aero bed cap questions
 

Would like some help with designing my own aero bed cap. I have Google searched and searched through this forum and have yet to see anyone do an aero cap on an ext cab s10. I have looked at and downloaded the streamline template, but im very new to all this and im not sure how to interpret it. I plan to build the frame using 3/4" electrical conduit pipe, and i have a connection to get large sheets of 1/16" clear acrylic plastic. What id like help with is how to calculate the appropriate angle and curve for my truck. Not sure if it matters, but my ext cab s10 is lowered 3.5"f/4"r. Any help would be greatly appreciated

Side note, id also like to know hkw some people have made the streamline template transparent, allowing them to place it over a picture of their vehicle as a reference

Pssst! ;)
http://ecomodder.com/forum/showthrea...ion-21952.html

I'm not a fan of using acrylic as yer panels as they won't be able to take any significant amount of physical impact without shattering or cracking. Try some Coroplast or cardboard to experiment with first. ;)

The Template is not fit for purpose. It is for a free body moving against a ground plane. An aerocap is a special case. It needs to transition from a tight fit against the cab to a low arc at the tailgate, pace aerohead.

http://i1271.photobucket.com/albums/...itled-16_2.jpg
http://ecomodder.com/forum/showthread.php/baby-template-car-darko-2016-a-32673-26.html#post537059

Here is how I laid out streamlines:

http://ecomodder.com/forum/member-fr...9-100-0629.jpg

Here is the material I would use, Polymetal is stiff as 5/8" ply and skinned with aluminum. More expensive, but prefinished:

http://ecomodder.com/forum/member-fr...1-100-0866.jpg

But 1/8" ABS would be better that acrylic. This is for a teardrop, but it shows how you could use large sheets with minimal cutting. Think Armadillo:

http://ecomodder.com/forum/member-fr...17-trdrp1a.jpg

There is a recent aero-cap thread where wood slats were used. Seek it out, I might be able to find it. I'm mentioning it because he said he made a slight mistake not following the template true which no one else could see. You don't want to make the same error, apparently it is all to easy to make.

I've done over a hundred of these overlays, and I have to say an issue came up today when doing one for you.

I'm hoping Aerohead can make a clarification, it's a real puzzle.

Part of a photo Aerohead posted recently, flipped 180- degrees and given an Aero-template overlay. Oh yea, ground plane was out of tilt by 1/2 degree - fixed it.

Source profile photo:
5-175.jpg Photo by aerohead2 | Photobucket

Aerodynamics by George Kachadoorian | Photobucket
http://i184.photobucket.com/albums/x...psw2l4pyiq.jpg

The pink vertical line isn't supposed to be the line-up mark, but that's how it came out. I think we are supposed to use the yellow line, but I've seen people use the middle point of a flat roof (orange line). I wish I knew what to tell you.

Anyway.......... you have an extended cab, the 3-door, right?

This is the most conservative use of the template shifted all the way back.
http://i184.photobucket.com/albums/x...psbivvs9y7.jpg

This is the middle point, which I see used more often.
http://i184.photobucket.com/albums/x...psrj4vyvds.jpg

Base image so you can try your own.
http://i184.photobucket.com/albums/x...psbln0sjw2.jpg

There are slightly longer and shorter versions of the aero-template floating around, I use this green one just because I like the color to be honest. I think Bim-Bow-Blam or something like that made it up for the sticky thread at some point in time.

While trying to find the latest aero-cap posted in the forum, that nice wood one, I found the following.

Would you rock this topper on your ride? - Page 2 - Toyota Tacoma Forum
http://i4.photobucket.com/albums/y10...an-bed-cap.jpg

The above has too steep of an angle, but it is sexy looking.

There are quite a few other examples in that thread as well, some of them may have been posted in this forum before.

thanks guys...and this is why I made a thread. I found a few different things and I really only wanna do this once. ive seen the one that's on the crew cab Dakota an I have to agree that it looks very well built. I'm glad I asked for guidance cause I was actually using that one as a reference. only difference being that I knew I would have a different angle on mine cause that's a crew cab short bed and mine is an ext cab reg bed. different bed length and different wheel base.

kachi22i, ive seen ppl use the template in those same ways you've posted. and yes I do have an ext cab that has the third door. I'm glad I'm not the only one with an s10. I know its not the most efficient of small pickups out there, but I'm a GM guy born and raised. I considered a Nissan frontier, but didn't like the lack of aftermarket support compared to the S-series. from an aero point of view, id say they look about the same

http://i4.photobucket.com/albums/y10...an-bed-cap.jpg

That's a very interesting example. I don't think those are compound curves.

