Aerocap for a Tacoma Pickup?
 

Okay, I've lurked around this forum a bit and found a handful of aerocap or aerolid including Bondo amazing aerolid, sepp's Nissan Aerocap (both versions), electricmans dakato aerocap along with akashic concept on his 1st gen tacoma and even the production version of aero canopies style they offer in Europe.

So I've reviewed many of the aero discussions about the optimal kamm back angle to avoid the dreaded seperation. Originally I was thinking of designing an aerocap with the magically 11-12 degree angle just for simplicity but then began reading the threads about the streamline template. Take a look at the image and let me know if I did that right and what do you think. When I overlay a 12 degree with a small transition curved area, it almost matches the template perfectly.

I also have been looking around for a cap to my '10 Nissan Frontier. Great start.

Going to go with a clear section to see through?

How about side windows/cargo compartments?

Do you have any other use requirements, like it needs to be able to come apart and stowaway while carrying larger cargo that will not fit underneath?

I thought about the see through issue but the location that is most important is right at the bend above the tailgate. I'm pretty good with just side mirrors but might like that rear viability of tailgaters. I might have to think about that some more.

Side cargo windows also would be nice. I found a dealer on ebay that makes custom picture windows for campers. I figure at least one from the cab to see back and then maybe a couple small side ones.

Hopefully it can be light enough so I can disconnect and lift it off with two people. I would say 95 percent of the time I can get away with a roof rack and storing gear underneath. I was thinking a hitch rack for bike transport would take the place of bikes in the bed. I think that'd be more aero.

I think the hardest part is lining up the aerocap with the back of the cab. The Tacoma has quite the contour on the sides and back. However, i want to keep this simple without any complex curves.

i am glad i found this forum. i have a 2002 tacoma 2.4 4 cylinder 2wd 5 speed regular cab that i am collecting the wood to make a aero cap for shortly. i am currently getting just above 30 mpg. i have been figuring the back angle also and if i make the angle 11 degrees there will be only a 9' drop from the cab to the tail gate. the cab is about 21" so the verticle will be 12". but the caps i am seeing on this forum like the nissan and the ford f150 ones are 5" to nothing verticle at the tailgate. i am trying to figure how high i should make the back?

my truck is in pretty rough shape so i dont mind if it isnt the prettiest thing. i am planning on making it out of wood because of the trade i am in. i am figuring i can make it out of 2 sheets (39lbs) of plywood and 8 8' 2x2's (my guess 40lbs). so i am thinking it will weigh around 80lbs. i am not thinking of making it so i can see through it. if it bothers me i will install a back up camera mounted on the licence plate that can be bought at auto part stores. i am going to make the back panel above the tail gate removable so i can take a few screws out and i will have the height of the tail gate plus maybe about 10" to get in the bed. i also want to be able to remove the cap easily so i am going to try and mount it with some cap clamps from the inside.

template
 

That IS the way to use the template.
I did a more comprehensive thread with "aerodynamic streamline template" which has a better "minimum" criteria for attached flow if you want to do a search for that.

ok how do i post pics?

Variety of options.

Simplest being imageshack.us

here is some pics of the frame work of my aerocap. this is with a 9" drop from cab to tailgate. which calculates out to a 11.25 degree angle. i am thinking of putting a piece of wood in the center of the span so it makes it a little rounded. any suggestions? should i make change the angle steeper? it seems like most guys making them are making the angles steeper.

i am going to get it all framed out then put 1/2" plywood over the top

Why 1/2 plywood? You can make one that is much lighter.

angle vs curve
 

If you have an abrupt angle,you will lose boundary layer adhesion immediately,flow will separate,and there is a chance you'll have a violent buffeting,enough to "explode" your shell if not robust enough.
Please take a look at Metro's Permanent Kammback for Metro thread,or the Aerodynamic Streamlining Template thread.
You'll notice that the roofline begins with a subtle curvature,increasing with length.
Get a 20-foot length of 1-inch PVC pipe,lay it over the cab and study the curvature as it bends down toward the tailgate.

A smoother curve transition is better, but is not an insurmountable problem.

The angle is about right IMHO.

it is what i have around. i think 3/8ths plywood would be to thin

i am thinking of putting a piece of wood in the middle of the span that is about 1" taller so it bows the upper board up and gives the cap a rounded shape to it.

also should i make the top piece of plywood on the cap extend past the tailgate off the back a bit? i am thinking about extending the plywood as far back as the rear bumper off the back of the truck (about 5") and then on the sides at the back making little pieces that return to the tailgate. making kind of a little kamm spoiler

The smaller the trailing wake, the better. If you're willing to extend to the end of the bumper, your wake area will be that much smaller.

I did a similar thing on my car (Kammback out to the bumper):

http://ecomodder.com/forum/attachmen...1&d=1222298665

metrompg i put a protractor over the computer moniter and it seems like your kammback is 15 degrees. would it be better for me to make my cap at 15 degrees to make a smaller flat section behind the truck in turn making a smaller wake?

Your protractor doesn't lie.

The reason I can get away with 15 degrees is because of the gentle curvature at the back of the roof & upper surface of the hatchback leading up to that final angle. Also, the "shoulder" of my Kammback has a generous radius, permitting flow to transition from the sides without tripping.

If you use a "sudden" 15 degree angle/transition from your cab roof to the aero shell, you could end up with separated flow and dramatically reduced effectiveness of your hard work.

