Ultralight Design?

[mikeschn]

You guys talking about my orange brackets? Gage, back me up here... orange is kewl!

I haven't shown the bolts yet, but if the axle doesn't flex, then 1 bolt across the tongue and 2 bolts thru the axle...

Andrew brought up a good question... how far in does the rubber go? anyone know?



Mike...

[Chuck Craven]

Mike! If you bolt through the axel you will weaken the axel. All the stress is at that point where the tongue meets the axel. How about two-piece V tong? Bolted to the axel under the outside walls. You will have less stress on the tongue too. You have a triangle, which is much stronger and you can go with thinner material.
Chuck

[angib]

When you consider your tongue take a look at the possibility of including a tongue box as part of the structure.

That's pretty much exactly what I've been doing, except the 'tongue box' is all there is. Here's the profile so far:

Also, remember, this is a design for Mike and not those of us privileged to drive without major potholes in California and England. I do not know the last time you drove here but by spring, in Michigan and thirty other states, we have potholes the size of UK caverns on many of our roads. Therefore the twisting moments will be greater than normal.

This gives me the chance to repeat what I thought was one of the best jokes I've been told. While driving down a road through the dock system in Calcutta (Oops, of course I mean Kolkatta) (India), my colleague said "It gets dark in the bottom of some of these potholes, doesn't it?"

I would hope that the Ultralight might actually be stronger than other tears, not weaker. The true measure of suspension strength is more like a strength-to-weight ratio and the reduction in the weight of the Ultralight is a big benefit. Building heavy is not necessarily building strong, because the extra weight puts extra load on the structure.

As an additional thought, could you please give us a lesson on the real and imagined difference between half torsion axles and full ones. You often write that in Europe half torsion are the norm but we on this side seem to have the same aversion to them as we do for all wood construction rather than steel.

I don't think there is a functional difference between half axles and full axles and the choice between them involves loads of other factors. It's just as easy and cheap for you guys to buy full axles, whereas here they're much more expensive - that's just market tradition, I guess.

In the US, I would tend to go for full axles. I go on about half-axles just because people are inclined to say they mustn't be used because they're impossible to line up, or some such thing. To me, this is like a red rag to a bull!

And don't let me give you the idea that all-wood construction is any less unusual over here - it isn't. It certainly isn't an easy way to build a trailer, as it can't be done as simply. It is a just an interesting challenge and I get ornery when given a challenge.

Obsessed, moi? As Miss Piggy would say.

Whilst I am at it, I wish to add that besides shifting the paradigm from House building we might also consider changing the notion that woody details are merely decoration appliedto the exterior. They should be thought of as more integral to the structural design, sort of , the framing on the outside.

I understand. The one thing is that with woody framing, you are limited to what looks OK and it tends to have to be the same all over - if I want just 2 or 3 vertical frames and some 1x4s above and below the door, and no other framing, it's going to look awful if done on the 'woody side'.

Andrew

[mikeschn]

Chuck,

I'll have to look at a v-tongue in the morning.

Mike...

P.S. Right now all I see is and and outside the weather changed from sunny and warm to cold, dark and snowy...

But hey, there is a bright side... I got all the materials I need for an ultralight in the shed...

and once I start building this baby, I'll take lots of pictures for you guys...

I just have to get past the design flaws...

But like I said... tomorrow is another day!

[Chuck Craven]

Yes! I forget I am a night Owl.
From Wisconsin the worst day I remember started out 52 degrees and sunny, went down to 35 and ranning, then sleet, then snow, then high wind 62 MPH, Tornado warnings, power went out for 2 hrs and I woke up with 6” of snow on the ground an 18 degrees outside. We have a saying here “If you don’t like the weather wait awhile it will change!” Just not always for the better.
Chuck

[mikeschn]

And I am an early morning person... In a few hours I'll be at my peak having the most fun, cranking out the most material. I'll try to be beneficial to you guys, but every morning is different.

Tomorrow morning I'll be tugged by the ultra light design, the actual building of the same, and getting the Lil Diner ready for camping in a month or two...

Kerry said it right this morning... work only gets in the way of things that we want to get done...

Mike...

[Mitheral]

Andrew brought up a good question... how far in does the rubber go? anyone know?

No where near the centre. To get an idea look how short the non axle units are.

If you were afraid to drill a hole in the axle (a valid fear imo) you could weld a T on the end of the draw bar and then U bolt the draw bar to the axle. You'd need to make allowance in the torsion box for the ubolts.

