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The Beginner's Guide to RC Flying Copyright
1997 - 2000 © Howard Sullivan
Radio controlled aircraft
modeling is one of the most exciting hobbies available. It involves many
interests, disciplines, and skills. Some of these are aerodynamics,
electronics, mechanics, drafting and design, composite material construction,
and woodworking, and these are in the airplane alone. There are many other
fields of interest in the hobby of aircraft modeling; far too many and too
varied to try to list. Many people find that many new skills must be learned
before they are ready to begin to learn to fly. The hobby is constantly
changing as new technology is developed. A new modeler may become frustrated at
times but certainly not bored. To reduce the chance of
frustration, a new modeler should become involved with other modelers in order
to learn the necessary skills. This may involve simply visiting a flying site
and becoming acquainted with experienced modelers or joining a club. These
modelers are a source of knowledge and experience that can be invaluable to the
new modeler when he begins to build his first aircraft and when he begins to
learn to fly. An experienced modeler can act as an R/C flight instructor to
teach a new person the skills required to fly the aircraft properly and to
avoid the inevitable crash. New modelers must realize
that a radio controlled model aircraft is not a toy. It is a true aircraft in
that it flies and operates by the same principles as a full-scale aircraft with
the difference being the size and weight. The average model will fly in a range
of 20 to 60 MPH and weigh 5 1/2 to 6 pounds. The force of the model hitting an
object can be devastating especially if it hits a person. Models must be
controlled properly both for enjoyment and for safety. The skills required to
accomplish this must be learned from an experienced modeler. Before purchasing any
equipment, the beginner should ask himself, "Is this a hobby I want to try
to see if I like it or is it a hobby I am going remain involved in for years to
come?" If the beginner is going to
remain in the hobby for years, he might consider buying more expensive
equipment such as a ball bearing engine and a six (6) channel radio
system. Otherwise, he should try to
keep his initial outlay as low as possible.
A beginner can limit his spending to as little as $200 by buying good
used equipment but care must be taken to ensure that the equipment is
reliable. At the other end of the
scale, a beginner could easily invest $1000 on new equipment if he is not
prudent with his purchases. The topics that will be covered
will be relating to a beginner or novice and a trainer airplane. The
information relating to all aspects of R/C powered flight can be overwhelming
even to the most seasoned pilot. Those disciplines relating to the more
advanced levels of R/C flight will most likely be learned as the skill level of
the novice improves and the goals are more defined. The Basics of Flight A beginner should understand
the basic concepts of flight. The theories behind the physics of flight are
covered in many volumes of books. There are different and sometimes conflicting
theories and arguments as to how airplanes fly, but the one accepted principle
is that lift is generated as a result of the air pressure on the bottom of the
wing being higher than the air pressure on the top of the wing.
The Lift Diagram shows some
of the basic terms relating to a wing section.
These terms are common to R/C flight.
There are four (4) primary
forces that act on an aircraft in flight; thrust, lift, drag, and weight. Thrust is the force applied by the
combination of engine and propeller acting to pull the aircraft forward. Drag is the resistance against the aircraft
by the force of the air against the forward facing surfaces. Weight is caused by gravity. In order for a constant speed to be
maintained, thrust and drag must be equal.
In order for a constant altitude to be maintained, lift and weight must
be equal.
Lift increases as the
velocity of the air passing over the wing increases or as the angle of attack
increases as long as the flow of air over the wing remains smooth. Actual flight is attained when the force of
the lift equals weight. An aircraft pivots about
three (3) axes; the yaw or vertical axis controlled by the rudder, the pitch or
lateral axis controlled by the elevator, and the roll or longitudinal axis
controlled by the ailerons. It can pivot
about any one of these individually or in combination based on the control
surfaces that are moved and the direction of the movement.
