Simviation Forum - Contact points

Nov 4^th, 2007 at 11:29pm

garymbuska Offline
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I just finished a flight using the default CRJ in FSX and could not help but notice how bad the plane banks when turning I have actually noticed the tires sinking into the run way. Just wandering if any one else has the same problem and what numbers did they change.

contact_points]
point.0=1, -8.50, 0.00, -6.70, 1600, 0, 0.5625, 46.8, 0.80, 2.5, 0.55, 10.0, 10.0, 0, 260.0, 260.0
point.1=1, -56.50, -6.76, -8.60, 1600, 1, 1.0,    0.0, 0.90, 2.5, 0.65, 9.0, 9.0, 2, 260.0, 260.0
point.2=1, -56.50, 6.76, -8.60, 1600, 2, 1.0,    0.0, 0.90, 2.5, 0.65, 9.0, 9.0, 3, 260.0, 260.0
point.3=2, -65.00, -39.00, 0.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 5, 0.0, 0.0
point.4=2, -65.00, 39.00, 0.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 6, 0.0, 0.0
point.5=2, -43.00, 0.00, -3.80, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 9, 0.0, 0.0
point.6=2, -98.00, 0.00, 16.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 9, 0.0, 0.0
point.7=2, -8.00, 0.00, -2.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0
point.8=2, -80.00, 0.00, -1.50, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0

static_pitch = -1.8
static_cg_height = 7.3
gear_system_type=1       //Hydraulic
emergency_extension_type=2 //None=0,Pump=1,Gravity=2
any help appreciated Cool

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Reply #1 - Nov 5^th, 2007 at 7:44am

Brett_Henderson Offline
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I've notice that too.. and it's on my fix-it list..

The entries that matter are; "Static Compression", "Max/static Compression Ratio", and "Damping Ratio"...

contact_points]
point.0=1, -8.50, 0.00, -6.70, 1600, 0, 0.5625, 46.8, 0.80, 2.5, 0.55, 10.0, 10.0, 0, 260.0, 260.0
point.1=1, -56.50, -6.76, -8.60, 1600, 1, 1.0, 0.0, 0.90, 2.5, 0.65, 9.0, 9.0, 2, 260.0, 260.0
point.2=1, -56.50, 6.76, -8.60, 1600, 2, 1.0, 0.0, 0.90, 2.5, 0.65, 9.0, 9.0, 3, 260.0, 260.0
point.3=2, -65.00, -39.00, 0.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 5, 0.0, 0.0
point.4=2, -65.00, 39.00, 0.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 6, 0.0, 0.0
point.5=2, -43.00, 0.00, -3.80, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 9, 0.0, 0.0
point.6=2, -98.00, 0.00, 16.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 9, 0.0, 0.0
point.7=2, -8.00, 0.00, -2.00, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0
point.8=2, -80.00, 0.00, -1.50, 1000, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0

All the compression ratios are 2.5:1, which is pretty normal.. However, at first glance, the static compressions seem a little large for a plane that size. They're much larger than those of a Lear45, and about as large as those for a 737. Since the overall suspension travel is a ratio (2.5) of that static compression, it's probably TOO much travel. Combine this with the relatively low damping (kinda like the stiffness and shock-absorber value), and you'll get that uncomfortable wing-dipping while turning on the ground.

Another factor is the roll MOI, but tuning that for taxiing is not a good idea, as it changes the way the plane handles in the air (which is pretty good).

Make a backup of the aircraft.cfg file.. and then experiment by reducing the static compression, and increasing the damping. OR... maybe adjust the compression ration and the damping.. That way, you're less likely to have to go back and fix the vertical position of the contact point, and static CG, to keep the tire positioned propery on the ground (not floating or sinking)..

