Hi All.
Great job on this aero cap!!!
For as much as it cost it looks terrific.
This is my first post here to this forum. I have a 2000 GMC Sierra ext cab 4x4 very very similar to the subject truck in this thread. I am going to be driving it across the country again in February from Montana to Vermont. I have been sickened by the lousy highway mileage I have gotten in the past, 14-15 mpg . (I do have something of a lead foot
, which, I'm looking to cure on my upcoming trip by giving myself an extra days travel time, and plan to average 62 MPH or so instead of 72-78 MPH)
I have been thinking on my own how to build an aero cap since I know the drag in the back of the truck is a huge mpg killer.
Here is my twist on this, I have been thinking about removing my tailgate and building the aero cap down to the floor of the truck bed to the point where tailgate meets the bed. In my mind, this eliminates the huge square area being dragged behind the vehicle. It will look like heck I'm sure, and I'll have 2 vertical “fins” sticking up where my aero cover drops below the top of the cargo box. In my mind I don't see the fins as being much of a factor aerodynamically since the wind on the side of the truck would seem to be traveling parallel at this point on the outside. And the down sloping wind will just move around the fins.
My reasoning for removing the tailgate and dropping the mod all the way to the floor has to do with 2 things.
1st. Aircraft streamlining always seems to pay much more attention to how the air leaves the back of the airframe, look at the gentle taper of the rear of an airliner compared to the fairly steep slope of the front.
2nd. In observing the behavior of a tarp I have used as a temporary tonneau cover, I notice that the air really tries to mash it down in the area 2 to 3 feet in front of the tailgate. This indicates to me that the air really wants to go there and will remain attached to the aero cover.
3rd. I know based on reading other forums and from a Mythbusters episode, removing your tailgate does not help your mileage, but this is just removing the gate without putting something in the bed to fill the "void".
By doing this, I think it will eliminate a large area of vacuum which gets formed at highway speeds behind the tailgate itself creating a significant drag load.
Again, I know this is not a look for everyone. Factors influencing my decision are:
1) I don't care how it looks or what anyone thinks.
2) I don't need to haul anything in the back of my truck.
3) I can remove it and store it at my destination, so the aero mod will only be used for my 6000 miles of cross country highway driving.
I'm thinking of making it out of dimensional lumber for a frame and using 1/4" OSB for the skin. Although this build has me considering using shrink-wrap and an OSB space frame kind of a thing.
So what do you all think??
