flightgear/src/AIModel/AIFlightPlanCreate.cxx

/******************************************************************************
 * AIFlightPlanCreate.cxx
 * Written by Durk Talsma, started May, 2004.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 **************************************************************************/

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include "AIFlightPlan.hxx"
#include <simgear/math/sg_geodesy.hxx>
#include <simgear/props/props.hxx>
#include <simgear/props/props_io.hxx>

#include <Airports/runways.hxx>
#include <Airports/dynamics.hxx>
#include "AIAircraft.hxx"
#include "performancedata.hxx"

#include <Environment/environment_mgr.hxx>
#include <Environment/environment.hxx>


/* FGAIFlightPlan::create()
 * dynamically create a flight plan for AI traffic, based on data provided by the
 * Traffic Manager, when reading a filed flightplan failes. (DT, 2004/07/10) 
 *
 * This is the top-level function, and the only one that is publicly available.
 *
 */ 


// Check lat/lon values during initialization;
void FGAIFlightPlan::create(FGAIAircraft *ac, FGAirport *dep, FGAirport *arr, int legNr, 
			    double alt, double speed, double latitude, 
			    double longitude, bool firstFlight,double radius, 
			    const string& fltType, const string& aircraftType, 
			    const string& airline)
{ 
  int currWpt = wpt_iterator - waypoints.begin();
  switch(legNr)
    {
      case 1:
      createPushBack(ac, firstFlight,dep, latitude, longitude, 
		     radius, fltType, aircraftType, airline);
      break;
    case 2: 
      createTakeoffTaxi(ac, firstFlight, dep, radius, fltType, aircraftType, airline);
      break;
    case 3: 
      createTakeOff(ac, firstFlight, dep, speed, fltType);
      break;
    case 4: 
      createClimb(ac, firstFlight, dep, speed, alt, fltType);
      break;
    case 5: 
      createCruise(ac, firstFlight, dep,arr, latitude, longitude, speed, alt, fltType);
      break;
    case 6: 
      createDecent(ac, arr, fltType);
      break;
    case 7: 
      createLanding(ac, arr, fltType);
      break;
    case 8: 
      createLandingTaxi(ac, arr, radius, fltType, aircraftType, airline);
      break;
      case 9: 
	createParking(ac, arr, radius);
      break;
    default:
      //exit(1);
      SG_LOG(SG_INPUT, SG_ALERT, "AIFlightPlan::create() attempting to create unknown leg"
	     " this is probably an internal program error");
    }
  wpt_iterator = waypoints.begin()+currWpt;
  leg++;
}

FGAIFlightPlan::waypoint*
FGAIFlightPlan::createOnGround(FGAIAircraft *ac, const std::string& aName, const SGGeod& aPos, double aElev, double aSpeed)
{
  waypoint* wpt = new waypoint;
  wpt->name = aName;
  wpt->longitude = aPos.getLongitudeDeg();
  wpt->latitude = aPos.getLatitudeDeg();
  wpt->altitude  = aElev;
  wpt->speed     = aSpeed; 
  wpt->crossat   = -10000;
  wpt->gear_down = true;
  wpt->flaps_down= true;
  wpt->finished  = false;
  wpt->on_ground = true;
  wpt->routeIndex= 0;
  return wpt;
}

FGAIFlightPlan::waypoint*
FGAIFlightPlan::createInAir(FGAIAircraft *ac, const std::string& aName, const SGGeod& aPos, double aElev, double aSpeed)
{
  waypoint* wpt = new waypoint;
  wpt->name = aName;
  wpt->longitude = aPos.getLongitudeDeg();
  wpt->latitude = aPos.getLatitudeDeg();
  wpt->altitude  = aElev;
  wpt->speed     = aSpeed; 
  wpt->crossat   = -10000;
  wpt->gear_down = false;
  wpt->flaps_down= false;
  wpt->finished  = false;
  wpt->on_ground = false;
  wpt->routeIndex= 0;
  return wpt;
}

