Re: [Flightgear-devel] Wind confusion.
David Megginson [EMAIL PROTECTED] said:
No, that's not right after all. Following a message from Jon Berndt,
I took a peek at the property browser, and the wind-{north|east}-fps
is the to- direction, not the from- direction. JSBSim was using the
from- direction already, while the other FDM's were usign the to-
direction. In any case, the command-line option now works properly,
and all the FDMs behave the same way; it's just that the properties
need to be interpreted differently.
Note that those properties are also writable. This is a good thing since
at some point we'll probably want a way to manipulate weather changes without
restarting.
So, what do we do?
From where i sit the vectors should be from in the properties. Since the
property manager offers a way for non-programmers to affect the way fgfs works
(through xml or other methods), it should be in a term that most users will
understand.
I think we're all on the same page...but what i'm seeing is this:
The code in the last release displayed property values in fps from north or
east when using JSBsim. Those values could be changed during flight to alter
the wind direction or speed during flight. The values entered would be
interpretted as from their respective vectors. IMHO, without getting into
the internals, JSBsim and the interface to it was correct.
Best,
Jim
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Re: [Flightgear-devel] Wind confusion.
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Mon, Feb 18, 2002 at 10:27:58PM +, [EMAIL PROTECTED] wrote: release - both technical and home life. This has given me, at least, some time to think about it and I am going to try something I've had on my mind for a few weeks as a potential solution. But it will still be a short while until I can try it out. We acknowledge, though, that it does not work perfectly now and that this is an important problem to solve. Great! Looking forward to tuning my radios and still find myself on the runway afterwards. - -- Regards, I RADIS, do you? =Martin=http://www.iradis.org/ PGP: FE87448B DDF8 677C 9244 D119 4FE0 AE3A 37CF 3458 FE87 448B From: Martin van Beilen [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Re: [Flightgear-devel] Wind confusion. In-Reply-To: [EMAIL PROTECTED]; from [EMAIL PROTECTED] on Mon, Feb 18, 2002 at 10:27:58PM + X-S-Issue: [EMAIL PROTECTED] 2002/02/19 16:01:22 2c10af63d56441cfcd7134704052e439 -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) iEYEARECAAYFAjxyaMkACgkQN880WP6HRItcTwCfaXp1aD+0GDArGHZ4A+gDAKRn KjEAnj3BxqdO80jf2qcObOj+8mdh4D1w =L7WD -END PGP SIGNATURE- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Sun, Feb 17, 2002 at 04:15:01PM -0600, Jon S. Berndt wrote: We are talking about simulating an aircraft, about an aircraft-centric phenomena, and about a phenomena that is normally reported by humans in a particular way. Sitting on the runway, pointed with a heading of 20 degrees, and with a wind of 20 knots from 20 degrees (as is normally reported, that is, the *from* direction is given), the aircraft sees 20 knots headwind. This equation in FGTranslation shows this nicely: vAeroUVW = vUVW + State-GetTl2b()*Atmosphere-GetWindNED(); You are right. It is a meteorological convention to report wind with a 'from' heading. That's just what it is: a convention. In the same vein, it is a convention to report vertical winds as 'to' headings. Although vertical heading is binary, it is reported as 'to-up', not 'from-down'. So if you want to stick to the meteo conventions, your horizontal components should be 'from' components, while the vertical component should be 'to'. Getting confused yet? :-) Mathematically speaking, it is just a sign issue. Neither way is more 'mathematically correct' than the other. That's why it is possible to debate this topic for years without reaching consensus. My view is simply this: air is a moving body, just like every other moving body. It has a heading and velocity, just like every other moving body. I have no hard arguments for this, it just seems to me the logical way to think of it. I doubt that physicists use from-headings when they model wind as a three-dimensional vector, but I could be wrong. If there is a convention, it is not one used in general meteorology. At least I've never seen any of our local weathermen report wind as North and East components. :-) I know that the wind vector that originates in the NED axis points *at* 200 degrees and that the north component of this vector would be a negative number. But, what happens if you add the aircraft velocity and the wind velocity vectorially? You sure don't get the aircraft total sensed velocity vector. Depends how you define the aircraft's velocity vector. In terms of aerodynamic modelling, the aircraft is 'mounted' on the air, and moves relative to it. Add the wind vector, and you get true ground