Folding Aerocap
 

Hello Everyone -

This is the latest version of the Aerocap that I am working on for my truck. It consists of steel frame which is covered by a nylon/ canvas type material. The steel frame folds up similar to how a car's convertible top works and this Aerocap goes from "open" to "closed" in seconds. In the open position I have full access to the truck bed and I can load large items. This Aerocap can be completely disassembled and stored in a corner of the garage. It takes about 15 to 20 minutes to assemble/disassemble this Aerocap and it weighs roughly 40 or 50 pounds. I will be building a new version of this Aerocap soon as I would like to make some changes to the linkages of the steel frame and use a thicker, convertible type material for the top. I want to make sure the material is pulled tighter and the wrinkles are removed.

Here is a picture of the Aerocap closed:

https://ecomodder.com/forum/member-t...4-closed-1.jpg

And a picture of the Aerocap open:

https://ecomodder.com/forum/member-t...503-open-1.jpg

I would like to get any feedback from you guys (and girls) and any suggestions would be appreciated. Any thoughts on the aerodynamics of flexible materials, such as nylon canvas and convertible top material?

More pictures and info to come....

Looks good!

fabric
 

It would be susceptible to aeroelastic effects,causing it to deform from its intended shape when under load.A look through the rear-view could confirm.Other than that,she looks pretty sweet!:thumbup:

Can you post more of the folded images and closer up from different angles?

Overall it looks very cool.

How is the sound?

Any flapping or cascading ripples?


I like it.

Would the deforming be necessarily bad? If there was a high pressure area and it could push in vs a low pressure area that it could expand into. I guess the problem being the rigid parts that have to stay in one place.

How much does material make in the surface skin drag at say 70 mph? Would it be worth using a smooth fabric like Sunbrella vs rough duck canvas?

Actually Sunbrella is also woven, maybe PVC vinyl?

The local upholstery shop might have some tips on fit and material selection. Looks good.

Sweet.

Haartz cloth? Radiused leading edge?

How about cam-locks or inflated tubes to rigidify the shell. Is it rigid or flexible when not fastened to the bed?

Great build!
 

...ten years later. https://ecomodder.com/forum/showthre...html#post87074

Thanks! I didn't build windows in this version of my Aerocap, so I can't see what it happening when I drive, but I have observed the Aerocap from a chase car and sure enough the shape does deform. What suprised me was that it seemed to "inflate" into a nice rounded shape. From looking at the tufts, the are seemed to flow smoothly over the inflated shape. Below is a screenshot from a short video i took (I will post the video later if I can figure out how to remove the sound).

https://ecomodder.com/forum/member-t...ft-testing.png

Thanks Kach22i! There is no flapping or ripples that I am observing. My fabrication and sewing wasn't perfect, so when it is at rest, it is a little loose. But, once I get moving through the air it seems fill in pretty well. On my next version I hope to use a thicker material that fits tighter around the frame. I am hearing no sound from the aerocap. In fact, my truck seem queiter when I have the cap on. Here are more pictures:

https://ecomodder.com/forum/member-t...erspective.jpg

https://ecomodder.com/forum/member-t...e8508-tuft.jpg

https://ecomodder.com/forum/member-t...505-folded.jpg

I agree - I might have a professional sew up the next version of the top. I am going to look for someone that creates covertable tops for cars. I want the next version to have a similar fit and finish to a convertible mustang (or similar car). Just using this one as an experiment to iron out the kinks and learn how it will behave.

Thanks Freebeard!

I like the idea of cam-locks. I have some familiarity with sail camber inducers which might have an application here... I need to think about it.
The frame is rigid, but the cover is flexible when it is not connected to the bed.

Great minds think alike! I really like those renderings, botsapper! I agree with you, that a rigid frame with a soft covering is the way to go... From a cost, weight and functionality standpoint, it just makes sense. I just need to do more testing to figure out if it is more or less aerodynamic than an traditional fiberglass/ wood type aerocap.