FGAIFlightPlan::waypoint*
FGAIFlightPlan::cloneWithPos(FGAIAircraft *ac, waypoint* aWpt, const std::string& aName, const SGGeod& aPos)
{
  waypoint* wpt = new waypoint;
  wpt->name = aName;
  wpt->longitude = aPos.getLongitudeDeg();
  wpt->latitude = aPos.getLatitudeDeg();
  
  wpt->altitude  = aWpt->altitude;
  wpt->speed     = aWpt->speed; 
  wpt->crossat   = aWpt->crossat;
  wpt->gear_down = aWpt->gear_down;
  wpt->flaps_down= aWpt->flaps_down;
  wpt->finished  = aWpt->finished;
  wpt->on_ground = aWpt->on_ground;
  wpt->routeIndex = 0;
  
  return wpt;
}

FGAIFlightPlan::waypoint*
FGAIFlightPlan::clone(waypoint* aWpt)
{
  waypoint* wpt  = new waypoint;
  wpt->name      = aWpt->name;
  wpt->longitude = aWpt->longitude;
  wpt->latitude  = aWpt->latitude;

  wpt->altitude  = aWpt->altitude;
  wpt->speed     = aWpt->speed; 
  wpt->crossat   = aWpt->crossat;
  wpt->gear_down = aWpt->gear_down;
  wpt->flaps_down= aWpt->flaps_down;
  wpt->finished  = aWpt->finished;
  wpt->on_ground = aWpt->on_ground;
  wpt->routeIndex = 0;
  
  return wpt;
}


void FGAIFlightPlan::createDefaultTakeoffTaxi(FGAIAircraft *ac, FGAirport* aAirport, FGRunway* aRunway)
{
  SGGeod runwayTakeoff = aRunway->pointOnCenterline(5.0);
  double airportElev = aAirport->getElevation();
  
  waypoint* wpt;
  wpt = createOnGround(ac, "Airport Center", aAirport->geod(), airportElev, ac->getPerformance()->vTaxi());
  waypoints.push_back(wpt);
  wpt = createOnGround(ac, "Runway Takeoff", runwayTakeoff, airportElev, ac->getPerformance()->vTaxi());
  waypoints.push_back(wpt);	
}

void FGAIFlightPlan::createTakeoffTaxi(FGAIAircraft *ac, bool firstFlight, 
				FGAirport *apt,
				double radius, const string& fltType, 
				const string& acType, const string& airline)
{
  double heading, lat, lon;
  
  // If this function is called during initialization,
  // make sure we obtain a valid gate ID first
  // and place the model at the location of the gate.
  if (firstFlight) {
    if (!(apt->getDynamics()->getAvailableParking(&lat, &lon, 
              &heading, &gateId, 
              radius, fltType, 
              acType, airline)))
    {
      SG_LOG(SG_INPUT, SG_WARN, "Could not find parking for a " << 
       acType <<
       " of flight type " << fltType <<
       " of airline     " << airline <<
       " at airport     " << apt->getId());
    }
  }
  
  string rwyClass = getRunwayClassFromTrafficType(fltType);

  // Only set this if it hasn't been set by ATC already.
  if (activeRunway.empty()) {
      //cerr << "Getting runway for " << ac->getTrafficRef()->getCallSign() << " at " << apt->getId() << endl;
      double depHeading = ac->getTrafficRef()->getCourse();
      apt->getDynamics()->getActiveRunway(rwyClass, 1, activeRunway, depHeading);
  }
  rwy = apt->getRunwayByIdent(activeRunway);
  SGGeod runwayTakeoff = rwy->pointOnCenterline(5.0);

  FGGroundNetwork* gn = apt->getDynamics()->getGroundNetwork();
  if (!gn->exists()) {
    createDefaultTakeoffTaxi(ac, apt, rwy);
    return;
  }
  
  intVec ids;
  int runwayId = gn->findNearestNode(runwayTakeoff);

  // A negative gateId indicates an overflow parking, use a
  // fallback mechanism for this. 
  // Starting from gate 0 in this case is a bit of a hack
  // which requires a more proper solution later on.
  delete taxiRoute;
  taxiRoute = new FGTaxiRoute;

  // Determine which node to start from.
  int node = 0;
  // Find out which node to start from
  FGParking *park = apt->getDynamics()->getParking(gateId);
  if (park) {
    node = park->getPushBackPoint();
  }
  
  if (node == -1) {
    node = gateId;
  }
  
  // HAndle case where parking doens't have a node
  if ((node == 0) && park) {
    if (firstFlight) {
      node = gateId;
    } else {
      node = lastNodeVisited;
    }
  }

