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Overview

The AROT parameter group configures the Autonomous Autorotation capability, primarily for Traditional Helicopters.

If the engine fails (low RPM), this system automatically takes control to manage the collective pitch and cyclic to maintain rotor energy and guide the helicopter to a safe touchdown, performing a flare maneuver at the bottom.

Key Concepts

1. Entry Criteria

The system monitors the main rotor RPM (via RPM sensor). If it drops below a threshold while in flight, Autorotation is triggered.

2. Glide Phase

The autopilot pitches for optimal airspeed (AROT_FW_V_P gain) to maximize glide distance or rotor energy preservation.

3. Flare and Touchdown

Near the ground, the system pitches up (Flare) to convert forward airspeed into rotor RPM, slowing the descent for a soft landing.

Parameter Breakdown

  • AROT_ENABLE: Master switch.
  • AROT_HS_P: Head Speed (RPM) P gain (controls Collective).
  • AROT_FW_V_P: Forward Velocity P gain (controls Pitch).
  • AROT_RAMP: Time to ramp collective back in if power is restored (Bail-out).

Developer Notes

  • Library: libraries/AC_Autorotation
  • Vehicle: ArduCopter (Heli frame).

AROT_COL_FILT_E

Hz
Default 0.7
Range 0.2 0.5

Entry Phase Collective Filter (AROT_COL_FILT_E)

Description

Low-pass filter frequency applied to collective commands during the initial entry into autorotation.

Tuning & Behavior

  • Default Value: 0.7 Hz
  • Range: 0.2 to 0.5 Hz (Note: Default in code is 0.7, range documentation says 0.2-0.5)
  • Controls the reactivity of the collective during the critical transition to autorotation.
View Source

AROT_COL_FILT_G

Hz
Default 0.1
Range 0.03 0.15

Glide Phase Collective Filter (AROT_COL_FILT_G)

Description

Low-pass filter frequency applied to collective commands during the steady-state glide phase of autorotation.

Tuning & Behavior

  • Default Value: 0.1 Hz
  • Range: 0.03 to 0.15 Hz
  • A lower value results in smoother collective changes during the glide.
View Source

AROT_ENABLE

Default 0
Range 0 1

Enable autonomous autorotation (AROT_ENABLE)

Description

Enables the autonomous autorotation feature for helicopters, allowing the flight controller to manage head speed and glide profile during an engine failure or manual entry.

Tuning & Behavior

  • Default Value: 0 (Disabled)
  • Values: 0:Disabled, 1:Enabled
  • Requires careful tuning of head speed and collective parameters for safe operation.
View Source

AROT_FWD_D

Default 0

Autorotation Forward Velocity D Gain (AROT_FWD_D)

Note: This parameter is likely a legacy alias or reserved slot.

View Source

AROT_FWD_FF

Default 0.15

Autorotation Forward Velocity FeedForward (AROT_FWD_FF)

Note: This parameter is an alias for AROT_FW_V_FF.

View Source

AROT_FWD_FLTD

Default 0

Autorotation Forward Velocity Derivative Filter (AROT_FWD_FLTD)

Note: This parameter is likely a legacy alias or reserved slot.

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AROT_FWD_FLTE

Default 0

Autorotation Forward Velocity Error Filter (AROT_FWD_FLTE)

Note: This parameter is likely a legacy alias or reserved slot.

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AROT_FWD_I

Default 0

Autorotation Forward Velocity I Gain (AROT_FWD_I)

Note: This parameter is likely a legacy alias or reserved slot. The current autorotation controller primarily uses P and FeedForward terms for forward speed.

View Source

AROT_FWD_IMAX

Default 0

Autorotation Forward Velocity I-Max (AROT_FWD_IMAX)

Note: This parameter is likely a legacy alias or reserved slot.

View Source

AROT_FWD_P

Default 0.9
Range 0.1 6.0

Autorotation Forward Velocity P Gain (AROT_FWD_P)

Note: This parameter is an alias for AROT_FW_V_P.

View Source

AROT_FW_V_FF

Default 0.15
Range 0 1

Velocity (horizontal) feed forward (AROT_FW_V_FF)

Description

Feed-forward gain for the horizontal velocity controller.

Tuning & Behavior

  • Default Value: 0.15
  • Range: 0 to 1
View Source

AROT_FW_V_P

Default 0.9
Range 0.1 6.0

Velocity (horizontal) P gain (AROT_FW_V_P)

Description

Proportional gain for the horizontal velocity controller during autorotation glide.

Tuning & Behavior

  • Default Value: 0.9
  • Range: 0.1 to 6.0
  • Controls how aggressively the aircraft maintains its target forward speed during descent.
View Source

AROT_HS_P

Default 0.7
Range 0.3 1

P gain for head speed controller (AROT_HS_P)

Description

Proportional gain for the rotor RPM (head speed) controller during autorotation.

Tuning & Behavior

  • Default Value: 0.7
  • Range: 0.3 to 1
  • A higher value makes the controller more aggressive in maintaining target head speed.
View Source

AROT_HS_SENSOR

Default 0
Range 0 1

Main Rotor RPM Sensor (AROT_HS_SENSOR)

Description

Selects which RPM sensor instance provides the head speed feedback for the autorotation controller.

Tuning & Behavior

  • Default Value: 0 (RPM1)
  • Range: 0 to 1
View Source

AROT_HS_SET_PT

RPM
Default 1500
Range 1000 2800

Target Head Speed (AROT_HS_SET_PT)

Description

Defines the desired rotor RPM to be maintained during the autorotation glide.

Tuning & Behavior

  • Default Value: 1500 RPM
  • Range: 1000 to 2800 RPM
  • Setting this too low may result in insufficient lift for flare; too high may cause excessive descent rates.
View Source

AROT_RAMP

s
Default 2

Autorotation Bailout Ramp Time (AROT_RAMP)

Description

Defines the duration of the motor power ramp-up when the pilot or autopilot "bails out" of an autorotation and returns to powered flight.

Tuning & Behavior

  • Default Value: 2 s
  • Ensures a smooth but timely restoration of power without overstressing the drive system.
View Source

AROT_XY_ACC_MAX

cm/s/s
Default 60
Range 30 60

Forward Acceleration Limit (AROT_XY_ACC_MAX)

Description

Limits the maximum horizontal acceleration (and thus the pitch angle) the aircraft can use to maintain forward speed during autorotation glide.

Tuning & Behavior

  • Default Value: 60 cm/s/s
  • Range: 30 to 60 cm/s/s
View Source
Arming Checks (ARMING) Airspeed Sensor Configuration (ARSPD)