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Old 03-21-2008, 03:06 AM   This thread is in the EcoModder Project Library | #1 (permalink)
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Smile Truck Aero, Bed cover DIY tonneau?

I'm thinking of making my own bed cover for my truck, has anyone done any DIY stuff thats easy to do using stuff fom say, Home Depot?

Would a tonneau (bed cover) help more than hurt or should I go a different direction with it?

I've had an idea for a simple style of bed cover where it sits flush with the top of the bed, faily light and hundreds of dollers LESS than a fiberglass tonneau. hinges in the middle to open half of the bed.. Or maybe a tri fold setup? quick release to pull it off quickly and simply fold it up to use the bed..

I've also had an idea since seeing the Areo Camper shells that Bondo makes..
I've also wondered if adding a slight lip off the back of a flat bed cover helps or hurts aero?
like this..


I'm itchin to get my FE up because I cant seem to break away from 29.5mpg lately..

I dont want a soft cover tho.. any suggestions or links to DIY sites?

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Old 03-21-2008, 10:49 AM   #2 (permalink)
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If that truck bed is 4' X 8', you could use a 1" thick 4' X 8' sheet of extruded polystyrene, aka Styrofoam, from Home Depot, etc.. You could fiberglass both sides of it, for a very stiff but light panel. Or, with proper adhesive, you could skin it with upper and lower sheets of 2mm thick Coroplast or other suitable sheet plastic. This becomes a sandwich panel of incredible strength and stiffness. Styrofoam is nice to work with, as it sands and sculpts easily.

You want stiffness, lest the panel flop around in turbulence at highway speed. With stressed-skin panels like this, when you double the thickness between load-bearing skins, you get an eight-fold increase in stiffness, which increases with the cube of the thickness between flanges.

To keep prying eyes out, you probably don't want the panel to be transparent or even opaque. If that's not a problem, visit a greenhouse supply store, and pick of a sheet of duo-pane polycarbonate, which is extruded and just like Coroplast, but transparent and virtually impact-proof.

I doubt that lip does much if anything aerodynamically, but looks nice and probably sells a lot of those panels.
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Old 03-21-2008, 04:10 PM   #3 (permalink)
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The best shape is definately going to be a tear drop. Per dollar spent, I think you would see the biggest effect.

Phil Knox's Truck


Simple, Quality:
1/2" Foam Board,
Fiberglass,
Epoxy Resin

composite construction, faceted sides

Simple, Cheap:
Lightweight Tubular Skeleton
Coroplast skin
Duct Tape

faceted sides

If you just want a normal tonneau, you could buy a bunch of aluminum siding and pop-rivet yourself one by forming ribs w/ flanges attached to skins. Cheap, easy, and unique...

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Old 03-21-2008, 04:57 PM   #4 (permalink)
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Quote:
Originally Posted by LostCause View Post
The best shape is definately going to be a tear drop. Per dollar spent, I think you would see the biggest effect.

Phil Knox's Truck


Simple, Quality:
1/2" Foam Board,
Fiberglass,
Epoxy Resin

composite construction, faceted sides

Simple, Cheap:
Lightweight Tubular Skeleton
Coroplast skin
Duct Tape

faceted sides

If you just want a normal tonneau, you could buy a bunch of aluminum siding and pop-rivet yourself one by forming ribs w/ flanges attached to skins. Cheap, easy, and unique...

- LostCause

Polyester resin is much cheaper than epoxy, and would be fine for this application as long as it's chemically compatible with the foam. Check first. Most fiberglass boats are made with this stuff, and have been sitting in the weather for decades, apparently without ill effects. Any marine hardware store or hobby shop should have it. To get the smoothest surface, do the fiberglass layup on a plexiglass sheet, then while still wet, lay the foam sheet onto that, then vacuum bag it down tight until the resin sets up. When it comes off, it'll be as smooth as the plexiglass. Then do the opposite side of the sandwich panel in the same way.

Vinylester resin is cheaper than epoxy, but more expensive than polyester resin. Where strength is a major factor, vinylester resin has about the same strength as epoxy, unless heat cured in an autoclave, where epoxy is the best.
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Old 03-21-2008, 05:51 PM   #5 (permalink)
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Hi All,

Epoxy is used because Polyester is incompatible with Styrofoam. This started with surf boards. Fiberglass boats tend to use PVC foam, so either skin material can be used. Epoxy resists blistering better than polyester skin. A gallon of epoxy resin for laminating was like $75 the last time I was buying any. I imagine its twice that now. I prefer Epoxy because of the better cure one can get in the home shop situation. There are two main brands for this West Systems, and System III. System III is available at Wood Craft stores. West Systems is available at many boat maintenance shops.

The PVC foam is not cheap either. The main trade name of the PVC foam is Divinycell (spelling?), and a few others I forget. In Europe they may use Rohacell (its polyamidimid I believe), but its very expensive here, and probably more so now. DOW makes rigid Styrofoam brand board (its blue) which is good for composite construction. The pink insulation board stuff has been "ruggedized" so it wont break as easy itself, but this greatly decreases the compressive strength (so the board can bend), which is critical for stressed skin construction. Boats core materials can also be aluminum or polypropylene honeycomb, or edge grain balsa wood. Or just simply marine grade plywood. Remeber, boats can be allot heavier than cars.

