Airstreamer looking for some advice on mounting to a curved roof

[Wattson]

Had a hard time finding a datasheet on the VHB tapes, the US 3M website has a dead link. All they show is marketing crap and "For industrial/occupational use only. Not for consumer sale or use.". Awesome liability jargon.

Found this on the 3M UK website. Check out this crazy drop in tensile adhesion once it gets to only 50 F. The tape will face 170 F easily on a sunny summer day, on the roof of a trailer or RV. Meanwhile its down to 10% strength.




View attachment 65893

I'm surprised this isn't the spec sheet for eternabond. 4910 normal tensile strength is 100psi and 4951 (used by AM Solar) is 85psi @ 200F. That's what the rating is in the data sheet for each tape. Lets do some math shall we? Each of my panels are secured with 2 T-Rails 48"x 3/4' = 72sqin, 72 x 100 = 7200lbs (>3.5 tons) @ 200F. Does anyone here really think that mechanical fasters in sheet aluminum will withstand 3.5 Tons? Does anyone think the aluminum sheet it self wont fail first? Even in shear the strength of both tapes is 70psi! There are 100's of panels on dozens of Airstreams using this install method with the only failure reported so far is when half the bolts are lost and only 2 brackets are left. Does anyone think that 2 brackets secured with standard fastening methods would not have failed in just as spectacular a fashion? WAKE UP!

 

[PerryB67]

Had a hard time finding a datasheet on the VHB tapes, the US 3M website has a dead link. All they show is marketing crap and "For industrial/occupational use only. Not for consumer sale or use.". Awesome liability jargon.

I had no problem finding a data sheet outlining the various properties of 3M's versions of VHB tape on my first Google. I suggest you make an honest attempt.

Either install panels properly; with the correct mechanical fasteners; or stick to portable ground panels.

Running panels installed with just tape can kill someone.

So can installing panels with too thin of brackets, too few brackets, no washers, just using screws, etc. It doesn't matter what method you choose if you don't do your homework they'll fail, and if you do your homework the mounts will be successful. Your choice.

I do agree that some of you have no business using VHB tape.

Enjoy,

Perry

 

[McCarthy]

I'm surprised this isn't the spec sheet for eternabond. 4910 normal tensile strength is 100psi and 4951 (used by AM Solar) is 85psi @ 200F. That's what the rating is in the data sheet for each tape. Lets do some math shall we? Each of my panels are secured with 2 T-Rails 48"x 3/4' = 72sqin, 72 x 100 = 7200lbs (>3.5 tons) @ 200F. Does anyone here really think that mechanical fasters in sheet aluminum will withstand 3.5 Tons? Does anyone think the aluminum sheet it self wont fail first? Even in shear the strength of both tapes is 70psi! There are 100's of panels on dozens of Airstreams using this install method with the only failure reported so far is when half the bolts are lost and only 2 brackets are left. Does anyone think that 2 brackets secured with standard fastening methods would not have failed in just as spectacular a fashion? WAKE UP!

Why do you keep comparing your long, taped RAILS with the OP's small mounting feet? Oranges and apples.

How many install the tape on painted or oxidized surfaces that will fail MUCH soon than that rating you just cited. And guess what will stay in place longer: tape and paint, or screws / washers / nuts that go THROUGH the structure?

Ever did some aluminum TIG welding? Why do you need 100% argon WHILE welding aluminum? Because it oxidizes within a second when surrounded by oxygen. How many of you cleaned that aluminum roof AND used shielding gas to keep it free from new oxidation?

 

[Shamoke]

If there are not physical hardware holding down the brackets, be ABSOLUTELY CERTAIN you have steel cable security straps attached to catch the panels when they come loose at speed on the highway…

Ditto.
Think of all of the poor insurance adjusters having nightmares about solar panels flying off of camper roof tops at 65 miles per hour. I bet they don't get much sleep.

