Roof racks - good, bad, and horror stories

[flying kurbmaster]

Hard to beleive but if you want it to be more aero you would be better off turning it around, the party is at the back, if it was mine I would add the same spoiler you have on the front on the back, I considered making an alluminium enclosure to help keep it as aero as possible with slopped front sides and back, ideally that is between 12 and 15 degrees or so my research found. To eliminate the heat build up I was going to drill one to two inch holes along the sides but I didn’t intend on having tubes or storage, incorporated into it. I ended up with glue on panels so never built it.

 

[MrNoodly]

Must have never tried a black solar shower bag.

PVC and ABS pipe are much thicker than bags.

 

[bigskybob]

We found a black solar shower bag on a tree limb in Red Top Campground in the Yaak a couple of summers ago.We both tried it and decided it was a leaverite.Leaverite where you found it.

 

[maki2]

Of course there are solutions and then even there are even more solutions. Sure screens will help some but not as effective when not moving down the road. However you could think about using some of that solar power being generated to increase the air flow with some directional exhaust fans that pulll the air in from the front and send it out the back. That is going to be needed if you block off the area on the sides with insulating foam. The fans can have a thermal sensor located under the panel to turn them on and off as needed. I don't really see any other solution which would be as effective for preventing damage from excess heat build up. You will need to do some cfm calculations to find out what fans to install. They will of course need to be weather resistant for exterior use. You should also talk to the solar panel companies about the safe temperature range that will prevent damage to the panel substrate.

But you are spending solar power that could be used for other things.

By the way, there are vans and RVs with rooftop solar panels driving all over the country and they have no shrouds around them. Unless they messed up installing the brackets those panels seem to be holding up just fine. The installation has to be done right but there is lots of advice and parts available from the solar panel companies to help you do it right so that they don't blow off. They have years of experience for getting it right otherwise they could not sell any solar panels for RV use. No one is going to put up with a company who tells them to do stuff that does not work. Sometimes you can let the pros tell you how to do it instead of trying to invent it. I love designing stuff but I am a sensible person and look at what is proven to work before I put my spin on it.

 

[B and C]

Innovation is one of the things that makes this country great. Without it we would be back in the stone ages. If everyone does it the same old way because that is the way it has always been done is not always the answer.

It appears from your drawing that there is plenty of space around the edges of the panel for any breathing the panel requires. What is the worst case scenario?

Mine haven't caught on fire or degraded output that I can tell and there is very little ventilation with the velcro all the way around.

 

[VanTalk00]

However you could think about using some of that solar power being generated to increase the air flow with some directional exhaust fans that pull the air in from the front and send it out the back. 

Good idea!  I was going to watch it closely to see the temperature variations.  You've sensitized me to the need to thermally isolate the hinged rack from the stationary rack to cut down on some conductive heat transfer.  One interesting possibility might be to modify the Maxxair fan to divert air out the back instead of down into the cabin.  Don't know if it's possible.  Will have to look. 

One major reason for the tubes and wrap is to move water storage and other storage needs out of the tiny cabin.  In this case, the panel serves the dual purpose of a storage box "roof" and a pv panel.  That's a bigger motivation than the solar hot water gain.  I'm not counting too much on an abundant supply of piping hot water.  Lots of experimentation to be had.

I don't intend to do that much stealth camping, and I'm guessing when I'm stationary for long periods of time, I'll tilt the panel.  However, when I'm parked in the city for whatever reason, the fan may come on.

The latest iteration of rack design is attached.  I still have to add support to attach the front spoiler.  

While I have your attention, maki2, what is your opinion of countersunk rivets?  Thinking of those for the drawer channels and other places I don't want rivet heads sticking out.  Also, any recommendations for bending 6063 2" x 1/4" flats 90 degrees?  Have you done it?  6063 is supposed to be bendable, but 1/4" is pretty thick. That would really simplify my roof brackets.

As always, thanks for everyone's comments.

 

[maki2]

If you want to bend aluminum of that thickness take it to a sheet metal shop with the bend lines marked out and a couple of six packs of beer on a Friday afternoon. Sometimes you get lucky

It would be difficult to accurately and safely bend 1/4" thick 6061 T6 at home. Keeping the bend exactly at 90 degrees is best done on a brake rather than in a vise. The brake has a fence along one side and it clamps the metal and forms it over a die of the proper radius. That radius is the critical part of bending the metal to preserve its proper strength rather than destroying its integrity.