When the rudder is moved to
the right, the aircraft will rotate to the right about the yaw axis and vice
versa. When the elevator is moved up,
the aircraft will pitch the nose upwards. The ailerons move in opposite
directions. When the left aileron is
moved up and right one down, the aircraft will rotate to the left and vice
versa. The Basic Trainer Quite often a person has an interest
in model airplanes and visits a local flying field just to observe. He sees all types of airplanes from trainers
to pattern planes to scale World War II fighter planes. His interest is piqued by all the fabulous
looking models. He thinks, "I have to have one of those
Mustangs." He immediately sets out
trying to find a P-51 model to begin his modeling hobby. This is a serious mistake. Many hours of
training and practice are involved before a beginner has the ability to handle
the more advanced models. A beginner
must realize the dedication that is required to gain the ability to fly the
type of model that initially spawned his interest. He must begin the hobby with a basic trainer and progress through
different levels of models until his goal is reached. A trainer is a specific type
of model aircraft that is designed to be stable in flight. This means that it has an inherent ability
to correct itself and overcome the rotational forces applied so that it regains
straight and level flight. Most
trainers are designed to that they remain stable in slow flight so that they
are easy to land.
The Basic Trainer diagram
shows the components of a common trainer.
There are certain criteria
that a trainer should have in order to be satisfactory for a beginner. 1.
High Wing
- A high wing model is inherently more stable than a low wing model due to
pendulum effect. Since the weight of
the model is below the wing, the fuselage tends to swing downward like a
pendulum in order to equalize forces. 2.
Flat Bottom Wing - The wing cross section should have a virtually flat bottom. This type of cross section has more gentle
flight characteristics that are necessary for a beginner. 3.
Dihedral -
The wing should have some dihedral.
This means that the tips of the wings are higher than the center. The effect of the dihedral is to try to
equalize forces and keep the wings level or to return the wings to a level
orientation 4.
High Aspect Ratio - The ratio of the wing length or span should be at least 5 1/2 times
the width or chord. This will reduce
the rate at which the model responds to command input allowing more time for a
beginner to react. 5.
Constant Chord - The width of the wing should be the same from the center or root to
the end or tip. This distributes the
weight of the airplane evenly over the entire surface of the wing. 6.
Low Wing Loading - The weight of the model divided by the area of the wing should not
exceed 19 oz./sq. ft. This reduces the
speed required to maintain an acceptable rate that the model descends when the
power is reduced resulting in a lower landing speed. 7.
Moderate Size - Most trainers are for engine sizes between .15 and .60. The smaller ones are more susceptible to the
effects of wind and normally the wing loading is higher simply because of the
weight of the radio equipment. The
larger sizes are easier to fly and easier to see but are more difficult to
transport. Most trainers are for .40
size engines. These trainers have been
widely accepted as the optimum size. 8.
Structurally Sound - A trainer must be able to take the abuses imposed by a beginner. This is especially true for hard
landings. It must be able to withstand
minor crashes with minimal damage. It
should be relatively easy to repair. A trainer that meets these
guidelines will give the beginner excellent service without the frustration
that can occur with an inappropriate model.
With proper instruction, the beginner can progress quickly to his solo
flight and on to the novice stage and still get years of sport flying from the
trainer. There are several trainers on
the market that meet and far exceed the guidelines. These range from the most basic kit to beautiful Almost Ready to
Fly (ARF) models and Virtually Ready to Fly (VRTF) complete with engine and
radio. There are a lot of
considerations when choosing a trainer but the two most basic are time and
money. A trainer built from a kit
has the advantage of being less expensive in some cases. It gives the builder the pleasure of
building, the option of color and trim scheme, and the knowledge of the
structure to perform repairs. The
biggest disadvantage is the time required to construct the model when the
beginner would rather be learning to fly.
Another disadvantage in some cases is the emotional attachment the
builder develops having spent many hours on his creation. The big advantage of the ARF
models is that they can be assembled in a matter of a few hours and the
beginner can be ready to start his flying lessons. The disadvantages are the cost, the unknown structure that is
sometimes weak, and the fixed color scheme.
