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Old 02-20-2011, 04:36 AM   #21
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I think andy is referring to the issue that has been historically proven as true. It is not a permanently rigid teeter totter due to force being applied back there.

Putting a 50 pound bike 10 feet away from the center of the teeter totter results in 500 foot pounds of torque applied to the future hinge point ( assuming the rear end separation takes place and it is fully separated all the way until the axles)

When you hit a bump the torque applied is much higher.

The part of this that I believe is not entirely correct is that (mathematically at least) is that with even one rivet connecting the frame to the body, the body is helping out. Additionally, if the frame/body strength is actually enough that separation never occurs you are entirely correct.

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Old 02-20-2011, 05:18 AM   #22
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We purchased one of these. Expensive and it will only carry two bikes, but it is a great system.
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Old 02-20-2011, 06:30 AM   #23
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Jack, did you mount yours on the trailer or truck. That looks like a smart solution.

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Old 02-21-2011, 05:02 AM   #24
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Ours is mounted over the propane tanks on the trailer. Clamps to the "A" frame. The rack itself is removable and your left with two vertical tubes which are not in the way of accessing the batteries, etc. I also use a small step stool to be to lift the bikes onto the rack. Not difficult to do in my case. Jack
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Old 02-21-2011, 06:30 AM   #25
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When I was a kid...

Dad had a removable bike rack mounted to the rear bumper of our '72 31' Sovereign Twin. It was capable of holding two bikes. We used it on occasion, but eventually just placed the bikes inside leaning up against the front gaucho sofa. This was due more to convenience than to fear of rear end frame separation. It was just easier to roll the bikes into the trailer than fool around with the rack.

The brackets for the bike rack were eventually used to hold one end of the bungees used to hold the rear bath awning after the actual awning fixture wore out.

The trailer did get a pretty good case of rear end frame separation. Was that due to using the bike rack? Who knows as lots of other similar vintage Airstreams got the frame separation as well without bike rack installations.

I intend to use roof mounted bike racks on my Jeep if I take bikes along, or throw them inside the trailer like we did more often as a kid. I understand the physics that Andy and others talk about- but also like the mention of the spare tires and other gear the Caravanners loaded onto their rear bumpers on caravans.
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Old 02-21-2011, 06:58 AM   #26
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I don't think comparing what they did on the big caravans of yore to today's use is helpful. Consider that in 1959, they were not using trailers built in 1921. (which would be required to compare this to ME installing bumper mounted stuff on MY trailer in 2011.). I also don't have a mechanic following me around everywhere I go, and and entire factory at my disposal.

How do we know "they didn't have any problems?" From what I've read, they had a whole bunch of problems...but rotted floors wasn't one of them, and that is likely a key to the separation issues. No problems putting weight back there...until there's is movement possible, due to missing floor/broken bolts.
As someone else already mentioned, that can (will) happen eventually whether there's any extra weight back there, or not.

What I'd like to see as a solution is a method of attaching a rear receiver that doesn't put undue stress. In other words, what would it take to put a hitch back there, and NOT cause damage? long support arms, attached far forward on the frame? (I'm thinking of the custom receiver supports that Can-Am has done for unibody tow vehicles to distribute the stress). Beefing up the floor/frame attachments? how?
Restorers, mechanics, engineers: what exactly will it take so that I can carry bikes on the back of the trailer, without worrying about structural failures? price is no object...what'll it take?
(I'm sure that step 1 is "an eternally rot-proof floor"). what then?
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Old 02-21-2011, 09:13 AM   #27
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Not to take place of a response by someone who knows about this stuff, but would a 100 pound air-conditioning unit on the roof all the way to the back cause any concern? I would think not, because the weight would be distributed via the airstreams structure instead of it's back bumper.

If not, simply transferring some of the weight to the aluminum structure seems like it would make 100 pounds of bikes no big deal.

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Old 02-21-2011, 10:12 AM   #28
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Not to take place of a response by someone who knows about this stuff, but would a 100 pound air-conditioning unit on the roof all the way to the back cause any concern? I would think not, because the weight would be distributed via the airstreams structure instead of it's back bumper.

