UberLite -- Ultra Light-Weight design and build

[Trackstriper]

Regarding UberLite design parameters-

Is there any need for a rear hatch to provide a cooking facility in a very light tear? Is this part of the general definition of a teardrop that can't be violated?

It appears that Andrew's 48" wide design has no rear hatch, has standard side entry doors, and looks like a teardrop. It seems to be intended primarily as a sleeping pod with a storage shelf. I would think that by having a continuous roof skin from front to rear there would be a lot of inherent strength without having to "close" the box structure with partition walls and shelves as is done with a teardrop with a rear hatch. This could aid in making the trailer a fair amount lighter.

Can the rear hatch be eliminated in the interest of weight and complexity for those who desire a light trailer and don't want to be sleeping in a tent? Take the cooking gear in the TV...or is this part of the mystique of a tear?

Bruce

[kennyrayandersen]

Bruce,
You can leave the hatch off and not violate the teardrop. The teardrop is just the shape, which is sometimes violated, but then it ain't a real teardrop.

Yeas, you would save a bit of weight, though the structural difference isn't too much. The interior rear wall and shelf, which I was thinking of making out of the same material as the sides and top, will close out the ‘box’. As long as the axle is located at or forward of this wall, the body will effectively act as a torque box. If the axle were behind it, then there would be a structural penalty for the hatch. The hatch also doesn’t need any ribs – just a curved piece of foam skinned in fiberglass so the weight will be really low. There is additional weight for the hurricane hinge on top and some seals.

I guess if we wanted to make the ultimate in light it could be shaped similar to the old undertaker’s box, but made out of composites with a couple of moped wheels holding it up. That would be REALLY light; but, you know, the real problem there is someone would be forever trying to drive a stake through your heart!

The goal I had in mind was to make the lightest possible “full-featured” tear. I’d like a full size bed, decent width tear that is capable of the basics which wouldn't be that much -- a camp stove, maybe a small sink to wash and do food prep and a place to stash a cooler. I don't need a lazy boy, TV, toilet etc (that's project 2 ). I'm thinking cargo net instead of cabinet doors, and some basic shelves. In the end, if weight allows I'll do AC, because the spousal unit really can't take the heat. Even if you're going camping in a bag, you have to take some grub, water, cloths, bags whatnot. I'm thinking you ought to be able to do at least that level with your tear.

With every plan/scheme, I think people will want to modify or change it up a bit to their liking. I dare say there aren’t 2 tears out there that are the same. I think this is actually one of the cooler aspects of the craft. If someone wanted to just make a sleeping box, they could certainly use the same techniques coupled with reducing the features to lower the weight even further, but too much reduction and pretty soon you just as well be sleeping in the car.

Speaking of weight, my plane-building friend just sent me some shots of his vertical tail. Without covering, which will be a Dacron fabric (weight is really low), the tail weighs just 3.1 Lb. The control surface that goes with it weighs in at just 1.1 Lb. The construction is home depot foam and wood -- primarily thin plywood.

For Andrew,
For a comparison, the 2lb/cu. ft. core that I’m using in the aerospace application is good for 87 psi. The home depot foam, which weighs about the same, allowable stress is about as third as strong (considering the knockdowns for both), but the cost is about 20% or so. You get what you pay for – I just don’t want to pay for more than I need. Tests will verify the strength, but I think that I’m estimating on the conservative side as it is.

[angib]

Yes, the failure was in shear in the core.

On strength, most of a teardrop has a near-zero strength requirement - a bit of local strengthening on the sidewalls over the suspension, and a bit more on the front edge where the tongue crosses it, and a heavy cardboard box would be enough for the rest to carry overall loads.

Instead it's durability that will determine the required strength of the body over most of its area. A former boss described this as the ball-peen test - how hard do you want to be able to hit the structure with a ball-been hammer without it doing damage (puncturing one skin)? Clearly you want it to withstand a harder tap than, say, a large insect at 70mph, but you don't expect it to withstand, say, a full swing with the hammer (though solid 1/2" ply might).

Once the outer skin has been made thick enough for local strength (and here, thickness is as much use as strength, which is why a light material like plywood will probably have greater puncture resistance than the same weight of most composites), the core probably has minimal strength requirement - its main value will be stiffen the panel against buckling.

If you look at the Sleeper, a British small teardrop (another copy of the Piccolo), it has a quoted weight of 'about' 100kg (220 lb) and that appears to use just single-skin chopper gun fiberglass:



Andrew

[Mark McD]

Andrew,
Is that you standing in that tear?

