Installation

The gyro must be mounted with the supplied gyro pads and in a suitable location as far away from the engine as possible. This ensures that the gyro is not subjected to vibration and sudden temperature changes. In addition to this, the leads that exit from the gyro must not be taught or flapping against the gyro / frames.

Mechanics

The model helicopter mechanics must be running as smooth as possible and in perfect balance. All components must be tightened correctly and the tail boom must be well supported to obtain good gyro gain levels.

Engine

The engine is the main source of vibration, so unless the engine is running correctly, you will never release the full potential of the CSM SL 560 gyro. The signs of an incorrectly adjusted engine include frothing fuel in the tank, harsh / lean sounding, rich spluttering, over-revving or shaking of the mechanics. You will never achieve good gyro performance until you obtain a smooth consistent engine run, so it is worth spending as much time as is required to achieve this.

Gyro Gain

All tail rotor gyros work on the basis of sensing a movement and installing an opposing movement. We adjust the amount of opposing movement by adjusting the percentage of gyro gain. Too low and we are missing out on potential holding power, whilst too high and the gyro will over-compensate, which is indicated by a visible wag on the tail. The problem is that whilst our model helicopters are capable of having a higher gyro-gain in the hover, the gyro sensitivity increases in certain manoeuvres and modes of flight. So our aim is to run as high a gyro gain as possible without inducing a gyro wag whilst flying. However, the sensitivity of the gyro in certain modes of flight is depicted by many factors. So achieving the best overall gyro performance can only be obtained when the best compromise of all components has been obtained.

Tail rotor blade length

Model helicopters use fixed gear ratios for both the main and tail rotor blades. As such, a change in rpm on the main rotor blades will translate to a change in tail rotor rpm. If we raise the main rotor rpm, the tail rotor rpm will also be raised and vice-versa. For a fixed length of tail rotor blade, a change in rotor rpm translates to the potential tail rotor thrust being increased / decreased as the main rotor rpm is raised and lowered. Tail rotor thrust is usually referred to as ‘tail rotor efficiency’ and this has an effect on the value of transmitter gyro gain you will achieve. The lower the tail rotor thrust, the higher the achievable level of gain, whilst a high amount of tail rotor thrust will dictate a reduction in gyro gain for an identical mechanical set-up.

The CSM SL 560 has been designed to be at its most efficient when in the 75-80% transmitter gyro gain region. So if the tail rotor blades are too short, this will permit a very high gyro gain value, but the available tail power will be low. In flight, this will feel like the gyro is very locked in whilst in the hover and the tail will be insensitive to wagging (over-compensating), but it will fail to hold in aggressive 3-D manoeuvres. In opposition, a tail blade that is too long will give you plenty of power to hold the most aggressive manoeuvre, but will create a low and very sensitive gyro gain. In flight, this means that you will have to lower the gyro gain to avoid constant wagging through manoeuvres. In doing this, the tail rotor will feel much less locked in and the reaction time of the gyro to small deviancies will be low.

As a general rule; the correct size of tail blade is achieved by ensuring the tail has just enough power to hold the most demanding 3-D manoeuvre.

Main Rotor Speed Consistency

If the main rotor speed is deviating then the tail rotor rpm will be changing and the tail rotor power will vary. The result of this is that you will have to set the TX gyro gain to the highest average main rotor speed and you will be losing out on potential holding power at lower main rotor speeds. The more consistent the main rotor speed, the more overall gyro gain you will be able to release for a given mechanical tail set-up and the more effective the CSM SL 560 will be!

Servo Arm length

The faster the tail rotor can react, the better the potential reaction time of the tail rotor system. We are blessed with the fact that tail rotor servos have a rotary arm output. Whilst the actual operating speed of the servo is identical regardless of the length of the servo arm, we can change the effective reaction speed of the servo. The reason for this is that we can enhance the speed by fitting a longer servo arm and reducing the servo travel. Thus whilst the operating speed of the servo is identical, it does not have to travel so far to obtain full tail linkage travel on a longer servo arm.

Example:

I am using a tail rotor servo that operates at 0.10 of a second for 60 degrees of motion. I have then fitted a 10-mm servo arm to achieve 20-mm of linkage travel for 60 degrees of servo throw in each direction. By using the 10-mm arm quoted in this example, we have an actual servo response of 0.10 for the 60 degrees of motion required to obtain the correct amount of tail linkage travel. However, if I were to change to a 20-mm horn, the servo would only have to travel for 30 degrees to obtain the same 20-mm of linkage travel. So the servo is now moving half the distance and will in effect be twice as fast!

However, whilst a longer servo arm will increase the gyro reaction speed, the resolution (accuracy) of the servo will reduce and the gain sensitivity will increase as the servo arm length increases. So we have to adjust the length of the servo arm to match the overall tail rotor / gyro set-up.

