1980 Caravelle Shell Off Renovation

[timzog]

So I got sucked into an extensive and productive discussion in another thread regarding floor materials. http://www.airforums.com/forums/f36/...ams-92263.html
In the meantime, I've purchased 4 sheets of 4x10 1/8" 5052 aluminum sheet for the floor and 0.032" 5052 aluminum for the belly pan. I bought 0.060" aluminum for the bellypan under the grey tank. I may reuse the existing banana wraps but I am not sure yet. They will go on after the shell is back on the frame so I'll be really happy to have that problem.
Tim

[timzog]

I installed the grey tank last week and didn't post pictures. I attached it from underneath all around the perimeter with stainless self tapping hex head screws and fender washers. This worked fine everywhere except where I tried to screw into the main frame member which ended up in broken bits and cursing. I ended up running a long angle under that edge and attaching it to the frame with 4 stainless bolts. In the back I attached an aluminum angle under the lip of the tank that attached to the main frame with stainless bolts as well. All bolts were secured with loctite. A few pics are attached.






The tank is 40 gallons and will be rarely moved when it is full, but it will be nice to have the capacity when needed. When full, I assume that we'll be driving slowly to a dump station.

Tim

[Splitrock]

Whoa! That's big one!

[nvestysly]

Originally Posted by timzog

I am now ready to start on the floor,
I am thinking about the subfloor and really don't want to use wood. I've played out 100 scenarios in my head and I think I've decided on one. I'm going to build an aluminum torsion box with 1/8" aluminum sheet on top, .032" aluminum sheet on the bottom and an array of thin 3" aluminum c channels to provide the webs of the box. I'll fill all the spaces with 3" thick foam blocks to add rigidity. I'll use regular pop rivets on the bottom and countersunk pop rivets on the top. Where the top and bottom sheet meet the steel frame I'll use stainless rivets. Overall this should be lighter and stronger than the current system and be more resistant to water. I may beef it up a bit near the edges where it ties into the frame. I am trying to figure out the optimum spacing and where to get light c channel for the web. I may make he channel myself with really light weight sheet since the job of the web is only to keep the space of the skins at a fixed distance.
Torsion boxes have an amazing strength to weight ratio. I could use blown in foam to provide the web, but I am worried about long term durability under stress and don't want a totally sealed frame. I may seal the styrofoam to the aluminum web but not tot the steel frame to avoid locking moisture against the frame.

Has anybody tried this before??
Any experience would be appreciated.
Tim

I don't have any experience but I am curious about the 3" thickness. Where are you taking away the extra space within the volume of your trailer? The original floor is less than 1" thick. Those extra 2"+ have to come from somewhere. Are you raising the shell of the trailer by that much and adding extra belly pan? Are you simply loosing headroom in the trailer? Not that it matters... just curious.

Lucius

[timzog]

Originally Posted by nvestysly

I don't have any experience but I am curious about the 3" thickness. Where are you taking away the extra space within the volume of your trailer? The original floor is less than 1" thick. Those extra 2"+ have to come from somewhere. Are you raising the shell of the trailer by that much and adding extra belly pan? Are you simply loosing headroom in the trailer? Not that it matters... just curious.

Lucius

Lucius,
The top 1/8" aluminum plate will rest directly on the frame and the bottom belly skin will attach to the frame from underneath. Those aluminum sheets are the top and bottom of the torsion box so it doesn't take up any of the volume of the trailer at all. It will actually lower the trailer shell 1/2" while maintaining the same headroom.
Tim

[timzog]

Today I made C channel out of the good parts of my old belly pan. I made a form out of a Trex 2x4 which I ripped down to 1/16" shy of 3" wide on the table saw. I cut the aluminum sheet into 5" x 46" pieces. For the form I put the form on a big 2 x 12 board, put the sheet on top of the form and then put a heavy aluminum angle on top. I predefined holes in the angle and Trex so that I could attach the whole sandwich to the big board with 3" wood screws.



With the whole sandwich secure, I was able to partially bend the sides around the form with my hands and then I used a technique called flow forming to flatten out the sides. The main tool is a nylon insert for my rivet gun I bought at Aircraft Spruce.





By hammering the edge, I was able to make a nice bend on each side of the C and make pretty respectable C channel.









All in all it took me about 10 minutes for each piece including cutting, assembly, and forming.
Here's my pile of C channel. Alone it is weak,, but with the top and bottom attached to the skins, and maybe a few cross members for increased rigidity plus foams spacers, it will make a really strong torsion box system.




Tim

[timzog]

Today I cut out the 1/8" 5205 aluminum plate for the subfloor.

I tried several methods including a steel cutting skill saw blade, a jigsaw using a fence, and finally a jigsaw freehand. The freehand jigsaw was far at the fastest, most accurate and easiest way to cut. There was still about an 1/8" or so of slop in the cut but I was mostly able to turn the saw to keep it in line. This is the blade I found that worked best. I tried a couple of others but I was able to make about 35 feet of cuts using just two of these blades.







