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Old 12-28-2012, 03:45 AM   #1 (permalink)
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Project: ECOfamily Civic and its Aero Hitch Box / Boat Tail

In order to make the Civic a more perfect family car, it needs better aerodynamics, additional cargo space, (and an improvement of ICE efficiency by some method: P&G/EOC for now, maybe a taller transmission on the horizon). An Aero Hitch Box and other mods will improve aerodynamics and increase cargo space.

Aero Hitch Box status :
  • Aero Hitch Box on the road! (5/15/2013)
  • Gap filler added to close sides and bottom to the car after coast-down showed a benefit. (6/28/2013)
  • Full boat tail (added Kammback and gap-filler window). (11/10/2013)
  • Added rear-wheel skirts. (2/8/14)
  • Kammback was damaged and Kamm-to-AHB-gap-filler-window was destroyed in a side-wind. Lesson: need downward force and maybe leading edge fish-scale for side-wind resistance. (4/20/14)
  • IMPORTANT: Magnets for Kammback attachment are a big no-no, according to the state of Utah. My Kammback has been shelved for now (6/2014)
  • The AHB lid flipped up due to operator error and did a lot of damage to the metalwork. Repaired (12/2014).

My best guess for Cd is around 0.30, but the error margin on my estimate is very wide.

Crr probably around 0.12 at 45-50 PSI. (Stupid Les Schwab. I really should have upgraded.) I also have some winter tires on here, generally Nov through Apr.

Lower-hanging mod to-do list:
  1. Low rolling resistance all-season tires.
  2. Remake driver-side rear-wheel skirt (it adds cross section area).
  3. Replace missing wheel blanks (winter mode).
  4. Adjustable grille block, cooling ducting
  5. Air dam (probably in the articulating style of cfg83)
  6. Side skirts and rear-wheel tails
  7. Windshield wiper cowl
  8. I keep trying to think of something I can do to correct the a-pillars. They strike me as quite bad. Acrylic half-cylinder additions? Or maybe just vertical acrylic fins? If I get around to it I'll mock it up and tuft test it.
  9. Maybe boat-tailing both side-mirrors, or else upgrading all the way to cameras (but I'd need to get an exception).

Tail-end to-do list:
  1. Additional engineering / repair to prevent future side-wind problems with the Kamm-back.
  2. Paint the whole AHB to stop the corrosion.
  3. Expecting to need a rear-quarter belly pan.








Original post:
======================================
This thread will probably mostly be about my forthcoming hitch-mounted cargo box boat-tail. Okay, not exactly the first time we've seen the general idea, but maybe the first project thread applicable to a sedan. Also I'll have some brief descriptions of other mods on our 97 family-of-four Civic, and of course results.

Getting right down to it; my plan for the Aero Hitch Box (avoiding the 'copyrighted' name ):

Green - the part I'm fabricating. (Black is the hitch receiver on the car.) I'm thinking strip reinforced aluminum sheet, rivet construction. However, that method hasn't got the wife test green light yet. I could probably get it done just as fast in plywood, plus foam/bondo, and it would be more likely to pass the wife test that way, but I expect that would be heavier and less durable.

I've sized the space from the bumper to the front of the box to give enough clearance for the trunk to open, plus a half-inch for good measure.

I'm probably going to want to put a caster on the main steel post that it will be on to minimize damage in the event of a departure angle violation, but I probably need to experiment in my driveway.

Now, I see some aerodynamic gaps here to fill. The only question is how far do I need to go to get good results? I expect this to require some testing to be sure about it.
Possible Gap Fill Remedies:
Opaque Half-Kammback (orange) with clear plastic side fillers (blue):


Full-Kammback with hinged window (or louvers):

All the remedies attach to the car, so you can imagine with the aero box off the car roughly fits a Prius profile with a full Kammback.

Any thoughts so far?

Hoping to get this done before spring, but you never know with me.

============================================

Random background notes, if you want them:
  • Hypermiling by itself has phenomenal ROI, but I find it relatively incompatible with long-haul family travel.
  • A high goal that I have on my mind is MPG retrofit of numerous existing vehicles; I always have an eye out for mass production and market compatibility, although I kind of doubt that I'm the right guy to pull the trigger on this type of fabrication, even if I had the right project for it.
  • I just got my long-haul family MPG up from about 36 to 42. The primary factor was P&G, which I had never done on a long-haul in this car before. That's 42 MPG at 70+ MPH in <35F with minimal aero mods. Not bad, eh? The other project I've got kicking around in my mind, which is more closely matched to my skill set for production purposes, is a P&G cruise control. I'm still in an info gathering stage though.

