|
Jim,
I thought of an experiment I wish I had time to run before building my boat-tail. I'd like to know the maximum angle for mantaining attached flow across the underside of the tail. If I could get away with 9° instead of 7°, it would save a few inches of overall length, which would be great. Or if I can only get away with 4°, but I need 7° to meet my departure angle requirements, I'll make the first half 4° and the second half 11°.
Tuft testing at 30mph would determine that angle. Aerohead assures us Re* is achieved by that speed, so if flow is attached at 30mph, it will be attached at 80mph.
Attach a sheet of cardboard (with camera underneath) or plexiglas (with camera peering out through the hatch) to the stock rear diffuser, on a duct tape hinge. Attach 20 strands of yarn to its underside. Support the rear of the cardboard or plexi with a string, tied to the hatch. Adjust the length of the string with a clamp or something, to modulate the angle of the board (measured with protactor and plumb bob). Start at 0°, and test at various angles.
For extra credit, use a smoothly curved piece of cardboard or plexi.
Accuracy would improve if a cardboard boattail was already in place.
Did I just spend more time describing an experiment than it would take to execute it?
|