  *taxiRoute = gn->findShortestRoute(node, runwayId);
  intVecIterator i;
	 
  if (taxiRoute->empty()) {
    createDefaultTakeoffTaxi(ac, apt, rwy);
    return;
  }
  
  taxiRoute->first();
  //bool isPushBackPoint = false;
  if (firstFlight) {
    // If this is called during initialization, randomly
    // skip a number of waypoints to get a more realistic
    // taxi situation.
    int nrWaypointsToSkip = rand() % taxiRoute->size();
    // but make sure we always keep two active waypoints
    // to prevent a segmentation fault
    for (int i = 0; i < nrWaypointsToSkip-2; i++) {
      taxiRoute->next(&node);
    }
    apt->getDynamics()->releaseParking(gateId);
  } else {
    if (taxiRoute->size() > 1) {
      taxiRoute->next(&node); // chop off the first waypoint, because that is already the last of the pushback route
    }
  }
  
  // push each node on the taxi route as a waypoint
  int route;
  while(taxiRoute->next(&node, &route)) {
		char buffer[10];
		snprintf (buffer, 10, "%d", node);
		FGTaxiNode *tn = apt->getDynamics()->getGroundNetwork()->findNode(node);
    waypoint* wpt = createOnGround(ac, buffer, tn->getGeod(), apt->getElevation(), ac->getPerformance()->vTaxi());
    wpt->routeIndex = route;
		waypoints.push_back(wpt);
  }
}

void FGAIFlightPlan::createDefaultLandingTaxi(FGAIAircraft *ac, FGAirport* aAirport)
{
  SGGeod lastWptPos = 
    SGGeod::fromDeg(waypoints.back()->longitude, waypoints.back()->latitude);
  double airportElev = aAirport->getElevation();
  
  waypoint* wpt;
  wpt = createOnGround(ac, "Runway Exit", lastWptPos, airportElev, ac->getPerformance()->vTaxi());
  waypoints.push_back(wpt);	
  wpt = createOnGround(ac, "Airport Center", aAirport->geod(), airportElev, ac->getPerformance()->vTaxi());
  waypoints.push_back(wpt);
  
  double heading, lat, lon;
  aAirport->getDynamics()->getParking(gateId, &lat, &lon, &heading);
  wpt = createOnGround(ac, "END", SGGeod::fromDeg(lon, lat), airportElev, ac->getPerformance()->vTaxi());
  waypoints.push_back(wpt);
}

void FGAIFlightPlan::createLandingTaxi(FGAIAircraft *ac, FGAirport *apt,
				double radius, const string& fltType, 
				const string& acType, const string& airline)
{
  double heading, lat, lon;
  apt->getDynamics()->getAvailableParking(&lat, &lon, &heading, 
        &gateId, radius, fltType, acType, airline);
  
  SGGeod lastWptPos = 
    SGGeod::fromDeg(waypoints.back()->longitude, waypoints.back()->latitude);
  FGGroundNetwork* gn = apt->getDynamics()->getGroundNetwork();
  
   // Find a route from runway end to parking/gate.
  if (!gn->exists()) {
    createDefaultLandingTaxi(ac, apt);
    return;
  }
  
	intVec ids;
  int runwayId = gn->findNearestNode(lastWptPos);
  // A negative gateId indicates an overflow parking, use a
  // fallback mechanism for this. 
  // Starting from gate 0 is a bit of a hack...
  //FGTaxiRoute route;
  delete taxiRoute;
  taxiRoute = new FGTaxiRoute;
  if (gateId >= 0)
    *taxiRoute = gn->findShortestRoute(runwayId, gateId);
  else
    *taxiRoute = gn->findShortestRoute(runwayId, 0);
  intVecIterator i;
  
  if (taxiRoute->empty()) {
    createDefaultLandingTaxi(ac, apt);
    return;
  }
  
  int node;
  taxiRoute->first();
  int size = taxiRoute->size();
  // Omit the last two waypoints, as 
  // those are created by createParking()
  int route;
  for (int i = 0; i < size-2; i++) {
    taxiRoute->next(&node, &route);
    char buffer[10];
    snprintf (buffer, 10, "%d", node);
    FGTaxiNode *tn = gn->findNode(node);
    waypoint* wpt = createOnGround(ac, buffer, tn->getGeod(), apt->getElevation(), ac->getPerformance()->vTaxi());
    wpt->routeIndex = route;
    waypoints.push_back(wpt);
  }
}

