The INAV Fixed Wing Group dedicates itself to get people the help the need to get their INAV planes flying great. We get a lot of posts from members saying that their plane doesn’t fly as it should. With INAV, unless you’re in manual, you’re not directly flying the plane; the Flight Controller is really in charge. Your inputs on the transmitter are requesting actions from the flight controller, and it decides how the plane should react. But, there are things we can do to get the plane flying optimally in all modes. In this INAV Plane Tuning Masterclass, we do what we can to get your model flying the best it can.

This manual is for people who will get hands-on with their gear. Just as you don’t need to understand advanced aeronautics to know how to fly a plane; you don’t need to understand computer programming or the intimate details of how PIDs work. Just follow our suggestions. Each section is it’s own journey. There is a learning curve for all of it. Work one section at a time and keep good notes. As you figure things out, the next time you do it for another plane it will be a lot easier. If you apply yourself you’ll have a plane that is even more enjoyable to fly.

This Guide will consist of three major phases. Phase one will be the initial tuning with AUTOTUNE to get a nice and stable flight in calm conditions. Phase Two will be a manual fine-tuning tutorial, to get the plane ready for windy and gusty days and optimise it for different speed situations. In Phase Three we will go into some special features and optimisations to get automatic modes to work perfectly. So, let’s start!

Preparation

As many of you already know, our INAV builds are not just plug and play. Each plane has its own behaviour, characteristics, and moods. Let’s call it a personality. To get a plane flying as well as possible, INAV needs to learn what to do in any situation. This tuning process is necessary to get a plane to fly the way you are proud of and want to show to your friends.

Before starting with this tuning guide, you need to prepare a few things. First of all, you need a plane that is already completely set up. All final hardware needs to be installed, the correct battery in use, all your modes are configured, and the mixer is set up correctly. If this is not the case right now, look in our other guides first to get your plane ready.

To get through the whole tuning process, the following conditions need to be met. This includes equipment needed and some modes that need to be set up on your transmitter and INAV. If you are new to INAV and use an OpenTX based transmitter, we recommend that you to use our Beginners Setup Profile from Darren Lines. This pack has a model for OpenTX transmitters.

What you’ll need

  • A set up model with the flight controller running INAV (2.4 and up) and set, ready to go
  • A working GPS module (Compass optional but not recommended)
  • An active black-box with On-Board Flash/SD Card or alternatively FPV Recording with our provided Tuning OSD

Needed Modes

  • MANUAL
  • ACRO (when no other flight mode is active)
  • ANGLE
  • 3D CRUISE (NAV CRUISE & NAV ALTHOLD in same switch)
  • NAV RTH (optional)
  • NAV POSHOLD (optional)
  • SERVO AUTOTRIM
  • AUTOTUNE

A good physical setup of the model

Regardless of the flight controller, you need to set the plane up properly. The CG must be right. Likewise, the control surfaces set with the correct amount of movement and reflex, if needed. Make sure you set up the control surfaces in manual mode. This information should be in the documentation you get with your model. If your model is flying well in manual mode, without radio trim, you’re around 85% of the way to perfection. So, before we progress with this guide. It is essential to maiden the plane and get it flying straight and level hands off. Once the plane is flying good in manual, proceed on to phase one.

Phase One: Initial Tuning

If you did not maiden the plane before this point, that’s OK. But, you were just putting off the inevitable. Make sure your CG is correct and all hardware is bench tested. If that’s all good, you can do the maiden right now. Make sure you do the maiden with the Manual Mode active and do not use Autolaunch. Get someone else to throw the plane so you have full control over the launch.

Getting airborne and testing the base tune

Launch your plane in manual mode and make a few turns and see if everything is OK. The next step is to see if the default PIFF values can keep the plane in the air without getting unresponsive or “freaking out”. Ideally do this is via FPV. But Line of Sight is fine too.

Fly to a safe altitude and switch into ACRO mode. Continue flying around and watch the plane. Be ready to switch back to MANUAL if the plane behaves strangely. Maybe the plane will feel a bit sluggish. Worse, it could start to oscillate on one axis. In this scenario, switch back to MANUAL and leave the stabilisation disabled for now.

The plane can stay in the air for the next step. But if you had oscillations, lower the P and I values in PID Tuning Tab after landing and try again before continuing to SERVO AUTOTRIM.

Servo Autotrim

SERVO AUTOTRIM is a very useful tool. It allows us to fine tune the trim of the model for the current conditions. Sometimes it is a good idea to repeat the trim if the CG has slightly changed by a different battery size.

This is a very important section. People often do the Servo Autotrim process incorrectly. Please read this section carefully before attempting an auto trim.

As we are tuning the model, we need to ensure that it is flying as well as possible before tuning. So you should do the Servo Autotrim before the autotune. You can do Servo Autotrim as often as you like. If you do a good tune you don’t need to repeat the tune unless something significant has changed about the plane.

