On Fri, Jan 2, 2009 at 3:12 PM, John Denker <j...@av8n.com> wrote: > On 01/02/2009 03:28 PM, Alex Perry wrote: > > >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. > > I agree with all of that. And I have implemented it in the code, > including the extra lobes i.e. false glide slopes. > > =========== > > Tangential remark: I am surprised by this reference: > http://www.freepatentsonline.com/3757338.html > > which alleges > For reasons well known to those skilled in the art but > to minor importance here, the first significant side lobe, > that is a side lobe which comprises a stable false glide > slope indistinguishable from the true glide slope except > for its steepness, occurs at 5A. > > I'm wondering if that's a typo. A 9 degree false glideslope is > more-or-less followable but a 15 degree false GS would be too > steep to be followable without extraordinary effort. I've seen > students actually capture and try to follow a false GS. It's not > easy but it can be done. So I've implemented 6-degree periodicity, > i.e. 3, 6r, 9, 12r, etc. where "r" means reverse sensing. > > OTOH it might not be a typo. I haven't worked out the electrodynamics > of the situation, so I can't be sure what's actually going on.
Nor me. I recall seeing the analysis somewhere (but I don't remember where). It could be that 2A is a null rather than reversed, in which case 3A is the reverse, 4A would be the next null and 5A is indeed the next followable slope. 9 degrees is 1000 fpm for a C172 and is trivially achievable without special effort. 15 degrees implies intentional increase in drag. However, gear down and approach flaps _is_ an increase in drag ... so the additional drag of taking the engine to completely idle may be enough without adding more flaps. ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
