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

ckent323 said:
Jon,

Damping vs dampening. Oil canning vs Tin canning.

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




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
Click to expand...
Yes, I’m a mechanical engineer and an aircraft system safety analyst at work. Not that there’s anything wrong with that … (That’s a running joke from Seinfeld, in case you’ve never seen the show.)
 
Late to this topic, but I think I accidentally fixed my "tin canning" roof.

It was a dark and stormy night ... with the wind blowing fairly hard when the flexing woke us from our slumber. I reasoned that if I took my speaker stand and very gently extended it in pretty much the middle of the ceiling, the noise should stop since I would have pre-flexed the roof. It worked and sleep was regained. I removed the stand and stowed it the next morning. Next night, I deployed the speaker stand before bedtime since it was the same campsite with the same desert wind. It's been 5 years with plenty of windy nights and no flexing roof ever again. I think I must have deformed the roof enough to end the problem.

Your mileage will almost certainly vary.

Alan
 
Interesting idea. Bring a length of 2 inch diameter stiff pvc to go from floor to close to inside roof. Then push up on the roof and place a shim to arch up the roof. Just find a place to store.

Price is cheap enough to try.
 
Hey...great thinking out side the box! Place on the board across the front of the top inside...

Thanks...
 
Ok...would appreciate any input on "unintended consequences" for my approach to stopping the tin/oil canning in my '16 Hawk top sheet .

I tried weighted bags [two folding camp chairs: 7.9 and 8.1 lbs.] on roof in front of my forward [FWC installed] 160 watt solar panel; did this by raising rear of top and then stepping on passenger floorboard to slide one bag on each side of longitudinal top sheet spars/supports in areas of bubbling/wavey top sheet. Oriented the bags front to back. It seemed to stop oil canning and flexing of top sheet when I pressed top on top sheet and quickly released. I was then able to grunt the front of the top up into place and 'lock' it with the added 16lbs on the top.

Spars on passenger side are about 14" apart: One with the Yakima rail, next one in 'center' and last one with the passengers edge of the Fantastic Fan mounted to it [fan is off set to drivers side to catch this spar].

Three options that I see as feasible:

#1 Try to push the top sheet upward from inside with a pole on forward top lifting board to take up top sheet slack.

#2 Buy small sand bags [used for tents and speakers] and fill with sand or pea gravel...up to 25lbs capacity each about 29" long.. 4 for about $30 on Amazon. Place them as described above and hopefully stow them inside the bed of the Tundra through the Hawk shackle doors.

#3 Buy 2 six foot long, 3" wide by .313" thick aluminum [6061] bars [9 lbs. each] and mount them between the longitudinal spars from front edge and under the solar panel to the rear. $125 delivered. Mounting either by Velcro or adhesive.

=================considerations....

#1 may or may not work on my top sheet and having a pole in the center of the board is a non-starter for me. Getting up or down is tough enough.

#2 Sand bags could be adjusted to hopefully stop canning; but I believe what is needed is not just weight, but longitudinal weight over a significant length of the top sheet. Would require placing bags at each stop if windy and perhaps rain.

#3 Aluminum bar would remain in place BUT what are the consequences of that mass adhered to the top sheet on backroads with sometimes washboard or rock steps bouncing the Hawk forcefully up and down? Could this mass further stretch the top sheet? Driving 60+mph even with Hawk top down can also create up and down movement without adding the bars.

What am I missing? Currently ready to order aluminum bar.

Thanks for any input.

Phil
 
Phil, if it were me, I would just screw them down. I know you don't want to make holes though.

Curious, does the canning need more than one roughly 12" square (between frame members) section of the roof to happen? If so, then screwing them down would stop it, no?
 
Phil in my first post way back at the beginning of your thread,I suggested screwing
the roof down.Still do. There are "bunches" of older campers around and how many actually leek?

Option #1 is just another thing in your way,Your close to my age and it's enough to deal with getting up
into the "bedroom".

Option #2 why carry that much extra weight around?