It works out that the floor is exactly 16' long so I went with 4 sheets cut to 4' x 7' None of the joints are at a frame piece so I'll use short 1/8" pieces to splice the floor together with rivets to make one solid floor.
I cut the pieces one by one using the old floor as a template. Got a sliver from the old floor so I'll be happy to say goodbye to it.












Now I am going to start laying out the support and insulation for the floor.

[ddstech]

Looks interesting. Polish that floor up and the walls and you will really trip everyone out when they come in. It will be like a house of mirrors.

[timzog]

Originally Posted by ddstech

Looks interesting. Polish that floor up and the walls and you will really trip everyone out when they come in. It will be like a house of mirrors.

That would be awesome, but slippery. We'll have lots of options for floor covering on top of the aluminum, but we haven't decided what to use yet. All great ideas are appreciated

[MarkR]

Hi Tim,
This looks like very interesting. Have you considered thermal expansion? I am no expert, and I don't know exactly how to evaluate the numbers. When I look up Aluminum vs. Steel (skin/panel vs frame), the "coeficient" for Aluminum is twice the Steel numbers that are listed. There may be ways to deal with it, and you may have considered it already. Also, have you figured how the torsion box "closes" at the edges. Do you think possibly that the c-channel at the perimeter will provide enough rigidity? Seems like it might to me, but it's just a gut feeling.

Anyway, I'm enjoying your thread, thanks for posting it.
MarkR

[timzog]

Originally Posted by MarkR

Hi Tim,
This looks like very interesting. Have you considered thermal expansion? I am no expert, and I don't know exactly how to evaluate the numbers. When I look up Aluminum vs. Steel (skin/panel vs frame), the "coeficient" for Aluminum is twice the Steel numbers that are listed. There may be ways to deal with it, and you may have considered it already. Also, have you figured how the torsion box "closes" at the edges. Do you think possibly that the c-channel at the perimeter will provide enough rigidity? Seems like it might to me, but it's just a gut feeling.

Anyway, I'm enjoying your thread, thanks for posting it.
MarkR

That's a great point and I haven't thought of it. Thanks so much for bringing it up I looked up the expansion coefficients on this website. http://www.engineeringtoolbox.com/th...59.htmlhttp://
5202 Al has a coefficient of 15.2 microinches/inch/degF
Steel is about 7.
Worst case scenario (I hope) is about 200 deg F which would result in an expansion of .00304 inches per inch of length for Aluminum and .0014 inches per inch of length for steel so the differential expansion would be .00164 inches per inch of length for a 200 degree swing.
Across the 16 feet (192in) length of floor surface the difference would be 0.31 inches or about 5/16". Across the 7' (84") width it would be .138 inches or about 1/8".
Before you brought this up, I was going to splice the 4 sheets of 1/8" aluminum together tightly with a 1/8" x 6" wide plate across each seam with buck rivets to make a very solid and integrated floor, but it seems that an expansion joint filled with elastic material like Vulkem would be in order just like you would do for a big tile surface. If I expanded the holes by just a bit more than 1/16" and used washers, it would seem to give it the required room to expand and contract. If the main sheets are kept free to "float" then the expansion across each 4' length is a much more reasonable .079" or just a bit more than 1/16" A bad diagram of a way to join two pieces is shown below.

--------- T ---__---T------------ Main floor plates 1/8"
....... --- l ----------l-- splice 1/8"

The joint on the right would be tight fitting and buck riveted together.
The joint on the left would have enlarged holes to allow for horizontal movement with temperature changes. The gap would be filled with a bead of Vulkem.

As an aside, the thermal expansion coefficient of wood is 2-3 microinches/inch/degF which means that it would have a somewhat smaller but still significant differential expansion with steel resulting in a little less than 1/4" for 200 F difference. I don't think I've heard of problems from this, but wood is inherently more forgiving than metal. I also wonder if this has caused any bellypan problems in the past??
Tim

[timzog]

Originally Posted by MarkR

Also, have you figured how the torsion box "closes" at the edges. Do you think possibly that the c-channel at the perimeter will provide enough rigidity? Seems like it might to me, but it's just a gut feeling.
MarkR

Hi Mark,
I forgot to answer your other question because your first one was so good. The edge of the torsion box will still be the curved banana wrap. For the area around the entrance which will have the most traffic, I'm going to build a relatively small grid (6-8" spacing filled with foam) of C channel to give it more rigidity. The rest of the edges won't ever have anyone standing there since there will be cabinets, beds, and seating around the entire perimeter so I am not going to not add much support there. The 5/8" plywood that was there didn't provide much support over the edges anyway without the shell to hold it up. I will fill it with foam so that will add some rigidity as well especially if it is glued to the floor. I may add some adhesive to all the foam before I put it together to increase the rigidity of the system. All the inside of a torsion box has to do it keep the top and bottom skins at a fixed distance so adhesive may help with that.
Tim

[timzog]

Started work on the bellypan.
Used 1/16" x 1 1/2" angle to frame around the front of the grey tank. Buck riveted the .0625 5052 sheet to the angle and attached it to the frame with 3/16 rivets.