The PP Core has been used in land transportation applications. There is a company in Germany that makes a whole travel trailer, the kind that can be towed by cars, out of PP stressed skin construction, with about a 1 inch thick core. The brand name of this material is NIDA Core, and they are in Florida. This PP core has Polyester film stretched tight and bonded to the PP honeycomb, and the polyester has been scrimmed (made fibrous) on the outside for the glue to stick to. I have some (much too thick for car stuff) here and use it for vibration isolating platforms. PP being a polyolefin does not bond by gluing readily. NIDA Core has figured out how to do the bonding to the polyester film (probably thermally).

Another good core material, I forgot the name, for this stuff would be the PC (Polycarbonate) tetrahedral dimpled stuff. Its amazing too, and allot cheaper, but does not have the compressive strength of honey comb. But , I would think it would be very servicable for aero feature parts. PC can be glued directly. So, there is no need for the Polyester film and scrim, like with PP. It may not be available in thin enough core for this tho. Where the NIDA core can be made to order in its thickness.

Remember most of these materials are plastics, which can have tremendously variable modulus' with temperature. I made a sample with PVC foam, and Polyester fiberglass skins once, that was about 1 inch thick, 2 inches wide, and 9 inches long. At room temperature one could flex this about 1/8 inch over its length. At 10 F (I took it for a walk for an hour) the sample became very very rigid, and I could not feel any deflection at all hard as I tried to bend it.
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Old 03-21-2008, 07:02 PM   #6 (permalink)
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Pick ups are ment to carry 4X8 plywood so most beds are over that size at least side wise and the six foot beds are ment to carry them with the tailgate open.

I had been planing to make one out of two pieces of 1/4 inch chip board (a 4 and a 2 foot sections for the 6 foot bed) and maybe cover that with some waterproofing finish or covering. using 1x4 cross pieces (ribs) under it to give it the stiffness that it needs and cut that so it was slighted domed in the center so the rain would run off. but with the dome I could not think of any way to hinge it so I was just going to make it in one piece but you could make it any way you wanted. It was to be cheap so I could try different things and not stress the $$$. Later if i liked one enough I might think about fiberglass.

Now though I think I going to do a full aero cap instead using a different approach but still cheap so I can see what works and what doesn't.

Last edited by personx; 03-21-2008 at 07:13 PM..
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Old 03-21-2008, 09:57 PM   #7 (permalink)
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My beds 60"(5") X 76"(6'4")

I'm going to mock something up out of 1/8" thick board thats 4x8, and I've thought about making it so it hinges in the center for a half section..

Make it quick release and you can pop it off and fold it up and off to the side if I need to use the bed for larger objects.. Maybe even a trifold.. ? maybe not..

I'll use the 4x8's cut to size to they cover half of the bed, then frame the underside with 2x1's, Liquid nails wood adhesive and finish nails from the top into the frames..

2 hinges in the middle..

I just need to figure out a setup for a quick release, I'm thinking a bungie cord type deal with some brackets.. And so the flimsey 1/8" panel doesnt bow of flex because its whats on the topside of the bed, i'll jse L brackets placed so far that go on the wooden frame to the top of the bed.. Then use some campershell stick on foam to seal it up..

The only thing is that my tailgate is smooth and I have the handle flipped to the inside..

Then maybe hit it up with some marine epoxy paint to weatherproof it?
And if I'm feeling squirley I'll cover the top with some sort of material to hide the hinging point..

So far I'm about 35 bucks into it..
more to come.. I'm just going to make a flat one for simplicity and then use some of that round foam stuff used to insolate water pipes and shove it inbetween the bed and cab to kill that air section off

Nobody attached that lip idea, help or hurt?


as for making an Areo shell, homedepot has some sweet fiberglass sheets of 4x6 thats very VERY flexable..

I'd frame up an areo setup and cover it with that stuff in a heartbeat!
Too rich fo rme right now tho..
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Old 03-22-2008, 08:29 AM   #8 (permalink)
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I can only speak intuitively on this, but I think the lip would hurt. Personally, I'd radius the edge.

Interesting set-up you've got going there. The price is right.

Hopefully you could do some coastdown tests. I'd like to find out the reduction in drag you achieve. I don't know of anyone who's tested them before.

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Old 03-22-2008, 11:47 AM   #9 (permalink)
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I had some 1/8 inch panels that I had for something or other and they would warp and get wavy with just the hint of moisture (and this was inside my barn!). My 1/4 inch chip boards (not sure if that's their technical name) seem to handle the wet pretty good without any warping.
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Old 03-22-2008, 01:55 PM   #10 (permalink)
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Home Depot bedcover

Home Depot carries something called R-MAX,polyisocyanurate rigid insulation board,in 4 by 8 sheets,in thicknesses up to 3/4-inch.The board is like polyurethane,and is compatible with polyester resin,available in the paint department at Home Depot.

You can drape the bed of the truck with 1-mil poly painters dropcloth,and mockup the bedcover directly on the truck,cutting the foam with a utility knife,join the sections with masking tape,while using temporary supports underneath,then do wet layups until you've built-up enough glass to remove,and flip the unit for glassing the underside.

West System's epoxy is best,but Bondo's polyester will do .This is how I created my bedcover.Just don't let goats climb up on top of it!

Whatever you do,give yourself some vision to the rear and to the passenger side for safe backing,when leaving a parallel parking spot.With respect to the tailgate mounted rear spoiler,it is there to remind owners to keep the tailgate up for better economy.It is virtually useless aerodynamically and is more CRAFTSMAN-SERIES NASCAR hey-look-at me-I'm-a -high-performance-wannabe.

Final note,if you can build some compound curvature into your shell it will be even stronger,as it will become a geodesic structure with strength approaching that of an eggshell.Also better aerodynamically.Nature hates straight lines and right angles!

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