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Old 08-05-2024, 01:02 PM   #100 (permalink)
aerohead
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16-18-degrees

Quote:
Originally Posted by JohnForde View Post
Current plan: Cuff using HDPE. Cuff is 11 degrees and 18"L.
Doors of 55", just reaching 48" behind the bumper (legal). They can adjust the second break angle. Or just stay at 11 deg. I am hoping to tuft test and maintain attachment at 16 or 18 deg. This is to follow Aeroheads advice that drag is porportional to wake size, or as I call it, the 'aperture'.
Once I succeed on the basic tail I will put tail lights at the tips and add a foldable or detachable polycarbonate extension to ~96".
1) I'd focus on 'attached flow' as without it, there's no pressure recovery, and the 'wake' begins exactly at the point of separation.
2) If you can 'sneak up' on the 'cuff' with an 11-degree angle, and see 'where' it 'touches' the 'cuff,' that ought to be the actual 'origin' of the whale tail.
3) Don't rely on the 'cuff' itself for any meaningful pressure recovery. It's radius just isn't up to the task.
4) If you can get 11-degrees, just stay with it.
5) Any 'breaks' to a 'steeper' angle will be the trigger for an adverse pressure gradient that will kill flow attachment right then and there.
6) The new 'wake' size will be a function of the length of the tail. With drafting instruments, and a scale-drawing, you can ascertain what the new wake area will be, before you begin.
7) Another 'fly in the ointment' is vortex-induced drag. In 1984, P.W. Bearman reported on research of a proto-Windsor body of Cd 0.262 as a 'squareback'.
As rear downslope was introduced, creating a 'fastback', vortex drag initiated immediately, raising the Cd to as high as 0.37, depending on the angle.
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Last edited by aerohead; 08-05-2024 at 01:45 PM.. Reason: typo
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