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

From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] Plane drops after take off on energyadaptative loop
Date: Tue, 23 Feb 2016 21:57:24 +0100

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> 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> 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> 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 etc...

On Feb 23, 2016 20:56, "Tobias" <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" value="0.3"/>
<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" deroute="Standby"/>

this allows the plane to catch up.

cheers Tobi

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