Re: [Flightgear-devel] about fdm properties
On 10 May 2013, at 20:59, Stuart Buchanan stuar...@gmail.com wrote: On Fri, May 3, 2013 at 7:07 PM, Alan Teeder wrote: I think that you a right in assuming that the developers are not interested in the FDMs. I posted this a week ago http://sourceforge.net/mailarchive/forum.php?thread_name=C6C640DA467C4D118C9A794C6A46D433%40AlanPCforum_name=flightgear-devel and have not seen a single comment. It exposes a serious problem in JSBSim which affects all Datcom users. Perhaps eye-candy and endless mud slinging about the merits of various renderers is a more interesting subject. I think its more a reflection of the areas of expertise of the active developer right now. I have no academic aerodynamics background and haven't done physics since high school. I've spent some time reading the MIT opencourseware on fluid dynamics but certainly aren't competent to comment on these sorts of issues. In contrast I do have a degree in Computer Science which included modules on graphics, so that's where I can sensibly express opinions. I know that doesn't help at all with the particular issue... And I have (actually almost exactly!) the same academic background as Stuart. Also, I believe the JSBsim list would be a more appropriate place to report such issues. To be clear, it's not that I can't /guess/ at what such code does, and commit patches, but if we later discover breakage, I'm not in a position to fix it myself, using my own skills and knowledge. If this was discovered near release it would be quite disruptive. This is exactly why there's various YASim merge requests pending - it's not that I can say they're 'bad' patches, it's that if they basically work but someone reports YASim regressions in 3 months time, we have to revert each patch to find out the issue, because I (and Stuart, and others) aren't familiar with the code, or the science. James -Stuart -- Learn Graph Databases - Download FREE O'Reilly Book Graph Databases is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- Learn Graph Databases - Download FREE O'Reilly Book Graph Databases is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] about fdm properties
On Fri, 3 May 2013, Alan Teeder wrote: It exposes a serious problem in JSBSim which affects all Datcom users. Isn't it rather a missing feature than a fault in JSBSim? The JSBSim documentation and axis names are fairly clear on that the moments are specified around the yaw, pitch and roll axes (but the origin is at AeroRP rather than at the body frame origin/CoG so additional corrections according to the parallel axis theorem are added based on the distance from AeroRP to the actual CoG). If the DATCOM - JSBSim input translation is faulty (I have no professional grounding in aerodynamics and I cannot tell) the best place to get it addressed might be at the mailing list/group for Bill Galbraith's DATCOM+ program (I think it is the most commonly used way to generate a JSBSim configuration from DATCOM): http://tech.groups.yahoo.com/group/digital_datcom/ Cheers, Anders -- --- Anders Gidenstam WWW: http://gitorious.org/anders-hangar http://www.gidenstam.org/FlightGear/ -- Learn Graph Databases - Download FREE O'Reilly Book Graph Databases is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] about fdm properties
The problem is that it is not documented that JSBSim only accepts body axis derivatives/aero coefficients for the rotary axes. The linear axis has the choice of body or wind/stability axes. I had assumed (wrongly) that as it was not specified, the rotary axes used the same axis frame as the linear axes. The result was an aircraft that was unaccountably uncontrollable at high angles of attack. By posting here I was trying to bring this matter to Flightgear developers attention. I cross posted the same message to JSBSim and Datcom mailing lists. Jon Berndt has replied on the JSBSim list saying I don't recall seeing a set of rotational coefficients given in stability or wind frame. Unfortunately this is far from being the case. In my working life running the research simulator at BAC Weybridge the only body axis data that I can recall being given was for the Concorde, back in 1968/9. All other aircraft that I worked on used wind axis data. Datcom is of particular relevance to JSBSim FDM authors and gives its output in stability axes. Perhaps I should add this to the JSBSim bug list http://sourceforge.net/p/jsbsim/bugs/, but this still has open bugs from 2003/4. What is needed is at minimum is a documentation update. However, due to the number of Datcom based FDMs, it would be better to add full support for stability axes. I have cross-posted this to the JSBSim list. Alan -Original Message- From: Anders Gidenstam Sent: Saturday, May 11, 2013 3:41 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] about fdm properties On Fri, 3 May 2013, Alan Teeder wrote: It exposes a serious problem in JSBSim which affects all Datcom users. Isn't it rather a missing feature than a fault in JSBSim? The JSBSim documentation and axis names are fairly clear on that the moments are specified around the yaw, pitch and roll axes (but the origin is at AeroRP rather than at the body frame origin/CoG so additional corrections according to the parallel axis theorem are added based on the distance from AeroRP to the actual CoG). If the DATCOM - JSBSim input translation is faulty (I have no professional grounding in aerodynamics and I cannot tell) the best place to get it addressed might be at the mailing list/group for Bill Galbraith's DATCOM+ program (I think it is the most commonly used way to generate a JSBSim configuration from DATCOM): http://tech.groups.yahoo.com/group/digital_datcom/ Cheers, Anders -- --- Anders Gidenstam WWW: http://gitorious.org/anders-hangar http://www.gidenstam.org/FlightGear/ -- Learn Graph Databases - Download FREE O'Reilly Book Graph Databases is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- Learn Graph Databases - Download FREE O'Reilly Book Graph Databases is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] about fdm properties
On Fri, May 3, 2013 at 7:07 PM, Alan Teeder wrote: I think that you a right in assuming that the developers are not interested in the FDMs. I posted this a week ago http://sourceforge.net/mailarchive/forum.php?thread_name=C6C640DA467C4D118C9A794C6A46D433%40AlanPCforum_name=flightgear-devel and have not seen a single comment. It exposes a serious problem in JSBSim which affects all Datcom users. Perhaps eye-candy and endless mud slinging about the merits of various renderers is a more interesting subject. I think its more a reflection of the areas of expertise of the active developer right now. I have no academic aerodynamics background and haven't done physics since high school. I've spent some time reading the MIT opencourseware on fluid dynamics but certainly aren't competent to comment on these sorts of issues. In contrast I do have a degree in Computer Science which included modules on graphics, so that's where I can sensibly express opinions. I know that doesn't help at all with the particular issue... -Stuart -- Learn Graph Databases - Download FREE O'Reilly Book Graph Databases is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
