Commercially produced aerodynamic pickup bed cap

[JulianEdgar]

Originally Posted by Bicycle Bob

Also, since you are not racing, you can probably accept a bit of upforce if it reduces drag.

With proposed shape, a rear spoiler* can decrease lift and drag.

(* or even just flattening of the shape at the end)

[tomi_k]

Does taper / tear drop shape on the cap help, in general (looked from the top of a vehicle) ? Haven't seen a good tuft test or data of such....

[freebeard]

First result when you site search for 'tuft test pickup aerocap' is from 2009. I didn't check further results.

ecomodder.com/forum/showthread.php/video-road-tuft-testing-ford-ranger-aeroshell-aerotopper-11522.html

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

[JulianEdgar]

Originally Posted by tomi_k

Does taper / tear drop shape on the cap help, in general (looked from the top of a vehicle) ? Haven't seen a good tuft test or data of such....

Yes, typically if you reduce the base area - area in contact with the wake - you will reduce drag.

[tomi_k]

Planning to use plywood to make form on top of a wooden frame... just to give rough shape... details will be made with foam.

Any recommendation for a plywood thickness which would be easy to "bend" and form.....1/4" thick?

[JulianEdgar]

Originally Posted by tomi_k

Planning to use plywood to make form on top of a wooden frame... just to give rough shape... details will be made with foam.

Any recommendation for a plywood thickness which would be easy to "bend" and form.....1/4" thick?

Stiffness depends on the grade of plywood, so best to go handle a few sheets. Around here at least, 6mm (1/4 inch) ply may well be too stiff if you want to try to bend it at all three-dimensionally.

[Bicycle Bob]

Originally Posted by tomi_k

Planning to use plywood to make form on top of a wooden frame... just to give rough shape... details will be made with foam.

Any recommendation for a plywood thickness which would be easy to "bend" and form.....1/4" thick?

The thinner you go, the more you can bend it. Boatbuilders write whole chapters on "tortured" plywood." The grain direction matters a lot on 3-ply. I'd be inclined to try doorskins (1/8"). If the curve is not enough to make it stiff enough, you can add another layer where needed. You are only trying to resist air and rain, not falling trees. Going light saves both money and gas.

Boatbuilders have also discovered that plywood boats work better without framing - fiberglass tapes to join the panels still make the edges the strongest parts without extra wood inside, giving a light, neat product. See "Stitch 'n' glue."

[tomi_k]

Idea is to have just few outline, ends and only "ribcages" out of lumber and then form the shape out of plywood. Yes, thinner the better for bending and forming... Just try to gauge rough thickness range.... 1/8-1/4" sounds reasonable. If shapes are more complicated, plan is to cut narrower strips out of plywood and "shape" the form incrementally.... this will not be the final outer layer...

Still need to think what I want to use for prototyping the shape ... but underlying thought process is that I prefer to make the prototype shape so that after initial testing is done, I can keep going with same prototype (with minimal teardown) and finalize the shape....

[tomi_k]

the shape will be 3D surface, for sure, just need to keep in mind also how to ensure that the cap door will be usable / practical and ergonomic... and finally the cap door needs to be "waterproof"....

So initial framing is just to make the same for the final product, final product is targeted to be glass fiber cap as "classical" caps are....

[freebeard]

Vacuum bagged veneers.

Here is a layout for sheet material conformed to a compound curve by pie-cutting hexagonal sections:





The result is a series of shallow cones, stitched and glued.This is for the Arcimoto FUV, but you get the idea?