jsbsim-devel

[Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Hi,

I want to implement an airspeed hold autopilot. The autopilot needs to=20
calculate the airspeed error first. But I don't know which property (i.e.,=
=20
true airspeed) should be used to calculate the airspeed error=20
(=3Dairspeed_setpoint - true_airspeed). Could someone tell me?

A related question is: Should the output of the "airspeed hold autopilot" b=
e=20
ap/elevator_cmd or fcs/throttle-cmd-norm?

A third question is: How to make the aircraft fly a glide slope either=20
through a script or an autopilot?

Thanks a lot!

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Ron F. <ron...@at...>]

----- Original Message ----- 
From: Aaron Simpson
To: jsb...@li...
Sent: Wednesday, August 31, 2005 4:39 PM
Subject: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope


>Hi,

>I want to implement an airspeed hold autopilot.  The autopilot needs to 
>calculate the airspeed error first. But I don't know which property (i.e., 
>true airspeed) should be used to calculate the airspeed error 
>(=airspeed_setpoint - true_airspeed). Could someone tell me?

    As Tony said, 'CAS' is probably best.  Though real AC typically only 
have the IAS reading for speed.   'EAS' is virtually 'CAS' at prop AC 
speeds, and proportional to sqrt (qbar).    However, Jets climb at a certain 
IAS,  which drops relative to EAS at higher FL's.  Generally IAS is close to 
CAS at jet climb, cruise, and descent speeds.

    Above a certain flight level, jets switch to Mach Hold for speed.  A 
typical climb schedule is 300 kts IAS, switching to Mach 0.78 when that is 
reached.  Finally, accelerating to Mach 0.80 for cruise.  Some form of 
pitch/VS/Altitude hold is required at higher Mach levels, jets are generally 
statically unstable past Mach 0.72 or so.   That is often a 'Mach stability 
system', and is legally required to be operational to fly above the critical 
Mach Number.  However, ALT hold will do with a simulation.

    Be sure to use some Rate Feedback to damp the speed control.

>A related question is: Should the output of the "airspeed hold autopilot" 
>be ap/elevator_cmd or fcs/throttle-cmd-norm?

    Note AC tend to be unstable in vertical speed if  'speed' is held, but 
pitch (AoA) is set manually.  One also needs pitch control if holding speed.

    Holding speed by throttle is most common, however pitch control is nice 
for climb/descent.  Since vertical speed is then controlled by the throttle.


>A third question is: How to make the aircraft fly a glide slope either 
>through a script or an autopilot?
Thanks a lot!

    Note ILS and GS generally schedule the Gain, since control becomes more 
sensitive as the touchdown point is approached.

    Ron

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Thank you all for your help.

For my purpose, it seems that I can use pitch to control altitude and use=
=20
throttle to control airspeed when the aircraft is flying a glideslope. When=
=20
I try to write an airspeed hold autopilot XML script, I don't know how to=
=20
command the throttle. If the output of the autopilot is=20
fcs/throttle-cmd-norm, there will be runtime error ("property=20
throttle-cmd-norm is not bound").

How come fcs/aleron and fcs/elevator all can be the output of an autopilot=
=20
channel, but fcs/throttle-cmd-norm cannot?

How can I control the throttle with an autopilot (or autothrottle?) in=20
JSBSim?

Thanks!

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

I'll try and look at that this morning. It could very well be because we
have not yet "connected" a throttle with a property.

Jon

  -----Original Message-----
  From: jsb...@li...
[mailto:jsb...@li...]On Behalf Of Aaron Simpson
  Sent: Friday, September 02, 2005 11:23 PM
  To: jsb...@li...
  Subject: Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide
slope


  Thank you all for your help.

  For my purpose, it seems that I can use pitch to control altitude and use
throttle to control airspeed when the aircraft is flying a glideslope. When
I try to  write an airspeed hold autopilot XML script, I don't know how to
command the throttle. If the output of the autopilot is
fcs/throttle-cmd-norm, there will be runtime error ("property
throttle-cmd-norm is not bound").

  How come fcs/aleron and fcs/elevator all can be the output of an autopilot
channel, but fcs/throttle-cmd-norm cannot?

  How can I control the throttle with an autopilot (or autothrottle?) in
JSBSim?

  Thanks!

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

  For my purpose, it seems that I can use pitch to control altitude and use
throttle to control airspeed when the aircraft is flying a glideslope. When
I try to  write an airspeed hold autopilot XML script, I don't know how to
command the throttle. If the output of the autopilot is
fcs/throttle-cmd-norm, there will be runtime error ("property
throttle-cmd-norm is not bound").
Can you post an example of the component that you are using to control the
throttle?