Option #3 That could work by stiffening the roof skin,but if the skin has come off the adhesive the bars
probably won't help.

The roof screw option is a positive way to attach the skin to the roof framework.And with good sealant
in the screw hole and around the screw it should be weather proof.

Good luck. Hope one of these solutions works for you.
Frank
 
Phil, if it were me, I would just screw them down. I know you don't want to make holes though.

Curious, does the canning need more than one roughly 12" square (between frame members) section of the roof to happen? If so, then screwing them down would stop it, no?


======================================================

Vic....you can not 'take up' the "slack' between the longitudinal frame members by screwing the top sheet to those frame members; and, stop the up and down movement between those frame members....another addendum....if I press down on one side of the longitudinal frame in the space with the "extra" loose top sheet it seems to slightly reduce the movement of the opposite area of slack on the the other side of that frame member....my assumption is that the top sheet is not secured to the longitudinal frame member between the fan and the Yakima rail....

Honestly, if I thought screwing the top sheet to the "center" frame member [between fan and Yakima rack] rail would reduce the loose top sheet movement on either side of that frame stringer I would, but you can press down on the top sheet over that frame member and the canning still occurs.

You can see "waves" in the top sheet between the frame members. This loose "extra" top sheet runs from front of top to beyond the solar panel between the longitudinal stringers...

Phil

Yup on getting up to pee at O-dark thirty @ 80....and 16lbs is insignificant considering how much my Tundra is already over the GVW :rolleyes: My take is that if FWC had used a thicker top sheet [+16lbs?] oil canning would not be occurring..but I could be wrong
 
I would still consider a aluminum angle running East-West full length across the roof beams, Screwed down with sealer at the roof trusses. For the sheeting between, bond the roof sheet to the aluminum angle with VHB or very strong bonding material after cleaning the roof surface. You can place multiple angles spaced apart as necessary.
 
pvstoy said:
I would still consider a aluminum angle running East-West full length across the roof beams, Screwed down with sealer at the roof trusses. For the sheeting between, bond the roof sheet to the aluminum angle with VHB or very strong bonding material after cleaning the roof surface. You can place multiple angles spaced apart as necessary.
Click to expand...
Perhaps a good alternative to longitudinal but this would not be possible under solar panel and not sure how to "bond" top sheet to angle iron...top sheet is very uneven and in "waves"...even pushing from below on the inside insulation you can not push out these waves so not sure how contact would be made with VHB on angle iron....I had thought before of notching angle iron to drop it down toward the top sheet but again no way assure contact on VHB with the irregular surface of the top sheet...

Thanks for your idea....Phil
 
I've been following this thread with keen interest as I'm restoring my Eagle and adding a new roof. It occurs to me that the HVAC community has already solved this problem. Google "sheet metal cross braking" and you'll see how they've done it. Air flowing past large expanses of sheet metal always has caused noise so they add slight bends in pieces over a certain size. Of course, that does you with "oil canning" absolutely no good now.

However, I have some anecdotal evidence for you. I'm using smooth siding, exactly like the roof material (Aluminum, painted white, 0.024" thick) and it sings at the slightest movement, unless it has an S-bend on one side. The contrasting material I'm using is a black 0.024" thick aluminum with tiny diamond shapes embossed into the surface. I'll attach a pic of the door. While fitting the siding and door I noticed that the black material is MUCH more difficult to cut (tin snips and band saw) and drill. It is also almost impossible to get it to "oil can" and when I can it is a very low-frequency sound. That may or may not be a good thing.

My guess is that stamping the diamond pattern has cold worked the aluminum surface and made it much harder, thus stiffer. So, you could have a one piece roof that is smooth-ish, if you weren't opposed to having a pattern in it. The old peapod trailers often had a quilted pattern, akin to cross-braking, in their skins. Maybe it's time to go back ?

That was my two cents. Thanks for listening.

