Sink rate max for landing approach stage (TECS_APPR_SMAX)

Description

This parameter allows for a steeper maximum descent rate specifically during the auto-landing approach phase, overriding the general TECS_SINK_MAX limit. This is useful for aircraft that need to descend rapidly to clear obstacles before the runway threshold.

The Mathematics

$$ \dot{h}\_{\text{max}} = (\text{Land Approach}) ? \text{TECS\_APPR\_SMAX} : \text{TECS\_SINK\_MAX} $$

The Engineer's View

Defined in libraries/AP_TECS/AP_TECS.cpp.

• 0: Disabled. Uses TECS_SINK_MAX for all flight phases.
• >0: Sets the limit in m/s.

Tuning & Behavior

• Default Value: 0
• Warning: Ensure your airframe can handle the airspeed buildup or has enough drag (flaps/reverse thrust) to descend this fast without overspeeding.

Maximum Climb Rate (TECS_CLMB_MAX)

Description

TECS_CLMB_MAX sets the "Speedometer Limit" for going up.

Even if you command a 100-meter climb, the drone will limit its vertical ascent speed to this value. This ensures the climb is steady and doesn't exceed the motor's power limits or cause a high-pitch stall.

Tuning & Behavior

• Default Value: 5.0 m/s.
• Recommendation: Set this to roughly 75% of your plane's physical maximum climb rate at full throttle.

Flare Height (TECS_FLARE_HGT)

Description

TECS_FLARE_HGT defines the start of the "Touchdown" phase during an autonomous landing.

When the drone's altitude above the ground (via rangefinder) drops below this value, the autopilot enters the "Flare" state. In this state, it stops following the steep glide slope and instead tries to maintain a very gentle descent rate (TECS_LAND_SINK) while raising the nose to bleed off airspeed.

• Standard Setting: 1.0 to 2.0 meters.

Tuning & Behavior

• Default: 1.0.
• Too Low: The plane might hit the ground too hard before it has a chance to slow down.
• Too High: The plane will "float" along the runway for a long time, potentially running out of space.
• Dependencies: Requires an enabled and functional rangefinder (RNGFND_LANDING).

Height Demand Time Constant (TECS_HDEM_TCONST)

Description

TECS_HDEM_TCONST defines how "Softly" the autopilot reacts when a new altitude is requested.

When a mission or a pilot (in FBWB mode) changes the target altitude, the autopilot doesn't try to reach it instantly. Instead, it passes the request through a low-pass filter to create a smooth climb or descent path. This parameter sets the "Slowness" of that filter.

• Higher Value (e.g. 5.0): Very smooth, gradual altitude changes.
• Lower Value (e.g. 1.0): More aggressive reaction to altitude commands.

Tuning & Behavior

• Default: 3.0 seconds.
• Recommendation: Leave at 3.0 for standard transport or mapping drones. Reduce to 1.5 or 2.0 for high-performance aircraft that need to react quickly to terrain changes.
• Effect: Increasing this value reduces "Pitch pumping" (oscillations in pitch) during altitude transitions.

Height Estimator Bandwidth (TECS_HGT_OMEGA)

Description

TECS_HGT_OMEGA determines how much the autopilot trusts its sensors for altitude.

ArduPlane calculates its climb rate by blending the Barometer (slow but stable) with the Accelerometers (fast but drifty).

• High Value (e.g. 5.0): Trusts the Barometer more. Good if your IMU is vibey.
• Low Value (e.g. 1.0): Trusts the IMU more. Provides instantaneous climb rate detection. Better for high-performance acrobatics.

Tuning & Behavior

• Default Value: 3.0 $rad/s$.
• Recommendation: Leave at 3.0. Only increase if you see the plane "ballooning" (pitching up) during rapid acceleration due to EKF height spikes.

TECS Integrator Gain (TECS_INTEG_GAIN)

Description

TECS_INTEG_GAIN handles "Persistence."

If the plane is consistently flying 5 meters below the target altitude, the I-term builds up more throttle or pitch to force it up to the correct height.

Tuning & Behavior

• Default Value: 0.1.
• Too High: The plane will overshoot its target and then oscillate up and down slowly.
• Too Low: The plane will stay slightly below its target altitude or above its target speed indefinitely.

TECS Landing Airspeed (TECS_LAND_ARSPD)

Description

TECS_LAND_ARSPD overrides the cruise speed during the final approach.

