95 Dakota Extended Cab Aero-Topper
 

Ok everyone, i have 4 weeks to build an areo topper for my new truck so here is my plan. Please feel free to comment with any input (supportive is preferred) and thanks for reading!

Current Situation:
Attached is a 2D sketch of my roughed desired topper shape and dimensions. The only incorrect information is the height because the previous owner replaced the stock wheels (215/75r15) with some newer dakota wheels (245/75r16). These will eventually be changed back to normal.

The truck currently averages about 17.5 mpg. Problem is, it falls on it's face over 65mph. I'm hoping aerodynamics will help with issue because I don't plan to drive any slower XD

Design Goal:
The 6.5ft bed is pretty short to work with but I should still be able to get some better aerodynamics with it. The bed must remain fully functional and able to contain itself. I'm not going to crazy with this due to fear someone will screw with my work if i leave it parted on the street in Denver. Rearward visibility will not be a problem since installing a full-time reward camera to watch behind me.

Plan of Attack:
Fiberglass. I hate working with it but it works well, it's strong and its relatively cheap. Plus my dad is an expert with it so I'll be letting him do all the heavy lifting!
I'll build the skeleton frame from treated lumber because I have a woodworking shop with all the necessary tools. From there I'll have to use some type of fencing-like material to mold the shape and design. Next I'll hang the topper vertically from a tree to pull the fabric tight and eliminate low spots before starting to apply epoxy and more layers. Once complete, I'll cut out the door on top what will fold down to allow full functionality of the bed.
Based on my 2D sketch, you can see the rough dimensions I'm working with and aiming towards. I'm cheating with a 3 degree initial angle and ending at 12.5 degrees with a decrease in height of 13".

If anyone sees a big red flag in my design of plan please let me know! Also, would there be any considerable gains by simply extending the cover to the length of the tailgate in the down position since the angle has already been reached?

Here is a very crude image of what I'm thinking the shape will look like

Aaaaannnddddd using the aero template this is what I get (alligned with the top of the room). Looks like I'm a larger radius than optimal.

I detect a little added complexity where the cap meets the top edge of the bed.

Keep it simple is my suggestion if you want to build it in a reasonable amount of time.

For those trying to follow along at home, see my response at http://ecomodder.com/forum/showthrea...tml#post538300

http://ecomodder.com/forum/member-fr...perellipse.jpg

There are an infinite number of superellipses between the circle and the square. One should closely approximate your cab's lateral profile.

The Template coincidentally matches your circular arc, but not the design in Permalink #2.

For the longitudinal profile instead of your circular arc, follow Mair:

http://ecomodder.com/forum/member-fr...1215134663.jpg

Subject to your approval, of course.

The topper will extrude directly out of the bed, there is roughly a 1.5" gap between the cab and topper (not shown is my crude 3d model) which I'm just going to temporarily patch with duct tape and call it good lol. As for the sides (from an aerial POV), they will be shaped much differently than shown. I was at the end of my lunch break and just threw together what I could in a few mins.

Please don't reference my 3D model in post #2. It was a crude and dirty job making those sides due to a time constraint lol. As I told Kach22, I was nearing the end of my lunch break and didn't have time to create a proper loft with correct dimensions for a proper aero design. The actual design will be styled after a 1st gen Honda Insight rearend.

Here's my version of a cap for a pickup:

https://www.youtube.com/watch?v=KfDVlrb__m8

The darker profile on the back was the previous version, which was too low. The newere version is better, but I am not sure how close it is to the ideal.

????? Perhaps you should delete it? All I did was point to the Permalink. All we have to go on is what you post. If it's any consolation, my 3D models 'never get the refinement they deserve' as well.

Why did you pick that one detail out of the post to respond to? Overall it was about the mathematical tools to lay out the full scale patterns.

https://upload.wikimedia.org/wikiped...sight_Back.JPG
https://en.wikipedia.org/wiki/Honda_Insight

I can see that; the lower body is somewhat boxy. Are you going to use an Insight's glass or hatch?

You're changing from a convex curve to a reflex curve, are you just going to lift dimensions off an actual Insight? Compare the section through the Insight A-pillar and your B- or C- pillar.

rear corners
 

The rear corners of a pickup bed pose a real challenge with streamlining.
Ideally,we're instructed to maintain a rolled corner at the bed rail-to-bedcover interface
http://i1271.photobucket.com/albums/...ntitled285.jpg
This allows for a 'ring-vortex' 'fluid-tail' discovered (sort of) by Dr.Alberto Morelli in the Turin Polytechnic Institute in the 1970s.
Here you can see how Morelli has softened these edges
http://i1271.photobucket.com/albums/...titled7_22.jpg
This is a schematic of the ring-vortex in action
http://i1271.photobucket.com/albums/...itled12_20.jpg
When you do a pickup,you end up with something like this,which recorded a 22% drag reduction.It's a known quantity and worth doing if you can stomach the complication of the build.
http://i1271.photobucket.com/albums/...itled-16_2.jpg
It's taken me 6-weeks to do this modification to my bedcover.:p

4th gen Camaro/Firebird is like unto the GM EV-1. I was thinking of the actual glass but the contour is a little hard to see, so here's a louvered overlay.

http://www.andysautosport.com/images...d/sm__1383.jpg
http://www.andysautosport.com/window..._firebird.html

Hey everyone,

A quick thank you to FreeBeard, AeroHead, and NeilBlanchard for your input.

