Quote:
Originally Posted by RobertSmalls
The steeper the angle of the underside of a boat tail, the easier it is to live with. I want to know how steep I can make it without creating too much drag.
Here's what the test rig looks like. It's a tufted sheet of coroplast, with an L-shaped aluminium spine running perpendicular to the flutes to keep it straight. I attached the camera to the spine with shipping tape and bubble wrap, which is why the video isn't very stable.
A piece of mechanic's wire to adjust the angle is held in place by vise grips just inside the hatch. I made markings on the wire to indicate various angles, and calibrated with a protractor.
The good news is, even with a camera hanging off the back, it didn't come close to scraping at the end of my driveway. The bad news is, the airflow doesn't look great in ANY of the runs. I wonder what this test would look like on 3-wheeler's Insight with the smooth fiberglass underbody panels.
I was hoping to see a sudden flow regime change at a specific angle, but that didn't happen. I'm not sure what to make of the results. Thoughts?
I did four runs, at four different angles, which you can see at the following times in the video:
1. 10.5° 1:50
2. 13° 3:50
3. 7° 6:05
4. 4° 8:20
Vehicle speed: 25-35mph.
And yes, I tried to run some video editing software, but it's probably easiest if you just turn your monitor on its side and skip to the time marks indicated.
For comparison, there's some footage of MetroMPG's boattail tuft testing at 5:40 in the video here. |
Robert,just now got to see video.Great investigation,thanks!
Looks to me that 4-degree run was best.The tufts appeared to be forced onto the surface the best,rather than dangling out into space.The spanwise wiggling is indicative of turbulence,but it appears to be the least.
I'd be curious to see what less than 4-degrees looked like,but I realize the practicality of the shallow angle.
Thanks very much for the grunt work! These kinds of efforts are invaluable for all who will benefit.