Looks great! :)

This one looks taut:
https://ecomodder.com/forum/member-t...erspective.jpg
Where this one looks much looser.
https://ecomodder.com/forum/member-t...e8508-tuft.jpg
Is that a real difference or a trick of the light?

The tailgate bulkhead looks to be an opportunity to tension it. Fold into place and then pull back a fraction of an inch on the trailing edge.
There is a trailing step edge of 2-3" at the cab. It's reaching for the shape it wants to be. Is there room in the folding mechanism for curved front edges? Do you have a picture of the bare frame erected?

This is freaking cool!

What might be going on is the air under the cap is stagnant, and at ambient pressure or close to it, whereas the air moving over the outside of the cap, even though it's regaining pressure as it moves back, is at lower pressure. High pressure inside/low pressure outside => inflation. That's not necessarily a bad thing; this article-interview with a GM aerodynamic engineer quotes her as saying,

I think you'll need sensitive measurement to see any difference between this and a hard cover, but if you can manage that the results should be interesting as to which is better. I'm not sure which I'd put my money on.

Id spend a decent amount of money on that if you ever thought about selling a kit someone could assemble (weld/bolt together at home).....

Seriously I would just a thought.

If you were to sell a kit, the way to promote it would be to post a how-to on Instructables, and offer the kit if they don't want to fabricobble their own.

https://www.instructables.com/workshop/cars/projects/

Intuitively figured that the downward airflow will lift the fabric, that's why you might need sleeved seams or hoops on your fabric top and they wrap around transverse bars. In my old concept I left the aero-profile side/nerf bars rigid and you could attach cross bars and the fabric top could be zippered into place.
There are tension fabric structures are easy to install and quite hardy. https://www.youtube.com/watch?v=RuSfJseSoaA

Great shape and keeping close interest on your testing period...

Fair enough, I just wouldn’t mind paying a fair price for a product too. He spent a good amount of time and money and I just wouldn’t mind paying for a portion of the hard work if a kit or plan came available lol. I really like the folding idea for my truck as I use the bed a lot during certain times, then for months at a time I could use the aerocap for trips etc.

Would this be suitable for Etsy? :)

deformation
 

If you'd nailed a really clean shape,and then the airflow itself altered that form,you'd have a can of worms,as the deforming force would be varying as the square of the velocity and shape,all over the place,depending on elasticity.The stiffer the fabric the better.
It's why fabric-covered aircraft are shrunk-tensioned and doped to 'fix' the shape.You don't want the center of pressure moving around on you.
Race car driver,Bernd Rosemeyer was killed when under-spec,weak sheetmetal deformed at high speed,producing uncontrollable,destabilizing aerodynamic forces. Early V-2 development rockets crashed for the same reason.Wernher von Braun had to risk his life,close to the crashing in order to figure out what was happening.
Skin friction is only a minor portion of air drag.You could probably use carpet back there if you wanted.That entire area is already within a turbulent boundary layer,with the free,inviscid flow a couple inches above it,flowing laminar over all,as if it were on Teflon'd glass.Aeroelasticity is not your friend.

You are correct, Freebeard, in one of the pictures the cover is fairly taut, while in the other picture the cover is much looser. The material that I used for the cover was some sort of heavy nylon canvas which I bought from a local fabric shop. Unfortunately, this material is very sensitive to the temperature and it expands when it is cold and shrinks when it is warm or the sun is on it, which is not optimal for this application. My next version of this cover will have a much more robust material (convertible canvas) that should not have this problem.

I'm pretty sure I could curve the front edge - below is a picture of the bare frame.

https://ecomodder.com/forum/member-t...hout-cover.jpg

I was thinking the same thing, VMAN. It appears that the air outside the cap is a lower pressure than the air inside the cap causing the shape change. From my tuft testing, it appears that this is a good thing... I think.

