Helicopter Primer
Which helicopter to start with
Simulator - you can learn everything you need to know on a good simulator. RealFlight and Phoenix are the best, but there's some free ones which are pretty good (FMS is lousy and should be avoided).
- Heli-X - download at http://www.heli-x.net/
- HeliSim - download at http://www.marksfiles.net/HeliSimRC/index.htm
Coaxial - These are helicopters with two sets of main rotor blades rotating in opposite directions. The two sets of blades cancel each other's torque effects, so a tail rotor is not needed. These helicopters are very stable and less maneuverable. Most of them will hover hands-off, and they are only suitable for flying indoors. The coaxial can teach you maintaining altitude with throttle, directional control using rudder (heading) and cyclic control to generate thrust in horizontal directions. The coaxial will not teach you the behavior of the other types of helicopters with a single main rotor, and may lead to some bad habits - it is not possible to roll a coaxial upside-down! Examples are the E-Flite Blade CX/CX2/CX3, E-Flite Blade mCX, and E-Sky Lama.
Fixed Pitch - These helicopters have a single main rotor, and an anti-torque tail rotor. The main blades have a fixed amount of pitch, much like an airplane propeller, and the lift of the helicopter is adjusted using changes in throttle. These helicopters are generally less expensive to purchase and maintain, but most people do not find them any easier to fly than the collective pitch helicopters. The fixed-pitch helicopter will teach you to manage the helicopter's attitude using cyclic control to create thrust in various directions. It will help you learn to coordinate cyclic and rudder controls to make turns, and help you learn throttle and cyclic coordination to make the helicopter fly in various directions. These helicopters are not very stable, and are more manueverable than coaxial helicopters, but are not usually as precise as the final type of helicopter, collective pitch type. Examples are the E-Sky Honey Bee, and the Hirobo Quark.
Collective Pitch - These helicopters share many features with full scale helicopters. They feature a single main rotor and an anti-torque tail rotor, both with variable pitch. Some collective pitch helicopters use a fixed-pitch tail rotor with a variable speed motor for tail control - these are generally not as easy to fly as collective pitch helicopters with a belt or shaft-driven tail rotor with variable pitch tail blades. Collective pitch helicopters are fully aerobatic, capable of flying inverted, and doing loops and rolls, sustained inverted hovering, and many other exciting maneuvers. In my opinion, they are actually not very hard to fly - but they require careful setup and a lot of practice. These helicopters are more expensive than the other types, and the mechanics are much more complicated, making them more difficult and expensive to repair in the event of a crash. The other types of helicopters are usually electric, but if you love nitro power, you're going to need a collective pitch helicopter. Examples of this type are the Align Trex, and the Thunder Tiger Raptors - both of which come in many sizes. Bigger ones are easier to fly, but can be very expensive to purchase and repair. For this reason, the 400-class electrics such as the Align Trex 450, Thunder Tiger Mini-Titan, and E-Flite Blade 400 are very popular.
Collective Pitch Helicopter Setup
The coaxial and fixed pitch helicopters are usually quite easy to set up and maintain, but the collective pitch type can be very difficult to get "dialed in" and they require periodic inspection and maintenance in order to fly properly. I think that learning to fly a collective pitch helicopter is possible and beneficial because you can avoid spending money on the other types which are less fun and provide fewer opportunities for flying time due to their poor handling in the wind. However, many beginners do not understand or take the time to properly set up the helicopter, and this can make it very difficult to fly, and can lead to costly crashes. An improperly set up helicopter can be nearly impossible to fly, even for an expert, so learning proper setup is very important. This is true even if you have a RTF helicopter, as they are often not adjusted properly from the factory. Tonight I am giving a basic overview of setup, from top to bottom. If you do this correctly, your helicopter should fly fairly well the first time, but it will still need fine tuning. There is a step-by-step process to perfect helicopter setup.
Build it right.
- Lock-tite screws that go into metal - very important on feathering shaft!
- CA on screws that go into composite plastics
- Ball links sized correctly
- Servos centered properly
- Parts in proper orientation (some parts can be backwards or upside-down)
- Gear mesh set properly (test with paper)
- Flybar balanced, and paddles aligned
- Rudder push rod straight
- Tail fins and support rods aligned
- Bearings lubed (Tri-Flow)
- Blade grip tension correct
- Belt tension correct
Set up the head. (Top-down method)
- Hold the blade grips at zero pitch throughout this procedure
- Adjust the pitch mixing links to equal lengths, and until the pitch mixing arms are both level - 90 degrees from the main shaft and level with each other
- Snap the radius arms onto the swash plate
- With the blades and paddles at zero pitch, adjust the washout links and the long mixing arm links until the washout arms are level - 90 degrees to the main shaft, and level with each other. This can be tricky because you'll need to get them both correct at the same time - use the suggested measurements from your helicopter manual as a starting point.
- At this point, the blades should be at zero pitch, the flybar cage level, and the mixing arms and washout arms should be 90 degrees from the main shaft, and level with each other.
