Helicopter doesn't reach target speed


We have performed several hours of normal operation with a 25kg MTOW gas-powered traditional helicopter.

On the latest operations we have noticed that the helicopter is not maintaining the target cruise speed, since it seems to be slowing down at each waypoint. For accuracy reasons, we must create waypoints separated up to 20m each, thus since the heli slows down when reaching each WP, it doesn’t have time to accelerate to the target speed.

In the following log, we intend to fly >5m/s, while it only reaches means of around 3.8-4m/s. We have tested with intended higher speeds (10m/s) and it presents the same behavior.


It seems that on past operations, the missions and parameter configurations were set up similarly but the target speed was reached without issues. We would appreciate it if someone could guide us on what might be causing this unintended behavior.

Thank you in advance,



Did you update the Arducopter firmware recently? What version are you currently using?

With the latest firmware I don’t see why you need to have waypoints at every 20 m. The firmware keeps the aircraft on course at a very tight tolerance.

Hello Bill,

Thank you for the fast response! We seem to have had this problem with different versions of Arducopter. On the shared log we were flying with v4.1.3.
Since this has happened on different Arducopter versions we think that we might have changed a parameter that unintentionally also changes this speed behaviour, that’s why we’d rather try to find the source of the issue instead of just updating versions.

On the other hand, we will definitely test the new tragectories of the latest firmware you mention.

Thank you for your time,


Is it possible that this behaviour is due to the S-Curves introduced on v4.1 and our waypoints being 20m apart from each other? If that’s the case, increasing the WPNAV_ACCEL and WPNAV_JERK parameters should allow for higher speeds? We now have them as WPNAV_ACCEL = 100 and WPNAV_JERK = 1, almost at its lowest.

Yes that was the point of my previous post. Scurves does not handle having waypoints close together. From what I understand. it will not allow speed to be higher than what it can stop with the distance between waypoints. So if you have your desired speed to be 10 m/s and the distance to stop is greater than 20 meters then it will slow down to a speed in which it can stop in 20 meters and that is the speed it will use to go between those waypoints.

Having higher jerk and accel does help because it shortens the stopping distance for a given speed. But remember with the higher jerk and accel, the aircraft will maneuver more aggressively.