You will find charts and tables online that have the minimum bend radius for all the various allows and thicknesses of aluminum. I am going to let you do that research because as a designer you need to get used to finding the online sources that give you that kind of design engineering data. I will help you by telling you what you need to look for and give you some keywords which are... bend radius aluminum ....use all of those three and you will get the relevant websites that show the tables. If you opt to open the images results you will even see the charts but as free education in design parameters it is good to go to the websites and read the text that goes along with the charts. You are also going to have to learn to layout the bend marks for the sheet metal shop. If you want Beer Friday prices for getting bends done on professional equipment you have to do all the work yourself except for putting the part into the brake and hitting the switch. The safety laws don't allow you to touch that equipment.

Remember....it is the minimum bend radius for a given thickness and alloy of metals that is the critical part of the design. All the designers of sheet metal either use a CAD program that contains those parameters in a list of materials options for sheet metal designing or else they look it up in the engineering charts.

I suggest if you don't have a 3D CAD sheet metal design program you take advantage of the free 30 day download of Ironcad. The sheet metal tutorial videos are on youtube.

 

[VanTalk00]

If you want to bend aluminum of that thickness take it to a sheet metal shop with the bend lines marked out and a couple of six packs of beer on a Friday afternoon. Sometimes you get lucky

Yeah, I've looked at a half dozen or so videos, plus web sites and online bend allowance calculators.  They all get to the point of putting the piece in a brake, and then assume you know all about brakes and how they work and their settings etc.  In my case, for lack of knowledge, I would have to experiment to a certain degree (what is the k factor of 6063, for example?), and then I will have gone through my six-pack of goodwill muy pronto.  (Btw, I would not try to bend 6061 without heat.)  This strategy would work if I were an old hand at using these machines, and I could tell them exactly what to do and what I want.
Probably easiest is straight pieces and a bunch of L brackets.  Then I could use the more available 6061.
What about the countersink rivets?  I'm worried that with 1/8" stock, I'd be thinning down the material too much.

 

[flying kurbmaster]

Yeah, I've looked at a half dozen or so videos, plus web sites and online bend allowance calculators.  They all get to the point of putting the piece in a brake, and then assume you know all about brakes and how they work and their settings etc.  In my case, for lack of knowledge, I would have to experiment to a certain degree (what is the k factor of 6063, for example?), and then I will have gone through my six-pack of goodwill muy pronto.  (Btw, I would not try to bend 6061 without heat.)  This strategy would work if I were an old hand at using these machines, and I could tell them exactly what to do and what I want.
Probably easiest is straight pieces and a bunch of L brackets.  Then I could use the more available 6061.
What about the countersink rivets?  I'm worried that with 1/8" stock, I'd be thinning down the material too much.

Why do you think you need 1/4 inch alluminium that is pretty heavy duty stuff. I don’t understand where you are using this. The drawing looks like tubing. I have a lot of experience on brakes, some days I bend aluminium all day long.  I have access to a very big manual brake which can bend 1/8 Ali. I tried bending 3/16 checker plate once on it and it cracked, I am pretty sure in order to bend 1/4 inch you would need some kind of hydrolic brake or a very large heavily weighted manual brake. Have you considered buying alluminium extrusion that is already 90 degrees like larger pieces of say commercial window bits that are 2x5 inch L. Looking at your design if I was sheeting this I would use the flat stock alluminium they use on continuous eve throughs  machines. It is thicker then the flat stock they use for flashing.

 

[VanTalk00]

Why do you think you need 1/4 inch alluminium that is pretty heavy duty stuff. 

You may be right, but 1/8" just seems pretty weak for a roof assembly.  I do have a lot of supports, so maybe it would be okay.  

I've pretty much given up on the idea of bending 1/4".  I'll use straight flats connected with brackets made of short pieces of L channel.  The pieces I'm talking about are the U type brackets you see in the figures.  They're 7" by 7" and surround the pipes in the images.  See the attached image for a comparison of the two types.

Regarding cracking, it depends on the particular aluminum alloy.  Most of what you get is 6061 and is brittle - will crack.  More flexible is 6063.  You need to heat 6061 to bend 1/8" or it will crack/break, but you can bend 1/8" 6063 without heat.

 

[maki2]

I suggest you rework your design to use parts that are readily available. If you don't have the equipment, basic knowledge or skills to fabricate your own parts then don't do it that way. Work it from the other direction.

 

[maki2]

woops sorry I got the wrong info, I had something to post but read the dimensions wrong

 

[Gr8ful]

If you have a hyd press you can bend 1/4" alum but unless you use a steel rod to bend a raidiused corner it will crack. I'd buy alum U or L channel & just cut how many you need.

