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“Out of the Box” idea for the Cabin Floor:

Hartstoc

Well Known Member
I’ve always felt that theRV cabin floor was the source of considerable noise and also a potential burn-through fire threat during an engine fire. The usual solution of thick, heavy spacing material under a carpet has never struck me as satisfactory. I now have 150 trouble-free hours on a light-weight, very successful solution I came up with. Just to get your attention I’ll start with a photo of the nearly complete installation, shown just prior to installation of my new panel and center console:

2v2eogeYyxBELK5.jpg


Think about the incredibly strong and rigid structural flooring used on airliners, consisting of thick Nomex-honeycomb sandwiched between layers of rigid carbon fiber pre-preg facings. I had the idea of adhering This fire-resistant core material directly to the cabin floor with a strong adhesive having a bit of give to it, then adding a layer of .016 aluminum similarly attached to its upper surface could result in a semi-rigid sandwhich that would serve as a sturdy floor just flexible enough to dampen out a good deal of the pounding energy from prop and exhaust that results in so much noise. It might even impart some fire resistance in the event of an engine fire.

I found some sheets of 1” thick x 1/8”density Nomex honeycomb on ebay to experiment with. The next challenge was finding a suitable adhesive, and I tried everything from various RTV formulations to assorted glues and contact cements, but was at first frustrated by the inability of these to “wet-out” onto the face of the honeycomb. When subjected to the “peel-test”, samples would come apart too easily and leaving the face of the nomex clean. A successful destructive peel test requires that both mating surfaces be covered with fractured adhesive.

Fortunately, I stumbled upon 3M 1300L adhesive. This tenacious stuff, applied to both surfaces and allowed to dry briefly before mating, wet out both the nomex and the painted aluminum floor beautifully, and passed the peel test with flying colors. It was, in fact, impossible to fracture, but an enormous amount of pull force would result in hundreds of tiny fibers per square inch stretching to about an inch before finally giving way leaving both surfaces coated. I later learned this to be the same adhesive used to attach de-icing boots to painted aluminum aircraft leading edges- PERFECT!

2v2eoWsdMxBELK5.jpg


Here’s the recipe:
1- Discard 4-pound carpet and clean painted surface with prep-sol.
2- make a paper pattern and cut the nomex to shape for each side of the floor

2v2eoWsSjxBELK5.jpg


3- Machine 1” thick Nomex honeycomb to slip over aluminum angle brace that runs down the middle of the floor. Carbide router bits worked great for this step.

2v2eoWsjNxBELK5.jpg


4- Adhere Nomex to floor with 3M 1300L. (The nomex was not installed in my center section, which was instead lined with .005 stainless steel then filled with 1/2” ceramic fiberfrax-type kiln insulation. The shallow aluminum pan is installed below the center console , which contains, among other things, my dual electric fuel pumps, dual stage selector valve with return lines, fuel flow transducer, and fuel pressure transducer. The pan would catch dripping should there be any leakage, and I can touch the bottom of the pan with my fingertip as part of preflight. MUCH more on this system in a future thread)

2v2eoWPoMxBELK5.jpg


5- Fit .016 upper skin to space(I included a 90° flange along each side of my center console to stiffen the narrow section of .016 that is not supported by Nomex.

2v2eoWP3dxBELK5.jpg


6- Adhere self-etching-primed .016 al-clad to upper surface.
7- Install anti-skid strips for ease of entry. (See top photo)

Results: WOW! 3# installed weight( vs 4# for thecarpet with padding that I discarded) , Feels rock-solid, but adhesive flexibility absorbs pounding vibration significantly reducing cabin noise. Enhanced resistance to external fires. You can get really good purchase with the anti-skid against your shoes to easily walk down into the seat or push yourself upright to exit. It feels like a 1/2” plate of aluminum, not the .016 aluminum that is actually under the anti-skid material!

Not shown in the first photo- cut to size pieces of black gorilla tape were later used to seal around the perimeter to prevent debris/washers, etc. from falling into that space.- Otis Holt
 
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Otis, structurally speaking I really like the honeycomb/aluminum panels.

