By Jeff Barrington
- Mid Devon Heli Club
Helicopter Gyros Explained
The purpose of the gyro is to stabilize the tail, without it the model
would be almost unflyable. Early gyros had a motor and two flywheels
inside and at the time worked quite well but they are no match compared
to piezo gyros, which have no motor but use an electronic sensor.
Modern piezo gyros have never been so good and are no longer an
expensive alternative but an essential part of the radio system. Modern
peizo gyros can cost anything from £40 to £300. So how much should you
spend and which one should you buy?
Well at the lower
end of the scale the gyro will be single rate adjusted on the gyro
itself and will not have pilot authority, while at the top of the range
it will probably be dual rate in both normal and heading lock mode
(sometimes called heading hold or AVCS), selectable from the
transmitter, and it will also have full pilot authority.
Modern piezo gyros
have a very fast response, and will need a servo, which can keep up with
the gyro output. Servo speed is measured by the number of seconds it
takes for the servo to turn 60 degrees so a digital servo with a speed
of 0.12s/60 to 0.08s/60 is the ideal but you will have to pay around £60
to £125 for it.
The best way to adjust gyro gain is to turn it up until the tail
wags in forward flight then turn it down a little. You should be able to
get near 100% gain, if you cant then try changing the length of the
rudder servo arm, there is no point spending serious money on a good
gyro and then only using 50% gain.
On a standard gyro when you input a rudder command the gyro will try
to correct the tail back to the centre, the higher the gain on the gyro,
the less tail authority you will have.
With pilot authority the gyro gain decreases as you input commands so
you can have 100% gyro gain and still have full tail authority.
With the gyro in normal mode the tail will weathercock to some
extent so when flying circuits or hovering in to wind the tail will tend
to follow the line of the model. In heading lock mode the tail stays
wherever you put it, so it is quite easy to fly the model sideways or
backwards at speed without losing the tail position. The only downside
to heading lock mode is that you have to steer the tail all the time as
it will not naturally follow the model, and if you enter a manoeuvre,
say a loop, with the tail offline it will stay offline throughout the
manoeuvre. If you are not sure which mode the gyro is in, with the radio
on and without the engine going, move the rudder control fully to one
side, if heading lock is selected the servo will stay at one end until
you move the stick back to the other side.
I have used Futaba, JR, and CSM gyros on JR radio systems with no
problems at all but I would advise the use of a matching rudder servo in
the case of JR or Futaba, as they would have been designed to work with
their own servo.
Barrington - Mid Devon Heli Club
If you have only recently started in this hobby you probably
have a 30-sized model with wooden blades and basic radio
equipment, fair enough, you don't want to spend too much on a
new venture, as you may not like it. As your flying progresses
you will want to improve your equipment accordingly. Here are
some of my suggeastions on what to upgrade.
I mention this first, as a quiet muffler is absolutely
essential, flying sites are lost due to noise complaints so the
quieter the better. Avoid tuned pipes as they are generally
noisier, the extra power is not needed and the engine is much
more difficult to set up.
Most carbon glass blades will be an improvement on the wooden
ones that came with the model. There are 2 main types or
sections, semi symmetrical which have a flat bottom to give more
lift, and fully symmetrical which are the same shape both sides.
Which ones you go for depend on your flying style but without
getting to complicated, symmetrical blades are better for
aerobatics. They give the same pitch inverted as they do the
right way up, where as semis generally perform better in
More of an essential than an upgrade is a PCM receiver, as PPM
receivers have no fail-safe system. If your transmitter is a
very basic one it might only have 1 or 2 pitch and throttle
curves and probably only 3 point curves at that. This will be
limiting, particularly if you want to progress to aerobatics.
The more expensive transmitters will have a minimum of 3 pitch
and throttle curves, and many more functions, which become more
useful as you progress.
Gyro, Servo and Tail Control
The best gyro you can afford along with a suitably fast rudder
servo will probably be the most noticeable upgrade you will get,
depending on what gyro you had before of course.
My Raptor 30 cost a little over £200 but the gyro and servo
cost nearly £300! The point is no matter how good the model it
will be much better with a good gyro. The control from the
rudder servo to the tail pitch control will vary from one model
to the other. A smooth straight direct control is desirable,
tail boom mounted servo brackets and carbon rod upgrades are
available to suit most models and these tend to work best.
The latest digital servos are much more accurate and responsive
and start at around £40, although if you have a 60 sized machine
you may want to spend more on higher torque servos.
Fuel Header Tank
There are at least 3 good reasons to fit a header tank, it will
stop problems with fuel foaming, it gives a consistent level of
fuel no matter how much fuel is in the main tank or what ever
the attitude of the model, and you get longer flight times.
There are plenty of after market metal upgrades available for
most makes of helicopter. They are usually anodised in purple or
gold colour and even if they are not needed they do look nice on
the model. A metal swash plate is probably the first upgrade,
followed by the washout assembly and many more.