PHI - Position and Homing Indicator: Difference between revisions

When you look at the cockpit of the [[http://wiki.flightgear.org/FIAT_G91R1B FIAT G91]] (but also of the F104) you can see in the center at the top a very particular instrument, particularly large and with 4 knobs on the sides. That instrument was one of the first navigation systems that used Doppler radar to determine ground speed.<BR>The accuracy of the instrument was, for those times, rather high, as it allowed to travel a long route up to 999 miles with a deviation in the position of the aircraft of 2-3%, a contained error that could be exploited both for flights both military and civilian in the transatlantic route, and in tactical flight in enemy territory or in areas with little radio assistance coverage. However, the real disadvantage in military use was that the instrument allowed to achieve this accuracy only with the use of the doppler radar, in the event that the pilot had disengaged the radar device, in order to be less visible to the enemy, the accuracy decreased a lot and was linked to the real knowledge of the local weather situation.

Programming The instrument allows you to sequentially follow up to 5 routes stored in the '' Station Selector '' (unit with the code NCU located to the right of the pilot). A route consists of two values: N-S and E-W coordinates measured in air miles of the next point <ref name = "AD091920"/>. The NCU allowed the insertion of a box containing 4 multiturn resistors (10 turns) to enter the distance N-S and other 4 multiturn resistors to enter the distance E-W. Once the route was planned, the navigator made a list of max. 5 pairs of coordinates, the first pair was not inserted into the device, but only communicated to the pilot, who set it on the display, the other 4 pairs were set by a technician using a special programming device and a screwdriver that turned the potentiometers placed on the programming box. The cassette could be inserted into the compartment with a light pressure and extracted using the ''release'' button <ref name="release">The ''release'' button in the G91R1B works, and then ejects/retracts the program cassette.</ref> dell NCU unit.<br>Programming The instrument allows sequentially follow up to 5 routes stored in the ''Station Selector'' (unit with the code NCU located to the right of the pilot). A route consists of two values: N-S and E-W coordinates measured in air miles of the next point <ref name = "AD091920"/>.<br>In the simulation, as will see later, the two coordinates have been replaced by a distance and an angle (heading), with respect to the geographic North. In this way it is possible to quickly integrate the polar coordinate programming method of the routes obtained from the route manager of the FGFS program with the N-S and E-W system used by the PHI.

To load the data into the PHI table (in fact it is as if you were programming the "Selector Unit Programmer" ('''NCU''') portable cassette, just click on the [Activate] button of the '''RM'''. you go now on the menu [''Fiat G91''] followed by [''PHI - route system''] opens a window showing various parameters among which we highlight 5 columns that correspond to the 5 'buttons '''NCU''', these columns have been filled in by the distance to cover, the direction and finally the altitude of the flight obtained by the Route Manager (if the altitude is zero in the '''RM''' this is set to 15,000 ft).

In reality the 5 columns corresponded to the programming of only 4 columns, the first was set manually by the pilot.