RC Helicopters
Author
Eric Hawkinson 319 Yellowstone Ave., Billings MT 59101 E-mail: [email protected]
Introduction
IT'S ANOTHER great month to enjoy Radio Control (RC) helicopters!
Whether you are starting your first helicopter project, mastering a complex maneuver, or working on a repair session, remember to include the enjoyment part—that's the whole point of a hobby/sport such as ours.
This column is primarily directed at newcomers to RC helicopters, keeping with the theme of the entire issue.
But many of the helicopter pilots who read this magazine are not new to RC—just to helicopters—so I'll skip the basics of the radios, engines, and flight, and look at the more common problems faced by first-time RC helicopter pilots.
There are three primary areas where the seasoned RC fixed-wing pilot will face new challenges when giving rotary-winged models a try: engines, gyros, and more-complex radio programming.
A fourth challenge is actually controlling the helicopter through flight maneuvers, but most people realize they will have to spend some time learning that.
Engines
Most modern RC helicopter engines are capable of giving good performance if installed and set up properly. Installation is usually simpler in a helicopter than in an airplane; there are no thrust settings to worry about and no holes to locate or drill.
Since all helicopters are designed from the start for a certain size of engine, all you have to do is buy that type of engine and align and bolt it into the predrilled mounts after you install the fan and the clutch.
You may be surprised to learn that helicopter engines come without mufflers. That's because the muffler must fit not only the engine, but the mechanical layout of the helicopter. Buy whatever muffler is recommended by the helicopter's manufacturer or by a trusted dealer.
It's usually best for the novice to stay away from tuned pipes on helicopters. Go for simplicity and reliability for now; you can add a pipe later, if you decide you need more power.
It's impossible to overstate how important reliability is, rather than maximum power or initial cost of the engine. You will have plenty of challenges learning to set up and fly your RC helicopter even with the most reliable engine.
Choose the best engine you can, put on a good muffler, use a fuel filter in your fuel can and on your helicopter, and keep all the fuel lines in perfect condition.
Pay close attention to the recommended fuels and glow plugs. Since we require our engines to run reliably in all flight conditions—especially at half throttle (where we hover)—the care and selection of the engine and related systems are critical.
Setting the needles will be a bit more time-consuming than airplane pilots are used to. You can't run up to full throttle and pinch the line to check the needle—this has obvious safety-related concerns. If you're just starting, you won't even see full throttle in flight for many sessions.
Set the needles per the engine's instructions, then set the idle mixture the same way you do in an airplane—by pinching off the fuel line and listening to the response while you are holding onto the head of the helicopter to keep the blades from turning.
(Do this when starting your helicopter, and make sure the throttle is at idle and that no idle-ups are activated.)
You are listening for the same thing as with an airplane engine; after two to three seconds, the engine should speed up as the mixture leans, then start to sag as it goes overly lean. If it takes longer than that, the idle is rich; if it starts to speed and sag immediately, the idle is too lean.
Adjust accordingly, but keep in mind that any major change in the main needle will require you to return to the idle.
Watch for a fairly obvious smoke trail while in flight (from unburnt oil and fuel being exhausted), and listen to make sure the engine is running smoothly.
Gyros
The next "new" thing for transitioning airplane pilots will be the gyro. Airplanes seldom use gyros, and they are practically never seen on fixed-wing trainers or sport airplanes.
On helicopters you should consider a gyro a necessity to "tame" the tail rotor (rudder) function to a manageable level. The gyro is installed in your RC system between the tail-rotor servo and the receiver.
You control the tail with the rudder stick, just as you do with an airplane. But in addition to your control inputs, the tail servo is also responding to the gyro to keep the tail positioned per your commands.
It is important to check the direction of control input that results from your stick inputs and the gyro's inputs; either or both can be backward, resulting in an uncontrollable helicopter.
Check to make sure that a rudder-stick input to the right gives a control input to turn the nose of the helicopter to the right; if it doesn't, go to the servoreversing function for your rudder channel and change it.
Then pick up and rotate the helicopter to the left, and watch to make sure that the gyro gives the command to turn right. (Watch that the servo arm or tail slider moves the same way as when you give right rudder input.)
If the helicopter does not turn right, reverse the gyro function according to the manufacturer's instructions. (It may be a switch on the gyro, a software setting, or sometimes simply inverting the sensor box.)
If you have selected a heading-hold gyro, you will also need to verify the settings for the gyro mode (heading-hold or normal), but that's a topic for another column.
There are good reasons to choose a heading-hold (Futaba calls it a VCS—Active Angular Velocity Control System)-capable gyro even as a beginner, but it usually adds a bit of complexity to the setup.
Radio setup and controls
Now for the rest of the radio setup. You should choose a helicopter that has collective pitch—most modern kits have it.
This means you will be using a minimum of five control functions for a basic setup:
- Throttle
- Collective pitch
- Elevator
- Aileron
- Rudder
(Rudder is actually tail rotor, and elevator and aileron are left/right cyclic and fore/aft cyclic respectively, but I'll use the simpler designations your radio will use.)
I'm not aware of any five-channel helicopter radios, so your radio will need a minimum of six channels plus five servos. You may want to start with an eight-channel system; these usually have a few more features that will be useful to you later, for advanced flying.
You do need to make sure you choose a radio that includes helicopter functions!
The basic control functions will be almost as simple as on fixed-wing airplanes; the aileron, elevator, and rudder are checked for proper direction of throw (fixed in the reversing menus as needed), and the servo-travel limits are set in the radio to make sure that no binding occurs at full control throw.