Just to further emphasise, you must never fly with active radio trim when in any stabilised mode. Also, this needs to be done in very calm wind conditions.

There are two recommended methods to do the trim. One is easier to handle and one is much more precise. The first Method is the default one recommended by the INAV documentation and you do that in ACRO mode. this needs to be done at a calm day without gusts.

  1. Fly at a comfortable cruise speed, faster than normal but not full throttle
  2. Keep the plane in a straight line, just do very gentle stick corrections with small movements
  3. The PIFF controller should keep the plane from drifting on roll or pitch axis and keep it in a straight line
  4. Hold the sticks in a constant position if needed or completely release them if the plane is stable (like in ANGLE mode)
  5. Activate SERVO AUTOTRIM via switch and keep it activated
  6. Wait at least 3 seconds before taking over control of the plane again
  7. Continue to fly normally if you want, then land and disarm the plane. Now the trim is saved.

The second method of trimming the plane is recommended for a bit more experienced pilots. If you do it wrong, the plane can become hard to control in extreme cases. You will also not be able to use stabilised flight modes to land the plane. If done correctly, the trim is very precise and is not influenced by any air turbulence.

  1. Fly at a comfortable cruise speed, faster than normal but not full throttle
  2. Switch into MANUAL flight mode (from this point you must not switch back to other flight modes and do not disable manual mode till the plane is landed)
  3. Trim your plane on your transmitter on roll and pitch
  4. Do the trim until the plane flies as straight as possible when you release the sticks
  5. Then land the plane in MANUAL mode but do not disarm yet
  6. After landing, do not touch the sticks and enable SERVO AUTOTRIM
  7. Two second later you might hear a small servo jump, that means the trimmed RC signal is applied as the new trim
  8. Disarm the plane to save the trims in INAV
  9. Move the radio trims back to centre (this is very important).

After the trim is done, it is important to move the trims from a software side trim into a hardware trim.

In disarmed state, switch back to manual mode and look at the control surfaces. Measure the deflection of each surface or just take a picture. Go to the configurator and go to the servo section in the Outputs page. Look at the midpoints of each servo. If the midpoints are in a range between 1450 and 1550, you are done. If the values are above 1550 or below 1450, you need to mechanically adjust the linkages.

To do this, reset the midpoints to 1500 and then mechanically move the control rods to get the servos in the same position as you have noted before. Then do another SERVO AUTOTRIM flight and check the midpoints again. All midpoints should now be close to 1500. If so, Servo Autotrim is complete.

Determine the physical limits of the plane

Next in the INAV Plane Tuning Masterclass, we will calculate the physical limits of your model. To be able to control the plane correctly and reliably, INAV needs to know the physical limits of the plane. Four values are essential:

  • Roll rate
  • Pitch rate
  • Yaw rate, if your model has a rudder
  • Stall throttle

The easiest way to get these values is by recording your flight with an on-board camera and DVR recording. If you only do LOS flights without camera equipment, you can also use the black-box data to analyse the rates. To do the test, just follow these steps.

Activate the Roll and Pitch angle view in OSD to use them as a reference when calculating the rates later. Also, the Throttle Value should be active in OSD. If you are a beginner pilot, you should let an experienced pilot do this for you because it needs some extreme maneuvers.

It is essential, that you perform this test in manual mode, at a medium to high airspeed.

Roll Rate

  • Fly level at a high airspeed
  • Do some roll manoeuvres at full stick deflections
  • On agile planes, you can even do a double roll to get the best results
  • On big planes and cruiser builds like a Mini Talon or an S1100, you should not do full rolls but hard left and right banks to more than 45 degrees to each side

Pitch Rate

  • Fly at the same airspeed as before, a good few mistakes high
  • Then go into a short dive with about a 45° nose down and instantly pull back full stick on pitch
  • Do a loop if possible with an agile plane
  • On bigger wings or planes that are not able to do a loop, just do a nose up to 45° and then level out again.

WARNING: If the plane suddenly rolls to one side and nose dives when you pull the pitch stick fully back, keep calm! This is a high speed stall because too aggressive angle of attack. Lower the throttle, pull out of the dive gently and not with full pitch!

If this happens, then stop here. You have too much Elevator or Aileron Pitch deflection, or your CG is too far back. Either you need to move the control rods to a lower position on the servo side / higher position on control horn, or you need to lower the mixer weight for the pitch axis. Also double-check your CG. Maybe move it a bit forward too if the deflection is within manufacturer specs already. This MUST be fixed so the plane cannot speed stall on full pitch input.

Yaw Rate

  1. If you fly a plane with V-Tail, Rudder, or differential thrust. You need to measure Yaw Rate too
  2. Fly level first. Then input a full Yaw deflection
  3. Use your Ailerons in the opposite direction to keep your wings at only a slight bank angle
  4. Do at least a 90° turn or better a full 360° Circle this way.