speed. If you want to go back from true ground speed to relative speed, you subtract the wind. Does that seem awkward to you? Of course you can do it a couple of ways. It just needs to be documented. We have fallen short there, apparently. As a last resort you could rename and clone the wind properties: /environment/wind-down-fps becomes both wind-from-down-fps and wind-to-up-fps. :-) - -- Regards, I RADIS, do you? =Martin=http://www.iradis.org/ PGP: FE87448B DDF8 677C 9244 D119 4FE0 AE3A 37CF 3458 FE87 448B From: Martin van Beilen [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Re: [Flightgear-devel] Wind confusion. In-Reply-To: 005501c1b800$8c154700$[EMAIL PROTECTED]; from [EMAIL PROTECTED] on Sun, Feb 17, 2002 at 04:15:01PM -0600 X-S-Issue: [EMAIL PROTECTED] 2002/02/18 11:20:58 a789bb439a5d67ea956cbb1380001bc5 -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) iEYEARECAAYFAjxw1ZIACgkQN880WP6HRIuQEgCeMGsKbfd2O7Ao9B5TAQSv2nNJ blIAnRqyvQR3gEAW69X4Skxd0HEtF110 =FM8s -END PGP SIGNATURE- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
From: Andy Ross [EMAIL PROTECTED] That is a to vector, by definition. Really, the from convention applies to a 1-dimensional compass direction; I'm not aware of anyone else trying to apply it to a 3D vector environment. Ooh! Yeah, that is a good point about the 3D part of it. It's been a while since I worked on the wind stuff. So, can anyone specify the following: What are/is the way[s] a user can specify wind on the FGFS command line? All I can see is this: --wind=DIR@SPEED: specify wind coming from DIR (degrees) at SPEED (knots) Was there a properties way to do it that is opposite to the above? Perhaps we are given too much power! ;-) Most/all users will only specify a from direction and speed. It would normally (IMHO) be up to the scenery model (giving us the terrain info) and the weather or FDM model to give us the up/down component, would it not? Perhaps the FGInterface object is not preparing the wind components properly for the FDM? I still think our (JSBSim) approach to winds is the most intuitive, but I am open to debate. Tony? Thoughts? Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
From: Martin van Beilen [EMAIL PROTECTED] In the same vein, it is a convention to report vertical winds as 'to' headings. Although vertical heading is binary, it is reported as 'to-up', not 'from-down'. So if you want to stick to the meteo conventions, your horizontal components should be 'from' components, while the vertical component should be 'to'. Getting confused yet? :-) Yes, I finally got this reading Andy's last message. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Jon S. Berndt [EMAIL PROTECTED] said: Was there a properties way to do it that is opposite to the above? Perhaps we are given too much power! ;-) In the /environment path there are variables for wind direction that specify a force value as fps from east and/or north, the sum of which articulate direction and speed I presume. I'm not sure how the translation from the command line degrees vector is done, not to mention if it is done the same way. The DIR vector is displayed in the environment path, if it is given, but I don't think changing it makes a difference after startup. I should double check but IIRC the up/down as represented by viewing the properties is counter-intuitive. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
On Mon, Feb 18, 2002 at 06:58:44AM -0600, Jon S. Berndt wrote:
What are/is the way[s] a user can specify wind on the FGFS command line? All
I can see is this:
--wind=DIR@SPEED: specify wind coming from DIR (degrees) at SPEED (knots)
Correct. And that's the way it *should* be specified.
I did some testing with the command-line option, and it appears
that both LaRCSim and YASim have it backwards. If I start up
heading 270, and specify a wind 270@50, I get _tail_ wind with
these two models. That's weird, because LaRCSim used to get it
right in 0.7.8.
And guess what I discovered when diffing 0.7.8 against 0.7.9? In
Main/options.cxx, around line 900, someone *commented out* the
line dir += 180;, thereby *changing* the definitions of
/environment/wind-{north,east}-fps! Okay, who did that? Just wait
till I get my hands on you! ;-)
Was there a properties way to do it that is opposite to the above? Perhaps
we are given too much power! ;-)
/environment/wind-{north,east,down}-fps
Most/all users will only specify a from direction and speed. It would
normally (IMHO) be up to the scenery model (giving us the terrain info) and
the weather or FDM model to give us the up/down component, would it not?
Or by an external wind model connected through a network
interface.
I still think our (JSBSim) approach to winds is the most
intuitive, but I am open to debate.
Wind heading as set by the user should be *from*.
Vector representations of wind should be *to*. (imho).
- --
Regards, I RADIS, do you?
