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freebeard · 09-09-2014, 11:46 PM

I like the cardboard egg-crating. But when people say PVC, I shudder. Why not get green timber bamboo, make your finalized shape and bake it?

As for your (don't take it personal) befuddlement, if you look at The Template, you will see it has a half-circular section. This is to prevent the introduction of vortexes. If you want to induce vortexes, just do what you're already doing.

If the top slopes faster than the sides, you get air moving up the side and curling over the edge with vortexes rotating into the center. If the sides slope faster than the top then the vortexes rotate outward and down. I think. What you are testing with will have interference drag, like a biplane.

Rather than flats or simple curves with edges, you want increasingly smaller duplicates of the shape at the point of tangency. Consider these three primitives; on the left is a circle, on the right a square. The one in the middle is called a 'squircle'.

Here is my own research:

The 'rudder' has a reverse camber. The solid former is where a 'pointy' tail would fall. The hollow former is at the original rear bumper location. Each would be a reasonable location. Part of what I was looking at here, was how much length I can live with. I can get a complete boattail in 3 additional feet on a 12' car—125%. I'm working with perfect side taper (ignoring the open wheel) and a too-fast roof.

About the coast-down testing. I just got in from an 1800-mile weekend road trip (and boy, my arms are tired). What I have tried is a small hill and simulating a soap-box derby racer. Back-and-forth on level ground doesn't do it for me. But Nevada (I'd call it Land of the Long Shadows) has looonnng grades, some of them 5-6%. On those I could maintain the legal limit with the transmission in neutral. On lesser grades where I slow down now, aero improvements would be quantifiable.

You're right it takes time, but a few vacation days at the Donner Pass Summit wouldn't be so bad. The rest room at the Driver Safety Rest Stop is a palace.

When I-5 put me into Oregon, I coasted from the Siskyou Summit to the first exit for Ashland, OR. that's 11 miles.

09-09-2014, 11:46 PM	#29 (permalink)
freebeard Master EcoModder Join Date: Aug 2012 Location: northwest of normal Posts: 28,557 Thanks: 8,092 Thanked 8,880 Times in 7,328 Posts	I like the cardboard egg-crating. But when people say PVC, I shudder. Why not get green timber bamboo, make your finalized shape and bake it? As for your (don't take it personal) befuddlement, if you look at The Template, you will see it has a half-circular section. This is to prevent the introduction of vortexes. If you want to induce vortexes, just do what you're already doing. If the top slopes faster than the sides, you get air moving up the side and curling over the edge with vortexes rotating into the center. If the sides slope faster than the top then the vortexes rotate outward and down. I think. What you are testing with will have interference drag, like a biplane. Rather than flats or simple curves with edges, you want increasingly smaller duplicates of the shape at the point of tangency. Consider these three primitives; on the left is a circle, on the right a square. The one in the middle is called a 'squircle'. Here is my own research: The 'rudder' has a reverse camber. The solid former is where a 'pointy' tail would fall. The hollow former is at the original rear bumper location. Each would be a reasonable location. Part of what I was looking at here, was how much length I can live with. I can get a complete boattail in 3 additional feet on a 12' car—125%. I'm working with perfect side taper (ignoring the open wheel) and a too-fast roof. About the coast-down testing. I just got in from an 1800-mile weekend road trip (and boy, my arms are tired). What I have tried is a small hill and simulating a soap-box derby racer. Back-and-forth on level ground doesn't do it for me. But Nevada (I'd call it Land of the Long Shadows) has looonnng grades, some of them 5-6%. On those I could maintain the legal limit with the transmission in neutral. On lesser grades where I slow down now, aero improvements would be quantifiable. You're right it takes time, but a few vacation days at the Donner Pass Summit wouldn't be so bad. The rest room at the Driver Safety Rest Stop is a palace. When I-5 put me into Oregon, I coasted from the Siskyou Summit to the first exit for Ashland, OR. that's 11 miles.