RC helicopter radios have some very interesting and different features/functions than standard fixed wing specific radios. Time to learn about these features and why you can’t fly a hobby grade RC heli without them.
“Can I fly a RC helicopter with my RC airplane radio?”
I get this question a lot. The simple answer is “NO” – especially if you are getting a hobby grade RC heli with collective pitch - as you know by now , that should be your only consideration.
You can however fly a RC airplane with a RC helicopter radio - you just won’t be using the heli specific features. So, if you were just getting into RC airplanes, but thought you would also give RC helicopters a try, your best bet would be to get a RC helicopter radio – make sense?
Wait a minute... We are living in the 21st century now!
All that was true up to a few years ago, but now we have computerized radios that have both heli and fixed wing software built into them. This means that you no longer have to make the choice between the two – one radio does it all. That is why I said on the RC radio gear page you should only consider getting a computerized RC radio when getting serious about the hobby.
First up is the one stick that is used to control two functions, or in other words two channel outputs are controlled with one stick - the throttle stick to be exact.
This is the main difference that a RC helicopter radio has over a fixed wing radio. The collective pitch and throttle are both controlled by the same stick on the radio (the left stick on a mode 2 radio). An airplane requires the throttle alone to be controlled by this stick.
Now this is important to understand because even though these two functions (throttle and collective pitch) are controlled with one stick, they are on two separate channels and take up two outputs on the receiver. One is the throttle channel and the other is usually the auxiliary 1 channel.
Why separate them? Why not just hook two servos up to one channel? This question leads us into the first of four other RC helicopter radio specific functions that are dependent on this separation.
1. Throttle Hold
The throttle hold function will allow you to lock the engine throttle/speed at a pre-set value, usually idle or electric motor off while still having full control over the collective pitch using the combined throttle/collective stick. This function is usually activated by a toggle switch on your RC helicopter radio.
Why would you want this function?
If you are practicing auto rotations , you need throttle hold to lower the engine power down to an idle or turn it off, but still have full collective control on your main rotors to perform the auto rotation. Throttle hold is also a nice safety feature for both fuel and electric powered helis because it will prevent the rotors from spinning up if you accidentally bump the throttle stick on your radio.
2. Idle Up / Flight Modes
Idle up is used for the same reasons as throttle hold – to have full collective control using the combined throttle/collective stick, while the engine is set at a constant speed – this time a high of full speed setting. This is used to keep the head speed more or less constant regardless of throttle/collective stick position. It also what allows aerobatics when higher rotor speeds are important and also allows you to keep your rotor speed high while pulling the throttle/collective stick down to give negative collective pitch while still maintaining a high head speed. This of course is required so you can fly the heli upside down.
Once again, the idle up function is usually selected by a toggle switch on the radio. Some RC helicopters radios have a multi position idle up toggle switch that allows you to set more than one idle up speed for more flexibility. Computerized radios will take this one step further... The idle up (now called the mode switch) is used to select different throttle and pitch curves giving the ultimate in flexibility - our next topics.
3. Programmable Throttle Curves
A programmable throttle curve function simply allows you to program specific throttle output settings to specific throttle stick settings. The most basic and simple throttle curve is called a linear curve – the kind that all non computerized RC radios produce. This would mean at low stick the throttle output would be 0% At mid stick the throttle output would be at 50%. At full stick the throttle output would be at a 100%.
The above image show a graphical representation of a basic linear throttle curve.
Computerized radios will allow you to customize this curve so you can now set the throttle speed to what ever value you want at different throttle stick positions to enhance what ever type of flying you are doing.
This graph shows an example of a throttle curve for full on aerobatic flying with a fuel powered heli. The throttle output at the low stick setting is set at 100% power to give maximum climb out power when the helicopter is inverted and using full negative collective pitch. At mid stick the power is set to 60% so the rotor head won’t overspeed with the reduced collective pitch rotor drag/loads. At full stick, the power setting is once again set to 100%, for the maximum climb out power with full positive collective pitch.
A good computerized radio will allow you to program at least 5 different throttle point settings throughout the range of stick movement - one setting at low stick, one at 25% stick, one at mid stick, one at 75% stick and the last one at full stick. This would be called a 5 point throttle curve.
A good computerized RC helicopter radio will also allow you to see this information on a graph, just like the ones pictured above. This is important in case you mess up on one of the settings, it will be very easy to identify a curve programming blunder if you can see it visually.
4. Programmable Pitch Curves
Programmable pitch curves work the exact same way as programmable throttle curves – they allow you program specific collective pitch angles to specific stick settings.
There is no single adjustment you can make to a collective pitch RC helicopter that changes how it flies more so than changing the collective pitch range. That is exactly what programmable pitch curves allow you to do, easily and quickly; to turn the same helicopter from a docile trainer to an insane 3D monster. Click here for more information on pitch set up.