/*******************************************************************
 * CreateTakeOff 
 * A note on units: 
 *  - Speed -> knots -> nm/hour
 *  - distance along runway =-> meters 
 *  - accel / decel -> is given as knots/hour, but this is highly questionable:
 *  for a jet_transport performance class, a accel / decel rate of 5 / 2 is 
 *  given respectively. According to performance data.cxx, a value of kts / second seems
 *  more likely however. 
 * 
 ******************************************************************/
void FGAIFlightPlan::createTakeOff(FGAIAircraft *ac, bool firstFlight, FGAirport *apt, double speed, const string &fltType)
{
    double accel    = ac->getPerformance()->acceleration();
    double vTaxi    = ac->getPerformance()->vTaxi();
    double vRotate  = ac->getPerformance()->vRotate();
    double vTakeoff = ac->getPerformance()->vTakeoff();
    double vClimb   = ac->getPerformance()->vClimb();

    double accelMetric    = (accel * SG_NM_TO_METER) / 3600;
    double vTaxiMetric    = (vTaxi * SG_NM_TO_METER) / 3600;
    double vRotateMetric  = (vRotate * SG_NM_TO_METER) / 3600;
    double vTakeoffMetric = (vTakeoff *  SG_NM_TO_METER) / 3600;
    double vClimbMetric   = (vClimb *  SG_NM_TO_METER) / 3600;
    // Acceleration = dV / dT
    // Acceleration X dT = dV
    // dT = dT / Acceleration
    //d = (Vf^2 - Vo^2) / (2*a)
    //double accelTime = (vRotate - vTaxi) / accel;
    //cerr << "Using " << accelTime << " as total acceleration time" << endl;
    double accelDistance = (vRotateMetric*vRotateMetric - vTaxiMetric*vTaxiMetric) / (2*accelMetric);
    cerr << "Using " << accelDistance << " " << accelMetric << " " << vRotateMetric << endl;
    waypoint *wpt;
    // Get the current active runway, based on code from David Luff
    // This should actually be unified and extended to include 
    // Preferential runway use schema's 
    // NOTE: DT (2009-01-18: IIRC, this is currently already the case, 
    // because the getActive runway function takes care of that.
    if (firstFlight)
    {
        string rwyClass = getRunwayClassFromTrafficType(fltType);
        double heading = ac->getTrafficRef()->getCourse();
        apt->getDynamics()->getActiveRunway(rwyClass, 1, activeRunway, heading);
        rwy = apt->getRunwayByIdent(activeRunway);
    }

    double airportElev = apt->getElevation();
    // Acceleration point, 105 meters into the runway,
    SGGeod accelPoint = rwy->pointOnCenterline(105.0);
    wpt = createOnGround(ac, "accel", accelPoint, airportElev, vRotate);
    waypoints.push_back(wpt);


    accelDistance = (vTakeoffMetric*vTakeoffMetric - vTaxiMetric*vTaxiMetric) / (2*accelMetric);
    cerr << "Using " << accelDistance << " " << accelMetric << " " << vTakeoffMetric << endl;
    accelPoint = rwy->pointOnCenterline(105.0+accelDistance);
    wpt = createOnGround(ac, "rotate", accelPoint, airportElev, vTakeoff);
    waypoints.push_back(wpt);

    accelDistance = ((vTakeoffMetric*1.1)*(vTakeoffMetric*1.1) - vTaxiMetric*vTaxiMetric) / (2*accelMetric);
    cerr << "Using " << accelDistance << " " << accelMetric << " " << vTakeoffMetric << endl;
    accelPoint = rwy->pointOnCenterline(105.0+accelDistance);
    wpt = createOnGround(ac, "rotate", accelPoint, airportElev+1000, vTakeoff*1.1);
    wpt->on_ground = false;
    waypoints.push_back(wpt);

    wpt = cloneWithPos(ac, wpt, "3000 ft", rwy->end());
    wpt->altitude  = airportElev+3000;
    waypoints.push_back(wpt);

