In flight navigation the same techniques are used as in general navigation , but with a different weighting. Every aircraft, whether a balloon, glider, powered aircraft or jet aircraft (“jet”) moves at its own speed in three-dimensional space. Therefore, in order to navigate safely, a pilot must be able to carry out the following five determinations:
- Flight attitude determination
- vertical positioning
- Speed detection
- horizontal location
The order of these 5 subtasks corresponds to their average priority in manually controlled aircraft - among other things to ensure correct aerodynamics and airspeed as well as a sufficient altitude above ground. However, the priority can shift (e.g. when using autopilot or at high or very low altitudes). In gliding, for example, the most important target values, altitude and speed, are the motto "speed is half life", which is familiar to every student pilot .
Monitoring the attitude
The determination and periodic monitoring of the flight attitude is no problem during daytime and normal weather conditions.
Under visual flight rules ( Visual Flight Rules , VFR) should the pilot to control the attitude based on the horizon (only LR D CTR) possible and to the floor. With precipitation or heavy haze , it can be much more difficult or even impossible. Even experienced civil or test pilots can be subject to vertigo without seeing the earth . D. H. lose spatial orientation without noticing this in the balance organ or buttocks. The instrument flight rules ( Instrument Flight Rules , IFR) allow cloud or nighttime . The artificial horizon shows the flight position relative to the earth's surface (“direct system”); However, this mostly most important navigation instrument can also be replaced by a combination of turn indicator and level indicator ("indirect system"). The indirect determination of the spatial position requires a good imagination and some experience that has been tested under stress.
The air pressure decreases with increasing altitude . A barometric altimeter on board an aircraft can therefore be used to determine the flight altitude ( altitude serve). Before take-off, the current air pressure of the airport must be reduced to sea level (QNH) on the calibration scale of the altimeter. As a result, the height of the airfield above sea level ( elevation ) is normally displayed to an aircraft standing on the ground . For flights in traffic patterns or near the field, the air pressure ( QFE ) prevailing at the airfield is usually set on the altimeter, since only the relative height above ground is decisive here. With this setting, an aircraft standing on the ground is displayed as zero altitude. From a regionally agreed flight altitude (often 5000 ft or 10000 ft) the altimeter is set to the so-called standard atmosphere (1013.25 mb ) so that the same altitude is displayed in all aircraft to avoid collisions. This setting is then used to fly on so-called flight areas .
A radio altimeter , the altitude of the aircraft, in addition to the ground ( height detect). A radio signal is emitted from the aircraft to the ground, reflected by it and received again by the aircraft. The height can be determined from the duration of the radio signal. However, a usable display is only obtained above level terrain (e.g. the sea), since unevenness on the ground affects the display.
The variometer is used to determine the rate of climb and descent of the aircraft . Here, the pressure difference in the air during ascent or descent is the measure of vertical speed.
The artificial horizon shows the pilot whether and how much his machine is inclined along the longitudinal and transverse axes. The position of the horizon line to the alignment mark corresponds to the actual horizon. The course is determined using a magnetic compass or a compass- guided course gyro .
In the early days of aviation, sight was flown. Church towers, mountains and other bearing points were used to determine the position. This was known in the aviation language under Franzen . Radio location is used today in aircraft with an electrical power supply . By aiming at several transmitters with a directional antenna, the exact course of the aircraft can be determined.
Inertial navigation is completely independent of external signals . Before take-off, the exact position of the aircraft (height above sea level, direction, geographical longitude and latitude) is entered into the on-board computer. Three accelerometers measure every acceleration and thus the course or the change in speed. A computer calculates the information on the display from the data.
One way of positioning is in addition to the various methods of radio navigation , the satellite navigation ( GPS , GLONASS or Galileo ). By aiming at several satellites, you can determine your own position to within a few meters, but the determination of the altitude is less precise. This inaccuracy is due to atmospheric changes in the signal propagation time and occurs particularly over the equator. Cleverly distributed control stations (in Europe the EGNOS system) recognize the inaccuracy and send a correction signal. This is sent free of charge and processed by a so-called DGPS receiver into a cleared signal for the navigation application.
This correction signal is sent too seldom for the requirements of civil aviation. In order for a GNSS to be certified for instrument flight , it must be able to process a coded signal, which is subject to a charge, and which is transmitted much more frequently. Such a (chargeable) reliability service is already planned for Galileo.
A distinction must be made between
- the wind speed according to size and direction,
- the speed relative to the surrounding air and
- the speed over the ground.
The size of the wind speed ( knots ) and the wind direction are provided by the meteorological service. These must be taken into account when planning the flight.
The speed of aircraft relative to the surrounding air is determined by measuring dynamic pressure with the airspeed indicator . The difference between total pressure ( air pressure + pressure due to the movement of the aircraft relative to the air) and static pressure (air pressure) is measured and displayed ( IAS, Indicated Air Speed ). If this speed display is corrected by the air pressure / flight altitude, one speaks of the TAS, (True Airspeed) . This then also serves to determine the speed as a percentage of the speed of sound ( Mach ).
The speed over the ground ( GS, ground speed ) can be calculated from the speed obtained in this way as well as the wind speed and wind direction.
- Jeppesen Sanderson: Private Pilot Study Guide . 2000, ISBN 0-88487-265-3 .
- Jeppesen Sanderson: Private Pilot Manual . 2001, ISBN 0-88487-238-6 .
- Jürgen Mies: Radio navigation . 1999, ISBN 3-613-01648-6 .
- Peter Dogan: The Instrument Flight Training Manual . 1999, ISBN 0-916413-26-8 .
- Walter Air: CVFR textbook . Mariensiel 2001.
- Wolfgang Kühr: The private pilot . Technik II, Volume 3, 1981, ISBN 3-921270-09-X .