Quote:
Originally Posted by RobertSmalls
I was under some mistaken impressions about what the tufts would look like, hoping for a sudden and easily discernable transition from attached to separated.
I studied this video of an airfoil for a while. It's a more intuitive flow visualization than tufts. It looks to me like a very thin seperation bubble begins to form around 4s into the video. It becomes quite thick, with corresponding increase in drag until 6-7s, but the airfoil hasn't stalled until 8s.
Comparing this airfoil to my tufts, I have to agree, the higher angles I tested have higher drag. The seperation bubble moves farther forward the steeper I make the tail.
I guess the tuft test confirmed that the underside of the tail will be a compromise between drivability and drag (neither of which I have good data on). I'm leaning towards 7°. However, another idea is to just go with 12° in fiberglass, and have a clip-on tail extension extension for road trips and FE runs, to bring the underside angle to 7° or even 3°. Although, would the reduction in drag underneath the car make up for the increase in transom area?
Btw, Jim, thanks for the tip on the brake cables. Those things annoy me every time I see them dangling from my car. |
Robert,I've gone back to 1922 and worked forward looking at tails 'n such.
It looks like everything 'helps' whether ideal or not.
The very existence of 'some' tail appears to offer,for lack of a better expression,a 'stuffing the wake' effect,which helps force where vorticity of the turbulence can go,keeping it closer to the outer,more energetic air rather than tumble 'deeply' into the void which would otherwise exist should the tail not be there.
Not very scientific,but it's my best take on something I have no specific data on.
Unless you can 'swing' the diffuser up and down,you've got to compromise or she'll get knocked off.
I'd just go for it and live with the difference.
Given more time,I might be able to accurately' predict' the drag difference,but I'm not there yet.
I can get away with murder with the trailer because of the inter-axle span,but that's not for everyone.