Most ARF models perform as well or almost as well as any kit built model
on the market. Any beginner who
purchases an ARF model should get an experienced modeler to check the model
before assembly is started. An
experienced modeler can point out areas that may need to be reglued or
reinforced. There are several models that
are widely accepted as being the best in the field although there is
disagreement as to which is the "All Time Best". The list is not an all-inclusive but
includes those that are most widely accepted and therefore are most widely
recommended by novices and seasoned veterans of the hobby. Some of the trainers are also available in
.20 and .60 size but the .40 is the most widely accepted. BEST TRAINERS
Most if not all of the models
listed have been reviewed by one of the major model magazines. A beginner can get information from these
reviews that may help in deciding which model to buy and the areas of assembly
that need special attention. Regardless
of the amount of advice that the beginner gets from experienced modelers, the
final decision is the beginner's. The
choice of a model is an individual choice and all the pros and cons must be
weighed. Each person must decide which
model is pleasing in appearance and performance and which one will meet his
needs. The final consideration should
be that the model should be considered disposable. Many trainers are destined
for the junk pile when it has served its purpose. The Basic Radio System There are many modern radio
systems from which the beginner can choose.
There are several common brands including Futaba, Airtronics, JR, Hitch,
and Ace. Each of these offers a wide
range of options from a simple 2 - channel to a computer assisted 8 - channel
system. The buyer is limited only by
his budget. A beginner should discuss his choice of systems with his intended
instructor. There are several reasons
for doing this, the primary reason being that the student's systems must be
compatible with the instructor's system if it will be used as a buddy box. This issue will be covered in more detail
later. All
basic radio systems consist of four (4) basic components.
There are specific
frequencies assigned by the Federal Communications Commission (FCC) for use
with airborne R/C models. A beginner
must ensure that the system that he chooses is tuned to one of these
frequencies. Most radio system
manufacturers place a sticker on the outside of the carton that says, "For
airborne use only". There is
frequency reference chart available that lists the purposes of all of the
frequencies that are assigned for R/C use. The radio that is chosen must
meet the 1991 specifications for narrow band receivers. The beginner need not know the actual
requirements of these specifications because the systems are required to be
certified to this standard. The owner's
manual for the system will note that the requirements are met and many of the
transmitters and receivers will have a gold sticker to signify this fact. The radio system may transmit
and receive on either an AM frequency or a FM frequency. The FM frequencies are less prone to
interference than the AM frequencies although those using AM frequencies seldom
have problems with interference. Some
radio systems use an internal system, called PPM, to help to nullify
interference. Regardless of the brand of
system, the number of channels, or the price, all transmitters have the same
basic components. Transmitters may have
additional switches, slides, and displays depending on the functions they
perform but the basic components remain the same.
There are two (2) primary
modes of operation, meaning the way the gimbals are set up for operation. There are unsettled debates as to which mode
is the easiest to use and best for a beginner.
The modes of operation have become switched between the United States
and most European countries. Mode I is
primarily used in Europe while Mode II is used in the United States.
Mode I started in the days of
reed actuated proportional systems. The
transmitters were uniformly set up in this manner. The thought was that the elevator and rudder or ailerons were the
primary controls and each should be operated by an opposite hand for precision
control. Later this carried over into
the more modern proportional systems since this was the mode used by most
modelers.
In later years, the thinking
changed to the Mode II configuration. More modelers believed that it was easier to control the primary
surfaces effectively with the same hand.
