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Another truck aero cap idea...
Now that I have all this coroplast...I was thinking... Make an aero cap strictly just fer aerodynamics and not security. Make it with 3 layers of 4mm coroplast with the middle layer sandwiching some lexan fer viewing. Maybe even incorporating some real side glass from a used vehicle... ;)
It would still need some sort of framing to keep it on the truck bed lip. I guess the key would be to git the correct angles to make it effective and simple to access the bed with. I know I don't want to use a bunch of adhesive to stick the sheets together...maybe some spaced out spots instead of slathering it on the coroplast. I guess fer a second step (if this proves successful) is to cover it with aluminum flashing to make it somewhat secure from knives or what not... :D Thoughts? ;) |
I was thinking the same thing the past couple of days, but decided against it due to the very security reasons you brought up.
to attach it wouldnt need to be all that hard, you could use double stick tape with wide head pop rivets (or wide spacers + pop rivets) placed every 12", should hold it nice and tight to whatever frame work you go with. if you have the coro to work with and a little time on your hands, I cant see why you shouldnt just go for it. |
I'm thinking about chopping the top off of my spare camper top so only the bottom frame, front (with sliding glass window), sides (minus the sliding glass windows), and a little bit of the top are left. I can then build up dual layers of coroplast on the sides and git the correct slope angle to the rear. This platform should allow me to adjust the slope angle just by chopping the sides down. I can always put in windows as I progress... :D
The rear hatch will not have a window in it while I test. I'll eventually have to git a rear camera system installed so I won't be totally blind back there. |
Got the camper top off and went fer a test drive empty. :D
I left my sliding window "umbrella" in place on the roof which sorta acts like a ducktail. Combined with my extended air dam, full belly pan, 11" side skirts, and rear diffuser, I found it interesting that my short run up North with the tailgate down gave me some pretty good mileage...22.95 mpg. With the tailgate back up, I got 25.53 mpg on the return trip. :D Currently working on my grid panel with 2" spacings so I can git a better idea of where the slope should be. I'm surprised someone hasn't made something like this before. I plan to stick the panel in the stake holes in the bed and then take my photos. ;) http://i164.photobucket.com/albums/u...0/IMG_7645.jpg http://i164.photobucket.com/albums/u...0/IMG_7649.jpg |
Here's a quick mock up of my grid panel... ;)
http://i164.photobucket.com/albums/u...0/IMG_7654.jpg A quick extension to the ducktail... http://i164.photobucket.com/albums/u...0/IMG_7658.jpg |
Side view of the extended ducktail...
http://i164.photobucket.com/albums/u...0/IMG_7655.jpg |
The extension to the roof ducktail was bending the main piece down...so I took the extension off fer now until I make a bigger ducktail to put on there. :(
Just got done making my stake hole supports...it will bolt in place to hold the main rails in place. Two bolts per side and it can be removed fairly quickly. :D I'm making a quick half tonneau with a steel stud support frame to git some quick numbers. I can make it into a full tonneau with another sheet of coroplast. :D |
Got my main rails bolted in...
http://i164.photobucket.com/albums/u...0/IMG_7669.jpg Was doing some thinking and some messing around. Came up with an idea of using 2 sheets of 4x8 coroplast fanned out so it will cover the span of the top of the cab to the width of the bed. This is just a mockup... ;) http://i164.photobucket.com/albums/u...0/IMG_7671.jpg |
Thinking about using some ¾" Sch 40 PVC pipe and drilling holes in the main rail at the proper angle. I can then insert them into the holes and they should be able to stand on their own. :D
I plan on putting a landing on top of the pipes so the top can be supported as it lays down. ;) |
Good start, BZP, but it looks like you are making the same mistake I did...too steep a downward angle.
Mine was 17 degrees. I should have had the height above the tailgate to be about 8 inches. Do the trig. I do like the ducktail. How are you planning to attach it? Your side curtains are killer. |
Well...it's not set in stone fer the angle. The scrap steel stud was handy fer me to prop up the end at the time just to git an idea. What yer seeing mostly is the droop in the coroplast as it gits away from the steel stud.
The height between the top of the tailgate to the coroplast is about 11" and the height from the bed to the top of the cab is about 21". The distance from the bed to the end of the tailgate is about 78". With the mockup as it is now...I can see pretty good out the back. ;) Keep in mind that the rake of my truck is rather...um...severe when compared to other trucks. I'll have to measure the rake angle at some time to give you an idea of what it is. You can see it in the "grid" piccie above (post #5). :D The current ducktail is duct-taped on fer the moment. I'm thinking about putting down some 3M foam tape or Gorilla gluing a metal strip with some threaded studs facing up to fasten it on with. Not exactly sure what's gonna work though... I'm still building up my half tonneau first and see how well that works out. I really like seeing out the back window a lot compared to when I had the camper top on with the tinted windows. ;) |
Is there any aerodynamic benefit to sloping from the center fer the rear part of the cap? It's doing it naturally because of the lack of support...but should I build it that way or should I put in a support beam to make it straight?
