Types Of Radio
There are many available radio systems, ranging in cost from under £100 to over £2,000! With such a variety available the choice can be quite daunting for someone new to the hobby.
Before even looking at the actual specifications of radios, you should be aware of the “buddy box” feature. While learning two transmitters are required; you hold one transmitter and your instructor holds a second transmitter. The plane actually responds to the instructor’s transmitter, but by holding in a spring-loaded switch, the instructor can give you control for a short while. If you get into trouble (say, you’re about to fly out of the permitted area, or you’re getting too low), your instructor simply releases the switch and immediately has full control to get the plane back somewhere safe. The instructor can then hand back control once the plane is again flying straight and level at a safe height and speed.
All modern radios should support the buddy box feature but it is implemented differently by different radio manufacturers, so usually both transmitters usually need to be of the same brand. Both transmitters also need to be set up correctly for the plane. The link between the instructor and student transmitters is either done with a special cable or wireless via a 2.4GHz link / Bluetooth. The “student” transmitter can be a very basic, or even a second-hand, as you won’t need it once you’ve gone solo. There are often old low-end transmitters sold quite cheaply second-hand, which are fine as a student transmitter.
What are all these different radio systems? 35 MHz, 2.4 GHz, DSMX, FASST, etc?
For a long time, aircraft radio control in the UK was done on the 35 MHz radio band. However, all modern equipment now uses the 2.4 GHz band, and you should definitely get a 2.4 GHz system if you’re starting out now. There are still people using 35 MHz equipment (you can recognise them because their transmitter will have a long telescopic antenna), and it’s still legal to use, but unless you’ve got a big investment in existing 35 MHz equipment, and you know the extra quirks of this system, then you should go for 2.4 GHz. (Note however, that old 35 MHz transmitters often CAN be used as student transmitters for buddy box use, even if the plane and the instructor’s transmitter use 2.4 GHz.)
With the shift to 2.4 GHz and computerised transmitters came lots of different systems, all using the same radio frequencies but with different ways of encoding the information, and slightly different capabilities. Often, the same manufacturer has gone through several different systems, sometimes compatible with each other and sometimes not. (For example, Futaba have had FASST, S-FHSS and now FASSTest, and Spektrum have had DSM, DSM2 and now DSMX.)
The technical differences between these systems almost certainly don’t matter to you when you’re only just starting out, so it’s much more important to look at some different people’s transmitters at the flying field, and ask questions.
Another consideration that you might overlook at first is the cost of receivers. Most people in the club have several aircraft, and usually have multiple receivers as a result. The cost of official receivers varies hugely between different brands, and even between the different systems from the same brand! Again, someone at the field can advise. Regarding popular brands of radio in the club, Futaba, Spektrum Hitec and Taranis systems are the most popular.
How many channels do I need?
The most obvious difference between different radio sets is the number of channels they support, most commonly between about 4 and 18. Each channel controls a single function on the aircraft, usually a single servo. A 4-channel radio is just enough for a basic primary trainer aeroplane (aileron, elevator, throttle, and rudder), but we would not recommend so few channels as this will be very limiting when you outgrow your trainer. (For example, it is very common now to use a separate servo on each aileron, and while you could use a Y-cable to connect both to the receiver, it is better to use a 5-channel radio as it allows more control.)
When deciding how many channels to go for, you should consider how long you plan on holding on to the radio system. You could choose to go for a basic system now, and maybe have to upgrade it in a couple of years if you outgrow it, or you could choose to spend more now and hopefully not have to upgrade. As usual, we’d recommend discussing this with someone at the flying field. However, we will say that there is absolutely no point in buying a transmitter costing more than £500 when you’re starting out!
Computerised transmitter features
Above all else “model memories” is one of the most important features you need when considering a radio. For each model you control from your transmitter, you need the ability to save the settings so that each time you fly the model behaves in a predictable way. Some of the setting that need to be saved to radio include:
Servo reversing – controls which way each servo moves for a particular direction of stick movement. You wouldn’t want to drive a car which turned left when you move the wheel right, and it’s the same with a plane.
Dual rates – means you can reduce the range of movement of the controls to make the plane more docile for learning, yet at the flick of a switch you can have the full range back if you want to do some aerobatics.
Exponential (often called just “expo”) – reduces the servo movement around the centre position of the stick, while still giving you the full movement at full stick movement. This helps to make the plane less “twitchy”, especially while you are learning (most people tend to over-control the plane at first).
Endpoint adjustment – allows precise control over exactly how far each servo moves for full stick movement. This is particularly useful in engine-powered aircraft, as you need to set up the throttle endpoints so that full throttle on the stick opens the engine throttle the right amount, but low throttle on the stick only sets the engine to idle, not stopped completely!
Trims – allow small adjustments to the servo position when the transmitter stick is in the neutral position. These are used to get the plane flying straight and level without any stick inputs.
There are many other advanced features supported by modern transmitters, but you probably won’t use them on your trainer.
Each model you own and fly from your transmitter will need different settings so nearly all modern computerised transmitters support storing settings for more than one model. Each collection of settings is called a model memory. There are a few very low-end transmitters which don’t support model memories, and we would strongly recommend you avoid these, as they would limit you to only one model or having to keep writing all the settings down, changing them manually, and re-checking the plane every time you switch between models. Even basic 6-channel radios will usually support at least 10 model memories. Some higher-end radios also allow you to store model memories on an SD card or transfer them to a computer, which means you are effectively unlimited in how many you can have.
Mode 1? Mode 2?
“Mode 1” and “Mode 2” (and the much rarer “Mode 3” and “Mode 4”) refer to how the four basic controls are assigned to the two main control sticks on the transmitter.
At CAMFC everyone is almost exclusively Mode 2 which has the throttle and rudder on the left-hand stick and the elevator and ailerons on the right-hand stick. We feel this is the easiest arrangement to grasp because the right-hand stick mirrors the controls in a full-size aeroplane (up/down/left/right). Whilst we do have a couple of members who fly Mode 1, once you’ve learnt to fly one way it’s generally not possible to switch to another mode because your muscle memory that you rely on to fly will react instinctively in the wrong directions.