Servo Arm Neutral Position

Very few model helicopters have truly corrected tail rotor geometry and this creates a natural flaw in the tail rotor’s ability to stop at equal speeds form left and right hand pirouettes. When hovering a right-hand rotation model helicopter, we need about 8 degrees of tail rotor pitch to hold the tail stationary. If we then make a demand for full right tail rotor, the tail pitch changes from 8 to about 40 degrees. This equates to a change of 32 degrees of tail pitch from neutral to full right tail rotor. If we now return the tail linkage to neutral and then apply full left tail rotor, the ideal change in tail rotor pitch would be from 8 degrees of right tail to 40 degrees of left tail rotor, which equates to an overall change of 48 degrees of tail rotor pitch. So the tail rotor linkage will obviously take longer to move from neutral to full left in comparison to neutral to full right. So when stopping from a right hand pirouette, the servo will reach full left tail linkage travel slower than when stopping from a left-hand pirouette where right tail is activated. In real terms, this means that the gyro gain is in effect higher for the right hand direction and lower for the left direction. This has the effect of producing a slower stop from a right-hand pirouette and a swifter stop from a left pirouette. This is why the CSM SL 560 has an interface function called ‘dual gain tracking’ to help balance out incorrect tail rotor geometry.

However, there is a natural limit to any gyro's ability to compensate for incorrect tail rotor geomettry. So it does help to introduce a mechanical differential on the servo arm to assist the gyro in this respect. This is best thought of as a mechanical offset and in the case of a right-hand rotation machine, the servo arm is offset in the right direction of tail rotor. This has the desired effect of reducing the servos mechanical effectiveness for the right direction of travel and enhancing it for the left. By offsetting the servo arm and using the ‘dual gain-tracking feature’, it is very easy to achieve an equal speed to the stops for each direction.

An example of the combined effects

Obtaining the best possible performance from your CSM SL 560 gyro dictates that all of the above variables have to be are adjusted to achieve the best overall performance. Whilst we do publish the best possible set-up for specific models, it is impossible to test and publish results for all model helicopters. So I have set out an example of how these effects can influence each other in the setting up process.

Example 1:

I have found that the CSM SL 560 gyro works at its best with a TX gain of between 75-80%. So I initially ensured that the TX gain was within this operating range and obtained a value of 80% gyro gain for a main rotor speed of 1750 rpm and a 20-mm servo arm length. To ensure I was obtaining the best possible all round performance of both the model and gyro, I then experimented with the overall set-up.

The first step was to experiment with main rotor rpm to assess the model’s performance. As I raised the rotor rpm to 1850 rpm, the tail rotor naturally turned faster and produced more thrust. This enhanced the gyro performance and I found that the tail would overcompensate and wag, thus I had to reduce the gyro gain to 70% to alleviate this. In further experiments, I then dropped the main rotor speed to 1650 rpm to find that the tail rotor was less effective and I could raise the TX gyro gain to 90% with no wagging. I finally settled on my first main rotor speed of 1750 rpm, but then found that my 95mm tail rotor blades did not provide enough tail power for aggressive 3-D manoeuvres. So I decided to increase the length of the tail blades to 100mm, which then increased the tail rotor power then started to overcompensate / wag again. To stop this, I then had to lower the TX gyro gain to 75%.

However, when I flew the model sideways or in windy conditions, the tail would wag profoundly and I had to lower the gain to 70%. So I was now in the situation where I had enough tail power to hold the most aggressive 3-D manouvers, but I felt the TX gyro gain was too low at 70%. So in this example, I then reduced the servo arm length from 20-mm to 18-mm to reduce the sensitivity of the tail linkage set-up. So after re-adjusting the linkage throw in the ‘quick set-up’, this then allowed me to increase the gyro gain from 70% to 75% and I had now achieved the best possible tail-rotor set-up!

Example 2:

On another model, I initially obtained a TX gyro value of 80% for a main rotor speed of 1850 rpm and an 18-mm servo arm length. To ensure I was obtaining the best possible all round performance, I then experimented with the overall set-up of both model and gyro.

The first step was to experiment with main rotor rpm to assess the model’s performance. As I raised the rotor rpm to 1950 rpm, the tail rotor naturally turned faster and produced more thrust. This enhanced the gyro performance and I found that the tail would overcompensate / wag. Thus I had to reduce the gyro gain to 70% to alleviate this. In further experiments, I then dropped the main rotor speed to 1700 rpm to find that the tail rotor was less effective and I could raise the TX gyro gain to 95% with no wagging. I did however prefer the feel of the model at 1700 rpm, but did find my 90-mm tail rotor blades did not provide enough tail power for aggressive 3-D manoeuvres at this much lower main rotor rpm. So I decided to increase the length of the tail blades to 100mm, which then increased the tail rotor power and in turn the gyro started to overcompensate / wag again. To stop this, I then had to lower the TX gyro gain to 85%.

