Setting up & flying your T-Rex
Written by Nigel Fraser Ker Friday, 21 January 2005 00:00
Simulators
Setting up the Controls
Mechanical Setup
Throttle & Pitch Curves
Transmitter Setup
Starting Up for the First Time
Range Check
Flying the T-Rex for the First Time
Tips on Flying Small Electric Helicopters
Radio Interference and Range Problems
Fine Tuning
Practise
Glossary of Terms
Safety Checks
So you've bought a T-Rex...
So you've got your brand new T-Rex, you've followed the assembly instructions, you've built your model and installed the radio gear. But what about setting it up and flying it? Whilst the manual is very good, it assumes a fair amount of knowledge about radio control equipment and it doesn't cover learning to fly the model. Well, this article is intended to help you if you're new to radio controlled helicopters and it may even help those of you with a bit more experience. In a later article I'll be covering aerobatics and 3D flying in more detail.Please note that where I have used technical words I have explained them in the Glossary of Terms.
A Word About Simulators
Flying radio controlled helicopters isn't easy and practically every good pilot I know has used and recommends radio control flight simulators for beginners. I won't cover them in detail here but suffice to say that your learning will be made a lot easier and cheaper if you practise on a simulator first. For more detailed information on how to get the most from your simulator, see my notes here.
Setting up the Controls
The first thing to say about setting up the controls is that the instruction manual describes the setup using a Mode 1 transmitter. If you have a Mode 2 transmitter bear in mind that some of the functions are assigned to different sticks. More about this later.
If you've already fully assembled your helicopter it may be a bit late to say this but before installing the radio receiver, the Electronic Speed Controller (ESC) and motor it's probably a good idea to test them and check that the motor works as per the manufacturer's instructions. In the main, the transmitter can be set up after final assembly but because the motor is so powerful it's best to configure this particular item early on. On a general safety note, when you're about to switch on your radio gear, always* move the throttle to its lowest position and always switch on your transmitter before you power up the receiver. This prevents your servos from moving to extreme positions and also ensures that your ESC is set to zero power - you don't want to connect your battery and suddenly find that the motor is set to full throttle! Another point to note is that electric motors can easily over-speed if they are run without a load. Follow the manufacturer's guidelines but if you're unsure about testing electric motors without a load, run them as slowly as possible. Do not run them up to see how fast they will go - the chances are that you will permanently damage them.
*except in accordance with the manufacturer's setup procedures
ESCs can be dangerous if they're not set up correctly so before I connect the ESC to the receiver I plug a servo into the throttle channel and test the radio gear. This way, I can check that the ESC is definitely connected correctly. If you have a throttle hold feature on your transmitter now would be a good time to get it working correctly, i.e. while the test servo is connected to the throttle channel. Make sure that when you select throttle hold the test servo moves to one end of its travel and stays there even if you move the throttle stick. This is a nice safety feature because keeping it on when you're not flying will prevent an accident if someone bumps the throttle stick. At this stage, you don't know if this throttle setting is low or high because you haven't yet determined which way round your ESC works. You may need to reverse the throttle channel so to set it up correctly consult your ESC manual. Usually, the ESC will make a particular sound when you switch the power on, e.g. one for low throttle and one for high. Different ESCs have different setup methods and because these little motors are so powerful you should follow the manufacturer's guidelines carefully. The ESC is probably the most difficult thing on the helicopter to setup because you can't see what's going on inside. In any case, if you have any doubts you can always contact your dealer for more information.
Assuming you have followed the ESC setup instructions, let's look at the channel assignments. In Step 9 of the instructions you will have plugged the servos and the ESC into the receiver. Make sure that they are plugged into the correct channel numbers - not all radios are the same. For example, the normal channel assignment for Futaba and JR transmitters is as follows:
| Radio Channel Assignments | ||
| Function | Futaba | JR |
| Aileron | 1 | 2 |
| Elevator | 2 | 3 |
| Throttle | 3 | 1 |
| Rudder (tail) | 4 | 4 |
| Gyro Gain | 5 | 5 (Gear) or 7 (Aux 2) |
| Pitch | 6 | 6 (Aux 1) |
Without the motor being connected, test the controls to make sure you are happy that they are connected to the correct channels. If you have a gyro whose gain can be set from the transmitter and you are unsure what signals are being sent to it, you can plug a servo into the gyro channel (channel 5 or the 'gear' channel on JR receivers) just like we did with the throttle to see what it's doing. Chances are that the instructions recommend you do this anyway!
