Prop-Hang Relax

In a prop hang the propeller's torque tries to roll the aircraft the opposite way to the prop. On a 3D model that torque roll is part of the flying. A rate gyro sees it as an unwanted roll and builds up roll I-term until the ailerons cancel the torque, so with the gyro on the model hangs without rolling at all.

Prop-Hang Relax spots a prop hang and holds the roll I-term back, so the torque can roll the model again. It is on by default.

How it works

• Detection. A hang is all of these at once, for half a second:
• the nose within the Angle of straight up,
• the model neither climbing nor sinking faster than 2 m/s, which is what tells a hang from a vertical up-line,
• plain rate flight: not Angle mode, Attitude Hold, Trainer, GPS Rescue, RTH, Loiter or failsafe, which all need the roll I-term to hold their target.
• While hanging. Roll I stops building up, and the roll I it was already holding drains away over about half a second, so the ailerons stop holding the model against the torque. P and the stick still work: you can stop or steer the torque roll, and a gust is still damped. Roll only: the rudder and elevator keep steering the nose.
• Exit. When the hang ends, the roll I-term comes back over the Fade-out time.

It needs an altitude estimate, which on most flight controllers means a barometer. Without one an up-line can't be told from a hang, so nothing is relaxed.

It works in every plain rate mode and needs no switch.

Settings

Per PID profile. In the Configurator they are in Profiles → PID Settings (Expert Mode). On the radio they are on PID Controller (Ethos) and Profile - Various (EdgeTX).

Setting	CLI	Range	Default
Strength	prop_hang_strength	0-100 %	100
Angle	prop_hang_angle	5-45°	20
Fade-out	prop_hang_fade	0-2000 ms	500

Strength 0 turns it off. Lower values only partly hold the roll I-term back, for a slower torque roll.

Tuning

• The model still won't torque roll: check the hang is being detected (see below). If it is, raise Strength towards 100.
• It torque rolls in vertical up-lines or slow climbs: lower the Angle, so only a hang close to vertical counts.
• The roll I-term snaps back when you fly out of the hang: lengthen the fade-out.
• You want a locked, still hang instead: set Strength to 0.

To see it working, log with debug_mode = PROP_HANG (see the CLI reference).