Contact points; Explain please

[OleBoy]

My focus has been building the Aeronca "K" more than anything. The aircraft.cfg currently in use is that of the FS2004 Aeronca "K", built by Steven Meyers.
As I know just enough to fiddle with any adjustments, I'm getting to where I need to adjust things to get the aircraft so it sits on the tarmac. Currently it's about 3ft. above that.

Going based on these CP settings I'm not sure which to adjust to bring it down to earth. Understanding them is (for me) a little confusing.
Will someone give me some pointers please?

//0 Class
//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) =16"



[contact_points]
point.0=1, -15.00, 0.0, -1.05, 1200, 0, 0.238, 30.0, 0.300, 2.5, 0.20, 0.0, 0.0, 0.0, 0.0, 0.0
point.1=1, 1.24, -3.0, -5.00, 1600, 1, 0.728, 0.0, 0.54, 2.5, 0.65, 0.0, 0.0, 2.0, 0.0, 0.0
point.2=1, 1.24, 3.0, -5.00, 1600, 2, 0.728, 0.0, 0.54, 2.5, 0.65, 0.0, 0.0, 3.0, 0.0, 0.0
point.3=2, -1.00, -17.7, 1.80, 800, 0, 0.000, 0.0, 0.000, 0.0, 0.000, 0.0, 0.0, 5.0, 0.0, 0.0
point.4=2, -1.00, 17.7, 1.80, 800, 0, 0.000, 0.0, 0.000, 0.0, 0.000, 0.0, 0.0, 6.0, 0.0, 0.0
point.5=2, -14.40, 0.0, 4.50, 800, 0, 0.000, 0.0, 0.000, 0.0, 0.000, 0.0, 0.0, 9.0, 0.0, 0.0
point.6=2, 5.40, 0.0, -2.20, 800, 0, 0.000, 0.0, 0.000, 0.0, 0.000, 0.0, 0.0, 4.0, 0.0, 0.0

[Hughes-MDflyer4]

Contact points with a type of "1" are wheel contact points. The next 3 numbers separated by commas are the X, Z, and Y locations of the points. Adjust the Y value (third value) to bring the points up/down.

Lets look at the first point as an example.

point.0=1, -15.00, 0.0, -1.05, 1200, 0, 0.238, 30.0, 0.300, 2.5, 0.20, 0.0, 0.0, 0.0, 0.0, 0.0

After the = sign, there is a 1. This number defines the type of point it is. (2 = scrape, 4 = float, 3 = skid, 1 = wheel) In this case, it is a wheel. The second number is -15. This is the X coordinate (moves the point foward/back). 0.0 is the Z coordinate (moves the point left/right). And -1.05 is the Y coordinate (moves the point up/down). Again, the Y value will be what you want to change in this case. It is very helpful to map Ctrl+R to the "Aircraft (Reload)" command. This way, you can make a change, save the cfg, then reload the aircraft to see the change without restarting the sim.

Hope this helps!

[beercan]

Another answer,

http://msdn.microsoft.com/en-us/library/cc526949.aspx#mozTocId836373

[N2056]

You need to get into the SDK and read the section on contact points. Each parameter is explained there. Keep in mind that the units used are decimal feet. Also understand that unless you have already established your datum reference point you will be doing this over again...:eek:

The trick where you add lights using the same coordinates as the contact points to "see" them is also good. ;)

Class will convene on TS later today...

[bstolle]

I'm getting to where I need to adjust things to get the aircraft so it sits on the tarmac. Currently it's about 3ft. above that.
//6 Wheel Radius (feet) =16

wheel radius has no visible effect on plane height, it's only used to set the correct rotation speed animation

[OleBoy]

Thanks all for the assistance. The bold reference I noted was meant that this is the only one I understood, somewhat.
The info that's derived in the SDK is obviously the way to go in learning anything relative in a modeling crusade, although in technical terms.
I like laymens terminology for explanation so I can grasp things at first. Then after understanding the principal in the objective things are easier for me all the way round.

Hughes-MDflyer4 put things into the terminology I was looking for. Thanks for that. I recall reading a thread somewhere that explained the contact points like this, but could not find the post again to reflect back on it.

Class? I won't be late! :)

[warchild]

yeahhh, theres three things that control the altitude of the object above a surface, whether thats wheels, skids floats, or water rudders. thos three things are the reference datum point, the static CG height and the individual contact coordinates.. it can get a bit confusing though.. raising the static CG raises the plane/boat, lowering the Reference datum point raises the plane or boat. Unless your sure you have those two worked out, dont even go near the individual contact coordinates. its just make you madder than a hatter and destroy any fun your having..
best thing to do is find a well done three view thats close if not too scale, and make a print out. then use a ruler to find your scale and take measurements..
If your working with an existing model, you can find something close to the default reference datum point the modeler used by opening the menu and bring up the aircraft. Tape a piece of onionskin or other semi transparent paper over the aircraft on the screen and draw an X from each coner of the preview window. Where the X meets in the middle is the modeled reference datum point.

[Milton Shupe]

I would recommend that you position your aircraft project in gmax something like I show in the attachments.

Center-line, 1/4 wing root cord, and at the prop spinner.

In the aircraft.cfg, this is the FS Reference point at 0,0,0.

Once it is positioned there, select a vertice on the bottom of your tire to get the exact x,y,z coordinates for the gear.