Mechanical Setup
Before moving on to the more detailed set up of the radio gear we need to make sure that the mechanical setup is correct. Getting this bit right will make your life a lot easier later on. Take a look at the 'Parts and Equipment Assembly Illustration' in the manual. Make sure that your model is set up just like this drawing. What you can't see on that drawing is the collective pitch servo because it is a picture of the right-hand side of the model. Make sure that when the pitch servo is in its centre (neutral) position the servo horn is as near horizontal as you can get it and the end of the collective pitch control arm is at the zero degree point as shown in the manual...
Throttle and Pitch Curves
One of the things you're going to do in the next section is to set up your throttle and pitch curves. I'd like to take a little time to explain these now so that you understand what figures you're putting into your transmitter.
By now you should be aware that the throttle stick on your transmitter actually controls two separate functions - the throttle and the pitch. If the relationship between these two controls was simple (i.e. the pitch moved the same as the throttle) then you wouldn't have needed to spend all that lovely money on expensive computer radio gear. As you will have guessed, it's more complicated than that. In fact you need to be able to program the transmitter so that for any given stick position, you get the correct throttle and pitch setting which will not be the same.
Why do we need separate throttle and pitch settings and what are we trying to achieve? Well, in an ideal situation, during flight our helicopter will have a constant head speed. You might think that all we would have to do to achieve this would be to set the throttle at a fixed value and that would be that. However, if we want to change altitude, we have to change the pitch of the main rotor blades. Raising the pitch will make the helicopter go upwards (because the blades are producing more lift) - lowering the pitch will make it go down. When you change the pitch (more correctly known as the collective pitch) the amount of effort the engine has to expend to turn the blades will change too. If we tried to fly with a constant throttle, when we increased the pitch to gain altitude the head speed would decrease. If the head speed drops below a certain point you will lose control with unfortunate results. This means we have to increase the throttle when we increase the pitch by just the right amount to make sure that the head speed stays the same. This is not as easy as it sounds and requires a certain amount of fine tuning. The good news is that the manufacturers of your T-Rex have tested their helicopter and come up with some settings that ought to work pretty well as a starting point. By using their figures, we will make sure that for any given pitch setting, we will have about the correct throttle setting.
The relationships between the stick positions and the settings of the throttle or the pitch are called 'curves'. Transmitters with lower specifications often only allow you to program three points on the throttle and pitch curves. This means that you can only program the transmitter to give a certain throttle setting for low, middle and high stick positions and likewise for pitch (the transmitter will automatically 'draw' a straight line between these three points so that you get a smooth transition between them). More expensive transmitters have a 5, 7,13 or even 17-point curve capability and top-of-the-range models even draw nice smooth curvy lines between the points. All this allows the pilot to set up his helicopter with great precision but don't worry about getting too fancy yet - perhaps leave it until you're competing at the World Championships!
For our purposes a 3-point curve will be sufficient but a 5-point curve is better and happens to have been used by the manufacturers in the instructions. If you look in the instructions at the bottom left-hand side of the 'Final Pre-Flight Adjustments' section, you will find the figures for the throttle and pitch curves for hovering flight...
Put in layman's terms, this is what the table means...
| If you move the throttle/pitch stick to... | ...the throttle should be set to.... | ...and the pitch should be set to... |
| its highest position | full power | around +10 degrees |
| three quarters of the way up | 85% power | around 8 degrees* |
| the centre position | 65% power | around +6½ degrees |
| a quarter of the way up | 30% power | around 4 degrees* |
| Its lowest position | off | 0 degrees (i.e. the blades will be horizontal) |
If your transmitter only has a 3-point curve capability then you can forget about the quarter and three quarter stick positions. For a simple hovering curve like this it really doesn't matter too much since the curves we are looking for are fairly simple.
