Anyone ever use balsa core for an ultralight build

[Oldragbaggers]

I'm just thinking.....(dangerous)....
I haven't finished my first tear, but of course I'm already thinking ahead to a possible second

If I were to build another one, it would be all about lightweight, for pulling behind my Hyundai. It would be a simple 4x8 so I could go with standard size materials this time. I was wondering, has anyone here attempted to build a sandwich wall tear with balsa core? I know it's very strong, as we've had it in the deck of every boat we've owned, and extremely light. I wonder if one could take just 3/4" balsa core, laminate 1/8" plywood skins on both sides, only use lightweight framing around the door and outline.

Perhaps the floor too, a sandwich construction with 1/4" or 3/8" ply on top, balsa core and 1/8" ply on bottom, lightweight framing around the outside only, fiberglassed with one layer of lightweight cloth on the bottom side to seal out water. Standard foam insulation in the roof. One layer of lightweight fiberglass cloth on the entire outside.

I am not comfortable with the foamie idea because it just seems to fragile and easy to damage.

I know there are a lot of boat builders on this forum and I imagine some of you have worked with balsa. We replaced a balsa deck in one of our boats once and it seemed to me the fiberglass shell covering it was pretty thin. We had some pretty hefty folks running around on the deck and it was solid as a rock, but yet I was amazed at how light the stuff was.

I know it's not cheap. Lets not even have that discussion. I'm just inquiring as to the feasibility of building that way.

Anyone.....anyone.....

[Roger W]

I havn't used balsa defore so I can't offer an opinion. But thinking and pondering new ideas are where new techniques come from. Keep those gears turning. Happy New year.

[jstrubberg]

Balsa is very fragile.

If you want to go very light and very strong, think about using Sitka spruce for bracing and something like Okumwe for your ply. I've seen boats done this way and a sixteen foot, two person canoe that only weighed 35 pounds.

[Larry C]

I'm just thinking.....(dangerous)....
I haven't finished my first tear, but of course I'm already thinking ahead to a possible second

If I were to build another one, it would be all about lightweight, for pulling behind my Hyundai. It would be a simple 4x8 so I could go with standard size materials this time. I was wondering, has anyone here attempted to build a sandwich wall tear with balsa core? I know it's very strong, as we've had it in the deck of every boat we've owned, and extremely light. I wonder if one could take just 3/4" balsa core, laminate 1/8" plywood skins on both sides, only use lightweight framing around the door and outline.

Perhaps the floor too, a sandwich construction with 1/4" or 3/8" ply on top, balsa core and 1/8" ply on bottom, lightweight framing around the outside only, fiberglassed with one layer of lightweight cloth on the bottom side to seal out water. Standard foam insulation in the roof. One layer of lightweight fiberglass cloth on the entire outside.

I am not comfortable with the foamie idea because it just seems to fragile and easy to damage.

I know there are a lot of boat builders on this forum and I imagine some of you have worked with balsa. We replaced a balsa deck in one of our boats once and it seemed to me the fiberglass shell covering it was pretty thin. We had some pretty hefty folks running around on the deck and it was solid as a rock, but yet I was amazed at how light the stuff was.

I know it's not cheap. Lets not even have that discussion. I'm just inquiring as to the feasibility of building that way.

Anyone.....anyone.....

Becky...
Thanks, I needed this to get me off the couch! (get back to building)
The pursuit of ultralight Teardrop's is rapidly being forced upon us all with the current crop of light weight fuel efficient, under-powered vehicles. I think this is going to be the trend going forward. This is exactly why my build, which is very slowly being constructed will follow this need for weight reduction.

I applaud your way of thinking, but I think Balsa is a very expensive product for the weight savings you will gain. My build is being done with 1/8" skins over cedar(light weight) interior framing where needed, and foam in between. My walls are being made with 1/8" cedar strips for the inside, and 4MM marine plywood on the outside, with thin glass on both sides. My floor (5X8) is constructed with 1" Southern Yellow Pine stringers with 1/8" ply both sides, and foam in between. Both sides glassed (thin). My 5X8 floor which has heavier materials than my walls, weighs 60#.

The chassis is probably the heaviest part of most builds. Mine currently weighs 45# without the axle and wheels/tires. This spartan chassis will require the 5'x8' "box" be well constructed as it must be self supporting, it will be cantilevered rear of the axle.