You can do the same for prop/engine, lights, tail wheel, etc.

If you measurements are in meters, convert them to feet to enter in the aircraft cfg.

You will find a contact point setup tute here that shows how to pick off your coordinates.

http://www.sim-outhouse.com/sohforums/showthread.php?944-Perfecting-Suspension-Setup-%28Repost%29

You can download the Aircraft Container SDK here:

http://download.microsoft.com/download/9/f/5/9f57691b-7c5f-4031-aa29-2ab00f676ba6/aircraft_container_setup.exe

[warchild]

I would recommend that you position your aircraft project in gmax something like I show in the attachments.

Center-line, 1/4 wing root cord, and at the prop spinner.

In the aircraft.cfg, this is the FS Reference point at 0,0,0.

Once it is positioned there, select a vertice on the bottom of your tire to get the exact x,y,z coordinates for the gear.

You can do the same for prop/engine, lights, tail wheel, etc.

If you measurements are in meters, convert them to feet to enter in the aircraft cfg.

You will find a contact point setup tute here that shows how to pick off your coordinates.

http://www.sim-outhouse.com/sohforums/showthread.php?944-Perfecting-Suspension-Setup-%28Repost%29

You can download the Aircraft Container SDK here:

http://download.microsoft.com/download/9/f/5/9f57691b-7c5f-4031-aa29-2ab00f676ba6/aircraft_container_setup.exe

Your awesome Milton.. thank you.. I'm so accustomed to working with off the shelf default fm's I've never considered it from a modelers point of view..

[hairyspin]

Like Milton says. :salute:

Most people tackle this from a completed and compiled model already in .mdl format. We modelers have the gmax source file advantage for our own work. Just make sure, if the undercarriage is animated, that you do this for keyframe 0

[OleBoy]

Great info all.

Also Milton, your images provide me with other visual aspects pertaining to the mesh that is useful.

The data, coding and animation portion of the modeling process is slowly approaching. Of which I am trying to avoid like a cold.
Eventually I am going to have to deal with it.

[fliger747]

A dear departed program called Aircraft Container Manager showed wire frame models of the aircraft and the location of any desired contact object, weight and ight items. Only worked in XP and Vista but was a great utility. Not sure if you can find the program and a key.

T

[Milton Shupe]

Like Milton says. :salute:

Most people tackle this from a completed and compiled model already in .mdl format. We modelers have the gmax source file advantage for our own work. Just make sure, if the undercarriage is animated, that you do this for keyframe 0

For retractable gear, key frame should be at 100 for "hanging" gear (and to get contact points vertical distance to ground), and 200 for fully compressed (to calculate total suspension movement and determine max-static ratio).

I don't think he has animated the gear yet.

[hairyspin]

For retractable gear, key frame should be at 100 for "hanging" gear.

D'oh! Another senior moment from me... Cheers Milton!

[Dev One]

If you set your model up in Gmax as Milton says it also helps when you want to get the C of G position correct when you come to fly it, & dont forget the eye position, engine location etc.......
Another frustrating thing later on if you separate out your interior from your exterior is to get both models located at 0,0,0, 'cos when your interior model has all the bits removed that you will not see, Gmax automatically relocates the model......
Keith

[hairyspin]

You can avoid that with a parent node above the interior and exterior sections in the model hierarchy. The exterior or interior can be deleted without screwing up the other. Just don't delete the top node.

[Dev One]

Hairyspin, now you are talking 'computerese' to an old timer!!! At least as long as I remember my system (sometimes with difficulty at 74) I can get a reasonable result....I am though learning quite a few things from these forums, so thanks to all for publicizing them.
Keith

[n4gix]

Hairyspin, now you are talking 'computerese' to an old timer!!! At least as long as I remember my system (sometimes with difficulty at 74) I can get a reasonable result....I am though learning quite a few things from these forums, so thanks to all for publicizing them.
Keith
Okay, let's say the same thing in 'modelese' then...

Create a tiny planar polygon 0.01' using the "Create from Keyboard" method. It will automatically be placed at 0,0,0 coordinates. Link all current toplevel objects to this polygon. It will then serve as an 'anchor' to keep all the other objects in place.

[Dev One]

Thank you Bill, thats my type of aircraft engineering draughtsman/designer speak! KISS!!!
Keith

[hairyspin]

Sorry Keith, that wasn't talking computerese, it was gibbering gmax (a capital offence in a number of states).

Making a dummy object or tiny poly as Bill suggests and organising the other parts as follows gives a hierarchy like this:-

Aircraft

fuselage


l_wing
r_wing
tail etc...


virtual_cockpit_shell


instrument_panel
yoke
throttle quadrant etc...



and deleting fuselage and all its sub-objects will leave the VC hierarchy complete and still in place: Aircraft is the parent node for the whole model. Equally, deleting virtual_cockpit_shell and its sub-objects will leave the external model intact.

The objects are listed in the Select By Name dialog (key H), there's also a checkbox there to Display Subtree - that changes the display to show the model's hierarchy. Another checkbox for Select Subtree lets you select an object and all the sub-objects linked to it on down the hierarchy.

http://imageshack.us/a/img6/3396/hierarchyl.jpg



I think that's enough gibbering for now.

[Dev One]

Hairyspin - lovely, just what I needed, very well explained for the idiot like me! I now understand, thank you very much.
Keith