Quote:
Originally Posted by JohnForde
Before I cut the very expensive aluminum and polycarbonate I decided to do a plywood prototype. I am glad I did. It helped me think thru top corner intersections and attachment mechanisms.
Here are 5 pics. The angle on these is 28 degrees. I am aiming for 22.
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1) According to W.A. Mair's reporting, the boundary-layer would not survive the flow deceleration of 22-degrees until an elongation of 81.1" was obtained, and that's predicated upon all of that 81.1" constituted a lead-in curvature from the rectangular-cylinder 'box' body, necessary to maintain attached flow.
2) If using Mair's contour, your 'full whale-tail' would be 157.75" in total length.
3) Walter Korff of Lockheed Aircraft Corp. gives 156.24" total length.
4) GM's 1980 'OPTIMUM' tail gives 158.2" total length.
5) None of these tails exceeds 22-degrees on 'top'.
6) None of these tails exceeds 22-degrees on their sides.
7) 'Diffusers' run from 15-degrees, to zero.
8) NASA's curvilinear 'Shoebox' tail, at 45", was separating at 22-degrees.
9) ATDYNAMICs' 'Trailer Tail', positions it's tearing edge at an EBLA of 12.5-degrees @ 48" elongation
10) The Ahmed body achieves lowest drag at 9-degrees EBLA on top, the 'tail' portion constituting 21.5% of total body length, which would occur at 67.0" elongation on the ZEVO.
11) Paul Jaray's 'whale-tail' is the shortest, @ 115.6"
12) Walter Lay's, the 'longest', @ 211.4".
13) Lawrence Livermore National Laboratory never exceeds 15-degrees, their 'best' tail is limited to a EBLA of 11-degrees.
14) Renault chose 5-degrees for top/sides/ and diffuser on their V.I.R.A.G.E.S. semitrailer.
All the tails must be considered with respect to their particular geometries.
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The wake area/ delta-Cd relationship is valid only with attached flow.
Nothing but 'curvilinear' tails, known not to produce flow separation, can perform this hat trick.
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If you cannot stomach the 'curvilinear' construction, try to place the top, sides, and diffuser tearing edges where the 'curved' path would have been located. This dates to Dr. Hermann Burst, with his PORSCHE 911 RS ducktail spoiler, presently used on the Hyundai IONIQ 6, and M-B Vision EQXX, Lightyear Zero.