Solar "Hump" for aerodynamics for Class A RV

justgary

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I don't find a apples to apples comparison in pull out strength.
I think the rivet pull out looks higher because they test it through two thicknesses of sheet metal, whereas the rivnut is tested through one. In all cases, the rivnut will have more surface area to hold the panel because of its larger diameter. The rivnut also will have much higher shear because of the greater cross-sectional area, especially when you consider the 1/4" bolt in place as well.

The rivnut can be recompressed by tightening the bolts. The pop rivets are compressed once and then the mandrel breaks. Repetitive motion will eventually pry them apart, which will then lead to motion that will shear them. If you extend your brackets a bit you can get two or more rivuts along the truss, which will greatly improve your chance of holding the panels in place.

One additional advantage of rivnuts is that you can easily remove the panels for maintenance or upgrade without having to leave the angle brackets in place.
 

corn18

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I love rivnuts. I started using them to mount things in my truck bed. I used them to install my solar panels with tilt mounts. Makes it a lot easier to tilt the panels. No nuts to lose. Rivnuts are like hot sauce: I use that *%$! on everything.

IMG_4931.jpg
 

eXodus

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I think the rivet pull out looks higher because they test it through two thicknesses of sheet metal, whereas the rivnut is tested through one. In all cases, the rivnut will have more surface area to hold the panel because of its larger diameter. The rivnut also will have much higher shear because of the greater cross-sectional area, especially when you consider the 1/4" bolt in place as well.

The rivnut can be recompressed by tightening the bolts. The pop rivets are compressed once and then the mandrel breaks. Repetitive motion will eventually pry them apart, which will then lead to motion that will shear them. If you extend your brackets a bit you can get two or more rivuts along the truss, which will greatly improve your chance of holding the panels in place.

One additional advantage of rivnuts is that you can easily remove the panels for maintenance or upgrade without having to leave the angle brackets in place.
that are all good arguments.

My concerns are:
Locating a 1x1 square tube aluminum stud under 1/8 - 1/4 osb and getting a rivnut square in the middle of it.

When I drill a hole in the roof - I don't know where I get into. The locator could be off - the trusses are not wide enough for a large margin of error.

I'm not finding Rivet nuts for thick material - I have to account for the Roof decking OSB + the Wall thickness of the Aluminum Truss.
Another question - I'm basically riveting the OSB of the roof to Aluminum truss. Is the OSB strong enough to resist a rivnut being pressed in?
 

justgary

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315
that are all good arguments.

My concerns are:
Locating a 1x1 square tube aluminum stud under 1/8 - 1/4 osb and getting a rivnut square in the middle of it.

When I drill a hole in the roof - I don't know where I get into. The locator could be off - the trusses are not wide enough for a large margin of error.

I'm not finding Rivet nuts for thick material - I have to account for the Roof decking OSB + the Wall thickness of the Aluminum Truss.
Another question - I'm basically riveting the OSB of the roof to Aluminum truss. Is the OSB strong enough to resist a rivnut being pressed in?
You should have the same concern no matter what fastener you use. Hitting the structural member is important.

A 5/16" rivet nut should be able to grip 0.312", so that should cover you if your OSB is 1/8" and the truss is 1/8".
 

eXodus

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You should have the same concern no matter what fastener you use. Hitting the structural member is important.

A 5/16" rivet nut should be able to grip 0.312", so that should cover you if your OSB is 1/8" and the truss is 1/8".
1642589820360.png

I just looked up the 5/16 and the grip range is only up to 0.137 - which is about 1/8 (I really dislike fractions, why didn't someone come up with a Micro-Inch or some smaller unit?)

The Sandwich on my roof is - EPDM, OSB, Aluminum Truss. So my math puts out - I need a Rivnut with a grip range of at least 1/4 or 0.25 inches. 3/8 0.375 would be preferred. I haven't found one, any leads?

When I use are regular rivet - I need an even longer one - since the sandwich then includes also the bracket:
Bracket, EPDM, OSB, Aluminum Truss. 0.25 - 0.5 grip range.

