The Basics of Flight

The concepts of flight should be understood by a beginner. 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 which 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 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 which are most widely accepted. Some of the trainers are also available in .20 and .60 size but the .40 is the most widely accepted.

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 pro's and con's 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 radio that is chosen must meet the 1991 specifications for narrow band receivers. The actual requirements of these specifications need not be known by the beginner 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 an 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 one of two types of internal systems to help to nullify interference. These are called PPM and PCM. Each has its advantage but they are only available in more expensive radio systems and should not concern the beginner.

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. If a beginner chooses to use only three channels, he can set up the trainer so that the ailerons are not used initially and then add them later. 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 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.

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.

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.

When the right stick is pushed forward, the elevator moves down. This causes the nose to pitch downward reducing the angle of attack of the wing and reducing drag. As the airplane descends its speed increases until drag and thrust are again in balance.

When the right stick is moved right, the left aileron moves down and the right aileron moves up. This causes the airplane to roll to the right meaning that the left wing moves up and the right wing moves down. It will continue to roll as long as the stick is held in the same position. When the roll takes place, lift is no longer oriented vertically so the effective lift decreases. As the angle of the roll increases, effective lift continues to decrease and the airplane will begin to drop.

When the right stick is moved left, the left aileron moves up and the right aileron moves down. This causes the airplane to roll to the left meaning that the right wing moves up and the left wing moves down. It will continue to roll as long as the stick is held in the same position. When the roll takes place, lift is no longer oriented vertically so the effective lift decreases. As the angle of the roll increases, effective lift continues to decrease and the airplane will begin to drop.

When the left stick is moved right, the rudder moves to the right. This causes the airplane to swing or yaw to the right. This causes the left wing to move slightly faster through the air causing an increase in lift. The combination of the yaw and the lift increase on the left wing results in a gentle turn to the right as long as the stick is held in position.

When the left stick is moved left, the rudder moves to the left. This causes the airplane to swing or yaw to the left. This causes the right wing to move slightly faster through the air causing an increase in lift. The combination of the yaw and the lift increase on the right wing results in a gentle turn to the left as long as the stick is held in position.

When the left stick is moved forward, the throttle is opened resulting in an increase in speed of the airplane. This causes an increase in lift and results in a tendency for the aircraft to climb. When the left stick is moved back, the throttle is closed resulting in a decrease in speed. This causes a decrease in lift and results in a tendency for the aircraft to descend.

It is obvious from the descriptions of the effects of stick movement, that any movement can adversely affect the flight of a model. These effects can be overcome by using a combination of control surfaces to achieve the desired results. For instance, the right stick can be moved back when it is moved left. The result of this action would be that the nose of the airplane would be raised to overcome the loss of lift resulting in a banked turn without a loss of altitude.

In order to understand how to properly use the controls, a change in thinking may be required of a beginner who has some basic knowledge of control surfaces. A beginner must remember the forces acting on a model in flight and how they affect the model.

These items should cost about $40. This can vary depending on the brand of the items and the place from which the items are purchased. An assortment of screwdrivers, pliers, and Allen wrenches may also be needed to perform field maintenance.

These items will cost in excess of $130. The cost will vary depending on the brand of the items and the place from which the items are purchased. Field box kits are available for a wide range of prices but can be built from readily available materials. Plans are available for a simple field box that will fill the needs of a beginner or for a basic necessities field box for a beginner who wants something a little more sophisticated. An assortment of screwdrivers, pliers, nut drivers, and Allen wrenches may also be needed to perform field maintenance.

Using a Flight Simulator

A flight simulator cannot teach a beginner to fly. There are no magic programs built into a simulator that teach the user the correct way to perform a maneuver or alert the user when a maneuver is done incorrectly. A simulator is exactly what the name implies, a program that simulates the actions of an airplane. It is an easy and convenient way to practice the simplest turns to the most complex maneuvers even when it is dark, wet, windy, cold, etc. A simulator can benefit a beginner greatly if used properly. For a beginner, a simulator can be invaluable in developing approach coordination. When a model is flying toward the flyer or approaching, the controls are backwards. To make the model go to the flyer's right, the stick is moved to the left. Being able to move the stick in the correct direction without thinking takes a lot of practice. This can be done on a simulator.

There are three (3) commercially available R/C flight simulators that offer simulation of powered airplanes. Each of the simulators is DOS based but will run under Windows 95. The system requirements are 386 processor or higher with a sound card. All simulators use vector graphics to generate the images of the models and the surrounding area. Each one has its own distinctive features, requirements, advantages, and disadvantages. A prospective buyer should examine each of these carefully before choosing the one to buy.

A beginner can benefit from the use of an R/C simulator by using it between flying sessions to practice the things that he has been taught by his instructor. Using the instructions he has been given, he should practice only those things that he has been taught while working to improve coordination and developing a feel for each maneuver. He can use it prior to a flying session to build confidence in his ability to control the model.

With the help of experienced modelers, a beginner should be able to make a somewhat educated guess as to which trainer system best fits his needs. There are many sources from which a beginner can purchase the equipment that he will use to begin the hobby. Most people live in or near a city that has a hobby shop that carries R/C equipment. The prices may be higher than those from a mail order house but the owner of the shop can be a big benefit to the beginner. Mail order houses usually have a larger selection than local hobby shops but the beginner must know exactly what he wants to buy and place the order for everything at the same time to avoid incurring multiple shipping charges.

When a beginner makes the decision to become involved in R/C aircraft modeling, he must be willing to devote his time and money to the hobby. He must be willing to tolerate disappointment and frustration. Although R/C modeling can be frustrating and disappointing at times, it can be very rewarding and a lot of fun.