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Old 01-19-2013, 05:11 PM   #1 (permalink)
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F150 aerocap design and construction

Hi all,

Inspired by the aerocap threads here on ecomodder, I have been encouraged to build my own and report fully on my design and construction experiences here.

Over the next couple of months I'll be posting full construction details, with detailed photographs, and afterwards, if anyone wants to copy my design (which is, to be fair, somewhat inspired by Bondo's fantastic design, but is constructed very differently) I will even mail out templates on paper to anyone who asks.

My design will have a light wood frame, covered in strips of 1/4" plywood to make the shape, then covered in fiberglass and bondo to get a great finish. I'll then finish paint it to match my truck.

The design will have an opening lid section, and will be insulated on the inside.

So far, the only mod I have done is a fan/shroud delete, replaced with an electric thermostat and two 16" e-fans. This has bought me a small gain in FE, mostly with cold starts and in town driving, where I get around 1.5mpg improvement. From here on I'll enter details on the site, since I am no de-lurking

If anyone has any questions, suggestions or support, I'm all ears

Dave in Austin

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Old 01-19-2013, 07:14 PM   #2 (permalink)
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How I arrived at my curve:

I decided that many people have already done good research on the terminal angle for the aerolid - I think there's a consensus that the final angle in Bondo's design is perfect. However, I wanted to have a curve that happened a little later to maintain headroom inside the bed.

I took a 1x8 board, and angled the two ends so it would sit in position, with 2" of fixable surface at the front, and 1" of height at the back. There is over 4" of contact on the bottom edge.

From here, I drew a line at the terminal angle from the back, and a line level with the roof from the front. I then got a piece of PVC pipe and made it into the curve that naturally intersected the lines I'd drawn at both ends.

This gave me an even curve. I didn't want that, but wanted more of the curve biased towards the front of the lid, and the rearward portion to be a flatter curve.

I printed out a few side images of others' aerocaps, cut them out then stood back and compared them with my drawn curve. A couple of tweaks and I was happy with my curve, just by gut feel.

I rough cut it on a table saw, as straight lines within 1/4" of the intended curve. Then I created the curve on the table saw, which I find the most accurate way of making large diameter curves.

I used a belt sander and my eye to take out a couple of 1/16" variations, and ended up with a curve I am completely happy with.

Next, I'll duplicate the curve to three more pieces of 1x8. I'll make two pairs, then drill a hole for a nut/bolt/washers hinge about 3" from the front. My idea there is to let the hatch open and have an EPDM rubber strip sealed to both sides of the hinge outside so it is flexible, doesn't interfere, and is aerodynamic.

Also, I note there's a gap between the cab and the front of the cap. I intend to put a curved piece of wood in there to bring down the gap to 1/2", then fill and shape the section with foam to create a more smooth join.
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Old 01-21-2013, 01:24 PM   #3 (permalink)
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My topper is a straight line in side view. The air flow is pretty good, but there is a thick boundary layer right behind the cab. Loose snow barely blows off the first foot or so of the topper.

A larger lead edge radius plus some curvature would improve it.
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Winter 2011-2012 was warm, so average mileage only dropped to 30.1 MPG. Summer 2012 was also warm, so average mileage increased to 37.1 MPG.
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Old 01-21-2013, 04:47 PM   #4 (permalink)
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The photos of your shell were part of what made me take the leap of building my own. Thanks

I chose to not do a straight one for that exact reason. I also didn't want to exactly copy anyone's curve, or be too original either.

In the end, the way I selected my curve was quite complicated to explain, and really simple to do

My curve is the natural intersection of the side curve. I will take a photo that should explain it a lot more clearly when the sun is in a better position, tomorrow. What this does is make it easier to keep a uniform side profile and top profile, and just have them intersect. Words don't do it justice but one photo tomorrow will make it completely clear
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Old 01-22-2013, 10:19 AM   #5 (permalink)
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This is a project I wish to take on soon so I will be following this closely.
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Old 01-22-2013, 01:58 PM   #6 (permalink)
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Well, you're in Richmond, so next time I drive to Houston I can drop by and show you what I have done, if you like?

Meanwhile, I have been reading a couple of threads on cold air intakes. It seems a CAI is good for increasing power, which isn't my goal, but a warm air intake might do a better job of getting the fuel atomized and improve economy.

I think I will monitor intake air temps using my Ultragauge, and do some ABA testing of cold/ambient vs warm air intakes. I've looked for a definitive thread where someone has done this, but never seen one.

Ok, now to go outside and take that photo I was talking about yesterday.
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Old 01-22-2013, 02:19 PM   #7 (permalink)
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New photos :)

Ok, here we go.

The first photo is standing right behind the truck. Note the line of the curve as compared to the line of the cab. The curve is the intersection of 1" inside the contour of the cab, give or take a quarter inch or so. This means I can maintain the edge contour from front to back, which I think is really clean.

Ford did a lot of work on the airflow over the top and side of the truck, so why ignore all their effort?

The second photo shows looking straight up the curve, so show how it and the hinged section will angle down, making the lid a trapezoid.

The third photo is a clearer shot of the curve from the side.
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Old 01-23-2013, 07:16 PM   #8 (permalink)
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Progress report...

Today I made good use of my templates.

First, I made three copies of my main curve. This creates the two hinged sides. I pinned them together and sanded them to be uniform and match the first piece.

Next, I used the roof contour template to make a few cross-pieces. These will be used to make the opening hatch. I was careful to mark the centerline, then I pinned them together and sanded them to be nice and even.

Then I pinned the main curves into pairs, and using a temporary block, I put them in position. I made eight side templates, then positioned them and cut them to fit. That gave the curve from the bottom. I then positioned them against the main curve and made a consistent curve from the top. Now, I have all the framing needed for the aerocap.

The next step will be to glue, pin and screw the side pieces, sand them, then assemble the lid section. I'll need to go get some hardware to make the hinge/pivot - a 2 1/2" bolt, nut, and some washers for each side. The interesting part is that the bolts need to be aligned to each other, which is NOT parallel to the wood they're mounted in. I'll need to watch that carefully when I get to that stage of construction.
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Old 01-23-2013, 09:55 PM   #9 (permalink)
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Great update,
Gonna be in Austin this weekend for a conference,
Msg me if you have time to show off your progress.
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Old 01-23-2013, 11:33 PM   #10 (permalink)
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PM'd.

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