Full Vs. Partial Aerocap

[mosby]

Hi Y'all, I have a dumb question.

I'm considering replacing the tonneau cover on my Ram shortbed with an aerocap, but don't like losing the rear/passenger side visibility.

Do you think I'd see any gain from building a partial aerocap, only going up to the level of the rear view mirror?

[PaleMelanesian]

http://ecomodder.com/forum/showthrea...bums-3541.html

[mosby]

Thanks for the chart. What I'm really looking for is info on a half height aeroshell, only going halfway up the back of the cab. Has anyone tried this or have any info on something like this?

[Big Dave]

I would think a half-height aeroshell, combined with a duckbill would give performance approximating a full (and properly sloped) aeroshell.

Obviously, nobody has done one, but there's always room for pioneers.

I'd start by using cardboard or paperand see how high you can bring up the bulkhead end of your semi-aeroshell without blocking off an unacceptable amount of your rear view. This figure would vary driver to driver. Tall dudes could probably tolerate the bottom 60% blocked but shorties might not hack with more than 30% of the rear view blocked off.

At say 50% you could slope your semi-aeroshell at nice 8 to 10 degree angles.

A wing or duckbill off the top of the cab would transition the flow down about 10% and the gap would be minimal for the flow.

[Big Dave]

If I could see out the back of my cab, I wouldn't be so dependent on side mirrors and could use smaller mirrors.

[PaleMelanesian]

This is Phil's current version. See how the sides of the cap step in from the side of the cab? That sounds just like what you're looking for. Also, see at the taillights - the step in there works, since the shape farther back comes back to meet the ideal taper form.

Rather than a low angle all the way back, I'd do a fairly flat top, out to about halfway back, then from there follow the standard ~12 degree taper.

[PaleMelanesian]

Here's what I mean. The yellow line, instead of the standard aerocap in red.

[mosby]

I think mine will be a bit more angular, since this is supposed to be a cheap experiment. And not following the geometry of the cab uprights will make construction easier..

You've got to admit, Phil's latest looks like his bed was attacked by an upside down dingy

Maybe in the future I could build a foldable boat and just use the stern as an aerocap?

Thanks for the help.

[PaleMelanesian]

That's because it IS a dinghy. It turns out that hydrodynamics is about the same as aerodynamics.

Since you have a short bed, you might have to finish the cap several inches above the tailgate to maintain the ideal angle. Phil's got a fairly low cab and a long bed to work with.

[mosby]

Well, I'll be dipped in.....it's really a dingy. I guess the difference in density let's you use a low speed displacement hull for much higher air speeds.

As I recall, displacement hulls tend to be very efficient, making the greatest speed with low power like human power.