On 2 Jan 2009, at 22:28, Alex Perry wrote: > No. The standard design is based around 3 degrees slope. With that > design, the usable range is 1.4 degrees high, from 2.1 to 3.7 degrees > and offers 0.35 degrees per dot. Therefore, a dot equals 50ft per > mile range from the touchdown zone of the runway. When the standard > design is scaled for terrain or other approach spaces, all that is > modified is where the antenna array has the intensity maximuma. > Consequently all those numbers grow by up to 8% or shrink by up to > 16%. > >> From the point of view of implementation in a simulator, just take >> the > actual slope number for a specific runway and combine that with the > aircraft's position to generate a ratio. Repair the ratio to allow > for the side lobes (which as I recall are the standard series with a > negative at 6 and one you can follow at 9). Then pass that ratio to > the instrument implementation. The instrument should probably show > full scale from 0.6 to 1.4 with center at 1.0 and dots at 0.77 0.88 > 1.11 1.23
Okay, trying to steer this back to things I have more of a handle on: - everyone seems agreed that the GS is a 1.4 degree volume, so 0.7 degrees above and below the GS line. And the '0.35' degrees per dot comes up, which basically implies 2 dots from the center line to the 0.7 degree limit. Referring back to the ICAO docs that John Denker posted, and the Mk-VIII manual, which says 0.0875 DDM per dot on the GS, and the ICAO docs say the GS 'sector' is 0.175, and the half- sector is 0.0875. I.e two 'dots' would be the very edge of the sector (0.175 DDM). This is important because the 'soft' alert limit is defined as 1.3 dots, and the hard limit is 2 dots. Which again makes sense, and brings us back to the fact that most high-end GS indicators (Primus, Honeywell/ Boeing) use two dots either side for the indicator. Sooooo .... my inclination is to add the degrees deviation properties as discussed, and to avoid 'dots' in the navradio code, but to add - ddm properties. Obviously I won't touch the existing 'deflection' properties, but I hope over time they'll rot. For the Mk-VIII, I'll convert to 'dots' using the terms defined in the INSTALL manual, which of course match the ICAO 'half-sector' values exactly. I'm not sure where all of this leaves Syd, or other panel designers. Working in DDM seems a little awkward, unless we define the maximum deflection as a property (entirely possible) or provide a normalised version (also entirely possible). A normalised version would probably be the easiest thing to use in simple displays (like in the current C172) but also in glass displays. Comments? James ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
