Project: ECOfamily Civic and its Aero Hitch Box / Boat Tail

[christofoo]

Originally Posted by California98Civic

The wheel well skirt clips can be made to hold tightly if you design them to allow for a bolt that can be used to tighten them only the wheel well lip. That's what I did, following I think a design by metro. I also was not satisfied with how far the poked out, and have since adjusted them with aditional clamps to pull them into a position more flush with the vehicle side. Thanks for all the write-up deets and the pics.

That design was my starting point. Not really sure which I like better or if there's a reason to prefer one or the other. Making space for the bolt makes me nervous about a collision between the tire and clamp hardware if you hit a bump and see a lot of suspension travel, but I guess no one has reported that issue.

[christofoo]

First off, our Southern Utah trip had great mileage - 48, 43, and 45 MPG, for a trip average of 45.6 MPG over 1111 miles. Not bad! This trip always has lower speeds than my other long-hauls, and a lot less air conditioning. The big question is whether the winds were favorable. The Arches/Moab/Hanksville area can be very windy, but there's a real shortage of wind-socks, so I usually don't have much idea what the balance of wind direction was. It's tempting to assume it always hurts more than helps because it's not a conservative force (unlike gravity), and in fact wind is very nonlinear (V^2 for aerodynamics), and even side-winds are expected to hurt.



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The Kammback was destroyed at the beginning of the 3rd tank.



I'm really glad it didn't hit another vehicle or do any real damage to my vehicle. (I'm also really glad there were no witnesses, for the sake of my ego, and also really glad this is not the scenario where all our belongings get strewn across the road by a failed cargo box.)

On I-70 W I had a really horrible side-wind, I'm estimating it was well north of 30MPH steady, plus gusts. I saw there was a problem and I made two stops to attempt to strap it down. However, I thought that the only hazard was coming from the Kamm-to-box window section lifting off, so that's where I duct-taped. Right after the second stop, as I was accelerating, the side-wind got under the Kamm right-hand side-window and there was enough leverage to break the right-hand magnet loose. Once that happened I saw the whole structure break loose in the mirror and blow away - just like that. The hinge and aluminum brace holding the left hand magnet twisted and took a lot of damage when it was pried off.

These are beefed up magnets, they were strong enough I could open the trunk all the way and over-center the Kammback plus Kamm-to-box-window without any trouble. However, in order to accommodate the roofline curvature there was a hinge between the two magnet sections, so although it was a lot stronger against slide-off, it wasn't really stronger against a side-wind.

I made a snap decision to salvage some components (the camera, magnets, and trunk linkage), and leave the rest on the road side. I've had some thoughts about going back to retrieve what's left, but I'm not sure.

Lesson learned: this type of structure needs enough downward force at the trunk to secure it against side-winds. I didn't imagine this failure mode until I saw it happen. If I could also aerodynamically fish-scale the leading edges (EDIT- at the c-pillar) against a side-wind that would be really effective. I think I prefer attaching to the roof-rack mount channel rather than magnets, but neither is good enough unless the side-window is secure against lifting up in a side-wind. Correction: I'm pretty sure it's the lateral forces that caused it to break free. Enough lateral force from the right will cause the right-hand magnet to slide down the roof, then the curved roofline and turbulence on the side break the magnet's grip. One approach to correcting the problem is lateral tie-down webs hooked onto the trunk.

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I also have some really interesting grille ducting I want to report. I have a real shortage of posting time.

[aerohead]

Welcome to the Exploding Kamm-back Club.
It is a good thing that it didn't end any more awkward than it did.Now,thanks to your report,we have some important and critical DIY fabrication knowledge.That's a clear victory.
And your mpg is impressive.
I'd say,that we all came out ahead.
Thanks for soldiering on with the project,and sticking it out through all the warts and moles of it.
I've collected photos of the before 'explosive deconstruction' configuration and they'll be viewed by the North Texas Renewable Energy Group this May.
Thanks for all you've done and continue to do at the University of Hard Knocks.

[NachtRitter]

Major bummer! Thanks for the update though!

[Xist]

It is terrible that happened to you, but yes, it is very good that your Kamm-back did not damage anyone or anything, and I hope that you are able to engineer through that. You have done outstanding work so far.

