First Electric van boat tail

[Piotrsko]

If aerodynamic were easy there wouldn't be a advanced degree required to be one to get hired.
Even the ones that made my head hurt explaining stuff to me admitted they didn't know everything.

You're in good company

I would think testing inthe rain would be helpful if it's waterproof

[Piotrsko]

So: no rain driving then?

[aerohead]

Originally Posted by JohnForde

Rainy here so with time on my hands I get wordier and my posts longer.

Amazon is selling me these 3 in the photo: Digital Manometer, Pitot & tubing. VMan455 is generously sending me pucks.

Tomorrow after the rain I shouid be able to do my first tuft test. Chaotic yarn will explain my lack of drag reduction. Attached flow would be perplexing.

In the mean time I have 2 theories: 1. Cuff needs smoothing, and 2. Corners leak to much air weakening sequestration. I will work on both today or tomorrow between rain showers. Then tuft test. Pressure test will have to wait a week.

I really am kind f surprised to see no improvement with 3 huge 11 degree slopes.

Thoughts anyone?

I laid in bed 'til after 2:00 AM thinking about it:
1) The black rubber 'corner' transition on each side is 'loose' aerodynamically. They need to be 'conformal' to a 'round-to-square' transition, and 'airtight', plus the region behind them, all the way to the trailing edge.
2) At the bottom, the 'floor' is positioned too 'high' aerodynamically, and it doesn't extend as far as the trailing edge of the tail.
--------------------------------------------------------------------------------------
3) At the top, the longitudinally-attached vortices which would be present on a semi-trailer's 'all-square' edge boat tail, would not 'present.'
4) The pressure recovery would be contaminated by the leakage, as you've mentioned.
5) At the bottom, the belly pan of the ZEVO does not project into the new length, so it's laminar flow has become 'all-turbulence'. On the semi-trailer it doesn't matter, as, even though it is 'skirted' along the sides, there is no 'belly' ( NASA is the only semi-trailer project which ever had one ), and in between the skirts there'd only be turbulence. On a 'car' this might make for a delta-Cd 0.015 drag increase. Delta-Cd 0.035 increase if there were a working rear diffuser.
6) Between the top and the bottom, there could be enough added drag in play, as to 'occlude' the benefit of the tail.
------------------------------------------------------------------------------------- It all has to do with the Bernoulli Theorem:
* ZEVO's forebody has 'displaced' 'calm' air, which was 'all - static - pressure', and accelerated it to dynamic flow, of mandatory 'lower-static -pressure', the primary SOURCE of aerodynamic drag of road vehicles.
* The tail is attempting to give the flow an 'off-ramp' from this accelerated condition, 'de-displacing' the streamline filaments along a diminishing cross-section, towards the position they resided in before ZEVO came along.
* If the tail has 'holes' in it, the low pressure ' forwards', where the flow is faster, telegraphs through the 'breach', diluting what would have otherwise been higher pressure from the separation line at the 'rear' of the tail, moving at its lower velocity.
------------------------------------------------------------------------------------
With project 'Spindletop,' the shape of the diffuser section of the CRX's tail made over a 1.5-mph difference in top speed at Bonneville, almost a 5% difference in Cd.
Jeff Howell et. al., at Loughborough University, is getting a Cd 0.295 Windsor body, down to Cd 0.133 with a full 3D boat tail, of 'rounded' edges, and lacking a diffuser of any kind.

[JohnForde]

Thanks

Originally Posted by aerohead

I laid in bed 'til after 2:00 AM thinking about it:

Thanks Aerohead. Me too.

1) The black rubber 'corner' transition on each side is 'loose' aerodynamically. They need to be 'conformal' to a 'round-to-square' transition, and 'airtight', plus the region behind them, all the way to the trailing edge.

I taped and screwed corop[last to seal the corners. Imperfect shape but pretty airtight.

2) At the bottom, the 'floor' is positioned too 'high' aerodynamically, and it doesn't extend as far as the trailing edge of the tail.

I need to position the floor high enough to keep the license plate visible.
Floor is only 4" shorter than walls & 7" shorter than top.

--------------------------------------------------------------------------------------
3) At the top, the longitudinally-attached vortices which would be present on a semi-trailer's 'all-square' edge boat tail, would not 'present.'
4) The pressure recovery would be contaminated by the leakage, as you've mentioned.

I don't think leakage is an issue.

5) At the bottom, the belly pan of the ZEVO does not project into the new length, so its laminar flow has become 'all-turbulence'. On the semi-trailer it doesn't matter, as, even though it is 'skirted' along the sides, there is no 'belly' ( NASA is the only semi-trailer project which ever had one ), and in between the skirts there'd only be turbulence. On a 'car' this might make for a delta-Cd 0.015 drag increase. Delta-Cd 0.035 increase if there were a working rear diffuser.
6) Between the top and the bottom, there could be enough added drag in play, as to 'occlude' the benefit of the tail.


