AC_WPNav: increase max accel to 8m/s/s

libraries/AC_WPNav/AC_WPNav.h

@@ -13,7 +13,7 @@
 // loiter maximum velocities and accelerations
 #define MAX_LOITER_POS_VELOCITY         500         // maximum velocity that our position controller will request.  should be 1.5 ~ 2.0 times the pilot input's max velocity.  To-Do: make consistent with maximum velocity requested by pilot input to loiter
 #define MAX_LOITER_POS_ACCEL            250         // defines the velocity vs distant curve.  maximum acceleration in cm/s/s that loiter position controller asks for from acceleration controller
-#define MAX_LOITER_VEL_ACCEL            400         // max acceleration in cm/s that the loiter velocity controller will ask from the lower accel controller.
+#define MAX_LOITER_VEL_ACCEL            800         // max acceleration in cm/s/s that the loiter velocity controller will ask from the lower accel controller.
                                                     // should be 1.5 times larger than MAX_LOITER_POS_ACCEL.
                                                     // max acceleration = max lean angle * 980 * pi / 180.  i.e. 23deg * 980 * 3.141 / 180 = 393 cm/s/s