Used 3/16" pan head rivets from vintage trailer supply to attach the .032 5052 bellypan to the frame. Used a 4 x 10 sheet cut into two 5' lengths to span the main frame members and leave 3" on each side which I will use to attach to the curved section of the belly wrap around the perimeter.

[Wabbiteer]

If you push the project outside and rivet only in full sun at peak heat of the day it's all shrinkage after that, pull everything up taut like guitar strings when it's -10°F. Okay, that's no fun, but it would beat locking stuff in place at -10°F and letting it storage soak all summer at 100°F

Looking good, glad you declined notching the front floor sheet curved cuts like sharks teeth...

[timzog]

Originally Posted by Wabbiteer

If you push the project outside and rivet only in full sun at peak heat of the day it's all shrinkage after that, pull everything up taut like guitar strings when it's -10°F. Okay, that's no fun, but it would beat locking stuff in place at -10°F and letting it storage soak all summer at 100°F

Looking good, glad you declined notching the front floor sheet curved cuts like sharks teeth...

100 degrees will be easy this summer. So will it not cause problems to have the aluminum shrink and tighten up? Does it have enough flexibility that it won't warp or start ripping out rivets?

[Wabbiteer]

Subfloor insulation and floor coverings will go a long way to moderating temperatures.

Probably best to have everything at some median temperature midway between the two extremes it will experience. Even with a sun-warmed shell and the camper on hot asphalt there is still 1/2 of the shell working as a heatsink - the time that would worry me is jumping a curb at 2AM in -30°F weather, or eating a Florida highway alligator semi-rig retread road hazard at 60mph @ 2PM in 130°F road conditions.

What is your spacing on the countersunk rivets, 2, 4, 6, 8 inches?

Your expansion differential from center point on the 8' width at 0.00656/in or 1/8" for 48"/200°F) may* rock the outer fasteners gently - I'd think double/triple up on the center line as a control point and let it go where it may. I don't see a tear situation, more like stretch and relax on select fasteners dependent on the precision they go together with.

I apologize, the mental image of pre-heating the frame & flooring sort of just escaped into the keyboard, it may have some merit but likely not enough to follow though on

[perryg114]

Tim why 5052 alloy, that alloy is not considered a structural alloy and it tends to have a low yield strength. It will tend to bend easily and permanantly. I would think 6061-T6 would be better for the floor since you want it rigid.

I like your idea of the aluminum floor. How do you plan to attach the ribs to the floor plate?

Perry

Originally Posted by timzog

So I got sucked into an extensive and productive discussion in another thread regarding floor materials. http://www.airforums.com/forums/f36/...ams-92263.html
In the meantime, I've purchased 4 sheets of 4x10 1/8" 5052 aluminum sheet for the floor and 0.032" 5052 aluminum for the belly pan. I bought 0.060" aluminum for the bellypan under the grey tank. I may reuse the existing banana wraps but I am not sure yet. They will go on after the shell is back on the frame so I'll be really happy to have that problem.
Tim

[Wabbiteer]

Tim why 5052 alloy, that alloy is not...

Shhh, now... Its actually just a precision template for the house sheathing chip board he'll really using, to make the yearly change-outs easier...

[timzog]

Originally Posted by perryg114

Tim why 5052 alloy, that alloy is not considered a structural alloy and it tends to have a low yield strength. It will tend to bend easily and permanantly. I would think 6061-T6 would be better for the floor since you want it rigid.

I like your idea of the aluminum floor. How do you plan to attach the ribs to the floor plate?

Perry

Because that was what my local supplier had, to be honest. 6061 would have had to be ordered or made for me which in my small quantities would have jacked up the price beyond my ever growing budget I think 5052 is a reasonable compromise between properties and price. With the additional supports I think it will be good enough, but I will be sure to let you know how it works out. I've started laying in the foam insulation and thin C channels and I think the system will be very rigid especially compared to the 5/8 plywood that was there before. Here are the first few pieces going in.



The U channels attach directly to the ribs so I will attach the U channel to the floor with al buck rivets plus some stainless bolts. I don't recall a point on the ribs for direct connection to the floor but I may be wrong.

[perryg114]

Well for the ribs to do anything they need to be attached to the bottom or top skin, preferably both. Flush rivets would be good or counter sunk stainless screws. You want to create an I-beam out of your materials. You have the stringers going in the right direction though. Spot welding would be ideal if you had the rig for it.

Perry