Sunday 25 June 2023

Simplified INAV

How to simplify INAV model setup and start flying sooner.

The key to simplicity is having a plane that is trimmed and balanced well mechanically, and not starting with the complicated AUTO modes. With INAV 6.1.1 the default tuning PIFFs (stabilisation parameters) will be good out of the box.

Auto Launch, Auto Tune, Auto Trim and Missions will greatly complicate your first INAV experience. It is much simper to get the model flying well first then add the fancy stuff later.

This article is intended for competent fixed wing pilots, who know how to mechanically set up a model for correct throws, trims and CG. 

Start with a well behaved model that has adjustable push rods.

Important first step 

With the model in Manual Mode, or even before you install the flight control board, adjust the pushrod lengths and connection holes to give reasonable throws and level flight, without needing reduced rates and radio trims. Also establish the correct CG for stable level flight with all gear installed. 

Doesn't have to be perfect and it's OK if the plane is a little too agile with these full throws, as long as it is flyable.

Essential INAV Modes

The only modes you need to set up initially are ACRO, RTH, MANUAL and ANGLE 

ACRO is the default INAV mode and is active if no other mode is selected. In ACRO the plane is stabilised against any un-commanded rotations, like a side gust of wind. The model will tend to hold its attitude but respond normally to your stick inputs. ACRO is arguably the best general flying mode.

RTH mode is great when you want the model to come back to you automatically or in a "loss of signal" failsafe situation. In the INAV Failsafe screen choose RTH.

MANUAL is a mode that has to be selected, it is not the default mode. MANUAL is used to check trim and CG balance, and for safety if something is wrong with other modes. Experienced pilots may prefer to fly in MANUAL mode.

ANGLE is the fully self levelling mode and is also used to check board pitch trim. Model airplanes usually need a few degrees of nose-up angle of attack to maintain level flight. This trim setting can be found in the PIDS page - Mechanics Tab - LEVEL TRIM (deg). I usually start with +4 degrees then check if the plane is rising or descending in ANGLE mode.

Flying in ANGLE mode may feel odd to experienced pilots because you have to hold the sticks at the angle you want to fly at and  it will self level when you centre the sticks. 

The above modes are all you need for a basic setup

Non-essential INAV modes to add once you have a working model

You can enable "Continuously trim servos" to automatically trim servo mid points.

NAV LAUNCH is fun to play with but I prefer to launch normally with full control. It is easy to muck up the switch sequence and cause a failed launch. 

CRUISE and LOITER modes are useful for FPV flights but not essential.

AUTO TUNE / AUTO TRIM are not required if your model is mechanically trimmed and balanced for CG.

Mode switches

It is best to have your starting switch positions with no modes selected, which means the board will always start in ACRO

Here are my modes for the simple setup

CH 5 ARM (essential for ELRS receivers)



Add the fancy modes later



Check the control surfaces are responding correctly to stick movements. 

Check the control surfaces are responding correctly for stabilisation. Switch to Angle Mode and check Left wing lifted makes left aileron raise, tail lifted makes elevator raise.

ACRO Throws

Check the control surface throws in ACRO Mode. They may be too small for sufficient control. Ideally they should be about 80% of the Manual Mode throws. If the throws are too small go to the PID Tuning page and increase the FF parameter for Roll and Pitch, then check throws again. If there is no difference between ACRO and MANUAL Mode throws reduce the FF parameters. 

This will ensure you have enough control to launch in ACRO Mode and some headroom for stabilisation.

First Flight adjustments

On the first flight I will launch in ACRO and fly a few circuits to make sure the plane is flying OK.

Then switch to MANUAL to check roll and pitch trim and CG. Don't use the radio trims, because they will only work for Manual Mode.

If needed I will land and make trim adjustments by adjusting the pushrods, and CG adjustments by shifting the battery.

Then launch again and repeat until the plane is flying level without needing stick inputs. Don't touch the radio trims.

Use ANGLE to check LEVEL TRIM (deg)

Once the control surfaces are trimmed I will launch again and switch to ANGLE mode. Take note of whether the model holds altitude or climbs or descends. If you haven't entered anything in the Fixed Wing Level Trim window then the plane will most likely descend.

I usually start with +4ยบ and adjust more or less from there.

Launch again, climb to about 50m, fly out a bit then try RTH. Your model should turn and fly back to the arming site and circle above you at about 50m altitude and radius of 75m.

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