"Wedge" Cap for pick up trucks

[rdefayette]

The intent of this design was originally to help improve fuel mileage by utilizing a “wedge” type bed cover to eliminate/reduce laminar airflow separation that is normally associated with traditional tonneau bed covers and bed caps.
Originally, it was just going to be a non-removable “wedge” but after thinking about it, it did not take much to make it much more functional for a variety of uses.
The main frame, semi-removable (bolted to the truck bed), consists of 3"x3" steel angle that runs the length of the bed on both sides and across the front of the bed. These angles have four tie downs attached on both sides for fastening loads in the bed. If required for load retention, tie-downs will also work under the steel angle anywhere along the length of the bed. There is a front “hoop” fabricated from 2" x 6" rectangular steel, roughly conforming to the cab profile. The hoop uprights also have tie-downs attached in order to facilitate fastening down loads when the cap is removed. The top cross bar of the front “hoop” also extends beyond the uprights, roughly to the width of the truck bed, and has 6”x6” steel plates welded onto both ends, which have two ½” holes to accept ratchet straps for the retention of long loads with the “wedge” removed. Again, the rails and front hoop assembly is bolted to the bed and remain in place when the cap is removed.
The “wedge” frame is fabricated from 1" square steel (aluminum could be used to save weight) and is covered with .040" black anodized aluminum. The “wedge” is hinged at the top horizontal bar of the hoop and raised/supported with gas lift struts.
If you notice in the pictures with the white skid/load in the bed of the truck, I have also made two adjustable struts for the back/rear of the “wedge” in order to adjust the height of the cap when carrying taller loads. The cap is normally in the full closed position but these adjustable struts allow secure closure at various raised and locked positions (up to slightly above horizontal).
When closed and locked/pinned in the full closed position the “wedge” cannot be opened IF the truck has a locking tailgate (either factory or aftermarket). There is no need for lock-type hardware on the “wedge” itself.
The “wedge” itself weighs approx. 100#. The “wedge” is removed from the frame by taking out the hinge pins that attach it to the top of the front hoop and disengaging the gas lift struts. This takes less than 5 minutes and only requires two people.
Briefly this “wedge” can be used and has the benefits of a tonneau/bed cover with additional height, can be used in a like a conventional cap (but not weather tight) in a raised position or completely removed for oversize/long loads.
It is not weather tight as I have constructed it right now but would be weather tight with the addition of a front window and weather-strip around the “wedge” perimeter.
To satisfy D.O.T. requirements for a third/high mounted brake light I installed two brake light/turn signals in the trailing edge of the “wedge” that operate from the trailer light connector and can be unplugged when the “wedge” is not on the truck.

Yes, compromises were made for functionality. I could leave the "ears" off but I needed these to secure long loads with the "wedge" removed. I also didn't follow the contour of the cab again due to time restraints and ease of fabrication.

I also mounted a rear view camera under the right "ear" and one on top of the left "ear". These are wired into my 7" GPS through a SPDT switch in the overhead console, switch left view behind the truck and to the left, switch center GPS, switch right down and to the right of the truck. Only blind spot is directly behind the tailgate.

My original goal was met, with an improvement in fuel mileage of 1.4 MPG, in real numbers, so far.

For those concerned about weight, the framework could be fabricated from aluminum.

With some minor modifications to the bed rails, not making them full length-shorter in the front with a partial rail near the tailgate, this would probably work on a truck with the "Ram Box" option.

If interseted I can send a link to my dropbox folder with additional pictures.

[HydroJim]

I applaud your effort, but there are some things that can be improved.

1: From the pictures, it looks as though you're adding a significant amount of frontal area to the truck which negates your aerodynamic benefits. Simply lowering the height of the aero cap where it transitions to the truck cab would improve the aerodynamics.

2. It also appears the angle of your cap is too steep. By following the streamlining template, flow could probably be significantly improved.

3. The corners are square. rounded corners will prevent a fuel robbing vortex from forming and help to improve your design.

4. You could definitely cut down on the weight. The biggest potential I see is all the steel that goes around the top of the truck bed. It doesn't really appear to serve a purpose in the cap's strength, so you could probably shed some serious weight there.

All of this is based on the photos, so if I'm seeing something wrong, let me know.

[rdefayette]

Originally Posted by HydroJim

I applaud your effort, but there are some things that can be improved.

1: From the pictures, it looks as though you're adding a significant amount of frontal area to the truck which negates your aerodynamic benefits. Simply lowering the height of the aero cap where it transitions to the truck cab would improve the aerodynamics.

2. It also appears the angle of your cap is too steep. By following the streamlining template, flow could probably be significantly improved.

3. The corners are square. rounded corners will prevent a fuel robbing vortex from forming and help to improve your design.

4. You could definitely cut down on the weight. The biggest potential I see is all the steel that goes around the top of the truck bed. It doesn't really appear to serve a purpose in the cap's strength, so you could probably shed some serious weight there.

All of this is based on the photos, so if I'm seeing something wrong, let me know.

Thank you,
1) If you are looking at the picture of the bare frame it was above the cab.
Changed it, now dead even with the top.
2) 13*
3) Yeah, I know. Form follows function.
4) Like I said can be made from aluminum ($$$) which would also result in loss of funtion.
The "hoop" allows me to strap 12' planks to the truck with the cap off and the steel in the wedge allows me to strap (done it) 1500# to the top of it if needed.
Can't do that with 'glass or aluminum.
Thank you though.
Maybe gen 2.
Bob

[t vago]

Don't let the perfect be the enemy of the good. That's a really nice design, Bob.

[rdefayette]

Originally Posted by t vago

Don't let the perfect be the enemy of the good. That's a really nice design, Bob.

Thank you, I guess that's why they have new car models/designs every year.
Over 100 years and haven't got it right yet!

[2000neon]

That looks good, I like it.

[crashnzuk]

Has it produced any gains in economy?
Travis..

[wmjinman]

Originally Posted by crashnzuk

Has it produced any gains in economy?
Travis..

In his first post, he says 1.4 MPG improvement.

[justme1969]

Nice I wonder when you were reading my thoughts?
glad to see it posted though.

[ChazInMT]

Indeed this is an excellent build, and is probably the strongest looking cap I've seen.

If you do a Gen2, you'll probably want to consider going at about an 8° angle, this would raise the back 6 to 8 inches off the top of the tailgate. It has shown this will have a good combination of Cd reduction and also reduce the lift coefficient considerably which will make your truck feel much more planted at highway speeds. Additionally you'd gain some under cap volume.

It is a common misconception that you want the back as small as possible, and while quite good, it is not ideal. You're probably getting 70% of the benefit of a very well designed cap.

Sorry to nitpick, you have done a great job. I just want this here as a guide for anyone else who looks in on this and it will help them design a better cap.

Thanks for sharing!

What did you use for a cover? Is that coroplast?

Here's a pic of my angle analysis. The wing shape is the Ideal Template overlayed on the truck. If you don't curve the top, it's best to go with less angle to compensate. The line is at 8°.


And here's a link to a Bigger Version of the illustration.