Commercially produced aerodynamic pickup bed cap

[tomi_k]

Been reading this forum and checked your videos (Julian, thanks for those, they are excellent) and yes, miniature scale models, environment etc. are subject and prone to all sort of bias.... Mostly, I wanted to make these models to have hands on "feeling" how a cap could look like but at the same time give "inspiration" through actual models and see things by myself how "aerodynamic" things work on small models... sometimes they are not so visible but sometimes they are (especially when relative comparison is made).....

[samwichse]

Maybe with EV F150's coming out, people will care more about aero toppers

[Bicycle Bob]

Hi Tomi, and welcome aboard. If I was making a pickup cap, I'd use Coroplast, and keep it light enough to hinge up from the side for easy bed access. I'd expect it to be mostly self-supporting, rather than fully framed. Using two or three layers stiffens it up wonderfully.

[freebeard]

Been reading this forum and checked your videos (Julian, thanks for those, they are excellent) and yes, miniature scale models, environment etc. are subject and prone to all sort of bias.... Mostly, I wanted to make these models to have hands on "feeling" how a cap could look like but at the same time give "inspiration" through actual models and see things by myself how "aerodynamic" things work on small models...

Does that mean I don't need to repost that picture of Polymetal again? Stiff as 5/8ths plywood at 1/10th the weight (and 3 times the cost at pre-COVID prices). I can demonstrate how to get a arbitrary compound curve out of a flat sheet with minimal cuts.

The size model you have can work; just upside down in a water tunnel with hydrogen bubbles. See ecomodder.com: graysgarage: Automotive Aerodynamics (video series)

[JulianEdgar]

Originally Posted by freebeard

The size model you have can work; just upside down in a water tunnel with hydrogen bubbles. See ecomodder.com: graysgarage: Automotive Aerodynamics (video series)

I have seen this done at university level and emphatically *not* working. Yes, that was the person, too.

I had people asking me all sorts of weird questions based on his testing... like why did their Toyota MR2 have separation from the leading edge of the bonnet (hood) - something I've never seen in on-road testing of real cars in 30 years.

[freebeard]

I did not know that. Do you think it could work?

tomi_k -- I have to admit, I don't know what scale that is, maybe 1/10th? In an air tunnel, 1/4th to 1/5th is considered necessary (subject to Julian Edgar's agreement). graysgarage used 1/24th.

[Bicycle Bob]

You might want to try good 'ol CAD - Cardboard Aided Design, full scale. With a day's work on some intercepted cardboard boxes using mostly layout tools, a knife, and hot glue, you can do a pretty good mock-up cap. This can be tested and altered about quite readily, and also tell you what structure you will and won't need in the finished product.

[JulianEdgar]

Originally Posted by freebeard

I did not know that. Do you think it could work?

tomi_k -- I have to admit, I don't know what scale that is, maybe 1/10th? In an air tunnel, 1/4th to 1/5th is considered necessary (subject to Julian Edgar's agreement). graysgarage used 1/24th.

When I was working on the car aero history book, Professor Howell was at pains to suggest to me that if I quoted any Cd for models, even at 1:8, I should put in a qualification re the data (eg not quote that figure as if it were for the full-size car). Where there was any doubt at all, I did it.

[freebeard]

There's got to be a line somewhere between what works and what doesn't. So -- 1/4 to 1/5th for air and 1/8th for water?

[JulianEdgar]

Originally Posted by freebeard

There's got to be a line somewhere between what works and what doesn't. So -- 1/4 to 1/5th for air and 1/8th for water?

I don't know enough to comment. Professor Howell talked about lots of corrections for accuracy eg compensation for pressures changes over the wind tunnel test section, etc, that apparently have historically often not been done.