The Trunk

[bredlo]

Originally Posted by Wild-Air

...I'll slap it right back on after properly reinforcing the frame. For now, it'll sit on the ground until the dust settles.

I'm sure the concerns and warnings are valid - many of them stem from folks who've seen their share of Mods Gone Wild. Surely there've been lots of uneventful examples though, as well.

You might take a couple things as you continue to evolve the design:

1, Look at how Airstream has sidestepped frame limitations via their bike rack:


That corner bracing (which I'm guessing attaches to internal ribs) is probably worth considering, especially given the amount of weight you're dealing with.

Makes me curious if tying into the rib structure would help reduce the effects of polar moments, polar arms, or polar bears.

2, Look into modifications regularly made by Andy Thompson and crew up at Can-Am RV in London, Ontario. Granted, many of their frame mods are focused on unibody tow vehicles rather than ladder-type trailer frames. But they often extend typical bolt-on receivers forward via additional bracing, and welding them on vs. bolting. I don't know that it would make a difference in your situation, but if there's any way to move that imaginary pivot point of the receiver up towards the axle... do it.

I'm sure smarter people than any of us on this thread have thought about these things... but in the case of RV engineers they're likely having to consider the limits from corporate bean counters, the cost concerns, fearful insurance companies, and the likelihood that whatever extra capacity you design... there's sure to be an idiot who'll use it to kill himself.

You, on the other hand, only need to find the realistic limits of your trailer and your specific need. Good luck, and keep us posted.

[Inland RV Center, In]

Originally Posted by daveswenson

I think the key is reinforcing the frame. With all the talk of tail droop on here I'm nervous just filling up the rear storage that I have. I'd also be concerned about decreasing the tongue weight too much. If those issues can be solved I think your trunk is brilliant.

Reinforcing the frame, will only add to the problem.

First of all,keepin mind that the shell holds up the frame. The frame is a burden as it is the the monocoque method of construction.

Adding more weight, by beefing up the frame, will only add more stress to the fasteners that hold the shell and frame together.

Airstream does fasten the shell to the frame correctly. Adding weight to the rear end, becomes a added weight, which is a burden.

Also, remember that because of moment arm, adding a simple 100 pounds of weight to the rear end of a 31 foot trailer, is really adding about 1300 pounds, sitting still. When hitting a bump, that weight rapidly multiplies.

In short order then, damages will appear, that will not be covered by warrant or insurance.

Think of a "crow bar", if you wish. The longer the handle the more force you can exert. Same with moment arm. The point of last support, is the start of the measuring point.

Also, ever wonder why aircraft tails are lightly loaded, or else. Again, moment arm.

Bottom line, then is "IF" you beef up the frame, at the rear, you only add to the problem.

You also will be subtracting from the necessary tongue weight, which is not a good idea.

Andy

[daveswenson]

Originally Posted by Inland RV Center, In

Reinforcing the frame, will only add to the problem.

First of all,keepin mind that the shell holds up the frame. The frame is a burden as it is the the monocoque method of construction.

Adding more weight, by beefing up the frame, will only add more stress to the fasteners that hold the shell and frame together.

Airstream does fasten the shell to the frame correctly. Adding weight to the rear end, becomes a added weight, which is a burden.

Also, remember that because of moment arm, adding a simple 100 pounds of weight to the rear end of a 31 foot trailer, is really adding about 1300 pounds, sitting still. When hitting a bump, that weight rapidly multiplies.

In short order then, damages will appear, that will not be covered by warrant or insurance.

Think of a "crow bar", if you wish. The longer the handle the more force you can exert. Same with moment arm. The point of last support, is the start of the measuring point.

Also, ever wonder why aircraft tails are lightly loaded, or else. Again, moment arm.

Bottom line, then is "IF" you beef up the frame, at the rear, you only add to the problem.

You also will be subtracting from the necessary tongue weight, which is not a good idea.

Andy

I stand corrected.

[Wild-Air]

Thanks, Brad.

Doing some further digging into the weakness of the AS frame, I found that during the time Beatrice Foods owned them the frame rails went from 4" to 3". There were 31' Excella models with rear baths that were sagging pretty regularly. When the redesign happened in 2000, the frames were resized to their former cross section and the sagging problem stopped.

There are frame strengthening kits and tips out here, but they're for 30-40 year old trailers. Mine is 1 year old and still perky.

I'm going to dismount the trunk for now, but with every intention of reconnecting it when I have more confidence in the frame reliability arena. I'll probably contact AS and try to get through to an engineer (if they have one) so it can be hashed out. I think the idea and design is good, and my intended use if reasonable too - it's not for hauling 1,000 pounds of gold bullion or a bunch of rocks! Ha!

I'll let you all know how it comes along.

[SteveSueMac]

Originally Posted by Wild-Air

Thanks, Brad.

I'll probably contact AS and try to get through to an engineer (if they have one) so it can be hashed out. I think the idea and design is good, and my intended use if reasonable too - it's not for hauling 1,000 pounds of gold bullion or a bunch of rocks! Ha!

I'll let you all know how it comes along.

Please do. I think your idea and design are excellent - and not being an engineer myself, I have no idea about the separation impact others here suggest is imminent with the design. An AS engineer would obviously have the right guidance and who knows - maybe you're on to something they can incorporate as an option with some tweaking?

Good luck either way and congrats on your design.

[JamuJoe]

Wild-Air,
Nice job. We'll appreciate your sharing user experience and any feedback/advice that you receive from Airstream. There's more urban legend than fact on the topic. Airstream / Fiamma debunked some of that by offering the chassis/bumper supported rear bike carrier for newer models.