Starting with a rectangular sheet, you can make a simple conic curve starting from one corner, or have a flat diamond in the center with the four corner/tips bent or curved. Mixing the two might set up tensions in the sheet that would fight the fasteners on every jiggle, but maybe #1 on the side triangles and #2 on the top?

ok, so I used the streamline template and came up with this. does that look about right?http://s478.photobucket.com/user/yet...]=1&sort=1&o=0

Nada.

Oddly, the IMG tag doesn't display as Code. Maybe add a space at "right?[IMG]". But delete "?filters[user]=77882641&filters[recent]=1&sort=1&o=0" and try again.

Ca_Yeti, email it to me, I'll post it for you if you cannot get it to post.

If I cut and paste just this much, it takes me to the Photobucket page which fails to load the image. The problem may be with them.

Why not just create an album here and use it?

http://ecomodder.com/forum/member-ca...-aero-mods.png


aahh there we go lol

You mentioned a Dakota thread. Did you see this one?

http://ecomodder.com/forum/showthrea...ild-34179.html

I found it................was on the homepage of this forum.

http://ecomodder.com/forum/showthrea...-34179-15.html
http://ecomodder.com/forum/member-ma...161212-hdr.jpg
http://ecomodder.com/forum/member-ma...162550-hdr.jpg

https://lh3.googleusercontent.com/-Q...=w1597-h899-no
http://ecomodder.com/forum/showthread.php/1st-gen-toyota-tundra-aeroshell-build-34179-2.html#post520579

The CNC ribs would look good under clear plastic.

did I apply the template properly? how to I interpret it to calculate my angles? do I have to have compound curves?

that all wood one on the taco is just gorgeous, but waaay out of my skill and budget lol

Your photo is close to a direct profile, but not quite. So the overlay is approximate, but not precise. I think the angles are labeled on the profile drawing? And yes, the curve is compound, I think.

If you cut ribs from foam, and use 1/4" foam as a skin, you can fiberglass that, and get the shape with a lot less effort.

so should I try to take a more direct 90deg side profile and re-apply the template?

Thee Template is a harsh mistress. I think it's a distraction. It is dependent on a bluff hemispherical nose to set up the air flow over the rear tail section. It has a half-circular lateral section and your vehicle doesn't. I produced this to try and loosen it's grip on people's minds:

http://ecomodder.com/forum/showthread.php/why-does-template-have-half-body-revolution-23333.html

http://i.imgur.com/GlVjc.png

Once you get away from a pure body of revolution, what's happening at the front bumper will affect what happens at the top of the tailgate. :(

IMHO as long as you can get a seamless tangent at the cab and it doesn't taper too fast you're good to go. Consider the front of this car. The A-pillar and that front bumper approximate the shape of a cab and tailgate. This shows that you can approximate closely with two rectangles and a triangle.

http://ecomodder.com/forum/member-fr...6-100-0620.jpg

The challenge with a pickup is a two part problem, since you can't taper the bed. I view the Beetle similarly with the rear fenders substituting for the bed.

http://ecomodder.com/forum/member-fr...-untitled2.png

If the sides of the aerocap taper faster than the top, I think it would act like a tail-fin and improve directional stability on the road.

For your second question, you are looking for lofting in naval architecture.

Foam and fiberglass can turn out good, doesn't take that many tools just some patience if you want it to look good when you are done. Look up how to build a foam/fiberglass surfboard, same idea just with a aeroshell.

Here is my car with a second-hand wakeboard control arm split and lashed to the roof rack of my car.

http://ecomodder.com/forum/member-fr...2-100-1120.jpg

They are lightweight tempered aluminum, so they have good stiffness. In practice this would be cut down and transferred to my '58 Beetle. I bought three altogether, for various purposes, from five to eight feet long.

http://ecomodder.com/forum/member-fr...0-100-1101.jpg

They could be used as lateral or longitudinal formers.

my angles
 

I wish we had a proper,technical drawing of your truck,showing true lengths.
Anything you do back there is gonna help,but if you really wanted to 'nail it',you'd want something more like a 'blueprint' image to work from.
If you're put off by the compound curves you could maybe create single-curve panels (like Cadillac does with their CTS coupe).It's not ideal,but be maybe 3-X more simple to construct.

