Basic RC Component Installation: The components that make up your airborne RC system include the receiver, servos, battery pack, switch harness, and an aileron extension cable if you are using aileron control (on the wings of your aircraft). You will need a servo for each control function: rudder, elevator, aileron (if applicable), and engine throttle. That is typical for a fuel-powered model.
If you were flying an electric-powered airplane, the throttle servo would be replaced with an Electronic Speed Control (ESC). You plug the ESC cable into the same throttle port (connector) on your receiver as you would a throttle servo. Operating the throttle control stick on your transmitter would then vary the motor’s speed.
Not to complicate the initial story, but most ESCs, intended for the smaller-size electric-powered models, contain an internal Battery Eliminator Circuit (BEC). It will allow you to use one battery pack to power your model’s motor and your RC system (on a shared basis). I’ll write more about this when I get into electric-powered models.
Placement of the RC components involves a couple of considerations. Most important, these radio parts add weight to your model. The components’ location can affect your aircraft’s center of gravity (CG) or balance point. An improperly balanced model (too tail-heavy or nose-heavy) is not going to fly well, or at all. Another consideration is the length of the cables supplied with the various components. Failure to arrange them in a logical order can leave you with cables that are too short or too long.
Traditionally, the RC battery pack is placed up front, just behind the engine and fuel tank. Most basic aircraft designs have shorter nose lengths and longer tail lengths, hence the need for more weight forward. Your battery pack will probably be the heaviest weight in the system. You can put that weight to the best possible advantage while attempting to achieve the correct balance.
Working your way back from the model’s nose, the item behind the battery pack should be the throttle servo, which must be mechanically connected to the engine carburetor. If you have an electric-powered aircraft, the ESC should be located in roughly the same area as the throttle servo. After this we should be approximately at the position of the wing’s leading edge (the front of the wing).
The wing usually covers the model’s “RC compartment.” When you remove the wing (be it located on the top or bottom of the fuselage), you are able to access this section. The front portion of this compartment is where the RC receiver is generally installed. Behind the receiver (in roughly the middle of the space) is a good place for the power (on/off) switch and the charging jack. The rudder and elevator servos go toward the aft portion of the compartment.
Some modelers locate the throttle servo back at this position (shown on the mock-up). If they do, they must run a control rod back forward to the engine throttle. With this kind of arrangement, all the servo cables (and the ESC cable for electric power) can easily reach the mating connector block on the receiver.
If you are using aileron control, it’s a good idea to first plug an aileron extension cable into the receiver. The other end of this extension can pass up toward the wing-mounted aileron servo. When you attach the wing before flying, that aileron servo must be connected to the extension cable. In the same regard, you must disconnect the aileron servo cable from the extension cable when you remove the wing for transportation or storage.
The remaining installation involves running control rods back to the rear or tail surfaces of the aircraft. The output of the rudder servo up front must be connected to the movable rudder at the model’s tail, and the elevator servo output must be connected to the elevator control surface in the rear. More details of these control-rod hookups will be discussed in the installment dealing with model assembly.
Most aircraft have a tail-dragger configuration, in which the model’s tail rests on the ground. A tail wheel is attached to the rudder and moves with the rudder to steer or maneuver the aircraft when it is taxiing on the ground. As you will learn, aircraft that do not have ground-maneuvering capability are usually hand launched.
The other popular aircraft configuration is the tricycle landing gear (trike gear). In this arrangement the aircraft sits relatively level on two rear-mounted main wheels and a single nose, or forward, wheel. That nose wheel is mechanically connected to the rudder servo such that the aircraft can be steered while on the ground. Trike gear is probably the easier configuration for the rank beginner to handle and learn, but hooking up the nose-wheel steering can prove more complex.
The last, but important, item of concern is deploying the receiver antenna wire properly. Each modern RC receiver has a wire antenna measuring approximately 40 inches that exits its case. The smaller the aircraft, the harder it is to “deploy” this antenna wire properly.
The time-honored method is to run the antenna wire from the receiver directly to the outside of the fuselage (through a small-diameter hole), then out to the rear of the aircraft where it can be attached to the top of the vertical fin or the tip of the stabilizer.
The antenna should never be attached to a movable tail surface such as the rudder or elevator; the constant flexing could eventually break the wire. Under no circumstances should you reduce the antenna wire’s length. To do so might detune the output stage of your receiver and greatly reduce radio range. Several excellent reduced-size antennas are available for use with the smaller models; I will get to that later. For now the beginner should concentrate on using the full-length antenna.
These wire receiver antennas can pick up more than received radio signals; they can pick up, for instance, electrical noise generated by the motors inside the servos. Keeping this in mind, it is important that you keep away from the servo actuators when routing your antenna wire to the rear of the aircraft. Try to get the antenna outside and away from these noise generators.
RC System Mock-Up: To put everything in the proper physical size and location, I have included a mock-up of a typical airborne RC system. It is laid out exactly as the RC equipment would be installed in your aircraft. Keep it as a reference for RC-model installations.
I have reached another cutoff point. By now you should have a good idea of what to buy and how to install it in your aircraft. Next month I’ll take up the subject of RC-system operation. From there this series will go into selecting and assembling an Almost Ready-to-Fly, or ARF, trainer, how to fuel and start your engine, and how to make that all-important first flight.
Please keep writing in with your questions addressed to “From the Ground Up” in care of Bob Hunt, Box 68, Stockertown PA 18083; E-mail: firstname.lastname@example.org. We try to think of everything, but there will be missed items or ones with which you have concern. Model Aviation wants this series to grow! MA
Click on photo to view large image with caption