This graph shows a linear pitch curve on a RC helicopter that has a maximum and minimum collective pitch of plus and minus 10 degrees. At low stick the pitch angle will be negative 10 degrees. At half stick the pitch angle will be 0 degrees. At full stick the pitch angle will be plus 10 degrees. This would be the kind of pitch curve an aggressive 3D heli pilot would use.
is a more docile pitch curve for normal or scale type flying. It produces negative 3 degrees of pitch at low stick, plus 5 degrees at half stick,
and plus 10 degrees at full stick.
Once again, just like programmable throttle curves, a good computerized RC helicopter radio will show the pitch curve on a graph for the same reasons and have at least 5 setting points – this would be called a 5 point pitch curve.
Programmable throttle and pitch curves have caused much confusion, especially for those new to RC helis. After all, there are literally hundreds of variables you can set.
The whole idea behind pitch and throttle curves is to produce the right amount of power for a given pitch angle based on your flying style and the machine you are flying. If you think of it that way – pitch and throttle curves are pretty easy to understand.
Keeping things simple, I always set my pitch curves first. Most heli kit instructions will include the recommended pitch settings for different types of flying. I then set my throttle curves to give smooth and steady power throughout the pitch range. Like I said before, having this information displayed graphically on your radio is a big feature. You always want nice smooth pitch and throttle graphs, no erratic values or sudden changes.
In short - Smooth pitch and throttle curves produce smooth flying birds.
5. Tail Rotor Compensation / Revolution Mixing
The next RC helicopter radio specific function is Tail Rotor Compensation. This is also called revolution mixing by many people/radio manufacturers.
Tail rotor compensation as the name suggests compensates for this. Basically this function mixes additional tail rotor pitch to compensate for the added torque when the throttle/collective stick is increased. Like wise, it reduces the tail rotor pitch when the throttle/collective is decreased.
On non computerized RC helicopter radios, this function is controlled by two dial knobs, one for up mixing and one for down mixing. The up setting is used to adjust how much the tail rotor pitch is increased as the throttle/collective stick is increased. The down setting is used to adjust how much the tail rotor pitch is reduced when throttle/collective stick is decreased.
On a computerized RC helicopter radio, this function is programmed on a menu screen in the same way – a mixing value for up and one for down. Good radios will have two and sometimes three different settings for different types of flying such as normal, sport, or 3D.
Tail rotor compensation settings are adjusted by trial and error and are never perfect - but they are better than nothing.
Once again – technology is making this function obsolete. You only have to use tail rotor compensation with a yaw rate gyro . If you are using a heading hold gyro in the heading hold mode, tail rotor compensation is never used – the gyro handles the changing torque and does so with much more precision than the best tail rotor compensation settings ever could.
In addition to that, you must never use tail rotor compensation if you are using a heading hold gyro – make sure your compensation dials or settings are set at zero. If not, the compensation will send tail rotor commands to the gyro. The heading hold gyro will see these commands to turn the heli and it will do just that.
6. Gyro Gain
The gyro gain function uses a radio channel and toggle switch to remotely change the amount of gain on the tail gyro. The gain output can be adjusted from 0 to 100% based on what gain setting you wish to use on your specific gyro. Generally you will have at least two selectable amounts of gain for different head speeds/tail speeds. Most computerized radios allow you to assign the gain channel output to a specific toggle switch. You might like it assigned to your rudder dual rate toggle or perhaps your flight mode toggle.
7. CCPM Mix Programming
I have already talked about CCPM (cyclic collective pitch mixing) in the best RC helicopter section , but it is also an important computerized RC helicopter radio specific function. Electronic cyclic collective pitch mixing called eCCPM has been made possible by computerized radios after all.
Most RC helicopter radios will offer at least 90° and 120° CCPM mixing modes. Some higher end radios will also offer others such as 135°, 140°, and perhaps 180° CCPM mixing.
you are just getting into this hobby and are looking for a good entry level computerized RC
helicopter radio that offers all the important functions and features
that I have just talked about - the 6 channel
Spektrum DX6i or the newer DX6 really can’t be beat (DX6i review) & (DX6 review).
If you know however you are going either start with or eventually get into larger collective pitch RC helicopters (larger than 500 size), you may want to consider a more intermediate level radio such as the DX7 or DX8. Not because the DX6i won't work with a larger model, it will work fine. It's just that you may start questioning the quality or robustness of an entry level radio controlling a $1K plus bird. I know I sure do...
Here is my page that talks about more computerized RC helicopter radios and covers entry level right up to advanced if you are interested in learning just what is out there and how different brands compare.