AI Aircraft Rock Side to Side

[Guest hotshotmaverick]

Happy New Year.

I am new to the forum and am looking for a possible solution to following problem with FS2004.

Problem: AI aircraft (airliners) rock side to side while taxiing to or from a runway.

Any advice would be greatly appreciated.

[CRJ_simpilot]

Are these the default AI aircraft? If not I'm wondering if the vertical height settings are messed up or you have an elevation issue. Is it just at one airport?

[ColR1948]

CRJ above is right, we need more details.

Is it all ai aircraft or just one in particular?

Is it at just one airport?

Is it just at one particular spot at the airport?

[Guest hotshotmaverick]

The aircraft are not actual AI models. They are the models from HJG, Vistaliners, etc.

It is all aircraft at all airports.

Side to side movement only occurs on taxiways.

I did not have this problem before when using HJG models or other non AI designated models. The problem started some time ago but I did not bother to try and rectify until now.

[ColR1948]

Hmm.. Shame in a way because if they didn't do it before it is more than likely something you added then and it might have been easier to eliminate.

Unless by some remote chance you remember what you added back then, I'm thinking may be something to do with airfields, may be an enhancement package or something similar, just a guess.

[CRJ_simpilot]

This sounds like an elevation issue. That's all I can think of. Did you add mesh?

[tiger1962]

Also check that the AFCAD taxiways are wide enough. I've had a few that were only 15ft wide and had to be changed to 50ft wide.

[Guest hotshotmaverick]

Did not add mesh. How would I check and rectify if it is an elevation problem? My problem involves all airports.

[mrzippy]

Because you stated that the failing aircraft are non-AI models that you are using as AI aircraft, how do they perform as flyable aircraft taxiing down the taxiways? Do they still rock side to side?

[Guest hotshotmaverick]

Yes, they push off gates, they taxi to runway and takeoff. They too rock side to side.

[CRJ_simpilot]

It's more than likely the gear height then. You would have to edit the aircraft.cfg.

[ColR1948]

You say its not just one aircraft so editing the AC cfg 's seems a bit too much, to me its more like a scenery problem.

Does the rock from side to side look like a dog wagging it's tail so to speak on just odd spots then it taxis normal or is it doing it the full taxi route?

[Guest hotshotmaverick]

Yes, it is like a dog wagging its tail. It happens from the moment the aircraft taxis from the gate until lined up on runway centre line. Once on the runway, the take off roll is normal.

 

Made an interesting discovery. Vickers aircraft such as the Viscount, Vanguard and VC10 do not have the tail wagging problem. They taxi straight and true. Interesting to see a Viscount taxiing normally in front of B737 whose tail was moving side to side.

[tiger1962]

Have you added a taxispeed gauge or utility to your airliners recently which affects differential braking? Maybe the Vickers aircraft don't have differential braking?

[Guest hotshotmaverick]

Have not added taxispeed gauge or utility. The Vickers aircraft show "differential braking" when only one brake applied.

[tiger1962]

Okay, have you installed any airport enhancements or global mesh recently, or any other kind of AI aircraft utility?

[tgibson_new]

AI tail wagging is not an uncommon problem; I have seen it many times. Increasing the MOI values in the plane's aircraft.cfg file can reduce it by quite a bit, along with moving the contact points for the main gear back by a foot or so.

[Guest hotshotmaverick]

Tom, thank you for your reply.

Would you be able to give me some more details as to which MOI's should be increased.

I am familiar with modifying the aircraft.cfg files I just need some specifics so I get it right.

Thanks.

[tgibson_new]

Since tail wagging is yaw, it would be:

 

empty_weight_yaw_MOI=2640000

 

That's the value I use for small airliners.

 

Hope this helps,

[CRJ_simpilot]

This link has helped me immensely. https://msdn.microsoft.com/en-us/library/cc526949.aspx

 

I'll add it to my sig.

[Guest hotshotmaverick]

I changed the Yaw MOI to 2640000 on my DC8, DC10 and L1011 aircraft and I am pleased to say the result was great. Unfortunately I did not have the same success with my B707, B727 and B737 aircraft. Any thoughts as to why the change would not work on the Boeing aircraft?

[CRJ_simpilot]

Perhaps the values need to be different for that a/c?

[tgibson_new]

Perhaps those also need the contact point change?

[Guest hotshotmaverick]

I do not have a clue as to what Contact Points to change or to what value. I have done editing to the aircraft.cfg file when I have imported or deleted aircraft but I have not really done anything with any of the more intricate sections of the file.

[napamule2]

This is for the FS9 B747-400

 

FSX is more demanding when it comes to MOI's. In FS9 you need less MOI values than in FSX. But you can 'stiffen' handling as Mr Wilson said by changing MOI value higher.

 

What is happening with the 'rocking' is that the sim is using yaw to make tiny, but constant, corrections or changes as the ac moves down taxi way. It's 'hunting'. This yaw changes is done with the rudder. The rudder has effect on roll (in air file, section 1011). These get amplified if the MOI for roll is wrong (low). The Boeings have a higher MOI value (example: 35,000,000) than MD's (example: 2,600,000).

 

But, butt, cigerette butt: if the gear compression ratio is 'loose' this also will amplify the 'side to side' (roll) when Sim is 'hunting' for the correct heading it is trying to achieve. Try the values below. It will 'stiffen' the compression. It's ONLY FOR AI so no matter if it's 'off spec'. You want 'damping' and this will do it. And also, maybe, your (axis) rudder sensitivity should be 90% with 5% null. Can't hurt.

 

//Gear

point.0=1, -25.0, 0.0, -17.5, 1000.0, 0, 2.0, 70.0, 0.5, 3.5, 0.900, 9.0, 8.0, 0, 220, 250

point.1=1, -114.0, -18.0, -21.3, 2000.0, 1, 2.0, 13.0, 0.5, 4.5, 0.900, 11.0, 9.0, 2, 220, 250

point.2=1, -114.0, 18.0, -21.3, 2000.0, 2, 2.0, 13.0, 0.5, 4.5, 0.900, 11.0, 9.0, 3, 220, 250

 

As this is a stiffer compression your gear may be off the ground by 0.200 feet. Does it matter (it's AI)? If it does then change the height values (-17.5 to -17.2, -21.3 to -21.0, and -21.3 to -21.0). OK? OK!

 

MS gave the B747-400 the SAME MOI's in FS9 and FSX. Change it? Perhaps (FOR AI ONLY) it's best to change the moments by doubling (yes 2X) the MOI's for the Boeings. Nothing bad happens as thes tubes are not going to be doing aerobatics and are mostly straight line flying type ac. It may make you AP turns bigger radius. But that you can handle I guess. It all depends on what you are willing to give up in order to gain the upper hand with your 'custom' mods to the Sim. Your call.

 

//FS9

;Moments of Inertia

empty_weight_roll_MOI = 23352310 //o=13352310

empty_weight_pitch_MOI = 44223159 //o=24223159

empty_weight_yaw_MOI = 69531785 //o=39531785

empty_weight_coupled_MOI = 0

 

PS:

Perhaps you can use one paint for AI and leave the other paints alone. Then use that one paint as the AI ac. Then you can fly the other paints normally. Good luck.

Chuck B

Napamule