[angib]

Is that you standing in that tear?

Nope, as the tattoo and goatee beard* should tell you, this man rides a trike: Sleeper on Trike forum which is where I linked to that photo.

Andrew

*In Britain, trikers without these two essentials are stopped by the police for improper attire......

[TinKicker]

Andrew, I'm glad that's not you in the photo because I've gotten somehow used to picturing you as a dashing young man with a woman's leg suspended seductively above your conniving (yet James Bondishly handsome) head. You devil, you.
The tats are just not you.

[angib]

Remind me never to post an actual photo 'cos, man, is you going to be disappointed.....

Back on the lightweight trailer subject, I've come across there two articles on an Australian university building a lightweight chassis and body for an electric-power cabin scooter, and it makes good reading:

Building an Ultra Light-Weight Car, Part 1
Building an Ultra Light-Weight Car, Part 2

The fiberglass-faced aluminium-honeycomb core panels they used won't be cheap, but the cost of this sort of thing is reducing all the time.

Andrew

[rmcelroy]

My tear is fairly taditional, and comes in W/mattress at 560#. I too can't stop daydreaming. Google geodesic canoes and let you imagination run wild.

Can you say Lead Zepplin

Mc

[Mark McD]

Andrew,
I'll just continue to imagine you as the "Ward Beaver " lookin' fellow in your avatar.

[TinKicker]

Building an Ultra Light-Weight Car, Part 1
Building an Ultra Light-Weight Car, Part 2

The story that these links point to that Andrew provided is AWESOME! I foresee teardrop construction going this way in the near future...at least for the well-heeled.
But think of the extra STUFF you could carry OR think of how much bigger you could build your trailer (more room!) if you used these techniques. For us armchair teardrop builders (at least for the moment) this gives us a lot of SketchUp fodder.
Now to find a commercially-available near-equivalent panel that would be more affordable...

[brian_bp]

...Back on the lightweight trailer subject, I've come across there two articles on an Australian university building a lightweight chassis and body for an electric-power cabin scooter, and it makes good reading:

Building an Ultra Light-Weight Car, Part 1
Building an Ultra Light-Weight Car, Part 2

The fiberglass-faced aluminium-honeycomb core panels they used won't be cheap, but the cost of this sort of thing is reducing all the time.

Andrew

That's fascinating stuff, and the end result looks good, but the technique has a worst-of-both-worlds flavour to me. The honeycomb-cored sandwich is fine and relieves the outer body of any structural requirement, but the foam and 'glass over top is the nightmare of massive finishing effort which Andrew has mentioned before - all the work and none of the benefit of other techniques. The foam isn't a structural problem, but it's also not a structural benefit.

To use these panels in a trailer, it would make sense if they could be the final shape themselves, and not need and envelope of foam-and-'glass around them. I don't know how you would get the desired teardrop curve with these inherently flat panels; they seem limited to internal structures or "origami" styling (which I don't mind, but is not classic teardrop).

As for the car project... if stealth aircraft can be built with nothing but flat surfaces and work aerodynamically, perhaps a car can be, too. Skip the whole carved-foam and fiberglass covering stage!

[kennyrayandersen]

OK,
I'm going to try my first picture posting. This is a pic of my buddy's plane he's building. You will notice there is no shortage of the pink foam. I is in every part -- horizontal tail and control surfaces, and the vertical tail and control surfaces. It will also be in the wings and in the fuselage. So, the thing to remember is that though the foam isn't so strong, it does have capability, and if the design is done properly, then it should be just fine. As it turns out I also have access to some computer modeling tools and so will make a model (finite element model) of the teardrop and will check all of the stresses etc including a person climbing around in the tear etc. Anyway, it will be fun to play with the idea and see what falls out.

OK, I had some trouble -- who knows why -- I'll try and post the pic from home.

http://tnttt.com/album_ ... c_id=46818
how's that?

[Mark McD]

Upload photo into your album, click on the pic you want to post from your album, copy address,paste into thread, highlight address,,then click the IMG tag above

[Mark McD]

Your friend does nice work. I can't imagine building something to the tolerances one would imagine are required for an airplane.

[kennyrayandersen]

Thanks, I knew I was getting warm!

Also, Nice Mini in your avatar. Andrew and I are BIG on small cars. When this gig is over, I'm heading to Italy to collect a FIAT 500. I hope to do the tear light enough that I can pull it with the 500. I may have to scale it back just a bit.