fix underired movement

lib_planes/custom_physics.lua

@@ -98,6 +98,10 @@ function airutils.physics(self)
 
         --self.object:set_velocity(new_velocity)
         --new_velocity = vector.subtract(new_velocity,vel)
+        if not self.driver_name and math.abs(vel.x) < 0.1 and math.abs(vel.z) < 0.1 then
+            self.object:set_velocity({x=0,y=airutils.gravity*self.dtime,z=0})
+            return
+        end
     end
 
     self.object:add_velocity(new_velocity)