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Old 07-26-2016, 04:44 PM   #15
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It depends on the aircraft, our C-130 uses built up aluminum floorboards and they contribute to the structure of the airframe and are easy to repair. Our Gulfstream V uses Carbon Fiber and they are structural over the wing center section and have limited repairability and cost a small fortune. Aluminum honeycomb is popular also but again easy to puncture and inserts have to be potted in to attach anything. With Airstream its all about the cost and plywood is cheap. But I do agree with you that there are better alternatives out there other then plywood. Airstream will most likely change the floor materiel when they start to wet seal the seams, which is NEVER.

Sorry about Hijacking your thread Boothy. But Airstreams' process specs, and quality control, or lack of them, gets me riled up
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Old 07-26-2016, 10:07 PM   #16
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Originally Posted by Aerowood View Post
It depends on the aircraft, our C-130 uses built up aluminum floorboards and they contribute to the structure of the airframe and are easy to repair. Our Gulfstream V uses Carbon Fiber and they are structural over the wing center section and have limited repairability and cost a small fortune. Aluminum honeycomb is popular also but again easy to puncture and inserts have to be potted in to attach anything. With Airstream its all about the cost and plywood is cheap. But I do agree with you that there are better alternatives out there other then plywood. Airstream will most likely change the floor materiel when they start to wet seal the seams, which is NEVER.

Sorry about Hijacking your thread Boothy. But Airstreams' process specs, and quality control, or lack of them, gets me riled up
Haha no worries! I enjoy all these discussions, and get just as worked up over poor design and build! The majority of the RV industry is pitiful, maybe Airstream needs a few of us on the payroll

Made more progress today, will post an update shortly.
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Old 07-27-2016, 11:18 AM   #17
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Update-
Got the front frame section test fit yesterday, I'll be taping off my weld locations then going to pick up some por-15 to treat the frame with. I removed the loose rust with a wire cup wheel on my grinder and it cleaned up nicely. There was a bit of metal loss due to corrosion on the second to front outriggers where the bolts went through, but its not a deal breaker, the por-15 should take care of it.

To fit the front frame piece without removing the belly pan I had to cut it in half. I planned on that most likely being the case for the front and rear sections so I welded two cross members into place on each side of centerline. It took some coaxing with a rubber mallet to get it in nice and tight but I'm very happy with the result.
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Old 08-22-2016, 10:16 PM   #18
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Looks great!
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Old 08-23-2016, 04:01 PM   #19
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How did you bend the 5/8 x 5/8?

I think that this is a good idea to get the plywood inside the body.
How did you bend the metal to get such a smooth and accurate curve?
How difficult was it?
Did you double it up to get the extra width to match the channel? Would it have been too difficult to bend larger material.
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Old 08-23-2016, 05:43 PM   #20
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Boothy, Perryg114 brings up a good issue. Galvanic corrosion. It's much worse in a marine setting, but must still applies to airstreams somewhat. I don't know if it has been a problem with the long term experience of steel base frames and aluminium skins.
1. Do you plan on any isolation of steel from aluminium? 2. Does anybody know of these issues in a trailer setting , rather than on boats?
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Old 08-23-2016, 08:23 PM   #21
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Yes it happens all the time. It is one reason the bottom skins fall off the trailer. Water and different metals = corrosion. There is no such thing as a totally dry Airstream. The aluminum acts as an anode and corrodes. The is especially a problem at the steel hold down plate at the back of the trailer that is riveted to the aluminum skin.