=Martin=http://www.iradis.org/
PGP: FE87448B DDF8 677C 9244 D119 4FE0 AE3A 37CF 3458 FE87 448B
From: Martin van Beilen [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: Re: [Flightgear-devel] Wind confusion.
In-Reply-To: 001901c1b87b$ff32ebe0$[EMAIL PROTECTED]; from [EMAIL PROTECTED] on
Mon, Feb 18, 2002 at 06:58:44AM -0600
X-S-Issue: [EMAIL PROTECTED] 2002/02/18 17:06:10
9132af46f20dcbed58f8fd6b83ece702
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Re: [Flightgear-devel] Wind confusion.
David Megginson writes:
And guess what I discovered when diffing 0.7.8 against 0.7.9? In
Main/options.cxx, around line 900, someone *commented out* the
line dir += 180;, thereby *changing* the definitions of
/environment/wind-{north,east}-fps! Okay, who did that? Just wait
till I get my hands on you! ;-)
It is now fixed. dir += 180 has been added back in, and the
JSBSim.cxx interface file has been changed to reverse the sense for
JSBSim.
No, that's not right after all. Following a message from Jon Berndt,
I took a peek at the property browser, and the wind-{north|east}-fps
is the to- direction, not the from- direction. JSBSim was using the
from- direction already, while the other FDM's were usign the to-
direction. In any case, the command-line option now works properly,
and all the FDMs behave the same way; it's just that the properties
need to be interpreted differently.
So, what do we do?
All the best,
David
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Re: [Flightgear-devel] Wind confusion.
fgfs --aircraft=c172 --airport-id=KSFO --heading=270 --wind=0@50 The JSBSim C172 actually takes off, weathervanes in the air, then lands again facing north. The LaRCSim C172 flips over, and the UIUC C172 starts sliding smoothly sideways. YASim takes the prize for this one, since it simply weathervanes on the ground until it's facing north, into the wind. I suspect the LaRCSim is the most accurate. It is possible to taxi (carefully) with those winds, but takes considerable planning and operation of the controls to make it work out safely. However, that crosswind is double what the aircraft can manage at takeoff speeds, so the aircraft is likely to flip over as soon as you get a significant groundspeed, unless you manage a lucky skid-yaw turn into the wind. You should try for the intersection with the north runway and use that. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
[EMAIL PROTECTED] writes: Is this now how the system works? The command-line option has always been meant (and documented) to give the from direction. I guess it's still up for grabs how the internal NED properties represent wind. All the best, David -- David Megginson [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Alex Perry writes: fgfs --aircraft=c172 --airport-id=KSFO --heading=270 --wind=0@50 The JSBSim C172 actually takes off, weathervanes in the air, then lands again facing north. The LaRCSim C172 flips over, and the UIUC C172 starts sliding smoothly sideways. YASim takes the prize for this one, since it simply weathervanes on the ground until it's facing north, into the wind. I suspect the LaRCSim is the most accurate. It is possible to taxi (carefully) with those winds, but takes considerable planning and operation of the controls to make it work out safely. The tests were run with the plane stationary, engine at idle, and no brakes applied. In those circumstances, wouldn't a weathervane be most likely? All the best, David -- David Megginson [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
David Megginson writes:
No, that's not right after all. Following a message from Jon Berndt,
I took a peek at the property browser, and the wind-{north|east}-fps
is the to- direction, not the from- direction. JSBSim was using the
from- direction already, while the other FDM's were usign the to-
direction. In any case, the command-line option now works properly,
and all the FDMs behave the same way; it's just that the properties
need to be interpreted differently.
So, what do we do?
Meteo convention is from - hence the command line should use
that.
All fdm writers can use whatever vector convention they wish
internally as long as they document it.
Since the wind-{north|east}-fps property may be accessed by any
fdm it should follow a clearly documented convention - I would
suggest the meteo convention.
Each fdm can then process the property however it likes when
converting into a vector.
For clarity, how about we rename the property from wind-
{north|east}-fps to wind-from-{north|east}-fps or wind-to{north|east}-
fps, depending on which is chosen.
How's that for a solution?
Cheers - Dave
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Re: [Flightgear-devel] Wind confusion.