Thanks, justinooo9! The only problem with trying to sell something like this is that all pickup trucks have different bed lengths and cab heights, which affects the length and position of all the levers and pivot points of the frame. So each type of truck would have to have its own aerocap frame and cover design.

Man, seeing these on more trucks would be awesome. Just not sure how to teach everyone to figure out the geometry of the frame....

Thanks botsapper - that's a good idea. I was also thinking that I am going to build more tension into my next version of the cap. By using a different cover material and beefing up the frame a little bit, I should be able to create quite a bit of tension which will resist the deformation. It will be interesting to see what happens.... I am kind of learning as I go.

Thank you for your input on this, Areohead, I really appreciate it! I wasn't sure if the deformation was a good or bad thing, but a post like this helps me know what direction I should work towards for my next version.

The other day I was on the highway and I was driving next to a Porsche 911 convertible with its top up. I was looking closely at his convertible top at speed and I noticed that it did not deform at all. No wrinkles, no shaking, no bulging... it acted as rigid structure. Although I don't have the resources that an major auto manufacturer does, I think I should be able to create a aerocap that performs similar to that convertible top. I've learned a lot from this first version of my cap and I hope to use all these lessons to create a better version.

It was a given with American convertibles 1965-1975 that highway runs were made with rear windows opened part way.

The expert in restoring Lincoln 1961-1967 four door convertible top mechanisms is an excellent subject in a series of videos and text (John Cashman, IIRC). Fascinating structure (back from when Americans were worthy of quality).

What’s the square footage of material that Lincoln roof?

.

That's the spirit. You could patent it and monetize it and sell a few, but show how and then offer the hard bits and you'll likely do as well if not better. The people who want one but can't afford a commercial product wouldn't be buying one anyway.

The geometry of the frame is the part I am curious about. How did you determine the dimensions you used? Feedback is available here.

tooo much blind spots

Great engineering. It will be interesting to see how it holds up under snow loads.

This is a fantastic concept. People buy trucks to haul things (occasionally). Most of the time most pickups are used as commuter cars. This would allow full use of the bed while improving highway mpg the rest of the time.

Perhaps v. II could have a small vinyl window below the third brake light.

With my 1985 Toyota Celica convertible, I noticed that my factory cloth top would "inflate" at speed even though the top was tight with support bows under the top. Just something to keep in mind. ;)

Hey, late to the game here, sorry about that. This looks great!!!! I appreciate you keeping it 6 inches or so off the tail gate in the back and not having been tempted to land right at the top. Here's something you I think will like, a lot. You could raise the back up another 4 to 6 inches creating more room under cap, and, it will lower the lift coefficient to make the truck even more stable at speed. In the winter icy driving conditions, you'll really notice the planted feel your truck will have. The higher rear panel will not affect the drag at all. These things I say are based THIS ARTICLE. Hope this helps.

Have you measured what impact this has on fuel economy?

Armadillo - belated welcome to the forum - great project!!


Acquaintances of mine have a boat canvas business.



Years ago (though not as long back as botsapper's thread) we brainstormed about doing something similar. They had the benefit of years of manufacturing folding frames and sewing taut tops to fit perfectly. They also regularly added clear plastic for windows (optional).



I suggested making a prototype for the most popular truck at the time, A-B-A testing it for MPG benefit, and posting the results online. They could have put together a kit (or gave away instructions for making the frame), and then sold the UV-resistant Sunbrella covering.



Ultimately I guess I wasn't persuasive enough! Nice to see someone finally do it.

Not a problem. Order the optional plastic window / digital camera package.

Old cabinetmaker's friend, tambour
 

Tesla used it...

https://www.youtube.com/watch?v=AC7U0UU-7mk

https://www.youtube.com/watch?v=TzuVGSZoRVw

Lightweight 'alu-mini-um' roller shutter https://www.youtube.com/watch?v=YVoygJsWmok

Nice design. Curious to hear what impact this has on your mileage?

OP. Do you have any numbers to post from a regular commute to give before and after mpg?