Plane: added TKOFF_THR_MIN for quadplane SLT

allows for higher min throttle to get past transition drag

ArduPlane/quadplane.cpp

@@ -4064,6 +4064,21 @@ bool QuadPlane::in_transition(void) const
     return available() && transition->active();
 }
 
+/*
+  return true if we are in a fwd transition for a SLT quadplane
+  and in an auto-throttle mode
+ */
+bool QuadPlane::in_slt_fwd_transition(void) const
+{
+    if (!in_transition() || tiltrotor.enabled() || tailsitter.enabled()) {
+        return false;
+    }
+    if (!plane.control_mode->does_auto_throttle()) {
+        return false;
+    }
+    return transition->in_fwd_transition();
+}
+
 /*
   calculate current stopping distance for a quadplane in fixed wing flight
  */
@@ -4554,6 +4569,15 @@ void SLT_Transition::set_last_fw_pitch()
     last_fw_nav_pitch_cd = plane.nav_pitch_cd;
 }
 
+/*
+  return true if in a forward transition
+ */
+bool SLT_Transition::in_fwd_transition() const
+{
+    return transition_state == TRANSITION_AIRSPEED_WAIT ||
+        transition_state == TRANSITION_TIMER;
+}
+
 void SLT_Transition::force_transition_complete() {
     transition_state = TRANSITION_DONE; 
     in_forced_transition = false;

ArduPlane/quadplane.h

@@ -106,6 +106,12 @@ class QuadPlane
     */
     bool in_transition(void) const;
 
+    /*
+      return true if we are in a fwd transition for a SLT quadplane
+      and in an auto-throttle mode
+     */
+    bool in_slt_fwd_transition(void) const;
+
     bool handle_do_vtol_transition(enum MAV_VTOL_STATE state) const;
 
     bool do_vtol_takeoff(const AP_Mission::Mission_Command& cmd);

ArduPlane/servos.cpp

@@ -517,7 +517,7 @@ float Plane::apply_throttle_limits(float throttle_in)
 
     const bool use_takeoff_throttle_max =
 #if HAL_QUADPLANE_ENABLED
-        quadplane.in_transition() ||
+        quadplane.in_slt_fwd_transition() ||
 #endif
         (flight_stage == AP_FixedWing::FlightStage::TAKEOFF) ||
         (flight_stage == AP_FixedWing::FlightStage::ABORT_LANDING);

ArduPlane/tailsitter.cpp

@@ -1034,4 +1034,12 @@ bool Tailsitter_Transition::allow_weathervane()
     return !tailsitter.in_vtol_transition() && (vtol_limit_start_ms == 0);
 }
 
+/*
+  return true if in a forward transition
+ */
+bool Tailsitter_Transition::in_fwd_transition() const
+{
+    return transition_state == TRANSITION_ANGLE_WAIT_FW;
+}
+
 #endif  // HAL_QUADPLANE_ENABLED

ArduPlane/tailsitter.h

@@ -189,6 +189,8 @@ friend class Tailsitter;
 
     bool allow_weathervane() override;
 
+    bool in_fwd_transition() const override;
+
 private:
 
     enum {

ArduPlane/transition.h

@@ -58,6 +58,8 @@ class Transition
 
     virtual bool allow_stick_mixing() const { return true; }
 
+    virtual bool in_fwd_transition() const = 0;
+
 protected:
 
     // refences for convenience
@@ -101,6 +103,8 @@ class SLT_Transition : public Transition
 
     void set_last_fw_pitch(void) override;
 
+    bool in_fwd_transition() const override;
+
 protected:
 
     enum {