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Re: [Paparazzi-devel] Plane drops after take off on energyadaptative loo

From: Joseph Muhlhausen
Subject: Re: [Paparazzi-devel] Plane drops after take off on energyadaptative loop
Date: Thu, 10 Mar 2016 23:16:55 -0500

Just to report, I re-trimmed the plane and re-tuned the pitch loop, I also increase the initial nominal cruise pitch to 1 degree and played with the energy total and energy diff gains, it seems to have solved the issue.

Thanks again!

On Wed, Feb 24, 2016 at 10:51 AM, Joseph Muhlhausen <address@hidden> wrote:
Thanks Guys!

It looks like I am flying too slowly, I honestly thought the AoA was around 5 degree and didn't think of checking the log. I will test the plane again this weekend with your recommendations and report.


On Wed, Feb 24, 2016 at 2:29 AM, Balazs GATI <address@hidden> wrote:
Dear Joseph!

Flying close to the stall speed is not the safest way of operation, because the aerodynamic behavior of the airplane changes very non-linear. Thus the controller won't be able to keep the demanded altitude, speed, AoA, as you would expect.

Of course UAV is the best device to research stall but I suppose you don't like it during take-off. :)


2016.02.23. 21:57 keltezéssel, Christophe De Wagter írta:
If the high pitch angle is fine for you, just type the desired-pitch
value you see during normal cruise as nominal cruise pitch in your
airframe file. Otherwise your controller will start with this value (in
your case about 20 deg) too little pitch and it takes a few seconds for
the controller to correct such a big angle, especially when you activate
it in (slight) underspeed, in which the initial reaction is to slightly
nose down a few degrees extra before it finally notices the dramatic
dive and starts to correct for this using the diff i  gain.

Nominal-cruise-pitch is  used as initial value for energy control. Put a
reasonable value in there ( in your case RadOfDeg(22) linking at your
graphs )

On Feb 24, 2016 02:17, "Joseph Muhlhausen" <address@hidden
<mailto:address@hidden>> wrote:

    Tobias, thanks! my plane is tuned pitch down to make landing easier,
    I will modify that. The standby waypoint in 50 m above the deroute.

    Christophe, thanks! Yes my nominal pitch is high because I fly
    really close to stall speed and thus need a high angle of attack.
    Could I instead increase the nominal throttle and fly with a pitch
    near 0?


    On Tue, Feb 23, 2016 at 12:57 PM, Christophe De Wagter
    <address@hidden <mailto:address@hidden>> wrote:

        It takes a few moments for the integrator to find out you need a
        20 degree pitch up to stay level, which explains the sudden dive
        followed by normal flight. As default value for the pitch
        integrator the cruise pitch from the airframe file is used.

        On Feb 24, 2016 01:53, "Christophe De Wagter"
        <address@hidden <mailto:address@hidden>> wrote:

            Fill the nominal cruise pitch (about 20 to 25 degrees) into
            the nominal cruise pitch: RadOfDeg(25)

            PS: your cruise pitch looks quite large. Might want to look
            at the tuning of your inner loop, the placement of your IMU

            On Feb 23, 2016 20:56, "Tobias" <address@hidden
            <mailto:address@hidden>> wrote:

                Hi Joseph,

                energy-loop is the way to go, just to answer your last
                question. :-)

                regarding the unwonted behavior - first thing to check
                is: is your airframe well tuned? I mean is it holding
                altitude and speed well. after a wile?
                If so you should check probably the values for ( )
                against the flight log for straight flight and climb.
                <!-- auto throttle inner loop -->
                        <define name="AUTO_THROTTLE_NOMINAL_CRUISE_THROTTLE"
                        <define name="AUTO_THROTTLE_NOMINAL_CRUISE_PITCH"
                value="0."/> <!-- default 0 -->
                        <define name="AUTO_THROTTLE_CLIMB_THROTTLE_INCREMENT"
                value="0.1" unit="%/(m/s)"/>

                in the scenario you described you are changing from
                fixed values to the energy loop - its always a good idea
                to have the plane in a rather similar attitude/speed to
                do this. So what is your alt for stby? just thing about
                it - if it is the same alt as your deroute from the
                previous block try to increase the stby alt or decrease
                the deroute alt
                       <exception cond="GetPosAlt() > ground_alt+50"

                this allows the plane to catch up.

                cheers Tobi

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Balazs GATI, PhD
associate professor
     Department of Aeronautics, Naval Architecture and Railway Vehicles
     Budapest University of Technology and Economics

Address:   Budapest
          Stoczek u 6. J. ép. 423
Tel:       +(36)-1-463-1960
Fax:       +(36)-1-463-3080

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