The difference in application is - I got a 1 inch truss - and the rivet is 0.18 inches - while the rivnut is .420 when I'm not dead center - with the rivet it's not a big deal - while the rivnut is running into the sidewall of the square tube truss.

Each of my panels is going to have 24 screws (roughly 3000lbs pull out strength) and I wanted to add 4 safety straps with rivnuts or rivets - with each strap going to have either 2 rivnuts or 4 rivets. each of the straps will be then around 1000-2000lbs strength.

I'm getting to a point where I can hang the whole RV from the panel (Fully loaded 10,200lbs) :) we are already in overkill territory
 

12VoltInstalls

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need a Rivnut with a grip range of at least 1/4 or 0.25 inches. 3/8 0.375 would be preferred. I haven't found one, any leads?
Yes there are deeper ones
For the safety straps, fewer holes, I’d try to plan well and locate through or next to the trusses. Though I have no idea how they are fabricated. I’d be concerned with a rivet nut crushing or pulling through thin osb myself.

Another option is to use big toggle bolts. Set them with the provided screw and then back it out and use a stainless bolt with urethane sealant (5200). I haven’t done anything for a few years but I think it was fastenal or ACE used to have toggle bolts to 3/8.
 

eXodus

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the stud finder I ordered is pretty useless to pinpoint a thin 1 inch aluminum stud.
I starts showing it around 1,5 inch on both sides of a known stud. So 3 inches of error on a 1 inch target. Pretty bad :p

I guess the use case for that thing is - not to drill into metal pipes. Need to order another one, which is more accurate.
 

12VoltInstalls

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So 3 inches of error on a 1 inch target. Pretty bad
So mark the edges of the weak signal and mark halfway between. But depending on how the aluminum rafters are constructed centered may no work, either.

I really prefer looking into the ceiling versus gambling with extra holes in the roof if someone is paying me.

My own stuff? Judgement call. I’d probably buy 2-1/2” plastic flush hole plugs in advance and hope to not need them.
 

eXodus

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So mark the edges of the weak signal and mark halfway between. But depending on how the aluminum rafters are constructed centered may no work, either.

I really prefer looking into the ceiling versus gambling with extra holes in the roof if someone is paying me.

My own stuff? Judgement call. I’d probably buy 2-1/2” plastic flush hole plugs in advance and hope to not need them.
yeah, I'm not drilling any more holes in the roof as necessary, and just doing exploratory surgery is not really what I want to do.
The 1,5 inches are just a guestimate - depending how I hold and move stud detector it's wider or more narrow.

There must be another truss in front and back of the roof vent - but the range the stud finder gives me for those is just unreal wide. Either the manufacturer put in a metal sheet - (which I didn't see when I removed the vent) or it's picking up something else.

I have one known truss in the roof. That one I can see through the antenna hole from below. Everything else pretty good hidden from view in the roof sandwich.

When I manage the technique of locating that one known - I can have some confidence of locating the other know unknows.

I'm not in a hurry yet, I just order another metal only stud finder.
 

12VoltInstalls

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yeah, I'm not drilling any more holes in the roof as necessary, and just doing exploratory surgery is not really what I want to do.
Often you can do it in a cabinet or by removing vent trim or light fixture or aircool vent trim
or it's picking up something else.
A strip of HDF or plywood on the truss?
I have one known truss in the roof. That one I can see through the antenna hole from below. Everything else pretty good hidden from view in the roof sandwich.
You can find others by testing visual cues with a magnet for staples unless they merely use adhesive…
order another metal only stud finder.
Affirm that it works for non-ferrous
 

eXodus

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A strip of HDF or plywood on the truss?
the Roof Sandwich is:

EPDM
OSB or Luan (some wood product 1/4 - 1/8 thick)
Aluminum truss embedded in Styrofoam.
More hard white foam.
A 1/8 interior luan wood board.
Wallpaper

I guess the whole thing was glued and vacuum bonded together. It was a fairly high end model in it's time.

You can find others by testing visual cues with a magnet for staples unless they merely use adhesive…
I haven't found a single staple or screw in the ceiling assembly yet.
Further I I don't think they would staple into a aluminum truss.

