Silverado aerocap build thread

[bluetwo]

This thing is frikin awesome man, good job!! I'd SO buy one of those if you made it for the shortbed Colorado.

[strange306]

How do you determine the appropriate slope? I want to build a similar cap with thin wall 1" X 1" metal tubing and cover it with polycarbonate (plexi or lexan) for visibility. 2005 crew cab tacoma shortbed.

[Christ]

Originally Posted by strange306

How do you determine the appropriate slope? I want to build a similar cap with thin wall 1" X 1" metal tubing and cover it with polycarbonate (plexi or lexan) for visibility. 2005 crew cab tacoma shortbed.

With the "appropriate slope", everything will appear as a distorted shadow through all but the purest sheets of polyacrylic (plexiglass) or polycarbonate (lexan) plastics. Even glass distorts at that angle.

[ChazInMT]

Hey Christ, Thanks for that heads up. I was considering putting in a clear area on my build but you just save me a ton of time and I'm sure aggravation trying to get a "View Port" in there right.

Strange, IMHO, you can't make it too steep if you go from the back of your cab roof down to your tailgate top. You do want to be sure to make it a curve shape. Your aero cap will have a flat area on top just behind the cab and will have it's steepest slope just in back above the tail gate. Air flow hates any sudden changes here.

[Christ]

If you want to cut a view port, you'll sacrifice some aero (not much), but you can use screening painted black. OSHA determined that screens used to protect machine operators in industry had to be black because everything is in contrast with black to the human eye, and you don't see light, you see contrast. As long as you're not focusing on it, you'll be able to see through the black screen, and screening acts like a smooth surface under high-speed flow.

The potential problem is pressure differential. IF the pressure in the bed area exceeds the pressure above the cap, or vice versa, there will be flow across the screen media.

[strange306]

I have a crew cab short bed. That would be a 20" drop over about 64". Isn't that a little steep? 1 to 3 pitch.

[MetroMPG]

Bondo (Brett) has added a small window (presumably lexan or equivalent) to the top of his aerocap. You might want to ask him whether it's functional to the driver or not.

[Christ]

Wow -

I just noticed that he's got a third brake light on that cap... never saw it until now.

Strange, take a pic of your trucks' side view, then lay a protractor down and measure the angle. I don't feel like figuring it out from the dimensions, but it's probably a little too steep for an unoptimized front end. No more than 14* seems to be the generally agreed upon figure, with 10-12* being the most accepted.

With a curve, opposed to a slope, you can get away with a much steeper exit angle, but the overall angle is still relatively the same. For the sake of clean separation, a "razor edge" is best for the edge of the cap, something that doesn't allow the flow to attempt to round a curve and dip down toward the tailgate, so you can get a few inches past the tailgate with that as well.

[mjboks]

Originally Posted by strange306

I have a crew cab short bed. That would be a 20" drop over about 64". Isn't that a little steep? 1 to 3 pitch.

Quick trig: 12 degrees over 64" is 13.3 inch drop leaving a 7.7 inch up from the tailgate. Even a streamlined arc will not get you to the top of the tailgate. You're bed is about the same size as mine.

[PaleMelanesian]

Quick google "sin 12 degrees" gives 0.2079... Multiply that by 64 inches to give you 13.3056.