If a friction decrement with speed is used (input on card 12, field 7), at high speeds friction and thus maximum possible tire force will be reduced. Also, if both steering and traction inputs are included for a given tire, the vector sum of these inputs cannot exceed the maximum possible force for that tire. If too large a force is entered, the program will substitute the largest possible value (i.e., a value equal to the product of the weight on the tire multiplied by the coefficient of friction).
To illustrate the tractive/braking force input process, some examples are provided.
Example of Tractive/Braking Force Input. It is desired to apply the brakes of the rear wheels of a 4,000-lb vehicle (V1) strong enough to lock those wheels during the interval from 1.5 to 1.7 seconds after the program starts. Brake forces are zero at other times. (Steering input would be handled in a similar manner as this braking example.)
The inputs for Card 8 are as follows:
The brake pulse of -2000 lbs at the rear wheels comes on between 1.4 and 1.5 seconds, is the desired level of -2000 lbs. per rear wheel from 1.5 to 1.7, and then returns to zero at 1.8 seconds.
For any table inputs, the table values (torque or steer) before and after the start and end times for the tables are set equal to the beginning and/or ending values for the table, respectively.
Notice that the braking force input (-2000 lbs. on each rear wheel) exceeds the maximum friction force available at that wheel (approximately 1/4 of vehicle weight x friction coefficient). This is done to insure skidding. The program will combine this force vectorially with any steering forces present, and limit the resultant to the maximum friction force.
*Note: If using the articulated vehicle options, inputs must also be provided for the left and right trailer wheels.