Alex Perry writes: I suspect the LaRCSim is the most accurate. It is possible to taxi (carefully) with those winds, but takes considerable planning and operation of the controls to make it work out safely. David comments: The tests were run with the plane stationary, engine at idle, and no brakes applied. In those circumstances, wouldn't a weathervane be most likely? I'm not sure; I've never been in sustained winds that strong. A weathervane is a weakening effect as rotation starts; enough wind to cause rotation will also cause the aircraft to tilt over on the landing gear. Terrain shape in the vicinity of the aircraft will modify the wind flow; if there is a tiny upward component near the upwind wing, you're in trouble. Either the aircraft rolling slightly, or the wing flowing upward slightly, is enough to expose a positive angle of attack of the main wing to the wind. The wing aspect ratio inverts, so it becomes an extremely effective lifting body on the upwind side; the downwind side is baffled by the airframe and the detached boundary layer on the upper side of the wing and so has very little lift. This converts the wind-based lift into a roll torque that increases _quadratically_ with the angle of rotation (i.e. no pilot warning). For a slight headwind, or a slight tailwind, you can use the ailerons to modify the effective angle of attack and oppose that rolling torque. However, the stated example is exactly at 90 degrees and thus this would have no effect. In real life, you'd zigzag down taxiways and very carefully change the control positions as you go (watching windsocks like an eagle). ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Alex Perry writes: For a slight headwind, or a slight tailwind, you can use the ailerons to modify the effective angle of attack and oppose that rolling torque. However, the stated example is exactly at 90 degrees and thus this would have no effect. In real life, you'd zigzag down taxiways and very carefully change the control positions as you go (watching windsocks like an eagle). I have a feeling that if I were a real C-172 pilot looking at 50 kt surface winds, I'd just leave the plane tied down and take a bus. All the best, David -- David Megginson [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
BTW, it's good to see that people have started experimenting with various combinations of wind and FDM's. There are interesting differences in ground handling between various models. Speaking of ground handling, all aircraft have the tendency to slowly float sideways, even with zero wind, brakes applied and engine(s) stopped. What's up with that? Ground handling - and *very* especially handling in a *stopped* condition - is an acknowledged bitch to model by everyone who endeavors to model it. NASA, X- Plane author Austin **??** (can't recall his last noame at present), myself, etc. We have ground handling pretty much figured out, but the quirks of modeling a vehicle at rest are still being worked out. For us particularly (JSBSim developers) there have been other issues to tackle for this current FlightGear release - both technical and home life. This has given me, at least, some time to think about it and I am going to try something I've had on my mind for a few weeks as a potential solution. But it will still be a short while until I can try it out. We acknowledge, though, that it does not work perfectly now and that this is an important problem to solve. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Mon, Feb 18, 2002 at 04:09:37PM -0500, David Megginson wrote: I have a feeling that if I were a real C-172 pilot looking at 50 kt surface winds, I'd just leave the plane tied down and take a bus. I think you wouldn't feel very comfortable in a bus either. :-) When winds aloft are at 50-60 kts, a surface wind of 20-25 would be more realistic anyway. That is why you want multiple layers of wind. You want to do that non-stop trip from Amsterdam to Rome (fuel!), but you also want to be able to take off. - -- Regards, I RADIS, do you? =Martin=http://www.iradis.org/ PGP: FE87448B DDF8 677C 9244 D119 4FE0 AE3A 37CF 3458 FE87 448B From: Martin van Beilen [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Re: [Flightgear-devel] Wind confusion. In-Reply-To: [EMAIL PROTECTED]; from [EMAIL PROTECTED] on Mon, Feb 18, 2002 at 04:09:37PM -0500 X-S-Issue: [EMAIL PROTECTED] 2002/02/19 00:58:45 4b2f043144af2e0f6669867ab3c4d54d -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) iEYEARECAAYFAjxxlT0ACgkQN880WP6HRIvvXACdEYz4HeyQuYUqRW8b10IXtomO r8UAn3gF2nkDmVXYs6noCtcygoH3PlcT =62jO -END PGP SIGNATURE- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Sat, Feb 16, 2002 at 04:06:13PM -0800, Alex Perry wrote: [..bait snipped..] Purely on principle, I think it is more important to let each FDM subsystem use whatever conventions that its authors believe will make for a consistent and easy to maintain