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

I wonder if an easier modification would be to add something to change the airflow situation over the roof, like stall fences that are used on airplane wings, at the edges. Those could be very light plastic angle extrusions glued or taped down, running fore and aft so they don’t add drag. Has anyone noticed whether the noisy oil canning occurs with side winds versus front or rear winds?
 
Good thinking by many on this...would add that wind direction varies as does velocity during the tin canning.. My experience although not well defined is that wind coming from a frontal direction cause more tin canning that from abeam. No hard data points.

Hatching a plan to put lateral flat aluminum bar between my Yakima rails and using the rails as removable attachment points [no idea of how to attach but have bar stock flat against the top] so I can vary them in an attempt to determine exactly where the top sheet needs the bars...Since rails are screwed to frame and bars are flat it should not create unwanted movement or tension on the rails.

Turbulent air vs laminar flow is an unknown and while I do wish to stop the TCing I will try to avoid creating drag on the roof, imperil my solar panels while driving or adding significant weight to the top . Kinda of operating from a "do no harm" position.

Testing any retro fix for this issue will be a bear; unless I can find a wind tunnel to use.... :cool:
 
If you can reliably repeat the problem, use weights to locate optimal placement (sand bags, bar bell weights, etc.). The closer to the crest(s) and trough(s) you can get the better the results.

Then I would use a product designed to dampen vibration like Dynamat, Kilmat, et.al. aluminum/butyl or lead/butyl self adhesive mats.
 
JaSan,

CLD tiles might work well. I used the CLD tles from Sound Deadener Showdown to help damp the sound in my truck cab. But SDS is gone )owner retired). The tiles from Resonix seem to be as good, perhaps better.


See here

https://resonixsoundsolutions.com/product/cld-squares-10-pieces-sound-deadening/


If you need to do any kind of sound damping I recommend looking at the products these folks sell. Prices are a lot more reasonable on a per db damping perspective than other products like Dynamat.

https://resonixsoundsolutions.com/independent-testing-data/

I hope this is helpful,

Craig
 
For another data point, I tried Jon's experiment on my 2016 Hawk roof (pulling up on the roof using gaffers tape). My roof doesn't have any penetrations except the two vents and the solar connector. No Yakima rails, no solar panels. I've never had any appreciable oil canning, at least not enough to bother me, despite having camped in windstorms strong enough for the sound of the vinyl walls billowing in the wind to keep me awake.

It's clear that on my camper, the roof is still firmly bonded to the aluminum longitudinal frame members. I was surprised by how much the roof sagged in the center (between the frame along the vents and the frame towards the passenger side). I was able to pull that area up almost an inch.

Inside the camper, I tried pushing up on the headliner. In most places, it's clear that the insulation is not bonded to the roof. In those places, it was easy to push the insulation panels up until I felt them contact the roof. It seems that the insulation panels are loose and resting on the headliner. The area where I noticed the roof sagging from the top was one of the areas where the panels seemed loose. I did find one or two spots where it did seem that the insulation was still attached to the roof, but most of the insulation panels seemed to be loose.

I'm guessing that my 2016 Hawk was manufactured after FWC started adhering the insulation panels to the roof to minimize oil canning, as Stan mentioned. So my conclusion is that the adhesive between the panels and the roof has failed in my camper. Possibly that might have happened due to differing thermal expansion of the polystyrene and aluminum. I think that generally for that combination of materials you'd want a fairly thick layer of adhesive with a good amount of elasticity when cured, in order to handle shear stresses due to differential expansion.

I think that if I start having problems with oil canning, the first thing that I would try would be to open up the headliner and reattach the insulation panels.

As others have noted, surface prep is critical when using adhesives. The adhesive manufacturers have spent a lot of time and money developing optimal application processes for different materials, so following their recommendations goes a long way to having durable adhesive bonds.

- Rusty
 
I’m wondering if those insulation panels that seem unattached are actually attached in the middle with a small piece of that expensive vhb tape and when you push them up they feel like the insulation is loose until the edge areas of the insulation touch the roof metal. Again, it will be easy to check with the tape pull up method but requires two people. I’ll see if I can check it this evening.

I also can see quite a bit of sag between the frames after two years compared to what I recall it looking like just after delivery when I put my solar panels on. My roof has never had snow on it. I have not experienced oil canning noise, but I have not yet camped in high winds either.
 
I counted 36 screws (40 if you count the ones I added for the rack). That's a lot of potential leak points. Some people prefer the two piece roof over the one piece. I don't have oil canning but I have resealed the roof twice. If I were in the market for a new camper I'd have to think hard about which way to go.
 
I personally would take a 1 piece roof over a 2 piece (with screws and a seam) even with the "tin canning".... I bet there are a few cases where the 2 piece roof leaked and having one with screws and the amount of maintenance required, I'll take the 1 piece.
Ted said:
Wallowa,

I agree it is not feasable to replace the roof. My statement is aimed more at FWC. They prefer to keep the smooth look and single piece despite this known issue and the fact that the seam in the two piece roofs never leaked. I don't have an answer as to what to do as it was never resolved in our camper.
You can get pieces of aluminum like that at places like Lowes and Home Depot, but only in shorter lengths. I think 3' and maybe 6' might be it. Not sure if that would be long enough, but if it is then the cost of shipping is the gas you use to drive there.
Click to expand...
 
The 2-piece roof was replaced on our 2005 Eagle with the 1-piece roof, and I no longer needed to reseal the screws every year or two. Our first encounter with roof leaks, of course, happened early in week spring trip in the Pacific North Wet. We now have a 2015 Hawk and have not had any leaks and, fortunately, no canning.

