Roll Gradient/Stiffness
Roll Gradient/Stiffness
(OP)
I'm a little confused about the roll gradient equation given by Milliken in Race Car Vehicle Dynamics. A simplified version is at the bottom of p586, and the complete version including some derivition is found on pages 681-682.
My question came about when I was correlating some real world data to the output of the equation, and was out by a factor of 10. Milliken's equation states the result in rad/g, however I believe the acceleration units shouldn't be normalized to g's? So for example, if I'm working in metric units, the result should be rad/ms-2?
The force due to the lateral acceleration is F=MAy, with M being the unsprung mass, and Ay being the lateral acceleration (actual acceleration, not g's). This creates a moment about the roll axis which is H distance below the CG: Moment = FH = MAyH. So, if we have roll stiffness K in Nm/deg, then Moment/K = MAyH/K, so deg/Ay = MH/K. At no stage is Ay normalized to arrive at this equation.
Have I missed something obvious?
My question came about when I was correlating some real world data to the output of the equation, and was out by a factor of 10. Milliken's equation states the result in rad/g, however I believe the acceleration units shouldn't be normalized to g's? So for example, if I'm working in metric units, the result should be rad/ms-2?
The force due to the lateral acceleration is F=MAy, with M being the unsprung mass, and Ay being the lateral acceleration (actual acceleration, not g's). This creates a moment about the roll axis which is H distance below the CG: Moment = FH = MAyH. So, if we have roll stiffness K in Nm/deg, then Moment/K = MAyH/K, so deg/Ay = MH/K. At no stage is Ay normalized to arrive at this equation.
Have I missed something obvious?





RE: Roll Gradient/Stiffness
I hope this isn't what it sounds suspiciously like . . . and I suspect that your answers aren't "out" by exactly 10.0 either.
Norm
RE: Roll Gradient/Stiffness
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Roll Gradient/Stiffness
When Milliken says ay, he means the acceleration due to gravity.
When Milliken says Ay, he means ay/g.
His use of symbols is listed on the inside of the front cover.
RE: Roll Gradient/Stiffness
ay is lateral acceleration, not acceleration due to gravity.
I should never post before my first cup of coffee.
RE: Roll Gradient/Stiffness
Perhaps you can't plug and chug like you can from a textbook. I'm not convinced that is a bad thing.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Roll Gradient/Stiffness
RE: Roll Gradient/Stiffness
RE: Roll Gradient/Stiffness
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.