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Contact points, explained and some fixes

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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Tue Apr 19, 2005 9:13 am 

This is part one of this thread.
The reason for this thread is to explain and offer some user fixes and enhancements to the visuals as well as actual handling of the aircraft.
The visual is: that you can see the aircraft wheels touching down exactly on the runway without sinking etc., as well as seeing 2 rubbermarks from each bogey instead of only one, more realistic smoke coming from ALL wheels and bogeys instead of only '1' wheel per bogey.
The handling is: You can feel the gear more and better because there are more 'contact points'. You can feel this during taxiing, takoff and landing.

Basic info: The contact points are located in the aircraft.cfg file that is located in the main aircraft folder of each aircraft in the flight sim directory.
They appear as- [contact_points] Underneath this heading is typically 3 lines of information which defines the wheels. Even if it is a 747 with 18 wheels, there are only 3 'computer wheels' I am looking into the main reason as to why the aircraft designers do it this way.
Underneath the '3 wheels' are the scrape points. There may be 3 or 4 scrape points or even more than 10!
Scrape points are the contact points where the aircraft can become damaged from 'contacting' the ground.
A typical contact point looks like this:
point.0=1, -8.5, -15.9, -18.0, 1574.8, 1.000000, 5.826899, 23.0 ,1.000000, 2.500000, 0.900000, 18.000000, 18.000000, 2.000000, 0.000000, 0.000000
Many of these numbers are a reference in distance. If you change them, they 'move' the wheels back, forth, up and down etc. For example that number above that is -8.5? This means that this 'wheel' is minus 8.5 feet from the main measuring point (Datum) of the aircraft.

Cont.
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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Thu Apr 21, 2005 10:40 am 

... sometimes 'crashes' occur when landing etc.,, even while taxiing! You know? When the aircraft jumps around,, causing smoke to come from the nose wheel? Also, you may see the nose wheel sinking into the ground. WELL!!! Guess what!?!?!?! If the nose wheel sinks into the ground tooooooo much--- the scrape point for the nose wheel will contact the runway/taxiway and WHAMMOOOOO!!! crash time!!! The way to fix this is to go into the cfg file and do one of or all of the following- 1. go tio the static cg info at the bottom of the contact points and raise the nose a little. 2. go to the scrape point for the nose wheel and '//' it! 3. go to the nose wheel contact point and raise the nose wheel.

static_pitch=-0.719605
static_cg_height=12.890305
gear_system_type=0

See where it says static_pitch=-0.719605 ? well, if you change it to: 0.819605 this will raise the aircrafts nose. It is like adding more air to the strut, or shifting the weight a little back towards the rear. Experiment with it. Use a copy of the cfg file. This way if you 'muck' it up, all you have to do is put your original back in.

point.0=1.000000,103.68,1.000000,-10.500,1574.803150,
point.1=1.000000,103.68,-1.000000,-10.500,1574.803

These lines are the points that I.D. the nose wheel assy. There are 2 lines because with this aircraft (A380) there are 2 nose wheels. Anyway, the 4th number represents the 'height' of the nose wheel. See where, in the lines, it reads -10.500 ? Well, this means that the nose wheels are 10.5 feet from the aircraft mounting point (Datum) So! If you make this no. 10. 8 feet, it will push the wheel into the runway. If you make it 10.0 feet, this may raise the wheel to where it appears to be floating in the air!!!

Cont.[/b]
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Elkinallen
First Officer
First Officer

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Joined: Sep 24, 2004
Posts: 448
Posted: Fri Apr 22, 2005 9:13 am 

What are the numbers you can change and what do they do?

[contact_points]

//0 Class <0=none,1=wheel, 2=scrape, 3=float>
//1 Longitudinal Position (feet)
//2 Lateral Position (feet)
//3 Vertical Position (feet)
//4 Impact Damage Threshold (Feet Per Minute)
//5 Brake Map (0=None, 1=Left, 2=Right)
//6 Wheel Radius (feet)
//7 Steer Angle (degrees)
//8 Static Compression (feet) (0 if rigid)
//9 Max/Static Compression Ratio
//10 Damping Ratio (0=Undamped, 1=Critically Damped)
//11 Extension Time (seconds)
//12 Retraction Time (seconds)
//13 Sound Type
//14 Airspeed limit for retraction (KIAS)
//15 Airspeed that gear gets damage at (KIAS)

