Thrust Vector Attitude Hold

Thrust Vector Attitude Hold (THRUST VECTOR ATTITUDE HOLD) holds attitude and heading on the Thrust Vector loop only, independent of whatever the aerodynamic control surfaces are doing. This is aimed at jets and other aircraft with a vectored-thrust nozzle: engage it and the nozzle holds heading/attitude on its own while ailerons, elevator, and rudder stay in plain rate/acro under your stick -- useful at low airspeed or post-stall, where the surfaces have little authority but the vectored thrust still does.

It only has an effect while THRUST VECTOR is also engaged. It has its own switch and its own target, independent of Attitude Hold and Angle mode -- engaging either of those still stabilizes the main Roll/Pitch/Yaw loop (and so the control surfaces) as normal, and does not move TV Hold's own target. Enable both switches together if you want the whole aircraft, surfaces included, to hold attitude.

Like Attitude Hold, TV Hold doesn't bound stick authority to any particular orientation, and it runs the same hold engine: each axis tracks or freezes on its own stick, holding the attitude it was in once that stick is inside Deadband and the axis has stopped rotating, and giving full unmodified authority above the deadband while continuously re-capturing its target, so a future freeze is seamless. See Attitude Hold for how the release, give-up and I-term behaviour work; they are the same here.

It defers automatically to Angle Mode, GPS Rescue, Failsafe, GPS Loiter and GPS RTH whenever one of those is active -- those already drive the shared setpoint to a safety-leveled value, and TV Hold never fights that with its own frozen target. Attitude Hold does not switch it off: the Thrust Vector loop reuses the main loop's final setpoint, so while it is active, TV Hold works on top of that setpoint.

Axes without a nozzle actuator

TV Hold only holds the axes the nozzle can move. An axis that no Stabilized TV mixer rule uses is left free, and is read when the switch engages. On the usual pitch/yaw nozzle that is roll: the hold keeps the direction the thrust points and ignores rotation about it. A pusher in a hang torque-rolls with nothing to stop it. Holding roll there built an error that turned the pitch/yaw correction with the airframe, so a pitch correction ended up on yaw.

Tuning

Gain (default 45) sets how aggressively TV Hold corrects the thrust-vector output back to the frozen attitude. Max Rate caps how fast it's allowed to rotate the held target while doing so. Both are configured on the Thrust Vector tab, under Attitude / Heading Hold -- separate from Attitude Hold's own Gain/Deadband/Max Rate on the Profiles tab, since this is an entirely independent hold engine tuned for the thrust-vector actuators specifically. Like the rest of the Thrust Vector tab, Gain/Deadband/Max Rate are per Thrust Vector profile.