Another Pickup Aerolid

[Big Dave]

Many guys have proposed some variant of the "fastback" sloping down at various angles. Some seem to work better (in reducing drag) than others but all have the same problem: They restrict vision out the rear window.

Here's another idea.

Currently my truck is running around with a A.R.E. hard tonneau. Big-timeflow separtion but I see out of it nicely.

What I am thinking about is a series of flat plates, stepping down trying to keep the flow attached at a ten degree angle. I should be able to see out OK.

What do you think?

The tonneau

http://www.youtube.com/watch?v=QGXA3m_hicM

Two plates with no duckbill

http://www.youtube.com/watch?v=dojFwEj8K5k

Two plates with duckbill

http://www.youtube.com/watch?v=HmeFrcwkk-4

Three plates with duckbill

http://www.youtube.com/watch?v=prqFjIQ-NSk

I'm not too sure my duckbill is doing much for me. It is 18 inches long and drops 3 inches.

Big-time thanks to Carlos for his help with this.

[Frank Lee]

Well it is dangerous to venture into armchair aerodynamics but I'm gonna give it a shot anyway: I think when we "break" a rear slope then re-attach thus trapping a vortice, the vortice really needs to be trapped so it sits there "rolling". If there is flow through that region I'm guessing it won't allow a trapped vortice to form. I think if flow comes in through the sides and goes out the back that yes, the flow down the back could be nice. The "but" is the same thing I've said about ducts: now you have internal and external flow drag.

And then there is the ever-present cross-wind flow...

If I EVER get around to finishing my aerolid I am going to incorporate a rear window treatment as the Chrysler PNGV car has.

[COcyclist]

Frank makes a good point. Flow Illustrator is only in 2-D cross-section. A vehicle moves through the air in 3-D. Do we assume that the sides of this cap are solid like Bondo's hinged aerocap, with flat plates instead of a hatch? I sure would like to see someone build and test a version of this idea.

[slowmover]

I rather liked the earlier idea of yours of a rear cover similar to the Camaro/Firebird rear window "slats" as a visibility "solution".

[Big Dave]

Talking about end conditions is little premature until I get a section I like. It looks like the duckbill+3 plates keeps the flow attached the best.

Probably the aftmost plate will have solid sheet metal supports on the ends (sides?) You can’t see under that plate anyway.

The intermediate plate (or plates) will probably be supported by struts. At first just threaded rod til I can work out angles and heights. The whole point is to have some visibility to the rear and to the quarters.

The duckbill will get a tapered side support.

The duckbill worries me. In the sims the duckbill does not even begin to turn the flow and we get separation.