I know there are many people that don't know their vehicle’s CD and would like to get a good baseline without spending hours in the wind tunnel. I am throwing around the idea of a 3 run package deal for first time customers, which will allow us to calculate where you stack up and get wind tunnel data without the 2 hour minimum that we currently have. This would also allow you to have an A2 speed report with all required data for our program. Take the guess work out of what your think your vehicle is and get a more accurate measure of what it really is.
3 Run Package: $250 First time customer
Run1: Baseline- as you race to have a comparison
Run2- Change1
Run3- Change2
I would like to put in M2c here for anyone taking the trouble to go to a wind tunnel to do 3 to 5 other test points:
1 degree nose up
1 degree nose down
1 degree right (or left)
nose-up/right
nose-down/right
Measure side force and weight on wheels at each point.
Moment (normal force) data from these points vs. your CG may save your life. At Bonneville this year, at least two vehicles diverged from controlled "flight" and crashed due to aerodynamic instability in pitch and yaw. I am not a life-long LSR practitioner, however I do know aerodynamics. I saw an alarming number of aerodynamically unstable vehicles on the salt, and was even told of rules that led (unintentionally) in the direction of instability.
It is important to understand the interaction between vehicle mechanical and aerodynamic stability. We can have a marginally mechanically stable vehicle at low speed that is stable as aerodynamics take over at higher speed. We can also have a mechanically stable vehicle at low speed that is aerodynamically unstable and never know it until it hits the speed at which the aerodynamics overpower the mechanics. Then we have a problem and no time to solve it.
NOT a simple subject. At the risk of sounding arrogant, all LSR teams above 200 mph need to do more analysis and testing. By that, I mean real-live stability and control derivative math, and real tuft testing. Everyone I talked to thought they knew where the air was going on their cars. Not one knew: by my standards, anyone who tells me that their air is going more than 45 degrees off of the direction of the oil streaks needs to do some testing. The biggest names had no better idea than the smallest. Test, dammit.
Yarn tufts are the simplist test and will scare the pants off of most builders. That's why you should do it. With all due respect (and I DO respect them) to the highly experienced members of the LSR community both inside and outside of the governing bodies: qualifying a mechanically stable vehicle at a given speed is no guarantee that 10 mph more won't lead to an aerodynamic instability causing an uncontrolled departure (crash).
Analysis isn't a guarantee either. I would suggest that any vehicle with a CP ahead of its CG in yaw or pitch should not be allowed to run above 200 mph. This would be a more formal expansion of the ruling against "dustbin" fairings on bikes.
M<HO