When I flew the model sideways or in windy conditions, the tail was found to be very insensitive and I did not have to reduce the gyro gain any further. So I was now in the situation where I had enough tail power to hold the most aggressive 3-D manouvers, but I felt the TX gyro gain was a touch high at 85% and a quicker tail linkage set-up would enhance the gyro performance. So in this example, I then increased the servo arm length from 18-mm to 20-mm to increase the speed / sensitivity of the tail linkage set-up. This dictated that the gyro gain had to be reduced from 85% to 80% and I now felt that the tail responded swifter and I had achieved the best possible tail-rotor set-up!

Further Fine tuning…

Only once you have achieved the best possible performance from a stock CSM SL 560 gyro, can you then look towards the interface function to fine tune the gyro to your model and flying style. Whilst there are many interface functions, I have found that unless the gyro is being used for an unusual specialist application, just the following five functions require fine-tuning. I strongly recommend that you adjust just one function at a time and carefully assess each change before re-adjusting or moving on to the next function.

1-Acceleration Gain:

Amongst other in-built functions, this controls how quickly the tail rotor can start and stop a pirouette. The lower the value, the quicker the gyro will start / stop a pirouette, whilst a higher value will slow the start / stop of a pirouette. However, the gyro can only start / stop pirouettes at a speed the model helicopter mechanics will allow. Smaller less efficient models tend to be less capable of starting / stopping fast, whilst larger models tend to be more capable. As such, the CSM SL 560 comes pre-set with a value of 90% to cater for average model helicopters with an average set-up. To enable the helicopter to start / stop faster from pirouettes, lower this value in 5-10% steps and assess the tail rotor performance. If you find a slight decline in general handling and a slight bounce has developed when stopping from pirouettes, then raise the value back up in 5-10% increments until the best compromise has been achieved.

2-Heading Lock Decay:

This function is designed to allow the tail rotor to slowly drift back to neutral after being carried out to the flying field. The pre-set value of 60% is generally small enough to be unnoticeable in flight. However, you may experience a slight change in tail rotor trim when operating your model at different rotor speeds for separate flight conditions. If this is noted, try reducing the value in 10% steps all the way down to 0% where required, until you feel the effect is eliminated.

3-Dual-Independent Stop Tracking Controls:

This function allows you to adjust the gyro gain for the left and right travel independently to balance out left / right stops from pirouettes. If the model helicopter stops slower from a right-hand pirouette, then increase the value. If regardless of the amount of right stop control, the helicopter still stops quicker from a left-hand pirouette, then reduce the left value until the stops are equally balanced.

Linear Stick Sensitivity:

This function adjusts the feel of the tail rotor response around centre stick. If you feel that the tail rotor is too responsive to small inputs, then reduce the value until you obtain the feel you like. If however, the tail rotor feels too unresponsive to small tail rotor inputs, then raise the value until you obtain the feel you like.

Exponential Stick Sensitivity:

Raptor 001: To help overcome poor tail rotor geometry and balance out the left / tight stops, I have offset the servo arm in the right tail rotor direction. This is the position of the servo arm at neutral in a standard Raptor 50 tail rotor servo installation.

Raptor 002: When using a rear servo mount on the Raptor 50, I still offset the servo arm in the right tail rotor direction. This is the position I set the servo arm at neutral.

Raptor 003: I have found the gyro works slightly better when the self-adhesive mounting pads are placed across the frames. I have also ensured that the leads are not taught or flapping against the gyro / frames.

Raptor 004: I have found that lowering the boom supports improves the rigidity of the tail boom and enabled me to raise the gyro gain by 3-4 points. To achieve this, move the fuel tank out of the way and carefully drill 2-MM pilot holes and then use the existing screws to re-fix the boom supports.

Raptor 005: Another trick to improve the Raptor 50 frame rigidity is to file two notches in the lower carbon plate. Then drill and tap into the engine mount and use spacers to lock the mount to the lower carbon plate. This alone gained me extra 2-3 points of gyro gain.

Raptor 006: For those looking for the ultimate right hand pirouette stop performance, try relieving the tail pitch slider as shown with a round file to increase the left tail rotor throw. This modification provides 40 degrees of tail pitch in both directions and enhances the gyro performance.

Fury 001: The standard fury gyro mount is slightly too tall for the CSM SL 560 to clear the canopy. So an easy solution is to cut the frames with a hacksaw as shown to lower gyro mount. This entails re-drilling the right angle gyro mounts and using four fixings as shown. I took this stage further and fixed a square carbon gyro plate to lock the frame assembly rigidly in this area.

Fury 002: This photo clearly shows the gyro platform I fabricated from a small piece of sheet carbon fibre.

Fury 003: I have found that the CSM SL 560 gyro performs better when the mounting pads are sited across the frames as shown.

Fury 004: To enhance the right hand pirouette stops, I offset the servo arm in the right direction at neutral as shown.

Fury 005: The CSM SL 560 gyro works at its best when using a fast tail rotor set-up. So I simply re-drilled the front tail rotor bell-crank as shown to enhance the servo throw. This is also shown at the servo neutral position.