Seems to me that if you need to screw down a 1-piece, you are no worse off than the 2-piece roof when it comes to leak prevention.

Check out Metals Supermakets, https://www.metalsupermarkets.com/
for aluminum and other metal stock. Cheaper than Home Depot or Lowe's and they cut to order, usually same day or next day. They have stores in most major cities and do online as well.
 
Question:

Those you with tin canning noises and with a single top sheet....have you ever had a snow load on that roof?

Thanks...Phil

[Reason for question to follow.... :cool: ]
 
Not me... ok, maybe 1/4".

Kevin
Wallowa said:
Question:

Those you with tin canning noises and with a single top sheet....have you ever had a snow load on that roof?

Thanks...Phil

[Reason for question to follow.... :cool: ]
Click to expand...
 
New Information:

First FWC says that tin canning almost always is associated FWC that have had a snow load. Take that at their word. I guessed that the top sheet on my '16 Hawk is about 88 sq/ft.....using the table in this article [scroll down for chart] you can see that any appreciable snow of a variety of types [water content/density over time] can quickly exceed the FWC statement that "the top can take 1,000 lbs of snow". Hypothesis, WAG, is that too much snow either bowed the top sheet and or top frame and stretched the aluminum top sheet creating bowing in areas between roof framing. https://roofonline.com/weights-measures/weight-of-snow/

Recent Observations and Clue For A Fix:

The top of my Hawk has 6 length wise aluminum frame members [look location of these above the inside liner wooden strips]. The obvious areas of bowing/flex from distorted top sheet on my top was between these frame members. A lot of convex bowing of top sheet between those frame members. Bracing laterally across these frame members did not stop the tin canning, but putting weight [used 2"x 4"x 3ft for area and weight test] longitudinally and centered between these 6 roof frame members did dampen or eliminate the movement up and down of the top sheet in those spaces and tin canning.

My 2 solar panels [on Yakima Rails] cover about 30 sq/ft of the top sheet and while top sheet does flex more in uncovered areas of top sheet the 'why' tin canning can occur under the solar panels is a puzzle. Perhaps the weight on Rails caused top sheet distortion.

I have been skiing with the Hawk and have had up to 12" of fresh [powder, low water content] overnight on top sheet before I scraped the top off with a rubber snow remover rake. Never did the snow sit long on the top and most of the other times I had a maximum of 6" snow for brief periods on top sheet. Never ice or "Sierra Cement".

So, all this and $3 with get you a cup of crappy coffee....My next move will be to purchase aluminum flat bar and using 100mph tape place sections of the bar between the longitudinal frame members of the top sheet while seeing if I can replicate wind produced tin canning with my hand.

Phil

Weight of my two Zamp panels [160 & 170w] and mounting frames about 55lbs; no idea of weight of rails or two power roof vents.
 
Wandering Sagebrush said:
FWIW, my camper never had a snow load, it occurred on our very first trip. That dog don’t hunt…
Click to expand...

Take that to FWC...

Regardless of the 'why', right now my money is on weighting down the loose/distorted sections on the top sheet between the top longitudinal frame members...I will try aluminum bar, unless someone has a better idea of how to lessen or stop the TC.
 
Thanks Pat...shipping costs are through the roof for 6 foot lengths....nominal cost for 2"x1/4" is $6+ per foot....right now Amazon seems the best bet...

Question for Collective Wisdom: Is the bar length or the bar weight the most significant factor in reducing tin canning ?

Perhaps there is an optimal combination? FYI...2"x1/4"X6ft aluminum bar weight is 3.51lbs.

Phil
 
Just thinking out loud here so don't take it a known value.

If using flat bar then weight and surface area might gain the most benefit.

If using a angle piece (like a "L") taped down then weight may not be a issue as long as the length is ridged enough to keep the roof from popping up and down. Angle is strong and can be smaller and lighter than flat stock.

If a piece of angle is run east/west the full width of roof, 90 degrees to the roof trusses with bonding material, then the slop that goes up and down with as with your tape pulling example would be controlled. I might be tempted (and If it was my roof I would) screw it to the trusses as it crosses 90 degrees at each truss. By having the angle captative at the truss locations, the bonded space between has no place to flex up and down to.

I have no issue screwing it down to the truss as the full length roof tracks are done that way but running north south. If you have truss up front that is not covered by roof rack tracks that would be a good starting place.

Long winded but just some thoughts. Patrick
 
I'm picking up my new 2023 Grandby in July. It's a full build out, and as everyone on the discussion knows, I'm forking out a pretty penny. Ya'll have got me a little worried now. I will definitely be asking a lot of questions to the rep when I pick it up. He better have the answers.
 
Phil really doesn't want to make any holes, I think.

Phil, I wonder if you are open to pulling off the ceiling liner and tackling this problem from inside/below? I bet that attaching the East West frame members with VHB would help, as would (re)glueing the rigid insulation to the one piece top sheet.
 
Wallowa said:
..... Question for Collective Wisdom: Is the bar length or the bar weight the most significant factor in reducing tin canning ?.....
Click to expand...
For vibration damping:
placement is the most important factor. At the peak or trough gives maximum attenuation. At a node gives no attenuation.
Second is mass for low frequencies (1 to 250 hz), friction for mid range (250 to 2000 hz).

If you can reliably reproduce the oil canning, experiment with weights to find correct placement.

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