I see, to recall being a part of the original decision to do body axis only
rotational coeffs. It made all kinds of sense to me then and still does today.
That said, however, I have since learned that stability axis coeffs aren't
that unusual. So, my bottom line is that with the mechanisms already in place,
why wouldn't JSBSim extend that support to the rotational axes?
Tony
Follow your heart, don't give up, and try like hell to not be stupid.
On May 11, 2013, at 10:32 AM, "Jon S. Berndt" <jonsber...@comcast.net> wrote:
> I agree that - at least - we should mention it in the documentation. We could
> hypothetically also accept data in any of the supported frames.
> Unfortunately, a lot of the data present in technical reports
> (NACA/NASA/AIAA) that I have seen is ambiguous as to frame for the rotational
> coefficients. When I get aero data it has usually already been reduced by the
> supplier. I do recall seeing aero data being supplied in stability frame,
> once. By default, we'll always assume rotational coefficients are expressed
> in body frame. We will think about adding support for other frames, but
> another thing I've done is to do the conversion inline as a function in the
> aerodynamics element.
>
> Jon
>
> ----- Reply message -----
> From: "Alan Teeder" <ajtee...@v-twin.org.uk>
> To: "FlightGear developers discussions"
> <flightgear-devel@lists.sourceforge.net>
> Cc: "issues Development" <jsbsim-de...@lists.sourceforge.net>
> Subject: [Jsbsim-devel] [Flightgear-devel] about fdm properties
> Date: Sat, May 11, 2013 9:28 AM
>
>
> 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
> _______________________________________________
> Jsbsim-devel mailing list
> jsbsim-de...@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/jsbsim-devel
> _______________________________________________
> The JSBSim Flight Dynamics Model project
> http://www.JSBSim.org
> _______________________________________________
>
> ------------------------------------------------------------------------------
> 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
> _______________________________________________
> Jsbsim-devel mailing list
> jsbsim-de...@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/jsbsim-devel
> _______________________________________________
> The JSBSim Flight Dynamics Model project
> http://www.JSBSim.org
> _______________________________________________
>
------------------------------------------------------------------------------
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
