By now you have a plane that is flying. Since last week we’ve uncovered some updates with the autotrim process, and flight stabilization process. Week 7 was about bringing your plane into the INAV 3.0 or later realm. This week we’ll go over all you need to know about autotrim, auto level and auto tune.

Autotrim, once or continuous

I guess it’s a fair question to ask why we trim in the first place. After all, shouldn’t planes just fly right from the start? Perhaps your plane weighs more on one side than it does on the other, or the VTX antenna on one side creates drag. You will need to make some minor adjustments to account for the many things that are different about your plane. The one guy who didn’t understand trim at first was, me. My first line of sight planes meant that I always had to have my finger on the right stick otherwise the plane would fall out of the sky. When I discovered how radio trims worked it meant I could safely sneeze, or even go hands off for a while. When I discovered that manual trim made the plane fly, exponentially, and I do mean exponentially better, I was sold.

If you can get your plane to fly well in manual with no radio trim, everything else is a piece of cake. I know it’s not a lot of fun being pragmatic about CG and manual trims. You want to get on to the fun of flying and since you’re almost done, why not simply blow right through this? Your CG off a bit and you cannot get a good manual tune to save your life, so why not just let INAV fix the rest for you? Garbage in, garbage out. Seriously, if you really want to love your INAV flying experience, take your time and put some effort into getting your plane to fly well in manual without trims. When you’re close, we move on to autotrim.

There are three options for autotrim.

Option 1: Do nothing

Perhaps you’re a person with expertise in RC flying and you’re the master of hand tuning your plane. Perhaps you believe that all INAV can do is make your perfect tune worse. If you’re flying around in manual and you have the most perfect tune imaginable you do not need to do an autotrim. Other than to say, why not at least give it a try? If you try it and it’s worse than your hand tune you can simply reset all servos to 1500 and you’re back in business.

I will remind you that we don’t use radio trims in INAV. But then again, this is your plane. If you do set radio trims it will affect the way your plane flies in non-manual modes. If your plane doesn’t perform well, or crashes, can you really blame INAV? The rule is simple; if you use transmitter trims, stay in manual mode until you physically adjust the control surfaces and zero the trims.

If you believe in your trim and don’t want to check it, go to the autotune. I did a manual trim on my plane before doing the autotune in INAV 3.0. I was confident in my tune. The autotrim changed the trims ever so slightly. But, at least I had confirmation.

Option 2: Autotrim on a switch

Some people just want to go through the autotrim process once and save their settings and never have them change. If you would like to do this you will have to turn on the autotrim mode in the modes tab of the INAV configurator. To perform an autotrim:

  1. Take the plane up to a comfortable altitude and switch on the Angle mode.
  2. Keep flying until you’re able to be hands off the pitch/roll stick for around 5-seconds. You should practice letting go of the sticks for this period of time to see if the plane can fly somewhat level.
  3. Engage the autotrim switch and you’ll see autotrim on your OSD. Let the plane fly for between 3 and 5 seconds. Make sure a gust of wind doesn’t blow the plane around. If it does disengage the switch and try again.
  4. Once you’re happy with the trim; keep autotrim enabled, land and disarm. The autotrim is automatically saved when you successfully disarm. You can then switch off autotrim.

Option 3: Continuous servo trim

In INAV configurator, in the configuration screen, right side, very bottom you will see Continually trim servo for fixed wing (shown on the left). If you engage this option, you will no longer be able to have autotrim enabled on a switch. Instead, it’s always on.

Follow the steps above. Get the plane flying in acro, switch to angle and attempt to go hands off the sticks. Land and disarm. What is important is that your servo readings, you do need to check, are between 1450 and 1550. If not, do the following.

Plug your plane in, let it warm up a few seconds. The servos may move slightly. When they are done moving, unplug your battery pack. Stick pins in your control surfaces so that the don’t move. You will somehow disengage the control arm from the servo. This could be unclipping a clevis, unscrewing a grub screw, or removing a ball joint. Reset the servo so that it’s at 1500 and once again standing straight up. The servo standing up at 1500 and the control surface wherever it is located need to be held constant.

If you have a control arm with a clevis or a ball joint. You will need to screw the clevis/ball joint to adjust the length of the arm. You will either increase or decrease its length. I often put sewing oil on the clevises so that they turn easier. If you have a grub screw control arm, the process is even easier. You loosen the joint, reposition the servo to 1500 and then tighten it back up.

Remove the pins. Try the continuous trim process again. Don’t go any further until your control surfaces are between 1450 and 1550. Just repeat the process til it’s there. Your plane will fly much better if they are between these two values.

Auto level

What does Auto level do?

Auto level calculates the flight controller board alignment offset, to get the plane flying level. The flight controller will have the plane fly in a level orientation. This is not Altitude Hold and thus your plane can increase or decrease altitude while flying with Auto level on. Auto level only works in two modes, Angle and Horizon modes. There are three options for Auto level.

Option 1: Off (default)

By default, INAV has Auto level turned off when you set it up. Thus if you plan to use it, go to options 2 and 3.

Option 2: On with Angle and/or Horizon modes

You can enable this mode to work whenever you turn on Angle and/or Horizon modes, and have it off for all the other modes. It is only active with Angle and Horizon modes anyway.

Option 3: On (Switch method)

There are a few reasons why you may want to try this out with a switch first. You may want to know how this mode works Thus you can turn it on or off with a switch and see what it does and how you like it. That way you can compare results. The second may be that your flying style or type of plane you’re flying doesn’t lend itself to the Auto level feature, but you may want the option to turn it on when you feel like it. If you do just want it on all the time, you should just use Option 2.

Auto tune

The importance of auto tune cannot be overstated. Up until INAV 3.0 you would have to come up with a rates number for your plane. It used to be found by doing rolls and flips and counting frames on your video feed and putting it into a mathematical formula. Next to nobody actually did this. We often just estimated what would work and we were often very wrong.

Now, we give you default rates that are very, very low. Your plane will fly and it will come back with a return to home. The problem is, the plane won’t be that much fun to fly as the rates are purposely slow. If you never do an auto tune your plane will never fly near as well as it should and could. I am sure there will be people who post videos about how poorly INAV flew, and yet never did an auto tune.

Here’s a link to Marc Hoffman’s description of how the new Auto tune works. You really should watch it. You can always go back later on and perform an auto tune again; should you think that you didn’t do a good enough job on the first go around.

The future of INAV

Now you have a plane that is setup and ready to fly. Thank you for participating in Project Rosetta Stone. This is the end of the project, but really just the start of INAV. You can keep the fun going with new INAV builds. This was an interesting time to launch Project Rosetta Stone. As people were collecting their gear for Project Rosetta Stone we were testing the pre-alpha versions of certain features of INAV 3.0. Release Candidate 1 came out around week 6, and release candidate 2 came out between weeks 7 and 8. INAV 3.0 was very well received and it looks like it will be the build that brings people to INAV for fixed wing.

The original goal with Project Rosetta Stone was to help people with weeks 7 and 8 because this was where people had the most problems. Now, it’s looking like the thing that will slow people down is improper building and improper center of gravity. INAV will never be finished. There’s always something new and exciting to check out. Once you have the S800 under your belt there are other fantastic planes to check out. We’ll be updating our Top 21 planes of 2021 list fairly soon on www.INAVFixedWingGroup.com. There should be some great ideas there.