 

[12VoltInstalls]

another term I coined years ago:
Static Object Syndrome

This disease is what causes people staying in hotels and guest rooms to pull towel bars (not designed for large loads) off the walls and - while StOSy is not mentioned in the code- ADA specifies that grab bars be affixed with screws or bolts.

Just because some people do it doesn’t mean that is actually ok for anyone to do it.

With polyurethane adhesive caulking so readily available, mounting a nicely designed base/rack of pleasing esthetics to securely mount a solar array will not create leaks- that adhesive coupled with mechanical fasteners will be very secure. Expense probably isn’t much of a concern- by the time you can buy into an airstream a few hundred bucks or a thousand bucks isn’t an obstacle, now is it?

 

[12VoltInstalls]

aluminum TIG welding? Why do you need 100% argon WHILE welding aluminum?

Yes, cleaned aluminum oxidizes in seconds. For structural adhesive bonding to aluminum this is a concern to be aware of.
Not being mean just picky-uni, in good nature about welding gas:
The shielding gas does keep O2 out, but its primary purpose is to keep any impurities out of the weld pool so the weld isn’t incorporating them becoming weak or brittle, as well as ‘push’ away impurities that come to the surface of the molten metal. Ancillary O2 shielding, push, and the cooling effect are sorta by products- necessary or not.

 

[Wattson]

Why do you keep comparing your long, taped RAILS with the OP's small mounting feet? Oranges and apples.

How many install the tape on painted or oxidized surfaces that will fail MUCH soon than that rating you just cited. And guess what will stay in place longer: tape and paint, or screws / washers / nuts that go THROUGH the structure?

Ever did some aluminum TIG welding? Why do you need 100% argon WHILE welding aluminum? Because it oxidizes within a second when surrounded by oxygen. How many of you cleaned that aluminum roof AND used shielding gas to keep it free from new oxidation?

In his original post he stated he was thinking of using these Unistrut rails. In post #8 he showed us the way he planed on installing the panels and that he was leaning toward using them (Unistrut). The Unistrut is 1-5/8" wide and I'm pretty sure that the panels are ~20' wide. Since the Unistrut is rounded on the edges lets take off 1/8" per side making the bonding width ~1-3/8". So 20" x 1.375" x 3(struts) = 82.5sqin. 82.5 x 85(I assume he will use the 4951tape) = 7012.5#/panel. Seems really close to my install.

The data sheet clearly states that they used 2 aluminum plates during the test. so the the normal bond strength numbers are 100% accurate since I'm sure the aluminum plates had corrosion on them. As far as paint/roof coatings are concerned I agree that they can be an issue and should be addressed during install.

 

[Freddmc]

Seeing as how the problem seems to be air getting UNDER the panels to severe the connection (of any type) why not put an aid deflector at the leading edge of the panel forcing the air over top the panel.
Like this (https://oriondesigns.ca/)

 

[Mike 604]

On our overlanding vehicle we have a James Baroud roof top tent.
When we first added our two PV panels we used a ground mount set up.
This was bothersome and a hassle to set up and take down. So we decided to roof mount them on the RTT.
We used an adhesive that GM uses to glue Corvette panels together as I didn't want holes in the fibreglass tent.
That was in 2014, zero issues.

 

[Short_Shot]

The reason the other poster used VHB tape and Sikaflex to mount his panels is from this video.

If AM Solar uses this method to install panels on customers projects I thought it was worth looking into (especially if I don't have to drill holes in the roof). I was skeptical on the bonding surface area as stated by another poster here, but I saw another video of someone using T-Track to mount panels to another Airstream roof. They used screws/rivets plus tape, but I thought the tape might work on its own (I can always rivet them down at a later date). Each panel on the roof of my trailer has 72 square inches of bonding area which seemed to me to be a little more secure than the smaller tabs. All the research I did on similar installs on AM Solars forums and Airforums indicate zero failures so far after a few years of use. I plan to watch the install like a hawk because I'm still not 100% convinced the tape will last over time.

