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Old 10-29-2008, 02:45 PM   #1 (permalink)
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Underbelly smoothing options

A few thoughts...

One, has anyone tried using some sort of fabric stretched under their vehicle to smooth the airflow? (Are there any suitably stiff and fireproof fabrics out there?)

Maybe even sheet rubber with foil or something adhered to it where necessary. Or multiple 15' - 20' lengths of landscape edging (LE) attached to each other with metal strapping. These LE bands might better follow the undercarriage / suspension contours.

I imagine fibreglass fabric could be stretched out, attached, holes cut or spaces created for the critical heat and wear areas and then coated with the hardeners. It would likely require midway attachments or reinforcing to prevent it coming loose in the middle of the underbelly.

Two, this might only be appropriate for trucks and vans but has anyone used sheet coroplast or sheet metal to minimize all the cutting and fitting by building a drop frame and just covering the whole underbelly? You'd likely loose a couple inches of road clearance and still have to cut around the suspension and deal with exhaust heat but would this simplify the process?

Three, rather than filling the voids with coroplast or something, instead would two or three underbelly spoilers or airdams do the trick. (Or would turbulence negate their effect?)


Last edited by Sunwapta; 10-29-2008 at 02:54 PM.. Reason: add points
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Old 10-29-2008, 03:14 PM   #2 (permalink)
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It's an interesting idea... Dacron has been used for home built aircraft -- when heat is applied, it shrinks to form a tight, smooth, surface...

At the same time, that might be an issue around hot parts... Just throwing that out there.

For super low tech... Wool is fireproof - and I imagine if supported and mounted properly, it'd be stable. Might not handle other environmental variables, however.
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Old 10-29-2008, 03:29 PM   #3 (permalink)
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Most fabric will flap in the breeze, which will create more turbulence. You want something stiff enough that it won't move when air flows over it.

Fabric used on aircraft gets "doped" with a paint-like stuff, and turns into a pretty stiff substance. Most especially when used directly over a plywood skin, but also when merely stretched over stringers.

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Old 10-29-2008, 03:49 PM   #4 (permalink)
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Yes - "flap in the breeze" and then tear or wear rapidly. Glueing, riveting laminating on nylon strapping might do the trick.

There's kevlar, nomex and probably lots of others - at a price.

Back to my list - I'd think the underbelly spoilers would be the easiest modification. You could probably pull those old aluminum rear spoilers off wrecked suburbans, etc. and retrofit them underneath at a mild downward angle. Or just stretch across some tin flashing and bend it down where needed to smooth the airflow.

hey - maybe retrofit a couple of those black plastic hood protectors/ bug deflectors (go underneath and bolt a couple on upside down).

Last edited by Sunwapta; 10-29-2008 at 04:01 PM.. Reason: adding points
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Old 10-29-2008, 04:15 PM   #5 (permalink)
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An air dam is easier; a belly pan is better. Look at the most efficient vehicles - they go for smooth underbodies.

Someone here used metal screen (like window screen) to create their undertray, then painted it - the paint fills the holes in the screen, making it a smooth "air tight" surface. I thought that was pretty clever.

Someone else here has a Saturn with framing underneath, and the panels were attached to it. Sorry I can't remember which one!
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Old 10-29-2008, 05:06 PM   #6 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
...

Someone else here has a Saturn with framing underneath, and the panels were attached to it. Sorry I can't remember which one!
That must be lovemysan :

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Old 10-29-2008, 05:11 PM   #7 (permalink)
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Not to steal your thread, but I think it kindof relates so...

If someone has a full front air dam... like down to the ground almost, would a belly pan help any?

Also, what parts need to be avoided when building a belly pan? I would imagine the muffler, jack mounts, and access to the oil filter, but what else?
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Old 11-02-2008, 02:49 PM   #8 (permalink)
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The Metal Screen sounds absolutely brilliant!!!

A couple layers might create even less permiability and I imagine screen creates an air buffer of sorts over much of the horizontal portions of underbelly. It would wouldn't trap moisture either. Very interesting. Does anyone have the link and any followup on this?

It might still flap if it weren't stiffened in places but that should be an easy fix - even thin wire or cable might do the job. Could it melt if it were too close to very hot drive train components?

Where it must direct air downwards I imagine paint or even landscape fabric or some heavy fabric could be glued or sewn on very easily.
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Old 11-03-2008, 07:34 PM   #9 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
For super low tech... Wool is fireproof - and I imagine if supported and mounted properly, it'd be stable. Might not handle other environmental variables, however.
Going even more low tech you might consider papier mache.

Before you fall about laughing Toyota trialled it on one of their Le Mans sports cars in the late 1960's and found it was tough enough to hang together at around 300 kph (180 mph ) or so.

Many fire proofing agents are readily available if that is a concern.

A mix of PVA glue (commonly known as white glue or woodworker's glue) and water ( 50 / 50 ) provides a workable solution when wet and adds stiffness when dry. A suitable varnish will make it water proof.

A former is needed to give it a shape but this can be removed after the material is dry enough to be self supporting. Maybe the aluminium fly wire can be used for this?

Cheers , Pete.
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Old 11-04-2008, 07:42 PM   #10 (permalink)
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Quote:
Originally Posted by Peter7307 View Post
A mix of PVA glue (commonly known as white glue or woodworker's glue) and water ( 50 / 50 ) provides a workable solution when wet and adds stiffness when dry.
I tried this same approach when I attempted a grill block a few months ago. I was able to achieve the exact shape I wanted, but the block wasn't very stiff when dried. I did about 8 layers of paper followed by 1 layer of an old cotton sheet. Not enough? Or was I missing something else?

For anyone else trying this, wear latex gloves when working with the glue. It turned my fingers orange and it took several days for the color to fade.

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