codebase. We want them to work! Any sign (or axis) mismatches can be dealt with in the interface class. FWIW, that's what I was trying to say: Internal (and external) interfaces should be standardized. That's what interfaces are for, right? - -- Regards, I RADIS, do you? =Martin=http://www.iradis.org/ PGP: FE87448B DDF8 677C 9244 D119 4FE0 AE3A 37CF 3458 FE87 448B From: Martin van Beilen [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Re: [Flightgear-devel] Wind confusion. In-Reply-To: [EMAIL PROTECTED]; from [EMAIL PROTECTED] on Sat, Feb 16, 2002 at 04:06:13PM -0800 X-S-Issue: [EMAIL PROTECTED] 2002/02/17 10:09:58 aaccadb4366757ec7f3788cb9f66b74b -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) iEYEARECAAYFAjxvc20ACgkQN880WP6HRIsKQwCgo2PGlVYpezy8v7PSKSecnyS+ rt8AnRG2HTIM444HPuw96cf+BFCgxdMt =krCX -END PGP SIGNATURE- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Tony Peden [EMAIL PROTECTED] said: I'd be happier if we kept it as is. Wouldn't be the first time engineers have traded correctness for pragmatism. Ah pragmatism! Is that the excuse engineers use when they get their vectors math bass-ackwards? ;-) Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
On Sun, Feb 17, 2002 at 04:00:03PM -, Jim Wilson wrote: Tony Peden [EMAIL PROTECTED] said: I'd be happier if we kept it as is. Wouldn't be the first time engineers have traded correctness for pragmatism. Ah pragmatism! Is that the excuse engineers use when they get their vectors math bass-ackwards? ;-) Bah humbug. Engineers, seeing that there were two incompatable standards simply choose to break the one normally seen by people who should be able to understand the problem and adapt. Obviously, in this case, they chose the wrong group. :) -- James (Jay) Treacy [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Bah humbug. Engineers, seeing that there were two incompatable standards simply choose to break the one normally seen by people who should be able to understand the problem and adapt. Obviously, in this case, they chose the wrong group. :) Ha! Someone made the suggestion that we are doing this bass-ackwards. I disagree. We are talking about simulating an aircraft, about an aircraft-centric phenomena, and about a phenomena that is normally reported by humans in a particular way. Sitting on the runway, pointed with a heading of 20 degrees, and with a wind of 20 knots from 20 degrees (as is normally reported, that is, the *from* direction is given), the aircraft sees 20 knots headwind. This equation in FGTranslation shows this nicely: vAeroUVW = vUVW + State-GetTl2b()*Atmosphere-GetWindNED(); I know that the wind vector that originates in the NED axis points *at* 200 degrees and that the north component of this vector would be a negative number. But, what happens if you add the aircraft velocity and the wind velocity vectorially? You sure don't get the aircraft total sensed velocity vector. This approach we have taken is a compromise between what is easily understandable by most people when it comes to wind speed and what makes sense in a mathematical sense (see the above equation). Of course you can do it a couple of ways. It just needs to be documented. We have fallen short there, apparently. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Martin van Beilen wrote:
I think I am beginning to understand what the source of the
confusion is. As most of you know, weather reports specify the winds
as a _from_ heading. However, in simulated space I tend to think of
wind as a vector, i.e. a _to_ heading. Apparently, two out of three
FDM's agree with my point of view. So what is the consensus on this
one? To or from?
Tony Peden wrote:
From is the accepted convention in aviation, hopefully that's what
JSBSim treats as positive. I'll attempt to verify later.
I took my hint from the naming of the accessor functions:
FGInterface::get_V_{north|east|down}_airmass();
These imply pretty strongly that they return the velocity of the
airmass, in the (horrifically ugly but well-understood) local
coordinate system. That is a to vector, by definition. Really, the
from convention applies to a 1-dimensional compass direction; I'm
not aware of anyone else trying to apply it to a 3D vector
environment.
That being said, I'd be happy to negate my wind vector if that's what
folks decide.
I also found an interesting glitch with YASim: the airspeed
indicator displays the ground speed. I thought I was going to stall,
but didn't. :)
Yup, so it does. That's a problem. I'm setting the output stuff in
FGInterface wrong, somehow. Ah, found it: in YASim.cxx, you'll note
that I call set_V_rel_wind(); try to find out where the wind gets
added in. Oops.
I need to remember where I keep the wind and what conventions are used
to fix this, but need more urgently to go to bed. I'll have this
fixed tomorrow.
Andy
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Re: [Flightgear-devel] Wind confusion.