Jon

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Here is what I did:

<!--beging--->
<!-- Calibrated Airspeed hold -->

<!-- The Airspeed Error component below computes the Airspeed error,=20
subtracting
the desired Airspeed (airspeed_setpoint) from the actual Airspeed.=20
-->

<channel name=3D"AP Throttle Airspeed hold">
<component name=3D"Airspeed Error" type=3D"SUMMER">
<input> -velocities/vc-kts </input>
<input> ap/airspeed_setpoint </input>
<clipto>
<min>-100</min>
<max> 100</max>
</clipto>
</component>

<component name=3D"Airspeed Error Lag" type=3D"LAG_FILTER">
<input> fcs/airspeed-error </input>
<c1> 1 </c1>
</component>


<component name=3D"AP Airspeed Hold Switch" type=3D"SWITCH">
<default value=3D"0.0"/>
<test logic=3D"AND" value=3D"fcs/Airspeed-Error-Lag">
ap/airspeed_hold =3D=3D 1
</test>
</component>

<component name=3D"Airspeed Integral" type=3D"INTEGRATOR">
<input> fcs/ap-airspeed-hold-switch </input>
<c1> 0.00001 </c1>
</component>

<component name=3D"Airspeed Proportional" type=3D"PURE_GAIN">
<input> fcs/ap-airspeed-hold-switch </input>
<gain> 0.02 </gain>
</component>

<component name=3D"Airspeed Control Summer" type=3D"SUMMER">
<input> fcs/airspeed-integral </input>
<input> fcs/airspeed-proportional </input>
<clipto>
<min>-1.0</min>
<max> 1.0</max>
</clipto>
</component>

<component name=3D"Airspeed Throttle cmd norm" type=3D"PURE_GAIN">
<input> fcs/airspeed-control-summer </input>
<gain> -1.0 </gain>
<output> fcs/throttle-cmd-norm </output>
</component>
</channel>
<!--end-->

Thanks!

On 9/3/05, Jon Berndt <js...@ha...> wrote:
>=20
>  For my purpose, it seems that I can use pitch to control altitude and us=
e=20
> throttle to control airspeed when the aircraft is flying a glideslope. Wh=
en=20
> I try to write an airspeed hold autopilot XML script, I don't know how to=
=20
> command the throttle. If the output of the autopilot is=20
> fcs/throttle-cmd-norm, there will be runtime error ("property=20
> throttle-cmd-norm is not bound").
>=20
> Can you post an example of the component that you are using to control th=
e=20
> throttle?
>  Jon
>

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

    <component name="Airspeed Throttle cmd norm" type="PURE_GAIN">
      <input> fcs/airspeed-control-summer </input>
      <gain> -1.0 </gain>
      <output> fcs/throttle-cmd-norm </output>
    </component>
  </channel>
  <!--end-->

This looks OK, but you might try:

     <output> fcs/throttle-cmd-norm[0] </output>

Theoretically, you really need to specify the engine number. If that doesn't
fix it, there are some other approaches that should help.

First, make sure that the entire config file is getting read properly. Look
at the information that is echoed out at startup as the config file is
parsed. Make sure there are no errors.

Second, you can set an environment variable in your shell that will give you
a lot of information. All but the last few lines are probably unneeded, but
you can do this:

setenv JSBSIM_DEBUG 63

-or-

export JSBSIM_DEBUG=63

Then, run JSBSim like normal and watch the results.

Jon

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

Aaron:

I think I have identified the error. Will get back to you later.

Jon

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Thanks, Jon!=20

Looking forward to hearing from you!


On 9/5/05, Jon Berndt <js...@ha...> wrote:
>=20
> Aaron:
>  I think I have identified the error. Will get back to you later.
>  Jon
>

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

Aaron:

Your autopilot (autothrottle) definition includes this, as you have
mentioned:

<component name="Airspeed Throttle cmd norm" type="PURE_GAIN">
  <input> fcs/airspeed-control-summer </input>
  <gain> -1.0 </gain>
  <output>fcs/throttle-cmd-norm</output>
</component>

Unfortunately, at this moment, the "fcs/throttle-cmd-norm" property has not
yet been created (that is, it has not been Tied to a class attribute or
access function). The autopilot components are read in prior to the flight
control components, and the "bindmodel" function call that creates the
fcs/throttle-cmd-norm property is not called until all of the flight control
components are loaded. The problem is, then, understood and straightforward.

