Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
Andy Ross wrote: Melchior FRANZ wrote: 1. YASim delivers a positive /velocities/airspeed-kt on backward flight. This strikes me as correct behavior. If you stick a pitot tube into an airstream backwards, you will get exactly the same reading as forward (well, modulo viscosity and mach effects). With a certain understanding of gas dynamics this is hard to believe. Do you have any pointer that backs your assumption ? Cheers, Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- - This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
On Mon, 17 Jul 2006, Melchior FRANZ wrote: Seems that there are two bugs that make the bo105 ASI show positive speeds when flying backwards: 1. YASim delivers a positive /velocities/airspeed-kt on backward flight. The second is easy to fix, but I have no idea about the first. /orientation/side-slip-* - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
* Joacim Persson -- Monday 17 July 2006 10:00: On Mon, 17 Jul 2006, Melchior FRANZ wrote: 1. YASim delivers a positive /velocities/airspeed-kt on backward flight. The second is easy to fix, but I have no idea about the first. /orientation/side-slip-* So, as you didn't bother to write a whole sentence and leave the interpretation to the reader, which I find quite annoying, is it the following what you are trying to say: YASim is right, (airspeed-kt) is *not* meant to be forward-speed and has to be interpreted together with the side-slip angle, and it's really a bug in Systems/pitot.cxx only, because it isn't doing that? Or was it just an accident with your email program? m. - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
Melchior Seems that there are two bugs that make the bo105 ASI show positive speeds when flying backwards: 1. YASim delivers a positive /velocities/airspeed-kt on backward flight. 2. Systems/pitot.cxx wouldn't handle negative values correctly, anyway, as it squares the speed without checking for negatives. The second is easy to fix, but I have no idea about the first. A pitot tube compares the pressure along the _forward_ axis of the tube, caused by forward flight, with the static pressure. I don't think such a device will measure the speed backwards. It is only accurate when the airflow is co-axial with the tube. You need some other device to measure backward velocity. In the only case with which I am familiar (Westland Wessex HAS1 and 3) there was a Doppler radar. Used to get into difficulties over calm seas when attempting an auto-hover IIRC. Vivian - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
* Vivian Meazza -- Monday 17 July 2006 12:30: Melchior 2. Systems/pitot.cxx wouldn't handle negative values correctly, anyway, as it squares the speed without checking for negatives. A pitot tube compares the pressure along the _forward_ axis of the tube, I know, and this was not the question. The problem now is that it delivers (positive) pressure when flying backwards, and the question was if it's a pitot bug *only*, or also a YASim bug. I guess Andy will finally be able to answer that question. m. - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
On Mon, 17 Jul 2006, Melchior FRANZ wrote: /orientation/side-slip-* So, as you didn't bother to write a whole sentence and leave the interpretation to the reader, which I find quite annoying, is it the following what you are trying to say: YASim is right, (airspeed-kt) is *not* meant to be forward-speed and has to be interpreted together with the side-slip angle, and it's really a bug in Systems/pitot.cxx only, because it isn't doing that? Or was it just an accident with your email program? I'm trying to help you solve a problem and you're biting my head off. But hey, it's Monday so knock yourself out. ;) (I assumed you were proficent in basic trigonometry -- why I didn't bother to go into further details on how to tell the difference from forward and backwards flight using a sideslip angle value.) Think about this way: Why should airspeed (true, not indicated by a pitot or other device) be visavi a particular direction of the aircraft in the sim (in /general/)? What shows up on the instrument depends on the design and placement of the probe. Obviously, there is no general formula there which will fit every possible simulated aircraft model, so it's a job for the model designer to create a realistic instrument for the aircraft in question. Sideslip is of course not the only factor affecting the indicated value from the pitot, but it's a start. What I wonder now is how airspeed is measured, techincally, on aircrafts like the Harrier -- or the Chinook. Do they have extra pitot tubes pointing 360° around? Since the Chinook has a speed limit of 50kts when flying backwards, it better show up on some instrument on the dashboard so the pilot can respect the backward flight speed limit. (According to the pilots it's even possible to do an ILS departure on autopilot flying backwards with it.) - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
* Vivian Meazza -- Monday 17 July 2006 12:30: You need some other device to measure backward velocity. I implemented a radar doppler based drift indicator already a few weeks ago, thanks. But we are speaking about a display error in the ASI. m. - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] ASI: YASim Systems/pitot bug ?
Melchior FRANZ wrote: 1. YASim delivers a positive /velocities/airspeed-kt on backward flight. This strikes me as correct behavior. If you stick a pitot tube into an airstream backwards, you will get exactly the same reading as forward (well, modulo viscosity and mach effects). If what you want are the actual airstream velocity with direction, those are provided as a 3 element vector. If the gauge in the actual aircraft is bidirectional, it's probably because it's a special design and you'll need to model that separately. Andy - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnkkid=120709bid=263057dat=121642 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
