Hi all,

The APM 2.6 in auto mode cannot seem to get the plane (wing wing z-84) down to the target cruise speed of 12m/s.  During missions in still conditions it flies at 15-20m/s. Stall speed is 6-8m/s.

I am not using an airspeed sensor.


Some parameters are:

Stall prevention is OFF

Max throttle: 40%

Cruise throttle: 25%

Cruise air speed: 12m/s

Max air speed 22m/s

Min air speed 8m/s

Originally I had TECS_CLIMB_RATE set to 2 m/s and the plane cruised even faster (25 m/s). I changed this to 10 m/s and it slowed it down to 15-20m/s.

Can someone please advise me on how to tune the plane to achieve the desired cruise speed in terms of parameters to play with.  Even being an engineer myself its not the simplest thing to understand how TECS works in terms of all the parameters.  I feel there should be a parameter to change if your plane cruise speed is over shooting or undershooting.

Lastly, I am not comfortable with my max throttle being 40%.  Id like it to be 100% but that will make the plane fly even faster while cruising.

Thank you,

Jon

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Replies

  • I have the same problem with nearly the same Plane (Bormatec Ninox) without Airspeedsensor. 

    Will it be possible with APM Planner to use the groundspeed to set the right speed. If I use "do_change_speed" in Mission planner it doesnt work. I hope it is only a bug in mp( as I founfd in the web). But does my apm plane (Arduplane firmware 3.7) allow me to change the speed (based on groundspeed) without Airspeedsensor?

    But anyway, when I have the choice between Arspeed and groundspeed it should work! I hope! 

    I am actually using the plane in very high altitude (4.500 m m a.s.l.) and it is way to fast in the thin air!!! i need to controll the speed. 

  • How did you end up doing with this? does it fly well?

    Do you mind giving a close up image of all the electronics?

    • I think my min ground speed was set to 9000 which was 90 meters per second and meant it was flying as fast as max throttle will allow.  I don't have the plane anymore,  crashed during manual flying with a loop too close to the ground. There is a picture in my earlier replies of the set up. Basically had the hkpilot micro mounted in the wing just near the opening for the internals and the GPS was on the other side. Plane flew pretty well in auto and fbwa

  • I have this exact plane which I have set up as a mini-FPV aircraft. It's a lot of fun, flies well and most importantly is small enough to throw in the car for whenever I have an opportunity to fly.

    As with your setup, I don't have an airspeed sensor, as there is not much room to fit one. 

    My understanding is that when an airspeed sensor is not used, the throttle % is the method the autopilot uses to control the speed of the aircraft. Changing the target airspeed probably won't have any effect. While the autopilot does calculate an airspeed estimate, even without an airspeed sensor, it would be dangerous to rely on it so I think the code just doesn't.

    Your only real option is the change the throttle % target. You can do that in parameters or via a do_change_speed command in a mission (set the first parameter to 1 to indicate throttle %).

    Hopefully a developer can chime in, but that is my understanding of how it works.

    • They are lots of fun and very convenient, and cheap.  The air frame in the picture supplied actually split in half after a meeting with a tree (when I was a bad pilot) and it was so easy to glue it back together and it may even fly better.

      I have read up on a lot of the wiki and I did suspect without an airspeed sensor that that airspeed target might not be used.  I've also read about the TECS pitch and throttle methods for achieving flight speeds.  I do wonder if they are used if no airspeed sensor.  

      I guess if a developer could confirm the parameters which are meaningful without an airspeed sensor that would help a lot. Also how the TECS_CLIMB_RATE and MAX throttle percent work together (if they do).  I read something about a linear relationship between what pitch/throttle.  i.e. max pitch = max throttle.


      Thanks for the advice James, I will give it a try.

      • The Max Throttle is a hard limit that will never be exceeded during autopilot. The Climb Rate is a target and it is used for planning so the autopilot can predict its best climb rate. For a max performance climb it will use max throttle and you will get whatever climb rate that gives you.
        You need to tune the TECS so that climb_rate coincides with Max throttle. Set your max throttle that you are comfortable with, then look at your logs to see what climb rate that gives you. Do it on a 50% battery. Same with the descent. Put the plane in the maximum throttle off dive you are comfortable with, (with a stable airspeed).
        If you take the time to set the flight envelope via the TECS parameters, the plane will fly much better.
        • This is very helpful. Thank you.

          I wish it was clearer what parameters to change with or without airspeed sensor.  Mission planner should grey out parameters that are not used depending on what configuration you have. 

    • Agreed. No airspeed sensor means the airspeed Params are not used. Just adjust the cruise throttle % to adjust cruise speed.
      • Hi iskess,

        Thanks for your reply. If I adjust it to say 20% in no wind conditions, will the autopilot adjust throttle if there is high winds? Ie if there is a strong head wind, will throttle increase to maintain any ground speed or something if there is no airspeed sensor.

        • I don't know exactly what the code does, but I have oserved the throttle being modulated in response to ground speed (wind). Most of my airplanes have airspeed sensors because I find the autopilot behaves better.
This reply was deleted.

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