Here are the proper technical drawings for the truck, obviously the one with the tires would have the ground plane moved up to be scaled properly based on the drop of his truck.

http://i67.tinypic.com/wb58p5.jpg

Based on this paper, (page 103/116, or 85) I'd go with this plan. It's about an 8° slope overall which will get you within 5% of the achievable maximum aero drag gain, but you'll drop your aerodynamic lift by 60% or so. In addition, you'll have a lot more practical space under the cap to use, and depending on how you design the back of the cap, you won't have to stoop as far to reach under it. Your height above the tailgate will be about 7.5 inches.

Blue line is the Template, Green is the 8° line, Red....well I think we all know what that would be don't we?

Let me know if you want to do this, I can make accurate drawings that you could take to anyone with a large format printer and get life size templates made.

Blue line is the Template, Green is the 8° line, Red....well I think we all know what that would be don't we?

actually no im not sure what the red would be. a guess would be the outline of a cap, but it doesn't follow that 8deg slope you mentioned. I apologize for the ignorance, but I am VERY green to all this aero stuff. I would love the technical drawing for it. would you want any $$$ for it?

I would like to thank everyone for their input. I'm very grateful. I feel like I should take some intro to aerodynamics type courses to keep up with some of this stuff lol

4.7 Pickup truck model with 3D curved Aerocap

==>http://csus-dspace.calstate.edu/bits...d-finished.pdf<==

Where's the Blink tag when you need it. :)

Everybody obsesses about that profile. Spend some time looking at wooden boats on Guns Oil & Dirt

http://68.media.tumblr.com/6f304dec7...bha2o4_500.jpg
http://68.media.tumblr.com/fead5bd0b...zyno1_1280.jpg
http://68.media.tumblr.com/tumblr_lx...q4yvo1_400.jpg
http://68.media.tumblr.com/6f7ffac4e...zyno1_1280.jpg

I could go on and on...:)

I talked to a local plastics manufacturer who suggested using polycarb rather than acrylic because it's waaay more durable and easier to drill into. Hail damage is a strong consideration, as well as for liability reasons if the acrylic somehow cracks and pieces fly off the back onto following vehicles. The major downside of polycarbonate is that it is somewhat more of a process to heat-bend into shape. This is only because it has some moisture in it that will make poor bends look like they're 'blistering' as the water vapor tries to escape. The simple solution is to bake it first or leave it out in the sun over a black surface for a few hours to get the moisture out. It also gives off toxic fumes when laser-cut, if you care at all. Also, I learned that extruded acrylic sheet is not good for drilling into and doesn't heat-bend as well as cast acrylic sheet. But at the price point of cast acrylic sheet you might as well just go for polycarb. I was quoted $126 for a standard, uncut 48"x96"x1/8" sheet of clear polycarbonate, plus about $10 if I want some hue to it. I recommend getting smoked/greyed/bronzed to try to match your window tint (aesthetics), obfuscate UV yellowing, and to avoid constructing a mobile greenhouse. Also, the professional I talked to suggested taking advantage of the bendy material property of base sheet to avoid having to heat-bend each curve, as in some curves can be done by just warping it into form and bolting it down to the frame. Potentially these kinds of pre-loaded forces in the body of the shell could also add to its rigidity. I guess we'll find out how well all this works once I try it in the next couple weeks. I'm making an aerocap as my first ecomodding project, too, right after finals week is over (I'm a mechanical engineering major). I'd been intending to use a similar construction technique for a few weeks before I found this thread, except I definitely intend to use polycarbonate.

Why 3/4" rather than 1/2" conduit? What kind do you plan to use? EMT, IMT, or Rigid? Dirt cheap EMT really entices me but scares me since it's rolled not extruded tube. I'd be afraid it would buckle, and not being threaded also worries me.