Normally, the plane flies at AIRSPEED_CRUISE. But for landing, you usually want to fly slower (closer to stall speed) to reduce energy.

Tuning & Behavior

• -1 (Default): Use AIRSPEED_CRUISE.
• Value: Set to 1.3 x Stall Speed for a safe, slow approach.

TECS Landing Damping (TECS_LAND_DAMP)

Description

TECS_LAND_DAMP smoothes out the pitch commands during the landing phase.

If the plane "Pumps" the elevator (rapidly pitching up and down) while trying to hold the glide slope, increasing this value can help dampen those oscillations.

Tuning & Behavior

• Default Value: 0.5.

TECS Land Integrator Gain (TECS_LAND_IGAIN)

Description

TECS_LAND_IGAIN allows you to have a different "Error Memory" for the final landing approach.

Normally, the flight controller uses TECS_INTEG_GAIN. However, during landing, ground effect and changing air density near the floor can cause persistent height errors. This parameter lets you set a dedicated integrator to trim out these errors for a more precise touchdown.

• 0 (Default): Use the standard TECS_INTEG_GAIN.

Tuning & Behavior

• Default Value: 0.
• Recommendation: If your plane consistently lands too short or too long due to wind/drag offsets, try setting this to 0.2.

Landing Pitch Damping (TECS_LAND_PDAMP)

Description

TECS_LAND_PDAMP allows for a more "Solid" pitch response during the critical landing approach.

Landing often happens in ground effect or turbulent air near the runway, which can cause the plane's nose to bounce or oscillate. This parameter allows you to add extra damping specifically for the landing phase without affecting the feel of the aircraft during normal cruise.

• 0 (Default): Uses the standard TECS_PTCH_DAMP value.
• Non-Zero: Overrides the standard damping with this value.

Tuning & Behavior

• Default: 0.
• Recommendation: If your plane "Pitch pumps" (constantly moves the nose up and down) while on the landing glide slope, set this to 0.5 or 0.8.
• Effect: Higher values make the pitch response more sluggish but significantly more stable against external disturbances.

TECS Landing Pitch Max (TECS_LAND_PMAX)

Description

TECS_LAND_PMAX prevents the autopilot from pulling the nose up too high during flare.

If the plane flares too aggressively, it might balloon up or strike its tail on the runway.

Tuning & Behavior

• 0 (Default): Use normal pitch limits (LIM_PITCH_MAX).
• Recommendation: Set to 10 or 15 degrees to ensure a safe flare attitude.

Sink Rate for Final Landing Stage (TECS_LAND_SINK)

Description

TECS_LAND_SINK is the "Soft Landing" target.

When the plane is just a few meters above the ground, it enters the Flare stage. Instead of following a steep glide slope, it aims for this very gentle descent rate to ensure it touches down without bouncing or breaking the landing gear.

• 0.25 (Default): A very soft touchdown (0.5 knots descent).
• 0.5: A firm landing. Good for rough grass where you want the wheels to dig in.

Tuning & Behavior

• Default Value: 0.25 m/s.
• Recommendation: If your plane consistently "Floats" and refuses to touch down, increase this to 0.5. If your plane "Slam-Lands" and bounces, decrease to 0.15.

TECS Landing Speed Weight (TECS_LAND_SPDWGT)

Description

TECS_LAND_SPDWGT is the "Safety vs. Accuracy" slider.

• 2.0 (Speed Priority): The plane will aggressively pitch down to regain airspeed if it gets too slow, even if that means diving below the glide slope. Prevents stalls.
• 0.0 (Height Priority): The plane will prioritize staying on the glide slope, even if airspeed drops dangerously low.
• -1.0 (Default): Uses the standard TECS_SPDWEIGHT value.

Tuning & Behavior

• Default Value: -1.0.
• Recommendation: Set to 2.0 if you are landing in gusty winds and stall prevention is critical.

TECS Landing Height Source (TECS_LAND_SRC)

Description

TECS_LAND_SRC tells the plane what "Ground" is.

• 0 (Baro/GPS mix): Standard. Lands at the altitude of the Home waypoint (Relative 0). Good for flat fields.
• 1 (Rangefinder): Uses Lidar/Sonar. Required for precision auto-landing. The plane will follow the actual contour of the ground.
• 2 (Terrain DB): Uses map data stored on the SD card. Useful for landing in hilly areas if you don't have a Lidar.

