FWC Single Sheet Roof "Tin Canning"...Why?

[Wallowa]

Thanks to all for chiming in....first, I experimented with laying a rigid weight "east/west" [laterally] at 90* to top frame members....did not work, since frame to top sheet areas under that brace were at the frame height and top sheet had 'troughs' and 'peaks' below that frame to frame level. Still could pop and down. As suggested stiffening/dampening/weighting must hold down these 'troughs'/'peaks' which occur below frame height.

Reproducing tin canning is easy....press down with your hand on the top sheet in differing areas and quickly release the downward pressure; if it makes the tin canning racket then that area is going to tin can in a wind. I liken the top sheet to the swells on the ocean, vertical displacement up and down [swells/trough] flexes the aluminum and generates the noise. This does not occur over frame members but in between those supports.

I do not have sufficient knowledge to gauge if thin aluminum such as used on our top sheets can "stretch". I assume it has since I do not have any flat top sheet areas between top sheet frame members but areas of undulations that will move up and down with pressure changes. Hence it was originally loose and floppy or it has stretched. I believe it distorted/stretched over time with pressure loads from wind/snow or flexing while off road on tough tracts.

"Instead of Macgyvering a solution why not use a product engineered to attenuate vibrations?"

OK I am willing to use such a product....what would that product be? And how and where would you use it?

Vic...coming from the inside through the headliner might work if you place more insulation on top of existing insulation until you contact the areas tin canning...again stopping the up and down movement in the slack areas requires pressure on the top sheet...BIG project and one I could really mess up knowing my abilities.

Phil

 

[pvstoy]

If you come in from the inside and deal with the headliner you could add aluminum square or angle between trusses. Use bonding tape between roof. This would support the weight of the roof, eliminate sag. You would need to screw the blocks into the side of the roof trusses. Think of blocks between floor joist to keep the joist separated.

 

[Vic Harder]

Vic...coming from the inside through the headliner might work if you place more insulation on top of existing insulation until you contact the areas tin canning...again stopping the up and down movement in the slack areas requires pressure on the top sheet...BIG project and one I could really mess up knowing my abilities.

Phil

Big job indeed. I made it a bit easier by not taking apart the whole roof but still. What Patrick said is true too... IF you willing to tackle it from the inside, I would order new headliner from ATC/FWC and schedule a week to tackle it... may only take 8 hours but the frustration will take many beers and recovery time before going back at it, at least, that was my experience.

FWIW, I cut foam insulation with very tight tolerances to fit into the spaces between the frame members, added standard fibreglass pink batting to ensure any gaps were stuffed, used duct tape to seal the whole roof and then added Reflectix before re-installing the headliner.

 

[Wallowa]

Vic...I have and continue to admire your ability to construct not just electrical systems but structural components.

Not so much for me. If I can't "KISS" it, then my judgement is to leave it alone so I don't make matters worse.

Removal of my top liner and doing the retro-fix you describe would result in a huge FUBAR.

May just go with aluminum bar and if that does not work, ear plugs!

Phil

Ps...Still holding out hope that FWC will come up with a viable alternative to correct the tin canning...I know, kind of like a "wish sandwich".

 

[JaSAn]

. . . OK I am willing to use such a product....what would that product be? And how and where would you use it? . . .

There are a number of companies that make vibration damping products for automobiles (posts #64,65). Pick a couple and talk to their application engineers. Explain your problem and see what they say.

 

[Wallowa]

There are a number of companies that make vibration damping products for automobiles (posts #64,65). Pick a couple and talk to their application engineers. Explain your problem and see what they say.

I will take another look at the sound dampening sheets/material referred to in these posts….my take is that lessening sound or temperature via these insulations to attenuate them is an entirely different proposition that stopping the long wave movement of the aluminum top sheet as it creates tin canning noise. With sound you are dampening, absorbing vibrations in air and in the top sheet you must dampen movement of the top sheet. Yes, wave forms, but entirely different media. My belief is that you must physically limit or stop top sheet movement and that there is no way to 'absorb' that movement without physical restraint of the bowed material in the top sheet.

But hey, I could be wrong...

Phil

 

[kmcintyre]

I was just out 303'ing my vinyl...found something very interesting while doing the inside windows. If I push slightly on the drivers side, rear of the vinyl from the inside, it tin-cans. The other windows didn't do it.

