Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
David Megginson said: > Ampere K. Hardraade wrote: > > > One explanation for the violent maneuvers that I thought of is this: as the > > distance between the plane and the waypoint decreases, the accuracy required > > in the course calculations increases. Since it takes time for the autopilot > > to respond, and takes even more time for the plane itself to respond to the > > commands of the autopilot, the plane will never align itself perfectly with > > the waypoint. Hence, the autopilot will keep trying to "catch" the waypoint > > until the very last moment, thus causing the violent maneuvers. > > Yes, that happens with student pilots as well -- localizers, VORs, you name > it all become very sensitive as you get close. > > > One solutions to the above problem is to pop the waypoint when the plane is > > still some distance away, thereby preventing the autopilot from making all > > those course adjustments. > > Or simply increase the allowable error at close distance, or use some other > kind of filtering function. > There is a look ahead filter in the current autopilot code. It is being used to anticipate ILS radial interception for the 747. Maybe thrust control too. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
All these issues are a matter of adjusting the autopilot coefficients to specific aircraft dynamic characteristics. In order to avoid the "spiral into waypoint" problem, you should try and implement something like this: compute a track to the waypoint from the present position, memorize it, and subsequently correct the trajectory so as to remain on that track (not heading). It's also better to correct this by using a lateral error (distance to the memorized track, not only angle), which makes these corrections independent from the distance to the waypoint. The inputs are: aircraft track (not heading, or you have to allow for a difference between held heading and desired track), desired track, lateral error. The output is a rate of turn. The "pop waypoint" condition is more efficient this way: aircraft beyond a line orthogonal to the desired track to the waypoint, and located at a distance 'd' from the waypoint (see diagram attached). In real-life IFR, if you are flying a non-RNAV aircraft, you're actually supposed to overfly the waypoints. I know, it sounded weird to me too. Of course, no one will really scold you if you manage to nicely anticipate the turn in order to find yourself just on track to the next waypoint. RNAV aircraft are supposed to anticipate every turn so as not to overshoot airways. -- Jorge Van Hemelryck <>___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
My observations are similar to this. However, I don't think that it's a problem with the accuracy of the calculations as such. The route manager code is relatively old and tries to set a straight course to it's next waypoint. It doesn't consider the wind blowing the aircraft off its lateral track. The autopilot tries to compensate by keeping the aircraft on a heading straight to the next waypoint. Now, as we get closer, this happens at an increasingly greater rate, until the rate of required course adjustment exceeds maximum turn-rate. I've seen a few occasions where the 747 couldn't reach the next waypoint because of this phenomenon and started flying around it in endless circles, until I manually popped it. Cheers, Durk On Saturday 05 June 2004 03:28, Ampere K. Hardraade wrote: > The violent maneuvers I was describing occur when the plane is a few > kilometers away from the waypoint. Therefore, it should have little to do > with the way that pid controller reacts to the jump in waypoints. > > One explanation for the violent maneuvers that I thought of is this: as the > distance between the plane and the waypoint decreases, the accuracy > required in the course calculations increases. Since it takes time for the > autopilot to respond, and takes even more time for the plane itself to > respond to the commands of the autopilot, the plane will never align itself > perfectly with the waypoint. Hence, the autopilot will keep trying to > "catch" the waypoint until the very last moment, thus causing the violent > maneuvers. > > One solutions to the above problem is to pop the waypoint when the plane is > still some distance away, thereby preventing the autopilot from making all > those course adjustments. > ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
Ampere K. Hardraade wrote: One explanation for the violent maneuvers that I thought of is this: as the distance between the plane and the waypoint decreases, the accuracy required in the course calculations increases. Since it takes time for the autopilot to respond, and takes even more time for the plane itself to respond to the commands of the autopilot, the plane will never align itself perfectly with the waypoint. Hence, the autopilot will keep trying to "catch" the waypoint until the very last moment, thus causing the violent maneuvers. Yes, that happens with student pilots as well -- localizers, VORs, you name it all become very sensitive as you get close. One solutions to the above problem is to pop the waypoint when the plane is still some distance away, thereby preventing the autopilot from making all those course adjustments. Or simply increase the allowable error at close distance, or use some other kind of filtering function. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