[perryg114]

Where is the bathroom on these newer trailers? That has alot to do with the loads. A rear bath is marginal anyway and you add more stuff to the rear you are asking for problems. If it is a rear bedroom or rear dinet then the loads back there are alot less.

Perry

[Wild-Air]

Perry,
The bathroom on mine, along with the black tank, is just forward of the wheel well. The kitchen and refer are basically above the axles. The only thing in the back is the dinette and overhead storage.

[perryg114]

That is going to help you a lot and you don't have a real long trailer either. I can't see your box being heavier than a full bath with storage thanks. You are probably talking 200lbs of extra junk even with empty tanks. If you have 5" tall frame members you are probably ok. If you have 4" frame members, I would worry. You can probably call Airstream to find that out.

Perry

[m.hony]

Originally Posted by Wild-Air

Thanks for your concern and expertise, Andy. The frame not being suitable to support the shell was not something I was aware of. I understood the shell formed somewhat of a monocoque due to the ribs being attached across the frame, but I didn't know the roof was a stressed member front to rear. I wonder if that's why my cabinets have never lined up properly.

I think the cabinets not lining up is more so because the trailers are basically hand built. No two are the same. They are autonomous beings. The workers build them as they go. You can see where they used a coping saw or jigsaw on the curved areas that meet the roof. As I study my trailer, nothing lines up. Stack windows, vista view windows, trim, roof airs, vents, doors, awning. The spacing of the ribs must not be exactly the same from one to the next and the workers finagle everything into place.

[ROBERT CROSS]

Originally Posted by m.hony

....... and the workers finagle everything into place.

What a perfect descriptive term...

I see an honest ad campaign on the way.

"Airstream....let us finagle you a great adventure."

Bob

[overlander63]

Originally Posted by ROBERT CROSS

What a perfect descriptive term...

I see an honest ad campaign on the way.

"Airstream....let us finagle you a great adventure."

Bob

We just need to finesse our finagling...

[ROBERT CROSS]

Terry,

"We?"

History proves that OODM has been successfully finessing for years!

Bob

[switz]

When I was at the factory tour last October, I watched the ribs being placed into what appeared to be an over 30' long jig in the shape of the trailer. In most rib areas there were multiple locations for each rib groove individually color coded. As long as the person putting the ribs into the slots is not color blind, then the ribs should be uniformly located on similar models.

It became apparent that the side panels might be of uniform height on both the 8' and 8' 5.5" models and the roof panel determines the width. Since the roof rib is slightly arched, the wider units have a higher center ceiling point.

In that same area is a very large flat table with a computer controlled cutting head. A new piece of aluminum is placed on the table and after a period of time, all opening are cut with a small strip of metal on each of the openings sides (round openings are similar) remaining. Leaving the hole in the donut, so to speak, helps maintain structural strength to prevent bending while handling the metal to put it onto the jig and align it. They use hand shears after the ribs are attached to trim those last inch areas and the center piece then is removed leaving the opening. After being riveted to the ribs, the side curve shape gives the metal sheet more strength.

So I would have to think there is potential more for uniformity in the exterior skin than ever before.

Hanging the cabinets did not appear to use a standard support from the floor to move between the various cabinets to ensure exactly the same height. They appeared to use tape measures. They do seem to have to fit the cabinets against that curved surface.

All in all, the new units seem to have great build results. I did not see any "seconds" for sale at discounted prices on the factory lot.

[dbj216]

I think Airstream went to full boxed beams for the frame rails back in the early eighties. And I think they went to a C section aluminum piece that captures and surrounds the wood subfloor to help avoid seperation due to wood rot. A new Airstream may be strong enough for your trunk.

I saw a quite good trailer being built in Jackson Center when I was there last fall. Airstreams are unique. It's like camping in a small Lear jet fuselage. Not much room in them, but very efficient, and very nice once you squeeze inside.

Your trunk is very novel. Let us know what the Airstream engineers think about the extra weight out back. If they don't recomment it, then start charging fees for extra baggage like the airlines do!

David

[DoubleNickel]

Hey Russ, any update on the mechanics of your upgrade from the Airstream engineers?

[Valacidor]

Does this talk of weak frames on rear bath models mean I should not travel with anything in the rear holding tanks?
Hopefully taking a trip to AK next summer and planned on boondocking along the infamously rough Alaska Hi way. Any thoughts or suggestions?
TomJ

[Inland RV Center, In]

Originally Posted by Valacidor

Does this talk of weak frames on rear bath models mean I should not travel with anything in the rear holding tanks?
Hopefully taking a trip to AK next summer and planned on boondocking along the infamously rough Alaska Hi way. Any thoughts or suggestions?
TomJ

Traveling with some liquids in the holding tanks, is not the problem.

The issue becomes a problem, when the running gear (tire, wheel, hub and drum) is not properly balanced, and/or bad axles.

The following article will help you check out the axles.

The Dura-Torque Axle

Airstreams must have a soft ride. If not, many different issues can happen, including rear end separation, to mention just one major one.

Andy 14.7

[perryg114]

It would be wise not to travel with much in the tanks.

Perry

Originally Posted by Valacidor

Does this talk of weak frames on rear bath models mean I should not travel with anything in the rear holding tanks?
Hopefully taking a trip to AK next summer and planned on boondocking along the infamously rough Alaska Hi way. Any thoughts or suggestions?
TomJ

[Valacidor]

I'll just try to find a dump daily, thanks.
TomJ