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Old 12-07-2008, 01:51 AM   #1 (permalink)
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T100 Question

And I hope the creator will weigh in



The step features on the bed cap.... What are they and what function do they serve?


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My CFD has ground to a halt at the moment - so I've been diving into pictures/text books and socratically asking questions to rationalize shapes and features

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Old 12-09-2008, 04:43 PM   #2 (permalink)
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steps

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Originally Posted by trebuchet03 View Post
And I hope the creator will weigh in



The step features on the bed cap.... What are they and what function do they serve?


------
My CFD has ground to a halt at the moment - so I've been diving into pictures/text books and socratically asking questions to rationalize shapes and features
The uppermost step is for 3rd brake-light visibility.The lower fenestration is to allow for some direct rear visibility when backing.-------------- Also,away from the camera,on the passenger side,is a side window for outward vision while backing out of parallel parking spaces.-------------- Note: the bedcover was completely destroyed by goats a couple years ago.------------------ Currently,I'm using the hull of a Chrysler-Marine Sailboat for a bedcover (it's very strong and goat-proof!).
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Old 12-09-2008, 06:15 PM   #3 (permalink)
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Quote:
Originally Posted by aerohead View Post
The uppermost step is for 3rd brake-light visibility.The lower fenestration is to allow for some direct rear visibility when backing.-------------- Also,away from the camera,on the passenger side,is a side window for outward vision while backing out of parallel parking spaces.-------------- Note: the bedcover was completely destroyed by goats a couple years ago.------------------ Currently,I'm using the hull of a Chrysler-Marine Sailboat for a bedcover (it's very strong and goat-proof!).
I'm glad I asked I totally neglected my third brake light

Did you use a rear windscreen? Or is it completely open to the bed? If you did, is there any particular reason why you chose to make it vertical rather than flush and following the lines of the cover?

Thanks for the input
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Old 12-09-2008, 09:06 PM   #4 (permalink)
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Quote:
Originally Posted by aerohead View Post
Currently,I'm using the hull of a Chrysler-Marine Sailboat for a bedcover (it's very strong and goat-proof!).
"Screw the boat-tail -- I'll just use a boat!"

I really think that demands pictures... (Shall I take a poll?) I would like to know how to make a goat-proof aeroshell out of a boat.
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Old 12-10-2008, 12:04 AM   #5 (permalink)
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^
I vote on that one!

Cool thing with the visibility thing. Most people wouldn't have even though about those things.
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Old 12-10-2008, 12:26 AM   #6 (permalink)
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Cool thing with the visibility thing. Most people wouldn't have even though about those things.
hmm... I don't know about that... Seems to me that any time I mention putting something on the back of the truck, some worry-wort goes, "Well, how are you going to see???"

"Uhh...I'll use the mirrors???" At least that's what I used to say (or at least think to myself). But now that I'm infected with mirror-delete-on-the-brain disease, I'm the one thinking to myself, "Well how the %!@# am I supposed to see???"

I need transparent coroplast. That's the answer. "Clearoplast". Google, are you listening?
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Old 12-10-2008, 12:29 AM   #7 (permalink)
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Well, I meant to put that they usually don't put it on there. most people want to put the boat tail on there and don't think about the windows until AFTER they build it. Thats why I love prototypes. YAY prototypes!
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Old 12-10-2008, 03:55 PM   #8 (permalink)
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rear windscreen

Quote:
Originally Posted by trebuchet03 View Post
I'm glad I asked I totally neglected my third brake light

Did you use a rear windscreen? Or is it completely open to the bed? If you did, is there any particular reason why you chose to make it vertical rather than flush and following the lines of the cover?

Thanks for the input
trebuchet,the upper brake light opening was left uncovered as,at about 10-degrees,a clear cover would reflect most of the red light down and refraction of such an inclined clear cover would diminish visibility of the light.---------------------------- With repect to the lower opening,yes,I did have a vertical plexiglass windshield there to weatherproof the shell.Had I attempted to cover that portion with a sloping clear cover,rear vision would have(as in the upper opening) been compromised due to refraction within the plex itself,and also do to internal reflections. This is why windshield angles have a practical incline limit,as,at some point you quite literally lose "vision". Aerodynamically there is a tradeoff,however from Hoerner,and others,the captured- vortex over these regions behave as a phantom surface,with the flow field passing over as if they were solid structures,and little drag penalty.Hope that helps,Phil.
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Old 12-10-2008, 04:26 PM   #9 (permalink)
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Quote:
Originally Posted by aerohead View Post
Aerodynamically there is a tradeoff,however from Hoerner,and others,the captured- vortex over these regions behave as a phantom surface,with the flow field passing over as if they were solid structures,and little drag penalty.Hope that helps,Phil.
Oh, really... Does there appear to be some rule of thumb regarding the size of such openings or other conditions to suggest when this will happen vs. when significant drag appears?
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Old 12-10-2008, 05:09 PM   #10 (permalink)
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rule of thumb

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Oh, really... Does there appear to be some rule of thumb regarding the size of such openings or other conditions to suggest when this will happen vs. when significant drag appears?
akashic,it's a good question and the short answer is,no,I don't have a rule of thumb,although the phenomena appears to be operating at the scale of bedcovers and rear spoilers,fog light openings,turn signal fenestrations,fuselage openings,rear gun turrets,etc..------------------------ With respect to the T-100,the aftbody flow is already established behind the windshield header and A-pillars.Since the flow divergence over the bedcover respects streamline flow,there exists no separation over the entire surface of the cover,save for the portions of the cut-outs. Windtunnel smoke trace or,in my case tuft testing,would reveal circulation within the cut-outs,with the outer flow-field separating at the beginning of the chop,then re-attaching to the trailing part of the chop,just as if it was a solid body. The whole premise of Texas Tech's research on their cab-wing/half tonneau was predicated on this phenomena. General Motors has a US Utility patent utilizing the effect. So a way to answer your question about the size which can effectively be exploited is at least the size of the open bed of a full-size 1/2-ton pickup. Note: I have no empirical data for extended -cab short-bed pickups,as they did not exist in the marketplace during the time of the aero investigations(circa 1988) and remain an unknown quantity to me.

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