Adding scissor jacks for side to side leveling

[vtraudt]

My Forest River Salem has electric 'stabilizer' jacks (pivot, won't work for side/side leveling even IF they were strong enough). And the usual front A frame jack.

I do NOT like to drive onto (2x6, lego blocks, curvy plastic thingies, etc). I rather put the trailer exactly where I want it, THEN do all the leveling.

Front/back leveling with the front A frame jack is no issue.

For side to side, I would like to add scissor jacks on (or near, 3/4 points, else) the main frame at each corner. From this weeks stay, it seems that most (all?) not so new trailers have just that. I watched dozens setting up (some with hand crank, some with power drill/impact).

My trailer has a max weight of 7000 lbs.
The main rails are one piece, going from front to back (no welds, no steps).

a) is it ok to 'lift' at the ends or near the ends of the main rails?
b) with theoretically 1/2 of the weight (3500 lbs) on one jack, should I pick 3500 lbs jacks, or go even higher?

I am not sure yet if I will permanently mount (if it works, I likely will), either weld on or bolt on (only reason not to would be weight/inertia added to the rear.

Also, if it works, I would REMOVE the electric stabilizers (the jacks will level AND stabilize) and maybe use the MOTORS (2 on hand. would by 2 more) and add 2 more switches for 'electric' leveling (not AUTO leveling).

Does someone have experience with this modification?
Concerns, suggestions, ideas?

[JRscooby]

vtraudt wrote:

Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car)

You must have some weird trailer. Other than the ones with floating tongue, any of the hundreds, if not thousands of trailers I have been around, jack the front up, the rear goes down. When pivot on the suspension, there is no force to flex the frame.

[vtraudt]

Huntindog wrote:

People also ask
What is a cambered chassis?
In the structural engineering world, camber is known as having a slight arc or bend induced in a beam.

Yes, cambered means using a pre bent beam.
Take a piece of steel, and bend it over your knee. Now it cambered.
Adding weight of top of that piece of steel, and it gets flatter (fi the pre bent was up).

Putting some welding lines on top of a piece of steel will induce stress, and bent the piece of steel. EVERY weld does that. That is why when welding pieces of steel together, the welder is using a certain sequence to equalized the bending if a straight, NOT bent work piece is desired at the end.

You could also use a TORCH and heat up one side of your beam, and then quench (to induce thermal stress). If you have a high carbon content steel, you could actual HARDEN that material (think knives and swords).

That bead of weld - while bending the beam for the intended purpose - does NOT make it stiffer. Sorry.

[Huntindog]

vtraudt wrote:

Huntindog wrote:

[img] Click For Full-Size Image.[/img]

The few lines of surface welds induce some heat stress to the beam, which then bends up. This helps to end with a someone flat beam when load is applied and axles put underneath to push up.
It does NOT add any strenght. It only changes the bending line (crooked before weight, somewhat raight when loaded 'dry', somewhat crooked again when additional load is added (full tanks, food, storage, stuff on the rear bumper, stuff on the A frame, etc).

There may ONE very special/rare load condition when this beam is STRAIGHT. For practical terms, it will NEVER be straight. The amount of bending depends ONLY on a) the stiffness of the frame (fixed, and NOT influenced by the pre bending) b) the load and load distribution.

Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car), will add equal (but in reality less) than the normal static flex. Less, because A the axle is not in the middle of the lifting point and be the load is heavier on the front section ('tonque weight').

So lifting on the rear corners will ADD static bending (in the opposite direction. NO QUESTION.

The AMOUNT of bending could be the range (but opposite direction of the 'empty load' (the weight of the chassis itself, plus weight of the empty 'house'). In my case: 4400 lb weight empty, assumpe 2200 on 'rear' half. Lets call this the 'flat static' (assuming pre bend frame to make it 'flat' with this load). Now adding 120 gal of fluid (black, grey , fresh water) (on earth, roughly 1000 lbs) near the rear bumper. That ADDS 50% to the static bend.

Now we bounce it over a speed bump at 3 g. That is now an additional 2 g or 2000 lb near the rear bumber for a total of 3000 lbs. That is 1.5 TIMES the bending amount of the static 'assume flat with pre bent beam).