Fire protection is questionable. I've not checked honeycomb with the burner, but Nomex is not as fireproof as folks assume, and the rubber adhesive will generate smoke. I have burn checked Nomex wool, photo attached. I will say this panel is probably better than the foam so often found under carpets.

Insulating the inside of an aluminum panel guarantees it will melt through with less applied heat energy. Think of it this way; temperature rise = energy in minus energy out. Insulate the back side and you block a lot of the energy out.

If you want one smoke/fire checked, laminate a 16" x 18" panel and send it to me.

From the DuPont "Technical Guide for NOMEX Brand Fiber":

Flammability, Smoke and Off-Gas Generation

The Limiting Oxygen Index (LOI) of NOMEX® is
approximately 28. Thus, when exposed to flame at room
temperature in a normal air environment, NOMEX® will
not continue to burn when the flame is removed. At
temperatures above approximately 800°F (427°C),
NOMEX® carbonizes and forms a tough char.
The composition and quantity of off-gases varies widely
depending on rate of heating, presence of oxygen and
other factors. Burning NOMEX® brand fiber produces
combustion products similar to those of wood, wool,
cotton, polyester and acrylic. At combustion
temperatures, NOMEX® releases carbon dioxide and
carbon monoxide; and, sometimes traces of hydrogen
cyanide and nitrogen oxides are detected. Under less
stringent heating conditions, NOMEX® degrades very
slowly, releasing small quantities of a wide variety of
organic compounds. These may include carbon dioxide,
acetone, acetamide, acetaldehyde, benzene, butane,
toluene and many other compounds in trace amounts
depending on exposure conditions.


And from the MSDS:

NOMEX® fiber is inherently flame resistant, but can be ignited.
Burning normally stops when the ignition source is removed.


Note the "when the flame is removed" and "when the ignition source is removed". Here's the point to remember: You can't remove a red hot firewall.

Interesting master's thesis research at the link below. The researcher identifies the ignition temperature of Nomex as 1600F.

http://archives.njit.edu/vol01/etd/1...td1977-008.pdf

CONCLUSION
The gaseous products generated by flaming combustion of
Kynol and Nomex fibers under the same conditions (temperature
³00-700°C, in air) were quantitatively analyzed by infrared
spectrophotometry, gas chromatograph, mass spectrometer and
a colorimetric tube method. These four techniques were
chosen to examine the wide range of volatile and condensable
products because of the differences in capabilities, limitations,
and sensitivities of each method used. Combustion
of Kynol and Nomex produces copious amounts of smoke and
toxic gases which could cause asphyxiation to people trapped
in the area of a fire.
 

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Otis, structurally speaking I really like the honeycomb/aluminum panels.

Fire protection is questionable. …
Dan- Thank you for the thoughtful and detailed response, But no argument from me whatever on this point! At best, and ideally in conjunction with some strategically positioned stainless steel exterior shielding(which I do not yet have in place), the 1” layer of Nomex might buy you part of a minute to get on the ground in the event of an engine fire. I hope I was clear in de-emphasizing any presumption of a fire protection feature. On my particular installation, however, I would claim some benefit from the stainless steel shim-stock I installed on the upper surface of the aluminum floor in the 8” wide center section, and from the 1/2” thick blanket of ceramic wool insulation on top of that. This is intended to delay burn-through to my center console, which contains some important fuel system componentry(even if it accelerates melting of the underlying aluminum panel).

The real benefit here really is the lighter weight, the functionality of a sturdy, flat, rigid floor that supports anti-skid panels, and some meaningful noise attenuation. Unfortunately, my bird was already out of service for myriad modifications when I conceived of this idea, so I did not have the opportunity to collect any before and after data on noise. I can say with some confidence that the tendency to experience extended bouts of tinnitus after long flights has, for me, diminished significantly! Regards- Otis
 
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Otis any PIREP yet on how it does with the good ole feet buzz/ noise?

As for noise, see my response to Dan above. The feet buzz, if that refers to constant hammering vibration of the floor panel, is pretty much completely gone!- Otis
 
Lovely. I'm looking for a replacement for my flexible heavy foam backed rubber.