The first idea I have for a solution is to bind the throttle (and mixture
and prop-advance) properties in the AddThrottle function itself - just after
the throttle is created. That might work. That way, the throttle properties
would be created and available just after the propulsion system is loaded.
So, then, the AddThrottle() function in FGFCS.cpp might look like this:

void FGFCS::AddThrottle(void)
{
  ThrottleCmd.push_back(0.0);
  ThrottlePos.push_back(0.0);
  MixtureCmd.push_back(0.0);
  MixturePos.push_back(0.0);
  PropAdvanceCmd.push_back(0.0);
  PropAdvance.push_back(0.0);

  unsigned int num = ThrottleCmd.size();

  bindThrottles(num);
}

And, bindThrottles() could look like this:

void FGFCS::bindThrottles(int num)
{
  char tmp[80];

  snprintf(tmp, 80, "fcs/throttle-cmd-norm[%u]",num);
  PropertyManager->Tie( tmp, this, num, &FGFCS::GetThrottleCmd,
                                        &FGFCS::SetThrottleCmd);
  snprintf(tmp, 80, "fcs/throttle-pos-norm[%u]",num);
  PropertyManager->Tie( tmp, this, num, &FGFCS::GetThrottlePos,
                                        &FGFCS::SetThrottlePos);
  snprintf(tmp, 80, "fcs/mixture-cmd-norm[%u]",num);
  PropertyManager->Tie( tmp, this, num, &FGFCS::GetMixtureCmd,
                                        &FGFCS::SetMixtureCmd);
  snprintf(tmp, 80, "fcs/mixture-pos-norm[%u]",num);
  PropertyManager->Tie( tmp, this, num, &FGFCS::GetMixturePos,
                                        &FGFCS::SetMixturePos);
  snprintf(tmp, 80, "fcs/advance-cmd-norm[%u]",num);
  PropertyManager->Tie( tmp, this, num, &FGFCS::GetPropAdvanceCmd,
                                        &FGFCS::SetPropAdvanceCmd);
  snprintf(tmp, 80, "fcs/advance-pos-norm[%u]", num);
  PropertyManager->Tie( tmp, this, num, &FGFCS::GetPropAdvance,
                                        &FGFCS::SetPropAdvance);
}

Of course, if the above is done, then the existing bindmodel() function will
need to have the code that does the binding of the throttles, mixture, and
prop-advance removed.

I'll be investigating this change, but I thought you might like a heads-up
on a possible solution.

Jon

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

Correction:
  void FGFCS::AddThrottle(void)
  {
    ThrottleCmd.push_back(0.0);
    ThrottlePos.push_back(0.0);
    MixtureCmd.push_back(0.0);
    MixturePos.push_back(0.0);
    PropAdvanceCmd.push_back(0.0);
    PropAdvance.push_back(0.0);

    unsigned int num = ThrottleCmd.size() - 1;

    bindThrottles(num);
  } 
This seems to work.

Jon
 

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Hi, Jon,

Thanks for your reply.

I added the code. But I still see this error at run time "Failed to tie=20
property fcs/advance-pos-norm[0] to indexed object methods". I tried using=
=20
"fcs/throttle-cmd-norm", "fcs/throttle-cmd-norm[0]" and=20
"fcs/throttle-cmd-norm[1]" in the following:

<component name=3D"Airspeed Throttle cmd norm" type=3D"PURE_GAIN">
<input> fcs/airspeed-control-summer </input>
<gain> -1.0 </gain>
<output> fcs/throttle-cmd-norm</output>
</component>

Here is part of the log that shows where that error message appears:

--begin--
Loading Component "Airspeed Error" of type: SUMMER

INPUTS:=20

-vc-kts

airspeed_setpoint

CLIPTO: -100.0000, 100.0000



Loading Component "Airspeed Error Lag" of type: LAG_FILTER

INPUT: airspeed-error

C1: 1.0000

C2: 0.0000

C3: 0.0000

C4: 0.0000

C5: 0.0000

C6: 0.0000



Loading Component "AP Airspeed Hold Switch" of type: SWITCH

Switch VALUE is 0.0000 by default.



Switch VALUE is 0.0000 if=20

airspeed_hold =3D=3D 1.0000





Loading Component "Airspeed Integral" of type: INTEGRATOR

INPUT: ap-airspeed-hold-switch

C1: 0.0000

C2: 0.0000

C3: 0.0000

C4: 0.0000

C5: 0.0000

C6: 0.0000



Loading Component "Airspeed Proportional" of type: PURE_GAIN

INPUT: ap-airspeed-hold-switch

GAIN: 0.0200



Loading Component "Airspeed Control Summer" of type: SUMMER

INPUTS:=20

airspeed-integral

airspeed-proportional

CLIPTO: -1.0000, 1.0000



Loading Component "Airspeed Throttle cmd norm" of type: PURE_GAIN

INPUT: airspeed-control-summer

GAIN: -1.0000

OUTPUT: throttle-cmd-norm



Flight Control (FCS: c172)