Tuning & Behavior

• Default Value: 0.
• Recommendation: Use 1 (Rangefinder) if you have a Lidar installed (RNGFND_LANDING enabled).

TECS Landing Time Constant (TECS_LAND_TCONST)

Description

TECS_LAND_TCONST controls how aggressively the plane corrects altitude errors during landing.

• Higher Value: Slower, smoother corrections. Better for calm weather.
• Lower Value: Faster corrections. Better for turbulent conditions where the plane gets knocked off the glide slope.

Tuning & Behavior

• Default Value: 2.0 seconds.

Landing Throttle Damping (TECS_LAND_TDAMP)

Description

TECS_LAND_TDAMP allows for more aggressive throttle corrections during an autonomous landing.

During an approach, the plane must stay precisely on the glide slope while maintaining airspeed. If the throttle response is too slow, the plane might fall behind the power curve. This parameter allows you to add damping (which actually increases throttle activity to counteract speed/height errors) specifically for the landing phase.

• 0 (Default): Uses the standard TECS_THR_DAMP value.
• Non-Zero: Overrides the standard damping with this value.

Tuning & Behavior

• Default: 0.
• Recommendation: If your plane's airspeed varies wildly during the approach, or if it struggles to stay on the glide slope in wind, try setting this to 0.5.
• Effect: Higher values result in more frequent and faster throttle movements to maintain the energy state.

Cruise Throttle During Landing (TECS_LAND_THR)

Description

TECS_LAND_THR is for planes without an airspeed sensor.

Normally, TECS calculates the throttle needed to maintain landing speed. If there is no speed sensor, it can't do that. This parameter allows you to hard-code a fixed throttle percentage (e.g. 40%) that you know is safe for a slow descent on your specific airframe.

• -1 (Default): Disabled (Use speed-based calculation).
• 45: Hold 45% throttle during the entire landing approach.

Tuning & Behavior

• Default Value: -1.
• Recommendation: If you don't have an airspeed sensor, set this to the lowest throttle that keeps your plane flying safely above stall speed (e.g. 35-45%).

Extra TECS Options (TECS_OPTIONS)

Description

TECS_OPTIONS unlocks advanced cruise behaviors for the Total Energy Control System.

• Bit 0 (1): Glider Only.
  If set, ArduPilot treats the motor as a "Launcher" only. Once at altitude, it optimizes everything for zero-thrust glide performance.
• Bit 1 (2): Allow Descent Speedup.
  Normally, ArduPilot tries to maintain your cruise speed during a descent. If this bit is set, and the drone needs to descend rapidly, it is allowed to increase its airspeed to help bleed off potential energy faster. This makes descents much quicker but carries a risk of overspeeding if the airframe is fragile.

Tuning & Behavior

• Default Value: 0.
• Recommendation:
  • Long-Range Mapping: Enable Bit 1 to save time on mission returns (descending from survey altitude).
  • Soaring Glider: Enable Bit 0.

Maximum Pitch in Auto Flight (TECS_PITCH_MAX)

Description

TECS_PITCH_MAX acts as a "Nose Limiter" for autonomous flight.

While the global PTCH_LIM_MAX sets the hard physical limit for the whole aircraft, TECS_PITCH_MAX is used specifically by the climb controller. It ensures that the drone doesn't point its nose so steeply into the sky that it loses all its airspeed, even if the flight controller thinks it needs to climb faster.

Tuning & Behavior

• Default Value: 15°.
• Recommendation: Set to the angle your plane can comfortably sustain at full throttle without losing airspeed.
• Gliders: Can be set higher (25°) for aggressive climbing.
• Heavy Cargo: Set lower (10°) to ensure the plane always keeps the nose down enough for speed.

Minimum Pitch in Auto Flight (TECS_PITCH_MIN)

Description

TECS_PITCH_MIN prevents the drone from "Diving" too steeply when it needs to lose altitude.

• 0 (Default): The drone will not point its nose down during autonomous flight. It will only descend by reducing throttle.
• -10: The drone can point its nose 10° down to help reach its target altitude faster.

Tuning & Behavior

• Default Value: 0.
• Recommendation: Use -5 or -10 if you find the drone "Over-climbs" and takes too long to get back down to its target altitude.

Pitch Damping Gain (TECS_PTCH_DAMP)

Description

TECS_PTCH_DAMP prevents the plane from "Nodding" its head.