Now if we push UP the rear end of the empty trailer, that is 2200 lbs. This will result in roughly 50% LESS bending as the 'bump' with full tanks'.

Ditto, if the trailer is full (here: 7500 lbs, or 3750 on the rear portion), if we lift the rear, the bending is about equal to the amount exerienced during every 3G bump no the road (but only done once every time to jack it up, so say one per vacation, vs xxxx during driving).

Just some perspective on the issue.

Your perspective...... Why won't you try the experiment I suggested? Perhaps you do not want to see another perspective?

As for it not adding any strength, see the exerpt from my previous google quote:
Cambering beams allow smaller beams to be used in place of larger beams to support the same load.May 29, 2016.
(that is a very cost effective way of making an RV lighter.)

I am done here. It is obvious that you will not be detered.
As always, your money, your choice

[vtraudt]

Huntindog wrote:

[img] Click For Full-Size Image.[/img]

The few lines of surface welds induce some heat stress to the beam, which then bends up. This helps to end with a someone flat beam when load is applied and axles put underneath to push up.
It does NOT add any strenght. It only changes the bending line (crooked before weight, somewhat raight when loaded 'dry', somewhat crooked again when additional load is added (full tanks, food, storage, stuff on the rear bumper, stuff on the A frame, etc).

There may ONE very special/rare load condition when this beam is STRAIGHT. For practical terms, it will NEVER be straight. The amount of bending depends ONLY on a) the stiffness of the frame (fixed, and NOT influenced by the pre bending) b) the load and load distribution.

Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car), will add equal (but in reality less) than the normal static flex. Less, because A the axle is not in the middle of the lifting point and be the load is heavier on the front section ('tonque weight').

So lifting on the rear corners will ADD static bending (in the opposite direction. NO QUESTION.

The AMOUNT of bending could be the range (but opposite direction of the 'empty load' (the weight of the chassis itself, plus weight of the empty 'house'). In my case: 4400 lb weight empty, assumpe 2200 on 'rear' half. Lets call this the 'flat static' (assuming pre bend frame to make it 'flat' with this load). Now adding 120 gal of fluid (black, grey , fresh water) (on earth, roughly 1000 lbs) near the rear bumper. That ADDS 50% to the static bend.

Now we bounce it over a speed bump at 3 g. That is now an additional 2 g or 2000 lb near the rear bumber for a total of 3000 lbs. That is 1.5 TIMES the bending amount of the static 'assume flat with pre bent beam).

Now if we push UP the rear end of the empty trailer, that is 2200 lbs. This will result in roughly 50% LESS bending as the 'bump' with full tanks'.

Ditto, if the trailer is full (here: 7500 lbs, or 3750 on the rear portion), if we lift the rear, the bending is about equal to the amount exerienced during every 3G bump no the road (but only done once every time to jack it up, so say one per vacation, vs xxxx during driving).

Just some perspective on the issue.

[Huntindog]

valhalla360 wrote:

Huntindog wrote:
It certainly is what cambering is. Do some googling as I did. There is more than one way to do it. But I found articles of some really big semi type stuff being cambered by welding. In addition at one time, Northwoods RV had a picture of welds on one of their frames stating it was cambering for more strength. I also toured the Palomino Sabre factory back in 2010 when I bought my Sabre. I took a lot of pics. One of them shows the cambering welds. I have that pic, but I haven't posted a pic in so long, I forgot how to do it

And welding certainly does change the way a length of steel feels.
I tried it and felt it it myself. If you still don't believe me.... Break out a welder and see for yourself.

Flatbed semi's, the beams are often cambered. If you see them running empty, the curve is easy to see but they are built for many tons of load. Far different from your average travel trailer.

I've seen a fair number of travel trailer frames and not seen cambering...at least not enough to visually see anything. They will sometimes reinforce where the axles connect but that's different from cambering.

I suspect what you are confusing is looking at the strength of flat sheets vs an I or box beam working together but that's different from cambering.

Google has a LOT of info on it. This was the first hit:

People also ask
What is a cambered chassis?
In the structural engineering world, camber is known as having a slight arc or bend induced in a beam. Positive camber is when there is a hump in the center of the beam, with its shape resembling a frown. ... Cambering beams allow smaller beams to be used in place of larger beams to support the same load.May 29, 2016.


