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LNAV Behaviour, obvious cause ?!


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  • 3 weeks later...

and to continue ...

Arrival at LRSV via ILS 34, TOMUC Transition, the ND is showing a left turn intercept (wrong) while there should be a right turn at LIVNU.

 

The aircraft followed the arc nicely before it started turning the wrong way inbound LIVNU. Pilots intervention , back to the ILS inbound -> safe landing.

NAVIGRAPH (CRJ and MSFS, latest revision (2)

Oliver

FlightSimulator_6CAaT01vpd.png

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Jup …

 

departure EHAM 27 … KUDA2P … NAV on … but overflying the first nav point after takeoff … NAV off/on  solves 

 

same wobbling after SU6 as before ( since day 1 in March ) … sharper turns at cruise … overcorrecting 

arrival LEBB (think it was  DOSUL) … not following the arc at all
 

departure from LEBB from rnw 30 this morning …. No arc following and turning left instead of right ( MAPA3A )

 

Waiting for an update that finally solves these issues for a while now …. Despite i thing the issue is known for a while And even explained … so not sure why the wait on the wobble fix (for example).

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I'm not sure if this is the same LNAV issue, but I'm still seeing the constant waving back and forth on some of my flights. This was supposedly fixed in one of the previous CRJ patches but that is not the case, although it's at least not as common. You can ignore the TURB button at the beginning -- I had tried activating that to see if it made any difference but it did not. 

 

 

 

 

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  • 3 weeks later...
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Great that the twin otter is almost ready but how about the issue that people have for 10 months ??

 

see below EHAM-EGPH and the return flight. Wobble wobble … still overshooting 

 

 

2F728862-CCE0-4DF5-8365-A366AE269700.jpeg

FE4290A5-C28C-4B96-9061-9AFB39C5FCBD.jpeg

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I'll try my usual test route when I have a spare hour, the aircraft seems to follow the route better than a few months back ( or the -900 is just better behaved, thinking about it ). I'll have to try and work out how to hide my historic trails from LNM though.

 

BTW you can File->save map as image ( or copy map image to clipboard ) and it'll save a copy of what you're looking at, will save you taking a photo of the screen :)

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Thanks for the tip 👍

 

made the email on my iphone though so the picture is faster for me. But did not know what you suggested so thanks for the tip ! 

 

i am only flying 700. Will not ever buy another Aerosoft product before this issue is solved.
 

10 months … 

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Seems to me, the FD will consistently command a turn starting at 2X the distance required.  If it were to hold course until the waypoint is half as far as it is now, the constant-bank turn would fit the angle nicely and the aircraft wouldn't wobble chasing back onto track afterwards.

 

Look at the pictures above, and this tendency to double the turn start distance becomes clear - Imagine those same turns starting at half the distance to the waypoint than they do.  If they started there, the other side of the arc would be tangent to the next leg.

 

Some simple analytical geometry to illustrate:

 

image.thumb.png.3e2fb4ed60a0308040d8d0bf70ec51c7.png

 

The blue and red circles are identical, note their tangents against the waypoint legs and how the blue one matches up properly.

 

Remember, the CRJ can only turn at a fixed bank angle, so it is this timing of where to start the turn that determines how it'll converge upon the next leg. As the bank angle is constant, then so is the turn radius (as long as airspeed stays constant) - The initial point for the turn is then given by the solution presented here:

 

https://stackoverflow.com/questions/51223685/create-circle-tangent-to-two-lines-with-radius-r-geometry

 

 

May we have this fixed soon?

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EGPF/23LUSI1A LUSIV L612 ELBUS UL612 CROFT UP16 NOKIN N862 IPZOL DCT EX

Hold at EX

EGTE ILS26 via EX1

CRJ-egpf-6.thumb.jpg.e183a1283c064394437f1dd02bbdbfe6.jpg

CRJ-900, current AIRAC data from Navigraph. Used NAV a bit more than I would usually, to see what happens. It's not the ideal route for the approach but it's the one I took today.

 

Put the AP in at 1300ft or so, before XETUN, climbing FL130 as asked to at 250kts

CRJ-egpf-1.thumb.jpg.7dac8a0d6295493a10993ebd51d3e3a0.jpg

I thought it was going to end up pointing the correct way there, but then it suddenly swung left.