------------------------------------------------------------------------------------- It all has to do with the Bernoulli Theorem:
* ZEVO's forebody has 'displaced' 'calm' air, which was 'all - static - pressure', and accelerated it to dynamic flow, of mandatory 'lower-static -pressure', the primary SOURCE of aerodynamic drag of road vehicles.
* The tail is attempting to give the flow an 'off-ramp' from this accelerated condition, 'de-displacing' the streamline filaments along a diminishing cross-section, towards the position they resided in before ZEVO came along.
* If the tail has 'holes' in it, the low pressure ' forwards', where the flow is faster, telegraphs through the 'breach', diluting what would have otherwise been higher pressure from the separation line at the 'rear' of the tail, moving at its lower velocity.
------------------------------------------------------------------------------------
With project 'Spindletop,' the shape of the diffuser section of the CRX's tail made over a 1.5-mph difference in top speed at Bonneville, almost a 5% difference in Cd.
Jeff Howell et. al., at Loughborough University, is getting a Cd 0.295 Windsor body, down to Cd 0.133 with a full 3D boat tail, of 'rounded' edges, and lacking a diffuser of any kind.

[JohnForde]

I have removed the 22" extension to 6'. I need to get numbers at 4' first.

My most recent effort addressed 2 areas: corner seal and rough cuff.

The corner is sealed with coroplast. I think successfully.

I tried to smooth the cuff with 1/8" HDPE. I taped the leading edge and screwed the rear. Unfortunately with a little sunshine the black HDPE expanded. This led to no improvement in cuff smoothness.

I saw no reduction in drag.

Next week I will begin pressure testing. Thanks to Vanm455 for sending me pucks.

My plan is to rebuild the cuff's 16" plywood by reducing its angle from 11 to 6 degrees. Then adding the doors at 10 degrees. I will; also flatten the top to 10 or less. I will seal against leakage then tuft & pressure test.

Thanks to everyone for your input.

JF

[freebeard]

What are doing for tail lights and the license plate?

[JohnForde]

Originally Posted by freebeard

What are doing for tail lights and the license plate?

I have not considered moving the license plate. Maybe I should. Sounds tricky/difficult.

The added tail lights are skinny, 46" behind the bumper and attached to the end of the wood doors. I have a 22" polycarbonate twin wall extension behind that. I just took it off until I get attached flow at 4'. Then I will re attach and try to get attached flow at 6'

[freebeard]

I'm perplexed by your indifferent results. The Trailer Tail[tm] seems to work Okay.

I'd try a curved panel (pace Mair) that could have an overlap onto the van, with the 1/4in edge beveled, sealed with aluminum tape,

[JohnForde]

Originally Posted by freebeard

I'm perplexed by your indifferent results. The Trailer Tail[tm] seems to work Okay.

I'd try a curved panel (pace Mair) that could have an overlap onto the van, with the 1/4in edge beveled, sealed with aluminum tape,

Interesting. Technically difficult. I will probably try.

[JohnForde]

Originally Posted by aerohead

I laid in bed 'til after 2:00 AM thinking about it:
1) The black rubber 'corner' transition on each side is 'loose' aerodynamically. They need to be 'conformal' to a 'round-to-square' transition, and 'airtight', plus the region behind them, all the way to the trailing edge.
2) At the bottom, the 'floor' is positioned too 'high' aerodynamically, and it doesn't extend as far as the trailing edge of the tail.
--------------------------------------------------------------------------------------
3) At the top, the longitudinally-attached vortices which would be present on a semi-trailer's 'all-square' edge boat tail, would not 'present.'
4) The pressure recovery would be contaminated by the leakage, as you've mentioned.
5) At the bottom, the belly pan of the ZEVO does not project into the new length, so it's laminar flow has become 'all-turbulence'. On the semi-trailer it doesn't matter, as, even though it is 'skirted' along the sides, there is no 'belly' ( NASA is the only semi-trailer project which ever had one ), and in between the skirts there'd only be turbulence. On a 'car' this might make for a delta-Cd 0.015 drag increase. Delta-Cd 0.035 increase if there were a working rear diffuser.
6) Between the top and the bottom, there could be enough added drag in play, as to 'occlude' the benefit of the tail.
------------------------------------------------------------------------------------- It all has to do with the Bernoulli Theorem:
* ZEVO's forebody has 'displaced' 'calm' air, which was 'all - static - pressure', and accelerated it to dynamic flow, of mandatory 'lower-static -pressure', the primary SOURCE of aerodynamic drag of road vehicles.
* The tail is attempting to give the flow an 'off-ramp' from this accelerated condition, 'de-displacing' the streamline filaments along a diminishing cross-section, towards the position they resided in before ZEVO came along.
* If the tail has 'holes' in it, the low pressure ' forwards', where the flow is faster, telegraphs through the 'breach', diluting what would have otherwise been higher pressure from the separation line at the 'rear' of the tail, moving at its lower velocity.
------------------------------------------------------------------------------------
With project 'Spindletop,' the shape of the diffuser section of the CRX's tail made over a 1.5-mph difference in top speed at Bonneville, almost a 5% difference in Cd.
Jeff Howell et. al., at Loughborough University, is getting a Cd 0.295 Windsor body, down to Cd 0.133 with a full 3D boat tail, of 'rounded' edges, and lacking a diffuser of any kind.

If sequestration is important wouldn't a back wall be helpful? Only $26 worth of polystyrene.