Metrics on ROLL PITCH and YAW

[memy009]

Good morning everyone,

Can someone explain to me what are 'metrics/bw-ft', 'metrics/cbarw-ft' and why the table 'metrics bw-ft' is used both for the YAW and the ROLL.

Thank U.

<axis name="ROLL">

        <function name="aero/moment/ROLL__CMl">

            <description>ROLL from CMl</description>

            <product>

                <property>aero/qbar-area</property>

                <property>metrics/bw-ft</property>

                <property>aero/coefficient/CMl</property>

            </product>

        </function>

        <function name="aero/moment/ROLL__Rotor">

            <description>ROLL from CMl</description>

            <product>

                <property>aero/force/M_FL_1</property>

                <property>aero/force/M_FL_2</property>

                <property>aero/force/M_FL_3</property>

                <property>aero/force/M_FL_4</property>

                <property>aero/force/M_FR_1</property>

                <property>aero/force/M_FR_2</property>

                <property>aero/force/M_FR_3</property>

                <property>aero/force/M_FR_4</property>

                <property>aero/force/M_AL_1</property>

                <property>aero/force/M_AL_2</property>

                <property>aero/force/M_AL_3</property>

                <property>aero/force/M_AL_4</property>

                <property>aero/force/M_AR_1</property>

                <property>aero/force/M_AR_2</property>

                <property>aero/force/M_AR_3</property>

                <property>aero/force/M_AR_4</property>

            </product>

    </axis>



    <axis name="PITCH">

        <function name="aero/moment/PITCH__CMm">

            <description>PITCH from CMm</description>

            <product>

                <property>aero/qbar-area</property>

                <property>metrics/cbarw-ft</property>

                <property>aero/coefficient/CMm</property>

            </product>

        </function>

    </axis>



    <axis name="YAW">

        <function name="aero/moment/YAW__CMn">

            <description>YAW from CMn</description>

            <product>

                <property>aero/qbar-area</property>

                <property>metrics/bw-ft</property>

                <property>aero/coefficient/CMn</property>

            </product>

    </axis>

        </function>

    </axis>

[seanmcleod]

Are you familiar with how aerodynamic coefficients are defined?

Here are a couple of definitions for some of them, and in particular how they're defined for the pitch, yaw and roll axes.

And now the nomenclature mapping between the textbook symbols and the names in JSBSim.

PropertyManager->Tie("metrics/Sw-sqft", this, &FGAircraft::GetWingArea, &FGAircraft::SetWingArea);
PropertyManager->Tie("metrics/bw-ft", this, &FGAircraft::GetWingSpan);
PropertyManager->Tie("metrics/cbarw-ft", this, &FGAircraft::Getcbar);

So take an example from the 737 model.

            <function name="aero/coefficient/Cmalpha">
                <description>Pitch_moment_due_to_alpha</description>
                <product>
                    <property>aero/qbar-psf</property>
                    <property>metrics/Sw-sqft</property>
                    <property>metrics/cbarw-ft</property>
                    <property>aero/alpha-rad</property>
                    <value>-0.6</value>
                </product>
            </function>

[memy009]

I'm not familiar with these. Thank U for the response.

[seanmcleod]

If you're going to try and understand existing JSBSim FDMs and want to be able to edit them you'll need to become familiar with them.

[memy009]

Yes I'm trying to, I wanted to be sure because I'm currently documenting some xml's (trying to understand them) ... So I prefer to be sure with y'all ...