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HMS Beagle

Napa, California

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Posted: 05/25/21 02:20pm Link  |  Quote  |  Print  |  Notify Moderator

JoeChiOhki wrote:



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.


From an engineering point of view, square tubes of the same dimensions are stronger in every direction than round, and not by just a little: for example a 2" square tube with 1/16 wall is 70% stronger than a 2" round tube with the same wall (though only 20% stronger if bent on the diagonal). If the round tube is bigger or thicker, then sure.

Happijacks explanation must be out of an "abundance of caution". Suppose you had a camper with the CG 4 feet off the floor and 2 feet back from the front of the box. Most large campers would sell their soul to get the CG that far forward. To tip it to the balance point you'd have to get it 26 degrees nose down. With 4' of jack travel and a short box camper, you might just be able to manage that. Not sure why you would try, it's kinda like telling kids not to put beans in their nose.


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StirCrazy

Kamloops, BC, Canada

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Posted: 05/26/21 06:43am Link  |  Quote  |  Print  |  Notify Moderator

HMS Beagle wrote:


Happijacks explanation must be out of an "abundance of caution". Suppose you had a camper with the CG 4 feet off the floor and 2 feet back from the front of the box. Most large campers would sell their soul to get the CG that far forward. To tip it to the balance point you'd have to get it 26 degrees nose down. With 4' of jack travel and a short box camper, you might just be able to manage that. Not sure why you would try, it's kinda like telling kids not to put beans in their nose.


I am not rich enough to have electric jacks so I am constantly lifting the back end higher than the front and vise versa when loading and unloading as I dont have enough arms to pump all 4 jacks at the same time. I have checked to see how stable it is and it is real stable at a slight inclanation so I am not concerned with how I do it, but it would be nice to be able to do all 4 at once and eliminate that whole procedure.

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mkirsch

Rochester, NY

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Posted: 05/26/21 09:35am Link  |  Quote  |  Print  |  Notify Moderator

StirCrazy wrote:

HMS Beagle wrote:


Happijacks explanation must be out of an "abundance of caution". Suppose you had a camper with the CG 4 feet off the floor and 2 feet back from the front of the box. Most large campers would sell their soul to get the CG that far forward. To tip it to the balance point you'd have to get it 26 degrees nose down. With 4' of jack travel and a short box camper, you might just be able to manage that. Not sure why you would try, it's kinda like telling kids not to put beans in their nose.


I am not rich enough to have electric jacks so I am constantly lifting the back end higher than the front and vise versa when loading and unloading as I dont have enough arms to pump all 4 jacks at the same time. I have checked to see how stable it is and it is real stable at a slight inclanation so I am not concerned with how I do it, but it would be nice to be able to do all 4 at once and eliminate that whole procedure.


OBVIOUSLY we are not talking about, "If you raise the rear even a FRACTION OF AN INCH higher than the front, you will open a portal to hell and release Satan and all his demonic minions."

It has to be some significant amount. Why they don't specify, is because it's easier to say "Don't do it AT ALL!" and not leave it open to interpretation.

"Don't raise your camper more than 25 degrees," gives the end user ideas. Plus if the weight distribution of the camper is not "standard" that number will change. Let's say they loaded the cabover storage with bricks, and it tips over at 24 degrees.


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HMS Beagle

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Posted: 05/26/21 01:06pm Link  |  Quote  |  Print  |  Notify Moderator

But, if I load 2 pallets of bricks on the roof rack at the back, then I can tip it over the back jacks too.

Unfortunately in the modern society we live in, you can't just say "don't do anything stupid", because it assumes too much.

silversand

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Posted: 05/27/21 08:46am Link  |  Quote  |  Print  |  Notify Moderator

....round steel tubes vs. square: one resists torsional twisting; one resists load bearing when horizontal. But every application is complex, and situational.

....just adding to Matt's excellent explanation:

Also, remember that putting a (pay)load in a truck will drop the truck (and bed) from a few fractions of an inch, to 2 or 3 or more inches in the rear. Measure the slope of your truck bed before applying the truck camper load.....then after. The unloaded truck bed will sit quite a bit higher in the rear, and if your truck camper nose is a bit low, when you pull the truck forward whilst unloading, the rear bed surface may "beach", potentially severely "bending" the jack leg(s).....


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HMS Beagle

Napa, California

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Posted: 05/27/21 09:33am Link  |  Quote  |  Print  |  Notify Moderator

There is no mystery to the engineering of steel tube, round, square, or otherwise. Both shapes resist torsion and bending. And a square tube will resist both more bending, and more torsion (and more compression while we are at it) than a round tube of the same dimensions. This is very well worn and reliable science that can be found in any properties of materials textbook.

I think these myths stem from the fact that using a given amount of material, you can make a round tube that is slightly stronger than a square one. In other words, the same amount of material used to make a 2" square tube could have been used to make a 2.5" round tube, and the round tube will be stronger. But at the same dimensions - 2" tube to 2" tube - the square tube is stronger.

JoeChiOhki

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Posted: 05/29/21 08:48pm Link  |  Quote  |  Print  |  Notify Moderator

HMS Beagle wrote:

There is no mystery to the engineering of steel tube, round, square, or otherwise. Both shapes resist torsion and bending. And a square tube will resist both more bending, and more torsion (and more compression while we are at it) than a round tube of the same dimensions. This is very well worn and reliable science that can be found in any properties of materials textbook.

I think these myths stem from the fact that using a given amount of material, you can make a round tube that is slightly stronger than a square one. In other words, the same amount of material used to make a 2" square tube could have been used to make a 2.5" round tube, and the round tube will be stronger. But at the same dimensions - 2" tube to 2" tube - the square tube is stronger.


I was thinking more specifically to point loading in the classic square vs a circle stress format.

Happijacs have notoriously buckled from side loads at the point where the outer tube is applying sidewall pressure to the inner jack tube, where as similar round tube jacks have bowed and deformed, but not completely buckled in on themselves (they've taken on a curve, like bending a roll cage).

They haven't been known on this forum as "crappijacs" for nearly two decades for nothing, between their tube wall weaknesses and the sheer pin problem that would literally cause the camper to plummet to earth, and all of this BEFORE Lippert got ahold of the company, a company notorious for poor quality steel trailer frames.


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stevenal

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Posted: 05/30/21 07:45pm Link  |  Quote  |  Print  |  Notify Moderator

When picking up my 1st TC in 98, the dealer demonstrated loading. No motors on the HJs, so my help was needed. We lowered the TC until it was an inch or 2 off the bed, and even. Then we dropped the front until it made contact before dropping the rear. The slant of the uploaded bed combined with the front down 1st philosophy put the TC front well below the back while in this part of loading process. The jacks survived this and every other loading without failure. Dealer approved and time tested.


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HMS Beagle

Napa, California

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Posted: 05/30/21 09:27pm Link  |  Quote  |  Print  |  Notify Moderator

I hear ya, square tubes with their flat sides may have buckling modes that round do not - depends on the thickness of the wall. I've had Happijacks on two campers and I'd consider them about par for RV equipment, which let us be honest is an extremely low bar. And Lippert isn't the top drawer of that low set either. I've yet to have a Happijack catastrophically fail, I have had them slowly self destruct and need rebuilds or parts. My expectations of them - like other RV equipment - is low, so I treat them gently.

But you can find as many complaints about their competitors. Like many things in RV land, you have to build it yourself or adapt it from another industry if you want reliability and quality.

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