Mode II grew in popularity and is used almost exclusively in the USA. A beginner does not have to be concerned
about which mode he should select since most manufacturers install the gimbals
according the most widely used mode for the nation to which the radio system is
being shipped. There have been discussions
over the years involving the number of channels with which a beginner should
start. Some people say that only three
(3) channels should be used; rudder, elevator, and throttle. The argument here is that it is easier for a
beginner to only be concerned with using the rudder to make turns and not be
concerned with the ailerons. Others
contend that four (4) channels should be used; rudder, ailerons, elevator, and
throttle. The contention in this
argument is that by not using ailerons, a beginner must go through a second
phase of beginner training that being learning how to use ailerons. A four (4) channel system offers better
control of the model during takeoffs and landings in cross wind
conditions. The four (4) channel
approach to training is more widely accepted today. A beginner might consider
buying one of the more advanced six (6) channel systems to get some of the
features that are not available in the basic system such as dual rate
controls. This feature allows the user
to reduce the sensitivity of the sticks thereby reducing the chance of over
controlling. If the beginner is relatively
sure of future goals that involve the use of a six (6) channel system, he can
consider this an investment in his future modeling and therefore save
money. A lot must be determined before
the initial purchase and should be discussed at length with experienced
modelers, especially the intended instructor, before the purchase is made. The Basic Engine The primary engine type used
by modelers today is a single cylinder, two (2) cycle, air cooled reciprocating
engine that uses a glow plug ignition and a special fuel mixture of methanol,
nitromethane, and castor oil. Most of
the components of the engine are made of cast, forged, or machined
aluminum. The power that can be achieved
from these small engines is phenomenal and can vary greatly from one design to
another. A typical inexpensive .40 size
engine can produce 1.1 horsepower at 11,500 RPM. The same size racing engine
can produce 2.4 horsepower at 20,000 RPM.
All of these engines are the same in their basic components.
The design of the engine
affects its power output, reliability, and longevity. The prop shaft is supported by bushings or bearings. Wear takes place between the piston and
cylinder wall and the prop shaft and bushings or bearings. Most engines on the market today are
classified as ABC meaning the they have an aluminum piston and chrome plated
bronze cylinder sleeve. This
combination normally produces an engine that yields many hours of trouble free
operation if properly maintained. Those
engines that have ball bearings for supporting the prop shaft normally produce
about 25% more power and last much longer. New .40 size engines can
range from $55 to over $400. There are
several that are accepted due to price, reliability, easy starting, and
longevity. BEST ENGINES
The entry-level engines are
more than adequate for the average trainer and are a good investment. They will normally outlast several trainer
airplanes if properly maintained. Construction of the Trainer The subject of actual
construction of a trainer is far too involved and lengthy to be covered in
depth here. The trainer that the
beginner chooses should have a good set of plans and step by step instructions
that guide the complete assembly of the trainer including the installation of
the radio system. There are many books
and articles on this subject that are excellent sources of information. A beginner who has no experience in building
balsa models should seek help from an experienced builder to avoid the mistakes
that can have disastrous effects. A beginner should consider using
a strong, slow curing adhesive to allow time to correct mistakes during
construction. One of the best is an aliphatic resin called Titebond. This cures slowly but yields an
exceptionally strong joint and it sands easily after curing. All joints that are subjected to high
stresses such as the firewall and center wing joint should be joined with a
slow cure epoxy. The main thing that a
beginner must be careful with is the alignment of the wings. Wing alignment is critical in the flight
performance and stability of the trainer.
The kit's building manual should give detailed instructions as to how
this is accomplished and special care should be taken to follow these
instructions. Effects of Control Surfaces The new radio systems are
proportional control meaning that the control surfaces move in proportion to
the amount of movement of the stick. If
the stick is moved half of its total travel in one direction, the corresponding
control surface will move half of its total travel in the corresponding direction. A beginner must first know the effect that a
stick movement has on the model. During
normal flight, the throttle is set so that a constant speed is maintained. This means that thrust is equal to drag and
lift is equal to weight. From this
stable condition, the effects that the stick movements have on the trainer are
described.
When the right stick is
pulled back, the elevator moves up.
This causes the nose to pitch upward increasing the angle of attack of
the wing and increasing drag. If power
is not applied, the airplane will slow down and eventually stall. This means that the air passing over the
wing becomes turbulent and lift decreases until weight exceeds lift and the
airplane will begin to drop.
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