[freebeard]

Ouch! I've had that happen carrying hollow-core doors on a clip-on roof rack—twice. The load was lashed to the rack and the whole thing flew off. The 2nd time was right downtown @ 35-40mph, so I know about the embarrassment.

So what's the solution? Stronger hinges on the roof? Jeep hood clamps at the rear sides?

[christofoo]

Originally Posted by aerohead

Welcome to the Exploding Kamm-back Club.
It is a good thing that it didn't end any more awkward than it did.Now,thanks to your report,we have some important and critical DIY fabrication knowledge.That's a clear victory.
And your mpg is impressive.
I'd say,that we all came out ahead.
Thanks for soldiering on with the project,and sticking it out through all the warts and moles of it.
I've collected photos of the before 'explosive deconstruction' configuration and they'll be viewed by the North Texas Renewable Energy Group this May.
Thanks for all you've done and continue to do at the University of Hard Knocks.

I'd love to hear more about your NTREG presentation - are you a member? Have any TX policy-makers been attracted to the group? Any comments you get on the presentation would interest me. Naturally I have higher resolution photos if you want them, harass me about it and I'll zip them up and send them your way. I'm honored.

Originally Posted by freebeard

Ouch! I've had that happen carrying hollow-core doors on a clip-on roof rack—twice. The load was lashed to the rack and the whole thing flew off. The 2nd time was right downtown @ 35-40mph, so I know about the embarrassment.

So what's the solution? Stronger hinges on the roof? Jeep hood clamps at the rear sides?

I was thinking about the solution on the drive back yesterday (... next post ...). Maybe I'll recycle the nylon coated hooks previously used to to strap the AHB to the trunk's front lip. Now I'll run a strap between the Kammback frame and the trunk's bottom lip. I might even have all that hardware lying around. Cruel irony - I was thinking about doing this during Kammback design, at some point I decided the Kammback's own weight was adequate, and it seemed like the hooks would have been a pain - they would drop off when slack - but really, it doesn't take that much extra effort to include a strap retainer somewhere to keep the hooks from falling when the strap is slack.

[christofoo]

My wife was thoughtful enough to write down a mile-marker. (Would have saved myself some walking if I'd just spent a second to record my GPS position in the first place.)

(I didn't think I would do this, for one thing I hate to blow almost 9 gallons on travel to recover an item intended to save some unknown quantity of gas, but later on I realized that a) I really like the shade in the back seat from the Kamm, at least for some angles, and b) 9 gal is actually not a large fraction of the gas that the modding kit as a whole (is supposed to) save in 1 year. So...)

It took a while, but I in fact found it and brought it back.

Road-side engineering: I've just un-bent and restored 1 of 2 of the anchor magnets here. I brought my drill and rivets, and 2 new hinges:

(By the way, the white car in the background is presumably doing 75MPH. Mind boggled by Galaxy S4 shutter speed, at least in broad daylight. 1/2000 of a second, or so?)

Addition of a tie-down strap makes this orders of magnitude more secure. I think the duct tape around the C-pillar edges is also a big deal. Plenty of duct tape in other places out of paranoia / aerodynamic-lust.

This got me home without a hitch, through some windy conditions that I think might have been as bad or worse than the conditions that broke it. So I just need to engineer this into something more usable (partially described above).

I saved one piece from the Kamm-to-AHB-window for kicks, but as you know that shattered. Actually I think it was made from PETG, and the black lid was pushing it past glass-transition temperature in sunlight and it had already become rather concave, and so was well on its way to self-destruction anyways.

Oh, and, I drove for mileage on this one. 54 MPG over 470 miles (estimated), probably centered at about 65 MPH. P&G / EOC as usual. This trip ends up with a lot of I-15 mileage on it, which me and my family have noticed has almost magical effects on MPG.

[COcyclist]

I've been secretly hoping you would go back and retrieve the Kamm-back. Nine gallons is not much in the name of science and for the contribution to readers of this forum. I have learned from your successes and mistakes. Thank you for your efforts.

[freebeard]

I like the part where you just had to go home and get your tools to complete the trip.