Stall throttle

  1. Fly level again at about mid throttle
  2. Gradually start to lower the throttle very carefully
  3. Lower the throttle in small steps and try to keep the plane at the same altitude with your pitch control
  4. While doing this, keep an eye on your throttle percentage in the OSD (recording helps here)
  5. When the plane becomes unstable, loses altitude or pitches the nose down, raise the throttle again
  6. The throttle percentage when this occurs is your plane’s stall throttle.

This test will need to be redone if you change the weight of the model. Do this test at the highest planned take-off weight. So the heaviest battery is used and all the equipment installed.

Calculate the rates

After doing these manoeuvres, land the plane and get to a PC. If you recorded your FPV feed with the active OSD elements, open the video file with any media player that can do a frame by frame stepping of videos (like VLC).

For Pitch and Roll rates, look at your video and search to the point where your manoeuvre already has reached its maximum speed. Write down the angle shown in the OSD and skip frame by frame while counting them. If you did a full roll or loop, just count the frames of half of the manoeuvre. For rolls, start counting the frames when the OSD shows 90° bank Angle. Then stop counting the frames on -90°. With pitch, start at 90° pitch and stop at -90°. For Yaw you count the frames depending on compass position and a 180° turn. Then calculate each rate by the following formula.

axis rate = measured angle x (FPS / counted frames)
PAL has a frame rate of 25 FPS
NTSC has a frame rate of 30 FPS
DJI HD and some other DVR record 60 FPS

The result is the maximum rate for the axis in Degrees per Second. Set these values in the PID Tuning page under the Rates & Expo tab in INAV configurator. Better set these slightly lower (by 10%) or as low as you like them to be, but never set them higher!

INAV Configurator - PID Tuning - Rates & Expo

To get your safe cruise speed, look at your OSD during your stall test. Write down the throttle value when the plane starts to descent, pitch down, or even stall. Add 20% throttle to the shown value to get your minimum cruise throttle. This is the lowest safe speed during navigation. To calculate the cruise throttle, use the following formula.

cruise throttle value = 1000 + (stall throttle [%] × 12)

So if the stall throttle was 40%, your minimum safe cruise throttle value would be 1480 in configurator. You can set this in the Advanced Tuning page. It is always safer to go even higher if you are not aiming for maximum flight time.

AUTOTUNE

Please read this section two or three times before attempting an Autotune. You should do it on a calm day, after the AUTOTRIM.

Now let’s get into the serious stuff. After a lot of preparation, INAV will now finally learn how to control and stabilise the plane in a smooth and reliable way. For AUTOTUNE you need to fly in calm conditions with ideally no wind at all. For windy conditions, this needs some manual adjustments. We will do this in Phase Two. Enable the ROLL and PITCH values in your OSD to see if the values actually change.

  1. Start flying around in ACRO mode
    • You can also use ANGLE mode on bigger planes, if you primarily will fly in self levelling modes like cruise or autonomous modes. However, we don’t recommend Angle, as it is not possible to do very sharp manoeuvres needed to do a good tune
    • Alternatively, you could use HORIZON Mode to keep the security of self-levelling
    • If you don’t want to do these manoeuvres for yourself, because you don’t have enough experience. Ask an experienced pilot to do this for you.
  2. Turn on AUTOTUNE in flight via the switch
  3. When doing this the first time, the plane might become a bit sluggish
  4. Immediately start doing roll and pitch manoeuvres with full stick deflection in each direction, and quick stick centring
  5. The craft will become more stable after a few movements
  6. Continue flying the plane with most aggressive moves you would normally do in a flight
  7. Do this until the PID values in your OSD settle down and you don’t see big changes anymore.

Always do this at a medium high speeds, especially if your Motor setup is very powerful. This method will calculate the PIFF controller values depending on the airspeed and control authority you have. If you fly too fast, the plane will become sluggish again at low speeds or when landing. So, medium speed is better. The high-speed tuning will be done in Phase Two. After the AUTOTUNE is done, disable the mode again and land your plane. Disarm the Motor and save the new tune either through the INAV OSD Menu (Save & Exit) or via Stick Command by pulling both sticks towards you and away from each other (Mode 2).

INAV Plane Tuning Masterclass – Phase One Conclusion

Now we are done with the basic tuning of Phase One. The plane should now fly stable and smooth in calm conditions, NAV CRUISE, NAV RTH, and NAV POSHOLD modes should now work okay but you should test them carefully. More tuning is needed for GPS assisted flight modes (see Phase Three). For new pilots, it is now time to fly some batteries to get experience and confidence in your plane. After that, we can continue to Phase Two.

At this point I recommend you run through our Autolaunch Guide: How to setup NAV LAUNCH Correctly