Roylnn
 

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A lot of good info and suggestions but I'm not going to resolve this issue by putting any holes in my roof. I've had too many water issues (at my house) and not going to let a leaking roof ruin any camping trips. It's probably never going to happen but with my old Eagle, the maintenance and hassle of tending to roof screws isn't worth if for me.

At this point in time, I'll put up with the noise and hopefully FWC will address the issue at some point but doubt they can do much now.
 
kmcintyre said:
A lot of good info and suggestions but I'm not going to resolve this issue by putting any holes in my roof. I've had too many water issues (at my house) and not going to let a leaking roof ruin any camping trips. It's probably never going to happen but with my old Eagle, the maintenance and hassle of tending to roof screws isn't worth if for me.

At this point in time, I'll put up with the noise and hopefully FWC will address the issue at some point but doubt they can do much now.
Click to expand...
I concur....patterned/ridged tops sheets but no screws and I doubt screwing the top sheet to the longitudinal frame members would do anything to stop the movement of the bubbled top sheet between those frame members...the few transverse frame members would not remove that slack top sheet either, or so I believe...but I could be wrong.

I just ordered two 6ft X .313" thick X 3" wide 6061 aluminum bars....will attach with 2" VHB tape [LLT]....if I can figure out how to post photos I will show my installation along with the solar panel configuration on my '16 Hawk...

The additional 13.19 lbs of the bars will not hinder me raising the top and hopefully will dampen out the flexing of the "ocean waves" in my top sheet along with the noise...6 foot bars will depress the extra material and the weight will dampen or stop the movement...or so I hope...

Phil
 
Phil, there are a couple of pinned threads in the Member Support area that help with posting images. If you want, send me your phone number, and I’ll help you with it.
 
Thanks Sage...

I will try to figure it out and then PM you if I can't.

All of the discussion on this thread begs the question: What caused the waves in the FWC single top sheet? Why does the top sheet seemingly stretch and develop these slack area waves?

They were not there as delivered but seem to develop over time and under specific conditions. Rough roads? Other items attached to top sheet? Wind during 70mph highway travel? Frame flexing? Failed VHB? Combination of all these?

Moot point for me; since I need to rectify the problem regardless of the reason it exists.

Phil
 
I don’t think the metal itself is yielding and sagging due to being actually stretched. We’d be having worse issues if that was occurring. I suspect instead that the roof edge attachment part of the assembly process, which I assume is done by hand, leaves a certain amount of extra material, probably due to the edge assembly process not tightly creasing the sheet where it bends over the edge of the roof frame. Subsequent air or snow loads on the roof pull at that edge attachment and tighten the bend over the edge, which creates additional slack in the flat field of the roof,
 
Wallowa said:
All of the discussion on this thread begs the question: What caused the waves in the FWC single top sheet? Why does the top sheet seemingly stretch and develop these slack area waves?
Click to expand...
The primary cause of oil canning in your case is wind, with road vibration exacerbating the problem. A search under 'oil canning' will show examples of metal roofs having a similar problem.

Your roof had stretched; there is a lot of energy in vibration. The aluminum roof is a large inelastic drum head that doesn't relax after it has been 'hit' (permanent deformation).
 
Jasan,

Yup I understand the mechanics of what creates the noise ["oil canning"]....what I do not know is if the single sheet top sheet used by FWC has actually stretched due to aforementioned possible mechanical stressors; thus, creating the slack waves seen in my top sheet.

Doubt slack was due to insufficient tightening around the edges when installed. Top sheet was flat when new and now it is not; this would indicate the aluminum was stretched due to loads and movement. Prevention of this stretching is not my concern, but only how to abate the movement and therefore the oil canning noise. The top sheet is damaged as is and nothing will restore a flat surface.

Phil

Ps... I also feel that in my case snow load to a lesser degree and a lot of tough off-roads with the attendant twisting of the Hawk's frame stretched and deformed the top sheet. Once deformed then wind generated by freeway speed can only make it worse; but if it was flat without waves, then wind alone should not create enough force to stretch the aluminum.
 
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