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LNAV Behaviour, obvious cause ?!


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Hi,

for those still having trouble with an acting up LNAV:

 

If you are having one of those Mods installed, at least one of them is causing issues.

I flew a departure out of UKOO (Odessa, RATN-1E)  twice with those mods loaded and VNAV was acting up, doing left /right turns and not catching up on the course.

Next flight i tried without the "navigational" Mods and LNAV did a perfect departure, doing that "INTC" part just right.

 

So i recommend re-/moving these mods when flying the CRJ and put them back only when needed (for other a/c)

 

The mods are for now:  PMS GNS 430/530, PMS GTN750, WT G3000 and GX.
I'd like to find out, which one(s) exactly are responsible, but don't have all that time right now.
If one knows already for sure, be so kind and chime in , Thank you

 

Oliver

 

Navigraph_Charts_8UEtCKC29v.png

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vor 22 Stunden , JetNoise sagte:

Hi,

for those still having trouble with an acting up LNAV:

 

If you are having one of those Mods installed, at least one of them is causing issues.

I flew a departure out of UKOO (Odessa, RATN-1E)  twice with those mods loaded and VNAV was acting up, doing left /right turns and not catching up on the course.

Next flight i tried without the "navigational" Mods and LNAV did a perfect departure, doing that "INTC" part just right.

 

So i recommend re-/moving these mods when flying the CRJ and put them back only when needed (for other a/c)

 

The mods are for now:  PMS GNS 430/530, PMS GTN750, WT G3000 and GX.
I'd like to find out, which one(s) exactly are responsible, but don't have all that time right now.
If one knows already for sure, be so kind and chime in , Thank you

 

Oliver

 

Navigraph_Charts_8UEtCKC29v.png

 

 

So, i did the test flights with this SID (RATNO) and i am sorry to say, that EACH combination of the above mentioned MODS is causing the reported issues with the CRJ (at least)
100% that using the CRJ without these MODS (residing inside the Community Folder)  has the a/c fly that SID and others exactly as it should . (some very litle corrections on the INTERCEPT part)

 

After having done flights (3) , all went smooth and without obvious issues.

 

Oliver

 

I will further watch the general LNAV behaviour in the future ....  (also in reference to "North Bug" thread) 

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Interesting findings!

 

Out of curiosity: Do you know whether there is an inference with the WT CJ4 as well since their G3000 and GX are causing issues?

 

If have it installed and in some rare cases, the CRJ's LNAV is not working perfectly, e.g. overshooting or overturning with a subsequent correction maneuver. But all in all I didn't notice any severe issues.

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vor 2 Stunden , SinusJayCee sagte:

Interesting findings!

 

Out of curiosity: Do you know whether there is an inference with the WT CJ4 as well since their G3000 and GX are causing issues?

 

If have it installed and in some rare cases, the CRJ's LNAV is not working perfectly, e.g. overshooting or overturning with a subsequent correction maneuver. But all in all I didn't notice any severe issues.

Hi,

overshooting: depending on your speed, the angle and the type of waypoint (overfly).  I am currently watching, if that still happens on my flights. (EDDP-EGSS now)

2nd flight today and so far, no LNAV issues. Knock on wood 😉

overturning: yes, i have seen this as well, but in general it is doing a good job. But see the above.

 

CJ-4: havent flown her for a while, but for now, i will install/remove whatever System is (not) / needed., for the respetive a/c. Just to be safe 😉

 

DC-6: I haven't noticed any issues together with all mods installed.  I am either using the GNS430/530 Mod or the 750/650 PMS. Or no GPS. Depends

 

Oliver

 

 

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Thanks for your reply!

 

vor 5 Minuten, JetNoise sagte:

overshooting: depending on your speed, the angle and the type of waypoint (overfly).  I am currently watching, if that still happens on my flights. (EDDP-EGSS now)

2nd flight today and so far, no LNAV issues. Knock on wood 😉

overturning: yes, i have seen this as well, but in general it is doing a good job. But see the above.

Yes, I can confirm that. Overshooting is quite rare. But overturning happens more often, roughly 1-2 times per flight, which are usually about 1 hour each for me.

 

vor 6 Minuten, JetNoise sagte:

CJ-4: havent flown her for a while, but for now, i will install/remove whatever System is (not) / needed., for the respetive a/c. Just to be safe 😉

Yeah, that is probably a good idea. There seem to be some interference between the more complex mods. I guess I'll remove the CJ4 and A32NX from the community folder just to be sure. But you noticed no issues with this specific add-on, did you?? I was wondering whether the overturning is one of the LNAV issues you were referring to.

