# What does gravity compensation do in flight control?

In flight control designs for lateral directional movement, there is a block named "gravity compensation". This block changes yaw rate measurement from "$$r$$" to "$$r-g/Vcos(\theta)sin(\phi)$$" before it is sent to the controller. How does this block change the equation of motion?

• can you provide an image example? have you studied the equation of motion? – Federico Mar 9 at 8:54
• I provided an image example – shooshool Mar 9 at 9:14

It simply makes sure that during a turn the rudder will anticipate the need for that $$r$$ component and thus helps making the turn coordinated.
Since the term is complete (i.e. there is also the $$\theta$$ component) this will work also for climbing/descending turns.
• @shooshool no, it is a feedforward. the fact that is added to $r$ instead of the rudder command does not change its nature. source: I've implemented it several times on our research aircraft. – Federico Mar 9 at 10:56