If not, simply transferring some of the weight to the aluminum structure seems like it would make 100 pounds of bikes no big deal.

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It's not the weight, but what matters is "WHERE" the weight is located.

Something related to this issue, is where is weight put on an aircraft?

As we all know, the tail end of any aircraft is kept as light as possible, therefore luggage or containers are never put at the rear end of any aircraft.

Yes, it could be done, but the wing would have to drastically change and be relocated. That then creates other weight and balance problems, as well as the center of gravity, within the fuselage.

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Old 02-21-2011, 12:50 PM   #29
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Andy, ironically after initial design, aft weight is actually helpful in an airplane. Increased weight at the tail reduces induced drag of the tail because the required tail down force ( like lift but pointed down ) is decreased due to the help of gravity. Sorry to sound like an airplane nerd.

My thought on the ac unit is that, like you said, the location and distribution of the weight makes it acceptable. That makes me wonder if you can transfer that weight to the structure via straps. I could swear I saw a guy on here that did exactly that by using straps from the window.

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Old 02-21-2011, 01:09 PM   #30
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Andy, ironically after initial design, aft weight is actually helpful in an airplane. Increased weight at the tail reduces induced drag of the tail because the required tail down force ( like lift but pointed down ) is decreased due to the help of gravity. Sorry to sound like an airplane nerd.

My thought on the ac unit is that, like you said, the location and distribution of the weight makes it acceptable. That makes me wonder if you can transfer that weight to the structure via straps. I could swear I saw a guy on here that did exactly that by using straps from the window.

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HowieE makes reference to using the window for support of his rack installation.

Bike Rack Hitch - Airstream Forums
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Old 02-22-2011, 06:18 AM   #31
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Thanks Kevin. That is the one I remember.

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Old 08-31-2011, 09:13 AM   #32
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Front of Tow Vehicle is My Vote

We added a hitch to the front of our F350 ($150 with a small labor cost I believe) allowing us to use our Thule Bike rack for 3 bikes or a small outboard motor rack. It also allows you to insert a cargo carrier - typically seen on the back of a SUV etc which was also good for hauling the kids bikes or even our large marine cooler. Easy to load and off load or top off with ice and cold beverages. Just be sure the clearance is right or you will crush something pulling into a gas station etc. I also had to remind myself often that the carrier was there so as to not pull in too close in a parking lot. Cabellas and others stock a folding aluminum version which you can tip up in front of your grill/bumper when not in use - like a brush guard. NOT TOO REPEAT the 5 million posts on the subject but dont even try and think you are the first person in history to figure out how to attach a rack at the rear of your AS - it will either screw up your trailer or cost you a small fortune in engineering costs. I once strapped a small trolling motor onto the top of my 68' bumper and drove a mere 500 miles - visible separation and damage. Very little weight but a whole lot of torque. The front mounted Arvika unit posted earlier looks slick!
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Old 08-31-2011, 10:29 AM   #33
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bumper attachments

THe weight added to the rear end of any travel trailer, typically causes frame separation, especially on an Airstream or Argosy.

The problem is called "moment arm".

Simply measure the distance from the most rearward axle, to the weight location.

As an example, lets say it's 12 feet.

Multiply the added weight then, by the 12 feet.

So, if we added a total of 50 pounds to the rear end, times 12, that equals to 600 pounds.

That is a dead weight, not in motion.

Then when the trailer is moving, obviously it hits bumps, here and there. When that happens, the 600 pounds can and does multiply as much as 5 to 6 times.

Now we have a rear end weight of 3000 to 3600 pounds.

Need more be said, that the Airstream products are not designed to take that momentary load.

Also, keep in mind that the frame DOES NOT hold up the shell, but indeed, the shell holds up the frame.

Andy
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Old 08-31-2011, 10:47 AM   #34
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I also added a hitch to the front of my airstream to carry bikes. The hitch was about $130 and it only has 4 bolts. Real easy to install. The first time we used it, I borrowed my brothers bike rack. It sat too high and made it difficult to see. I had to take all the seats off the bikes and put all the handlebars on the passenger side. I then decided to buy my own rack and modify it. Here is the one that I purchased. I had to drill a few extra holes in the upright to make it sit lower, and I had to drill another hole in the tilting part, to make the bikes sit level with the ground. Now I can see perfect. When the bikes are not on it, I can't even see the rack. I take the rack off when we are not on vacation. Here is a picture:

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Old 08-31-2011, 12:21 PM   #35
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I also added a hitch to the front of my airstream to carry bikes.

