On 02/25/2007 12:32 PM, Alex Perry wrote: > There are three types of altimeter in common use: (1) Air data computers, > which go to a lot of > trouble to report the instantaneous value.
Right. > Aircraft with such instruments should use the > "environment" value, Is that a typo? I don't know of any "environment" variable relevant to altitude other than /environment/pressure-inhg. Using that bypasses the lag associated with the /systems/static/pressure-inhg which seems like a small and unimportant part of the overall air-data task. It also bypasses the /systems/static/serviceable check, which seems like a bad idea. There is no reason to have a long lag in the static system. It's unrealistic, as you can verify by /gently/ blowing a breath of air /towards/ the static port while somebody observed the airspeed indication. The response time is very fast. I did say gently, right? I did say towards the static port, so as not to make a tight seal, so as not to create very much pressure, right? Let's just get rid of the long static-system lag. > (2) Basic barometric altimeters, which should have a long lag (second or so, > in my experience). Small aircraft manufactured before the 1970s tend to have > these, I believe, > and this behavior is modelled by the "systems" value, I'm moderately happy to say I've never seen an altimeter with such a long lag. > (3) Corrected barometric altimeters, which > have a relatively short lag that is just about observable by eye (therefore > presumably around a > tenth of a second) when operated in an IFR-like way. Small aircraft of > recent manufacture tend > to have these, unless the aircraft is aerobatic. As far as I know, we don't > have a model for this > in FlightGear. > > Correcting altimeters contain a small accelerometer that detects the vertical > component and, > using a small bellows, Really? I know that's how an IVSI works, but I've never seen an altimeter that did that, or needed to do that. Do you have a reference that gives information on that? I get 29 hits from http://www.google.com/search?q=correcting-altimeter only one of which seems even tangentially relevant. Does it perhaps go by another name? Googling for "instanteous altimeter" is not rewarding. Compared to an altimeter, a VSI has a much harder problem. An ordinary VSI (not IVSI) has a verrry annoying time lag, comparable to a student pilot's reaction time, and therefore more-or-less guaranteed to cause confusion and PIO (pilot induced oscillations). ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