Loading Component "Pitch Trim Sum" of type: SUMMER

INPUTS:=20

elevator_cmd

elevator-cmd-norm

pitch-trim-cmd-norm

CLIPTO: -1.0000, 1.0000



Loading Component "Elevator Control" of type: AEROSURFACE_SCALE

INPUT: pitch-trim-sum

GAIN: 0.0175

OUTPUT: elevator-pos-rad

MIN: -28.0000

MAX: 23.0000



Loading Component "Roll Trim Sum" of type: SUMMER

INPUTS:=20

aileron_cmd

aileron-cmd-norm

roll-trim-cmd-norm

CLIPTO: -1.0000, 1.0000



Loading Component "Left Aileron Control" of type: AEROSURFACE_SCALE

INPUT: roll-trim-sum

GAIN: 0.0175

OUTPUT: left-aileron-pos-rad

MIN: -20.0000

MAX: 15.0000



Loading Component "Right Aileron Control" of type: AEROSURFACE_SCALE

INPUT: -roll-trim-sum

GAIN: 0.0175

OUTPUT: right-aileron-pos-rad

MIN: -20.0000

MAX: 15.0000



Loading Component "Yaw Trim Sum" of type: SUMMER

INPUTS:=20

rudder-cmd-norm

yaw-trim-cmd-norm

CLIPTO: -1.0000, 1.0000



Loading Component "Rudder Control" of type: AEROSURFACE_SCALE

INPUT: yaw-trim-sum

GAIN: 0.0175

OUTPUT: rudder-pos-rad

MIN: -16.0000

MAX: 16.0000



Loading Component "Flaps Control" of type: KINEMAT

INPUT: flap-cmd-norm

DETENTS: 4

0.0000 0.0000

10.0000 2.0000

20.0000 1.0000

30.0000 1.0000

OUTPUT: flap-pos-deg

Failed to tie property fcs/throttle-cmd-norm[0] to indexed object methods

Failed to tie property fcs/throttle-pos-norm[0] to indexed object methods

Failed to tie property fcs/mixture-cmd-norm[0] to indexed object methods

Failed to tie property fcs/mixture-pos-norm[0] to indexed object methods

Failed to tie property fcs/advance-cmd-norm[0] to indexed object methods

Failed to tie property fcs/advance-pos-norm[0] to indexed object methods


Aerodynamics:=20

1 dimensional table with 13 rows.
...
--end--

Thanks again!

On 9/6/05, Jon Berndt <js...@ha...> wrote:
>=20
> Correction:
>=20
> void FGFCS::AddThrottle(void)
> {
> ThrottleCmd.push_back(0.0);
> ThrottlePos.push_back(0.0);
> MixtureCmd.push_back(0.0);
> MixturePos.push_back(0.0);
> PropAdvanceCmd.push_back(0.0);
> PropAdvance.push_back(0.0);
>   unsigned int num =3D ThrottleCmd.size()* **- 1*;
>   bindThrottles(num);
> }=20
>=20
> This seems to work.
>  Jon
>

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

OK. I'll check in my changes. Then, you'll need to do an update. We'll see
if that eliminates the problem. If not, at least we'll be able to have a
common starting point. The only thing that is not yet complete in my current
code is that some normalized values are not available. That can be dealt
with in at least a couple of ways.

Jon

  -----Original Message-----
  From: jsb...@li...
[mailto:jsb...@li...]On Behalf Of Aaron Simpson
  Sent: Tuesday, September 06, 2005 2:21 PM
  To: jsb...@li...
  Subject: Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide
slope


  Hi, Jon,

  Thanks for your reply.

  I added the code. But I still see this error at run time "Failed to tie
property fcs/advance-pos-norm[0] to indexed object methods". I tried using
"fcs/throttle-cmd-norm", "fcs/throttle-cmd-norm[0]" and
"fcs/throttle-cmd-norm[1]" in the following:

    <component name="Airspeed Throttle cmd norm" type="PURE_GAIN">
      <input> fcs/airspeed-control-summer </input>
      <gain> -1.0 </gain>
      <output> fcs/throttle-cmd-norm</output>
    </component>

  Here is part of the log that shows  where that error message appears:

  --begin--
   Loading Component "Airspeed Error" of type: SUMMER

        INPUTS:

         -vc-kts

         airspeed_setpoint

        CLIPTO: -100.0000, 100.0000



      Loading Component "Airspeed Error Lag" of type: LAG_FILTER

        INPUT: airspeed-error

        C1: 1.0000

        C2: 0.0000

        C3: 0.0000

        C4: 0.0000

        C5: 0.0000

        C6: 0.0000



      Loading Component "AP Airspeed Hold Switch" of type: SWITCH

          Switch VALUE is 0.0000 by default.