Finally, I need to say a word about governors. If you have a brushless motor the ESC may have a neat feature called 'governor mode' or something similar. This allows you to determine what your head speed is going to be electronically rather than by using the throttle curve. It's a bit like the cruise control on a car. Refer to your ESC's instructions on how to set up the governor mode. Once done you don't have to worry about accurately setting up the throttle curve to achieve the correct speed over a variety of different pitch settings. Instead, and depending on your ESC, you will probably just use the throttle curve to determine the head speed and it will look something like this...
Transmitter Setup
This is perhaps the area that beginners find most difficult. Computerised transmitters are necessarily quite complicated. They are all setup in different ways and the manuals are often written with the assumption of some prior knowledge. I will try to give you an idea of what you're aiming to achieve and hopefully, by running through everything in a logical manner, we will be able to get your helicopter setup correctly.
If you are unsure of what you're doing with your transmitter perhaps the best way to start is to make sure that you have a completely new helicopter model setup in the active memory of the transmitter. You'll have to read your transmitter manual to find out how to do this but clearing all the data and starting afresh is often called a 'Reset'. You only need to reset the model you have in memory, not your whole transmitter. If your transmitter is used for other models be careful not to erase the model memories you have allocated to them. Make sure you are using a helicopter model type without CCPM mixing. You should also ensure that your transmitter modulation setting is the same as your receiver, e.g. PPM or PCM depending on what receiver you have.
I will now give you some simple pointers as to what to set up. It's hard to do this in detail without writing an entire book on the subject so I'll keep it short. Before you start, make sure the motor is disconnected.
| Step | Function to Adjust | What to Do | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 1 | Servo Reversing | Go through each of the first 6 channels on your transmitter and make sure each control works in the correct direction (see the control test below). If you have been following my notes in this article you should already have set the throttle channel direction for the ESC. If you haven't then do so now and also set the gyro gain channel correctly, always following the manufacturer's instructions . | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2 | Mechanical Centring | With the radio gear switched on and all the sticks and trims in the centre positions, look at every servo and make sure that the servo horn is centred correctly and that the device it controls is also centred. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 3 | ATV (also known as End Point Adjust, EPA, Travel Volume or EPoint) | Move each control and check that you are getting the correct amount of movement and that it is the same each side. The ATV allows you to set how far each control moves each side of the centre position. A value of 100% on an ATV setting means that the control will move 100% of the way across. A value of 110% means it will move further and a value of 90% means it will move less and so on. Set your ATV's so that the controls are balanced and don't bind. To set the ATV for each side of a servo's movement you'll probably have to move the stick in that direction to indicate to the transmitter which side you want to change. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 4 | Gyro Gain | You'll have to consult your own manual to discover how to set this up on your transmitter. Often it is simply set up with the ATV values on channel 5 (the 'Gear' channel with JR transmitters). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 5 | Pitch Curve | Depending on how many points are available on the curves in your transmitter, set the pitch curve percentages as follows:
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| 6 | Throttle Curve | Depending on how many points are available on the curves in your transmitter, set the throttle curve percentages as follows:
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| 7 | Revo Mixing | This is the 'revolution mixing' function which alters the tail servo neutral position in proportion to the amount of throttle employed thus compensating for the increase in torque. This function is relatively old fashioned and modern 'rate gyros' don't require it. Refer to your gyro manual for details. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 8 | Fail Safe | It is unlikely that on a model as small as the T-Rex you will have a PCM receiver but if you do, you should set the failsafe settings on your transmitter in accordance with your transmitter's manual. The throttle setting should be as low as you can make it to ensure that it you lose radio contact with your model, it will default to an 'engine-off' state. |
One question you may be asking yourself is "Why does the pitch curve start at 50%?". This is because as a beginner you will be using only half of the total pitch range, i.e. from 0° to +11°. You will expand your pitch range, eventually up to its full travel (i.e. -11° to +11°), when you become more experienced. Negative pitch gives negative lift which is effectively positive lift if you happen to be flying inverted, e.g. when you are at the top of a loop. More about this in the aerobatic and 3D article.
Starting Up for the First Time
Okay, this is it - we're going to start up our nice gleaming new helicopter. The first time you do this it's a good idea to do it without either the main or tail rotor blades on. Here's your checklist...
* Check that the transmitter battery is charged and that you have installed (but not yet connected) your flight battery
* Fit a training undercarriage if you are not an experienced pilot.