Perry
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Old 08-24-2016, 08:13 AM   #22
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This reminds me of a question that pops into my head when we talk about rotten floors etc. What do aircraft manufacturers use for floor boards. Isn't is some kind of sandwich board with aluminum sheet top and bottom? Wonder why Airstream doesn't do something like that to permanently do away with the rotten floor problem and maybe lose some weight in the process.
Many smaller airplanes actually are made almost completely of wood (wings, ribs, fuselage, etc). The trick is to coat these woods with a moisture barrier and they look like new after 50 years. Spar urethane works great and it is very disheartening that anyone builds an RV floor without protection. If you notice Airstream is now coating all edges and the tops and bottom of the subfloor perimeter with a sealant. Simple? Hell yes and should be done from the get go.
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Old 08-25-2016, 12:37 AM   #23
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I think that this is a good idea to get the plywood inside the body.
How did you bend the metal to get such a smooth and accurate curve?
How difficult was it?
Did you double it up to get the extra width to match the channel? Would it have been too difficult to bend larger material.
I made a template out of ply based on the interior curves of the trailer and then mounted that template to a full sheet of 4x8 ply to create a rudimentary bending jig. Cut a few of the scraps up and make stops with them and you've got a pretty configurable setup. start with bending each corner from the center line of the trailer and brace it then weld it across and tack it together at center. You then have a completed single layer and basis to expand the jig and add the second/outer layer of square tubing.

Bending was very easy, I laid the setup on the flattest section of floor I could find and put my weight on the jig to hold it in place. Just wear kneepads. Surprisingly there was little to no twisting or distortion, if one uses care when welding.

doubling the material up achieved two things- strength, and ease of machining. When you double up the two squares you end up with a 1/8th I-beam in the center of subframe framing. I feel that it was the only way to get adequate strength. It is VERY difficult to bend rectangular material, and I could not find anywhere in the bay area with tooling for 5/8 square anything. Not to mention all 4 curves are different!
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Old 08-25-2016, 01:01 AM   #24
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Originally Posted by wdgwdg View Post
Boothy, Perryg114 brings up a good issue. Galvanic corrosion. It's much worse in a marine setting, but must still applies to airstreams somewhat. I don't know if it has been a problem with the long term experience of steel base frames and aluminium skins.
1. Do you plan on any isolation of steel from aluminium? 2. Does anybody know of these issues in a trailer setting , rather than on boats?
1. Yes. I pre-coated the entire subframe with por15 which will stand up to just about anything. Then I wrapped it in Poly insulating tape. If the metals cant touch, a corrosion circuit cannot occur.

2. Galvanic Corrosion depends on a lot of factors from humidity, salinity, and the amount and thickness of dissimilar metals in contact. While there are common practices each application is different. Im considering placing sacrificial zinc anodes along the bottom of the belly skin and frame rails so that the trailer frame doesn't turn the belly skin into swiss cheese.

I am a failed Mech Engineer and made it through material sciences so am familiar with galvanic issues. The airstream is parked about 100' from the wrath of the pacific near SF so this will come to play.

I've done some rough back of the envelope calcs and the corrosion cell could generate between 1-2V. The Al being the cathode and the steel being the anode in the varying thicknesses it would take a VERY VERY long time for substantial corrosion to occur IF the trailer is kept sealed and maintained. This frame is not an excuse to not maintain, seal, etc.
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Old 08-25-2016, 01:03 AM   #25
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Originally Posted by Kemblkr View Post
Many smaller airplanes actually are made almost completely of wood (wings, ribs, fuselage, etc). The trick is to coat these woods with a moisture barrier and they look like new after 50 years. Spar urethane works great and it is very disheartening that anyone builds an RV floor without protection. If you notice Airstream is now coating all edges and the tops and bottom of the subfloor perimeter with a sealant. Simple? Hell yes and should be done from the get go.
Fascinating stuff! Amazing the things straight grain wood can do!
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Old 08-25-2016, 01:12 AM   #26
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Update-

Trailer frame has been completed.

Added extra outriggers and bracing to maintain rigidity offered by ply tied into trailer frame.

Center section of trailer has no subframe cross supports so it will be easier to deck out in one run.

Everything worked out awesome. The added cost for the steel and consumables was about 120$ and about 20 hours of additional time.
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Old 08-26-2016, 01:16 PM   #27
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Great job

Thanks for sharing and your detailed reply. You have done a great job and I may very well take inspiration when I build the chassis on my 1949 Curtis Wright.
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