The red curve in the above image appears to refer to the tangent curve from the plane of the roof to the approximate intersection of the 8° line with the plane of the tailgate.
I don't understand why 8° is being suggested, other than for alleged cargo volume improvement and less lift. The heresy of suggesting something other than 12° like the Holy Theses have commanded! Also imo it's prettier to have the trailing edge of the shell as vertically close to the top of the tailgate as possible unless you intend to have an eave/overhang. With other opaque projects, like with the infamous, beautiful, Wooden Taco Topper, the slope was pretty low presumably so that the driver could still see out the window at the boat's keel, but obviously that doesn't apply to us.

Personally, I'm going with the "Holy 12°" for mine. I don't intend to hijack this thread with discussion about my personal project, because I intend to make my own thread once I start construction. Briefly, I've already made a quick 3d sketch in Autodesk Inventor (my go-to CAD), and the 12° works well for me because I don't care about rear lift since my beloved '06 Ridgeline is FWD over ~15mph (pls do not pollute this thread with criticism of my choice of quality utilitarian vehicle - that dead horse belongs on ridgelineownersclub.com - and it was inexpensive after all the fanboys upgraded to the 2017 remake... so far with my driving style and no mods I get ~20mpg for both city and highway but I don't doubt both will increase 3-6mpg by the time I'm done with all my planned mods). Also, since my box walls are so tall, there is only 1.5" between the lowest point of my aerocap's trailing edge and the rear point of the box walls, while the widest point, over the shorter tailgate (the engineers assumed everyone would get a tanoe), it has like a 3.5" gap, which I've obfuscated by including a slight Kamm-ish overhang. The quick model I made is compound sloping on the sides as well, just because that's what is intuitive to match the sides of the RL's box. So far the slopes are straight lines rather than convex because it would be easiest to construct and I've yet to be convinced of a significant advantage of either convex or concave other than following those damn teardrop templates to the T or for aero-aesthetic. Same goes for the corners joining the top sheet to the side sheets, whether I should leave them angular for easy fabrication and intentional flow separation or to gently round them for that dubious aero aesthetic that would take many hours with a heat gun and potentially 'blister' the polycarb. I can't yet post links to my little photobucket, but it's under the same username, if anyone's curious.

Again, I don't want to hijack this thread so please answer in the context of OP's project :)

no worries, I appreciate the input as hail and "rolling greenhouse" is something I never really considered.

so does the blue line represent a 12deg slope?

The blue curve section should be near 12° but I wouldn't put too much faith in those templates (don't fight me on this, guys, I'm sure they're great...). I would just measure the cab height and do some trig. I don't want to sound pretentious at all but here's the procedure to do it by hand if you don't feel like measuring a bit of CAD (which is what I did considering my goofy box sides):
To get the vertical displacement of the end of the shell (truncating the eave/overhang) from the rear of the tailgate:
h_rear = h_cab - box_length * tan(Θ)

From what I understand from other truck threads (I think I've read most of them at this point), the measurements of the simplified flat-profile shell also work for those that are curved to be tangent to the cab roof. Allegedly, so long as you follow the Kamm principle and don't round the rear edge to be tangent to the back of the tailgate, you can get away with a convex shell without significant flow separation even though it clearly is more than 12° past the midpoint. Like I said earlier, I am not yet convinced convexity is worth that flow separation risk and extra effort?

Still definitely curious about your frame choices, as to diameter and EMT vs. Rigid or IMT.

I am beyond a noob. I need to start doing more reading and brush up on my math, cause I'm barely following what you're saying at this point. I have no idea what EMT or rigid IMT is. I only chose 3/4" electrical conduit pipe because I saw a thread with a crew cab f250 on here, and that's what the member used. its also because I happened to come into about 10 6'-8' lengths of it for free through my work. so it was also a convenience thing.

Back to how ignorant I am to all of this, I was only first considering a convex cap because that's what most members had done with their trucks, in following the template. Although I had seen a couple members to flat/straight line caps with rounded edges. I joined this forum and want to do these mods out of necessity. Budget and fuel savings are the biggest reasons. I also mainly started this thread because there were things I was unsure about and can really only afford to do this once. So far, the more this thread goes on, the more I feel over my head. Not to say its any member's fault, its just showing that I really have no idea what I'm doing when it comes to the more technical part of this stuff.

The stuff you got is EMT if it has a thin wall and isn't threaded.