* Carry out your normal safety checks
* If you're flying near other r/c fliers (near means within a two mile radius to be safe!) make sure you're not on the same channel. This is for your safety as well as theirs. If you are flying at a club or at a fly-in, use the frequency control system.
* Switch on your transmitter and check the battery voltage.
* Hold the blade grips firmly and plug in your flight battery. If your ESC has a switch, switch it on.
* Wait for your gyro and speed controller to initialise. Don't move the helicopter at all while it is doing this.
I will now go through each control and describe what is supposed to happen on the helicopter if you are using a Mode 2 transmitter. This is the more common type but if your transmitter is Mode 1 (as is the one shown in the instructions) then the throttle/pitch control will be on the right-hand stick and the elevator control will be on the left-hand stick. For more details about transmitter modes see this article.
Important! Make sure that 'Idle Up' or 'Stunt' facility on your transmitter is disabled or inhibited before proceeding! If you can't disable it, make sure that any switches that control it are in the 'Off' position. You should get into the habit of putting the switches to their 'start-up' positions before every flight.
| Control Test The following tests assume that you are standing behind the model which is facing away from you. |
|
| Control | Action |
| Aileron | When you move the right-hand stick to the left and right the swashplate should tilt accordingly left and right. The stick should spring back to the centre when you let go of it. |
| Elevator | When you move the right-hand stick forwards and backwards the swashplate should accordingly tilt forwards and backwards. The stick should spring back to the centre when you let go of it. |
| Throttle | When the left-hand stick is to the rear the throttle should be off and the motor should be completely motionless. The stick should stay to the rear when you let go of it. Gently move the throttle stick forward and confirm that the motor starts. Normally they get going quite quickly so be prepared! Now move the stick to the rear again and (for safety) engage the throttle hold switch if you have one. |
| Rudder | When the left-hand stick is pushed to the left, the rudder yoke (as illustrated in Step 3 of the Tail Rotor System assembly instructions) should move right (in other words, in the opposite direction). The stick should spring back to the centre when you let go of it. |
| Gyro |
Put your finger between the tail rotor yoke and the tail unit housing like this...
Rotate the helicopter so that the helicopter's nose goes to the left. You should feel your finger get slightly pinched by the yoke because the gyro will attempt to correct the helicopter's movement. If it moves the other way check your gyro setup. If you have a gyro that doesn't use a transmitter controlled gain channel then you can ignore the rest if this section. The gyro gain channel will either be allocated to a dedicated switch on the transmitter or it is set by the flight mode of your transmitter. Some gyros have indicator lights which show which mode they are in. Refer to the gyro and transmitter manufacturer's setup instructions for guidance on checking that this is working correctly.
|
| Pitch | Gently move the left-hand stick forwards and the swashplate should move upwards (without tilting at all). If the main rotor blades were fitted, their pitch would increase. If the motor started up, you didn't have the throttle hold feature engaged. |
If all those tests worked okay then well done! You're getting there. In theory you're ready to fly!
Range Check
It is very important to perform a range check before you fly the model. Disconnect the motor before you try this. You should refer to manufacturer's instructions and your national governing body's guidelines for details on this test but, as a guide, I would recommend that you should be able to retract the antenna and walk about 25 metres away with no problems/interference, etc. The British Model Flying Association's handbook says that you should "Look for a minimum range of around 50 metres with the transmitter aerial down." However, this test was not written for receivers designed for small electric models and you may find that 50 metres is a 'tall order'.
Flying the T-Rex for the First Time
Micro helicopters are sensitive to fairly light winds so it would be a good idea to make your first few flights in calm conditions or, if you have access to it, a large indoor area such as a gym or hall.
Disconnect the flight battery and fit the main and tail blades. Remember to get them the right way round!
Here's a useful tip. Whatever flight batteries you are using, it's a good idea to make sure that the terminals can't accidentally short circuit. A good way to prevent this happening is to get a couple of inch-long pieces of r/c fuel tubing and when you disconnect the battery, slip the fuel tubing over the battery terminals.
The blades must not be too tight or too loose. Tighten up the main blades so that they are just tight enough to stay in position when you tip the helicopter on its side. The tail blades should be just loose enough to fall under their own weight when the tail is slowly rotated.
