Add force at position with respect to rotation

hello, Im trying to simulate helicopter in unity, Im adding force at the center of the object upwards (or downwards, depend what key is pressed), though when it rotate, even with force, its still going only up and down... any idea how to add force and count for rotation aswell? (eg: if the object is tilted to the right, then add force upwards and to the right side..) I tried looking for answer on google, but didnt quite found it... thanks!