It is easy to get confused, as many people have many different ideas about what and how to build an aerodynamic bedcover. This is mainly because there is no one right answer. Even some of the "wrong" answers that go against everything everyone suggested so far are better than no bed cover. I built mine the way I wanted (matched to AST-II in side view) out of the materials I wanted (foam/fiberglass). When I build my next one I plan to build it differently (AST-II in both plan and taper view, aluminum structure).

You get the benefit of doing the same, decide how you want to build it that best matches your needs, desires, and skill set and based on what design balancing complexity, utility, and aerodynamics. I will say that copying what other members have completed and proven to work probably is easier than plowing new ground.

that's basically what I was hoping to do. ive considered a version and method similar to yours. as well as considering a few others

The outline of the cab and the bed side-rails are defined. The profile at the tailgate is your preference. That's half your pieces. The others can be longitudinal stringers.

Get a tubing bender and you're ready to get started.

unsure
 

After 40-years of this I'm never sure of a thing.But the chance to succeed always trumps any apprehension.
Dyson said that he never learned anything from his successes,only his failures.
Elon Musk is paying over $67 an hour for this stuff.Failing your way to victory is cheaper in the long game.:)

Materials info dump: While looking at conduit at Menards I found that the Rigid/IMT conduit has the same screw threads as the steel water pipe of the same diameter, which happens to be cheaper and sturdier anyway. From what I gather, the only difference is that conduit is post-processed a bit more to be smoother inside so as to not damage any cables. Another cost saving measure would be to use Black rather than galvanized pipe (looks better anyways since most cars have some black plastic to match already). Then I checked Ace and found that the same exact black pipe (Wheatland brand) is cheaper than their EMT and a third of the price, at $2.49/10ft, which is just nuts. Definitely suggest thin water pipe over EMT conduit because it's much stronger (won't buckle or split at the seam) and can be threaded rather than just connected with compression fittings. It's harder to bend into shape, but that's kinda the point isn't it. I'll just use Tee intersections and 45° fittings and such instead, since there's a wealth of threaded plumbing fittings. I'm gonna buy a tap/die to thread the cut-sections of odd lengths, then I might sell it again once I'm done with it.

Welcome to Ecomodder...


Why would you pay new prices for tubing?

Why would you not look for aluminum tubing?

Why would you use threaded couplers instead of glued-and-riveted internal lugs?

Thank you for asking questions. Half of throwing ideas at a wall is making sure the wall will bounce them back :)

Used: I hadn't thought of that and I don't know where to get used tube/pipe.

Aluminum: Generally more expensive and not immediately available at a hardware store. Though I could be convinced to go to a local manufacturer to get a quote. Imo for a 4500lb truck, in my case, the weight of the tubing is a smaller concern than cost and strength. I'd save maybe 10lbs maximum in the switch. Some math: If I'm lucky I'll get a 3-4mpg increase, so a reasonable hope is +3.5mpg. With baseline 19mpg and $2.20/gal ave. in my state, I'd save 1.85 cents per mile. So for every dollar I spend it takes another 55.6 miles to break even. At my budget of $140 (most is for a good polycarb sheet), which I'm already probably going to break, it'll take almost 8k miles to break even. Damn northern oilsands making gas too cheap to properly ecomod :)

Glued and riveted internal lugs: I hadn't thought of that. I'm not very familiar with this method. I had considered riveted connections when I was looking at EMT. What are the advantages? Screwing something in then gluing it seems easier and perhaps stronger.

Here's what I like: wakeboard control arms:

http://ecomodder.com/forum/member-fr...0-100-1101.jpg

I bought three of those five for IIRC $8-10 each. Not tested to destruction yet, but they're very light, stiff and curved.

IDK where to look in Nebraska. Maybe something like Habitat for Humanity. Maybe Goodwill or St. Vinnie's for TV antenna masts, etc.

"Glued and riveted internal lugs" I made that part up. Bicycle frames would have external lugs and brazing.

Kamm
 

Kamm advocated convexity.
http://i1271.photobucket.com/albums/...ad2/02-071.jpg
He's remembered for the pragmatism of a limited-length tail truncation.
And while he advocated a clean chop off to the aft-body,he never actually did it in practice,as a concession to aesthetics.
http://i1271.photobucket.com/albums/...29BampW1-1.jpg