Now we are ready to start up again. Remember to switch on your transmitter first, make sure the throttle is low, all the switches are in the correct positions and then plug in the flight battery with the helicopter on the ground. If your ESC has a switch, switch it on. Wait for the gyro and ESC to initialise before you move the helicopter. Then...
1. Engage the throttle hold
2. Place the helicopter in an open space and stand about 3 metres away from it.
3. Test all the flight controls
4. Make sure the throttle is at the low position and disengage the throttle hold.
5. GRADUALLY open the throttle. The motor should start up (possibly a little more suddenly than you expected), the main rotor blades should start to turn clockwise (looking from the top) and as the tail rotor goes round, whichever is the bottom blade should be travelling forwards. GRADUALLY keep increasing the throttle and watch the main rotor blades. Don't try to take off yet. Ask yourself the following questions...
* Is the rotor disk leaning in any particular direction? If it is noticeably leaning left or right, try adjusting the aileron trim. If it is noticeably leaning forward or backwards, try adjusting the elevator trim. If this doesn't work, make sure that your swashplate is level.
* Is the helicopter vibrating excessively? If it is, stop the motor, engage the throttle hold and check that your main rotor blade grips are not too tight, that your blade grips are correctly located (i.e. pulled out correctly) and that your tracking is not very different on the two main blades. If none of these work then your blades may be out of balance. Balancing and tracking the blades is covered in the 'Main Rotor Adjustment' section of the manual. Check that your flybar is also balanced properly and that the paddles are the same distance away from the axis of rotation.
* Is the rudder working correctly? With the blades rotating at a moderate speed, try moving the rudder from left to right. You should see the tail try to move right and left. To be clear, when you move the rudder stick to the left, the nose of the helicopter should try to move to the left.
6. Keep increasing the throttle and keep testing the controls. As you start to lift the weight off the skids, if the helicopter suddenly starts to rotate on the spot, stop the motor and disconnect the battery. The probable cause of this problem is that the gyro 'sense' is wrong (rather than correcting any small movements it detects, it is exaggerating them). Check the gyro manual and correct.
If all is well, as you increase the throttle, you should eventually get into the air.
Tips on Flying Small Electric Helicopters
I have already mentioned that simulators are an excellent way to get used to the controls of radio controlled helicopters. If you have taken my advice, you should find that learning to fly the real thing is a lot easier.
Here are a few pointers towards making your flying easier...
* Concentrate on keeping the tail pointing towards you - the cyclic controls will be more natural this way.
* Keep the helicopter very close to the ground until you gain more confidence.
* If the helicopter starts to turn to the right or left and you aren't good enough yet to correct it, land quickly but smoothly. When the helicopter is on the ground you can take your time to turn the helicopter away from you again.
* Make sure the helicopter is properly trimmed...
o If the helicopter keeps turning (yawing) to one side, land the model and adjust the rudder trim on the transmitter.
o If you notice that the helicopter keeps tipping to the side, correct this with the aileron trims on the transmitter.
o If you notice that the helicopter keeps moving forwards or backwards, correct this with the elevator trims on the transmitter.
o Keep trimming the helicopter until it is as stable as you can get it.
* If the tail seems to wag quickly from side to side, adjust the gain of your gyro downwards. If the tail seems to wander, raise the gain setting. You are aiming for a balance between the gyro gain being too high and it not being high enough. If you can't seem to get the balance right, it may be for one of two reasons - either you have too much slop in the tail pitch control linkage or your tail servo may be too slow. Another cause of problems with gyros is vibration, usually either from the main or tail rotor.
* If you notice that you are having to push the throttle further and further forward to stay in the air, then your battery is probably running low. Land and wait until the battery is cool before recharging.
Radio Interference and Range Problems
It's worth saying a few words about radio interference - a problem that is particularly common in small electric models. The small 'micro' radio receivers that are most often fitted to electric aircraft typically do not have as high a specification as their larger cousins and must therefore be tested carefully and treated with some caution.
