Helicopters very unstable during spool up

Ryan Douglas

Staff member
Just to be clear, I am using 1 servo mode, which to the airplane guys is and means that the radio outputs an elevator signal (only) for elevator stick inputs, aileron signal (only) for aileron stick inputs and collective via standard throttle stick to collective channel pitch curves. The CCPM 'mixing', if there is any, is done in the sim not the radio. Except for the collective channel, I use my transmitter as if it was flying an airplane.
This does get confusing. If the above is true, then I think it should work as you expect. Contrast that with an eCCPM setup (e.g., 120° 3 Servo), which I don't expect to work with RealFlight.

It's possible that the collective channel, in combination with the setup options, is a factor here. I have a few follow-up questions:
  1. Which radio profile are you using in RealFlight? If it's a custom profile, please post a screenshot or otherwise list all of the settings (including the checkboxes at the bottom).
  2. Which channel is your radio using for throttle?
  3. Which channel is your radio using for collective (if it's using a mode where it sends that)?

Here's where I think a conflict might exist: If you're using RealFlight's software radio, things are not going to work correctly if your radio is 1) using its own throttle/pitch curves, and/or 2) using a separate channel for collective. The software radio takes care of such things for you, so if your radio profile has it enabled, you should set up a simple airplane-type model in your transmitter and use that instead. This is what Jim was talking about when he mentioned "setting up the radio as a joystick".

On the other hand, if you want to use your own throttle/pitch curves to fly helis, that is fully supported. It just requires a different approach. You must disable RealFlight's software radio in your radio profile. Then, you must make sure your radio's collective channel is mapped appropriately for the model you want to fly.

Let's look at the stock Gaui X7 as an example. I will describe how both approaches work. Note that I'm going to talk about the channel numbers that are coming out of the radio profile (the numbers on the right). Depending on your radio type and mapping, they may be different than the numbers on the left, which are probably what you're accustomed to seeing.

Method #1 - Using the Software Radio
If the software radio is enabled in the selected radio profile, then when viewing the X7 in the aircraft editor, the Software Radio section is present. Expand that and you'll see a range of output channels from 1-7. Output channel 3 is used for throttle (which you can see if you look at the Headspeed Governor under Electronics). It takes channel 3 from the channel mapping dialog as an input, which should be mapped to your radio's throttle channel. This software radio output channel 3 has four different inputs curves that are used under different conditions. One is for normal flight mode, one is for idle up 1, one is for idle up 2, and one is used when throttle hold is engaged. This is where the different throttle curves that we have set up are coming from. If any exist on your radio, they will be combined with ours, and that would be bad.

Now let's look at output channel 6 in the software radio. The X7 uses this for collective (which you can see if you look at the Collective Servo under Electronics). Like output channel 3, it has 4 separate inputs that are used under different conditions: normal, idle up 1, idle up 2, and throttle hold. This is where the different collective pitch curves are coming from. Note, however, that the input channel for all of these curves is input channel 3 from the channel mapping dialog, the same as for software radio output channel 3 (throttle) above.

That's because the software radio is expecting your radio to essentially function as a joystick. Your radio should be in airplane mode, even though you're flying a heli. When you move the throttle/collective stick, it should send data on only one channel. The software radio splits that up into the two different functions which are processed separately. In short, it makes the magic happen.

If you want to handle all of that on your own radio instead, you can. Here's how that works.

Method #2 - Disabling the Software Radio
Disable Software Radio Mixes in the selected radio profile. Go back to the editor. Note that the Software Radio section is completely gone from the tree. It is no longer a factor in your setups. Any mixes you want to happen will have to be set up on your own radio or they simply won't exist. But that's what you want, so that should be no problem, as long as you set things up correctly.

Now, with the software radio out of the picture, the output values from the channel mapping dialog (the numbers on the right) shoot straight through into the various electronics components. Remember those channel values I mentioned in the Electronics section for the Headspeed Governor and Collective Servo? You need to make sure your output values match up correctly. If they don't, you'll need to edit the model as needed (or edit the channel mapping in your radio profile, but that's probably the wrong direction from which to drive things).

So in the case of the X7, its governor expects throttle on output channel 3. Make sure your throttle stick is mapped to output channel 3, then set up whatever throttle curve(s) you desire on your radio. It should work exactly as expected. The X7's collective servo expects collective on output channel 6. Make sure your radio is sending collective data on a separate channel, and make sure that channel is mapped to output channel 6. (I assume your radio must be in heli mode to do this; I can't say I've ever tried it in airplane mode.) Set up whatever pitch curve(s) you desire, and it should work exactly as you expect.

Note that other models may expect the throttle and collective signals to come in on different channel numbers, in which case some editing would be required. However, all of the stock heli models in RealFlight should follow the above convention, at least.

I realize this is complicated and probably difficult to follow. I hope it proves helpful, though. Again, all of the above assumes your radio is sending separate channel inputs on discrete channels (aileron, elevator, etc.) instead of mixing them together. Based on your quote above, it sounds like yours is. You can perhaps see now why eCCPM would be problematic.


New member
My radio outputs collective on channel 6. I can confirm this by watching the blue transmitter setup position bars in response to moving the throttle stick in normal, idle-up, and throttle hold modes. The position bars move as they should for throttle on channel 3 and collective on channel 6.

The transmitter setup position bars also confirm that there is no mixing (eg. CCPM) happening in the transmitter.

No software radio in use.

Transmitter channels 7, 8 & 9 are fixed at center position and do not change.

I have to ask why the helicopter oscillates on the ground, but is fine when airborne?


If you choose to un-check software radio mixing function, then you need to edit the helicopter as Ryan explained. You need to edit each helicopter for this to work. Did you do that??


New member
I believe so.

I used the information in the model editing window to learn how to map my transmitter to the model and verified using same that the mapping was correct. The actual mapping was done in the transmitter mapping screen so that helicopters did not need to be edited; the transmitter mapping would now be correct for all helicopters. After that, the helicopter (in this case a Gaui X7) flew fine off the ground. I have proper pitch, yaw, roll, collective, throttle, and governor operation.

I did add a mix in the transmitter to tie the transmitter flight mode switch to governor rpm setting and that works fine too.

Is it possible the flight control gain in the model is too high and that causes the ground resonance?


New member
I have the same issue: instable spool-up. I don't know the reason but it's related to the simstick interface. After the spool-up all works perfectly. It happened also with the previous versions.