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Old 12-14-2020, 07:55 AM   #81
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Quote:
Originally Posted by waninae39 View Post
FYI

just like the FIAMMA rack, it best to have some upper support on the back ( ie close to the rear lights where the vertical AS internal frames are)

this helps resisting twisting and torque movement as your are driving.
the tongue moment will try to lift the front end as the bike moves back and forth

my 2 cent as a long term Professional Engineer
So, let me see if I understand this correctly.
There is in most cases 1,000 lbs sitting on the trailer tongue.
3 to 4 tons sitting on the axles
Therefore 125 lbs of hitch and bike combo bolted solidly to the rear end of the frame will whipsaw all of that mass back and forth.
Got it !
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Old 12-14-2020, 09:37 AM   #82
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Originally Posted by franklyfrank View Post
So, let me see if I understand this correctly.
There is in most cases 1,000 lbs sitting on the trailer tongue.
3 to 4 tons sitting on the axles
Therefore 125 lbs of hitch and bike combo bolted solidly to the rear end of the frame will whipsaw all of that mass back and forth.
Got it !
He's not wrong.

Geometry of structures and projection of forces, are completely different between what you point out. May be worth keeping an open mind.
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Old 12-15-2020, 12:13 PM   #83
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[QUOTE=pteck;2440663]He's not wrong.

Geometry of structures and projection of forces, are completely different between what you point out. May be worth keeping an open mind.[/QUOTE

Please !

I have spent 40 years of my life managing my own Infrtructure construction business.
Utilizing 3 heavy/wide load lowboys moving excavators weighing 165 k lbs to shovels and everyting else inbetween, building roadways to wastewater treatment plants. I also owned 25 semidumps so my daily life was a constant concern with loading and weights.
I have been towing my Airtsream all over the country with 2 bikes on a bike rack on back end for the last five years without any problems whatsoever.
What you are implying is complete nonsense scaring inexperienced newbies away from viable and much better options than the Fiamma bike carrier.
BTW for what its worth I am a civil engineer . What I learned about engineers along the way is that most are very rigid and loth being challenged.
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Old 12-15-2020, 01:06 PM   #84
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At the very least, it will promote rear end separation. For those that are not familiar with this phenomenon. Anything placed on the back of the trailer that hangs out will exhibit a cantilever type situation.

If you look at most rear Airstream frames, you would see reinforcement tabs under the frame where the shell meets. If you place load in the manner that was suggested, regardless if you loose control or not, you WILL begin at some point to see the body separate from the frame. There are only a few bolts holding it on back there and the cantilever effect will add unplanned stresses to that section of the trailer. This is why a special designed bike rack is sold.

I have seen others place a hitch but it's attachment point to the frame was further in from the reinforcement tab, negating the issue.

One other thing to point out, heavy machinery is not the same as a semi-mono alum shell with a few bolts holding it to a frame. Distortion will happen much sooner with alum than with heavy steel of construction equip.

If you contact the factory and ask them if this is recommended, the factory will give you a flat out no, don't do it, for the reasons outline here and possibly more.
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Old 12-15-2020, 01:24 PM   #85
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I am an engineer also. I agree with @franklyfrank

adding a weight at the back simply moves the horizontal centre of gravity. This can be offset by adding a similar weight an equal distance to the front. This is how a lever work

Add 1/2 the weigh double the distance is the same.

Its best to go to a SCALE and get 2 runs, with and without WD and sway.

then, do the same again with whatever load you add.

then you can make a decision with FACTS as to what weight needs to be added and where

always measure BEFore and After. Then you can make a real decision, not some NAG or estimate
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Old 12-15-2020, 02:31 PM   #86
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Originally Posted by waninae39 View Post
I am an engineer also. I agree with @franklyfrank

adding a weight at the back simply moves the horizontal centre of gravity. This can be offset by adding a similar weight an equal distance to the front. This is how a lever work

Add 1/2 the weigh double the distance is the same.

Its best to go to a SCALE and get 2 runs, with and without WD and sway.

then, do the same again with whatever load you add.

then you can make a decision with FACTS as to what weight needs to be added and where

always measure BEFore and After. Then you can make a real decision, not some NAG or estimate
So I guess it would be ok to put my small 250 pound dirt bike on a rear rack as long as I move 250 pounds of gear in cabin to the the front.

I think there might be a bit more to this.
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Old 12-15-2020, 02:31 PM   #87
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I've been following with some amusement. The 'engineers' point out that the Airstream frame is designed to work with the shell attached.
So, I think, won't the shell be attached when I'm adding my bike rack?
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Old 12-15-2020, 09:09 PM   #88
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There is a reason Airstream condones the Flamma carrier. Not at anytime will you find Airstream recommending a hitch be installed on the back of the trailer that does not connect north of the support tabs.

We can go round and round, but the proof is, I would encourage anyone having done this, or considering it to contact and open a support ticket with Airstream and you will quickly find out that attaching a connection in the methods that have been suggested, with all due respect to the engineers participating on this thread, will eventually lead to frame separation, where the shell slowly but surely begins to detach from the frame....again, contact Airstream technical support for the engineering details as to why it's not considered a best practice to do what I have seen here via the pictures. You may have several years where this does not seem to be an issue, however, over time, you may see that you have weakened the connection between the shell and the frame over time.

In the end, it's your trailer, and you can and will do what you feel is best, but when the body does eventually separate, you cannot say you were not warned- but please, don't take my word for it, contact Airstream directly and share what they suggest.

Unless Airstream changed something between all the conversations I've read on this subject, on this forum, I don't see any change, unless I see something in writing from Airstream saying you are good to go.
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Old 12-15-2020, 09:32 PM   #89
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Quote:
Originally Posted by waninae39 View Post
I am an engineer also. I agree with @franklyfrank

adding a weight at the back simply moves the horizontal centre of gravity. This can be offset by adding a similar weight an equal distance to the front. This is how a lever work

Add 1/2 the weigh double the distance is the same.

Its best to go to a SCALE and get 2 runs, with and without WD and sway.

then, do the same again with whatever load you add.

then you can make a decision with FACTS as to what weight needs to be added and where

always measure BEFore and After. Then you can make a real decision, not some NAG or estimate
So you as an engineer are willing to help people like me who are not engineers figure this out on a forum? That is an amazing gift you are offering. Thank you....
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Old 12-16-2020, 10:55 AM   #90
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When will Airstream provide a hitch mount as an alternative to the Fiama bike rack?
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Old 12-16-2020, 11:04 PM   #91
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This is a great topic. Airstreams in the past had hitches attached to the frame. Not sure why they stopped, but I have seen many hitches attached to the frame and the hitch end protrudes out below the bumper. Airstreams of portland installs these all day and all night for 750. I would rather have this system than the fiamma system anyway.

Just my pennies opinion
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