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Old 02-15-2018, 04:07 AM   #41 (permalink)
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Yes, your #25 and Kach22i's #27 gave me the idea of isolating spillover between the air mass under the tail, and the air masses beside the tail. Then I thought, since the top view profile is a truncated triangle, (or a trapezoid,) and the side view is, as well, if I could wall off that area under the tail with an open ended 3 sided U section box that begins as a thin horizontal rectangular opening at the bumper, and transitions into a taller, narrower rectangular opening at the license plate end, maintaing an equal area for any cross section, I could eliminate the pressure drop, and thus the negative lift and the turbulence on the bottom of the tail, The sides of that box could confirm to the profile, and be a bit wider than the sides of the tail, so that if the skid pads hit the road, the lower box could slide up over the tail sides, perhaps with some sort of seal between the two pieces, and at full collapse would give the near 30 degree ramp angle of the car. (Drawing not to scale) Am I being more ambitious than it's worth?

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Old 02-15-2018, 09:21 AM   #42 (permalink)
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Whether you utilize a pressure relief method (diffuser) or attached flow method (2.8 degree plane) for ejecting the air moving under the car, I think after seeing the belly of a stock Prius you need to incorporate a full belly pan to any design you are considering.

Just in case I wasn't clear before.

Anything you can do to limit the mass and surface area of your "bustle" is a good thing in my opinion. Weight and handling will be affected by the mass. And cross winds pushing on your stern will be affected by the surface area.

The initial want or inspiration of doing something big and simple is not lost on me, however if your are up to the challenge of doing something craftier there may be benefits to it.

I do see a transformation in thinking taking place as the thread progresses, and that is a good thing in my opinion. Exploring all your options is the fun part, the hard work is in getting it built and suffering the disappointment and heartache of the setbacks to come. Overcoming these as now unforeseen setbacks is the ultimate test and the ultimate reward.
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Old 02-15-2018, 11:45 AM   #43 (permalink)
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Thanks.I design by change. I start out with an idea, and while I'm building, have a better idea. I'm learning a lot from you guys. I originally thought a 15 degree top and sides, and a 30 degree bottom (for ramp clearance) was all I need, along with a rear piece of license plate size.Then I learned that the bottom would cause turbulence and drag, and that I neede to make it 2.8 degrees, and movable. Then, of course, there's "The Holy Profile", but that runs just short of 15 degrees to just over 15 degrees where it would be applied to the boat tail, so a straight 15 degrees would probably be nearly as good, and much easier to build. I'm wondering if you think the lower pan on my latest design is worth the trouble?
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Old 02-15-2018, 11:55 AM   #44 (permalink)
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Quote:
I do see a transformation in thinking taking place as the thread progresses, and that is a good thing in my opinion.
Agreed. Some would come with the [line/attitude] "I did this now how do I fix it?" But at some point you have to start making mistakes in CAD (Cardboard Aided Design) or Coroplast.

It's true that a single fix is suboptimal. At least, if I understand correctly, the Toyota HSD is immune to needing gearing changes. I base that on someone's comment that HSD is unaffected by tire diameter, FWIW.

Perfect is enemy of the good. It's hard to get a one-piece wall to wall, front to back bellypan between the four tires. But maybe 3 or four partial belly pans where effective leaving the flatter parts un-panned will get 90%. Maybe a wedged out air dam and modest boxed cavity in back would get you 80%.

Specifically at this point I would look at the [un]parallelepiped defined by you leading and trailing openings. It would reshape the flow but not add or remove energy. But it would have skin friction.

The high-momentum mudflap shown at Permalink #40 is converging, the Bonneville FIAT is diverging.

What happens to the air flow if the floor of the diverter is deleted? What would be left would be two retractable skegs. The force of any ground strike would be along the length of the skeg, not across the whole leading edge of the floor. Less likely to be ripped right off.

Two skegs and a simple curved roof is still an exponential [half-]horn, as at D below.

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Old 02-15-2018, 12:53 PM   #45 (permalink)
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Quote:
Originally Posted by freebeard View Post
at some point you have to start making mistakes in CAD (Cardboard Aided Design)
I see you are a fan of Project Binky too.

