FGTrim

class jsbsim.FGTrim

The trimming routine for

FGTrim finds the aircraft attitude and control settings needed to maintain the steady state described by the FGInitialCondition object . It does this iteratively by assigning a control to each state and adjusting that control until the state is within a specified tolerance of zero. States include the recti-linear accelerations udot, vdot, and wdot, the angular accelerations qdot, pdot, and rdot, and the difference between heading and ground track. Controls include the usual flight deck controls available to the pilot plus angle of attack (alpha), sideslip angle(beta), flight path angle (gamma), pitch attitude(theta), roll attitude(phi), and altitude above ground. The last three are used for on-ground trimming. The state-control pairs used in a given trim are completely user configurable and several pre-defined modes are provided as well. They are:

• tLongitudinal: Trim wdot with alpha, udot with thrust, qdot with elevator

• tFull: tLongitudinal + vdot with phi, pdot with aileron, rdot with rudder and heading minus ground track (hmgt) with beta

• tPullup: tLongitudinal but adjust alpha to achieve load factor input with SetTargetNlf()

• tGround: wdot with altitude, qdot with theta, and pdot with phi

The remaining modes include**tCustom**, which is completely user defined and tNone.

Note that trims can (and do) fail for reasons that are completely outside the control of the trimming routine itself. The most common problem is the initial conditions: is the model capable of steady state flight at those conditions? Check the speed, altitude, configuration (flaps, gear, etc.), weight, cg, and anything else that may be relevant.

Example usage:

FGFDMExec* FDMExec = new FGFDMExec();

FGInitialCondition* fgic = new FGInitialCondition(FDMExec);
FGTrim fgt(FDMExec, fgic, tFull);
fgic->SetVcaibratedKtsIC(100);
fgic->SetAltitudeFtIC(1000);
fgic->SetClimbRate(500);
if( !fgt.DoTrim() ) {
  std::cout << "Trim Failed" << std::endl;
}
fgt.Report();