Look in the aircraft.cfg of any stock FSX airplane and you will see the contact points section
For example:
//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)
//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
[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
In the above the first 3 contact points are Class 1 = wheels. Class 2 contact points are what you want as they stipulate the external points on the airplane model. For example contact points 3 and 4 look like the wing tips.
Roy