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gerade, SinusJayCee sagte:

Thanks for your reply!

 

Yes, I can confirm that. Overshooting is quite rare. But overturning happens more often, roughly 1-2 times per flight, which are usually about 1 hour each for me.

 

Yeah, that is probably a good idea. There seem to be some interference between the more complex mods. I guess I'll remove the CJ4 and A32NX from the community folder just to be sure. But you noticed no issues with this specific add-on, did you?? I was wondering whether the overturning is one of the LNAV issues you were referring to.

No need to remove, i guess. I had them installed all the time during my tests. Just remove the MODS  G3000, GX, PMS if in the CRJ for now...

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Not sure what you mean by "Overturning" but keep in mind that the CRJ has a "FIXED BANK" turn angle on the auto pilot...  So above 31000 feet and at high speed this means it has to start the turn further out and it can not "adjust" the angle so you will see an "imperfect" turn....

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vor 35 Minuten, LesOReilly sagte:

Not sure what you mean by "Overturning" but keep in mind that the CRJ has a "FIXED BANK" turn angle on the auto pilot...  So above 31000 feet and at high speed this means it has to start the turn further out and it can not "adjust" the angle so you will see an "imperfect" turn....

Ja, one more reason ..., missed that in my answer above 😉

 

Oliver

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vor 33 Minuten, LesOReilly sagte:

Not sure what you mean by "Overturning" but keep in mind that the CRJ has a "FIXED BANK" turn angle on the auto pilot...  So above 31000 feet and at high speed this means it has to start the turn further out and it can not "adjust" the angle so you will see an "imperfect" turn....

I observe this behavior mainly at high altitudes, so it could indeed be the case that this is cause by the fixed bank angle.

 

I made a professional drawing to illustrate my observation. Blue is the planned route and red is the observed flight path. Flying direction is from bottom to top:

 

Untitled.thumb.png.927874cd2bfe7a9c356465afbd286733.png

 

Is this what I would expect to see?

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1 minute ago, SinusJayCee said:

I observe this behavior mainly at high altitudes, so it could indeed be the case that this is cause by the fixed bank angle.

 

I made a professional drawing to illustrate my observation. Blue is the planned route and red is the observed flight path. Flying direction is from bottom to top:

 

Untitled.thumb.png.927874cd2bfe7a9c356465afbd286733.png

 

Is this what I would expect to see?

Yup I get that with the WT CJ4 sometimes and with the SR22 using the new NXi sometimes...

 

That first turn looks like an overfly waypoint...  So it cant turn early..

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vor 16 Minuten, LesOReilly sagte:

Yup I get that with the WT CJ4 sometimes and with the SR22 using the new NXi sometimes...

 

That first turn looks like an overfly waypoint...  So it cant turn early..

I get this for regular enroute waypoints, not sure whether they are set to overfly by default.

 

It could be the case that my drawing is not 100% accurate and that the CRJ initiates the turn in fact earlier. I will check this during my next flight.

However, probably because of the 1/2 bank angle automatically activated at high altitudes/speeds, it ends up "overshooting" the next leg, then turns too much and makes a correction maneuver. I also had it once or twice that it turned too much in the opposite direction as well requiring a second correction maneuver.

 

*edit*

Here is a drawing of what I tried to describe. Imagine the curves all have the same radius ;)

Unnamed2.thumb.png.5b3d1a01173c1d90ce5c88eb13958c60.png

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@SinusJayCee

 

that 2nd drawing is more correct. Turning in to hard initially. And the zigzagging and over correcting until on track.

 

this is happening since day 1 in March unfortunately 😞

 

search the forum on zigzagging… think u will find a few results.

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vor 2 Stunden , DGH sagte:

@SinusJayCee

 

that 2nd drawing is more correct. Turning in to hard initially. And the zigzagging and over correcting until on track.

 

this is happening since day 1 in March unfortunately 😞

 

search the forum on zigzagging… think u will find a few results.

Thanks for information! I did some research and the last statement I found is saying that this was supposed to be fixed with the update for SU4:

 

Does someone know whether this has been reintroduced with SU5 or what else happened?

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vor 10 Stunden , SinusJayCee sagte:

Thanks for information! I did some research and the last statement I found is saying that this was supposed to be fixed with the update for SU4:

 

Does someone know whether this has been reintroduced with SU5 or what else happened?