          Switch VALUE is 0.0000 if

           airspeed_hold == 1.0000





      Loading Component "Airspeed Integral" of type: INTEGRATOR

        INPUT: ap-airspeed-hold-switch

        C1: 0.0000

        C2: 0.0000

        C3: 0.0000

        C4: 0.0000

        C5: 0.0000

        C6: 0.0000



      Loading Component "Airspeed Proportional" of type: PURE_GAIN

        INPUT: ap-airspeed-hold-switch

        GAIN: 0.0200



      Loading Component "Airspeed Control Summer" of type: SUMMER

        INPUTS:

         airspeed-integral

         airspeed-proportional

        CLIPTO: -1.0000, 1.0000



      Loading Component "Airspeed Throttle cmd norm" of type: PURE_GAIN

        INPUT: airspeed-control-summer

        GAIN: -1.0000

        OUTPUT: throttle-cmd-norm



    Flight Control (FCS: c172)



      Loading Component "Pitch Trim Sum" of type: SUMMER

        INPUTS:

         elevator_cmd

         elevator-cmd-norm

         pitch-trim-cmd-norm

        CLIPTO: -1.0000, 1.0000



      Loading Component "Elevator Control" of type: AEROSURFACE_SCALE

        INPUT: pitch-trim-sum

        GAIN: 0.0175

        OUTPUT: elevator-pos-rad

        MIN: -28.0000

        MAX: 23.0000



      Loading Component "Roll Trim Sum" of type: SUMMER

        INPUTS:

         aileron_cmd

         aileron-cmd-norm

         roll-trim-cmd-norm

        CLIPTO: -1.0000, 1.0000



      Loading Component "Left Aileron Control" of type: AEROSURFACE_SCALE

        INPUT: roll-trim-sum

        GAIN: 0.0175

        OUTPUT: left-aileron-pos-rad

        MIN: -20.0000

        MAX: 15.0000



      Loading Component "Right Aileron Control" of type: AEROSURFACE_SCALE

        INPUT: -roll-trim-sum

        GAIN: 0.0175

        OUTPUT: right-aileron-pos-rad

        MIN: -20.0000

        MAX: 15.0000



      Loading Component "Yaw Trim Sum" of type: SUMMER

        INPUTS:

         rudder-cmd-norm

         yaw-trim-cmd-norm

        CLIPTO: -1.0000, 1.0000



      Loading Component "Rudder Control" of type: AEROSURFACE_SCALE

        INPUT: yaw-trim-sum

        GAIN: 0.0175

        OUTPUT: rudder-pos-rad

        MIN: -16.0000

        MAX: 16.0000



      Loading Component "Flaps Control" of type: KINEMAT

        INPUT: flap-cmd-norm

        DETENTS: 4

          0.0000 0.0000

          10.0000 2.0000

          20.0000 1.0000

          30.0000 1.0000

        OUTPUT: flap-pos-deg

  Failed to tie property fcs/throttle-cmd-norm[0] to indexed object methods

  Failed to tie property fcs/throttle-pos-norm[0] to indexed object methods

  Failed to tie property fcs/mixture-cmd-norm[0] to indexed object methods

  Failed to tie property fcs/mixture-pos-norm[0] to indexed object methods

  Failed to tie property fcs/advance-cmd-norm[0] to indexed object methods

  Failed to tie property fcs/advance-pos-norm[0] to indexed object methods


    Aerodynamics:

      1 dimensional table with 13 rows.
  ...
  --end--

  Thanks again!


  On 9/6/05, Jon Berndt <js...@ha...> wrote:
    Correction:
      void FGFCS::AddThrottle(void)
      {
        ThrottleCmd.push_back(0.0);
        ThrottlePos.push_back(0.0);
        MixtureCmd.push_back(0.0);
        MixturePos.push_back(0.0);
        PropAdvanceCmd.push_back(0.0);
        PropAdvance.push_back(0.0);

        unsigned int num = ThrottleCmd.size() - 1;

        bindThrottles(num);
      }
    This seems to work.

    Jon

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

  OK. I'll check in my changes. 
 Done.

Jon

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Thanks! I'll check them in.=20

On 9/6/05, Jon Berndt <js...@ha...> wrote:
>=20
>  OK. I'll check in my changes.=20
>=20
>  Done.
>  Jon
>

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Sorry, I meant check them out.


On 9/6/05, Aaron Simpson <air...@gm...> wrote:
>=20
> Thanks! I'll check them in.=20
>=20
> On 9/6/05, Jon Berndt <js...@ha...> wrote:
> >=20
> >  OK. I'll check in my changes.=20
> >=20
> >  Done.
> >  Jon
> > =20
>=20
>

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Erik H. <er...@eh...>]

Jon Berndt wrote:
> Unfortunately, at this moment, the "fcs/throttle-cmd-norm" property has 
> not yet been created (that is, it has not been Tied to a class attribute 
> or access function). The _/autopilot/_ components are read in prior to 
> the flight control components, and the "bindmodel" function call that 
> creates the fcs/throttle-cmd-norm property is not called until all of 
> the _/flight control/_ components are loaded. The problem is, then, 
> understood and straightforward.