Lot's white hard foam (like Styrofoam, but a bit harder) in the ceiling, the air ducts are molded into the foam, they ran pex through the foam and inside the pex tubing there are the wires. Never seen that before but looks sleek.

Magnets don't work anywhere aside the underside of the RV - it's all aluminum construction on the walls and ceiling.
 

12VoltInstalls

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the Roof Sandwich iwas glued and vacuum bonded together.
Probably so
I haven't found a single staple or screw in the ceiling assembly yet.
Further I I don't think they would staple into a aluminum truss.
If they had a strip of 3/8 plywood or whatever to spread out psi is what I imagined. But then nobody’s ever called to consult with me to correct their designs.
Lot's white hard foam (like Styrofoam, but a bit harder)
Doubtful foamed PVC probs a two part urethane
in the ceiling, the air ducts are molded into the foam, they ran pex through the foam and inside the pex tubing there are the wires. Never seen that before but looks sleek.
I worked in a camper (major roof leaks) a few years back that had cardboard hvac tunnels in foam, but the bulk of it was fiberglass under some mdf-like product.
I thought it was bizarre but apparently they do that stuff..,
Magnets don't work anywhere aside the underside of the RV - it's all aluminum construction on the walls and ceiling.
Nice! Def not an entry-level unit.
 

eXodus

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Nice! Def not an entry-level unit.
Thanks, yeah it has some issues, but most those are down the antique p30 chassis :p and a former owner or two no keeping up with some maintenance items.

Tomorrow hopefully going work on the second solar panel and a air deflector for the front.
 

eXodus

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PXL_20220121_144534557.jpg

The thing I noted - that the front fiberglass cap is about half a inch taller then the roof itself. So in the middle the panel is only about 1,5 inches taller then the front.

at the sides is about 2,5 inches. Very likely going to use some aluminum flashing to build a deflector between the upper edge of the panel and the front fiberglass cap. Just with some VHB tape to fasten the flashing against the panel and the cap.

And yes, I'm going to dicor lap seal the heck out of those screws. They are already set in Sika - so won't leak from sides and below - but will still cover them.
 
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eXodus

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I've added wind fairing to the front panel, before I took a 600 mile trip through Florida.
It's a simple 1,5 inch aluminum angle - a with piece of roof flashing - and some VHB tape. Further then I secured the corners down with self tapping screws and self leveling RV roof sealer.

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So far the fuel efficiency signal I'm getting is positive. I've ran 3 tanks of gas and all of them had been better then before.
No proof yet, but 1-2mpg improvement so far.

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gelmjw

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Nov 19, 2019
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Oklahoma
This topic has prompted me to consider reducing the frontal area of the solar on my van.
View attachment 78881

I can hang the unistrut under the crossbar. Then move the panel forward up against the crossbar.

The result should be about 1/2 the current frontal area.

Comments?
I dropped the panels. The rack's leading crossbar is now the leading edge with the panel directly behind. Plus, round is a better leading edge than the flat edge of the panel.

What I did notice right away was a dramatic reduction in noise during a test drive at various speeds. I read that as less turbulence.
lowered-panel-rack.jpg
 

Bugwubber

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Nov 24, 2021
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Unistrut Rails have been working great for almost 2 years now. 10.5” off the deck to clear ACs and vents. About 10’ back from leading edge.
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eXodus

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Unistrut Rails have been working great for almost 2 years now. 10.5” off the deck to clear ACs and vents. About 10’ back from leading edge.
Looks like a Diesel Pusher? Any before and after the Solar system MPG numbers?

That the intention of this thread, finding out if solar panels cause more drag and if that can be mitigated or even used to reduce the drag.
Have you thought about installing a deflector at the front - to keep the air from going underneath the panels while driving?
 

Bugwubber

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Looks like a Diesel Pusher? Any before and after the Solar system MPG numbers?

That the intention of this thread, finding out if solar panels cause more drag and if that can be mitigated or even used to reduce the drag.
Have you thought about installing a deflector at the front - to keep the air from going underneath the panels while driving?
 
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