Plane: added TKOFF_THR_MIN

this allows for a minimum throttle to be applied during a takeoff or a
forward transition in auto throttle modes. This is useful on high drag
aircraft where normal TECS throttle control results in a slow
transition or takeoff

ArduPlane/Parameters.cpp

@@ -1245,6 +1245,15 @@ const AP_Param::GroupInfo ParametersG2::var_info[] = {
     AP_SUBGROUPINFO(precland, "PLND_", 35, ParametersG2, AC_PrecLand),
 #endif
 
+    // @Param: TKOFF_THR_MIN
+    // @DisplayName: takeoff minimum throttle
+    // @Description: The minimum throttle to use in takeoff or in a quadpane forward transition in automatic throttle modes. This can be useful to ensure faster takeoffs or transitions on aircraft where the normal throttle control leads to a slow takeoff or transition. Set to zero to disable.
+    // @Units: %
+    // @Range: 0 100
+    // @Increment: 1
+    // @User: Standard
+    AP_GROUPINFO("TKOFF_THR_MIN", 36, ParametersG2, takeoff_throttle_min, 0),
+
     AP_GROUPEND
 };
 

ArduPlane/Parameters.h

@@ -574,6 +574,8 @@ class ParametersG2 {
 
     AP_Int8         axis_bitmask; // axes to be autotuned
 
+    AP_Int8         takeoff_throttle_min;
+
     // just to make compilation easier when all things are compiled out...
     uint8_t unused_integer;
 };

ArduPlane/servos.cpp

@@ -540,7 +540,21 @@ float Plane::apply_throttle_limits(float throttle_in)
     throttle_watt_limiter(min_throttle, max_throttle);
 #endif
 
-    return constrain_float(throttle_in, min_throttle, max_throttle);
+    auto throttle = constrain_float(throttle_in, min_throttle, max_throttle);
+
+    /*
+      apply TKOFF_THR_MIN if enabled and in an auto-throttle forward
+      transition
+     */
+    if (use_takeoff_throttle_max) {
+        const auto tmin_thr = g2.takeoff_throttle_min;
+        if (tmin_thr > throttle) {
+            throttle = MAX(throttle, tmin_thr);
+            TECS_controller.reset_throttle_I();
+        }
+    }
+
+    return throttle;
 }
 
 /*