* Carry out a regular range check of your equipment
* Ensure that the crystal is properly seated in the receiver
* Run the receiver aerial as far away from the other electrical devices on the helicopter as possible, especially the motor and speed controller
* Be very careful with transmitter and receiver crystals - they are very sensitive to mechanical shocks and care should be taken not to drop them
* If possible use high quality dual conversion receivers
Things that can cause radio reception/interference problems are:
* Loose metal-to-metal contacts on the helicopter
* Poorly sited receiver antennas
* Faulty radio control equipment
* Nearby radio transmission masts or microwave transmissions over the flying field
* Poorly suppressed commutator contacts on brushed motors
* Metal objects such as the frames of metal buildings, metal fences, etc. Even buried metal objects have been known to cause problems
* Faulty or damaged crystals in your transmitter or receiver
* Nearby mobile telephones
If you really can't get rid of your radio interference problems, you may need to consider upgrading your receiver. A couple of 35MHz dual conversion models that might be suitable are the Hitec Electron 6 (17g) or the Futaba R147F (26g). These are larger than the 'micro' receivers in common use with small electric helicopters but may get better results.
Fine Tuning
Now that you have made it into the air, we need to ensure that the throttle and pitch curves are set correctly and that you are flying at the desired head speed.
You should be hovering with the throttle stick at about the middle position and your head speed should be around 2,200 rpm. If this is not the case, you will need to adjust the throttle and/or pitch curves. To simplify matters, I have drawn up a table of the adjustments you need to make...
(Note: If you are using a governor setting on your ESC then you should only need to worry about the parts of the table in blue.)
| If your head speed is... | ..and you are hovering... | ...adjust the centre point of your throttle curve... | ...adjust the centre point of your pitch curve... |
| too low | at about mid-stick | up | down |
| about right | at about mid-stick | - | - |
| too high | at about mid-stick | down | up |
| too low | a little above mid-stick | up | - |
| about right | a little above mid-stick | - | up |
| too high | a little above mid-stick | down | up |
| too low | a little below mid-stick | up | down |
| about right | a little below mid-stick | - | down |
| too high | a little below mid-stick | - | up |
Keep adjusting the values of the pitch and throttle curves until you have got them about right.
Unfortunately the only really effective way to judge the head speed of a helicopter in flight is to use an optical tachometer. These little gadgets consist of a box with a hole through which you view the rotor disk of the helicopter. There is a moving vane inside the box which creates a 'waggon wheel' effect on the image of the helicopter. You adjust the speed of the vanes and when the blades appear to stop you read off the head speed on a digital readout.
Practise
Here is a little practice routine for you to use in your training. It will help you to concentrate on specific goals and hopefully teach you to fly with discipline and precision.
Practise the following with as much precision as you can muster. Don't let the model fly all over the place - you are flying the model so make sure that you, not the model, is deciding where it is going to fly.
1. Hover 1½ ft (0.5m) above a fixed point for 30 seconds. If it keeps wandering off the spot you probably need more practice!
2. Hover over a fixed point, then keeping the nose of the helicopter pointing to the front, fly the helicopter to the left by about 6 feet (2m) hover over a fixed spot there for 10 seconds and return to your original starting position.
3. Do the same as above only moving to the right-hand side.
4. Practise the above two manoeuvres, gradually bringing the nose towards the direction of travel as you travel out to the side and back.
5. Practise hovering slightly side-on, gradually building up to full side-on. Do this for both sides.
6. Develop what you have learnt in steps 3, 4 and 5 into a 'Lazy 8' - that is to say, fly a horizontal figure of eight, the model passing in front of you side-on.
7. Gradually open out the 'eight' into two large circles. Eventually, this will teach you the basics of circuits.
8. If you feel sufficiently confident, try slowing the helicopter down when the helicopter is flying towards you. Keep practising flying towards you slower and slower until, eventually you will develop this into a nose-in hover - a major step forward in your training!
Don't be surprised if you find flying on one side (normally the left-hand side) more difficult than the other. You just need to work harder on your weakest side until you are just as good on both. Don't be tempted always to stay in your 'comfort zone'!
And Finally...
Okay, you should be on the way to learning to fly your T-Rex by now. The best advice I can give you now is 1) keep practising and 2) try to join a club and/or go to local fly-ins - you'll learn a lot from other people and it's much more fun when there are other people flying too.
Good luck!
Nigel Fraser Ker
© January 2005
Disclaimer - This article is intended as a guide only and should not be relied upon absolutely. Always refer to the manufacturer's instructions, always abide by your local, state and national laws and always follow the guidelines laid down by your national governing body.