Have you broken out your welder yet to see for yourself?

I encourage you to do so. All you need are a couple pieces of fairly long angle steel. I used 16 ga 1.5" x 2" x 10'. One you run weld beads on similar to the picture I posted of my Sabres frame. the other one is just your baseline piece. Run the beads and then compare the straightness, and feel of the cambered piece to the uncambered piece.This is the pic of some cambering welds on my 2010 Sabre: [img][img] Click For Full-Size Image.[/img][/img]

Do this and then get back to me.

[vtraudt]

valhalla360 wrote:

Flatbed semi's, the beams are often cambered. If you see them running empty, the curve is easy to see but they are built for many tons of load. Far different from your average travel trailer.

I've seen a fair number of travel trailer frames and not seen cambering...at least not enough to visually see anything. They will sometimes reinforce where the axles connect but that's different from cambering.

I have only inspected the frame beam of our Forest River Salem travel trailer from the axels forward. And it most certainly is just a very thin wall, flimsy open open profile (no square tubing beam for example) simple beam. NO WELDS, no pre bending ("cambered").

I assume a heat treatmend ("welding" as some form of heat treatment, or to induce some stress on one side) would cost more (the process itself, but also multiple material cost for a steel that is suitable for such treatment) than nice stiff box beam or for that matter the entire welded steel base of the trailer.

That kind of technology (and material) may be used in some fance 100k trailer, but not in the category I have experienced.

[valhalla360]

Huntindog wrote:
It certainly is what cambering is. Do some googling as I did. There is more than one way to do it. But I found articles of some really big semi type stuff being cambered by welding. In addition at one time, Northwoods RV had a picture of welds on one of their frames stating it was cambering for more strength. I also toured the Palomino Sabre factory back in 2010 when I bought my Sabre. I took a lot of pics. One of them shows the cambering welds. I have that pic, but I haven't posted a pic in so long, I forgot how to do it

And welding certainly does change the way a length of steel feels.
I tried it and felt it it myself. If you still don't believe me.... Break out a welder and see for yourself.

Flatbed semi's, the beams are often cambered. If you see them running empty, the curve is easy to see but they are built for many tons of load. Far different from your average travel trailer.

I've seen a fair number of travel trailer frames and not seen cambering...at least not enough to visually see anything. They will sometimes reinforce where the axles connect but that's different from cambering.

I suspect what you are confusing is looking at the strength of flat sheets vs an I or box beam working together but that's different from cambering.

[Grit_dog]

Op, so now you bought a set of wheel ramps and are just having a theoretical conversation about the design of trailer frames? Never even once tried jacking it up?
Love some of these threads on here!

[GrandpaKip]

vtraudt wrote:

GrandpaKip wrote:
Why not use Andersen types of levelers? I put the camper where I want it, put the levelers down, roll forward or backward a few inches, watch my level, and, presto!, it’s done.

I may give that a try. Are those type levels tire size dependent?
I have 14" tires.

I measured my tires, then cut a 4x6 to fit. Had to make one a couple inches shorter than the other to fit between the tires. Been using them for several years. I also mounted a level on the camper that I can see in the mirror.
I believe that the commercial ones are generic.

[JRscooby]

vtraudt wrote:


That same hammer hitting upward at the suspension points is also hitting DOWN on the frame along to the ends (pressing down so it does not fly to the moon).

Or looked at the other way: if there were no force on the beam pushing down, they wouldn't need a beam going to the ends.

Note: a beam to only hold static load could actually be tapering down assuming an even weight distribution.

You are right about everything you are saying here. The fact is the frame could taper to nothing at the end if designed that way. (I have seen flat-beds where the crossmembers taper to pretty thin at ends) But what you are talking of doing, replacing the hammer in center with a press on the ends is well outside what the design calls for.
Mounting jack close to the suspension will reduce that problem somewhat. But will still need stabs at the end. And then there is the other force you need to take into consideration. Most trailers, when unhooked, brakes thru wheels/tires keep trailer from moving front/back. When brakes won't work, we chock the wheels. When you jack up to level, all the force causing the trailer to roll will be twisting at top of jack

[vtraudt]

JRscooby wrote:

Well sure gravity is a force on the whole unit. But the force I'm talking about is the equivalent of a 7000 lb hammer hitting upward where the suspension mounts.