I can't find a reliable-yet-removable fastening system to handle the shear of pushing up and out of the aircraft (currently leaving it shoved forward and rolled up at the firewall end). Will have a look at this!
 
...I would claim some benefit from the stainless steel shim-stock I installed on the upper surface of the aluminum floor in the 8” wide center section, and from the 1/2” thick blanket of ceramic wool insulation on top of that. This is intended to delay burn-through to my center console, which contains some important fuel system componentry(even if it accelerates melting of the underlying aluminum panel).

Perfectly reasonable, although after the installation of a stainless belly overlay on the outside, the stainless liner inside will be dead weight.

The real benefit here really is the lighter weight, the functionality of a sturdy, flat, rigid floor that supports anti-skid panels, and some meaningful noise attenuation.

Yep, again, I like the structural aspect very much, and it's way better than foam in terms of fire. The burn rig is set up right now, so if you want to check a panel, I'll be happy to do it. Two panels if you wish, one with a fiberfrax/foil overlay, one without. The wildcard here is the adhesive.
 
Lovely. I'm looking for a replacement for my flexible heavy foam backed rubber.

I can't find a reliable-yet-removable fastening system to handle the shear of pushing up and out of the aircraft (currently leaving it shoved forward and rolled up at the firewall end). Will have a look at this!

This is certainly a main advantage- people with mobility issues have a much easier time getting in and out.- Otis
 
Perfectly reasonable, although after the installation of a stainless belly overlay on the outside, the stainless liner inside will be dead weight.

Yep, again, I like the structural aspect very much, and it's way better than foam in terms of fire. The burn rig is set up right now, so if you want to check a panel, I'll be happy to do it. Two panels if you wish, one with a fiberfrax/foil overlay, one without. The wildcard here is the adhesive.

Hello Dan- It’s great to have you on board for this discussion. To be clear, there are no adhesives in the 8” center section. The .005 stainless, if I recall correctly, has 90° flanges on the two long edges secured by a few 3/32” ss blind rivets to the aluminum angles alongside. The 1/2” thick ceramix insulation slab sits on top of that and is trapped from above by the aluminum angle supports for my 25# center console assembly(which will be the subject of a couple of VAF threads to come). This region would take the majority of early-stage heat energy released by an engine compartment fire via the cooling exit of the cowling.

The larger portions of the floor covered by the nomex honeycomb are, of course, attached top and bottom with the adhesive. I’d eventually like to take you up on testing torch-able samples of both, but I’m pretty time-constrained at present.

Generally speaking, I think an important take away is that everyone should probably consider installing stainless steel heat shields covering the forward underside portion of the belly, as these will buy you quite a lot of time regardless of composition of the floor. My own take-away is that I might have left out the sentence “ It might even impart some fire resistance in the event of an engine fire.” In reference to the Nomex honeycomb, as that is pretty clearly not a strong argument.- Otis
 
That's stainless or titanium overlays, with Fiberfrax or another suitable insulator between that and the aluminum belly. Did that on my RV-3B.

Dave
 
Lovely. I'm looking for a replacement for my flexible heavy foam backed rubber.

I can't find a reliable-yet-removable fastening system to handle the shear of pushing up and out of the aircraft (currently leaving it shoved forward and rolled up at the firewall end). Will have a look at this!

My 7A has an Antisplat Easy Exit bar installed. It is pretty great. I step on it every time I get in or out of the plane. It is hard to imagine not having it there to step on.
 
My 7A has an Antisplat Easy Exit bar installed. It is pretty great. I step on it every time I get in or out of the plane. It is hard to imagine not having it there to step on.

If your panel is built from the deeper 12” tall aluminum blank, as mine is, there might be knee interference with the panel lower edge using the easy exit bar unless you have already “scootched” yourself up pretty far. Also depends how long-legged you are, of course.- Otis
 
Cabin Noise Reduction

Has anyone recently used Soundex panels? They are supposed to be providing good noise reduction and are fire resistant too?
 
I have almost the same thing but it has a fiberglass layer on either side. It is honeycomb core for boat building.
 
I have to wonder about the use of 1300L, which is a rubber based contact adhesive in an area that may be subjected to heat. Both from a durability and fire standpoint.
 
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