Introduction to RC Helis
Welcome to the world of R/C Helicopters. The helicopter is probably
the most challenging form of radio control model, being mechanically complex in
nature, and requiring 100% concentration while operating.
Flying a model chopper is not unlike balancing a metal bearing or a marble
on a piece of glass. If the mechanics of the chopper have been adjusted and
aligned very well, it is similar to having a flat piece of glass. If the chopper
is not set up just right, it is like having a convex piece of glass where the
bearing wants to keep rolling off to one side.
The first thing the budding helicopter pilot must realize is that the model
works on the very same principles as the full-size and controlling the chopper
is just as difficult, if not more-so due to size and orientation. It is not
simply a matter of pushing one button for up, and another for forward flight,
etc. Flying a helicopter, just like flying a model aircraft, is a skill that
must be learned and that can only happen with practice . . . now that I have you
thoroughly discouraged! Although building and flying a model chopper can be
complex, it is also extremely satisfying. Being able to accurately control a
vehicle which you can hover, fly forward, backward, sideways, and do all kinds
of interesting maneuvers and aerobatics, as well as land at your feet, is very
exciting.
Unlike learning to fly a model airplane where flying with an instructor is a
must, you basically learn to fly helicopters by yourself. Before you start
flying, however, some time with an experienced helicopter pilot will be
invaluable. He can help you set up your helicopter (it is extremely important to
have the mechanics set up accurately for safe and easy flying) as well as give
you some tips on flying; what to expect from your model and how to operate the
controls.
How does a Chopper Work?
There are basically two different types of helicopters, those that have
collective pitch and those that do not. Collective pitch is where the pitch of
the main rotor blades may be simultaneously increased or decreased to change the
amount of lift. This gives a quicker response to changes in vertical thrust as
controlled by the pilot. On helicopters without collective pitch, the amount of
lift is controlled entirely by the speed of the rotor blades or in other words
the speed of the engine (throttle control). The reaction time is longer and thus
the control is less responsive.
There is a trade-off, however, and that is the cost and complexity of the
rotor head. There are a great deal more moving parts in a collective pitch rotor
head and thus, they are more expensive. Most current choppers are of the
collective pitch variety.
On a standard, collective pitch helicopter there are four controls and these
are operated by five channels of your radio system. These controls are the
collective pitch, the fore and aft cyclic pitch, the side to side cyclic pitch,
and the tail rotor pitch. The collective pitch must also be coupled with the
throttle of the engine so that when more load is put on the main rotor blades by
increasing the pitch, more throttle is applied to help overcome the additional
drag.
The left stick of your radio transmitter controls the collective and
throttle in the vertical direction and the tail rotor pitch in the side to side
direction. Your right stick controls both cyclic operations; up and down for
fore and aft control and side to side for the cyclic side to side control. There
are also mixing functions which mix the throttle and collective functions, and
the throttle/collective and tail rotor functions.
Operation
The engine of a helicopter drives both the main rotor shaft and the tail
rotor via a series of gears and a clutch. As the motor comes to speed, the
clutch engages and begins to turn both rotor systems. Generally, at this point,
there is no pitch on the main rotor blades and thus no lift. The throttle is
increased until the main rotor blades are brought up to speed. To lift the
helicopter collective pitch is applied.
Because, for every action there is an equal and opposite reaction, when the
engine is forcing the rotor blades to turn in one direction, the body of the
helicopter will want to rotate in the opposite direction. The function of the
tail rotor is to correct this tendency. The tail rotor blades provide enough
thrust to the side to keep the helicopter pointing in one direction. By
increasing or decreasing the pitch of the tail rotor blades the direction the
helicopter is pointing can be changed.
The cyclic control permits the main rotor blades to be varied independently
making the helicopter move in a horizontal direction. If one of the rotor blades
increases pitch as it approaches the rear while the opposite blade decreases in
pitch while approaching the front during its rotation, more lift will be
produced in the rear, tilting the helicopter forward, and thus moving the
helicopter in a forward direction. The same principle applies for side to side
and rearward, allowing the helicopter to fly in any direction.
The control of the cyclic and collective pitch is transferred from the radio
servos to the rotor blades via the swash plate. Part of the swash plate is
stationary while the other part is allowed to rotate with the rotor head.
Control linkage is connected from the servos to the stationary part of the swash
plate as well as from the rotating part of the swash plate to the rotor head.
When flying a chopper, small control inputs are continually required by the
pilot to correct for deviations in the flight path. That is why 100%
concentration is required in chopper operation. The more accurately the chopper
is set-up, the fewer the number of corrections that are required by the pilot.
What Happens if the Engine Stops?
Auto-rotation is a way for helicopters to land successfully after a loss of
power from the engine to the rotor drive systems. This is accomplished with the
aid of a special device known as an auto-rotation clutch which allows the rotor
blades to free-wheel. As soon as power has been cut, the throttle/collective
control is brought back all the way. This will usually bring the main rotor
blades to have slightly negative pitch. As the helicopter starts to descend, the
air moving through the blades will keep them spinning. The spinning blades will
act like a parachute in reducing the helicopters decent. When the helicopter
nears the ground, the pilot increases the collective pitch making the pitch of
the blades again positive. The momentum of the blades is converted to lift,
slowing the descent of the helicopter down further, enabling it to land softly.
