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Old 04-26-2013, 10:17 AM   #1 (permalink)
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SuperTruck: AeroCap

Hey Guys,

I'm slowly working away on my "SuperTruck" DIY Plug-in Diesel/Electric Hybrid Pickup Truck project.

Nothing against me on the project except for time, skill, and money!

See the overall thought of the project at: http://ecomodder.com/forum/showthrea...uck-22080.html

I wanted to focus in the Aerodynamics forum on an aerodynamic pickup truck cap.

So here's my idea.....

So far, I've experimented with a few variations on simple/cheap tonneau covers made from recycled materials, one setup open right behind the cab for tool-box access, and most recently with a fiberglass flat cover, which turned out heavy and ugly.

What I've figured out from these exeperiments is that I do and do not have particular skills with particular materials, and other people around me with certain skill-sets.

In a nut-shell: Use what you have, Do what you know.

My Dad has been a carpenter and remodeler for his entire career. Recently, he built a cedar strip canoe. It turned out beautiful! Ended up building three of them between him and another guy.

In other news, somebody locally let me know of a barn that is slated to get burned down soon as part of a local fire-fighter training exercise. The barn is less than 50 years old, but the foundation is over 100, and in disrepair. I was offered salvage rights to strip off whatever barn-boards I wanted for projects, but when I saw it, was disappointed that it's "modern" boards, instead of the classic old-timey ones. What would be a good use for these boards.

That's when I realized that they were 14 feet long each, and I remembered that part of the expense of a cedar strip canoe is getting LONG lengths of knot-free wood.

I cut a sample of one of the boards to show to my Dad. To me, it looked like Cedar, but I wasn't sure. He looked at it and told me that it was Fir, which is sort of a hard softwood, and would bend fine once cut into strips.

So here's my idea; Build a "boat-tail" aero-cap for the pickup truck using actual boat building technology, in this case the style of a cedar strip canoe, using recycled barn boards.

I can work with wood easy enough, and there are plenty of extra boards for when I do screw up. My Dad has built the wood boats before and should be a great resource for advice and help on the project. His canoe is beautiful, light, and sturdy.

Mine will be more like a less graceful upside-down row boat!

Here's an example of a wood-strip cap from Sensible Living | Spruce And Cedar Strip Canopy

I'd be doing something similar, but without the ladder rack and sloping towards the rear of the truck.

Anyways, that's my idea. I have a few sketches I started doing (possibly with blind-spot windows, possibly not) and I'll have to figure out the right angle and whether or not I want a "Prius-style" back window in it.

Anyways, let me know your thoughts!

In other aero for the truck project, I'd be looking at a belly pan, front air dam, and rear wheels skirts - much of that most likely made from coroplast and similar light and sturdy materials.


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Last edited by bennelson; 04-26-2013 at 10:27 AM.. Reason: added photos
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Old 04-26-2013, 11:01 AM   #2 (permalink)
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Not a bad idear. It will be light, waterproff, and dureble. Just go on with it. Bouat building tekniques are good for cars too, because the can stand the wheather.
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Old 04-26-2013, 11:19 AM   #3 (permalink)
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...and it will look good, and it will be made from renewable material, too.

You can model it in SketchUp and the rib former profiles can be generated an those will be accurate to the shape you design.
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Old 04-26-2013, 11:40 AM   #4 (permalink)
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Boat-building techniques for better aero - no reason not to. You'd be following in others' footsteps for sure:

(was at http://ecomodder.com/forum/showthrea...ins-12031.html )
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Old 04-26-2013, 12:09 PM   #5 (permalink)
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Classic cedar strip construction can easily achieve a smooth, sexy shape for a bed cover. While canoe, kayak and other small boat builders typically use Western Red Cedar for the base material, that is based mostly on its relative lightness and easy workability with hand and power tools due its subdued grain structure. As a bonus, western red cedar ranges in color from almost white to deep maroon and brown offering the opportunity to create custom artistic effects in the hull.

Overall weight won't be a major issue in a bed cover however, and use of any relatively knot-free soft wood should do. (Knots up to the diameter of a pencil eraser while unsightly are acceptable so long as they are not at an edge.) Fir, while acceptable, can be a real PITA due its strong grain stricture. When shaping the edges of the strips, long, thin needle-sharp splinters are easily created. These are painful at least, and when broken off can affect, the strength of strip-to-strip joints. Other softwood such as pine, spruce, hemlock -- even poplar, cypress and redwood when weight is not a major consideration and the structure will be painted -- are greatly easier to work.

Most often the individual strips are made with a "cove and bead" treatment on opposite long edges; one side curves outward, the other inward. This creates sort of a modified ball and socket-like mating surfaces. This method allows adjacent strips to be pulled tightly together going around curves for maximum glue effectiveness making for tight, strong glued up. As a secondary effect the tightness prevents "show through," light shining through thin strips of cured glue between strips in the finished hull… a sure sign of an amateur, first time building effort… but not really a strength issue if they are small and far spaced apart.