- This sets the height of the swash plate at zero pitch.
- Center your cyclic servos, and adjust the swash plate links so that the servos and swash can be connected with the swash at the 'zero pitch' height, and the servos perfectly centered.
Program the radio.
- Set CCPM mode, 120-degree swash plate
- unplug the motor
- plug in the helicopter and let it initialize - center the throttle stick
- Move the throttle stick up and down a little bit
- All three cyclic servos should move up and down together - if one doesn't, reverse that servo only.
- Go to your pitch mixing setup
- Move the throttle stick up - all three servos should move together, and your blades should get more positive pitch. If not, change the pitch mixing number from positive to negative - we will set the actual number later, just getting the direction correct now.
- Move the cyclic stick to the right - your swash plate should tilt down on the right - if not, change the aileron mixing number from positive to negative. Again, we'll set the actual number later.
- Move the cyclic stick forward - the swash should tilt down on the front side. If not, reverse the elevator mixing number from positive to negative.
- Double check your settings - make sure that more throttle gives you more positive pitch, and the swash is tilting in the right directions.
- Check that the blades are at zero pitch with the throttle stick in the middle - you have not adjusted the pitch curve yet, so this should be the case.
- Put the throttle stick all the way up. Adjust the pitch mixing number until the swash moves up to the extreme - the washout block should nearly run into the head.
- Put the throttle stick all the way down. Make sure there is no binding, and the washout block does not slip off the washout guide rods. If it is going too far, be double sure you are getting zero pitch at mid-stick, and reduce the pitch mixing number if you need to.
- Go back to your servo reversing menu.
- Move the rudder stick all the way to the left - the leading edges of the tail blades should move to the right. If not, then reverse the rudder channel.
- Program the pitch curves - this is a matter of personal preference and flying style. I set mine up to give me maximum pitch in both directions, positive and negative. A 5-point curve for normal mode would be 30-40-50-75-100. For my stunt modes I use 0-25-50-75-100. It is important that the last three numbers be 50-75-100 in all modes, so that when you switch modes in flight, you don't get sudden pitch changes.
- Program the throttle curves - again, this is a matter of personal taste. For my normal mode I use 0-50-75-90-100, which gives me high head speed very early, makes the transition to stunt mode less severe, makes the helicopter a bit more stable in a hover, but also makes it more reactive. For my stunt mode, I use 100% all the way across. Some people prefer a v-shaped throttle curve such as 100-90-80-90-100.
Set up the gyro.
- First you need to set the gyro direction. To do this, wag the tail to the left - the leading edges of the tail blades should move right. The tail should try to fight your motion. If not, reverse the gyro direction on the gyro itself. You should not need to reverse the rudder channel if you do this, but double check it to be sure.
- There are many ways to set the gyro gain - most setups have a remote gain setting programmed in the radio by signalling the gear channel.
- To adjust the gain, you will need to fly the helicopter. The gyro does not understand what is happening when the helicopter is not flying, and it may do weird things such as stick the servo to one side and stay there.
- Move the rudder stick to both sides and hold it there. Make sure the servo is not capable of driving the pitch slider too far. Use the limit feature of the gyro, or change holes on your servo arm to limit the travel. Do not use adjustable rates on the radio to try to limit the servo travel - it will not work, and you will risk having the servo bind and strip in flight.
- Using training balls to fly your helicopter the first time, you will adjust the gyro gain higher until the tail starts to wag back and forth forcefully. Then lower the gain from that point until the wagging stops. You may find that the tail starts wagging again after hard spins or loops, or during turns. Lower the gain some more if this happens. See my Trex 500 video on the "arvadamodelers" Youtube channel for an example of gyro gain too high, not causing tail wag in hovering, but wagging in forward flight. I lowered it 1% from there, and now it's perfect.
Balance and track the blades.
- Before your first flight, make sure the blades are balanced. You can use a blade balancing tool, or a very accurate scale to do this.
- Now bring your helicopter into an eye-level hover, and have an assistant look at the blades - there should be no gap between them. If there is, you will need to adjust the pitch mixing links to close the gap.
- Usually, I just pick a link to adjust and see if it makes the tracking better or worse. Mark the link with a silver Sharpie, and adjust it in the other direction if it makes the tracking worse. Do one full turn at a time, as this is a very sensitive adjustment.
- If you use carbon fiber blades, and you zeroed your blade pitch properly, they should track perfectly - if not, be sure to check the pitch again before adjusting the tracking.
Final inspections and test flight.
- Lube all the bearings
- Pull on the ball links and make sure they are tight
- Check the belt tension
- Check the blade grip tension
- Check the rudder direction while spooling up
- Make sure everything sounds smooth
- Watch for vibrations when spooling up
- Fly for only a minute or two the first time
- Check the parts temperature after first flight - motor, servos, gyro, and battery. Hot parts can indicate a problem.
Remember - the helicopter is the only type of aircraft capable of crashing into itself! If you build and maintain properly, this won't happen.
