Andy was able to give me a measurement and was within 6 inches on my 69 tradewind (ehh I'll give it to him). On mine it was 101 inches back from the first rib, about a foot behind the rear vent, but not sure on a 68 since I think there was a body style change. I cut the hole myself, reinforced it, installed the AC all in a couple hours. If you have access to a couple sturdy ladders and some basic tools like tin snips and something to cut some aluminum stock to add bracing (sawzall or hack saw) then you should be able to do it. I'm a total rookie and when I got into it I realized how easy it was. I posted pics of it on the thread http://www.airforums.com/forums/f427...day-35176.html
Fabrication, in a word. The transverse pieces need to be curved, about 3/4" arch across 20". It's possible to shrink and stretch two complimentary "L" extrusions, then rivet their webs together to form an aluminum beam, but a nice piece of 2X lumber on a bandsaw is so much easier.
In addition, riveting aluminum braces in place would require the flanges to face toward the inside of the opening (bucked rivets, of course), which would result in a recess space all the way around.
Although not elegant, the wood works fine and should be dry if the A/C is installed correctly, so no rot.
Zep
__________________ MindsEyePhotoAirstreamDoctorPygmyKayaker "It must be laid down as a primary position and basis of our system, that every citizen who enjoys the protection of a free government owes not only a proportion of his property, but even his personal service to the defense of it." - Washington
Zep, I've been doing mental rehearsal on this in prep for installing one in our rig. One question I have is this: On the two wooden ribs running fore to aft, are they attached to the two aluminum traverse stringers fore and aft of the hole? Or do the four wooden ribs just attach only immediately around the hole?
Lynn
Zep, I've been doing mental rehearsal on this in prep for installing one in our rig. One question I have is this: On the two wooden ribs running fore to aft, are they attached to the two aluminum traverse stringers fore and aft of the hole? Or do the four wooden ribs just attach only immediately around the hole?
Lynn
Aluminum is far better than wood.
The stringers, for proper and adequate support, should be fastened to the fore and aft of the square hole, main bows.
Then 2 small stiffners should be added between the stringers, creating a 14" X 14" square hole.
Thanks, Andy, that's the fore-aft attachment info I was needing!
I probably will go with wood, though, given the bow in the roof on the older AS. Maybe I'll ante up for a big chunk of more rot-proof stuff for ribs.
Lynn
Interesting, I just added an A/C to my "59.
I found that I already had alum C channel running for & aft between the bows but about 1 1/2" away from each side of the 14" vent hole so I got 1 1/2" square alum tube (wall thickness 1/4") and used this to frame all sides of the 14" hole. There was not enough curve in the cross wise 14" to make a difference and this gave me solid framework where the A/C gasket is being compressed. Cut 1" holes for wiring with a hole saw.
...One question I have is this: On the two wooden ribs running fore to aft, are they attached to the two aluminum traverse stringers fore and aft of the hole? Or do the four wooden ribs just attach only immediately around the hole?...
Andy may be right about using aluminum and attaching the ribs that run fore and aft to the cross ribs, but I think the gain is marginal. If you do a good job installing the wood, tight screws and all, plus ensure that water can't get on the wood, it will last longer than you will. I think you'll find that if you merely bracket the 14" vent hole all around with 1-1/2 thick by 1-3/4" (the shell thickness), that after you screw the inner and outer skins to the wood you'll be able to do a pullup on the edge. It will easily support the a/c.
Besides, tell me how you're going to attach the longitudinal braces to the cross pieces (the ribs)? If you don't put some flanges in, then just running the braces up to them won't add substantial rigidity to the roof.
I have seen the same thing REGGIEMON has seen, eg, not much curve in some of the roofs. Don't have a clue why, as all the ribs should be the same curve. We just did Richard's a/c at the Albuquerque rally and I cut his cross pieces to have 5/8" or so arch across 18" and it wasn't enough--we had a very slight wrinkle in the outer skin because it wanted more arch. I think you need to trial fit the arch, but I recommend 3/4" of curve
Zep.
__________________ MindsEyePhotoAirstreamDoctorPygmyKayaker "It must be laid down as a primary position and basis of our system, that every citizen who enjoys the protection of a free government owes not only a proportion of his property, but even his personal service to the defense of it." - Washington
Andy may be right about using aluminum and attaching the ribs that run fore and aft to the cross ribs, but I think the gain is marginal. If you do a good job installing the wood, tight screws and all, plus ensure that water can't get on the wood, it will last longer than you will. I think you'll find that if you merely bracket the 14" vent hole all around with 1-1/2 thick by 1-3/4" (the shell thickness), that after you screw the inner and outer skins to the wood you'll be able to do a pullup on the edge. It will easily support the a/c.
Besides, tell me how you're going to attach the longitudinal braces to the cross pieces (the ribs)? If you don't put some flanges in, then just running the braces up to them won't add substantial rigidity to the roof.
I have seen the same thing REGGIEMON has seen, eg, not much curve in some of the roofs. Don't have a clue why, as all the ribs should be the same curve. We just did Richard's a/c at the Albuquerque rally and I cut his cross pieces to have 5/8" or so arch across 18" and it wasn't enough--we had a very slight wrinkle in the outer skin because it wanted more arch. I think you need to trial fit the arch, but I recommend 3/4" of curve
Zep.
Zep.
I agree that using the aluminum, does not offer far out benefits.
But, it does off a singular benefit that wood cannot possible give.
That wood, in a hidden area, can, because of moisture, gather mold. That mold then would, however slight, be in the exhaust air from the AC.
I don't think, anyone, would want to take the risk of having mold in the AC exhaust. There is no guarantee that it won't happen.
Bottom line, the aluminum is the only choice, especially for health reasons.
We have seen mold in that area in a few cases. To me, one case is more than I wish have to deal with.
One clue to this is not all AS trailers are the same shape.
One of the things we like about our 18 footer is the headroom and spacious feel to the interior.
I am going to show pictures of my 14" vent cut out but I am sure this will not apply to everyones trailer.
I agree with Andy on the mold. Living in South Texas on the coast with our constant humidity, it is a valid concern. (thanks for the new axle installation, Andy. This is one sweet towing trailer!)
First picture is looking aft. The bow is about 15" away & you see a flat "C " channel rivited in place by someone before me.
2nd & 3rd picture are side views showing "C" channel also installed by someone else with interior & exterior rivits
When I tightened down the A/C bolts the exterior surface would start to curve down ward.
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