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Old 08-31-2013, 06:43 AM   #31 (permalink)
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Originally Posted by Frank Lee View Post
Seems to me that hollow box thing is for when it isn't practical to put a real boattail (or built-in boattail form) on.
Clean, sharp air detachment.

There's nothing there to attach to even when it swirls back 180.

Lights, plate and fittings can go inside the "box" - out of reach of the airflow.

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Old 08-31-2013, 07:48 AM   #32 (permalink)
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Epiphany! Thinking about using shaped foam rubber like couch cushions coated with liquid plastic for a smoother surface as a flexible gap filler with velcro attachments to trailer... This should allow trailer turns without binding just letting the foam rubber squish and should maintain my radius and be easy to create. I'm sure someone must have thought of this, but, I haven't been able to find it anywhere. BB
Have you done the math on how much space you need to allow for cornering, meaning the distance from the front corners of your trailer to the back of your car? Looks to me like the minimum practical is 1/2 W of the trailer so at 5 feet, you'll need 30", which in a tight turn will shrink to 6" on one side and stretch to 54" on the other. The shrink is easy to engineer, the stretch is where it gets interesting. But I suppose you really don't need to fill the gap in a turn since at highway speeds the gap differences from side to side will be small, so all it really needs to do is crush. Still, a daunting challenge, which is why I think we see so few gaps filled.
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Old 08-31-2013, 09:58 AM   #33 (permalink)
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I'm working on a rear profile, floor plan / top view, and other details this weekend. At some point I'll put it on Sketchup or Blender.

Your train of thought and then reasoning at the end of the post followed mine... I only need it to crush and won't worry about even large gaps when turning, since almost all turns at highway speed are very gentle. The gaps will occur in town when aerodynamics is not needed. The application doesn't seem too daunting with my proposed method :-) :

1. Needs to crush / deform very well, 2. can not be abrasive or solid enough to dent things, but, 3. needs to have a "slick" rigid surface, 4. needs to be easy to shape (cut to form), and scalabe 5. Must be easy to attach and will not detach when needed but easily removable. I think my method meets all criteria and seems rather simple to apply.

1. Foam crushes very small, especially low density, 2. rubberized surface is "soft" and should be non-abrasive, 3. Rubberized surface is "slick" and "rigid" (like a wrestling mat), 4. can shape foam with hot wire adn make it big or small (like pillows, mattresses or couches). 5. Velcro attachments should be easy to install and remove.

Major problems might be... uh...storage bulk, (I also thought of air, because of deflation but that causes other problems, such as difficulty of manufacture, and not as "crushy" without popping, might have to attach to air reservoir or pump).

Can you think of other possible problems or engineering criteria?
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Old 08-31-2013, 05:28 PM   #34 (permalink)
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Still, a daunting challenge, which is why I think we see so few gaps filled.
Can of worms.

Some things you might try:
  • Air mattress type thing on each side with a connecting air tube so when one side compresses it inflates on the other side.
  • A tongue like thing that extends and retracts on the top front of the trailer. The tip would have a roller ball that bears on the tow vehicle roof and can roll sideways in turns and front to back as the trailer rises and falls on the hitch.

To understand how a box cavity works, look at the advantage offered by a half-tonneau on a pickup truck. It is a cavity that points up right behind the rear wall of the cab.
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Old 09-02-2013, 12:33 AM   #35 (permalink)
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hot-linked from pinterest

You have to get past that siamesed front fork, and a few other things ( ), but I noticed how the flare on the tow vehicle, in a turn, would lay against that beveled corner. It looks like with a combination of turn and pitch or roll they would trade paint, though.

I wonder if a steering front axle, like a farm implement trailer, would reduce the vehicle-trailer angle for any given turn. I need to stop looking at the picture.
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Old 09-02-2013, 12:42 AM   #36 (permalink)
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I need to stop looking at the picture.
It's like gawking at an accident.
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Old 09-02-2013, 08:41 AM   #37 (permalink)
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To understand how a box cavity works,
No need to understand how it works - just take advantage of the fact that it does work beyond its looks ...

As a simple add-on, the box cavity is not nearly as aerodynamically pretty as a boat tail, it doesn't nearly conform to the ideal teardrop shape - yet it does help quite a bit.
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Old 09-02-2013, 01:37 PM   #38 (permalink)
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No need to understand how it works - just take advantage of the fact that it does work beyond its looks ...
Much as we don't understand how electrons work, yet we converse on Internet?

There're straight, curved and inset boxes. Which is best? Would a half-box on the back of a fat fender work?
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Old 09-02-2013, 07:03 PM   #39 (permalink)
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It's like gawking at an accident.
a horrific accedent
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Old 09-04-2013, 06:52 PM   #40 (permalink)
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best?

Quote:
Originally Posted by freebeard View Post
Much as we don't understand how electrons work, yet we converse on Internet?

There're straight, curved and inset boxes. Which is best? Would a half-box on the back of a fat fender work?
I suspect that a curved wall would win simply because it could give the gentle pressure gradient the boundary layer needs and would not generate a vortex of which we'd have to pay for all the circulation.
If NASA could have cheated on the boat tail for the Space Shuttle I believe they would have.Since they went with a more 'ideal' form,perhaps its form substantially out-performed the other design candidates.
That's not to say that it would 'win' with truckers.
I think that any form of cavity would help on a 'fatty.'

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