With fixed wing aircraft they will speed up slightly in the turns because the stall speed increases in a turn. To avoid stalling the software usually compensates for this. With rotary wing aircraft they can slow down when they approach a waypoint, especially if it is a sharp turn. They can come to almost a complete stop, then speed back up again heading to the next waypoint. This speeding up and slowing down wastes a lot of time. Try to set the pattern up such that the waypoint radius is larger, and the aircraft doesn’t need to slow up much in the turns.