What Will I Need?
The following is a description of the items you will require to start flying
a radio controlled model helicopter.
The Helicopter
When choosing your first helicopter you first have to decide which type of
chopper you wish to purchase, a collective pitch machine, or a non-collective
pitch machine. If you are starting the R/C hobby from scratch and must buy
everything, I would strongly suggest the collective pitch machine. Although it
is a bit more expensive initially, it is by far the more versatile of the two
and will help you enjoy more advanced stages of the hobby after you have learned
to fly. You will also find the learning process easier with a collective pitch
machine.
On the other hand, if you are already into radio controlled aircraft and
have an aircraft radio, and an aircraft engine in the range that would fit a
non-collective machine, this route may be desired to drastically reduce the
start-up cost and to get you involved in the sport with less money. Once hooked
however, you are bound to want to move up to a collective pitch machine. I am
going to assume you are starting from scratch and will continue with the idea of
starting with a collective pitch helicopter.
Unlike aircraft where there are specific trainer models geared solely for
the first time kit, the differences between helicopters is more with the major
difference being size and precision. The larger and more precision a machine is,
the better it will fly. These machines would make great training helicopters but
they are usually a lot more expensive, with high precision parts, and would be
very costly to repair in the case of a crash. They are better suited toward
competition and the experienced modeler where accidents are usually minimal.
Keep in mind, when learning to fly a helicopter you are bound to have a
crash or two and parts are going to have to be replaced. Replacing parts on a
precision machine could really run you a bill! A good place to start would be a
machine designed for a .30 size engine, a stable flyer with collective pitch,
and one with a good availability of parts.
The Radio
As mentioned earlier in this introduction, a proper helicopter radio differs
from a standard aircraft radio. There are certain functions that must be mixed
electronically and these are found only in radios designed for this purpose.
More and more often, one is able to find radio systems that have functions
suitable to both aircraft and helicopters. If you think you may be involved in
both aspects of the hobby, you may wish to choose one of these for your system.
Other things to think about when purchasing a helicopter system are the
servos and the battery pack. It is desirable to choose servos that have output
shafts that are ball bearing supported. Since the pressure and vibration on the
servos in a helicopter is usually greater than in a plane, bushing servos tend
to wear out very quickly and lose their precision which is extremely important
in the controlling of a helicopter. Because you are using a minimum of five
servos and a gyro (to be discussed later) in a helicopter, and the higher
frequency of control input, it is very desirable to have a larger battery pack
than the standard 600 maH pack that comes with most aircraft radios. A pack in
the range of 1000 to 1200 maH is a better pack to consider. Many helicopter
radios take both of these concerns into consideration and come packaged with
five BB servos and a large batter pack.
Gyroscope
A gyroscope, or gyro, is an electro-mechanical device used in a helicopter
to help semi-automate the response of the tail rotor. In the case of an R/C
chopper, the device fits electrically between the receiver and the servo that
controls the pitch of the tail rotor blades. A sensor measures any unwanted
change in yaw of the aircraft and will correct the situation by increasing or
decreasing the tail rotor pitch to stabilize the movement.
Although not absolutely necessary, it is strongly recommended that a gyro be
used in every helicopter. Controlling an overly sensitive tail of a helicopter
is most frustrating and the gyro can help make the flying much easier and more
pleasurable. Gyros are made by most radio manufacturers for operation compatible
with their systems.
The Engine
The helicopter engine is similar to a 2-cycle aircraft glow engine except
that it has a larger heat sink head for better cooling, and a carburetor with
improved mid-range adjustment. When purchasing the helicopter engine, the
muffler is not included. Usually the muffler comes with the helicopter kit.
Different motors facilitate different starting methods. Some come with a
pull start system for very simple starting. Others use a cone start where an
electric starter is used in a manner similar to starting an aircraft. Still
others use an electric starter and a belt for starting. Please refer to our
section "Introduction to Model Engines" to learn more about the
operation of the engine.
Tools
Since the helicopter is purely a mechanical device, tools for assembly
usually include items such as screw drivers, ball drivers, nut drivers,
wrenches, pliers, etc. In addition to these there are a couple of specialty
tools that come in handy when assembling and setting up the mechanics of your
helicopter.
One tool you may want to consider to assist in assembly is a set of ball
link pliers. The ball link is the most popular linkage piece on a helicopter and
virtually all choppers use them. The ball link pliers greatly assist in the
removing and adjusting of these links. A second tool that is extremely valuable
during set-up is the rotor blade pitch gauge. This device can help you line up
your rotor blades so that your pitch is correct. A blade pitch gauge can go
along way to helping avoid costly crashes and frustration down the road as so
much of your chopper's well being depends on how well it is set up initially and
maintained throughout its lifetime.
Field Equipment
The field equipment you require will depend largely on the type of motor you
have chosen for your helicopter. If you have a glow motor with a recoil
pull-starter, you will only require the basics of a fuel can & pump for
carrying and pumping fuel to your chopper, and a glow plug igniter to supply
current to the glow plug during starting. If you do not have a pull start, in
addition you will undoubtedly need an electric starter powered by a 12 volt
battery to turn the engine over. Please refer to the "Introduction to R/C
Aircraft" section for more information on field support equipment required.
It is virtually identical.
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Dubai RC Hobbies