Dave, Keith Turk has his car tested in a new Tunnel started by a private party and it might be cheaper than $2,000/hr. I was thinking of less than $50 of tubing mounted to the front of the car. We are only talking about testing a device 14" x 5" x 4" that weights a couple of pounds. It only needs to be stuck out in front a couple of feet (in front of the bow wave) of the car. Burt Rutan used the same technique when testing Space Ship One. They attached various shapes out in front of a flat bed truck and ran up and down the runway at Mojave.
Our tunnel (A2 Wind Tunnel
www.A2WT.com) is the tunnel Keith tested, but very few full size wind tunnels are capable of 360deg of yaw which is where you would need to develop the flaps for a particular car. I would say that most all cars have different aero characteristics and there is no one model that will tell you what every car would do in a spin. You can either try to give it your best educated guess in the placement or test in a wind tunnel that can yaw the car 360deg to see
1) if they deploy in the configuration you install
2) what kind of lift numbers your car has as a function of Yaw angle.
With the data you can see at which speed and yaw angle you will produce enough lift for your car to become airborne.
I appreciate alternative testing methods and thinking out side the box, I also worked at a company in Phoenix that built UAV's, and we did the same type of testing as Burt Rutain because we did not have a wind tunnel readily available. But I’m not quite sure what testing the flaps alone in front of a vehicle would tell you? The roof flap is part of a complete system (the car) and without the cars interactions to the flap you are just guessing at how they would react in a spin with your car. Look at all the different roof shapes, windshields, window edges, qtr glass, A-B-C pillars etc… out there. All of those interact with the air flow and pressure over a car and a sharp edge will change the air flow different then that of a smooth edge. There are so many variables with aero that when it comes down to it, there is no easy cost effective way to test the flaps.
Speed has nothing to do with it. A pressure differential between the inside of the car and the roof is what deploys the flap. A NASCAR spin at low speed deploys the flap. NASCAR has determined the angle and placement through testing. The correct location on your car may be different.
The pressure difference is how the flap deploys, but speed has everything to do with a car becoming airborne. As I'm sure you all know, the aerodynamic forces (lift or downforce) will increase with the square of the speed (speed^2). This means every time the speed doubles, the forces increase by 4 times the amount. If you spin at 100 mph, chances are you are not going to become airborne, but if you spin at 200+ the chance is increased significantly. An example: I will keep the #'s and static balance simple for illustration. Say you have a car that is 4000# static (2000# front 2000# rear) and you test in a wind tunnel to find that at 120 deg yaw and 125 mph you have 600# lift on the rear. This will not make the car airborne because 2000# is greater then 600#. BUT, at 250mph (double the speed) you now have 2400# (4 times the force as you double the speed) on the rear and this will lift the car off the ground making it airborne.