The violent maneuvers I was describing occur when the plane is a few kilometers away from the waypoint. Therefore, it should have little to do with the way that pid controller reacts to the jump in waypoints. One explanation for the violent maneuvers that I thought of is this: as the distance between the plane and the waypoint decreases, the accuracy required in the course calculations increases. Since it takes time for the autopilot to respond, and takes even more time for the plane itself to respond to the commands of the autopilot, the plane will never align itself perfectly with the waypoint. Hence, the autopilot will keep trying to "catch" the waypoint until the very last moment, thus causing the violent maneuvers. One solutions to the above problem is to pop the waypoint when the plane is still some distance away, thereby preventing the autopilot from making all those course adjustments. I should have explained this more throughoutly. Sorry for the inconvience. Regards, Ampere On June 4, 2004 06:19 pm, Lee Elliott wrote: > If I understand the problem correctly, changing the distance at which the > turn is initiated won't make any difference - it's the way that the pid > controller reacts to the jump in input as the waypoint is popped that's > causing the abrupt change. > > For example, if there are two waypoints, directly north and south of each > other, when one waypoint is popped the pid controller is presented with an > input change of 180 deg, regardless of how far away from the waypoint it > is. > > LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
On Friday 04 June 2004 23:30, David Megginson wrote: > Lee Elliott wrote: > > If I understand the problem correctly, changing the distance at which the > > turn is initiated won't make any difference - it's the way that the pid > > controller reacts to the jump in input as the waypoint is popped that's > > causing the abrupt change. > > > > For example, if there are two waypoints, directly north and south of each > > other, when one waypoint is popped the pid controller is presented with > > an input change of 180 deg, regardless of how far away from the waypoint > > it is. > > The 180-degree turn is a special problem no matter how you look at it -- > the key is to make sure that the autopilot will not overbank the plane. > > Otherwise, though, turn distance does matter -- if you switch to the next > waypoint at the right moment, the plane will turn smoothly to its new track > without overshooting the waypoint and possibly entering unprotected > airspace. > > > All the best, > > > David Ah - I don't think I understood the problem properly - I'll shut up. LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
Lee Elliott wrote: If I understand the problem correctly, changing the distance at which the turn is initiated won't make any difference - it's the way that the pid controller reacts to the jump in input as the waypoint is popped that's causing the abrupt change. For example, if there are two waypoints, directly north and south of each other, when one waypoint is popped the pid controller is presented with an input change of 180 deg, regardless of how far away from the waypoint it is. The 180-degree turn is a special problem no matter how you look at it -- the key is to make sure that the autopilot will not overbank the plane. Otherwise, though, turn distance does matter -- if you switch to the next waypoint at the right moment, the plane will turn smoothly to its new track without overshooting the waypoint and possibly entering unprotected airspace. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
On Friday 04 June 2004 15:37, David Megginson wrote: > Josh Babcock wrote: > > How do real life FMS's do it? Does this generally vary? If so maybe it > > would make sense to pick this number up from the autopilot XML with a > > default defined in preferences.xml. > > At any given speed, the same bank angle will give you the same turn rate > (for a coordinated turn), no matter how big or small the plane is. I don't > know the proper equation, but the rule of thumb for a rate one turn (3 > degrees per second) is knots/10+7, so at 120 kt you will need (roughly) a > 19 degree bank for a rate-one turn; at 250 knots, you will need (roughly) a > 32 degree bank. > > I don't think that fast passenger planes typically bank much more than 20 > degrees, though, so they will be doing a turn at considerably less than > rate one. Get the proper formulas, specify