The property system lets you add a property when it gets referenced but 
  it's not yet available, do you use that functionality at this time?

SGPropertyNode *n = getNode("/path/to/node", true);

The last parameter orders the code to create the property if non existent.

Erik

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

> The property system lets you add a property when it gets referenced but
>   it's not yet available, do you use that functionality at this time?
>
> SGPropertyNode *n = getNode("/path/to/node", true);
>
> The last parameter orders the code to create the property if non existent.
>
> Erik

Yeah, that's a good and useful capability in some cases. What I want to try to do with
JSBSim, though, is to avoid the use of that capability unless it's absolutely necessary.
In my opinion, using that feature within the flight control system might allow a typo to
get through, and leave the user wondering why things don't work as expected. So, requiring
a property to exist prior to referring to it, I think, tends to act as a sort of a syntax
check.

Regardless, JSBSim should better handle the situation where a non-existent property is
referenced. Right now I think JSBSim segfaults. That's not good, of course.

Jon

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

I've also gone through the code and made some tweaks to that if this situation was to
happen again you'd get a more graceful shutdown. Now, you'll get a message stating the
name of the offending property, and a program exit, instead of a segfault.

This has not yet been committed to CVS, as there is another pending change in my working
directory. I'm home sick today, so if I'm feeling up to it this change may be committed
today.

Jon

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Erik H. <er...@eh...>]

Jon Berndt wrote:

> Yeah, that's a good and useful capability in some cases. What I want to try to do with
> JSBSim, though, is to avoid the use of that capability unless it's absolutely necessary.
> In my opinion, using that feature within the flight control system might allow a typo to
> get through, and leave the user wondering why things don't work as expected. So, requiring
> a property to exist prior to referring to it, I think, tends to act as a sort of a syntax
> check.

Ok, that makes sense. Detecting typos is fairly easy in FlightGear due 
to the presence of the property browser. I an imagine you don't want to 
add *that* to JSBSim :-)

Erik

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

 Aaron:

By the way, the test value below:

<component name="AP Airspeed Hold Switch" type="SWITCH">
  <default value="0.0"/>
  <test logic="AND" value="fcs/Airspeed-Error-Lag">
    ap/airspeed_hold == 1
  </test>
</component>
 
should be:

  <test logic="AND" value="fcs/airspeed-error-lag">

(note case)

Jon
 

Re: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Aaron S. <air...@gm...>]

Hi, Jon,

I checked out JSBSim from CVS yesterday after you checked your stuff in.=20
There is an runtime error with the current CVS version when I use the=20
configuration files I sent you. Then I did a folder comparison and found=20
that your proposed changes, i.e., bindThrottles(int num), etc are not in it=
.=20


After adding your proposed changes to FGFCS.h and FGFCS.cpp, the log is=20
different but there is still run time error. Here is part of the log (notic=
e=20
the "Failed to tie property fcs/throttle-cmd-norm[0] to indexed object=20
methods" error message before the Aerodynamic in the log):

--begin--
Loading Component "Airspeed Error" of type: SUMMER

INPUTS:=20

-vc-kts

airspeed_setpoint

CLIPTO: -100.0000, 100.0000



Loading Component "Airspeed Error Lag" of type: LAG_FILTER

INPUT: airspeed-error

C1: 1.0000

C2: 0.0000

C3: 0.0000

C4: 0.0000

C5: 0.0000

C6: 0.0000



Loading Component "AP Airspeed Hold Switch" of type: SWITCH

Switch VALUE is 0.0000 by default.



Switch VALUE is airspeed-error-lag if=20

airspeed_hold =3D=3D 1.0000





Loading Component "Airspeed Integral" of type: INTEGRATOR

INPUT: ap-airspeed-hold-switch

C1: 0.0000

C2: 0.0000

C3: 0.0000

C4: 0.0000

C5: 0.0000

C6: 0.0000



Loading Component "Airspeed Proportional" of type: PURE_GAIN

INPUT: ap-airspeed-hold-switch

GAIN: 0.0200



Loading Component "Airspeed Control Summer" of type: SUMMER

INPUTS:=20

airspeed-integral

airspeed-proportional

CLIPTO: -1.0000, 1.0000



Loading Component "Airspeed Throttle cmd norm" of type: PURE_GAIN

INPUT: airspeed-control-summer

GAIN: -1.0000

OUTPUT: throttle-cmd-norm



Flight Control (FCS: c172)