Glossary of Terms
Autorotation - A way of 'gliding' a helicopter safely back to the ground without engine power. To achieve this you need to be able to set the main rotor blades to a negative pitch - not something we have covered in this article.
CCPM - Cyclic/Collective Pitch Management - a computer controlled system where three or four servos are used to control the collective pitch and cyclic controls on a helicopter. Each servo controls one part of the swashplate and the computer works out what position the servos need to be in to achieve the correct swashplate movements. This system is complicated but more precise and is typically the system used on larger, more expensive machines.
Collective Pitch - See Pitch
Cyclic Controls - Those controls which affect the helicopter's attitude in two directions namely rolling left and right (known as the aileron control) and moving the nose up and down (known as the elevator control). Confusingly, on an aeroplane, the elevator is said to control the 'pitch' of the aircraft. For this reason, with model helicopters we simply refer to the elevator so that it is not confused with the pitch of the main rotor blades.
Dual Conversion - A type of receiver in which the signal from the transmitter is filtered twice (instead of once) and thus suffers less from radio interference.
ESC (Electronic Speed Controller) - This is an electronic device which can control the power output of the motor. Some ESCs are designed to with an additional function called a 'Governor' - this controls the speed of the motor. This is handy for helicopters because we want to setup the helicopter so that it maintains a constant head speed.
Flight Mode - Some manufacturers refer to their transmitters being in different flight modes, e.g. Normal (for hovering), Idle Up or Stunt (for aerobatics) and Hold (for practising autorotations amongst other things). Each flight mode is selected by means of a switch and allows the pilot to select different throttle and pitch curves to suit the type of flying he is doing. In some cases, it can also determine other settings such as the gyro gain.
Flybar - Also known as the control rotor, the flybar is partially responsible for the cyclic control of the helicopter, the rest of this control coming directly from the swashplate. These two control methods - direct (the Bell system) and flybar (the Hiller system) - complement one another on many radio control helicopters offering a good compromise between responsiveness and stability. The degree to which each system affects the cyclic controls is defined by the mechanical ratio designed into the mixing arms on the flybar seesaw.
Flybar seesaw with mixing arms
Gain - The degree to which a gyro will attempt to correct an un-commanded change in yaw. If you set the gain too low the tail of the helicopter will not maintain its heading well - if you set it too high the tail will wag from side to side.
Gyro Sense - The setting in your gyro which tells its circuitry which way it should move the servo to correct errors in the yaw attitude of the helicopter. If this is set incorrectly, the helicopter will spin uncontrollably at take-off. It will do this because as soon as an error is detected it will attempt to correct it the wrong way. It picks up this error and again tries to correct it. This is a cumulative problem and happens so quickly that it is impossible to control.
Governor - With electric models, this is a feature on an ESC that allows the pilot to determine the head speed electronically rather than by using a throttle curve.
Head Speed - The rotational speed of the main rotor assembly - in other words how many times the head goes round every minute.
Heading Hold - A gyro mode in which the gyro will not only resist un-commanded changes in direction (yaw) but correct them as well. Some gyros are capable of both heading hold and normal modes.
Idle Up - Sometimes known as Stunt, Idle Up is a term that refers to a group of settings on your transmitter which enable the helicopter to perform aerobatic manoeuvres such as flying upside down. One of the most notable features of Idle Up is that it allows you to set the transmitter so that the throttle control is high when the throttle stick is low. You'll find more about this in the aerobatics article.
Normal Mode - (sometimes called Standard Mode) - usually refers to one of two things - either the basic transmitter mode which is used for taking off and doing hovering manoeuvres or the gyro mode which does not hold its heading - see Heading Hold.
Optical Tachometer - A gadget for measuring head speed consisting of a box with a hole through which you view the rotor disk of the helicopter. There is a moving vane inside the box which creates a 'waggon wheel' effect on the image of the helicopter. You adjust the speed of the vanes and when the blades appear to stop you read off the head speed on a digital readout.
Typical view through an optical tachometer
PCM - Pulse Coded Modulation - This is a better and normally a more expensive system than PPM and offers a function called 'failsafe' which allows the pilot to program the receiver with a set of default servo positions in case of radio failure. Want to know more? Take a look here.