That same hammer hitting upward at the suspension points is also hitting DOWN on the frame along to the ends (pressing down so it does not fly to the moon).

Or looked at the other way: if there were no force on the beam pushing down, they wouldn't need a beam going to the ends.

Note: a beam to only hold static load could actually be tapering down assuming an even weight distribution.

With only support in the center (and evenly distributed load) the mechanical model is (two) cantilever beams:
https://www.epsilonengineer.com/uploads/7/1/6/9/71698693/__5809977_orig.png

[JRscooby]

vtraudt wrote:

JRscooby wrote:

But the design expects force applied upward from the suspension and tongue. That force increases and decreases, but the location does not change.

Nope!

The bad thing about gravity: it works everywhere.

The force is NOT induced just at the tongue and suspension. There is mass (force) induced into the frame at any point along the length of the house (as long as there is gravity).

Well sure gravity is a force on the whole unit. But the force I'm talking about is the equivalent of a 7000 lb hammer hitting upward where the suspension mounts. Depending on road speed and the height of bumps, that hammer may swing a short or longer stroke, but it always hits the same spot.

Years back I bought a 28 (IIRC) foot TT that had been parked in a barn for about 10 years. The 20 something that sold it told me "Dad always set it level, put the jacks down, so he could use to hide" I expected and found mouse damage. Planning to gut for office, so not a problem. What I did not expect was not a door or window worked right, including cabinet doors. Decided to build a flatbed. Removed all the appliances, cut house loose from frame, put straps on it to hold house down, took it to a landfill. Back to yard, started figuring what it would take to make that frame stiff enough. Pulled the axles, cut rest for scrap.

[Huntindog]

This is some of the cambering on my 2010 Sabre.
the cambering wasn't the focus of the pic, I just happened to capture it.

THe Northwoods RV pic I spoke or earlier Had a different pattern. It was like this: //////

[img] Click For Full-Size Image.[/img]

[vtraudt]

Yes, the entire structure constantly flexes and moves, particularly when driving. The static flex is only a fraction of the dynamic flex.

And loads are very much changing from empty/parked to (for example) full black and full gey tank and full fresh water tank, and heavy loads hanging off the rear bumper getting thrown up and down with 2 or more G gorces (120 gal of water, times 3 G (3 times gravity)= you do the math.

BTW: pre cambering does not increase the stiffness (bending resistance) of the beam; it is more a pre bending to end up with a fairly flat beam when some of loads have been added.

[Gdetrailer]

Huntindog wrote:

vtraudt wrote:

GrandpaKip wrote:

As said by HDog, frames are cambered and you really shouldn’t be screwing around with that.

No plans on screwing around with the frames, or change anything if they are cambered (need to check, haven't noticed; if so, would only be in the axle area, certainly not forwards/backward from there).

I would not be certain of that. They can induce cambering wherever they feel it is needed.

Typically trailer frames ARE precambered slightly before the trailer floor is installed.

Once floor and walls have been placed, much of the camber will have disappeared or flattened out.

Without precambering the weight of the trailer box would cause the frame to sag in unsupported areas adding additional stress to the trailer wall structure.

Travel trailer frames are also built with lighter weight materials than what you will find with say a open flat bed trailer. The wall structure acts as additional structural reinforcement to the steel frame. The two parts become stronger when married together than what they would be separate.

Because of that one must take into consideration that everything on the trailer is structural and supporting it in places that were never intended to be supported (like the ends of the steel frame) it will cause racking.

Granted, some racking will not cause harm, but how much is too much is the problem. Unless you are a structural engineer and are able to properly assess the materials in use, How it was assembled and what stress it can handle, it is best to stay away from adding additional stresses that it was not designed for..

I know that on one of my trailers, it was very easy to rack the frame enough that the entry door would not open or close. So, I learned from my mistake, and never repeated that mistake again by moving my stabilizer further away from the frame ends and only add enough stabilizer to stop up and down bounce cause by walking.

It is yours to do what you want, do as you will, damage it, don't blame me, you have been warned.