Mello Mike wrote: Thanks, guys. Yes, those pics do help, but I'm still not seeing what's supporting all that weight in the overcab area, especially on the bottom. That's really the one thing I have trouble wrapping my head around. I guess I need to be an engineer to figure that out, LOL.
Don't have to be an engineer or physicist, but one does need to understand cantilevered structures. (something that 'sticks out' from it's support structure) Many bridge sections are cantilevered.
To greatly oversimplify, you can imagine the top of the body 'pulls' on the top of the cabover, and the bottom of the body 'pushes' on the bottom of the cabover. The push and pull creates a torque on the cabover, which is equivalent to a lifting force at the bottom front of the cabover.
A pair of cantilevered 'structures' occur in over half the population.
Mello Mike wrote: Thanks, guys. Yes, those pics do help, but I'm still not seeing what's supporting all that weight in the overcab area, especially on the bottom. That's really the one thing I have trouble wrapping my head around. I guess I need to be an engineer to figure that out, LOL.
Don't have to be an engineer or physicist, but one does need to understand cantilevered structures. (something that 'sticks out' from it's support structure) Many bridge sections are cantilevered.
To greatly oversimplify, you can imagine the top of the body 'pulls' on the top of the cabover, and the bottom of the body 'pushes' on the bottom of the cabover. The push and pull creates a torque on the cabover, which is equivalent to a lifting force at the bottom front of the cabover.
A pair of cantilevered 'structures' occur in over half the population.
Thanks, Cal. The lightbulb clicked on. I think I understand now.
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Mello Mike wrote: Thanks, guys. Yes, those pics do help, but I'm still not seeing what's supporting all that weight in the overcab area, especially on the bottom. That's really the one thing I have trouble wrapping my head around. I guess I need to be an engineer to figure that out, LOL.
Don't have to be an engineer or physicist, but one does need to understand cantilevered structures. (something that 'sticks out' from it's support structure) Many bridge sections are cantilevered.
To greatly oversimplify, you can imagine the top of the body 'pulls' on the top of the cabover, and the bottom of the body 'pushes' on the bottom of the cabover. The push and pull creates a torque on the cabover, which is equivalent to a lifting force at the bottom front of the cabover.
A pair of cantilevered 'structures' occur in over half the population.
"structures"
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Could someone here show Mike an (FEA) 2 dimensional drawing of a truck camper wall (with all finite elements: mesh, nodes, etc...make material properties real simple, set boundary conditions, then apply a load), then run it, and take a screen shot?
Nothing like FEA to describe load paths, and areas of stress to describe how the cabover stays supported...a photo is worth a hundred million words
Here is a site for DIY truck camper showing framing:
http://fareforwardtravellers.wordpress.com/2010/07/04/a-home-made-self-designed-truck-camper-part-two-the-design/
SkipJ
1992 Airstream B-190 van
1989 Airstream 25' Excella Trailer
Outfitter Apex 9.5 Truck Camper Ford F-350 Diesel 4x4
In addition to what is described above, my Weekender also has 2 metal straps that wrap from the underside of the cabover against the bottom of the camper all the way over the top and along the top to the back of the camper. It was one of the selling feature I liked when I bought a new one in 1996, and one reason I looked for a similar one when I bought this one used. Sorry Mike .. no photos
Dak
1995 Weekender model 910 extended cabover
Calvin, the 1996 creampuff Chev Silverado 3500 extended cab dually
The cabover design uses a cantalever method to support the load. While not as obvious in a newer metal framed unit where less material is needed, in an older wood camper, how it works is far more obvious.
What actually supports the load is the top stringer near the roof, it is tied into the wall a long ways back from the front wall, making it work in a fulcrum fashion.
Because the fulcrum point is far forward, the front wall and the overhanging piece that supports the load stretches in some cases all the way to the rear, the load carried is supported over a longer distance.
Everything below the bigger top piece simply acts as part of a truss, giving the wall rigidity and bearing the load of the cabover floor.
In a tubular frame design, the principle still applies somewhat, but depends more upon a narrow tube truss style construction to spread the load through the various pieces of the frame vs a laminated cantilever truss to bear the load.
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Also, if the side wall is one continuous piece then that will provide a heck of a lot of structural support. Think of it like a house of cards - a playing card can support virtually no weight when flat (just bends), but stand it on its edge with other cards at an angle to it to prevent it folding over, and it will take a much greater weight.
If you tried to support the cabover weight only on the walls (if you had some weird open-air camper) the walls would twist and the cabover would sag, but adding the front wall and roof plus structural timber prevent that twisting keeping the plywood taking the load in its strongest direction.
For me the wings of the camper are more impressive since it is only the back wall and front wall that offer the type of support that the sidewall offers for the cabover - so I guess in this case the framing needs to take more of the load.
Steve.
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