25-Jun-24 - 07:58 PM

Thermal Circle Text - Thermal Circle 05

Written by Hayden Daley - 03 December, 2007.
Welcome to this edition of the soaring circle. In this edition we will take a look at all that is necessary to know when purchasing radio systems for model sailplane use. This column is intended for newcomers to understand the use of functions and equipment when setting up a model; and the names used in RC terminology for model sailplane use.

A transmitter is the control unit used for flying model aircraft. The unit is also often called a TX. The number of channels states the amount of controllable channels it can have, two channel radios are the cheapest, with two functions and they are generally priced at around $100 for a complete system. Two channel systems rarely come with rechargeable batteries, meaning you get the radio converted to rechargeable batteries to fly at most club fields which is an added expense. Most two channel systems have two control sticks, one per channel. The rudder control is on the right joystick, and the elevator is on the left. Slightly more expensive four channel radios have both rudder and elevator on a single stick on the left side; and aileron and throttle on the right. Simple four and five channel radio systems are available for around $300. A four or five channel system of this type can be used to control beginner to intermediate sailplane model aircraft. Radios in the mid range are generally of 6-9 channels with computer operation and are around $700 to $900. The really hi-end system’s are from 12 to 28 channels as provided by the Robbe/ Futaba FX 40 and others and can cost from around $2000 dollars upward. Once you progressed to a computer radio, you will want to use it with all different types of models. Most computer radios now offer glider specific function’s and settings for helicopters and power models.

Transmitter and receiver battery packs that are provided with the radio system when purchased are suitable for most sport applications, when running more channels and digital servos larger battery packs are required. Look to purchase battery packs with at least 800mah to power 4 servos. The battery packs which power the transmitter and receiver will require charging after around 1hour and 20 minutes of normal use. Most clubs require that radio control systems are fitted with rechargeable batteries when used at club fields, please keep this in mind when purchasing RC systems. You must “cycle” batteries, discharge and recharge new nicad packs at least five times for them to work properly, this is critical, you will have problems if you do not complete this task. Sailplane radios are named because of the almost dedicated programming to provide use for sailplane applications. Multiplex, JR/Graupner and Robbe/ Futaba are the most common sailplane radios found in Australia. These radios directly support all of the sailplane functions, with specific names for the glider functions. They have programmable mixing functions to allow any channel to be mixed to any other and they give the pilot the most flexibility when setting up model sailplanes. Each control is adjustable, allowing the computer program to be custom programmed to precisely suit the airplane. These systems are expensive and really only required for scale or competitive soaring applications.

Computer radios have many different functions, when looking to purchase a radio model memories are an important feature. Top of the line systems can have up to 99 model memories or more. Look for a radio with around five or more model memories in the lower priced radio systems.

Dual rates allow you to adjust the movement on aileron, elevator and rudder when flying, by moving a switch. This is a useful feature when test flying a model as it allows for different settings if a model is too sensitive for example. With one switch position providing full movement and the other set for less movement models that are poorly trimmed can be saved by movement adjustment on the controls. This function was first introduced for competition aerobatics and first appeared in the 1980’s, modern radios often offer three rates or three settings and modern radios also have exponential. Exponential or “expo” is the name given to the function that reduces sensitivity of control while still offering full movement of the control surface. Exponential is set by percentage adjustment, generally between 30 and 90 percent is normally set and adjusted so that the user feels comftorble with the control movements and the controls are not sensitive around the center of the stick.

The sub-trim function provides for electronic adjustment of all servos in the model. This eliminates the need to mechanically adjust linkages in the aircraft. Sub trim can be also be used and is more suitable for a central trim setting in the model. When flying a new model you can trim in the air and when you have landed you can adjust the sub-trim so that the radios mechanical trims are centered. When changing model memories you can center the trim so that it will be adjusted correctly after the program is changed and will be set properly for the next flight. This is a highly useful feature found in all computer radios, that you will use when flying a number of different models.

Computer radios generally have one or more free mixes. When flying model gliders an aileron to rudder mix can greatly assist when turning. This mix is easily achieved with a free mix function. When purchasing a radio for model soaring at least one free mix and a v-tail mix are generally the minimum requirements. As the radio becomes more expensive more free mixers and other mixing options are provided. Crow mixing allows for 2 aileron and 2 flap servos to be mixed together to provide braking for the model when landing. With this mix the aileron servos deflect upwards and the flap servos move downward and provide a more effective braking system than flaps alone, the ailerons create more drag. Most six channel systems will have crow braking in the computer system and the crow system is operated by the throttle stick.