Now the caveot... I was on a slight incline towards that corner.... something to consider. No, I didn't so the scientific method and turn the truck around, etc. but headed out this week so will try it when on a flat surface.

Could be a hint to what is wrong.

 

[ckent323]

Wallowa, et al,

I used the sound damping products from Sound Dampener Showdown (aka SDS and now out of business) including CLD tiles, on the inside of my truck. The company at the link I posted previously in this thread offers the same or similar materials and may be a good resource for information and help curing the 'Oil Canning' issue. I recommend contacting them and explaining the issue and asking for suggestions.

The CLD tiles damp out the metal flex. For example if you rap on the truck bed door, hood, roof or side panel and hear it bang (at least on older trucks), after the CLD tile is on it becomes a thud. The CLD tile stops the resonant frequencies. Other materials are designed to decouple the sound from the metal of a vehicle so that it does not act like a speaker.

Caveat, the materials I used are designed for use on the floor, ceiling and side walls in the passenger compartment of a vehicle and on the underside of the hood, on the fender wells and firewall (to damp out sound from the engine compartment), but not necessarily for the exterior. I am not sure how the CLD tiles, which stick on, will hold up on an exterior surface but they do have an Aluminum top skin.

I think one can buy a single CLD tile to test it. They can be cut to shape and into strips as well.


I hope this is helpful,


Craig

 

[Wallowa]

Craig,

I used that sound damping material on the underside of the transmission tunnel in '62 Corvette after installing Tremec 6spd which initially had gear noise....worked OK but did not really stop trans noise; just lessened it. No bigee as I drive with top down and use ear plugs.

Good for the purpose intended but attenuating sound or heat is a heck of different animal from attenuating the up/down flexing of aluminum sheet in our top sheets...physical restraint/stiffening is need to lessen the TC on sheeting...such as weight and or rigid material in contact with aluminum surface between frame members. Wild card is how much weight? Where to place weight? Ditto for stiffeners.

Did more investigating and TC is common and almost unavoidable in many metal sheets used on roofs/siding...However, if the sheeting has small or wide ridges molded in as dampening braces oriented length wise it does lessen TC...much of the TC was attributed to smooth sheeting and sheeting subject to temp fluctuations; sheeting warps...evidently temp swings will generate waves/bubbles/troughs in non-braced areas of smooth sheeting....like between the roof frame members on my Hawk... and using too thin of a material for specific applications increases the likely hood of TC...

Phil

 

[ckent323]

Wallowa,

I used the CLD tiles on the inner ceiling of my 1993 Pickup cab. It used to oil can a bit. It does not do so any longer.

I am pretty familiar with how metal bends and resonates as well as with vibration testing airborne and spaceborne assemblies but I am not an expert in sound damping. However, there are folks out there that are.

 

[Wallowa]

Wallowa,

I used the CLD tiles on the inner ceiling of my 1993 Pickup cab. It used to oil can a bit. It does not do so any longer.

I am pretty familiar with how metal bends and resonates as well as with vibration testing airborne and spaceborne assemblies but I am not an expert in sound damping. However, there are folks out there that are.

Thanks for that....resonating/vibrating produces sound, of course in varying frequencies and amplitudes...cause of that movement and how to stop or greatly lessen that movement is the crux for dealing with our TC in FWCs. If tops sheet only "quivered" the sound might be a hum, but the rapid and significant displacement of the top sheet vertically produces very loud bongs/pops/rounds-going-off sound.

 

[rubberlegs]

Wallowa,

I used the CLD tiles on the inner ceiling of my 1993 Pickup cab. It used to oil can a bit. It does not do so any longer.

I am pretty familiar with how metal bends and resonates as well as with vibration testing airborne and spaceborne assemblies but I am not an expert in sound damping. However, there are folks out there that are.

Interesting. I also worked with aerospace structures, and we had to check for natural frequency -- I think over 33 Hz but my memory is fuzzy. We didn't want our wings resonating, that might frighten passengers, not to mention the pilots and the FAA. It would seem a flat sheet with boundary conditions at the camper framing could be calculated without fancy finite element modeling... but our roof is ok and I'm too lazy!

 

[pvstoy]

Thinking in a different direction.... roll on some camper roof coat between the rails, could add weight and sound dampenor.