Martin van Beilen [EMAIL PROTECTED] said: I have been playing around with the wind some more, and it seems that JSBSim doesn't only have the up/down winds inverted, but the north and east winds as well. Hmmm...doesn't look like it to me. Just rolling down the runway I applied a 200knot guest from the east and it blew me off the correct side :-) Also the other day I tested an autopilot nav final with a 30 knot crosswind and the plane seemed to be crabbed in the correct direction. North winds are coming from the north, not blowing to the north...which is correct imho. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Sat, Feb 16, 2002 at 09:57:25PM -, Jim Wilson wrote: Hmmm...doesn't look like it to me. Just rolling down the runway I applied a 200knot guest from the east and it blew me off the correct side :-) It may work well from the command-line. However, I am talking about the wind properties in /environment/. Try connecting with the telnet interface and playing around a bit with those values. - -- Regards, I RADIS, do you? =Martin=http://www.iradis.org/ PGP: FE87448B DDF8 677C 9244 D119 4FE0 AE3A 37CF 3458 FE87 448B From: Martin van Beilen [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Re: [Flightgear-devel] Wind confusion. In-Reply-To: [EMAIL PROTECTED]; from [EMAIL PROTECTED] on Sat, Feb 16, 2002 at 09:57:25PM - X-S-Issue: [EMAIL PROTECTED] 2002/02/16 23:31:56 24b4ecf6e536a36cee51907741fe94b6 -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) iEYEARECAAYFAjxu3eMACgkQN880WP6HRIug4wCgtfKBteWAxNjIh7zD0J6YVYxB XxYAoJ9rD4dPYIwG5QQjIgDp446OjL4s =BTNq -END PGP SIGNATURE- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Please note that there is a difference between fgfs's internal representation of wind, and the way it is set by the user. As an engineer, I am partial to using 'to' vectors internally. Yup, that is more mathematically correct. IMHO, I think the way JSBSim does it is more consistent from an EOM/weather/smulation POV. However, perhaps we can account for the difference in the FGInterface-derived class for the specific FDM? Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
On Sat, 2002-02-16 at 15:22, Jon S. Berndt wrote: Please note that there is a difference between fgfs's internal representation of wind, and the way it is set by the user. As an engineer, I am partial to using 'to' vectors internally. Yup, that is more mathematically correct. IMHO, I think the way JSBSim does it is more consistent from an EOM/weather/smulation POV. However, perhaps we can account for the difference in the FGInterface-derived class for the specific FDM? I'd be happier if we kept it as is. Wouldn't be the first time engineers have traded correctness for pragmatism. Jon ___ 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] Wind confusion.
Please note that there is a difference between fgfs's internal representation of wind, and the way it is set by the user. As an engineer, I am partial to using 'to' vectors internally. Yup, that is more mathematically correct. There is nothing mathematical about the wind vector convention; it's not as if we're actually modelling the wind as a particle field. A pressure sensor that is exposed to the wind and pointed in the direction specified as the wind direction will indicate a pressure above ambient. When pointed in the opposite direction, i.e. the direction that the air is travelling towards, the sensor will report the same as for the directions at right angles, namely no increase. Therefore, I could argue that the pilot viewpoint makes a whole lot more sense, for use in the context of aerodynamic modelling. Trying to standardize here is about as pointless as making the whole simulator use SI units exclusively for _every_ numeric value. IMHO, I think the way JSBSim does it is more consistent from an EOM/weather/smulation POV. However, perhaps we can account for the difference in the FGInterface-derived class for the specific FDM? Purely on principle, I think it is more important to let each FDM subsystem use whatever conventions that its authors believe will make for a consistent and easy to maintain codebase. We want them to work! Any sign (or axis) mismatches can be dealt with in the interface class. I'd be happier if we kept it as is. Wouldn't be the first time engineers have traded correctness for pragmatism. Yes. That's been suggested as the differentiator between engineers and scientists and formed the basis for many many jokes at each others' expense. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Wind confusion.
Tony Peden writes: One could apply a similar argument to a vane; it doesn't change the fact that the air is flowing the other way ( and that may well be why the aviation convention is from ) And here in the northern hemisphere when you refer to a 'north wind' you are usually talking about something cold, as in coming from the north. Yes. That's been suggested as the differentiator between engineers and scientists and formed the basis for many many jokes at each others' expense. The jokes I know are between engineers and mathematicians. 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] Wind confusion.
On Sat, 2002-02-16 at 16:56, Curtis L. Olson wrote: Tony Peden writes: One could apply a similar argument to a vane; it doesn't change the fact that the air is flowing the other way ( and that may well be why the aviation convention is from ) And here in the northern hemisphere when you refer to a 'north wind' you are usually talking about something cold, as in coming from the north. Yes, I have felt such north winds. You can keep them. (And David M. can keep his too, for that matter) ;-) -- 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