    // Finally, add two more waypoints, so that aircraft will remain under
    // Tower control until they have reached the 3000 ft climb point
    SGGeod pt = rwy->pointOnCenterline(5000 + rwy->lengthM() * 0.5);
    wpt = cloneWithPos(ac, wpt, "5000 ft", pt);
    wpt->altitude  = airportElev+5000;
    waypoints.push_back(wpt);
}
  
/*******************************************************************
 * CreateClimb
 * initialize the Aircraft at the parking location
 ******************************************************************/
void FGAIFlightPlan::createClimb(FGAIAircraft *ac, bool firstFlight, FGAirport *apt, double speed, double alt, const string &fltType)
{
  waypoint *wpt;
//  bool planLoaded = false;
  string fPLName;
  double vClimb   = ac->getPerformance()->vClimb();

  if (firstFlight) {
    string rwyClass = getRunwayClassFromTrafficType(fltType);
    double heading = ac->getTrafficRef()->getCourse();
    apt->getDynamics()->getActiveRunway(rwyClass, 1, activeRunway, heading);
    rwy = apt->getRunwayByIdent(activeRunway);
  }
  if (sid) {
    for (wpt_vector_iterator i = sid->getFirstWayPoint(); 
         i != sid->getLastWayPoint(); 
         i++) {
            waypoints.push_back(clone(*(i)));
            //cerr << " Cloning waypoint " << endl;
    }
  } else  {
      SGGeod climb1 = rwy->pointOnCenterline(10*SG_NM_TO_METER);
      wpt = createInAir(ac, "10000ft climb", climb1, vClimb, 10000);
      wpt->gear_down = true;
      wpt->flaps_down= true;
      waypoints.push_back(wpt); 

      SGGeod climb2 = rwy->pointOnCenterline(20*SG_NM_TO_METER);
      wpt = cloneWithPos(ac, wpt, "18000ft climb", climb2);
      wpt->altitude  = 18000;
      waypoints.push_back(wpt); 
   }
}



/*******************************************************************
 * CreateDecent
 * initialize the Aircraft at the parking location
 ******************************************************************/
void FGAIFlightPlan::createDecent(FGAIAircraft *ac, FGAirport *apt, const string &fltType)
{
  // Ten thousand ft. Slowing down to 240 kts
  waypoint *wpt;
  double vDecent   = ac->getPerformance()->vDescent();
  double vApproach = ac->getPerformance()->vApproach();

  //Beginning of Decent
  //string name;
  // allow "mil" and "gen" as well
  string rwyClass = getRunwayClassFromTrafficType(fltType);
  double heading = ac->getTrafficRef()->getCourse();
  apt->getDynamics()->getActiveRunway(rwyClass, 2, activeRunway, heading);
  rwy = apt->getRunwayByIdent(activeRunway);
     
  SGGeod descent1 = rwy->pointOnCenterline(-100000); // 100km out
  wpt = createInAir(ac, "Dec 10000ft", descent1, apt->getElevation(), vDecent);
  wpt->crossat   = 10000;
  waypoints.push_back(wpt);  
  
  // Three thousand ft. Slowing down to 160 kts
  SGGeod descent2 = rwy->pointOnCenterline(-8*SG_NM_TO_METER); // 8nm out
  wpt = createInAir(ac, "DEC 3000ft", descent2, apt->getElevation(), vApproach);
  wpt->crossat   = 3000;
  wpt->gear_down = true;
  wpt->flaps_down= true;
  waypoints.push_back(wpt);
}
/*******************************************************************
 * CreateLanding
 * initialize the Aircraft at the parking location
 ******************************************************************/
void FGAIFlightPlan::createLanding(FGAIAircraft *ac, FGAirport *apt, const string &fltType)
{
  double vTouchdown   = ac->getPerformance()->vTouchdown();
  double vTaxi        = ac->getPerformance()->vTaxi();

  string rwyClass = getRunwayClassFromTrafficType(fltType);
  double heading = ac->getTrafficRef()->getCourse();
  apt->getDynamics()->getActiveRunway(rwyClass, 2, activeRunway, heading);
  rwy = apt->getRunwayByIdent(activeRunway);
  

  waypoint *wpt;
  double aptElev = apt->getElevation();

