Failed segmented boattail experiment using drawer slides

[C4Evermore]

Great work! It's not a failure if you've learned something from it. Hopefully you make another attempt with what you've learned.

I'm on version three of my front wheel well covers, and I think I'm finally satisfied with it. I definitely spend hundreds of dollars and countless hours on the ones in the trash but it was worth it.

[kach22i]

Maybe this thread will inspire someone to do an inflatable one next (me?).

I have a contact that I can source used vinyl banners from, they kept one out of the dumpster for me once. Some contact cement and a 12V blower fan I could be in business.

I just don't currently own a car or truck that would be a good candidate though.

My S10 pickup truck has been sitting for 1.5 years with a bad transmission, and it seems to be decaying into the earth every time I take a critical look at it.

[Cd]

Originally Posted by kach22i

Maybe this thread will inspire someone to do an inflatable one next (me?).

I have a contact that I can source used vinyl banners from, they kept one out of the dumpster for me once. Some contact cement and a 12V blower fan I could be in business.

I just don't currently own a car or truck that would be a good candidate though.


My S10 pickup truck has been sitting for 1.5 years with a bad transmission, and it seems to be decaying into the earth every time I take a critical look at it.

' Aerohead ' has proven the idea in years past on his truck.
I'm sure by now everyone here has seen those large Inflatable holiday decorations.
They use a small blower and can inflate a 10' tall object in around 10 seconds.
The main drawback is that the blower is going constantly.
This helps with punctures though.
My first thought about your idea was to inflate the tail using air going into the wake from the sides of the vehicle through a system of ducts.
That might create a parachute effect though even if it exits at the tip of the tail.

I'm also wondering about visibility. Clear plastic that is flexible is hard to see through.
Also, what about retraction in an emergency ?
With the drawer slide design, you pull the cable, and it all retracts into itself within a second or two.

[freebeard]

My first thought about your idea was to inflate the tail using air going into the wake from the sides of the vehicle through a system of ducts.

I incorporated that on my folding boat tail design, but dropped it when someone pointed oiut an obvious flaw, which I have forgotten again.

[aerohead]

Originally Posted by 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.

I spent a few hours noodling the Honda.
With zero elongation, but 'optimizing' details, I came up with Cd 0.2177.
I allowed for the louvers, using Texas Tech University's GM Aero Shell vs Cab-Wing- half tonneau as a 'discounting' metric ( there was only a 5.94% drag penalty between to two! ).
Concentrating on the aft-body, and respecting 'ichtyoid' ENTRANCE / RUN proportions, it seems like a 77-inch tail extension would place the car in the drag 'bucket.'
I keep coming up below Cd 0.14 potential.
It would require sweating all the details, something some members might enjoy, just for the challenge.
Your rendering evokes really high performance. It's really inspiring.

[aerohead]

Originally Posted by Cd

' Aerohead ' has proven the idea in years past on his truck.
I'm sure by now everyone here has seen those large Inflatable holiday decorations.
They use a small blower and can inflate a 10' tall object in around 10 seconds.
The main drawback is that the blower is going constantly.
This helps with punctures though.
My first thought about your idea was to inflate the tail using air going into the wake from the sides of the vehicle through a system of ducts.
That might create a parachute effect though even if it exits at the tip of the tail.

I'm also wondering about visibility. Clear plastic that is flexible is hard to see through.
Also, what about retraction in an emergency ?
With the drawer slide design, you pull the cable, and it all retracts into itself within a second or two.

* I'm of the opinion that, ram-air is inadequate as a source for envelope inflation and tension static pressure.
* Bruce Ruefer, of Lubbock, Texas used upper snorkels to harvest ram air for his patented semi-trailer boat-tail, but his envelope was miniscule compared to what we're talking about.
* I do not believe that there'd be any parachute effect. Air would flow in until it 'pooled', flow would stop, then ram air would just continually attack the opening, maintaining internal pressure.
* For 'powered inflation' I designed a guillotine reversing-valve'd chamber, which allows the air mover to both 'inflate' as well as ' evacuate' the envelope, with the pull of a cable. It could be solenoid activated.
* I'm unsure how 'quickly' the envelope could be evacuated.