 

Idk,

anyway, even with a fixed angle of bank, even with "half bank" you are able to master sharp turns. It all depends on WHEN you start that turn. Think of trying to fit a round coaster fit into an angle ☺️, where the radius is dependent on the speed.

(All depending on the types of waypoints involved)

Question is, if the real aircraft does this calculation. (Turn anticipation ?)

 

So should the SIM CRJ. 😎

 

Oliver

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On 26.8.2021 at 09:26, JetNoise sagte:

 

Idk,

anyway, even with a fixed angle of bank, even with "half bank" you are able to master sharp turns. It all depends on WHEN you start that turn. Think of trying to fit a round coaster fit into an angle ☺️, where the radius is dependent on the speed.

(All depending on the types of waypoints involved)

Question is, if the real aircraft does this calculation. (Turn anticipation ?)

 

So should the SIM CRJ. 😎

 

Oliver

 

 

Two more examples of the weired LNAV behaviour. No-one would call these sharp turns. Speed at around 220-240kts. Low wind speeds (20-35kts).
 The pics do not clearly show the zigzagging as it happened, but it took about 3-4 turns to finally catch the new course.

 

Oliver

SimToolkitPro_Hb9nbTP7Fe.png

SimToolkitPro_WFD9oHaayC.png

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SimToolkitPro_edit.thumb.png.df64ea2cdb349db2cf107025308c5a05.png

 

Now the orange curve shows the same radius of the (green) initial turn. So with the same turn-radius (dep on speed) and the fixed bank-angle, the a/c should have turned later (red marks) to catch the course (orange line), without the need to constantly and excessivly correct back to course.
(the corrections are also done with the same bank-angle, (fixed), which leeds to the (self-induced) zigzag course.

 

Oliver

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2 hours ago, JetNoise said:

SimToolkitPro_edit.thumb.png.df64ea2cdb349db2cf107025308c5a05.png

 

Now the orange curve shows the same radius of the (green) initial turn. So with the same turn-radius (dep on speed) and the fixed bank-angle, the a/c should have turned later (red marks) to catch the course (orange line), without the need to constantly and excessivly correct back to course.
(the corrections are also done with the same bank-angle, (fixed), which leeds to the (self-induced) zigzag course.

 

Oliver

except that implies no wind correction...  you can only have that perfect of a curve if there is 0 wind or if you have an Auto Pilot that can have a Variable Bank Angle...  Even then as it is turning it will need to calculate the Wind Correction angle and compensate for that as the turn is progressing...

 

Not saying there is not room for possible improvement but I don't see how a plane with Fixed Bank Angle Turn is going to perform a perfect smooth turn while dealing with Wind Correction...

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Well … when in real life a CRJ is flying … its not wobbling left or right with sick passengers either 😬

 

so should be possible for planes with fixed bank angle … perhaps the radius is bigger per default ( less bank ) so they have room to compensate or something like that.

 

i never was in a crj that moved full bank left and the right and then left again just to make a 20 degree turn.

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The real aircraft handles course intercepts very well. Most wobbles are rather pilot induced e.g. when changing from HDG mode to NAV. In fact we often prefer the FMS over the APP mode for intercepts of the final approach course, because of the poor gain performance of the latter.

 

The following is an excerpt from the FMS-4200 Pilots Guide:

 

Turns

 

The FMS computes a turn to be accomplished using a nearly constant bank angle. For small turns, the amount of bank angle is small. The larger the turn, the greater the bank angle. It also computes when to start a turn based on the type of waypoint, the number of degrees of turn, the airplane’s true airspeed, the current heading relative to the new heading, and the wind conditions. During a turn, the FMS continuously computes the bank angle to compensate for changes in wind conditions, true airspeed, and the airplane’s heading relative to the new course. Bank Angle and Roll Rate Bank angle and roll rate for a turn are continuously computed by the FMS with consideration for the flight control system's bank angle limits. With the flight control system set to the normal operation mode (no bank limit selected), the bank angle is limited to approximately 25 degrees. With the flight control system set to the HALF-BANK mode, the bank angle is limited to approximately 12.5 degrees. Roll rate is set at three degrees per second for all turns.

 

 

Anticipation

 

As the airplane approaches a turn at a waypoint, in addition to computing the bank angle for the turn, the FMS computes the point at which the turn is to be initiated. This is called turn anticipation. Its purpose is to prevent the airplane from unnecessarily overshooting the new course during the turn. Essentially, the FMS cuts the corner of the turn to make a smooth transition to the new course. For flight plan leg turns at true airspeeds less than 350 knots, the turn initiation point is not further than seven nautical miles from the waypoint. At true airspeeds of 350 knots or greater, the turn initiation limit is no further than 12 nautical miles from the waypoint. A waypoint alert flashes the active waypoint identifier on the PFD display, and the active waypoint symbol and identifier on the MFD map appear approximately five seconds before the FMS initiates the turn to the new course. While turn anticipation prevents most overshoots, very large course changes may still result in some overshoot.

