First Electric van boat tail

[freebeard]

A simple curved rather than straight extension.

[Piotrsko]

Hmmm odd stuff happening with the tufts over and behind the rear wheel

[JohnForde]

I dropped the leading edge of the foam floor 12" I will need to re-position the license plate. Only tested 10 miles. Might be an improvement.

[JohnForde]

After tilting the floor yesterday today I tightened the angle of the doors from 11 deg to 16 deg. The wake width is reduced from 48" to 34". Tomorrow I will cut away excess.

[JSH]

11 degrees to 16 degrees is a big jump to make between tests.

[aerohead]

Originally Posted by JohnForde

After tilting the floor yesterday today I tightened the angle of the doors from 11 deg to 16 deg. The wake width is reduced from 48" to 34". Tomorrow I will cut away excess.

I've mentioned that we have no direct analogue to Zevo, as related to reported test data.
P. T. Bearman did test a prismatic 'Windsor' saloon body square-back in 1984, which included 11-degrees, through 16-degrees rear slant ( roof only, no sides, nor 'diffuser' ) :
1) 'Any' slant created vortex-induced drag.
2) 'Profile drag' DID fall between, zero-degrees and 5-degrees, then rose again.
3) At 11-degrees, vortex-induced drag was Cd 0.01428
4) At 16-degree, vortex-induced drag had risen to Cd 0.04693 ( a 328% increase ).
5) For 'ALL' slant angles, drag increased.
-------------------------------------------------------------------------------------
6) The Ahmed body ( van ) 'square-back' experienced a drag minimum, with a rear slant angle of 9-degrees.
--------------------------------------------------------------------------------------
7) The soft-sided, 'Windsor body' square-back, achieved a drag minimum with a boat tail of 8-degrees, top and sides, with soft sides.
8) As slant angle increased to anything beyond 8-degrees, 3D trailing vortices pushed vortex-induced drag higher, increasing the total drag.
-------------------------------------------------------------------------------------
9) Revisiting Lawrence Livermore's research:
A) The #1 tail, with the 'LARGEST' wake, had lower drag than the two tails with the 'smallest' wakes.
B) The #2 tail, with the 2nd-largest wake, had the lowest-overall drag.
C) The tearing edge of the #2 tail would constitute the 'intercept' with the 'reversal point' of a 'streamlined' contour, at which flow would reattach, a captured-vortex would form, and a compromised pressure recovery would be realized, plus Hoerner's 'Angle of Flow', towards the wake would be 'optimum
;' and base pressure the highest.

[aerohead]

Originally Posted by JohnForde

After tilting the floor yesterday today I tightened the angle of the doors from 11 deg to 16 deg. The wake width is reduced from 48" to 34". Tomorrow I will cut away excess.

For both examples, the 'floor' does not extend the full length of the tail, allowing lower-pressure flow to adulterate what pressure recovery the top and sides are contributing?

[JohnForde]

Originally Posted by JSH

11 degrees to 16 degrees is a big jump to make between tests.

It was a simple revolting - now with bigger pie tabs!

[JohnForde]

Originally Posted by aerohead

I've mentioned that we have no direct analogue to Zevo, as related to reported test data.
P. T. Bearman did test a prismatic 'Windsor' saloon body square-back in 1984, which included 11-degrees, through 16-degrees rear slant ( roof only, no sides, nor 'diffuser' ) :
1) 'Any' slant created vortex-induced drag.
2) 'Profile drag' DID fall between, zero-degrees and 5-degrees, then rose again.
3) At 11-degrees, vortex-induced drag was Cd 0.01428
4) At 16-degree, vortex-induced drag had risen to Cd 0.04693 ( a 328% increase ).
5) For 'ALL' slant angles, drag increased.
-------------------------------------------------------------------------------------
6) The Ahmed body ( van ) 'square-back' experienced a drag minimum, with a rear slant angle of 9-degrees.
--------------------------------------------------------------------------------------
7) The soft-sided, 'Windsor body' square-back, achieved a drag minimum with a boat tail of 8-degrees, top and sides, with soft sides.
8) As slant angle increased to anything beyond 8-degrees, 3D trailing vortices pushed vortex-induced drag higher, increasing the total drag.
-------------------------------------------------------------------------------------
9) Revisiting Lawrence Livermore's research:
A) The #1 tail, with the 'LARGEST' wake, had lower drag than the two tails with the 'smallest' wakes.
B) The #2 tail, with the 2nd-largest wake, had the lowest-overall drag.
C) The tearing edge of the #2 tail would constitute the 'intercept' with the 'reversal point' of a 'streamlined' contour, at which flow would reattach, a captured-vortex would form, and a compromised pressure recovery would be realized, plus Hoerner's 'Angle of Flow', towards the wake would be 'optimum
;' and base pressure the highest.

I can go back to 11 degrees. Simple repostioning. My enthusiasm for 16 degrees came from observing attached tufts.
I am going on a 1500 mile trip Oct 3-7 and should settle on a configuration.

[JohnForde]

Structurally, I need a square corner on top at about 44" behind the bumper. After that I could soften the corners by cutting up a 16" diameter concrete forming tube and using that 8" radius to coroplast the corner from sharp to rounded.

Could this be effective in addressing the vortices problem?