As with airplanes, maximum control throw is not usually needed or recommended for novices, so either reduce the travel limits or select a dual-rate function for initial flights.
If you choose one of the newer helicopters that uses CCPM (Collective and Cyclic Pitch Mixing) controls (where the servos are more directly hooked to the swashplate, and the collective and cyclic are mixed electronically rather than mechanically), programming will be a bit more complex.
Tail rotor and revo-mix
Another programming requirement involves the tail function—"revo-mix," or tail rotor pitch curves.
Since the proper "neutral" position of the tail rotor blades varies as the main-blade pitch and engine power settings change, the revo-mix function adds trim input to the rudder servo as the throttle/collective stick is moved.
This mix is required whenever running a gyro in "normal" mode, and is never used when running a gyro in heading-hold mode. Most radios have initial suggested settings for the mixing values that will put you in the ballpark.
You will normally have a tail-rotor setup as follows: at neutral rudder and midstick on the throttle/collective, the tail-pitch lever will be 90° to the tailboom and the tail blades will have approximately 5° of anti-torque pitch.
With the revo-mix properly set, as you move the throttle stick upward, the tail blades will have more pitch; as you move it below the midstick position, the tail blades will have less pitch.
You now have three controls that move the tail rotor blades: the rudder-stick movements, the revo-mix outputs, and the gyro's outputs.
More advanced radios use tail rotor pitch curves with five or more adjustment points, which is simply a more flexible and precise way of setting the throttle-to-tail-rotor mixing.
Throttle and collective pitch mixing (flight modes)
The last "big difference" with the helicopter-radio setup is the throttle and collective pitch mixing function.
This function is so important that nobody calls it a mixing function; rather, the pitch and throttle mixing is defined as the primary part of each flight mode, and the settings are called pitch curves and throttle curves (even on radios that only give three adjustment points, which is generally not enough to actually define a curve).
A flight mode is a switch-selectable subset of your helicopter setup that has its own unique pitch curve, throttle curve, or setting, and usually tail-rotor/gyro setting.
Most radios refer to the flight mode you normally hover in as the "normal" flight mode, and you have to at least set up this flight mode to start flying.
In normal flight mode:
- Low stick (throttle/collective stick in the full down position) gives idle power setting and your minimum pitch setting.
- Midstick gives you approximately half throttle, and traditionally moves the collective pitch to approximately 5° for hovering.
- Full stick is full throttle and maximum pitch in the main blades; this is usually 9°, but is dependent upon blade selection and power available.
Getting this relationship set up correctly for your current flying level is extremely important.
For first attempts at hovering only, I prefer a setup that has +2° of pitch at low stick. If you panic and jerk the throttle stick down (and you will), the helicopter will settle to the ground with some residual lift slowing the drop.
Most books tell you 0° at low stick, which is okay. But if you jerk the throttle off, the helicopter will drop like a nonlifting device (a rock), which is exactly what it is at 0° pitch and no airspeed.
As soon as you get past the panic stage—and definitely before you try forward flight—you will have to change the pitch curve (low stick is the idle setting on the engine in normal flight mode) to give you some negative pitch at low stick—preferably 4°, as soon as you can handle the more responsive controls.
In addition to the normal mode, you will have at least:
- One "idle-up" or "stunt flight" mode, and
- A "throttle-hold" flight mode.
Throttle-hold is used to practice and perform autorotations. Autorotations are the helicopter equivalent of fixed-wing "dead-stick" landings, but with a throttle-hold function you can practice autorotations without the engine actually being stopped.
Select a throttle-hold flight mode setting that gives you a good, reliable idle slow enough to disengage the clutch when the switch is actuated. The pitch setting is approximately 4–5° negative pitch at low stick, 9–11° positive at high stick, and 0–4° at midstick.
The idle-up or stunt mode(s) is used for aerobatics. For 3-D (three-dimensional) aerobatics, you will program a pitch curve that has approximately:
- -9° at low stick,
- 0° pitch at midstick,
- approximately +9° at high stick.
The low- and high-stick settings are dependent upon power available and blades used.
The throttle curve for this flight mode is at 100% throttle for low stick, 0% at high stick, allowing full-speed roll about upright and inverted. The -50% stick position will usually be less than 70% throttle—whatever is required to keep the head speed constant throughout the stick travel.
The gyro-mix function—if you are not using heading-hold—will be set to the same value for full up and full down, and close to zero tail-bleed pitch at midstick.
As a beginner, you will not initially use the 3-D curves I described above. However, if you are intent on moving on to advanced aerobatics, make sure your mechanical linkages are set up to accommodate the full 3-D pitch range so you can program for it when you are ready.
Also consider ditching some of the "normal" advice about what stick position to set which to hover. But that's beyond the scope of this month's column, so I'll take it up next time.
Closing
Don't let the more complex programming scare you away from helicopters. They have many advantages compared to airplanes: there is no wing, covering, sanding, covering, or painting on most helicopters, and when your model crashes you remove damaged parts and replace them with new parts—so you always have a "new" helicopter.
There is little time wasted at the field assembling and disassembling a helicopter, and you can probably find a suitable flying site for helicopters much easier than you can find a clearing with runways used for airplanes.
With shorter building times and much easier storage and transport in many cases, RC helicopters actually present fewer challenges than their fixed-wing cousins—not in programming and flying!
Until next month, fly safely and happy rotating! leo
Transcribed from original scans by AI. Minor OCR errors may remain.
