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Old 04-11-2017, 01:55 PM   #1 (permalink)
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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?

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Last edited by jviolet10; 04-11-2017 at 02:01 PM..
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Old 04-11-2017, 02:09 PM   #2 (permalink)
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Here is a very crude image of what I'm thinking the shape will look like
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Old 04-11-2017, 02:21 PM   #3 (permalink)
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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.
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Old 04-11-2017, 06:49 PM   #4 (permalink)
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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.
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Old 04-11-2017, 08:23 PM   #5 (permalink)
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For those trying to follow along at home, see my response at Pickup Truck Aerodynamics - CFD Study Chevy S10



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:



Subject to your approval, of course.
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Old 04-11-2017, 11:44 PM   #6 (permalink)
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Quote:
Originally Posted by kach22i View Post
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.
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.
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Old 04-11-2017, 11:45 PM   #7 (permalink)
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Quote:
Originally Posted by freebeard View Post
For those trying to follow along at home, see my response at Pickup Truck Aerodynamics - CFD Study Chevy S10

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:

Subject to your approval, of course.
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.
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Old 04-12-2017, 12:37 PM   #8 (permalink)
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Here's my version of a cap for a pickup:



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.
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Old 04-12-2017, 01:27 PM   #9 (permalink)
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Quote:
Please don't reference my 3D model in post #2.
????? 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://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.
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Old 04-15-2017, 01:19 PM   #10 (permalink)
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rear corners

Quote:
Originally Posted by jviolet10 View Post
Here is a very crude image of what I'm thinking the shape will look like
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

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

This is a schematic of the ring-vortex in action

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.

It's taken me 6-weeks to do this modification to my bedcover.

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