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Old 11-11-2014, 01:58 PM   #1 (permalink)
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A New Pickup Aerolid Build

Hello all,

I've got a small question that may not matter, but that I'm finding conflicting answers to. I'm hoping for someone to point me at what I've missed.

I'd been waiting for Bondo to get his company up and running so I could buy an aerolid for my 2013 SCrew. Well, it's been a long wait so I kinda decided to take matters into my own hands. I've got my materials, jigs, parts, screws, glue, etc. all together and I'm just a couple of days away (free time days) from bolting my lid(?) together and mounting it on my truck.

Which is when, of course, you remember things you should have previously thought about. But in an effort to make myself quit researching and move things forward I put on the back burner the question "does an aerolid affect the downforce on the rear of the truck to sufficiently change the rake angle when at highway speed".

The reason for asking is this: my build is a telescoping, stepped rig of four individual pieces of diminishing height and width following the 12º template curve in height and a 10º curve in width. I'm using Sintra foamboard formed to cover supporting ribs of flattened 3/4" schedule 40 PVC pipe. Front to back the sections are 10", 14", 14", and 14". Each section will telescope in 1" into the section in front of it, and is completely open front to back.

Think of taking a playing card and along its length folding down sides of equal height so that when you put it on the table you have two walls and a roof. Now with three more cards cut them so that you can make the same shape, but of diminishing size so that each smaller card (stepped) can be "telescoped" into the next larger.

Mine will be a 3/4 length "lid" (over a BakFlip G2 tonneau), which solves the problem of not being able to see out the rear, use of the cab top brake light, and bed access.

The individual pieces are easily removable (and broken down) which allows for easy use of the full bed length (if needed) and storage.

Its semi-rigid plastic construction should allow some side to side flexion in crosswinds- flattening on the windward side and bowing on the leeward (hopefully recapturing the airflow).

Where I get stuck is the 1º rake of the bed. Doing each individual piece with a added 1º front to back angle makes the thermoforming quite difficult and wasteful.

Early in this process I'd thought of using flaps (that I called "retrices" after the bird feather) attached halfway down the ventral surface of each "card" and extended past its length. In the case of airflow detachment over it, an individual "retrix" would lift into the low pressure area above it and effectively increase the length of the curve and hopefully flow re-attachment. IOW, an aerolid that dynamically changes its shape to capture the airflow.

But creating workable retrices is just too difficult and too unknown, and I really want this project over NOW!

Oh hell. After writing this I just don't think I've got another design change in me. Y'all give me a few weeks to slap this thing on and I'll try to get y'all some ABA 80 to 50 rolling times and some pics. Stick around- I'm sure it'll be worth a few laughs.

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Old 11-11-2014, 02:44 PM   #2 (permalink)
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Not sure what all of this was, but you may be overthinking it for the first time around! I would say finish something simple that works, start saving gas, then work on complex improvements.

Some drawings or photos might help explain the "playing card" design.
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Old 11-11-2014, 03:09 PM   #3 (permalink)
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Quote:
"does an aerolid affect the downforce on the rear of the truck to sufficiently change the rake angle when at highway speed".

Its semi-rigid plastic construction should allow some side to side flexion in crosswinds- flattening on the windward side and bowing on the leeward (hopefully recapturing the airflow).

Where I get stuck is the 1º rake of the bed. Doing each individual piece with a added 1º front to back angle makes the thermoforming quite difficult and wasteful.
Will these four pieces be compound-curved or flat?

How can 1% of difference affect the difficulty in manufacture?

An aerocap shouldn't produce up or down force. If it does it's not optimal for forward progress. Don't count on making the sides flappy to recapture air flow.
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Old 11-11-2014, 03:14 PM   #4 (permalink)
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Quote:
Originally Posted by Sven7 View Post
Not sure what all of this was, but you may be overthinking it for the first time around! I would say finish something simple that works, start saving gas, then work on complex improvements.

Some drawings or photos might help explain the "playing card" design.
Yeah, I gotta apologize for that. Prolly even shouldn't have posted it. Definitely overthinking the minutiae- it's a major problem of mine.

Once it's on the truck a single pic will explain it all. It's almost complete, save drilling a few holes and screwing things together. I don't even think I feel like painting it anymore- I just want to get it up and test it (this actually is the third iteration of this build).

