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Old 12-06-2009, 08:26 PM   #11 (permalink)
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Old 12-06-2009, 08:33 PM   #12 (permalink)
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here is some pics of the frame work of my aerocap. this is with a 9" drop from cab to tailgate. which calculates out to a 11.25 degree angle. i am thinking of putting a piece of wood in the center of the span so it makes it a little rounded. any suggestions? should i make change the angle steeper? it seems like most guys making them are making the angles steeper.

i am going to get it all framed out then put 1/2" plywood over the top
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Old 12-06-2009, 08:35 PM   #13 (permalink)
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Old 12-06-2009, 08:43 PM   #14 (permalink)
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Why 1/2 plywood? You can make one that is much lighter.
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Old 12-07-2009, 05:53 PM   #15 (permalink)
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angle vs curve

Quote:
Originally Posted by ccrider View Post
here is some pics of the frame work of my aerocap. this is with a 9" drop from cab to tailgate. which calculates out to a 11.25 degree angle. i am thinking of putting a piece of wood in the center of the span so it makes it a little rounded. any suggestions? should i make change the angle steeper? it seems like most guys making them are making the angles steeper.

i am going to get it all framed out then put 1/2" plywood over the top
If you have an abrupt angle,you will lose boundary layer adhesion immediately,flow will separate,and there is a chance you'll have a violent buffeting,enough to "explode" your shell if not robust enough.
Please take a look at Metro's Permanent Kammback for Metro thread,or the Aerodynamic Streamlining Template thread.
You'll notice that the roofline begins with a subtle curvature,increasing with length.
Get a 20-foot length of 1-inch PVC pipe,lay it over the cab and study the curvature as it bends down toward the tailgate.
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Old 12-07-2009, 08:28 PM   #16 (permalink)
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A smoother curve transition is better, but is not an insurmountable problem.

The angle is about right IMHO.
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Old 12-07-2009, 10:48 PM   #17 (permalink)
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Why 1/2 plywood? You can make one that is much lighter.
it is what i have around. i think 3/8ths plywood would be to thin
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Old 12-07-2009, 11:54 PM   #18 (permalink)
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i am thinking of putting a piece of wood in the middle of the span that is about 1" taller so it bows the upper board up and gives the cap a rounded shape to it.

also should i make the top piece of plywood on the cap extend past the tailgate off the back a bit? i am thinking about extending the plywood as far back as the rear bumper off the back of the truck (about 5") and then on the sides at the back making little pieces that return to the tailgate. making kind of a little kamm spoiler
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Old 12-09-2009, 08:03 PM   #19 (permalink)
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The smaller the trailing wake, the better. If you're willing to extend to the end of the bumper, your wake area will be that much smaller.

I did a similar thing on my car (Kammback out to the bumper):

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Old 12-09-2009, 08:28 PM   #20 (permalink)
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metrompg i put a protractor over the computer moniter and it seems like your kammback is 15 degrees. would it be better for me to make my cap at 15 degrees to make a smaller flat section behind the truck in turn making a smaller wake?

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