 

[Wallowa]

Time will tell if anyone actually lessens or eliminates tin canning on a FWC that is as bad as on my Hawk....roof coating would have to be damn thick to hold down the top sheet from fluctuating/bouncing up and down in a wind...and 'sound proofing' will only come when the movement of the slack areas in the top sheet is stopped...not by sound absorbing material unless it is rigid and can hold the top sheet still and stop the movement...or by piling on weight in the slack areas....

Structural analysis and modeling would be 'nice' but stopping the existing movement, not theoretical movement, real significant popping up and down, is paramount in stopping the TC noise....sure knowing the dynamics and causal factors which may define the issue would be great....but we need to eliminate the "effect" and stop the noise first....not the norm in science, but empirical solutions are what are needed...too late for design changes or thickness changes in existing top sheets...

 

[JaSAn]

Structural analysis and modeling would be 'nice' but stopping the existing movement, not theoretical movement, real significant popping up and down, is paramount in stopping the TC noise....sure knowing the dynamics and causal factors which may define the issue would be great....but we need to eliminate the "effect" and stop the noise first....not the norm in science, but empirical solutions are what are needed...too late for design changes or thickness changes in existing top sheets...

Theory is not the end all/be all of a solution but the first step. It should identify what possible solutions will not work well and what solutions are worth exploring. Testing still needs to be done.
Seat of the pants trial and error can deliver a solution but it is usually inferior and at higher cost.

My recommendation is still to first talk to application engineers that deal with these problems.

P.S: I was a shock and vibration engineer for Control Data and 3M for 37 years, retired for 12.

 

[Wallowa]

Jasan,

While I concur that seat of the pants solutions are truly a hit or miss proposition, as of yet I do not believe anyone has identified an application engineer that deals with this specific FWC problem....I do not discount the value of a methodical engineering analysis and testing protocol, but who will do it and when?

In the mean time the booming of the top piece continues...mine may be a haphazard approach but lessening or stopping the tin canning noise seemingly inherent in the FWC single sheet aluminum top sheet on my Hawk requires actions within my life time and like it or not determining what that action should be falls to me to figure out....all this assumes that there is indeed a feasible retro fix and not just to start over with a thicker top sheet and with designed in stiffening ribs as seen on metal roofs....Google "tin canning"; volumes on this as it is common with metal sheets used on buildings; seemly thicker material and with designed in stiffeners partially stops or at least lessens the tin canning. Cosmetic reduction in buildings of TC is not my objective, but elimination or reducing of the popping or booming sound is.

Phil

 

[Jon R]

Oil canning is the term used for this in the engineering world (referring to the intended popping characteristic of the bottom of an old-school oil can). A search on tin canning will yield results on food storage.

 

[Wallowa]

Jon,

You are correct...no idea where I got stuck on "tin" rather than "oil canning"....my error...never intended to can food in the Hawk!

https://roofonline.com/oil-canning-in-metal-roof-panels/#:~:text=%E2%80%9COil%20canning%E2%80%9D%20refers%20to%20real%20physical%20distortions%20of,a%20metal%20panel%20appears%20wavy%2C%20that%E2%80%99s%20oil%20canning.

Ps...Jon...educate me...why was oil canning intended on old style oil cans? I am old enough to remember the refillable oil bottles...

 

[ckent323]

Jon,

Damping vs dampening. Oil canning vs Tin canning.

You must be a fellow engineer. Your lexicon gives you away.




Wallowa, et. al,

Oil Canning Etymology: In reference to the technique used to operate an oil can, holding it between the index and middle fingers while applying pressure to the semi-flexible bottom of the can to pump out oil.

It makes a characteristic sound.

Generically it got applied to the sound of flexing sheet metal on a variety of assemblies and containers.



Craig

 

[Wallowa]

Jon,

Damping vs dampening. Oil canning vs Tin canning.

You must be a fellow engineer. Your lexicon gives you away.




Wallowa, et. al,

Oil Canning Etymology: In reference to the technique used to operate an oil can, holding it between the index and middle fingers while applying pressure to the semi-flexible bottom of the can to pump out oil.

It makes a characteristic sound.

Generically it got applied to the sound of flexing sheet metal on a variety of assemblies and containers.



Craig

Craig,

I course! I forgot about the oiling cans with the long narrow spout...I was imaging the oil cans used for vehicle motor oil....the abrupt sound those little cans made is what the top sheet produces but 1K time louder...

Thanks..Phil