1365460461_TurnsCourseIntercepts01.thumb.png.7c791481dc9649ac926bd8f93dfc6975.png

 

 

 

Flyover Waypoints

 

Selective waypoints designated as flyover waypoints require the airplane to fly over the waypoint before a turn is initiated. Examples include leg terminating waypoints such as a waypoint before a discontinuity, holding fix waypoints, and the last waypoint at the end of a flight plan.

1571316096_TurnsCourseIntercepts02.thumb.png.b6cc82e1f9095e8961c6242f80e29f8a.png

 

 

 

Intercepting a Track

 

The FMS can intercept an active course track at any converging angle. Whenever possible, the intercept is such that the airplane turns onto the active course without overshoot. However, if the intercept angle is great and the distance to the course is short, an overshoot will occur. If the intercept path is such that the intercept may not occur before the active waypoint, the message "NOT ON INTERCEPT TRK" shows on the CDU message page.

1386711035_TurnsCourseIntercepts03.thumb.png.af830006dcc9d23501d7fc6b7d5a7336.png

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image.thumb.png.5690da829f5b5f5b24c50bd87620ff16.png

 

 

That looks like a CRJ having some Wobbling on it's route there....  I am not arguing that they can't probably do something to try and improve things...

 

However I get some Wobble in the WT CJ4 sometimes and I get so back and forth on intercepts as well with the New NXi.....

 

 

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1 hour ago, LesOReilly said:

image.thumb.png.5690da829f5b5f5b24c50bd87620ff16.png

 

 

That looks like a CRJ having some Wobbling on it's route there....  I am not arguing that they can't probably do something to try and improve things...

 

However I get some Wobble in the WT CJ4 sometimes and I get so back and forth on intercepts as well with the New NXi.....

 

 


and you realy believe this is correct ?

these probably are inconsistencies in receiving signals of ac position. I have this on flightradar24 also sometimes. Sometimes signals stop to continue moments later. The software just draws a line between those positions.

 

you are showing some 90 degrees angles at the start of the “wobble” .. only UFO’s make those sharp 90 degree angles 😬

 

Below is how CRJ’s turn … have you read the FMS explanation above ? 
 

 

249BFD31-1C69-4199-8E79-A00FC7A1F6BD.png

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8 hours ago, DGH said:


and you realy believe this is correct ?

these probably are inconsistencies in receiving signals of ac position. I have this on flightradar24 also sometimes. Sometimes signals stop to continue moments later. The software just draws a line between those positions.

 

you are showing some 90 degrees angles at the start of the “wobble” .. only UFO’s make those sharp 90 degree angles 😬

 

Below is how CRJ’s turn … have you read the FMS explanation above ? 
 

 

249BFD31-1C69-4199-8E79-A00FC7A1F6BD.png

Dude it's ADS-B Data ...  The Plane is supplying this information via 1090ES OUT...  just like my C24R does....

 

Reading the Manual tells you what they "say it will do" you should read the manual of my Century 3 Auto Pilot... you would also believe that it would perform perfect wind correction and wind compensation...

 

You want to \say that the "Simulator" can't have issues and it must be perfect?  Then why is the Working Title Discord lit up the last two days with people having issues with G3000, Proline 21 and G1000 NXI users reporting that they are getting swaying back and forth as well as intercepts that some times rock back and forth as they go over it and back?

 

FYI here is the ADS B tags ... showing the heading Changing as it is moving... that is not a Radar hit.. that is an ADS-B Out message that provides that data from the plane..

 

image.thumb.png.be5cf0216e0183263be132d9ad5710d2.png

 

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@LesOReilly

 

so “dude” where in your ads data do you see 90 degree turns  like on you initial picture ??

ADS out or not …. How come your initial picture is showing hard 90 degree UFO turns ???

 

your ads show a FEW degrees movement and not even a real back and forth wobble  … that is something else then what we are describing

 

 Sure the simulator is bugged …. Sure the crj is wobbling …. And yes …. There are also planes that do not show this wobble in that same simulator that is bugged … 

 

anyway lets end this.  Going nowhere. Have a nice weekend

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