Mid range computer radios will generally have built in timers. This allows for the timing of flights to prevent flying longer than the safe operating time of the radio transmitter. When activated, you can fly set flight times with an audible warning when reaching the appropriate time. This feature is more useful in powered models but worth considering for electric powered soaring models.

Another useful soaring function being found in more mid range RC systems is Flight Modes. Normally the domain of hi-end sailplane systems, flight modes allow adjustment of controls and trim by the flick of a switch. Flight modes can be set to the throttle and are an extremely useful feature for RC soaring. When looking to purchase a radio with flight modes take into consideration how many different phases of flight you will have. Competition soaring requires a minimum of four flight modes and some people are using up to eight flight modes in the set up of f3b models, with three phases on the throttle controlled brake settings.

When preparing a model you will require a receiver that is suitable for the model. Receivers or RX’s have sockets for the servos to plug into and they come with varying numbers of channels; from 2 to 16 servos can be plugged into a receiver depending on the number of channels provided. The receiver interprets the signal from the transmitter and moves the servos. Each servo occupies one channel of the radio transmitter. Most radio systems are available without the flight gear allowing a choice of a cheaper transmitter cost if you already have “matching” equipment. The RC industry has adopted a similar plug for servo use allowing different radio mananfacturers servos to be used without problems with plugs matching receivers. Servos can be purchased in different sizes and power levels for different applications. Standard and micro-sized servos are most commonly used in model sailplane and between 2 -8kg torque are suitable for most sailplane servo applications.

RC receivers generally can be classified into three catergories , FM, PCM and the new 2.4ghz systems. FM receivers can be used with other manufacturers TX’s, however 2.4 ghz and PCM receivers have different signal coding and can only be used with the manufacturers transmitters. The advantage of PCM or pulse code modulation is a clearer signal. They generally have dual conversion coding in transmission which helps with models that are having problems with carbon fibre interference and PCM receivers also have failsafe. The failsafe function moves the servos to a preset position in case of interference. Failsafe can also be set to hold, where the servos stay in position after interference problems.

2.4Ghz receivers are named by the use of the 2.4 ghz band for receiving. A Ghz has approximately 5 billion channels (that’s a correct figure!) in it spectrum. These broad band receivers roam the channels constantly changing to prevent the need for separate channels and to deal with the problem of interference causing the model to crash. This new technology is an industry response to the “crowding” of model aircraft spectrums by toy models sold in toy shops. FM transmitters on the popular RC frequencies are now sold with toy helicopters in many toy stores. With the high cost of model aircraft including molded competition sailplanes. This new technology deals with the real threat of toy store products interfering with model aircraft transmitters; and provides technology for RC transmission that is impossible to scan.

This can provide great piece of mind and the radio control systems on the 2.4Ghz band are of a similar cost to radios on the other spectrums. Although certain radios are accepted by the modeling authorities as safe in Australia, this technology is now available but it must be purchased in Australia to be covered by MAAA insurance policy. Please do not purchase this gear overseas, you will not have insurance. I highly recommend the use of 2.4 ghz if purchasing new equipment and if purchasing second hand radios the older technology equipment will be cheaper on the older modeling signal spectrums. When purchasing second hand equipment there is many bargains to be had, but be selective in choice. The JR/Graupner MC18 and MC20 tray radios were particularly reliable and have many glider specific functions. The Multiplex 3030 tray radio had excellent reliability and all programming required for model sailplanes. When looking at a Profi 3030 keep an eye out for the Masters edition, it had more programming option’s, and the Robbe/Futaba FC28 was also a very useful glider radio. In the mid range radios the JR X388 and X347 had specific glider programming and enough options for most people uses, but the do no have flight modes. These radios are being sold at very good prices as people change over to 2.4ghz technology. When shopping for radios look for a clean well looked after unit, model aircraft radios must be treated carefully or they will eventually fail/break. These radios are well supported in Australia and can be repaired if you have a problem. If you have a personal computer, there are several second hand RC trading pages now operating, and you could place a “wanted” ad on these sites requesting a particular transmitter.

That’s it for this issue of the soaring circle, Happy Safe and Succesful Soaring. Hayden Daley

Click on any banner ad to transfer to the website

Text-based competition soaring information website established 2007