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Fishbreath

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Posted: 05/21/21 08:21am Link  |  Quote  |  Print  |  Notify Moderator

What is with all of the nasty comments to a new member? Here is a person asking a legitimate question and some old timers feel it is necessary to berate him.

Mt-Ed, please do not let these negative comments deter you from seeking advice on this forum. There are a lot of knowledgeable people here. Just remember that it is advice from the Internet and some of it will be speculation, conjecture, hallucinations and just plain BS. After you sift through the comments, you might just be able to come up with the correct answer.
If you feel that comments to your questions are not accurately answered, I would suggest contacting the manufacture for answers.
Good luck and welcome to the Forum

mt-ed

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Posted: 05/21/21 08:46am Link  |  Quote  |  Print  |  Notify Moderator

Fishbreath wrote:


If you feel that comments to your questions are not accurately answered, I would suggest contacting the manufacture for answers.
Good luck and welcome to the Forum


Thanks FB! Actually, the first place I went to was the mfgr.! I just thought I'd ask it on here as well, while I was waiting for the response from them. I intend to share their response to me on here once they get back with me. I'm more interested than ever to hear "their" response!

JoeChiOhki

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Posted: 05/21/21 02:37pm Link  |  Quote  |  Print  |  Notify Moderator

The logic I can see and its not just unique to Happijacks is the rear jacks in most cases have the tubes anchored the full length down the wall of the camper, allowing the camper to restrain the side to side movement of the jack tube. The fronts are only anchored on at a very small section of the tube turning them into giant fulcrums.

When you tip the nose higher the rear jacks are restrained by the camper itself and don't begin to flex to the side as the weight application changes.

When you go the opposite direction, the front legs have nothing to prevent them from flexing or twisting toward the rear, apply enough downward dog pressure and the jacks will either buckle or the anchor points will fail, because you've been applying a twisting forcing to that limited anchor area with a fulcrum. (Think of how using a cheater bar on a socket wrench amplifies the force at the nut or bolt, you're doing the same with your front jacks).


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bigfootford

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Posted: 05/22/21 09:13am Link  |  Quote  |  Print  |  Notify Moderator

JoeChiOhki wrote:

The logic I can see and its not just unique to Happijacks is the rear jacks in most cases have the tubes anchored the full length down the wall of the camper, allowing the camper to restrain the side to side movement of the jack tube. The fronts are only anchored on at a very small section of the tube turning them into giant fulcrums.

When you tip the nose higher the rear jacks are restrained by the camper itself and don't begin to flex to the side as the weight application changes.

When you go the opposite direction, the front legs have nothing to prevent them from flexing or twisting toward the rear, apply enough downward dog pressure and the jacks will either buckle or the anchor points will fail, because you've been applying a twisting forcing to that limited anchor area with a fulcrum. (Think of how using a cheater bar on a socket wrench amplifies the force at the nut or bolt, you're doing the same with your front jacks).


Exactly! Good explanation Joe!

Jim


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HMS Beagle

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Posted: 05/22/21 12:19pm Link  |  Quote  |  Print  |  Notify Moderator

I think the reason they say this is due to the potential for forward weight shift if carried to extreme. At normal angles, not a problem*. I don't think it is due to worries about bending the jacks, certainly carried to extreme you could bend the jacks, but you are nearly equally likely to bend them tilting aft as forward - the bending moment on the jacks is nearly the same - and they do not caution against tilting aft. It cannot be due to concerns about tipping over forward, it would be a highly unusual camper that would do that even at full jack travel.



* Take a 4000 lbs camper, vertical CG 4' above the box floor, 10' between jacks and longitudinal CG 3' back from box front. Level, front jacks take 2800 lbs. 5 degrees forward slope changes this to 3080 lbs. If the jacks are that close to failing you have many more issues to address. Yes, I am an engineer...


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mt-ed

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Posted: 05/24/21 04:42pm Link  |  Quote  |  Print  |  Notify Moderator

Well folks, as promised here is the official word from happijac....

If you raise the back of the camper higher than the front, you are displacing gravity on the camper. You are making the front end forward heaver which can cause the camper to fall forward.

I cut and pasted their response verbatim from their email.

Thanks for all the interest, input, advice, and conjecture everyone!!

jimh406

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Posted: 05/24/21 05:15pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks for posting their response.

That’s pretty funny. Funnier is that they thought they needed to add it to the manual.

Who wants to see how much higher they have to raise the rear of their TC to get it tip forward? [emoticon]

I’m wondering why they didn’t mention not putting one side higher than the other. [emoticon]


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JoeChiOhki

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Posted: 05/25/21 01:14am Link  |  Quote  |  Print  |  Notify Moderator

HMS Beagle wrote:

I think the reason they say this is due to the potential for forward weight shift if carried to extreme. At normal angles, not a problem*. I don't think it is due to worries about bending the jacks, certainly carried to extreme you could bend the jacks, but you are nearly equally likely to bend them tilting aft as forward - the bending moment on the jacks is nearly the same - and they do not caution against tilting aft. It cannot be due to concerns about tipping over forward, it would be a highly unusual camper that would do that even at full jack travel.



* Take a 4000 lbs camper, vertical CG 4' above the box floor, 10' between jacks and longitudinal CG 3' back from box front. Level, front jacks take 2800 lbs. 5 degrees forward slope changes this to 3080 lbs. If the jacks are that close to failing you have many more issues to address. Yes, I am an engineer...


I do also wonder if it has to do with Happijac's choice to use square tube jacks, as their jacks have been known to buckle at the pressure point between the outer and inner tubes before. Round tubing is naturally stronger by shape than square tubing and will take a good deal more strain without failing catastrophically than square tubing does.

mkirsch

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Posted: 05/25/21 05:58am Link  |  Quote  |  Print  |  Notify Moderator

mt-ed wrote:

Well folks, as promised here is the official word from happijac....

If you raise the back of the camper higher than the front, you are displacing gravity on the camper. You are making the front end forward heaver which can cause the camper to fall forward.

I cut and pasted their response verbatim from their email.

Thanks for all the interest, input, advice, and conjecture everyone!!


Um, okay? "Displacing gravity?"

In other words the person who answered your question had no clue. What they said is absolute nonsense. They just want you to go away.


Putting 10-ply tires on half ton trucks since aught-four.

mt-ed

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Posted: 05/25/21 01:34pm Link  |  Quote  |  Print  |  Notify Moderator

mkirsch wrote:



Um, okay? "Displacing gravity?"

In other words the person who answered your question had no clue. What they said is absolute nonsense. They just want you to go away.


Yes, I guess using happijacs bestows upon the user Super Hero powers! Haha. I pretty much felt dismissed. I'm really surprised by their response because they display this warning, in bold print, over, and over and over throughout their instructions. To me, such insistence would indicate failure to heed their warning would result in some catastrophic failure. Also, if it truly IS that important, how hard would it have been to put the "or else" clause after the "never" statement?

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