[Chuck Craven]

Mitheral
That is not good either. The problem is the axel has positive, negative and radial stress all at one point half way down the axel. The axel can amplify that stress point. Two positives or two negative stress points (the wheels) will add to each other at that connection point. The better approach is to have two drawbars mounted near the wheels at an angle to the stress points going to the hitch. This spreads out any stresses over a larger area negating any single stress point. There is a physics law for that (can’t remember the name). Look at a Beehive there is no single wall perpendicular to another always at an angle. The Beehive is very strong for the material it is made of “Bee paper, chewed up plant fiber/ pulp and Bee spit”. Same with a teardrop the roof is at an >90 angel to the floor. A curved surface is always stronger than an equal flat surface. I would think that most failures of a teardrop trailer will be where the walls meet the floor, or an under designed tow bar / hitch.

O
| > Put Put
O

Chuck

[alaska teardrop]

Mike - Went back, looked at your original post and realized that you must intend on bringing the hatch down to about 1 foot from the floor like Roly did. So, my comment about the tail compartment not being accessable seems stupid. Maybe we need a lightbulb Emoticon!

Roly - Your galley/hatch design really makes good functional sense. May consider it on the next AKTD. Fred

[dwgriff1]

Andrew, you were looking at my sketch book!

My plan to strengthen my wood tongue is with a box much like the one you show, exept I'd make mine triangular in plan, so it would be straight sided in profile. It would only open from the inside. My actual tongue stinger would be as short as yours. I would run a strong back back in the floor box, and increase the size of that as it goes under the tongue box.

As I understand these torsion whatevers (I went to art school) the idea is to keep the sides apart so they don't compress or stretch. There is not unlimited strength, but I am sure my 1" gizmo will have a LOT less flex than a hunk of 3/4 plywood. And, when filled with foam, will be plenty solid enough to hold my mattress and bride.

I would like to curve the sides as well. That would add strength, give me some new challenges with the doors, and make the shape more like the old VW bug when seen from above.

dave

[Mitheral]

Mitheral
That is not good either. The problem is the axel has positive, negative and radial stress all at one point half way down the axel. The axel can amplify that stress point. Two positives or two negative stress points (the wheels) will add to each other at that connection point. The better approach is to have two drawbars mounted near the wheels at an angle to the stress points going to the hitch.

O
| > Put Put
O

Chuck

Agree totally, I think we're talking about the same thing when I talked about an A-Frame:

An A-frame under the torsion box frame connecting the hitch to the axles might be better. Use angle rather than square tubing to reduce mass and the torsion box floor can be bolted to the A-Frame all along it. An additional piece under the front edge of the floor (sort of like the horisontal bar in the A) would allow you to pick up the heavy load of the front wall in a distributed way. A person wouldn't have to go overboard on the angle, even some 1 1/5 sould be sufficient.

[angib]

I'm in favour of the A-frame idea too. The single tongue has the problem that it connects to a 'hard point' at the front of the floor, where it is supported by the body front, but at the back it is connected to the middle of the floor - like putting a pillar on a trampoline! The A-frame will pick up the same hard point(s) at the front wall and ideally the other end will meet the body sides. Rock solid.

The downside of the A-frame is that, although it has as much sideways strength as you could want, the vertical strength will be less than a single tongue - two separate bars/tubes/angles never have the same bending strength as one bigger bar/tube/angle. But this isn't a big deal, it just means the tongue has to be a bit heavier.

Andrew

[mikeschn]

I figure the walls could be built up like this. You could build them right on your work bench, in the comfort of your heated workshop...



Mike...

[mikeschn]

If anyone would like to layout the outside profile on a piece of plywood, here are the x,y points...

Ultralight
x, y
6.79, 0
3.27, 3
1.35, 6
0.32, 9
0, 12
0.22, 15
.89, 18
2.03, 21
3.66, 24
5.82, 27
8.57, 30
12.01, 33
16.29, 36
21.67, 39
24, 40.10
27, 41.37
30, 42.5
33, 43.5
36, 44.37
39, 45.13
42, 45.81
45, 46.38
48, 46.86
51, 47.25
54, 47.56
57, 47.78
60, 47.93
63, 48
66, 47.95
69, 47.67
72, 47.14
75, 46.35
78, 45.27
81, 43.875
84, 42.08
87, 39.77
90.61, 36
92.66, 33
94.17, 30
95.2, 27
95.8, 24
96, 21
95.85, 18
95.4, 15
94.6, 12
93.5, 9
91.98, 6
90, 3
87.42, 0

I'm laying out the points myself right now, so I'll let you know how it works out...

Mike...

[angib]

No where near the centre. To get an idea look how short the non axle units are.

I think the suspension pivots and rubber rods may be longer in full axles, but this photo of a Henschen axle certainly suggest they don't get anywhere near the middle:



I think your U-bolt idea is perfect, as long as the clearance above the axle tube is sufficient.

Chuck, I'm not in the least worried about the load on the axle tube. Drilling any serious holes in it is another matter entirely - it's got to invalidate any warranty for a start.

Andrew