If you are really handy with a razor sharp, low angle block plane you can plane rolling. constantly changing bevels on the edges of adjacent strips so that they fit tightly together alone their full length. But this is usually the province of really experienced builders.

It is not necessary for every strip to run the full length of the structure. Typically end-to-end butt joints for the strips are acceptable if they occur one in every three strip runs and are widely spaced apart. This feature is often use to make mosaic-like artistic designs -- of even birds, fish, etc. -- in some hulls.

Coating the structure with the epoxy/'glass on the outer surface of a bed cover will be relatively easy due its convex curvature. On the inside concave surface the 'glass tends to pull away from the surface but this tendency can be over with patience and practice. Any unsightliness will not be apparent from the outside.

The cedar strip construction is covered with epoxy and fiberglass cloth which gives it the vast majority of its strength and puncture resistance. But epoxy left by itself in the sun suffers from gradual degradation due exposure to harmful ultraviolet light. This can be overcome by coating with multiple coats of a high quality varnish with UV blocker. For a structure essentially exposed to full sunlight everyday, that would be 8-10 thick coats at initial build, and at least four coats reapplied each year as the varnish gradually, imperceptibly ablates -- is burned off by the sun. On a bed cover, varnishing would be more a matter of ego than practicality. Might as well paint the structure for low maintenance.

I recommend that you visit some cedar strip building sites on the Inter-web, there are lots of them. Stay away from obvious slash and cut, quick and dirty presentations. When it comes to buying a book, Ted Moore's Canoecraft is the acknowledged bible.

Last edited by Rokeby; 04-26-2013 at 12:24 PM..
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Old 04-26-2013, 01:15 PM   #6 (permalink)
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I used wood strips for the highly curved portion of my topper lid. There was no need to twist any strips because the lid is curved in only one direction, so I did not cove them.

Clear finishes are beautiful, but high maintenance for anything that spends time in the sun.
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Old 04-26-2013, 01:25 PM   #7 (permalink)
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I know your drawings & such are all preliminary, but you may want to consider the template overlay as guidance for the top curve. Also, if you are going to leave the bed intact, you probably don't want to bring the sides in drastically as this will create 2 areas of high pressure differential in close proximity that could hijack any aero gains you would otherwise achieve.

Hope this helps.

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Old 04-26-2013, 01:25 PM   #8 (permalink)
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Phil Knox (aerohead) played with using part of a real boat to make an aerolid. He may have other thoughts but IIRC it worked pretty well.

How long is your bed? If it is 80" long you'd probably need only 8 foot or 8 foot 6 inch raw strips.

I don't see why fir strips wouldn't work. Steaming the strips would help ease them into shape and reduce any tendency of the lid flying apart in the future.

A crude lid is not too tough. I made one single-handed in two days using plywood and rubber stair runner material.

But long-term, crude doesn't get it. I couldn't see out of mine and was restricted in my access to the bed. I needed a lid and sort sort of window.

If you can get help from the old canoe-builder making an aerolid with a working lids is certainly doable.
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Old 04-26-2013, 02:05 PM   #9 (permalink)
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always wanted to do something like that myself, recently cut a sheet of plywood to cover the back half and a few inch overhang of the tailgate, on the ranger, seemed to have picked up a solid .5 mpg gain at least, cost 22$
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Old 04-26-2013, 09:02 PM   #10 (permalink)
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Part of my thoughts on this is that I have seen a three-wheeler with a cedar-strip body. I think it might be the one that Metro posted.

I believe my Dad has a copy of CANOECRAFT. I'll have to see if he does, and if I can borrow it.

The truck is the short-bed version.

Today, I headed out to the Jefferson Swap Meet, a big car parts rummage sale at the County Fairgrounds the next county to the west of me. I took the side roads, and on the way out there, found an old-school junk yard and stopped. I was looking for a manual steering box for an S-10, but didn't find one.

However, there was a pair of full-moon hubcaps there, and they were 15"-ers, which was the right size for my truck. Got the pair of them for $20. Too bad they only had two. I thought I would put both on the left side of the truck, as that's what everyone sees when they are passing me anyways.

I just post about truck aerodynamics this morning, and here I am by noon finding full-moon caps!

As for that barn wood I can get, here's a photo of the short sample piece I grabbed. I also split it to show off the grain. To me, it looks just like cedar, but it doesn't smell the same. It's three-inch-wide tongue and groove, and the full planks are 14 feet long.

As for using them to make a strip-based cover, I was planning on making a "cove and bead" by getting the right router bits and use my Dad's router table.

For the finish on the cap, I would do a single-layer of fiberglass and epoxy, the same as what was done on the canoes, which has been holding up well. It's amazing how TRANSPARENT the fiberglass on the finished canoes is. It really shows off the woodwork.


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