Roof to bed shell

[JaronLindow]

I put an experimental roof-to-bed half-shell in my truck about a week ago.

Too soon to say what effect it's had on MPG.

In speed tests it seemed to add 2mph, but there may have been other variables.

I'm not used to having my rear view blocked, so I'll likely be redesigning before long.

[2009Prius]

It may be better to extend the sloping tail further back so the angle will be shallower. Good luck!

[NeilBlanchard]

Welcome to EM, Jaron,

I think that the slope needs to be less steep, as well. Look at the other aero caps/lids on the site for a comparison. The air can't close down that quickly, I don't think.

[ChazInMT]

Jaron, having built a shell and having given it a ton of thought, I believe you should not do what you've done, I initially thought I'd do what you did, but instead put my cap to the tail gate. Even this I believe is too steep. You should only come down to only about 10 inches above the top of the bed on top above the tailgate. This will give you a shape which closely approximates the ideal aero shape which streamlines the airflow without creating a lift drag which you are doing now in a huge way if you are not in fact separating the flow. Also, you cant have an abrupt edge like you do, it needs to be radiused in order for the air on the sides to transition smoothly.

Congrats on building something though! You're way ahead of most people on this.

[JaronLindow]

I think you might be right about the lift. I had to abort the downhill speed test as the truck felt unstable before hitting 80.

Originally Posted by ChazInMT

creating a lift drag which you are doing now in a huge way if you are not in fact separating the flow.

[aerohead]

jayron,check out the
AERODYNAMIC STREAMLINING TEMPLATE Part-C with 'SearchEcoModder.com.
You'll find some tools which might save you time and trouble.
You're definitely working on the right end of the truck!

[JaronLindow]

I made a 2nd attempt at a bed cover using a flat 4x8 sheet of wood strapped to a metal frame.

The front is just low enough to see over and the rear touches the end of the tailgate.

I tested with and without a simple vortex generator taped to the cab. That didn't make a noticeable difference.

Tuft testing showed the airflow along the rear half was moving to the sides rather than backwards, which was a surprise.

[aerohead]

Originally Posted by JaronLindow

I made a 2nd attempt at a bed cover using a flat 4x8 sheet of wood strapped to a metal frame.

The front is just low enough to see over and the rear touches the end of the tailgate.

I tested with and without a simple vortex generator taped to the cab. That didn't make a noticeable difference.

Tuft testing showed the airflow along the rear half was moving to the sides rather than backwards, which was a surprise.

If you had been running a soft tonneau cover you would have noticed that the back half would have a birdbath depression in it,and the area behind the cab would be bulged up,as if Yoda were underneath trying to escape.
It's the classic pickup vortex with air slamming down at the back and then back-feeding onto the stationary low pressure vortex spinning sideways behind the cab ( dancing beer cans ).