under power, take the bull by the horns
and affect any adjustment that will enable you to get it into the air well enough to observe and
evaluate its performance. For example, if the plane turns wildly to the left under power, skimming
the ground, adjust the rudder slightly to the right (perhaps 1/16 inch on a small plane, 1/8 inch
on a large one). If the plane turns to the right, use left rudder. Naturally, rudder adjustments
affect the glide path, but the thrust line (an imaginary line drawn through and parallel to the
shaft of the engine) can be offset to one side or the other on subsequent flights, at which time
the rudder would be readjusted to normal. Everything is aimed at getting a look at the glide.
Observe very carefully how the plane behaves during its first hand-launched glide. The proper
glide path is straight. smooth, and without dips until the plane strikes on wheels. If the plane
dives slightly (B), increase the angle that the wing makes with the airstream, or decrease the
angle of the stabilizer. In severe cases, move the weights in the plane backwards. If the plane
stalls (C) or (D), increase the positive angle of the tail, or move weights forward. Be certain
when you launch the plane that you do not throw it nose up, or too fast, especially in high
winds, as this will produce a false stall, giving you an incorrect idea of the model's performance.
After the glide is reasonably correct, begin to make thrust line adjustments on subsequent short
flights, tilting the engine up or down, left or right, as required to offset the model's power-on
If the plane turns under power to the left, the thrust line would have to be inclined to the
right. If the plane noses up when the engine runs, but glides perfectly, the thrust line will have
to be tilted down, to pull down the nose. The latter is called downthrust. If, under power, the
plane noses down, the thrust line should be inclined upward. Downthrust usually is required.
All adjustments should be made minutely and progressively on repeated trials. Downthrust is imparted
to a radially mounted engine by inserting washers between the rear crankcase cover, at the top,
and the firewall. The washers may be slid onto the mounting bolts. In the case of a beam mounted
engine, put the washers between the mounting lugs and the bearers at the rear of the engine and,
again, the washers may be slid onto the mounting bolts.
by bit, the plane can be trimmed perfectly. Don't expect miracles. Walt Good, several times winner
of the National's radio-control event, once took over 100 flights to trim out his famous "Rudderbug"
exactly the way he wanted it.
Only when unquestionable control can be had all during the flight, should you increase the motor
run. Two to three minutes is maximum for safety on the first few dozen flights.
The operator can do much to smooth out a rough flight by careful use of the rudder. Stalls, for
example, can be alleviated by beginning a turn. The rudder should be applied as soon as it becomes
evident that the plane is going to nose up. Control action is more effective at high speeds; it
is usually absent at the point of stall, A plane may be stalled due to a hard launch, especially
into the teeth of a wind, or after recovery from a spiral or any descending turn, or upon turning
sharply into the wind. A straight ahead, nosing-up action, is a dead-end street; if the plane can
be turned slightly by applying the rudder at the crucial moment, a zoom or stall will be converted
into a climbing turn, dissipating the excess speed. Excess speed simply means excess lift, followed
by a stall.
Just as some auto drivers have a heavy foot, and others a light touch, so do some people tend
to over-control a radio model by forcing it to do things. A heavy hand on the switch prolongs turn
entries until the nose of the plane is screaming earthward. When the control is finally relaxed,
a zoom results. This makes for roller coaster flying, with narrow squeaks on every flight.
Try to develop a light touch, stay relaxed, don't get rattled - it's only a model, remember?
Begin a turn, when it looks steep allow the plane to recover, then resume the turn. The gentler
the flying technique, the fewer out-of-control flights.
For some strange reason it is always easier to maintain good control of a plane that is going
away from you, out in front of the transmitter, than it is when the ship is downwind and plodding
up behind you. Maintain as much distance upwind as possible, recovering ground after every maneuver.
Once the plane is downwind, a skilled hand is required to bring it back with surety. In a strong
wind the plane can be flown out a quarter mile or more, with the assurance that it will glide back
downwind into control again if anything goes wrong. Or at least, the chase will be shortened. The
importance of remaining upwind cannot be overemphasized to the beginner.
Every flier sooner or later gets himself into -hot water. The flier with a little experience
may get to stunting too close to the ground, then finds that everything he does magnifies his difficulties.
Or the beginner may become excited, turn wildly from side to side. The answer? Relax. The plane
is inherently stable and will recover by itself. When it gets right side up and begins to climb,
it will slow down and control may be resumed.
Here's another tip: a plane that is trimmed to glide well on a calm day may stall on a windy
day. If trimmed on a windy day, it will glide too fast or even dive on a calm day. Rudder control
that is adequate in calm weather may be inadequate in a wind. This sometimes fools the flier into
thinking he has lost control. In the wind, the same control must be held longer to obtain an equal
reaction. It is wise to know how thick a shim it takes to alter a stabilizer angle from windy weather
to calm weather trim, or vice versa.
The location of the center of gravity of the plane greatly influences the flying characteristics
of the plane. The CG should be located no greater than 40% of the chord (width) of the wing back
from the leading edge of the wing. The model can be flown successfully with the CG as much as 50%
back on the chord, but the further back the CG is located, the stronger the tendency for the plane
to rear up on turning into the wind, or on coming out of fast turns. Forward CG positions are associated
with better wind penetration. In fact, some builders place the CG so far forward that a negative
angle in the stabilizer becomes necessary to hold up the nose during the glide.
While everything that is known about flying an R/C plane cannot be condensed into two articles,
the fundamentals described in this article and last month's will help you get into the air successfully.
Once the plane is flying reliably, there is a coordination exercise that will quickly give you the
feel of the machine. With plenty of altitude, hold a turn for an eighth to a quarter of a circle,
then reverse the direction with opposite rudder, passing by the original heading to a point a similar
distance on the other side of the heading. Keep repeating the maneuver "S-ing" upwind. As you gain
confidence, hold the turns longer and longer, and you soon will learn how to fly the ship out of
Another valuable exercise is to make wide, shallow circles, by repeated applications of the rudder
in the same direction. This will teach you how to avoid unwanted rudder positions in the popular
self-neutralizing escapements, as well as how to make turns without loss of altitude or picking
up excessive airspeed. Repeated short flights is the way to learn safely.
Easy does it.
Posted August 7, 2012