 

Once it'd got on course again it tracked pretty well until here -

CRJ-egpf-2.thumb.jpg.24a70168676c0513e6d1990e409a4532.jpg

 

and got a bit out of sorts for the next couple of WPs

CRJ-egpf-3.thumb.jpg.7bfbc7e42dbdaff2e4e257474b98d6b8.jpg

 

After that, tracked right down the line, until the hold at EX. Oh boy. Here's the approach chart for ILS/26 at EGTE -

CRJ-egpf-5.thumb.jpg.41324bfacf07a77347cd592e7377b9d1.jpg

 

Aaand... here's what happened.

CRJ-egpf-4.thumb.jpg.02f4844c6cec8e3e0da1b7fb5cde0efb.jpg

 

I saw this wasn't going well on the outbound leg of whatever the a/c was flying & immediately armed the exit - it had EX programmed in again but almost immediately skipped that & tried to find the next WP in the approach. I hit APP pretty much as soon as it was in the ILS lobes & it almost immediately settled down laterally. What that doesn't show is the continual fight to keep the airspeed & alt in check, and the way the trim was running. I'm wondering if the trim issue isn't inadvertantly causing some course holding issues too just by the aircraft not doing what it's predicted to do.

 

--

 

Edit - 2nd flight, had the same wobble ( almost exactly the same, actually ) between CROFT & ROBVA, but this was the hold & procedural approach...

 

CRJ-egpf-7.thumb.jpg.5853ff3bdac1414eb6eaa534cd0a810d.jpg

 

... is it a cow maybe? I bemusedly left it doing whatever it was doing for a while. The missed approach wasn't too bad, at least - other than it just pointing the nose up when I put the alt hold back in ( despite being at the set alt already ).

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Caveat: noticed the WT G1000NX marketplace version still installed, will have a go without it when I can.

 

Edit 2: uninstalled WT G1000NXI from marketplace, no difference in behavior - I have no other complicated aircraft from the marketplace at all, only the Asobo stuff & the Spitfire. Flaps 8, flaps 20 no difference in behaviour. Wind is 277/5 so practically no crosswind in the hold. Outbound leg ( the one it makes a good attempt at ) seems to be a heading of about 300 .

 

Thought the hold behaviour might throw an obvious light on more subtle issues, so I set a route up just to test holding, and set the whole thing up to succeed as best I could. CRJ-900, 0 passengers, 0 cargo, 2480kg fuel. AIRAC from Navigraph up to date, installed with their FMS data thingy.

 

EGDY/26 DCT IPZOL DCT ATWEL DCT TIVER ( I put the approach in to get EX & then put the hold in, so it duplicated EX anyway )
Hold EX NW/287 107/L 185kts 3500ft 1.0 min
EGTE ILS26 via EX1

 

The hold page radial is always the reciprocal of inbd crs ( or the other way rtound ), you can't decouple them when you're setting up a hold... this doesn't seem right? is inbd crs not the course to the fix before you enter the hold, rather than while you're in the hold, which would be a bit pointless to enter. Surely you're not expected to overfly the fix on a precise track to enter a hold & turn to the correct outbound radial. In this case the entry would nominally be 126/L, but if I put that in the outbound radial is completely wrong and I can't change it without changing the entry!. The AP doesn't want to enter at 126 anyway. I'm only querying this & not taking it as the inbound leg of the hold ( like it originally appeared to be ) because in the flight the a/c seems to be attempting to fly the reciprocal of the course into the hold rather than what's set in the FMS.

 

FMS is definitely set to show Magnetic, although the declination in this part of the world is about -0.6 anyway...

 

CRJ-egte1.thumb.jpg.f7b1fff33f256b7e19c2c06a48e84a00.jpg

Route in FMS shows the hold is in the right place & roughly right shape

unknown_2022_01.09-19_11.thumb.png.5a66136e56c5b18c5a3facd341c01c5b.png

 

It cut the corner a bit much after ATWEL & missed TIVER by some way.

unknown_2022_01.09-19_12.thumb.png.6a9d5fda5b63376d660634c480806056.png

 

and here we get into the hold. I pulled the HUD down & controlled the speed as if I was formation flying, so the marker never left the 185kts bug. One notch of flap. I had to hit active pause to answer the door & when I unpaused we were doing 220kts(!), hence one turn is a bit wider. Altitude had crept up to 3700ft by the exit. Red dot is about where I armed the exit - FMS jumped straight to D112D rather than overflying EX again. Held the 185kts bug ( I'm not going to claim I held the exact speed ) all the way to the ILS.

CRJ-egte2.thumb.jpg.915138980f0498b98394b7cc1b6dcf9e.jpg.

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  • 2 weeks later...

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