Class a motorhomes aerodynamics

[freebeard]

Airplanes get doped Dacron, cars get triple-layered fabric.

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[Piotrsko]

Cetrified aircraft get certified procsss you describe. Hokebuilts do pretty much whatever they want. Want fibreglass tail surfaces?, go ahead. 3layer is not often done because it's heavier and more expensive. Possibly the two double plus ungood major bugaboos in homebuilt planes

[sregord]

Originally Posted by aerohead

I'll go on record as one who's not in agreement. The air is agnostic as to 'impermeable' membranes, whether fabric, composite, or metal.
I believe that presently, Porsche has 'fabric'-roofed' 911's running the Autobahn at 170+ mph.

Thank you aerohead.
I know I didn't describe the concept well ...as "fabric". of course you, freebeard, & I were discussing inflatable boattails back at 5-22-22 in this stream..where I mentioned billboard covers(vinyls/tarps)
https://ecomodder.com/forum/showthre...tml#post668627
They're like: https://www.ebay.com/itm/256297755605?
Something like this..as does coroplastic needs a "frame" to be strong at 70mph, plywood or aluminum sheet may not.

[j-c-c]

You guys are losing me.
Billboard covers are for finite use, they have a solid backing (PW?) in most applications for a number of reasons, mainly being to prevent any movement to enhance readability and/or the message, are effectively disposable and one-time usage, all of which has nothing in common with the aero fabric vinyl solution on the bottom of a long haul trailer posted here recently.

[sregord]

EcoModder Forum >
EcoModding >
Aerodynamics >
Class a motorhomes aerodynamics

Let me start ALL over.....
COULD "recycled" Hypalon-impregnated aerospace fabric(Billboard Tarp) be used as a cheap alternative for flat or shaped/closed/non-side flapping bellypan on a (8.5' x32'+) motorhome?

....not a commercial truck trailer...

I only made the comparison to airplane fabric to help guide the discussion from the first Betterflow video to airflow much like Luigi Colani designs, etc.
The diversions are fun though, as in many of these threads.

Have you ever handled "recycleable" Hypalon-impregnated aerospace fabric?

Sorry again for the confusing first ask.

[aerohead]

Originally Posted by sregord

Thank you aerohead.
I know I didn't describe the concept well ...as "fabric". of course you, freebeard, & I were discussing inflatable boattails back at 5-22-22 in this stream..where I mentioned billboard covers(vinyls/tarps)
https://ecomodder.com/forum/showthre...tml#post668627
They're like: https://www.ebay.com/itm/256297755605?
Something like this..as does coroplastic needs a "frame" to be strong at 70mph, plywood or aluminum sheet may not.

Yes, the frame allows tensioning of the fabric, which will then become a crude 'drumhead' with a percussive natural frequency of vibration ( flutter ), plus any resonant frequencies ( octaves ).
And as mentioned, 'stiffeners' might be a requirement.
When I attended the Solar-500 at Phoenix International Raceway, the pickup truck class was allowed to run full tonneau covers.
All of them were coated fabrics, like 'Naughahyde', and behind the cabs, it looked like Yoda was under the fabric, trying to stand up ( fabric sucked up towards low-pressure of the bed vortex ), while the rear half of the fabric was forced downwards into a 'pool', by the air passing over the vortex, and slamming into it from above.
No visible flutter was observed, but that doesn't say that it couldn't, at a different velocity.
NASA/ Lockheed has some great footage of the wings of a C-130 wind tunnel model coming apart due to flutter in the big tunnel at Marietta, Georgia.

[j-c-c]

"No visible flutter was observed, but that doesn't say that it couldn't,"

And a big reason I suspect was one side was a restricted confined space on one side that likely dampens the flexible material. Same applies to Billboards, and soft side semi trailers. The example previously discussed here on the bottom of a semi-trailer had no confined air volume on one side and was relatively open to aero forces on both sides, but I am now repeating myself.

[aerohead]

Originally Posted by sregord

EcoModder Forum >
EcoModding >
Aerodynamics >
Class a motorhomes aerodynamics

Let me start ALL over.....
COULD "recycled" Hypalon-impregnated aerospace fabric(Billboard Tarp) be used as a cheap alternative for flat or shaped/closed/non-side flapping bellypan on a (8.5' x32'+) motorhome?

....not a commercial truck trailer...

I only made the comparison to airplane fabric to help guide the discussion from the first Betterflow video to airflow much like Luigi Colani designs, etc.
The diversions are fun though, as in many of these threads.

Have you ever handled "recycleable" Hypalon-impregnated aerospace fabric?

Sorry again for the confusing first ask.

I believe that it's worth a try.
There's a hardwoods dealer in Fort Worth where I used to purchase rock maple to create Montessori teaching materials.
All of their outdoor inventory was protected under discarded billboard signage fabric. I spent enough time trying to destroy a piece of of it while I was there to conclude that it was extremely robust, and nut cases like us could probably re-purpose it successfully.
Gumby79's 100-mph Dodge aeroshell is covered with 'discarded' speedboat wrap, used during over the road trailer transport to marinas and ports. And a version of this same material has been approved for light aircraft construction.
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On my trip to Newport Beach, BNSF Railroad was transporting fabric-back US ARMY and Marine Corps transport trucks atop flatbed railcars, at 70-mph. Nothing more than the frameworks for those tarpaulin-covered truck boxes would be required to 'support' an underbody, stretched-fabric belly pan, as long as it was 'boxed in' around its perimeter, like an RV Coach/ Motorhome, with front airdam, matching rocker panels, and rear fascia, as long as care was taken with the wheel-wells, to prevent splash and spray broadcasting material onto the 'top' of the fabric.
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You could experiment with 'tension', and determine how close you'd have to space support ribbing to maintain an acceptable level of 'sag' in between supports.
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A local trim or upholstery shop would be able to sew in reinforcing strips with brass webbing eyelets, at any chosen location, which would allow you to lace the fabric onto your skeleton anywhere needed.

[Piotrsko]

I recall specs for irish muslin used in aircraft has a minimum of 70 PSI to be airworthy. Ceconite is higher

[j-c-c]

Another consideration of a significant downside not yet mentioned with "impregnable" fabrics used horizontally, especially with topside stiffeners, if any water is trappable above, from drainage above, rain or road spray, great efforts need to be made to ensure water buildup/ponding does not occur, by having needed slope/clog free drainage/or total sealing to prevent entry. Water is of course heavy and fabric failure is easy to visualize with enough water trapped in dynamic loading moving at speed.