diff --git a/lib_copter/control.lua b/lib_copter/control.lua
index 447c5c1..cb434fc 100755
--- a/lib_copter/control.lua
+++ b/lib_copter/control.lua
@@ -125,6 +125,7 @@ function airutils.heli_control(self, dtime, hull_direction, longit_speed, longit
                 self._acceleration = 0
             end
             self._acceleration = math.min(self._acceleration,self._max_engine_acc)
+            self._acceleration = math.max(self._acceleration,-1)
 
             if is_flying then --why double check? because I dont want lateral movement when landed
                 if ctrl.right then
@@ -152,6 +153,7 @@ function airutils.heli_control(self, dtime, hull_direction, longit_speed, longit
         end
 
         self._vehicle_acc = math.min(self._acceleration, self._max_engine_acc)
+        self._vehicle_acc = math.max(self._acceleration,-1)
         self._lat_acc = math.min(self._lat_acceleration, self._max_engine_acc)
 
         local hull_acc = vector.multiply(hull_direction,self._vehicle_acc)