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Old 09-11-2012, 09:25 AM   #561
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I received last night a challenge to my calculations of the strain on the chain. I am delighted that someone took the time to create a thorough argument with a different calculation. He is probably right, but I need to work through it today in detail, and be sure I understand it totally.

If I was wrong, I will be delighted to have learned something new in such a short time! And if so, I will of course announce my error!
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Old 09-11-2012, 11:55 AM   #562
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Originally Posted by Kosm1o View Post
Here is a question for you engineers that are keeping up with this new Andersen hitch. I have read in threads about using a hitch such as the Equilizer that uses weight distributing bars of various strengths. Users have been warned not to use a size that is too large for the job as there is a danger of bending the A frame, particularly when towing through a large dip in the road as one might experience going into a gas station from the highway. Going through that dip causes, as I understand it, a lot of strain on the frame because of the way the bars are leveraging the weight distribution. Since the Andersen accomplishes this using a horizontal force, rather than a vertically downward force, is the danger of bending the A frame lessened ? or the same ? or greater?
The Andersen chains pull the tongue forward not down. There is far less bending force on the tongue than with a conventional WD spring bar hitch. The bushings also lessen the impact forces.
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Old 09-11-2012, 11:57 AM   #563
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Hello All. Thought I would chime in as some of my material is being discussed. Hope you don't mind--I am not an Airstream owner but I am an Airstream admirer.

I revised the table that shows the axle weights after I learned that my assumption that the urethane springs are 3" is wrong. They are actually 2 15/16". Since I determined the amount of compression by subtracting the compressed length from 3", the amount of compression was off by 1/16". That has been corrected in the revised table contained at the end of this post. I have previously published this revised table on the Lance Owners of America forums, but I don't think I ever got around to putting it on rv.net.

I was intrigued by mstephens' method for determining chain tension so I did some measuring and calculating yesterday.

The distance from the center of the front wheels to the center of the hitch ball is 155".

I have the 2" ball on my Andersen hitch. The distance from the center of the ball to the center of the chain plate is 6.5".

Per mstephens' directions in other posts, I divided 155 by 6.5 and determined that the leverage ratio is 1:23.85.

At 3/16" spring compression, 180 lbs was transferred back to the front axle. I multiplied 180 X 23.85 and, per msephens' directions, determined that 4293 pounds of force was placed on the hitch.

Dividing that by 2, the tension for a single chain is predicted at 2146 lbs.

However, if you look at my Andersen Weight Distribution Hitch Estimated Chain Tension chart that was contained in an earlier post by another forum member, the actual chain tension at 3/16" compression is 970 lbs.

The actual chain tension measured by the Sherline scale is less than half of that predicted by mstephens' method. Can I explain this? Nope. I do not have an engineering background (social sciences, actually). Have never even taken physics class. But I am pretty confident that I have reasonably accurate estimates of chain tension.

(I am having difficulty in uploading the image of the chart--will try in a separate post.)
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Old 09-11-2012, 12:03 PM   #564
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Here is the revised table:
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Name:	Andersen Chain Tension - revised.jpg
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ID:	167981  
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Old 09-11-2012, 12:28 PM   #565
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Bruce thanks for posting. I was going to try and message you through the other forum this afternoon. But looks like your on top of things.. All your data looks very sound and thanks for putting the time and effort into collecting it..

Was my assumption correct about you mounting your bracket to your frame?
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Old 09-11-2012, 12:29 PM   #566
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After doing a complete inventory of parts, my hitch is missing a major part, the ball, it's mount, and it's retaining ring.

And, the dealer I bought it from does not answer the phone.
Steve where you able to figure out why stuff was missing??? you get a hold of that dealer?
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Old 09-11-2012, 01:27 PM   #567
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Bruce thanks for posting. I was going to try and message you through the other forum this afternoon. But looks like your on top of things.. All your data looks very sound and thanks for putting the time and effort into collecting it..

Was my assumption correct about you mounting your bracket to your frame?
Yes, I did use the set screw hole. I purchased the Andersen hitch in February and the only available bracket was for 5 or 6 inch frames--my Lance frame is only 4 inches where the bracket needs to be. However, the Lance A-frame has two 3/8" holes that are 1 1/4" apart 29" back from the center of the coupler. I contacted Lance Customer Services who said it was OK to use them for mounting the Andersen bracket. I drilled out the threads from the 9/16 threaded setscrew hole, inserted a bronze sleeve bearing with an O.D. of 9/16 and I.D. of 3/8 (which fit perfectly), and drilled another 3/8" hole 1 1/4" above it. Then sawed off the excess material. Attached the bracket with Grade 8 3/8" bolts which have a sheer strength of 10,000 pounds and a tension strength of 12,000 pounds.

Bruce
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Old 09-11-2012, 02:50 PM   #568
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Here are pics of the Sherline scale in action and the Chain Tension Chart:
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Name:	Sherline Scale.jpg
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Name:	Andersen Chain Tension.JPG
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Old 09-11-2012, 03:19 PM   #569
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Steve where you able to figure out why stuff was missing??? you get a hold of that dealer?
Yes, I have determined what parts are missing, and have communicated that info to the seller, hitchanything.com, and they have not been responsive at all. First of all, they don't answer the phone, but they do return e-mails once a day aparently.

