Bracing Frame on 1706FB?

Trout One · 12-06-2021, 07:45 PM

Just revived an electrical thread focusing on providing power while off-grid and it got me to thinking about strengthening our 1706FB's frame to allow us to go farther off into the wilderness at far less cost than a Black Series trailer.

What has me thinking about this are the various threads about carrying more weight on the rear bumper and how folks have reinforced - or replaced - their bumpers with welded-in square steel tubing.

I'm wondering if three square steel cross members welded in - one just aft of the hitch frame welds, one replacing the bumper, and one somewhere in between based on where it would fit around the axles, would provide more stiffness and prevent a lot of frame and b ox twisting that comes from our journeys over Forest Service or BLM roads.

Has anyone tried this? I'm sure there's some significant labor cost involved but am wondering if anyone has added any crossmembers to their C-channel framed Winnebago TT? Or considered it and rejected the idea for some valid engineering reason?
Many thanks!

R_Lefebvre · 12-07-2021, 04:53 AM

I have thought of this too. If you were to add tubing cross-members under the existing frame, IMO, it would add only minimal stiffness. Much better to weld them in the middle of the frame longerons. But that would be hard, and still, not a big improvement.

IMO, it would be easier, and far better, to build a twin frame out of 2x2, 2x4 or 2x6 box tubing, complete with some crossmembers, and weld that right underneath the existing frame. Would weigh a bit, but that would make it about as good as most of the off-road trailers.

It wouldn't even have to change the ride height of the trailer, if you consider they're already sitting on 6" spacers.

RocknRoll · 12-08-2021, 05:19 AM

From what I've seen, the Black Series has independent suspension complete with shock absorbers. IMO, welding cross members will only stiffen up the frame likely causing structural delamination's.

R_Lefebvre · 12-08-2021, 05:30 AM

Why would stiffening the frame cause structural delamination?

RocknRoll · 12-08-2021, 07:55 AM

Quote:

Originally Posted by R_Lefebvre

Why would stiffening the frame cause structural delamination?

I have some limited mechanical design experience, so here goes...

Simply, the frame will tend to absorb shock if allowed to flex, thus limiting shear stress. Especially true using unlike components (steel, wood and glue). Too much flex is obviously not good either. The Black Series has shock absorption to assist with the heavy, reinforced frame and allow the rig to take on uneven roads.

My trailer has already experienced multiple areas of delamination (counters to walls) and I have only traveled interstates. I can only imagine how much worse it would be if the frame was any stiffer.

I apologize in advance if I am off base, but something tells me I'm not.

R_Lefebvre · 12-08-2021, 03:20 PM

Ok I see where you're coming from, and you're not totally off-base. It's a common idea that many people have. Even some mechanical engineers.

I have quite some experience in this area previously being a Ford engineer, and now a naval shock survivability specialist.

So yes, if the system was designed such that the frame is supposed to actually act like a spring, then I'd agree with you. However, I would argue that that's a bad design right from the outset. They used to design cars like that, but they stopped doing it way back the 90's. Things that aren't supposed to move, should be designed to not move. And things that are supposed to absorb shock, should be designed to absorb shock in an intelligent way. There are some super complicated machines that are designed with controlled flex, like F1 cars. But I don't think that these things are engineered with anything like that amount of rigor.

Honestly, I really don't think that the RV puts any thought into this at all. ie: it's hard to screw up their design, because they didn't design it in the first place.

I mean, I imagine LCI did engineering on their frames to ensure that they will not fall apart, if subjected to the loads they are rating them for. But I don't think Winnebago did much engineering to design their camper bodies to work with the LCI frame characteristics. They designed the floor plan, and then just build them, based on the general experience they have building trailers for decades.

Anyway, I don't really plan on doing this at all I don't think. I suspect it would all fall apart no matter what you do to that frame. The rest of the camper just isn't made for it.