Just did the math with my measurements. Using this online trig calculator... Here's how I calculated it... First calculation: Opposite = 21" Adjacent = 78" Angle (calculated) = 15.07° Hypotenuse (calculated) = 80.7696" Since I have it 11" higher... Opposite = 11" Angle = 15.07° Adjacent (calculated) = 40.85" Hypotenuse (calculated) = 42.3079" I add the calculated adjacent side to the original to git 118.85" and plug that back in to calculate the actual angle with the 11" rise from the tailgate. Opposite = 21" Adjacent = 118.85" Angle (calculated) = 10.02° Hypotenuse (calculated) = 120.6953" If the top ended at the tailgate...the angle would be about 15°. Since I have it up 11" from the tailgate, the angle is about 10°. :D http://i164.photobucket.com/albums/u...0/IMG_7683.jpg http://i164.photobucket.com/albums/u...0/IMG_7675.jpg |
It's all about wake reduction, and to max that, you want no wake on the lid, leaving only the rearmost vertical area- tailgate, bumper, etc.- with wake behind them. If the lid has too much angle, flow separates on it and the lid becomes part of the wake zone. If the lid has not enough angle the upper part of it won't be part of the wake zone (good) but the rear area won't be minimized hence it's overall effectiveness won't be maximized.
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So I should try to keep this natural curve? http://i164.photobucket.com/albums/u...0/IMG_7678.jpg |
It looks quite nice... perhaps that post could be lowered some?
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I guess it could be lowered...but what is the ideal angle of the cap? I guess the angle would be some where between 10° and 15° based on the calculations I performed earlier. I guess I could make the next version from this to an adjustable angle to see what would be ideal. Obviously if I want that to happen, I'll have to keep spare side panels available to adjust the cap angle to... ;) |
Got the half tonneau sheet put on...just 4 screws in the corners and some duct tape on the front edge. ;)
http://i164.photobucket.com/albums/u...0/IMG_7687.jpg http://i164.photobucket.com/albums/u...0/IMG_7689.jpg |
Piccie at 40mph...
http://i164.photobucket.com/albums/u...0/IMG_7691.jpg |
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If you can make it adjustable and do tuft tests, that would be the best way to optimize that angle, moreso than us sitting around theorizing about it. |
I'm thinking about using multiple materials fer the next version...maybe some ¾" R-Matte and coroplast sandwiching it on the top and bottom. It would be lightweight, insulated, and pretty sturdy/durable. Still won't keep the thieves out though... :(
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Much better. I wish I’d done mine this way.
Back on your question. You could slope your cap down from the centerline out but you can’t get too crazed about it. I did some three-dimensional trig on the problem. You have established a ten degree slope on the centerline. This is good. The air flow should stick like Super-Glue. By my calculation, you could slope down away from the centerline at an eight degree angle (about a 1-in-8 slope) and maintain less than a twelve degree (1-in-5 slope) angle relative to the top of your cab, so the air flow should stay attached to the end. If your truck is 80 inches wide that would allow you to lower the height at the rail by 5 inches from the centerline. Nice thing is it will shed rain like a duck. If you read the thread about “commercially produced aero cap” you’ll see the evolution of Bondo’s cap. I can’t seem to find the video of it in the wind tunnel but I seem to recall seeing the smoke sticking to the cap all the way to the lip. That would make it the gold standard. Now Bondo held the height at the rails to the same as the centerline, but he is trying to maximize internal (payload) volume rather than seek the maximum wake area reduction. Somebody (I believe it was Frank) posted some tips on heat-bending coroplast. This might be useful bending that Texas-sized political sign into a righteous cap. |
Things I know I need to account fer in the next version are...
Front support rail fer hatch hinges Drip guard/rail fer the hatch Plexiglass/Lexan windows (clear window tint to protect from scratches) flush to outside coroplast layer Possible to use existing glass assemblies from other vehicles (Maxima's long sunroof comes to mind) with a possibility fer a defroster grid Easily disassembled/reassembled Basic latch to keep the hatch from opening on it's own (not sure if I want to make it lockable or not) |
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In the pic above was the tailgate up or down? The way it's buckled down in back between center and side supports makes me wonder whether that was due to (a) vacuum effect underneath or (b) positive pressure above. If (b) that would suggest attached flow. Tufts would be helpful. A passenger with a video camera could be very valuable. Our trucks are very similar. I have an 02 Tundra xCab. I believe our cab and bed body dimensions are the same. This is one aerocap design I have in mind. http://kamperbob.com/images/aero/Aer...cept%29.v3.png Cheers KB |
The tailgate was up.