 

[Gr8ful]

Sportsmans guide link. If you do buy link here thru active Junky & get a reate & $10 the 1st use plus a rebate https://www.activejunky.com/invite/1601749 you get an auto rebate & don't do anything but link thru AJ from many stores for active people, I've gotten over $400 the last 2 quarters on things I was buying anyway. Works Great!
https://www.sportsmansguide.com/product/index/guide-gear-universal-pick-up-truck-rack?a=1935501
Look at these & the ones below. All on clearence. You couldn't buy the material cheaper & can mod them into whar you want.

 

[Gr8ful]

Here's the one I'd buy from SG WX2-657783 as the sjpping is $49 & use the code sk1699 to save $33.80

 

[VanTalk00]

Sometimes, things work out - at least I hope.

The attached images give a better representation of the roof rack and the Maxxfan.  The photograph is the actual fan as unpacked from the factory.  Note that they thoughtfully include a "Garnish ring" which is about six inches long and is intended to span the space between the fan on top of the external roof and the bottom of the internal RV ceiling.  If you have a lot of insulation or roof trusses, etc., this ring will provide a path from the inside to the outside.  In my case, I can use that ring to elevate the fan above the actual van roof to a position flush with the top of the storage space around the fan by the pv panel.  The advantage is that, looking at the image of the rack viewed from below, I can cut a small door (shown in red) in the garnish ring and route air from the front of the spoiler (holes also shown in red) through the space below the PV panel, in addition to the air flow coming from the two holes cut in the bottom of the van floor. The overhead image shows the aluminum skin I'll put on top of the rack to allow the fan to open but otherwise cover the storage space around the fan. The other overhead shot shows the frame without the wrapper.

The trick in all this is knowing how big to make the holes in the spoiler, the van floor, and the garnish ring door.  To figure that out, consider the following scenarios:

1.  No holes anywhere, the fan lid is closed, and the fan is full on - The Maxxfan is not very happy - working hard and achieving nothing.
2.  The fan lid is full open, the fan is full on, and the input flow to the fan is equal to the fan output - meaning the input holes to the outside are at least as big as the maximum fan lid opening. The fan is happy - giving you the max flow it's rated for.
3.   The fan lid is full open, but the input holes only provide half the area of the output fan opening.  If the fan is throttled back to half power, it should still be happy because it's only needing to provide the outflow corresponding to the size-restricted input inflow.
4.  The fan lid is full open, but the holes in the spoiler are much smaller than the holes in the floor.  Very little flow will come across the roof storage space.  Most of the inflow will come from below.

So the output area of the fan is about 91 sq inches.  My  two 3" holes in the floor provide 14 sq inches of opening.  If I add another 14 sq inches to the spoiler, I should get about equal flow from the floor and the spoiler, but not enough to really allow the fan to operate at full power (28 sq inches of inflow vs 91 sq inches of outflow). I have to make some decisions.  To get 91 square inches of inflow opening, I'll have to open a window down below.  If I want equal flow from the roof and the van interior, I can increase the size of the spoiler holes to 5" instead of 3" to get about 39 sq inches of inflow from the spoiler.  I'm restricted to 3" on the floor for access reasons.  With the windows closed the larger flow will come from the spoiler (39 sq in), but with the windows cracked, I can equalize the flows. (This is another good reason for me to add a window to the rear passenger door - something I've been thinking about anyway.)

I'm no ventilation engineer, but this all seems logical to me.  If anyone knows something about this and can enlighten us, please do!

Thanks.

 

[flying kurbmaster]

You may be right, but 1/8" just seems pretty weak for a roof assembly.  I do have a lot of supports, so maybe it would be okay.  

I've pretty much given up on the idea of bending 1/4".  I'll use straight flats connected with brackets made of short pieces of L channel.  The pieces I'm talking about are the U type brackets you see in the figures.  They're 7" by 7" and surround the pipes in the images.  See the attached image for a comparison of the two types.

Regarding cracking, it depends on the particular aluminum alloy.  Most of what you get is 6061 and is brittle - will crack.  More flexible is 6063.  You need to heat 6061 to bend 1/8" or it will crack/break, but you can bend 1/8" 6063 without heat.

The sheeting I am referring to is less then 1/16 maybe 1/32 of an inch, and plenty strong with your. Tubing, The alluminium on airplanes is thinner then that. I still think you should be sloping  your design at the back or turning it around.

 

[VanTalk00]

 I still think you should be sloping  your design at the back or turning it around.

Maybe you can attach a pic of what you're talking about?  I don't think I've ever seen a van like that, and if it's what I think you're saying, I don't think I would have room for all my equipment on the roof by doing it.

 

[cheapliving]

How does anyone drill a hole in the roof, or anywhere else in/on their vehicle, without knowing what the drill bit might hit on the other side of the surface since they don't have X-ray vision?

 

[highdesertranger]

you look.

if you see something that might get damaged from drilling, then break out the tape measure and check.

highdesertranger