Fixing Aluminium Brackets to Vehicle Body

[rixster]

I would be grateful for some advice on how best to fix aluminium brackets (35mm x 100mm) to Promaster van. The brackets are used to support a large (25 kg) solar panel on the roof of the van. I am concerned about vibration, long term rubbing wear and electrolytic action of the dissimilar metals. I am thinking of using 2mm neoprene gasket between the van roof and the brackets, with stainless steel nylocked bolts. Is this the best method of fixing or can you suggest alternative methods ? Perhaps a Polyurethane adhesive ??

Thanks in advance

 

[EdStainless]

25kg panel on the roof while you are driving?
What makes you think that the brackets are nearly strong enough for the job?
You need to look into how the manufacturer attaches roof racks to this vehicle.
My guess is that they screw bolts through the roof into a threaded doubler plate.

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[rixster]

Thx for your comments. Perhaps I should expand a little....

There are 6 brackets each with 2 mounting holes. The M6 bolts will either be screw into rivnuts or into a spreader plate inside the van. The panel is 1.7m x 1m, so the weight/bracket(s) is evenly distributed. Also, as the panel is parallel (air gap approx 40mm) I don't think there is much wind loading as the moving air can pass freely over both upper and lower surfaces.

 

[IRstuff]

I don't think there is much wind loading as the moving air can pass freely over both upper and lower surfaces.

Unless you've run CFD, that's just a wild a$$ guess; if the panel isn't absolutely parallel to the airflow, you've got a monster spoiler or wing, depending on its angle of attack. There's a reason why OEM solar panels are embedded in the roof. Moreover, because the airflow is a function of vehicle speed, the structure will have periodic loading, which makes the fastening system all the more critical.

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[EdStainless]

And then there is the buffeting cross wind to deal with.
Any reason to not mount this 5-10mm from the roof and then add a fiberglass faring to blend it to the roof?
You might also need to tie the reinforcement plates in the roof together with some steel bracing.
I actually doubt that the standard frame for the solar panel will work in this application.
On the roof of my house the wind might be 60mph, on the roof of a van it could easily be >120mph (van + wind speeds) which would be roughly 4 times the mechanical loading.

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P.E. Metallurgy

 

[rixster]

It was my intention to fit a spoiler and I think I better make it a priority...along with more sturdy fixings. Thx for your comments.

 

[TugboatEng]

Lots of stuff to think about here. First, you need to attach to the structure that supports the roof and not the roof skin. Dissimilar metal corrosion is a minor issue. Bolting on to to rubber is rarely ideal as the rubber tends to extrude out from the joint before proper bolt tension is reached. Simply bolted joints are not water tight.

I personally prefer to use sealants over gaskets and use sealing washers under the bolt heads.

 

Any day now we'll see solar panels built into automotive spoilers, part of automakers' strategy to save the planet. Might as well put that extra aerodynamic drag to work

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