Re: [Flightgear-devel] Static port and altimeter
The static system itself needs a little more work, including support for multiple static ports, sideslip errors, and alternate air (from inside the cabin); those won't be hard to add, but if anyone (Alex?) wants to take a look at src/System/static.[ch]xx and add them in before I have a chance, feel free. Note that any improvements to the static system automatically propagate themselves to the instruments. You need to handle the special case of large dt (as well as negative) more carefully ... for the same reasons as I did in Steam's function. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
On Fri, 2002-09-27 at 15:09, Alex Perry wrote: The static system will probably be more challenging as that's where most of the subtle errors seem to crop up. Cessna gives tables relating IAS to CAS (which is largely the static source error). If that's standard practice, incorporating a table read-in and lookup might be a good idea. I don't think so. Static source errors occur mostly 1. In slips, especially for aircraft with one static port 2. When alternate static (i.e. cockpit) is selected Pitot source errors occur mostly 1. In slips, especially in full forward slips 2. At unusual angles of attack, especially no-flap slow flight And so, I stand by my statement. Most of the time the static errors are the ones that you need to worry about. You don't spend alot of time at either high angles of attack or high sideslip angles. The IAS calibration table is mostly for pitot, due to angle of attack. The ALT calibration table is mostly for static, due to the alternate. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel -- Tony Peden [EMAIL PROTECTED] We all know Linux is great ... it does infinite loops in 5 seconds. -- attributed to Linus Torvalds ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Alex Perry writes: The static system itself needs a little more work, including support for multiple static ports, sideslip errors, and alternate air (from inside the cabin); those won't be hard to add, but if anyone (Alex?) wants to take a look at src/System/static.[ch]xx and add them in before I have a chance, feel free. Note that any improvements to the static system automatically propagate themselves to the instruments. You need to handle the special case of large dt (as well as negative) more carefully ... for the same reasons as I did in Steam's function. Yes, if you use an int and track time in increments of 1 / 1,000,000 then you get about 30 minutes before you hit an anomaly. This bug caused problem in the past such as radio station searches to only happen every other 30 minute period, or panel text to stop updating. You have to be very careful to think through the amount of possible time accumulation when doing the math. This is a subtle bug because when you are developing code, you rarely test for more than a few seconds at a time. That said, I haven't looked closely to see if any of these problems are in the latest code ... but it's something to keep in mind when dealing with time sensitive code. Curt. -- Curtis Olson IVLab / HumanFIRST Program FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Alex Perry writes: You need to handle the special case of large dt (as well as negative) more carefully ... for the same reasons as I did in Steam's function. Nice timing. In fact, I copied your low-pass function into Main/utils.[ch]xx just a short while ago and am now using it. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Curtis L. Olson writes: Yes, if you use an int and track time in increments of 1 / 1,000,000 then you get about 30 minutes before you hit an anomaly. This bug caused problem in the past such as radio station searches to only happen every other 30 minute period, or panel text to stop updating. You have to be very careful to think through the amount of possible time accumulation when doing the math. This is a subtle bug because when you are developing code, you rarely test for more than a few seconds at a time. That said, I haven't looked closely to see if any of these problems are in the latest code ... but it's something to keep in mind when dealing with time sensitive code. Yep there is a problem if you try to run a FGFS session on a Windows box much over 49 days :-) Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Tony Peden writes: And so, I stand by my statement. Most of the time the static errors are the ones that you need to worry about. You don't spend alot of time at either high angles of attack or high sideslip angles. Unfortunately, the little bit of time you do spend in heavy sideslips and forward slips is the part of the flight where airspeed margins are tightest: final approach. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Curtis L. Olson writes: Yes, if you use an int and track time in increments of 1 / 1,000,000 then you get about 30 minutes before you hit an anomaly. This bug caused problem in the past such as radio station searches to only happen every other 30 minute period, or panel text to stop updating. You have to be very careful to think through the amount of possible time accumulation when doing the math. This is a subtle bug because when you are developing code, you rarely test for more than a few seconds at a time. That said, I haven't looked closely to see if any of these problems are in the latest code ... but it's something to keep in mind when dealing with time sensitive code. Since we pass a dt rather than a counter, it shouldn't be a problem. By the way, I modified main.cxx so that dt=0 whenever the clock is frozen -- that way, the instruments don't keep settling (or drifting) during a pause. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Norman Vine writes: Yep there is a problem if you try to run a FGFS session on a Windows box much over 49 days :-) I wouldn't know anything about that, and far be it from me to blatantly bash windows, but if you manage to have your windows box run that long, I'd definitely recommond that you also consider buying lottery tickets, ask your boss for a big promotion, and try googling for britany spear's home number; that kind of luck just doesn't come around every day. :-) Curt. -- Curtis Olson IVLab / HumanFIRST Program FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
David Megginson writes: And so, I stand by my statement. Most of the time the static errors are the ones that you need to worry about. You don't spend alot of time at either high angles of attack or high sideslip angles. Unfortunately, the little bit of time you do spend in heavy sideslips and forward slips is the part of the flight where airspeed margins are tightest: final approach. This is relevant to the discussion (thanks, Google): http://flighttest.navair.navy.mil/unrestricted/FTM108/c2.pdf Here's an excerpt: Errors in total pressure caused by the angle of incidence of a probe to the relative wind are negligible for most flight conditions. Commonly used probes produce no significant errors at angles of attack or sideslip up to approximately 20°. With proper placement, design, and good leak checks of the pitot probe, zero total pressure error is assumed. If any of the engineers on the list want to read all 89 pages and distill it down to something I can actually use, I will be very grateful. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Curtis L. Olson Norman Vine writes: Yep there is a problem if you try to run a FGFS session on a Windows box much over 49 days :-) I wouldn't know anything about that, and far be it from me to blatantly bash windows, but if you manage to have your windows box run that long, I'd definitely recommond that you also consider buying lottery tickets, ask your boss for a big promotion, and try googling for britany spear's home number; that kind of luck just doesn't come around every day. :-) Hmm... I can''t rememeber crashing this box in a long time and if it wasn't for needing to reboot in order to access the CVS ... Oh right I don't need to do that anymore :-) So remind me to send you one of these in a cople of months :-) 510 src $ cat /proc/uptime 263847.38 237946.24 511 src $ uname CYGWIN_NT-5.0 Cheers Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Norman Vine writes: Hmm... I can't rememeber crashing this box in a long time and if it wasn't for needing to reboot in order to access the CVS ... Oh right I don't need to do that anymore :-) So remind me to send you one of these in a cople of months :-) 510 src $ cat /proc/uptime 263847.38 237946.24 511 src $ uname CYGWIN_NT-5.0 I'll send you a dollar in advance so you can buy me a lottery ticket on that day. :-) Curt. -- Curtis Olson IVLab / HumanFIRST Program FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Static port and altimeter
Alex Perry wrote: Pitot source errors occur mostly 1. In slips, especially in full forward slips 2. At unusual angles of attack, especially no-flap slow flight IIRC, I read that the EuroFighter uses a system which selects the best source of data for this stuff taking into account the last good orientation, speed of the aircraft and direction data. Does this sound right or am I suffering from long term memory problems again ?! Regards, Matt. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