Quote:
It would reshape the flow but not add or remove energy. But it would have skin friction.
What happens to the air flow if the floor of the diverter is deleted? What would be left would be two retractable skegs.
Two skegs and a simple curved roof is still an exponential [half-]horn, as at D below.
I still need the 30 degree floor to clear any dip up to and including bumper scrapers (or in my case, receiver scrapers. 30 degrees is way out of laminar flow territory, so I designed the 3 sided movable diverter to restore that lower flow. Do you believe the added skin friction of the floor would be worse than the uncorrected 30 degree tail turbulence?

How does the AroCivic get by with the steeper tail flow?

(If I sound confrontational, I'm not trying to be. Text doesn't give itself easily to inflection )
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Old 02-15-2018, 02:05 PM   #46 (permalink)
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I don't really know. I've been offering counter-examples for consideration. It would take hours in a wind tunnel to separate fact from fantasy.

Given your departure angle requirement, retractable skegs sounds reasonable to me. They could have a polyurethane skateboard wheel at the tip. Sort of wide-spaced wheelie bars with fill panels. They could be shorter than the tail overall, or canted like on a 1961 Oldsmobile.

An important consideration would be a smooth transition from the Prius proper onto the added structure of the boat tail. I haven't done a complete boat tail myself, but the 1:1 scale study I did was to find the point of transition. It turns out on the Beetle with a Tropfenwagen tail, it's a V- or U-shape across the roof instead of a straight line. Instead of cardboard, I used 1/4" Redwood benderboard ripped in half. This could be extended to a wooden-canoe-like construction.



edit:
Looking for something else I found this old thread, A paper on aft-end underbody diffusers, and a Summary at Permalink #13.
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Old 02-17-2018, 01:24 PM   #47 (permalink)
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passive,articulated difuser

Some thoughts:
*the movable portion of the tail fits inside the fixed,upper portion.
*Anything which 'rides' on the ground (skid,wheel,etc.) would need to castor,with 2-degrees of freedom,or else in a sweeping
contact,the diffuser will be forced laterally,and will jam,and want to break out of the upper units perimeter enclosure.
*Ideally,you'd disable the diffuser until,say,45-mph,when on the open road,with no chance of any contact at all;before the lowering mechanism could be enabled.
*Automakers are relying on air 'suspensions' for active aero.
*A simple ram,with reversing valve would allow air to be applied to either side of the piston.
*A cruise-control logic unit and air solenoids would be enough to control the ram.
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Old 02-17-2018, 03:59 PM   #48 (permalink)
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Quote:
Originally Posted by aerohead View Post
Some thoughts:
Thanks for your thoughts, but I've changed my design. See my new thread "Trailer Hitch For One Wheeled Trailer"
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Old 02-17-2018, 04:46 PM   #49 (permalink)
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one-wheeler

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Originally Posted by Angel And The Wolf View Post
Thanks for your thoughts, but I've changed my design. See my new thread "Trailer Hitch For One Wheeled Trailer"
Digest all of BamZipPow's work.He's our resident expert on 1-wheelers!
He didn't write the book on 'em,but he could.
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Old 02-17-2018, 04:53 PM   #50 (permalink)
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Please stop.

http://ecomodder.com/forum/search.php?searchid=2964673

Since 20180124 you have started nine threads and six of them are on one subject. As OP you can change Trailer Hitch For One Wheeled Trailer to One Wheeled Trailer For Gen 3 Prius See Through Boat tail. ...and let the others fade in the rear view mirror. There are a bazillion dead threads on this forum.

You're making it hard to follow your thought process.

On-topic: My vote is for a flying tail with a skid, that deflects more stiffly from side to side than up and down to accommodate scrubbing. With a hairpin end to allow backing up into curbs. Like BamZipPow did.

So sad that his build thread is all Photobucketed.

edit:
Take another look at D in Permalink #44. Imagine the skegs are hairpin skids with a fabric airfoil insert held in tension for rigidity. On a ground strike on one side or the other it would wobble and spring back into shape.

This could be on the end of a tapered boat tail, remember Dave Cloud's Dolphin?

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