Hey ccrider, how's it going on the aerocap for your tacoma? I'm looking forward to seeing your finished project. I'm still dwelling on my design and hopefully use a bit of what you've done for inspiration.

i only get to work on it on the weekends with it getting dark so early. i didnt get any time to work on it this past weekend. i am hoping to work on it this weekend. at least i am getting more gas log data so i will have a good base to see how much it improves the mileage. the only problem i am always moving stuff with it so it throws the mileage off. but i am getting around 30 mpg on the highway at 65mph now. it would be nice to get 35mpg out of a truck.

The angle of that wood looks pretty conservative. Is that 10 degrees? I've never made a pickup cap or anything, but it feels like it could be more steep. Look at the rear window of some very aerodynamic cars.

winkosmosis it is 11 degrees. i dont know much about aerodynamics just listening to people on the forum with more knowledge than me.

I think it's just an optical illusion making it look shallower

here is my progress today. i have 2 more supports made that go in the middle of the bed. i will cut them depending on how much i can bow the upper piece of wood up to make it rounded. i hope to get it to bow up 1 1/2" in the center of the bed. if you notice the front support is rounded on the top and the back one is flat. the 2nd support back(that is not in the picture) is going to have a very little round to the top and the 3rd one is going to be flat like the back one. also the side angle lays down as it goes to the back of the truck. this was done so that the top piece of wood remains the same size all the way to the back of the truck. i am going to run the top piece of plywood 6" past the rear support to create a kammback and so when i pan off the bottom of the truck i will pan it off to the back of the bumper so the kammback will end at the same point as the bottom pan. the sides pieces of plywood at the top of the piece will be the same 6" past the rear support and the bottom of the piece will be cut back to the tailgate making a pie shape from the side.

feel free to give me advice.i would rather change it now than after it is built.

I can see the shape you are looking for, and I like it.

Next order of business is two or three intermediate supports for the sides.

Have you thought of this? Build essentially a topless top and use a commercially avaiable rollup toneau cover as your "roof." This way you get the aero advantage and the flexibilty a pickup needs.

Your wood frame would be the perfect support for a mold to make this baby out of fiberglass.

i did not think of making it topless. i guess i could do the torneau idea if the top gets annoying. i would have to leave the supports in the middle to stop it from collapsing so i could carry tall things but they would have to fit in between the supports.

i am thinking that i could take off the piece of plywood above the tailgate so it would give me about 7 more inches above the tailgate to get stuff into the bed. i am going to attack the whole cap with 4 brackets to the metal at the top of the bed. so if i need to take it off i will crawl in the bed with a battery drill and take off the 8 screws that will be holding it on and then stand up with the cap over my head. (sound good on paper HUH).

A fixed bed cover will get annoying. Mine has.

But maybe fixed is OK for a "Mark I" version thatcan be refined later.

FYI, just found a video of someone tuft testing a cap very similar to yours in construction, except 8 degrees decline.

Posted it in a new thread: http://ecomodder.com/forum/showthrea...per-11522.html

dont know if i learned anything from the video but it sure did make me dizzy. is that a 8 degree angle? the height of my cap at the tailgate is going to be 9" tall. that looks to be about the same if i had to guess. mine will have a bit of a round to it and i am going to try and get the gap between the cab tighter. his cap seems to be a little taller than his cab at the front of the cap. mine is actually about 1/2" shorter. which i hope would be better.

I kind of felt a bit sick at the end too! Camera work could have been steadier.

He says it's an 8 degree angle in the video details.

I think going shorter by 1/2 inch is a good call.

I didn't read the whole thread, so sorry if this was already mentioned... but you could use plywood on the top and hinge it near the cab, so it has a top, but it's openable.

Or you could have an opening where the cover is small enough to take off and put in the truck bed when you need extra height.

if i made a hinge on the front i would have the suports still in the the way of sldiding something big in. i dont think the sides would be sturdy enough to remove the suports. maybe i could remove the back 2 suports and have it hinge like the drawings that mjboks did. i guess it might work out to have the top to hinge up in the middle of the cap so it can flip all the way up and lay on the front half of the cap. this way when i am driving it will be secured down on the top an not sticking up in the wind.

i was looking at a new pruis yesterday and i noticed at the rear roof of the car there is a little kick up in the body shape. is this to create a high pressure area right at the rear of the vehicle to stop separation? should i put this same kick at the rear of my cap?

A rear spoiler at the end of the Prius could have been put there for several reasons, and unless we can talk to the aerodynamicist, we'll never know for sure which (or which combination of these) applies:

• as a styling element (ie. aerodynamically useless or even detrimental)
• to reduce rear lift
• to reduce drag by changing the "effective" rear slope
• to reduce drag by forcing cleaner separation where airflow might otherwise "wrap" around a surface

I would just carry on with what you're doing and not worry about a spoiler. The angle you're working with is fine, and that's the most important issue.

FYI, in your previous post you said you weren't sure if you learned anything from the Ranger tuft testing video. The key thing there was we saw the tufts streaming aft on both the sides and top surfaces of his aero cap, which indicates attached flow. It confirms that his angles weren't too extreme and that he should see an efficiency improvement from his work.

btw - great build here:
http://ecomodder.com/forum/showthrea...ead-11611.html

I've taking a closer look a the "ideal" aerocap for my tacoma and found there is a slight decline at the end of the double cab (its not just in the picture). So the top of the streamlined template is back just above the middle of the rear door. With the template moved forward it reduces the tailgate height a bit. I previous calculated about 8-9 inches and now it's around 5 inches. Although is it better to error on the side of caution and make it higher?

http://graar.org/Parts/tacoma%20aerolid.jpg

I will also have to deal with the gap from the top of the aerocap to the cab. It appears if I go straight up from the bed I'll have a 6 inch gap that would create a bit of turbulence. Either build it flush or have some type of filler.