Loading Component "Pitch Trim Sum" of type: SUMMER

INPUTS:=20

elevator_cmd

elevator-cmd-norm

pitch-trim-cmd-norm

CLIPTO: -1.0000, 1.0000



Loading Component "Elevator Control" of type: AEROSURFACE_SCALE

INPUT: pitch-trim-sum

GAIN: 0.0175

OUTPUT: elevator-pos-rad

MIN: -28.0000

MAX: 23.0000



Loading Component "Roll Trim Sum" of type: SUMMER

INPUTS:=20

aileron_cmd

aileron-cmd-norm

roll-trim-cmd-norm

CLIPTO: -1.0000, 1.0000



Loading Component "Left Aileron Control" of type: AEROSURFACE_SCALE

INPUT: roll-trim-sum

GAIN: 0.0175

OUTPUT: left-aileron-pos-rad

MIN: -20.0000

MAX: 15.0000



Loading Component "Right Aileron Control" of type: AEROSURFACE_SCALE

INPUT: -roll-trim-sum

GAIN: 0.0175

OUTPUT: right-aileron-pos-rad

MIN: -20.0000

MAX: 15.0000



Loading Component "Yaw Trim Sum" of type: SUMMER

INPUTS:=20

rudder-cmd-norm

yaw-trim-cmd-norm

CLIPTO: -1.0000, 1.0000



Loading Component "Rudder Control" of type: AEROSURFACE_SCALE

INPUT: yaw-trim-sum

GAIN: 0.0175

OUTPUT: rudder-pos-rad

MIN: -16.0000

MAX: 16.0000



Loading Component "Flaps Control" of type: KINEMAT

INPUT: flap-cmd-norm

DETENTS: 4

0.0000 0.0000

10.0000 2.0000

20.0000 1.0000

30.0000 1.0000

OUTPUT: flap-pos-deg

Failed to tie property fcs/throttle-cmd-norm[0] to indexed object methods

Failed to tie property fcs/throttle-pos-norm[0] to indexed object methods

Failed to tie property fcs/mixture-cmd-norm[0] to indexed object methods

Failed to tie property fcs/mixture-pos-norm[0] to indexed object methods

Failed to tie property fcs/advance-cmd-norm[0] to indexed object methods

Failed to tie property fcs/advance-pos-norm[0] to indexed object methods



Aerodynamics:=20

1 dimensional table with 13 rows.

0.0000 1.2030=20

0.1000 1.1270=20

0.1500 1.0900=20

0.2000 1.0730=20

0.3000 1.0460=20

0.4000 1.0550=20

0.5000 1.0190=20

0.6000 1.0130=20

0.7000 1.0080=20

0.8000 1.0060=20

0.9000 1.0030=20

1.0000 1.0020=20

1.1000 1.0000=20

Function: aero/function/ground-effect-factor-lift

1 dimensional table with 13 rows.

0.0000 0.4800=20

0.1000 0.5150=20

0.1500 0.6290=20

0.2000 0.7090=20

0.3000 0.8150=20

0.4000 0.8820=20

0.5000 0.9280=20

0.6000 0.9620=20

0.7000 0.9880=20

0.8000 1.0000=20

0.9000 1.0000=20

1.0000 1.0000=20

1.1000 1.0000=20

Function: aero/function/ground-effect-factor-drag

2 dimensional table with 17 rows, 2 columns.

0.0000 1.0000=20

-0.0900 -0.2200 -0.2200=20

0.0000 0.2500 0.2500=20

0.0900 0.7300 0.7300=20

0.1000 0.8300 0.7800=20

0.1200 0.9200 0.7900=20

0.1400 1.0200 0.8100=20

0.1600 1.0800 0.8200=20

0.1700 1.1300 0.8300=20

0.1900 1.1900 0.8500=20

0.2100 1.2500 0.8600=20

0.2400 1.3500 0.8800=20

0.2600 1.4400 0.9000=20

0.2800 1.4700 0.9200=20

0.3000 1.4300 0.9500=20

0.3200 1.3800 0.9900=20

0.3400 1.3000 1.0500=20

0.3600 1.1500 1.1500=20

Function: aero/coefficient/CLwbh

1 dimensional table with 4 rows.

0.0000 0.0000=20

10.0000 0.2000=20

20.0000 0.3000=20

30.0000 0.3500=20

Function: aero/coefficient/CLDf

Function: aero/coefficient/CLDe

Function: aero/coefficient/CLadot

Function: aero/coefficient/CLq

Function: aero/coefficient/CDo

1 dimensional table with 4 rows.

0.0000 0.0000=20

10.0000 0.0070=20

20.0000 0.0120=20

30.0000 0.0180=20

Function: aero/coefficient/CDDf

2 dimensional table with 26 rows, 4 columns.

