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Old 05-26-2008, 07:21 PM   #1 (permalink)
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Yet Another Pickup Bed Cover Idea

I keep a foot in both camps - ecomodders and pickup trucks. (BTW a good way to have two groups hate your guts. Ecomodders think I am trying to salvage a hopeless idea and the truck guys think I'm gay. Good thing I have a thick skin.)

One group of truck guys who really need something are the "drive-away" guys. These guys use dually pickups to deliver RVs. They never get backhaul so the return trip is just pure expense. Can't do much on the paying leg, but the return run offers a possibility.

Driveways have to have fifth wheel capability and a clear bed rail, although the bed rail could be a inch higher. When they are towing everything else has to be below the bed rail.

What I am thinking of is a quick-deployed bed fairing. Make it like a snap-on tonneau but sloped as much as possible. I'd have a hinged headache rack to provide front support. He puts up three or four unequal length wooden bows and pulls the tarp over it and snaps it on and drives home garnering better fuel mileage. Before he picks up another load, he folds his tarp up and lowers the headache rack, clearing the bed for towing action.

Using a tarp means the fairing has to be convex. Driveaways have eight foot beds and the cab top is roughly two feet above the bed rail. If I'm doing my arctangent right, that 2-in-8 slope is roughly 14 degees. Not optimal, but close.

But my prototype will be on my truck which is a short bed (80" long). I want to play with the angles. I'm thnking the front half of the bed will taper to 10 degrees (1-in-6 slope) then transition to a 12 degree (1-in 5) slope. this will reduce the height of the back of the tarp to 9 inches above the tail gate top rail. I won't get quite the wake area reduction I get now (one inch above tail gate top rail) but the gentler angles will keep flow from separating better (current average angle is 17 degrees) and maybe a tailgate "plug" can get me some more wake area reduction.

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Old 05-27-2008, 02:42 PM   #2 (permalink)
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bedcover

Sounds good.It will work.And if you'll start out gently(girly-man talk)with the angle as Kamm and everyone else recommends,the further back,the steeper it can be,as pressure is building and the airflow is decelerating.This is what I was trying to get across with my Cinderella and clockface analogy.If the back top of the cab is 12-o'clock high,the line of your canvas follows the sweep of the second hand.At five seconds after 12,your flow separates.If you scale the clock face up to that of the truck,such that your tires are sitting on the ground plane,which bisects the clock rim horizontally at the 5-second mark,and the top of the clock rim at 12-o'clock is at the back of the cab top,The line of the clock rim curving back and downward is what airflow will follow without separation.As long as you have attached flow up to that point,it will work for any vehicle.It's basically what Farman,Jaray,Klemperer,Kamm,and the rest discovered and it will work on those dead-heading trucks.Go for it,and good mpg to ya,Phil.
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Old 05-27-2008, 05:23 PM   #3 (permalink)
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Just who I wanted to hear from.

Which do you think is more important: maintaining flow attachment or reduction of wake area? Sure, we'd all like to do both, but I only have 80" of "run" to reduce 24" of "delta-y."

Would it be better to have 10 degrees and 12 degrees and the top of the thing 9" above the top rail of the tail gate or rather going 10/12/14 degrees and the top about 7" above the rail?

This is an interim for me follwing shooting off my mouth. Ultimately I'll make something like Bondo's fiberglass bed cover but I intend to build in a couple of faired in hard points for CCTV cameras. Here in Indiana I may be able to get an exemption from the requirement for side mirrors and my truck's mirrors are huge.

First things first. If the removable tarp thing works out I may do a side business selling to the driveaway guys. Then the hard cover.

The goofy fixed fairing I have (see garage) actually does very well at improving MPG. Its just not bed-user friendly.
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Old 05-28-2008, 05:32 PM   #4 (permalink)
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bed cover

Quote:
Originally Posted by Big Dave View Post
Just who I wanted to hear from.

Which do you think is more important: maintaining flow attachment or reduction of wake area? Sure, we'd all like to do both, but I only have 80" of "run" to reduce 24" of "delta-y."

Would it be better to have 10 degrees and 12 degrees and the top of the thing 9" above the top rail of the tail gate or rather going 10/12/14 degrees and the top about 7" above the rail?

This is an interim for me follwing shooting off my mouth. Ultimately I'll make something like Bondo's fiberglass bed cover but I intend to build in a couple of faired in hard points for CCTV cameras. Here in Indiana I may be able to get an exemption from the requirement for side mirrors and my truck's mirrors are huge.

First things first. If the removable tarp thing works out I may do a side business selling to the driveaway guys. Then the hard cover.

The goofy fixed fairing I have (see garage) actually does very well at improving MPG. Its just not bed-user friendly.
Big Dave,Kamm and Korff and all the other heavy-hitters insist that its more important to maintain attached flow.On his K-cars,Kamm never exceeded 10-degrees of roof slope.He could of,as Mair would later demonstrate.And if you look at pics of the K-cars,the roof does not descend a great deal before its chopped off.The trade-off was good rear visibility,good rear headroom,and a drag coefficient close to that of the full-boat-tail car.If the bed cover slope starts out too radically,the flow will immediately separate.It may re-attach somewhere downstream,however your fuel is wasted feeding that rotational energy which cannot be recovered .I did a post on "Rooflines" as one of my recent installments here in the aero section of ecomodder.I think you'll find it of interest.Much luck with the project,like what your doing,Phil.
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Old 05-17-2011, 01:47 PM   #5 (permalink)
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New to all this myself. Anybody seen an aero shell that's easy to remove, light weight, allows you to carry bikes clipped to the back of the cap, and that opens up? That's what I need to build and I'm looking for ideas. Cheers!

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