I would have to guess b since I could see where the air was pushing it down as I was speeding up. :D Yer aerocap design looks good. I guess yer approach is similar to a tonneau that caps over the sides...except the sides are extended up from the bed rails. :D During some brain storming...I was thinking about the same design but taking an actual tonneau and testing it out with the raised sides. I guess it would be pretty simple to build up a rounded shape on top of the tonneau then... ;) I guess that would be one way to approach current tonneau owners. Make a kit that made use of their tonneau to make it more aerodynamic. As I think about it...it wouldn't work because the width of the cab is smaller than the width of the bed. :( |
My Tundra came with nice fiberglass tonneau courtesy of the original owner. It helped my high score of 22 highway despite the EPA sticker. Being a 4.7L 4WD model I suspect further improvement is high fruit. Still, it's fun to think and rethink possibilities. I sold that cover because it's not 5th wheel friendly. Removal, storage and reinstallation were solved problems but a lot of hassle. I have a short cap that I may yet annex for off-towing season. Given other priorities and current situation right now, however, to just get through this Winter I'll probably just put my toolbox back on the front of the bed and close off the rest of the box to keep snow out. The short cap does create a blind spot that bothers my wife when she needs to drive it so in the grand scheme I'll probably have something to share about that mod before long.
Cheers KB |
Gitting ready to sacrifice a single sheet of coroplast and reusing the 1x2 wood from my test belly pan to make a quick frame/cover fer the hatch. I should be able to make the sides and compute the angles I need to taper the main rails to. :D
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Dr.Kamm recommended no more than 10-degrees and proceeded to break his own rule. Dr. Hucho suggests no more than 15-degrees. I know from experience,that at 13-degrees over that much span,you'll get immediate separation and then re-attachment downstream with a locked-vortex in between. With straight angles it's all a compromise.And Frank is totally correct in that if you push the angle too steep you get separation with zero re-attachment and little if any benefit. My cover that you saw at Burger King has zero separation.If you can stand to build curvature into the cover you'll get the biggest bang for the buck.:thumbup: |
Got my front support frame roughed out...the posts will be cut down to the wood support bar. ;)
Goal posts!! http://i164.photobucket.com/albums/u...0/IMG_7735.jpg Rear quarter shot... http://i164.photobucket.com/albums/u...0/IMG_7734.jpg A quick mockup... http://i164.photobucket.com/albums/u...0/IMG_7737.jpg Rear shot of the mockup... http://i164.photobucket.com/albums/u...0/IMG_7739.jpg |
The short cap does create a blind spot that bothers my wife when she needs to drive it so in the grand scheme I'll probably have something to share about that mod before long.
My wife dislikes the non-window cap on mine for the same reason. Happily she dislikes a heavy diesel with a man trans even more so it's rather moot. As to "blind spots" I have had very good performance from modifying stock mirrors with: Blind Spot Mirror Specialists - Safety Mirrors Online.com Takes about three days to get used to. The larger the mirror the better as "distortion" is lessened. No more looking over your shoulder to check blind spot!! Keep it rolling BZP! |
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Been busy this morning...got the test roof on!
Left side view... http://i164.photobucket.com/albums/u...0/IMG_7740.jpg Rear quarter panel view... http://i164.photobucket.com/albums/u...0/IMG_7741.jpg Rear view... http://i164.photobucket.com/albums/u...0/IMG_7744.jpg Rear support... http://i164.photobucket.com/albums/u...0/IMG_7746.jpg Right side view... http://i164.photobucket.com/albums/u...0/IMG_7752.jpg |
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Lookin' good.
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Added a 3rd sheet of coroplast on top to give it more stability... ;)
http://i164.photobucket.com/albums/u...0/IMG_7753.jpg Added in the 3rd brake light, too... http://i164.photobucket.com/albums/u...0/IMG_7754.jpg Added in the first parts of the side panels... http://i164.photobucket.com/albums/u...0/IMG_7765.jpg Current view from inside... http://i164.photobucket.com/albums/u...0/IMG_7768.jpg |
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Looking good, BZP. I can't wait to see test results. But I hope those sides rely on more than just tape to hold them. If (IF) tape starts to fail the whole thing could come apart before you could even stop. Even if flying coroplast didn't harm any vehicles behind it could freak out another driver and you'd be liable (sucks). Hopefully your well ahead of me there. :)
Cheers KB |
Thanks fer yer concern. Yes, I have some truss head screws on there. I've probably used over 250 of them on my project so far. Already had someone taking piccies of my truck today.
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BZP, do you think moving the skirts to the frame after the rear axle is hurting more than helping? Looking at the civic project in the same forums, there was a lot of work done to reduce tire turbulence.
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I still have to build my "aero mud flaps" to taper the air flow from the rear tires. I've still got a lot of work left in those areas. I've got my "heat tunnel" I need to finish at some point in time as well. ;) |
I've got a 2001 GMC 1500 that I'm looking at modding, so this is a very interesting thread. Giving me great ideas for next summer. Looking forward to some real results with these latest mods. Thanks and keep up the good work.
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