Edit.. to keep it simple at first.. try adjusting only the damping, and go from there... be advised that once you start messing around, you can end up chasing your tail (so that backup is doubly important).. But this is a relatively simple experiment.. have fun

Edit, edit: And...if you find the magic formula, be sure to share Grin

« Last Edit: Nov 5^th, 2007 at 1:01pm by Brett_Henderson »

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Reply #2 - Nov 5^th, 2007 at 12:57pm

garymbuska Offline
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Thanks Brett I will give it a try.
I might look at a CRJ that I have in FS2004 as well and see what it uses. One thing for sure is if I can not find a cure it is going to the bone yard as I can not stand a plane that tilts when taxing around corners. I do not mind a little drift but this is nuts! Cool

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Reply #3 - Nov 5^th, 2007 at 1:03pm

Brett_Henderson Offline
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That's fine, but remember that the amount of visual travel (animated into the model)is probaly not the same, and you can end up with sinking/floating tires..

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Reply #4 - Nov 5^th, 2007 at 2:36pm

garymbuska Offline
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Brett_Henderson wrote on Nov 5^th, 2007 at 1:03pm:

That's fine, but remember that the amount of visual travel (animated into the model)is probaly not the same, and you can end up with sinking/floating tires..

Yeah I know and I have to admit that bothers me a little but nothing ventured nothing gained as I always say Cool

I just downloaded this CRJ from AVSIM it is for FS2004 look at its contact points
[contact_points]
// 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
point.0=1, 36.00, 0.00, -5.30, 1181.1, 0, 0.8, 55.92, 0.35, 2.5, 0.6, 4.0, 4.0, 1, 250.0, 290.0
point.1=1, -4.00, -5.62, -5.95, 1574.8, 1, 0.8, 0.00, 0.35, 2.5, 0.6, 6.9, 6.5, 2, 250.0, 290.0
point.2=1, -4.00, 5.62, -5.95, 1574.8, 2, 0.8, 0.00, 0.35, 2.5, 0.6, 7.1, 6.5, 3, 250.0, 290.0

point.3=2, -18.5, -35.30, -1.28, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 5, 0.0, 0.0
point.4=2, -18.5, 35.30, -1.28, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 6, 0.0, 0.0
point.5=2, -50.70, 0.00, 3.24, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 9, 0.0, 0.0
point.6=2, -50.90, 0.00, 15.31, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0
point.7=2, 42.60, 0.00, -0.20, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0

max_number_of_points = 21

static_pitch= -0.5 //degrees, pitch when at rest on the ground (+=Up, -=Dn)
static_cg_height=5.62 //feet, altitude of CG when at rest on the ground
gear_system_type=1 //Hydraulic

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Reply #5 - Nov 5^th, 2007 at 7:10pm

Brett_Henderson Offline
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Try just increasing the damping from; .55, .65, .65 .. to .. .65, .75, .75 .. and see what happens.

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Reply #6 - Nov 5^th, 2007 at 10:10pm

garymbuska Offline
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Brett_Henderson wrote on Nov 5^th, 2007 at 7:10pm:

Try just increasing the damping from; .55, .65, .65 .. to .. .65, .75, .75 .. and see what happens.

I tried the values you suggested and they had absolutely no effect at all
Now my question do I have to completely re load the sim to test or is just changing aircraft good enough.

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Reply #7 - Nov 5^th, 2007 at 10:51pm

Felix/FFDS Offline
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garymbuska wrote on Nov 5^th, 2007 at 10:10pm:

Brett_Henderson wrote on Nov 5^th, 2007 at 7:10pm:

Try just increasing the damping from; .55, .65, .65 .. to .. .65, .75, .75 .. and see what happens.

I tried the values you suggested and they had absolutely no effect at all
Now my question do I have to completely re load the sim to test or is just changing aircraft good enough.

In your settings for FSX, you can configure a keypress (I use CTRL-SHFT-. (period)) to execute the command "Aircraft Reload"_)

I use it a lot when adding bits and pieces to the model.

Felix/FFDS

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Reply #8 - Nov 6^th, 2007 at 8:02am

garymbuska Offline
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Thanks Felix I was using the reset function on the main menu but was not sure if FSX reloads the aircraft cfg file. Because of the different way FSX seems to load from FS9 I thought it might preload the aircraft cfg files and not reload them unless you restarted FSX. Which I thought would be stupid but then remembered that this is Microsoft Wink

I tried several numbers in the damping area and it seamed not to have any effect at all which made me wonder if the aircraft cfg file was being reloaded. I am going to try some off the wall changes and see what happens. I made a back up of the original file. I will let every know what I discover. Cool

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