After reading the concerns of others here I looked up the removal procedures for my VHB tape and Eternabond.

Scotch 4910 VHB Tape:

Eternabond:

I leave any conclusions about toughness to each of you. As a side note I used the zip tie mounting squares shown above to secure the roof wiring, but i removed the double sided tape that came with it and put the VHB tape on instead. I hope this addresses some of the valid concerns with this install method.

I would like to point out that every industry is full of professionals who are not licensed PEs and often make decisions based on purely anecdotal data, and very often are not "best practice" but rather "easiest practice that survives the warranty period".

Now. This is not a comment on the validity of the method as described, but rather a comment on the validity of "professionals do this" as evidence that it's good.

I've seen licensed and state certified master electricians notch out 60% of a load bearing stud across 20 feet of wall just to save themselves the effort of walking to the truck for the drill bit.

"Professional" means nothing to me.

 

[Wattson]

I would like to point out that every industry is full of professionals who are not licensed PEs and often make decisions based on purely anecdotal data, and very often are not "best practice" but rather "easiest practice that survives the warranty period".

Now. This is not a comment on the validity of the method as described, but rather a comment on the validity of "professionals do this" as evidence that it's good.

I've seen licensed and state certified master electricians notch out 60% of a load bearing stud across 20 feet of wall just to save themselves the effort of walking to the truck for the drill bit.

"Professional" means nothing to me.

Nice classic Straw Man argument, I like it!

 

[Short_Shot]

Nice classic Straw Man argument, I like it!

Its not a strawman at all.

Its pointing out that the qualifier of "professionals do it" has no real merit and objective data is required. If "professionals do it" was all you needed, inspections would not be necessary.

 

[sunrise]

@PeteW Here is what I did with my 16' Airstream. I custom designed and made the bracket out of 1.5 x 1/8, 3 x 1/8 aluminum angle. Then the bottom bracket is mounted on roof with 3M VHB tape, then sealed with Sikaflex sealant. I am very happy with the brackets as they allow me to lose 2 nuts then lift the panel for cleaning. Also the brackets are hidden under the panel so the installation looks very clean.
===========

I few comments I want to make on VHB tape approach.

- My custom made bracket has 3x2" bonding surface with roof, more than double most of the off-shelf ones. I feel very comfortable with the strength of them.
- 3M 4950 VHB takes tremendous dynamic stress, but far less static stress. So make sure the install does not put long lasting stress on them. This include how you design your fasteners on the bracket,
- Surface prep is super important. I used alcohol to clean both bonding surfaces, and waited for the surface to dry. You also need to seal the contact area to protect the VHB tape.
- The roof aluminum sheet is very soft, so unless you can put nuts with washers on the other side the sheeting, the VHB tape will offer stronger install. I would not use rivets or sheet screws at all - It's not about drilling holes on roof, it's just that with that soft aluminum sheeting, screws will not be able to have a strong bite into the metal.
- I have watched many youtube videos on how people install panels on Airstream using VHB tape. The most important lesson I learnt from them is. Never drive behind an RV with Solar Panel on them.
There are people really should not be install solar panels on vehicle that moves @60mph.

 

[12VoltInstalls]

"Professional" means nothing to me.

Static Object Syndrome
(that’s what causes hungover hotel guests to step out of the shower and rip a traditional towel bar off the wall. Their small minds expect the fixed, mounted, static object to defy the laws of science and support their dynamically applied weight in shear and tension.)
Static Object Syndrome is a second order action in the implementation of Murphy’s Laws while expecting an illogically positive result.

 

[jwelter99]

Anyone who pretends that VHB is "ok" is either too naive to realize the danger they have caused or negligent and doesn't care of the danger they have caused.

It is not a suitable and safe way to hold a solar panel on. It is used to hold small plastic trim pieces and such on; which often also have a mechanical fastener such as clips and other mechanisms.