the maximum allowed bank angle, > then crunch the numbers to see how far ahead the plane will have to start > turning at its current airspeed to change course by a specified number of > degrees. > > > All the best, > > > David If I understand the problem correctly, changing the distance at which the turn is initiated won't make any difference - it's the way that the pid controller reacts to the jump in input as the waypoint is popped that's causing the abrupt change. For example, if there are two waypoints, directly north and south of each other, when one waypoint is popped the pid controller is presented with an input change of 180 deg, regardless of how far away from the waypoint it is. LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
Josh Babcock wrote: How do real life FMS's do it? Does this generally vary? If so maybe it would make sense to pick this number up from the autopilot XML with a default defined in preferences.xml. At any given speed, the same bank angle will give you the same turn rate (for a coordinated turn), no matter how big or small the plane is. I don't know the proper equation, but the rule of thumb for a rate one turn (3 degrees per second) is knots/10+7, so at 120 kt you will need (roughly) a 19 degree bank for a rate-one turn; at 250 knots, you will need (roughly) a 32 degree bank. I don't think that fast passenger planes typically bank much more than 20 degrees, though, so they will be doing a turn at considerably less than rate one. Get the proper formulas, specify the maximum allowed bank angle, then crunch the numbers to see how far ahead the plane will have to start turning at its current airspeed to change course by a specified number of degrees. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
Ampere K. Hardraade wrote:
I think it will probably be a good idea to increase the distance that triggers
the poping of waypoints. Right now, the plane practically gets on top of the
way point before switching to the next, which is causing some awfully violent
maneuvers.
Regards,
Ampere
On June 3, 2004 11:23 am, Durk Talsma wrote:
This is hardcoded in src/Autopilot/route_mgr.cxx, line 112:
if ( wp_distance < 200.0 ) {
pop_waypoint();
distance is probably in meters, but I might be wrong here.
HTH,
Durk
On Wednesday 02 June 2004 21:57, Seamus Thomas Carroll wrote:
Hi,
Does anyone know where the variable is kept that holds the distance to
a waypoint that triggers moving the current waypoint to the next
waypoint?
Seamus
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How do real life FMS's do it? Does this generally vary? If so maybe it would
make sense to pick this number up from the autopilot XML with a default defined
in preferences.xml.
Josh
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Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
Ampere K. Hardraade wrote: I think it will probably be a good idea to increase the distance that triggers the poping of waypoints. Right now, the plane practically gets on top of the way point before switching to the next, which is causing some awfully violent maneuvers. The best way to do this is to vary the distance based on an aircraft's airspeed, to give a rate-one turn or a roll of 20 degrees, whichever results in a shallower bank. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
I think it will probably be a good idea to increase the distance that triggers
the poping of waypoints. Right now, the plane practically gets on top of the
way point before switching to the next, which is causing some awfully violent
maneuvers.
Regards,
Ampere
On June 3, 2004 11:23 am, Durk Talsma wrote:
> This is hardcoded in src/Autopilot/route_mgr.cxx, line 112:
>
> if ( wp_distance < 200.0 ) {
> pop_waypoint();
>
> distance is probably in meters, but I might be wrong here.
>
> HTH,
> Durk
>
> On Wednesday 02 June 2004 21:57, Seamus Thomas Carroll wrote:
> > Hi,
> >
> > Does anyone know where the variable is kept that holds the distance to
> > a waypoint that triggers moving the current waypoint to the next
> > waypoint?
> >
> > Seamus
> >
> >
> >
> > ___
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Re: [Flightgear-devel] How to change minimum distance to activate next waypoint?
This is hardcoded in src/Autopilot/route_mgr.cxx, line 112:
if ( wp_distance < 200.0 ) {
pop_waypoint();
distance is probably in meters, but I might be wrong here.
HTH,
Durk
On Wednesday 02 June 2004 21:57, Seamus Thomas Carroll wrote:
> Hi,
>
> Does anyone know where the variable is kept that holds the distance to
> a waypoint that triggers moving the current waypoint to the next waypoint?
>
> Seamus
>
>
>
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[Flightgear-devel] How to change minimum distance to activate next waypoint?
Hi, Does anyone know where the variable is kept that holds the distance to a waypoint that triggers moving the current waypoint to the next waypoint? Seamus ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