I carry our bikes the same way on our GMC 2500HD and did previously on our GMC1500.

On the 2500 however, like you I found that the rack carried the bikes way too high.

I cut down the rack and rewelded it and now pretty ,much all is hidden below the hood line. Just enough of the handlebars showing that I know the bikes are still there.

I did have someone once tell me it was not legal to carry the bikes up front because technically, they present a bit of an obstruction to the headlights.

Could be true I suppose if some LEO really wanted to be picky, they do have minor effect to the illumination I believe, but hardly enough to worry about and it is seldom that we are on the road towing at night.

In any event I have carried our bikes this way now for over 12 years with never a problem.

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Old 09-04-2011, 06:49 PM   #36
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As we all know, the tail end of any aircraft is kept as light as possible, therefore luggage or containers are never put at the rear end of any aircraft.

Andy
Hmmm i remeber unloading 100+parcels and bags from the tail of a Ups plane daily for 5 years. The smalls where loaded in bags so id guess average weight at 30lbs. 3000+lbs every day is not "never"
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Old 09-04-2011, 11:08 PM   #37
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Just a thought

Would anyone here advise me not to install a second air conditioner, located at the rear ceiling vent due to structural concerns?
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Old 09-08-2011, 10:45 AM   #38
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THe weight added to the rear end of any travel trailer, typically causes frame separation, especially on an Airstream or Argosy.

The problem is called "moment arm".

Simply measure the distance from the most rearward axle, to the weight location.

As an example, lets say it's 12 feet.

Multiply the added weight then, by the 12 feet.

So, if we added a total of 50 pounds to the rear end, times 12, that equals to 600 pounds.

That is a dead weight, not in motion.

Then when the trailer is moving, obviously it hits bumps, here and there. When that happens, the 600 pounds can and does multiply as much as 5 to 6 times.

Now we have a rear end weight of 3000 to 3600 pounds.

Need more be said, that the Airstream products are not designed to take that momentary load.

Also, keep in mind that the frame DOES NOT hold up the shell, but indeed, the shell holds up the frame.

Andy
Andy et al,

I've always seen this argument and agreed with it, but I wonder about the applicability on my trailer? 5'6" is the distance from the centerline of the leaf spring mounting points (which is then where the axle is as well), going back to the rear most part of the bumper. If I plan to put ~40# there including carrier, on such a short frame, and after having rebuilt and strengthened the entire structure with thicker plywood, more bolts, etc, it seems like there is a chance I might be able to have a rear carrier.

Until now, I had been planning to mount a front receiver hitch on the TV or build a locking track system in the trailer interior to mount the bikes on. Thoughts?
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Old 09-08-2011, 11:03 AM   #39
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Andy et al,

I've always seen this argument and agreed with it, but I wonder about the applicability on my trailer? 5'6" is the distance from the centerline of the leaf spring mounting points (which is then where the axle is as well), going back to the rear most part of the bumper. If I plan to put ~40# there including carrier, on such a short frame, and after having rebuilt and strengthened the entire structure with thicker plywood, more bolts, etc, it seems like there is a chance I might be able to have a rear carrier.

Until now, I had been planning to mount a front receiver hitch on the TV or build a locking track system in the trailer interior to mount the bikes on. Thoughts?

How did you strengthen the shell?

Remember, the shell holds up the frame.

Therefore is doesn't matter whaqt you did to the frame.

Physics, doesn't allow us to practice "seems like".

Andy
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Old 09-08-2011, 11:30 AM   #40
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Mikeandnora,

In some climates a second A/C is required. If done properly it will be supported by the superstructure of the trailer. Mine is the second link.

Follow these link to the install of a bedroom A/C. Also you can look at my pitures in my profile on how I did mine this spring.

http://www.airforums.com/forums/f205...tml#post839907

http://www.airforums.com/forums/f427...-in-75958.html
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