Contact points, Smoke

[OleBoy]

I've been fiddling with the contact points getting things dialed in to what makes sense visually, and by the numbers if I have them. I've been studying the areas pertaining to the aircraft.cfg, in both FSX and P3D SDK's. Contact points are within reason for static, although as soon as I apply throttle, the tailwheel lifts off the ground and the whole aircraft appears to rock fore-to-aft like a teeter-totter. I adjusted the static-pitch for a bit more down pressure, and this seemed to help a bit. Even though this is not the "correct" setting to adjust solely.

My main issue of concern currently;
I'm also having trouble with adjustments of contact smoke, the wheels are several inches above the contact point, but smoke and a tire screech are both evident. I'm confused what has to be adjusted to make the smoke evident when the tire, contact point and ground meets at the same time.

I hope I make some sense.

 

[Dev One]

Bit of a guess here, but everything may not come together until you apply your animation deflections for the wheels.
As for the teeter - totter - try moving the mainwheel contact point forward - I'm not sure of the true definition of the contact point forward of the zero datum, but It is possible that that point is the distance projected normal to the aircraft datum with the tail down & not that point measured normal to aircraft datum when horizontal! As for the tailwheel lifting when applying power, again possible problem until animated, but when I get that problem I play with the deflection (Static Compression) & stiffness (Max/ Static Compression ratio) values in the .cfg.
HTH
Keith

 

[hairyspin]

Static pitch (and static height) are to set the height and attitude of the model when it first appears in the sim: after that simulated gravity takes over and the contact points determine where it settles. Get these wrong and you may start with this:-

which may quickly turn into this:-

although FSX might not be as spectacular as CFS3....


As for the teeter-totter do you have any other scrape points defined, especially if borrowed from another model? They might interfere with the model's behaviour.

 

[Milton Shupe]

It would help if you provide a screen shot of the aircraft in gmax with the Grid turned on (G).

For simplicity, place the aircraft at centerline, the wings at 25% MAC (1/4 back from leading edge of wing), and vertically at the CoG which should be about at the prop spinner. See attachments. Your Exterior/interior nodes/pivots must be set to 0,0,0 aligned with world.

In the cfg, you would have these statements to agree then with gmax location:

reference_datum_position = 0, 0, 0
empty_weight_CG_position = -0.0, 0, 0

Once you have the aircraft positioned correctly, use your x,y,z coordinates to get your cfg parameters. Just select a vertex in the tire tread for gear, lights, prop spinner, etc and convert them to decimal feet for the cfg.

If you have the engine locations higher than the CoG, it will cause the tailwheel to raise off the ground with power.

Until you get the suspension dialed in, she will appear stiff legged and bouncy. However, you can fake the suspension with proper contact points until then. Unless you have real world data, use .3, 2.5, 0.9 (this equates to 4" of static compression and 7.5" of total movement) for main gear.
For the tailwheel, try .2, 2.5, 1.0

 

[Milton Shupe]

Regarding static pitch and height, their purpose is to load the aircraft in the sim at proper ground height and angle.

Go into to slew mode to see how it looks; turn off slew to see how it responds. MS recommends loading less than 4" off the ground to minimize the drop coming out of slew mode. It's okay to set it at ground level and tweak the angle until it load perfectly on the ground i.e. mains and tail gear equidistant from ground.

Keep in mind when the aircraft first loads, the suspension is "hanging" and will compress when it comes out of load or slew mode.
However once in the sim, if you enter slew mode on the ground, the suspension is compressed.

Changing static angle has no effect of the flight model and ground characteristics other than at load/slew time.

 

[Milton Shupe]

Regarding teeter-totter: It is important to get CoG correct so you have approx 20% of your weight on the tail wheel. To do this, ...

If you have the aircraft set as I described above with the grid at 25% MAC and vertically set at the spinner (average pilot weight, fuel, and engine are about at the spinner level), and the cfg contact points are correct, and the engine location thrust is correct to the spinner, then thrust-line should pull aircraft forward without raising tail wheel unless you have brakes on.

If wheels are too far rearward, or if engine location is incorrectly above CoG, then you will get teeter-totter.