Like I said- sorry. But stay tuned- this has all the makings of an epic fail!
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Old 11-11-2014, 04:15 PM   #5 (permalink)
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Quote:
Originally Posted by freebeard View Post
Will these four pieces be compound-curved or flat?

How can 1% of difference affect the difficulty in manufacture?

An aerocap shouldn't produce up or down force. If it does it's not optimal for forward progress. Don't count on making the sides flappy to recapture air flow.
Simple, when viewed only from the rear. The top and sides follow the curves of the cab top and rear pillar when viewed from the rear. (took a pic, blew it up in Photoshop, and matched them to some known curves). But the decreasing height front to back make it compound.

Making a curve from a flat sheet requires a bit larger area to cut curves into the sheet. It's a lot to do by hand and hard to get accurate. The Sintra can be stretched somewhat to avoid puckering but really requires a 3D mold, a large oven to evenly heat the entire piece, and more than 2 hands to form it before it can cool. I don't have any of that.

I decided on flexible joining after my first attempt with aluminum angle and channel resulted in a bent frame when tested. The idea of all flexible construction was really to avert some of the buffeting of a crosswind or semi. I was also thinking if you can decrease even a small percentage of that it may improve drivability. And the Sintra isn't really "flappy" as it is flexible- you can easily displace a step an inch to the side and it comes right back.

And I also guess there isn't much difference in going from 12 to 13%. But as Sven noted above- I overthink things.
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Old 11-11-2014, 09:48 PM   #6 (permalink)
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Now we need to see pictures of the first attempt, as well as the Photoshop work.

Is there any taper in plan? If the sides are basically flat, you could use 12° triangles on the sides and have four very similar pieces to nest together when they collapse. For—you know—the fourth prototype.

Bucky Fuller always said it takes 3 iterations to work out the bugs.
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Old 11-12-2014, 05:36 PM   #7 (permalink)
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rake angle at speed

When at the Darko Technologies tunnel,the T-100 exhibited no change in inclination up to the 76-mph tunnel velocity.
Goro Tamai of MIT claims that this form is essentially zero-lift.
'Looks like the aerolid will not alter the 1-degree rake.
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Old 11-12-2014, 10:43 PM   #8 (permalink)
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Quote:
Originally Posted by freebeard View Post
Now we need to see pictures of the first attempt, as well as the Photoshop work.

Is there any taper in plan? If the sides are basically flat, you could use 12° triangles on the sides and have four very similar pieces to nest together when they collapse. For—you know—the fourth prototype.

Bucky Fuller always said it takes 3 iterations to work out the bugs.
So #1 was made of foam insulated building material, duct tape, folded aluminum flashing and held down with bungee cord. It was to help get a picture in my head. Might have made it to a full 25 mph before imploding. Quite funny. (No pics so far on any of these - I just don't think about it at the time and would rather just do pics of what works)

#2 was aluminum angle and channel drilled and screwed together that would only be sturdy enough with a lot of crossbracing. Carpal tunnel forced abandonment, but it was also looking ugly. On that note though I was looking a lot at how geodesic domes were constructed for inspiration.

And with my deepest regards to Dr. Fuller, I just don't got a whole lot of "try" left in me. I'm scared to death If I think too hard I'll find some minor flaw which would make me scrap the whole thing and start over. I'm considering just grabbing a beer whenever this happens to keep me distracted.
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Old 11-12-2014, 10:47 PM   #9 (permalink)
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Quote:
Originally Posted by aerohead View Post
When at the Darko Technologies tunnel,the T-100 exhibited no change in inclination up to the 76-mph tunnel velocity.
Goro Tamai of MIT claims that this form is essentially zero-lift.
'Looks like the aerolid will not alter the 1-degree rake.
Thanks pal, I appreciate the info.

Looks like I'm gonna have grab some beer on the way home tomorrow.

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Old 11-13-2014, 04:19 PM   #10 (permalink)
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beer

Quote:
Originally Posted by drrbc View Post
Thanks pal, I appreciate the info.

Looks like I'm gonna have grab some beer on the way home tomorrow.

'understand that!
I can't even tell you all the locations across the country 'littered' with pieces of my projects.And welcome to the implosion club! We'll get you your set of wings.
The failures have been the most valuable portion of fabrication for me.In the professional world,even the most educated,and highly funded projects can end in disaster.
The licks are worth the taking in the long run.'cause when you do get it right you'll be rewarded with a 'long run.' Free fuel riding on the wind.

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