0.0000 10.0000 20.0000 30.0000=20

-0.0873 0.0041 0.0000 0.0005 0.0014=20

-0.0698 0.0013 0.0004 0.0025 0.0041=20

-0.0524 0.0001 0.0023 0.0059 0.0084=20

-0.0349 0.0003 0.0057 0.0108 0.0141=20

-0.0175 0.0020 0.0105 0.0172 0.0212=20

0.0000 0.0052 0.0168 0.0251 0.0299=20

0.0175 0.0099 0.0248 0.0346 0.0402=20

0.0349 0.0162 0.0342 0.0457 0.0521=20

0.0524 0.0240 0.0452 0.0583 0.0655=20

0.0698 0.0334 0.0577 0.0724 0.0804=20

0.0873 0.0442 0.0718 0.0881 0.0968=20

0.1047 0.0566 0.0874 0.1053 0.1148=20

0.1222 0.0706 0.1045 0.1240 0.1343=20

0.1396 0.0860 0.1232 0.1442 0.1554=20

0.1571 0.0962 0.1353 0.1573 0.1690=20

0.1745 0.1069 0.1479 0.1708 0.1830=20

0.1920 0.1180 0.1610 0.1849 0.1975=20

0.2094 0.1298 0.1746 0.1995 0.2126=20

0.2269 0.1424 0.1892 0.2151 0.2286=20

0.2443 0.1565 0.2054 0.2323 0.2464=20

0.2618 0.1727 0.2240 0.2521 0.2667=20

0.2793 0.1782 0.2302 0.2587 0.2735=20

0.2967 0.1716 0.2227 0.2507 0.2653=20

0.3142 0.1618 0.2115 0.2388 0.2531=20

0.3316 0.1475 0.1951 0.2214 0.2351=20

0.3491 0.1097 0.1512 0.1744 0.1866=20

Function: aero/coefficient/CDwbh

Function: aero/coefficient/CDDe

Function: aero/coefficient/CDbeta

1 dimensional table with 3 rows.

-0.3490 0.1080=20

0.0000 0.0000=20

0.3490 -0.1080=20

Function: aero/coefficient/CYb

Function: aero/coefficient/CYda

Function: aero/coefficient/CYdr

Function: aero/coefficient/CYp

Function: aero/coefficient/CYr

1 dimensional table with 3 rows.

-0.3490 0.0311=20

0.0000 0.0000=20

0.3490 -0.0311=20

Function: aero/coefficient/Clb

Function: aero/coefficient/Clp

1 dimensional table with 2 rows.

0.0000 0.0800=20

0.0940 0.1900=20

Function: aero/coefficient/Clr

Function: aero/coefficient/Clda

Function: aero/coefficient/Cldr

Function: aero/coefficient/Cmalpha

1 dimensional table with 4 rows.

0.0000 0.0000=20

10.0000 -0.0654=20

20.0000 -0.0981=20

30.0000 -0.1140=20

Function: aero/coefficient/CmDf

Function: aero/coefficient/Cmq

Function: aero/coefficient/Cmadot

Function: aero/coefficient/Cmo

Function: aero/coefficient/Cmde

1 dimensional table with 3 rows.

-0.3490 -0.0227=20

0.0000 0.0000=20

0.3490 0.0227=20

Function: aero/coefficient/Cnb

Function: aero/coefficient/Cnp

Function: aero/coefficient/Cnr

Function: aero/coefficient/Cnda

Function: aero/coefficient/Cndr

Winsock DLL loaded ...

Successfully bound to socket ...

Output parameters read inline

Log output goes to file: JSBout172B.csv in CSV format output at rate 20 Hz

Properties logged:

- qbar-psf

--end--

Thanks again.

On 9/6/05, Jon Berndt <js...@ha...> wrote:
>=20
>  Aaron:
>  By the way, the test *value* below:
>  <component name=3D"AP Airspeed Hold Switch" type=3D"SWITCH">
> <default value=3D"0.0"/>
> <test logic=3D"AND" value=3D"fcs/Airspeed-Error-Lag">
> ap/airspeed_hold =3D=3D 1
> </test>
> </component>
>  should be:
>   <test logic=3D"AND" value=3D"fcs/airspeed-error-lag">
> (note case)
>  Jon
>

RE: [Jsbsim-devel] Airspeed hold autopilot and flying a glide slope

[Jon B. <js...@ha...>]

> For my purpose, it seems that I can use pitch to control altitude
> and use throttle to control airspeed when the aircraft is flying a
> glideslope. When I try to  write an airspeed hold autopilot XML
> script, I don't know how to command the throttle. If the output of
> the autopilot is fcs/throttle-cmd-norm, there will be runtime error
> ("property throttle-cmd-norm is not bound").

Hi, Aaron: Wanted to let you know I continue to look into this - you are not the only one
who has reported this. Two comments:

1) Are you using the latest code from JSBSim CVS? (I hope I haven't asked this, yet)

2) Can you send me offline your engine, aircraft, autopilot, thruster, and script files?
Using your files might be better/quicker than trying to duplicate a similar setup here
(thought I'm still going to try and do that).

Jon