This is an excerpt from the FS9 default 747-400's ac cfg file. Nice hmm? It explains what does what,,, kinda.
Really, the only numbers you r e a l l y want to mess with are the first 4.
The first 4 numbers define where each wheel is in relation to the axis if the airframe. I.e., How far back, to one side, and how far away (How high/low) E.g,
point.1= 1.0, 30.0, -15.0, -12.0, This is an example of a 'wheel'. It is a wheel because that first number is a '1'. If it were a '2', it would be a scrape point. The 30.0 says the wheel is 30.0 'feet' forward of datum (A invisible measuring point in the center, or about, of the airframe). The -15.0 says the wheel is 15.0 feet to the left of centerline (Of the fuselage) If there were no - sign, it would mean that the wheel was right of centerline. (a - sign means either left or below).
The -12.0 means that the wheel is 12.0 feet below the fuselage.

All the other numbers mean,,, well just what the excerpt above states.

cont.
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Elkinallen
First Officer
First Officer

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Joined: Sep 24, 2004
Posts: 448
Posted: Mon Apr 25, 2005 10:35 am 

RadarMan was right. Some of the runway/airport surface areas are 'uneven' as far as the computer interpretation goes. Seattle is bad for this. This is the airport that really causes nosewheel bumping/bouncing. This is the airport where I test all the planes I work on. I have found that adjusting the CG up and down elliminates the bouncing. Each aircraft reacts differently and requires individual attention (Adjustment) I have also found that the same aircraft will behave differently on different computers. I.e., I adjusted an aircraft to where it was performing perfectly. I saved the file and inserted it to the same aircraft on another computer and It didn't work!!! So, this means that the aircraft has to be adjusted for the 'computer it is on'.

HERE is the way to adjust bogey's so that upon landing/touchdown the wheels won't appear to be floating, sinking etc.

The reason the wheels appear to be floating on rotation or flare touchdown is because the [contact_point] is too far back behind the visual (Graphic) wheels. (The computer is registering the 'wheels' forward/aft of what you are seeing on the screen).
Aircraft with bogeys that are in a tilt position allways seem to be sunk in the runway on rotation and on touchdown. Such as a 747 or the A340. You notice how when the aircraft rotates, the bogey 'snaps' to its tilt position sinking the aft axle wheels in the runway??? OR when the aircraft is just touching down, the rear axle wheels sink into the runway and then the bogey 'snaps' to the flat position?!?!?! The reason for this is there is only ONE contact point for the ENTIRE bogey!!! and it is exactly below the gear leg. SO!!! The [contact_point] will not register touichdown until the 'one' point touches. The bogey would tilt properly AND touchdown properly if there were at least one contact point for each axle, meaning: A contact point right where each tire is instead of only one just below the main gear leg. GET IT?!?!

Cont.
Very Happy
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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Tue Apr 26, 2005 1:43 pm 

Here is how to add points to a wheel assy.

The line below shows the nose wheel and the left wing gear contact points of a 747 before being modified. Notice the 2nd and the 3rd numbers in the two lines? These numbers are the ones to change/add so that the contact points are where the actual wheels are.
The 3rd number in the nose wheel line reads- 0.0 This means that the wheel is perfectly centered below the aircraft's centerline (Laterally).

Now. Look at the 2nd and the 3rd numbers in the wing gear line and compare them to the modified lines below the first example.
(For simplicity, only the first few numbers are included in this example so that it fits neatly in the space here.)

[contact_points]
point.0=1, 86.8, 0.0, -17.4, 1574.8, 0.000000, 5.826899, 70.0

//wgl
point.1=1, -9.5, -16.9, -18.0, 1574.8, 1.000000, 5.826899, 23.0


NOW!!! see how there are 2 lines for the nose wheel? See how the 3rd number reads -1.0 and 1.0? This is because there are TWO! wheels for the nose gear and they are 1 foot to the left and 1 foot to the right of centerline (This is what the -1.0 and 1.0 means verses the 0.0) Get it?
NOW!! compare the numbers in the modified wing gear lines.
4 lines for 4 wheels. Check the 2nd numbers (For/aft distance) and the 3rd numbers (Lateral distance values).

