📄 gravity.htm
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<TITLE>FDC help: Gravity</TITLE>
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<H2>Subsystem <I><FONT FACE="Arial","Helvetica","Sans Serif">Gravity</FONT></I></H2>
<I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">Gravity</FONT></I> is a masked S<SMALL>IMULINK</SMALL> subsystem, contained in the system <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="gravity.htm">Beaver</A></FONT></I>. It is used to compute the forces along the aircraft's body axes, which arise due to gravity. The acceleration of gravity, <I>g</I>,is extracted from the outputvector of the masked subsystem <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="atmosph.htm">Atmosph</A></FONT></I>. The outputs from <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">Gravity</FONT></I> are sent to the block <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="fmsort.htm">FMsort</A></FONT></I>.
<H3>Inputvectors: <I>x</I> and <I>yatm</I></H3>
<PRE> x = [V alpha beta p q r psi theta phi xe ye H]' (states)
yatm = [rho ps T mu g]' (atmospheric properties, computed in
the block <A HREF="atmosph.htm">Atmosph</A>)
{V : airspeed [m/s] }
{alpha: angle of attack [rad] }
{beta : sideslip angle [rad] }
{p : roll rate [rad/s] }
{q : pitch rate [rad/s] }
{r : yaw rate [rad/s] }
{psi : yaw angle [rad] }
theta: pitch angle [rad]
phi : roll angle [rad]
{xe : x-coordinate in Earth-fixed reference frame [m] }
{ye : y-coordinate '' '' '' '' [m] }
{H : altitude above sea-level [m] }
{rho : airdensity [kg/m^3] }
{ps : static pressure [N/m^2] }
{T : temperature [K] }
{mu : dynamic viscosity [kg/(m*s)] }
g : acceleration of gravity [m/s^2]
</PRE>
The inputsignals which are not actually used by <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">Gravity</FONT></I> have been put between accolades.
<H3>Outputvector: <I>Fgrav</I></H3>
<PRE>
Fgrav = [Xgr Ygr Zgr]'.
Xgr, Ygr, Zgr: gravity force components along the aircraft's
body-axes [N].
</PRE>
<H3>Parameters to be defined in the M<SMALL>ATLAB</SMALL> Workspace.</H3>
<I>GM1</I>: vector with some important geometrical properties of the 'Beaver' aircraft, and its mass (which is assumed to be constant during the motions of interest). Here, the mass <I>m</I> is extracted from <I>GM1</I>. The vector <I>GM1</I> can be loaded into the workspace from file by running the utility <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="loader.htm">LOADER</A></FONT></I>. Run <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="modbuild.htm">MODBUILD</A></FONT></I> first if the datafile does not yet exist.
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