When the autopilot commands a pitch change to maintain height, it needs to stop that movement at the right time. Damping provides the "Brakes" for the pitch maneuver.

• Higher Value: Less oscillation, but too high can cause the pitch to be sluggish and unresponsive.
• Lower Value: More active pitch, but can lead to a "Porpoising" motion where the drone constantly bobs up and down.

Pitch Feed-Forward Gain (TECS_PTCH_FF_K)

Description

TECS_PTCH_FF_K allows the autopilot to "Anticipate" how much pitch is needed to achieve a target airspeed, rather than waiting for an airspeed error to build up.

When you demand a higher airspeed, the plane naturally needs to point its nose down. This feed-forward gain applies that pitch command immediately.

• 0.0 (Default): Feature is disabled.
• Negative Values: Apply downward pitch for increased speed demand.

Tuning & Behavior

• Default: 0.
• Recommendation (Gliders): Start with -0.04.
• Recommendation (Draggy planes): Start with -0.08.
• Effect: Reduces the "Lag" in airspeed tracking during altitude changes. If the nose drops too aggressively when you speed up, reduce the magnitude (make it less negative).

Pitch Feed-Forward Reference Speed (TECS_PTCH_FF_V0)

Description

TECS_PTCH_FF_V0 provides the baseline for the TECS_PTCH_FF_K feature.

It represents the natural "Neutral Speed" of the aircraft – the speed at which it glides with a neutral pitch command. When the autopilot demands exactly this speed, no feed-forward correction is applied. If it demands more speed, it pitches down. If it demands less, it pitches up.

Tuning & Behavior

• Default: 12.0 m/s.
• Calibration: Fly the plane in Manual or FBWA with neutral elevator trim and observe the resulting steady-state airspeed. Enter that value here.
• Requirement: This parameter is only used if TECS_PTCH_FF_K is non-zero.

Roll to Throttle Compensation (TECS_RLL2THR)

Description

TECS_RLL2THR is the "Turn Gas."

When a plane banks into a turn, it naturally slows down and loses lift. This parameter automatically "Pushes the Gas" when the wings are tilted, ensuring the plane maintains its airspeed and altitude through the maneuver.

Tuning & Behavior

• Default Value: 10.
• Recommendation: If the plane loses too much speed in sharp turns, increase this value. If it speeds up excessively while turning, decrease it.
• Physics: This is a feed-forward term based on the bank angle.
  $$ \text{Throttle}\_{extra} = k \cdot (1 - \cos(\text{roll})) $$

Maximum Descent Rate (TECS_SINK_MAX)

Description

TECS_SINK_MAX prevents the drone from diving too steeply.

While gravity is free, diving too fast can lead to structural failure or exceed the plane's "Vne" (Never Exceed Speed). This parameter caps the rate of descent to a safe, controlled speed.

Minimum Glide Sink Rate (TECS_SINK_MIN)

Description

TECS_SINK_MIN defines the "Glide Profile" of your aircraft.

It represents the vertical descent rate the plane naturally experiences when flying at its cruise speed with the engine at idle or turned off. This is a fundamental physical constant for the TECS (Total Energy Control System) to understand how much potential energy (altitude) is lost simply to overcome aerodynamic drag.

Tuning & Behavior

• Default: 2.0 m/s.
• Calibration: Fly the plane in Manual or FBWA mode, cut the throttle, and maintain a level cruise speed. Note your rate of descent on the GCS. Enter that value here.
• Gliders: Typically have a very low sink rate (0.5 to 1.0 m/s).
• Draggy Planes: (Like a Cub or a loaded cargo plane) may have a sink rate of 3.0 to 5.0 m/s.
• Effect: If this value is too high, the drone will undershoot its glide path during autonomous landings. If too low, it will overshoot (float).

Speed vs Altitude Weight (TECS_SPDWEIGHT)

Description

TECS_SPDWEIGHT is the "Priority Slider" for Plane flight control.

TECS (Total Energy Control System) views the plane as a battery. Altitude is "Potential Energy" and Airspeed is "Kinetic Energy." This parameter tells the autopilot which one is more important to maintain.

• 1.0 (Balanced): The autopilot treats speed and altitude errors equally. It will use both pitch and throttle to fix errors.
• 2.0 (Speed Priority): The autopilot will prioritize maintaining airspeed at all costs. If the plane slows down, it will immediately trade altitude (pitch down) to regain speed. (Safest for preventing stalls).
• 0.0 (Altitude Priority): The autopilot will prioritize holding its height. It will trade airspeed to stay at the target altitude. (Riskier, as it could lead to a stall if the motor is weak).

