Failed segmented boattail experiment using drawer slides

[kach22i]

Originally Posted by Piwoslaw

Fellow forumers, we need to coerce Cd to remove the word 'Failed' from the title of this thread.

Or just ask the mods, explaining it is misleading.:P

I agree, I see this creation as a working experiment and as a stepping stone to something even cooler.

[Cd]

I have started taking back things I bought for this project.
Total loss so far is over $411, which is ridiculous.
The main cost was aluminum bracing at $114.
I used 8' aluminum ( flooring ) transition strips at $14 a piece.
Actual aluminum bar is crazy expensive !
I think I would end up needing twice the amount I bought to create a strong structure, and that doesn't even include framing for the belly pan.
Next was the lights at $ 63. The main lights and the interior light that I planned to use as a reverse light.
After that was the drawer slides at $24 for a set of 2.
I bought two and stacked them on top of each other.
As the bottom slides forward, it carries the top sliders forwards.
What really sneaks up on you and adds up fast are little things like screws and bolts.
I spent probably $55 - $60 ...or more ! on nuts and bolts / screws and washers alone.
Then wiring and cable the ratchet strap etc.

I got all the Coroplast free from my job.
Just after Xmas is a great time to source it.
I told myself not to add all of this up and just go for it - but to save the receipts.
I added it up the other day and see I went over my target budget by over double.

I took back the lights and some other stuff, so I can deduct about $100 off of this experiment.

I started this with the intention of seeing just how compact of a boattail I could create that was effective.

I started out with a really steep angle. I used the Tesla Model X angle as a guide.

As I went farther into this though, my OCD took over and I was just like " Why the hell not ! " and I decided to go all out to test all four lengths on the car - Stock with small spoiler / retracted Kammback / Kammback with second extension out / and full length boattail.

Major goals were to have the entire tail be removable in 30 min or less.
So far, my best time is 14 minutes.
Also, I wanted to control the extending and retraction of the tail from the drivers seat while in motion.
(You pull a cable )
I tested it in a crude drive around my apartment driveway.
It worked.
I also took it over some speed bumps.
Nothing fell off or came loose in four test runs .

[Cd]

Here is everything off of the car :




Here is another image edit of how I inteded it to look when done :



And this was how far I got :

[aerohead]

I consider it a great success.'merican enginuity.'
Very Buckminster Fuller-esque.
Along with the narrative, we got something 'concrete' to help 'imagineering'.
I can see exactly where you were going with the project.
'Paying it forwards'.
Inspiring.
I'm indebted to you.

[Cd]

As far as a rough proof of concept, I'd call it a possible success.
But as far as actually road testing it, well that flopped.

I hope it gives others here on the forum some options on how to create a boattail without it being too long to not be cumbersome.

[freebeard]

....a possible success.

So long as you have the components, adding a ratchet strap spine is a testable configuration.

Else with the same sliding mechanism, substitute base plates for the Armadillo shell design.

[Piwoslaw]

Cd, you did an excellent job and I'm sure you did not pave the road for nothing. Once you have shown it is doable, someone will follow.

It is a pity that you did not get a chance to A-B test the different stages of extension, as seeing the real changes in Cd would motivate others to follow.
But I do respect your concern for safety above all else.

Once again - Thank you for doing this, and for documenting it!!

[aerohead]

https://www.wired.com/2011/05/x-priz...ts-207-5-mpge/

Originally Posted by Cd

As far as a rough proof of concept, I'd call it a possible success.
But as far as actually road testing it, well that flopped.

I hope it gives others here on the forum some options on how to create a boattail without it being too long to not be cumbersome.

The fundamentals you've incorporated have been tested and repeated time and time again.
Since no magic is involved, if one has success, and you mimic their architecture, physics demands that your performance would perform likewise.
The WW-II OPEL Blitz truck was manufactured by both GM's Adam Opel AG and Mercedes-Benz. If you stuck either one in the FKFS wind tunnel, you'd have the Cd for 'both.'
If Illuminati Motor's 2012 X-Prize entry can come in at Cd 0.165, then you ought to be in Cd 0.15 territory. You might have to glaze the 'louvered' area, but otherwise, I see no reason why 0.15 wouldn't be on the table.
Elliott G. Reid's isolated plan-taper research at Stanford University suggests that you could be below Cd 0.14. So I'm being conservative.
Your 'fundamentals' are spot-on.

[Cd]

Originally Posted by freebeard

So long as you have the components, adding a ratchet strap spine is a testable configuration.

Else with the same sliding mechanism, substitute base plates for the Armadillo shell design.

I'll have to create a new thread if and when I work on this again.
I'd like to find out more about that " spine " idea, and will post some images so that you can see what I am working with.
I like the idea of a second "throwaway" bumper, but that eats into my budget, as well as adding yet another piece that needs to be removed each time I take the tail off.

I appreciate all of your feedback and will be sure to ask for advice if I want to go farther with this.

[Cd]

Piwoslaw : Appreciate that.
Even if I do get this thing fully road legal, I don't drive much at all so wouldn't be able to do any testing.

Aerohead :
There would be a huge amount of drag where the louvers are.
The underside would also most likely not be smooth enough for good attacment all the way to the rear.
I planned a diffuser and a venturi tunnel, but it's a pain working under the car - especially since I live in an apartment and don't have a garage.

I planned to add window screen over the louvers. This would help the drag, but I'm not sure how much.

Overall, I would expect a cD similar to your truck, but much higher because of the louvers.

When the 5th generation Civic came out, Honda qioted a .32 cD for the Civic coupe, and a .31 cD for the hatchback .
However, Honda quoted a .36 cD for the coupe in 1996, when talking about how the Civic cD compared to the Insight.
The shape was identical to the 1992 - 1995 model though, with only the addition of a different headlight design.
So I'm guessing my cars stock cD to be at closer to .36 to start.