[Flightgear-devel] about fdm properties
Hi the quiet mailing list :) here are some questions about the fdm properties : - How come some fdm properties don't have the same meaning, dépending the fdm used? i'm thinking of properties in the following property trees: /accelerations /orientation /velocities /position if you want some examples, you can have a look at the bug reports 202: http://code.google.com/p/flightgear-bugs/issues/detail?id=202 and 901: http://code.google.com/p/flightgear-bugs/issues/detail?id=901 those are properties i needed to use and found buggy, but they could not be the only one affected. - is there anybody among the dev interested in this area of FG anymore? despite the bug report and the solution proposed, nothing change, except the need to have external patch to have this right. - would it be a good idea to document those properties somewhere? if so i can make a list, but i would let the description to english native users. imho, this make FG broken in some area (like hud trajectory marker with jsbsim for the sideslip, or the reported speed in radar2 for yasim planes) but the only comments i got in the bug reports were what will it break to put it right. jano -- Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with 2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] about fdm properties
For the sideslip question there is a well established sign convention. JSBSim at least should follow that exactly as it mechanises the equations of motion that are in use industry wide. The convention is Sideslip is positive when the sideslip is to starboard. In other words Sideslip angle Beta = V/U Note, as ever there can be confusion. The main confusion is between yaw and sideslip. Yaw to port is positive. If the aircraft is given positive yaw, but maintains flight in the original direction, then it will have negative sideslip, as the sideslip is to starboard. I think that you a right in assuming that the developers are not interested in the FDMs. I posted this a week ago http://sourceforge.net/mailarchive/forum.php?thread_name=C6C640DA467C4D118C9A794C6A46D433%40AlanPCforum_name=flightgear-devel and have not seen a single comment. It exposes a serious problem in JSBSim which affects all Datcom users. Perhaps eye-candy and endless mud slinging about the merits of various renderers is a more interesting subject. -Original Message- From: jean pellotier Sent: Friday, May 03, 2013 6:35 PM To: FlightGear developers discussions Subject: [Flightgear-devel] about fdm properties Hi the quiet mailing list :) here are some questions about the fdm properties : - How come some fdm properties don't have the same meaning, dépending the fdm used? i'm thinking of properties in the following property trees: /accelerations /orientation /velocities /position if you want some examples, you can have a look at the bug reports 202: http://code.google.com/p/flightgear-bugs/issues/detail?id=202 and 901: http://code.google.com/p/flightgear-bugs/issues/detail?id=901 those are properties i needed to use and found buggy, but they could not be the only one affected. - is there anybody among the dev interested in this area of FG anymore? despite the bug report and the solution proposed, nothing change, except the need to have external patch to have this right. - would it be a good idea to document those properties somewhere? if so i can make a list, but i would let the description to english native users. imho, this make FG broken in some area (like hud trajectory marker with jsbsim for the sideslip, or the reported speed in radar2 for yasim planes) but the only comments i got in the bug reports were what will it break to put it right. jano -- Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with 2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with 2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] about fdm properties
I did say there is scope for confusion Please amend my post to say yaw to starboard (right) is positive. I lost my pair of green and red socks which normally serve to remind me on this matter. With a red (and green) face. Alan -Original Message- From: Alan Teeder Sent: Friday, May 03, 2013 7:07 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] about fdm properties For the sideslip question there is a well established sign convention. JSBSim at least should follow that exactly as it mechanises the equations of motion that are in use industry wide. The convention is Sideslip is positive when the sideslip is to starboard. In other words Sideslip angle Beta = V/U Note, as ever there can be confusion. The main confusion is between yaw and sideslip. Yaw to port is positive. If the aircraft is given positive yaw, but maintains flight in the original direction, then it will have negative sideslip, as the sideslip is to starboard. I think that you a right in assuming that the developers are not interested in the FDMs. I posted this a week ago http://sourceforge.net/mailarchive/forum.php?thread_name=C6C640DA467C4D118C9A794C6A46D433%40AlanPCforum_name=flightgear-devel and have not seen a single comment. It exposes a serious problem in JSBSim which affects all Datcom users. Perhaps eye-candy and endless mud slinging about the merits of various renderers is a more interesting subject. -Original Message- From: jean pellotier Sent: Friday, May 03, 2013 6:35 PM To: FlightGear developers discussions Subject: [Flightgear-devel] about fdm properties Hi the quiet mailing list :) here are some questions about the fdm properties : - How come some fdm properties don't have the same meaning, dépending the fdm used? i'm thinking of properties in the following property trees: /accelerations /orientation /velocities /position if you want some examples, you can have a look at the bug reports 202: http://code.google.com/p/flightgear-bugs/issues/detail?id=202 and 901: http://code.google.com/p/flightgear-bugs/issues/detail?id=901 those are properties i needed to use and found buggy, but they could not be the only one affected. - is there anybody among the dev interested in this area of FG anymore? despite the bug report and the solution proposed, nothing change, except the need to have external patch to have this right. - would it be a good idea to document those properties somewhere? if so i can make a list, but i would let the description to english native users. imho, this make FG broken in some area (like hud trajectory marker with jsbsim for the sideslip, or the reported speed in radar2 for yasim planes) but the only comments i got in the bug reports were what will it break to put it right. jano -- Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with 2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with 2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with 2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