Tuning & Behavior

• Default Value: 1.0.
• Recommendation: Use 2.0 for takeoffs and landings to ensure you never stall near the ground. Use 1.0 for general cruising.
• Physics:
  • $$ \text{Total Energy} = \text{Height} + \frac{\text{Velocity}^2}{2g} $$
  • SPDWEIGHT adjusts the weighting of the Kinetic Energy term in the pitch and throttle demand calculations.

Speed Estimator Bandwidth (TECS_SPD_OMEGA)

Description

TECS_SPD_OMEGA determines how fast the autopilot reacts to speed changes.

It blends the Airspeed Sensor with the longitudinal Accelerometer.

• High Value: Trust the Airspeed Sensor more. Fast reaction to gusts, but noisy if the sensor isn't well-protected.
• Low Value: Trust the Inertial navigation more. Smooths out "jumps" in airspeed caused by turbulence.

Tuning & Behavior

• Default Value: 2.0 $rad/s$.
• Recommendation: Leave at 2.0.

Synthetic Airspeed Enable (TECS_SYNAIRSPEED)

Description

TECS_SYNAIRSPEED allows the autopilot to "Guess" the airspeed using internal sensors (accelerometers, gyros, and GPS) instead of a physical pitot tube.

This is extremely useful for small or budget drones where mounting a pitot tube is difficult. However, it is significantly less accurate than a real sensor, especially in gusty conditions or during aggressive maneuvers, as it relies heavily on a perfect wind estimate.

Tuning & Behavior

• 0: Disabled (Default). The autopilot will use its internal "Ground Speed to Airspeed" mapping or a physical sensor if available.
• 1: Enabled. The autopilot uses the EKF's synthetic airspeed estimate for longitudinal control.
• Warning: Do not enable this unless you have verified that your drone has a stable and accurate wind estimate in flight. If the wind estimate is wrong, the synthetic airspeed will be wrong, which can lead to a stall or over-speed condition.

Throttle Damping (TECS_THR_DAMP)

Description

TECS_THR_DAMP prevents the motor from "Pulsing" or hunting for the correct speed.

It smooths out the throttle commands sent to the ESC. If you hear your motor constantly changing pitch (speeding up and slowing down) while in a steady cruise, your damping might be too low.

Tuning & Behavior

• Default Value: 0.5.
• Recommendation: If the motor "Surges," increase this value by 0.1.

TECS Time Constant (TECS_TIME_CONST)

Description

TECS_TIME_CONST defines how fast the plane tries to fix altitude and speed errors.

It is effectively the "Damping" of the whole navigation system.

• Small Value (3.0s): Fast, aggressive control. The plane will snap back to the target altitude and speed quickly. Can cause the motor to pulse and the nose to bob.
• Large Value (10.0s): Smooth, relaxed control. The plane takes its time to reach the target. Good for long-range efficient cruising.

Tuning & Behavior

• Default Value: 5.0 seconds.
• Recommendation: Leave at 5.0 for most planes. Increase to 7.0 for very large, slow UAVs to prevent the autopilot from over-correcting.

TECS Takeoff Integrator Gain (TECS_TKOFF_IGAIN)

Description

TECS_TKOFF_IGAIN allows you to have a different "Memory" setting for takeoff.

Normally, TECS_INTEG_GAIN handles long-term errors. However, during takeoff, the dynamics change rapidly (ground effect, rapid acceleration). This parameter overrides the standard gain to ensure the plane tracks the climb rate accurately during this critical phase.

• 0 (Default): Use TECS_INTEG_GAIN.
• > 0: Use this specific gain for takeoff.

Tuning & Behavior

• Default Value: 0.
• Recommendation: If your plane tends to overshoot or undershoot the climb angle right after launch, try setting this to 0.4.

Vertical Acceleration Limit (TECS_VERT_ACC)

Description

TECS_VERT_ACC defines the "G-Limit" for vertical maneuvers.

When the drone needs to climb or descend suddenly, it will limit the force of the pull-up or push-down to this value. This protects the wings from structural damage and prevents the EKF from being overwhelmed by high G-loads.

• 7.0 (Default): Standard for most planes.
• 10.0: For high-performance, stiff airframes.