South Cotswold Soaring Association


SCSA Glider Advice

The radio set.
The radio control (R/C)set consists of a transmitter (the bit you hold) and in the model are a receiver, servo's and a battery. As you move the stick on the transmitter (Tx) it sends a signal to the receiver (Rx), which sends a signal to the servos, which then move the arm on top of the servo in response to you moving the Tx stick. This arm is then connected to the control surfaces on the model via some sort of pushrod. Please see the pictures below.

The most popular manufacturers of radio control radios are Futaba, Spektrum, JR, Multiplex, Sanwa and Hitec. The cheaper R/C sets are usually 2 channel (meaning you can only control 2 functions on the model, e.g. rudder & elevator) and the more you pay, the more features you get.

A 2 channel set will cost about £80, however if you can afford it you are MUCH better off spending a bit more and getting a 4 or 6 channel set with a few extra features. Useful features include servo reverse and "rates". These make it easy to set up your model so that the controls work in the right direction. Another very useful feature is extra model memories. This enables you to easily use the same Tx with several models.

Important facts
R/C sets are available on 4 radio frequency "bands":

  • The newest is the 2.4Ghz band
  • The 35Mhz band - reserved for aircraft only.
  • The 40Mhz band - purely for ground based models, i.e. cars and boats, NOT airplanes or gliders.
  • And finally the 27Mhz band - for use by anyone, i.e. planes, boats, cars.

The best choice at the current time (2010) would be to a 2.4Ghz radio. The main reason for this is that 2.4Ghz sets are pretty much interference free, because they work on a totally different principle to the other 3 types of sets. The 2.4Ghz radios constantly monitor the whole of the 2.4Ghz band and automatically set and change frequencies, meaning frequency clashes are impossible. Typical manufacturers include Spektrum, Futaba, JR, etc and the radios can easily be identified by a short aerial (approx 4" long)

Second choice would be a 35Mhz radio set. These were "the standard" radio sets for airplanes/gliders until the recent introduction of the 2.4Ghz radios. They operate on a number of fixed frequencies, which are controlled by swapping crystals (or by moving small switches) in both the transmitter & receiver. Please see below for more info on crystals.

The 35Mhz band has frequencies designated by numbers i.e. 57, 58 .......84, 85, 86 ...90. Only 1 person can fly on any individual frequency (or number) at any one time, but you can have 1 person on 84, one on 86, etc. As long as you use a different number to the other people flying at that time, that's ok.

Most clubs operate an "even frequencies only" or an "odd frequencies only" rule to reduce the chances of interference - so it's best to check what rule applies in the club you are thinking of joining. The SCSA operates an even frequencies only rule.

The disadvantage of using crystals to control frequencies, is that it's possible to get interference and lose control of your model if someone switches their transmitter on using the same frequency (or number) as you. This is impossible with 2.4Ghz radio sets. Having said that, the 35 Mhz radios have been in use for probably 20 years or more, with no major problems (apart from the occasional accidental interference) so they are still perfectly acceptable.

The advantage of 35Mhz is that the radio sets tend to be cheaper, as people are tending to buying 2.4Ghz sets nowadays. Typical manufacturers include Futaba, JR, Hitec etc. The radios can be identified by having a much longer telescopic aerial (approx 30" long when extended)

You can also use the 27Mhz band radios, but nowadays these tend to be very much "budget" radios and can't really be recommended for flying airplanes/gliders.

Photo of RX, servo and battery

This photo shows a typical 35Mhz receiver (Rx), servo and battery pack.

The Rx is the black box on the right, the blue object is the battery pack and a servo can just be seen within the red fuselage (It's the small black thing on the left with the white L shaped arm)

In the bottom RH corner of the receiver you can just see the top of the crystal.

This photo is about 2/3rds full size. 

Photo of crystal

Picture of a crystal. (as can be seen from the label, this crystal is channel 80 on the 35Mhz band..actually = 35.200Mhz)

NB: this photo is at roughly double actual size.

Photo of Spektrum DX6i transmitter

A typical 2.4 Ghz radio transmitter (Tx).

This particular set is an ideal beginners set, the Spektrum Dx6i

Note the short 2.4Ghz aerial


Photo of transmitter

A typical 35 MHz radio transmitter (Tx).

Note this is a mid-range Futaba FF8 and has lots of extra knobs & switches.

The typical beginners Tx is usually much more simple than this.

These sets come with a telescopic aerial, which is completely retracted in this photo.