  SGGeod coord;
  char buffer[12];
  for (int i = 1; i < 10; i++) {
      snprintf(buffer, 12, "wpt%d", i);
      coord = rwy->pointOnCenterline(rwy->lengthM() * (i/10.0));
      wpt = createOnGround(ac, buffer, coord, aptElev, (vTouchdown/i));
      wpt->crossat = apt->getElevation();
      waypoints.push_back(wpt); 
  }

  /*
  //Runway Threshold
  wpt = createOnGround(ac, "Threshold", rwy->threshold(), aptElev, vTouchdown);
  wpt->crossat = apt->getElevation();
  waypoints.push_back(wpt); 

 // Roll-out
  wpt = createOnGround(ac, "Center", rwy->geod(), aptElev, vTaxi*2);
  waypoints.push_back(wpt);

  SGGeod rollOut = rwy->pointOnCenterline(rwy->lengthM() * 0.9);
  wpt = createOnGround(ac, "Roll Out", rollOut, aptElev, vTaxi);
  wpt->crossat   = apt->getElevation();
  waypoints.push_back(wpt); 
  */
}

/*******************************************************************
 * CreateParking
 * initialize the Aircraft at the parking location
 ******************************************************************/
void FGAIFlightPlan::createParking(FGAIAircraft *ac, FGAirport *apt, double radius)
{
  waypoint* wpt;
  double aptElev = apt->getElevation();
  double lat = 0.0, lat2 = 0.0;
  double lon = 0.0, lon2 = 0.0;
  double az2 = 0.0;
  double heading = 0.0;

  double vTaxi        = ac->getPerformance()->vTaxi();
  double vTaxiReduced = vTaxi * (2.0/3.0);
  apt->getDynamics()->getParking(gateId, &lat, &lon, &heading);
  heading += 180.0;
  if (heading > 360)
    heading -= 360; 
  geo_direct_wgs_84 ( 0, lat, lon, heading, 
 		      2.2*radius,           
 		      &lat2, &lon2, &az2 );
  wpt = createOnGround(ac, "taxiStart", SGGeod::fromDeg(lon2, lat2), aptElev, vTaxiReduced);
  waypoints.push_back(wpt);
  
  geo_direct_wgs_84 ( 0, lat, lon, heading, 
 		      0.1 *radius,           
 		      &lat2, &lon2, &az2 );
          
  wpt = createOnGround(ac, "taxiStart2", SGGeod::fromDeg(lon2, lat2), aptElev, vTaxiReduced);
  waypoints.push_back(wpt);   

  wpt = createOnGround(ac, "END", SGGeod::fromDeg(lon, lat), aptElev, vTaxiReduced);
  waypoints.push_back(wpt);
}

/**
 *
 * @param fltType a string describing the type of
 * traffic, normally used for gate assignments
 * @return a converted string that gives the runway
 * preference schedule to be used at aircraft having
 * a preferential runway schedule implemented (i.e.
 * having a rwyprefs.xml file
 * 
 * Currently valid traffic types for gate assignment:
 * - gate (commercial gate)
 * - cargo (commercial gargo),
 * - ga (general aviation) ,
 * - ul (ultralight),
 * - mil-fighter (military - fighter),
 * - mil-transport (military - transport)
 *
 * Valid runway classes:
 * - com (commercial traffic: jetliners, passenger and cargo)
 * - gen (general aviation)
 * - ul (ultralight: I can imagine that these may share a runway with ga on some airports)
 * - mil (all military traffic)
 */
string FGAIFlightPlan::getRunwayClassFromTrafficType(string fltType)
{
    if ((fltType == "gate") || (fltType == "cargo")) { 
	return string("com");
    }
    if (fltType == "ga") {
        return string ("gen");
    }
    if (fltType == "ul") {
        return string("ul");
    }
    if ((fltType == "mil-fighter") || (fltType == "mil-transport")) { 
	return string("mil");
    }
   return string("com");
}