Pitch - More correctly called Collective Pitch, with helicopters this normally refers to the angle of the main rotor blades. Positive pitch creates lift. (Negative pitch creates lift if you are flying upside down.)
PPM - Pulse Position Modulation - Want to know more? Take a look here.
Rate Gyro - A rate gyro is one which controls the helicopter's rate of yaw and will set it depending on the pilot's rudder control. This is distinct from older type of gyro where the pilot effectively just controls the pitch of the tail rotor blades and the gyro endeavours to prevent the models from any yaw at all. In a sense, with these older style gyros the pilot was always 'fighting' the gyro. This is a subtle but very important difference and the introduction of rate gyros has made certain manoeuvres much smoother and easier to control.
Rotor Disk - An illusion, this is the transparent disk which appears to be formed when the rotor blades are rotating quickly.
Sense - See Gyro Sense
Standard Mode - See Normal Mode.
Swashplate - A device on a helicopter which connects the static non-rotating controls to the ones which rotate with the rotor blades. The swashplate always controls the cyclic controls and, on some types of helicopter, also plays a part in controlling the collective pitch.
Throttle Hold - A feature which is activated by a switch on the transmitter and which sets the throttle either to zero/near zero (on electric helicopters) or to a tick-over setting (on glow-powered models). It does this irrespective of the position of the throttle/collective pitch stick and does not directly affect the pitch unless the transmitter has a separate pitch curve for throttle hold. Typically the feature is used to practise autorotations but is also a useful safety feature which can, for example, be engaged when carrying the model to the take-off spot. It is also a useful means of recovering from a tail rotor/gyro failure during flight which, by removing the torque from the engine/motor will prevent the helicopter from spinning uncontrollably and enable the pilot to autorotate safely to the ground. It is worth noting that problems can occur when practicing autorotations with electric models which have an electronic speed controller programmed with a 'soft' start. This is because, if the pilot is forced to 'bail out' of a practice autorotation, flicking the throttle hold switch off again will not necessarily bring power back quickly enough to be effective. It may therefore be advisable to set the speed controller to a relatively 'hard' start to avoid this if you plan to practise this sort of manoeuvre.
Tracking - This refers to the degree to which the two blades on the main rotor are set at the same angle. If they are the same then the blades will rotate in the same plane and in flight the rotors will appear to form a single disk. If they are not at the same angle, then the two blades will not rotate in the same plane and in flight the rotor disk will appear to be split into two.
Transmitter Mode - The type of transmitter you have. If your throttle stick (the one that doesn't spring back to the centre when you move it forwards and backwards) is on the right-hand side you have a Mode 1 transmitter. If it's on the left-hand side your transmitter is Mode 2 (this is the most common type). For more details, see this article.
Yaw - A change in direction of motion of the aircraft which causes the nose to move either left or right.
Yoke - (Typically) the device which controls the pitch of the tail rotor blades, also known as the tail pitch slider or the Tail Rotor Control Assembly.
Appendix 1 - Safety Checks
These are the safety guidelines that I use for indoor electric helicopter flying and are based on those issued by the British Model Flying Association. However, you should always refer to your own national association and rules for local guidance.
A. CHECKS BEFORE DAILY FLYING SESSION
1. Check all ball links for slop and change as necessary.
2. Check that all rotor blades are in good condition with no damage apart from minor tip damage.
3. Check for loose or missing nuts and bolts.
4. Check that there is no backlash in the drive system apart from gear backlash which should not be excessive.
5. Check that servos are secure.
6. Check that the receiver aerial is secure and in good condition with no chafing or damage.
B. CHECKS BEFORE EACH FLIGHT
1. If a helicopter suffers damage or a heavy landing, re-check all of (A) above.
2. Check all controls before starting especially for binding links or slowing of servos.
3. Re-check controls at high rotor rpm just before lift-off.
4. Check for vibration and eliminate before flight.
5. Check main rotor blades for true tracking in hovering flight.
6. Check that the receiver aerial cannot become entangled with any moving or rotating part.
7. Check that the flight battery is properly secured and in good condition.
8. Double check that all switches on the transmitter are in their correct positions before EVERY flight.
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