Having not gotten what I consider adequate response from them, I contacted Andersen directly since the hitch was drop shipped dirrectly from them. They seemed to be very interested in helping me, I have e-mailed them pictures of the box so they can file a claim with UPS, and are supposed to call me back with shipping info on the parts.

So at this point I can advise folks NOT to deal with hitchanything.com.
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Old 09-11-2012, 03:36 PM   #570
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Yes, I have determined what parts are missing, and have communicated that info to the seller, hitchanything.com, and they have not been responsive at all. First of all, they don't answer the phone, but they do return e-mails once a day aparently.

Having not gotten what I consider adequate response from them, I contacted Andersen directly since the hitch was drop shipped dirrectly from them. They seemed to be very interested in helping me, I have e-mailed them pictures of the box so they can file a claim with UPS, and are supposed to call me back with shipping info on the parts.

So at this point I can advise folks NOT to deal with hitchanything.com.
Thanks for the Info. Glad to hear Andersen is making it right..

I almost got mine online. but paid the extra $50 and got if from local guy. Sometimes this works out sometimes it doesn't. someone else had this problem too. Stuff missing when they got it. My local dealer didn't even know they had different models. He thought it was one size fits all. Now he knows better.
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Old 09-11-2012, 04:09 PM   #571
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Bruce H. thanks for joining us. From what I was thinking your tension sounds right. My thoughts are that the tongue pushing on the ball has the same leverage as the chains pulling so the force required by each chain would be cut in half from what mstephens said. Also some of the weight being distributed to the front axle is pivoted on the rear axle which would drop the force a little more.
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Old 09-11-2012, 06:19 PM   #572
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Originally Posted by Bruce H. View Post
Hello All. Thought I would chime in as some of my material is being discussed. Hope you don't mind--I am not an Airstream owner but I am an Airstream admirer.

I revised the table that shows the axle weights after I learned that my assumption that the urethane springs are 3" is wrong. They are actually 2 15/16". Since I determined the amount of compression by subtracting the compressed length from 3", the amount of compression was off by 1/16". That has been corrected in the revised table contained at the end of this post. I have previously published this revised table on the Lance Owners of America forums, but I don't think I ever got around to putting it on rv.net.

I was intrigued by mstephens' method for determining chain tension so I did some measuring and calculating yesterday.

The distance from the center of the front wheels to the center of the hitch ball is 155".

I have the 2" ball on my Andersen hitch. The distance from the center of the ball to the center of the chain plate is 6.5".

Per mstephens' directions in other posts, I divided 155 by 6.5 and determined that the leverage ratio is 1:23.85.

At 3/16" spring compression, 180 lbs was transferred back to the front axle. I multiplied 180 X 23.85 and, per msephens' directions, determined that 4293 pounds of force was placed on the hitch.

Dividing that by 2, the tension for a single chain is predicted at 2146 lbs.

However, if you look at my Andersen Weight Distribution Hitch Estimated Chain Tension chart that was contained in an earlier post by another forum member, the actual chain tension at 3/16" compression is 970 lbs.

The actual chain tension measured by the Sherline scale is less than half of that predicted by mstephens' method. Can I explain this? Nope. I do not have an engineering background (social sciences, actually). Have never even taken physics class. But I am pretty confident that I have reasonably accurate estimates of chain tension.

(I am having difficulty in uploading the image of the chart--will try in a separate post.)
Hi,
You are not crazy. My initial calculations missed an element which was pointed out to me by a very knowledgeable fellow yesterday. In my initial method, I neglected to subtract a torque element from the weight taken off the rear axle. So my initial calc was wrong.

As to the right calculation, I am looking at the revised calculation method sent to me, and a different calculation of my own, and trying to reconcile. I am glad you posted the measurements of your distance and the ball to plate, because with your table I can now see how each figures out. Did you do axle weights on your car? Was yours the Honda Pilot?

I'll be working on this later this evening. Probably the one sent to me is the correct one. It does yield a little less than half of mine.

I am glad that I was wrong, because I like the simplicity of the design, and may be interested myself.
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Old 09-11-2012, 06:55 PM   #573
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Hi,
You are not crazy. My initial calculations missed an element which was pointed out to me by a very knowledgeable fellow yesterday. In my initial method, I neglected to subtract a torque element from the weight taken off the rear axle. So my initial calc was wrong.

As to the right calculation, I am looking at the revised calculation method sent to me, and a different calculation of my own, and trying to reconcile. I am glad you posted the measurements of your distance and the ball to plate, because with your table I can now see how each figures out. Did you do axle weights on your car? Was yours the Honda Pilot?

I'll be working on this later this evening. Probably the one sent to me is the correct one. It does yield a little less than half of mine.

I am glad that I was wrong, because I like the simplicity of the design, and may be interested myself.
I believe his cat scale weights are around post #355
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Old 09-11-2012, 07:04 PM   #574
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Hi,
Did you do axle weights on your car? Was yours the Honda Pilot?

I'll be working on this later this evening. Probably the one sent to me is the correct one. It does yield a little less than half of mine.
Yes, the table re the Honda Pilot and the Lance 1575 trailer is mine. Two trips to the CAT scales at the Flying J west of Lodi. Multiple weighs each time--luckily, each reweigh (up to 4) is only $1.

Very much looking forward to learning about your new method. I never had a WDH before this one, so a lot of my emperical research was just an effort to understand weight distribution in general as well as the Andersen hitch.

Bruce
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