Aerohead, regarding the ring-vortex you brought up. Would this be a worthwhile option for an additional accessory "box" with the shape mentioned that could mount to the tailgate? I could fold the tailgate down and attach the box that during long trip. Yet be able to store in the bed when in town (because I'm certain juveniles won't be able to resist tampering with it). Did you ever have problems with people messing with your builds?



Anyways, a quick update on my progress. I finally finished out my senior design project and get to move forward with my life lol. Attached below are two pics of a little progress I made last night on the cab. The hardware cloth seems like it will mold perfectly to my desired shape. There was a minor design change too, I needed more height at the tail to make it practical for my fatbike to go in and out of with the top on.

I'm still debating how to finish out the top lid.. I can't decide if I want to make my own tonno cover to roll down it or an actual hard lid.

The fiberglass and resin arrived and my application plans are to apply 2 layers, use a little bondo as needed to fill the divots, then finish it with 2 or 3 final layers.

Again, thanks for reading and any and all input is appreciated!

http://i1064.photobucket.com/albums/...pswy01uqyy.png

http://i1064.photobucket.com/albums/...pscv51drds.png

http://i1064.photobucket.com/albums/...psaunnfnk9.png

http://i1064.photobucket.com/albums/...psrugyiigt.png

The thing about the Morelli ring vortex is it is 360° with special attention to the wake coming off the back tires. It actually has turbines in the wheels that pressurize slots at the ring. The pickup bed tailgate hinge line falls about the middle of the ring.

[a]erohead has built pneumatically inflated tailgate add-ons. Check his albums.

http://www.boatdesign.net/forums/materials/pet-g-mylar-film-46223.html

I would do 2 or 3 layers of fiberglass, hit it with 80-grit sandpaper, and then do the last coat or two using Mylar. I always though you puddle it and squeegee it out, but the linked article suggests a toothed applicator.

There is some discussion of trapped air bubbles. I'd try pricking the Mylar to let the air out in that case.

accessory box
 

This is the inflatable boat tail which Freebeard mentioned.
It's basically a wooden box which encloses a 12-VDC blower fan which breathes through to a tailored bean-bag envelope,stapled to the perimeter of the box and attached to the tailgate.
It did require a stabilizing spar affixed to the bottom to prevent oscillation.A simple electrical umbilical cord ran under the truck and simply spring-clamped onto the battery terminals during testing.
It's very light and with the 1/2-tonneau and the cargo box in the bed,it gave 5+ mpg at constant highway speed.
http://i1271.photobucket.com/albums/...ohead2/208.jpg
The Naughehyde envelope created a square-to-rounded corner transition which kills attached longitudinal vortices and allows for the ring-vortex.:)

http://ecomodder.com/forum/member-fr...pe-ii-boat.jpg

If the box has a lid that hinges at the bottom, that would substitute for the spar.

Well guys, I made it to colorado :) Thanks again to everyone for the help and advice!

Summary: I suck at fiberglassing lol. I got 2 coats when building the truck but that was all I had time to do. The hinged lid works flawlessly so I was able to load everything into the truck with the topper in place.

Fuel Log:
I traveled a total of 1478 miles.
Starting elevation was 500 ft and final elevation is 5600 ft.
Estimated weight including furniture, 3 bicycles, and an extra passenger is roughly 800lbs.
Average speed from Ohio through Missouri was 70-75mph.
Average speed through Kansas and Colorado was 80-82mph.
From Dayton, OH to Columbia, MA I had to fight an awful storm that caused tons of flooding.
Since the sender unit was out and my credit card required pre-paying, I wasn't able to get all the individual numbers.


The final fuel consumption was 71gallons resulting in nearly 21mpg average in an automatic truck. As a bonus, even though my aero topper was hinged and I dealt with rain for almost 10hrs straight. ALL of my stuff stayed perfectly dry! I couldn't be happier with the end results. Thanks again to everyone for the input!

I'll upload photos within the hour anyone interested.

I'd love to see yer finished cap! :)

Here it is with the 1st layer of the fiberglass cloth but no resin yet.
http://i1064.photobucket.com/albums/...pssq6nbozv.jpg

My Firestone tire :) Destination A/Ts... I wanted a little extra traction for the dirt roads out here.
http://i1064.photobucket.com/albums/...pstvahbmgl.jpg

And here is it at the apartment complex in downtown Denver. Don't hesitate to enjoy a glace at the beautiful bikes in the back
http://i1064.photobucket.com/albums/...psvrwnewou.jpg

Will upload pictures of it open in the upcoming days

So jviolet, your getting over 25mpg with aero top and electric fan?? Or is there more you've done so far??

Yea, just those 2 main mods. Thats pretty much it besides a good tuneup on the engine.

It should also be noted that the fuel efficiency is naturally better in Colorado than other places since the air in Denver is only about 75% as dense as sea level. At my friends house in Alamosa, I was getting almost 30mpg in a 2010 highlander because the roads were perfectly flat holding a constant 65mph at 8k ft. elevation (approximately 65% air density)

Awesome!! It makes sense now that you mention co, I drove from knoxville tn to st george ut and noticed a 3-4mpg improvement on my tank through co!!

On my s10 I bypassed the ac and ps pump and was averaging around 26mpg, and got about 29 almost 30mpg through co. But I didn't keep the recipes!! ���� also its a standard!!

Loving it here! This most recent tank appears to be my best to date. I'll update it upon filling it up tomorrow.

http://i1064.photobucket.com/albums/...pskyvvwmwz.jpg