Well I will start not with the aircraft model but rather the state, or art of flight simulation:

 

Flight Dynamics Model This box does calculations on:

  • The Aircrafts Frame of Reference
    which is a 3-D Cartesian (orthogonal right-handed) coordinate system (x, y, z),Roll-pitch-yaw.gif

       which is centered (origin) at the rear of the aircraft. Where:

    • ROLL-axis passes through the propeller and tail. (Positive to the nose)
    • PITCH-axis passes though wing tip to wing tip. (Positive to right wing)
    • YAW-axis is a vertical axis, and is perpendicular to both the ROLL-axis, and PITCH-axis. (positive is down)
  • which contains a hierarchical model of the aircraft. In this way parameter data inputs can drive individual parts, such as control surfaces. Also parts may be attached to other parts in such a way that movement of one part will cause movement in an other.

 

 

  • The Local Frame of Reference which is
    a 3-D Cartesian (orthogonal right-handed) coordinate system (x, y, z), whose origin is defined to be the origin of the Aircraft’s Frame of Refence
    • North-axis
    • East-axis
    • Down-axis
  • all so factors such as wind, baro, temp,
    rain, lift, drag, thrust, control surfaces, etc. will factor
    into this module.
  • When the aircraft is flying North (0 roll, 0 pitch, 0 yaw) both Reference Frames will line up.
  • To transform points in the aircraft (AFR) to the LFR you must use matrix math.
  • To find out what attitude the aircraft is in you need to to perform integration on PITCH, ROLL, YAW
  • THIS MODULE Will run @ 100/fps
    • velocity += acceleration * Dt
    • value += velocity * Dt

 

  • Navigation Model This box does calculations on:
  • Earth Frame of Reference, which is a 3-D Cartesian (orthogonal right-handed) coordinate system (x, y, z), and whose origin is defined to be the center of the Earth. The Earth Frame of Reference is encluded here for referance only and only is used when you are off world or in space. So we will skip this step and convert directly to Geocentric (Spherical) Frame of Referance from
    the LFR.
    • Axis of Rotation (x) passes through the North Pole, Center of the Earth, South Pole. (Positive is North)
    • Axis of Prime Meridian (z) passes through the Prime Meridian at the equator and pass out the other side. (Positive is Prime Meridian)
    • Axis of (y) passes 90 deg from the Prime Meridian at the equator and passes out the other side. (Positive is East)
  • Tangential Plane, which is a 3-D Cartesian (orthogonal right-handed) coordinate system (x, y, z), parallel to the LRF and is tangent to the surface of the earth.

 

  • Geocentric Frame of Reference which is a spherical coordinate system, who’s origin is at the center of the earth.
    • Distance from Center of Earth to Aircraft: Ρ = √(x2+y2+z2)
    • Latitude of Aircraft on Earth: arcsin(x/Ρ)
    • Longitude of Aircraft on Earth: arcsin(z/√(y2+z2))

 

  • Geodetic Frame of Reference
    which is a ellipsoid model of the earth, World Geodetic System (WGS84).
  • this box does caululations Dead Reckoning Nav Model this box does calculations on
    • lat-new = (cos(heading)*Dt*V) + lat-cur
    • lon-new = ((sin(heading)*Dt*V)/cos(lat-cur)) + lon-cur

 

Navigation Management / Displays needs the following information when starting (maybe more)

  • Lat, Lon, Alt (from the Flight Dynamics and Nav Models
  • Temp
  • Barometer
  • Time (Zulu) most likely a time stamp, UNIX time would be good..
    The time should be derived from an NTP Server(Network Time Protocol). This would sync all boxes in the world to the same time.
  • Navigation can use ellipsoid models such as WGS84, or others.
  • Navigation can be both entered or displayed in both LAT/LONG or MILL-GRID.
  • Outputs to ADI, HSI, etc.

 

Out The Window(s) Sub-System or The Display Frame of Referance is a 3-D Cartesian (orthogonal right-handed) corrdinate system ( x, y, z ), and whose origin is defined as the pilot’s eye which is a vector in the Aircraft Frame of Rreferance.

  • Up (x) is defined as Up and Down or in the Aircrafts Yaw Axis (positive up)
  • Right (y) is defined in the Aricrafts Pitch Axis (right wing positive )
  • In (z) is defined along the Aircrafts Roll Axis ( Forward is positive )

 

 

keep tuned in more to come

Cris H.

 

Index to NexGen Blog

Flight Simulator 101 or back to college ( part 1 Frames of Reference )