[contact_points]
//ns
point.0=1, 86.8, -1.0, -17.4, 1574.8, 0.000000, 5.826899, 70.0
point.1=1, 86.8, 1.0, -17.4, 1574.8, 0.000000, 5.826899, 70.0


//wgl
point.2=1, -8.5, -15.9, -18.0, 1574.8, 1.000000, 5.826899, 23.0
point.3=1, -8.5, -18.9, -18.0, 1574.8, 1.000000, 5.826899, 23.0
point.4=1, -11.5, -15.9, -18.0, 1574.8, 1.000000, 5.826899, 23.0
point.5=1, -11.5, -18.9, -18.0, 1574.8, 1.000000, 5.826899, 23.0

To add points, all you have to do is copy/paste the nose line and one of the main gear lines and then change the lateral and longitudinal values to represent the peticular gear leg.

Other numbers to be aware of are the brake values. In order to keep differential steering on the mains, you have to make certain that the 6th number in each main contact point has a 1.0 for the left 'brake map' and a 2.0 for the right.

Go get'm boys!!!!!

Shocked Shocked Very Happy Very Happy Wink
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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Thu Apr 28, 2005 9:36 am 

I have a 747-200 that I allways fly. but it had a gear problem where when it landed.
The wheels would flatten out before the aircraft appeared to touch down. Also, the wheel smoke would appear, at touchdown, very far back behind the gear. what I found out was that; the way the aircraft was designed, it had to have the contact points this far back because of the center of gravity. SO!!! what I did was: I moved the gear where it was supposed to be. THEN the plane fell on it's tail. SO!! I added 1200 lbs to the forward cargo hold via the ac cfg weight and ballance section. NOW the aircraft lands with perfect whell touch/tilt effects with the smoke RIGHT at the wheels as they touch.

SO!! If some of you are experiencing the same and or similar problem, it may be that the contact points are too far forward/aft of the graphics.
Wink
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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Sun May 29, 2005 2:20 pm 

Adjusting nose wheel damping/suspension.

If the nose wheel of your aircraft does not 'damp' the way you want it to,,, when you break, does the nose wheel compress enough? Well if it does not, here's what you do: Add a contact point inline and forward 3 or so feet in front of each wing landing gear. This does a nice job. If you want more info on this let me know. What it does is makes the aircraft rock back and forth on the mains and the 'new' wheels that you placed.

Side FX can be: If you place the new wheels too far forward, the nose may sink too much static and moving.

Let me know.

Very Happy
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twistedsucker
First Officer
First Officer

Pro Member

Joined: Jan 26, 2005
Posts: 363
Posted: Sun May 29, 2005 3:33 pm 

Wow, very nice information down there. Thanks a lot!
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ranald
Captain
Captain

Pro Member

Joined: Oct 12, 2004
Posts: 663
Posted: Sun May 29, 2005 4:50 pm 

Thanks Elkinallen Cool I heard you are the one to come to to find out how to get the effect of spray when on a wet runway and how to get better smoke effecs for the sim. Hows is this done Question
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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Mon May 30, 2005 8:45 am 

I'll give you the short version now in that I am on the run.

Smoke, wing tip vapor, thrust rain/snow blast, dirt blast, touchdown noises (Reverser lever/ mech gear impact noise) and a few others are what I have.

All done with: nicks jet smoke, posky snow/rain spray, and the others are freeware addons that I found in avsim and flightsim. They all require that you go into the aircraft and panel cfg and copy/paste and or write a few lines. NO BIGGIE!! I'll help you if you wish.

I'll get back here later. Hang on. Wink Wink Wink
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Elkinallen
First Officer
First Officer

Pro Member

Joined: Sep 24, 2004
Posts: 448
Posted: Tue Jun 28, 2005 5:18 pm 

Sorry man. I was out for 3 weeks. I went to Italy to see for myself what it looks like compared to FS9 scenery. HA! HA! Just kidding I was in Italy though.

Anyhow, the smoke is from Nicks engine smoke. It is a free download and you install the files in the fx folder and then go into the aircrafts cfg file and add a few lines to the lights section so that the smoke comes on when the throttle is advanced to a predetermined setting. It is important that you use different lights for EACH engine. If you use one light for all engines, the FX won't work right. OR!!!! As you can see below, I had to arrange the lights in this order. Funny, but,, well, what can I say? Computers!!!

Anyway here is a sample from a 747.

light.6 =6, 1.005, -70.1, -9.0, fx_nicksmoke737 //Engine 1 thrust smoke
light.7 =6, 21.0, -40.9, -12.5, fx_nicksmoke737 //Engine 2 thrust smoke
light.8 =8, 21.0, 40.9, -12.5, fx_nicksmoke737 //Engine 3 thrust smoke
light.9 =9, 1.005, 70.1, -9.0, fx_nicksmoke737 //Engine 4 thrust smoke
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