===================================

I will be editing this post for current status and index.


Last edited by christofoo; 12-26-2014 at 10:46 PM..
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Old 12-28-2012, 10:47 AM   #2 (permalink)
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Sounds like a great project. I await more updates.
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Old 12-28-2012, 11:23 AM   #3 (permalink)
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Quote:
Originally Posted by christofoo View Post
The other project I've got kicking around in my mind, which is more closely matched to my skill set for production purposes, is a P&G cruise control. I'm still in an info gathering stage though.
Look forward to seeing your project! the cruise control sounds interesting! what is your skill set that will help with it? I find that my cruise control is a very aggressive. Do you think that you can limit the RPM or load?
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Old 12-28-2012, 12:19 PM   #4 (permalink)
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Old 12-28-2012, 04:55 PM   #5 (permalink)
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troposphilic

You've covered the major bases,so you can expect the out-of-the-park home run as soon as she's on the road.
Whereas the sky is presently experiencing tropos-fear when it see's you coming,that won't be he case later.
We'll induct you into the End-dependent Oil Producers Association,as your car will be producing nega-barrels of oil out of thin air as she 'barrels' down the highway once she's shaken her money-maker.
And don't be surprised should you receive a membership invitation from the (F)riends of (A)erodynamic (R)ennaissance (T)echnology,whom just love to pass gas (stations) with their retrodynamic cars.
Welcome to the past! I think you'll dig it.
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Old 12-28-2012, 05:15 PM   #6 (permalink)
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Shouldn't the top half of the hitch aero box conform to a taper from the roof line (From top down view), instead of the rear fender panel? The top half of the box should look like a miniature version of the silhouette of your car. That is, if you are trying to go for maximum aerodynamic efficiency.
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Old 12-28-2012, 06:29 PM   #7 (permalink)
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top half

Quote:
Originally Posted by theycallmeebryan View Post
Shouldn't the top half of the hitch aero box conform to a taper from the roof line (From top down view), instead of the rear fender panel? The top half of the box should look like a miniature version of the silhouette of your car. That is, if you are trying to go for maximum aerodynamic efficiency.
In the plan view layout you want to take advantage of any body camber already present in the host vehicle and then project from there with a contiguous contour extending back using the 'Template' or Mair's boat tail profile.
If the top portion is deleted you'll pay some in extra drag,but 'practicalities' may demand that you stray from the ideal.The missing link should create a locked-vortex of which the outer flow field will skip over.
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Old 12-28-2012, 06:56 PM   #8 (permalink)
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Quote:
Originally Posted by christofoo View Post
Green - the part I'm fabricating. (Black is the hitch receiver on the car.) I'm thinking strip reinforced aluminum sheet, rivet construction. However, that method hasn't got the wife test green light yet.
Sounds good to me though !
What's your wife's issue with sheet alu construction ?
It's visually the cleanest method of construction, lighter than wood and if you keep it galvanically separated from steel, more durable as well.

Quote:
Now, I see some aerodynamic gaps here to fill. The only question is how far do I need to go to get good results?
While not ideal, the air will fill the gap on its own
So you'll have a decent part the positive effects of a boattail even if you use just the cargo box.

What you might want to fill up is the hole between the cargo box and the car, so you won't have air cross-drafting and causing drag.
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Old 12-29-2012, 02:10 AM   #9 (permalink)
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I have heard about the idea before, but I did not know that it went anywhere. Make it so, Number One!
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Old 12-29-2012, 06:32 PM   #10 (permalink)
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Quote:
I'm thinking strip reinforced aluminum sheet, rivet construction. However, that method hasn't got the wife test green light yet. I could probably get it done just as fast in plywood, plus foam/bondo, and it would be more likely to pass the wife test that way, but I expect that would be heavier and less durable.
I'll never find the original thread, but someone who races dirt-track modifieds recommended an aluminum/plastic laminate that they use for those big wings they run. I did bookmark a source of the material, Polymetal. It comes in 1/8' and 1/4' thickness, with strength approx. equal to 5/8" plywood. A supplier local to me can provide it for $104 for a 4'x8' sheet: Sign Panels | NUDO&reg

Quote:
Now, I see some aerodynamic gaps here to fill. The only question is how far do I need to go to get good results? I expect this to require some testing to be sure about it.
The farther the better. Flush-headed rivets?

You could put the bottom contour at ~10 and extend a flap all the way to the back of the gas tank/spare tire well or whatever's under there.

What do you plan to do to keep the taillights visible?

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