One of the areas I think there could be a huge weight savings is the galley cabinets and framing. It seams like everyone wants to replicate a home kitchen, with quality hardwood cabinetry which is very expensive and heavy. Again, cedar and thin plywood is the way I hope to go.

I come from a backpacking, kayak camping/racing mindset, and I feel "less is more" which is the name of my build. I may not be able to meet my goal of <500# locked and loaded, but I am sure going to try. I must remember to slap my hand everythime I pick up a heavy piece of wood.

Ultralight construction is much much more difficult to achieve, but in the long run IMO/it's worth the effort unless you have a big V8 truck and $ is no object in your life.

Larry C

[StPatron]

I'm in the less is better camp, but have to wonder... isn't there a point you reach where you risk being toppled or blown off the road? An engineered calculation based on camper weight/width, exposed surface area and wind blast strength???

When pulling DD I tend to avoid interstate highways, preferring to explore via two-lane backroads instead. The wind blast from an oncoming semi can sometimes be a bit unnerving.

[chartle]

There are a lot of much cheaper and probably stronger materials then balsa.

Of course there is foam that you could skin on both sides that would act just like balsa and not rot. There is also plastic materials like coroplast.

If you don't need insulation you should look into torsion box construction and just replace the balsa with free air.

http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=torsion+box

My plan to make a lightweight TD would to use skinned foam panels instead of heavy oak for the cabinets.

You can make a very light 3/4" or thinner panel using 1/2" foam and either a skin of 1/8" plywood or even just veneer. Of course you would have to have a band of real wood so you can screw in hinges and other hardware.

[Larry C]

I'm in the less is better camp, but have to wonder... isn't there a point you reach where you risk being toppled or blown off the road? An engineered calculation based on camper weight/width, exposed surface area and wind blast strength???

When pulling DD I tend to avoid interstate highways, preferring to explore via two-lane backroads instead. The wind blast from an oncoming semi can sometimes be a bit unnerving.

I think the blown off the road risk is a myth. The axle, wheels, tires, and frame are the lowest point and weigh the most. Teardrop's are mostly aerodynamic, and if built strong enough, should not suffer the fate of being blown off the road. Has there been a documented incident that anyone knows of?
I would think an unloaded cargo trailer with it's tall straight sides would
be more prone to the wind blowing it around.

??
Larry C

[grant whipp]

Hi, Becky!

I used balsa core in boat construction back in the '50s-'70s and it worked real well ... until the 'glass got damaged, water got in, and the balsa got good & soaked ... ... not so light anymore! My brother also used to use it in his composite airplane construction in the early '80s until the foam-core technology came along, which has really revolutionized light-weight and ultra-strong aircraft construction (you want to talk about expensive? ... try including Kevlar® or carbon-fiber in your build ... ...!).

If you are thinking of "skinning" the framework with 1/8" plywood, anyway, I think I'd go the light-weight spruce framing method with ridged foam-board between the frame members, especially 'cause you are gonna 'glass the outside anyway ... foam-board has a higher insulative factor than balsa, and your overall panel strength is going to come from laminating the plywood to the framing.

In my mind, the ultimate lightweight teardrop is going to be molded carbon fiber with a foam core, compound curves, timeless lines, and slick as all get-out! But for the home-builder, there are still so many ways to achieve strength and light weight and not break the bank account! Just take a look at how some of the early wooden airplanes were built, and how so many light-weight canoes & kayaks are being built today!

Keep thinking in all directions! After all, the definition of insanity is doing the same thing the same way over and over and over and expecting different results ... ...!

CHEERS!

Grant

[StPatron]

I think the blown off the road risk is a myth. The axle, wheels, tires, and frame are the lowest point and weigh the most. Teardrop's are mostly aerodynamic, and if built strong enough, should not suffer the fate of being blown off the road. Has there been a documented incident that anyone knows of?
I would think an unloaded cargo trailer with it's tall straight sides would
be more prone to the wind blowing it around.

??
Larry C

Thanks for your comments, Larry. And, my apologies for the side-topic hijack, Becky.

I don't think a teardrop (with the "standard" construction methods that have been used) are in "blown over" danger while on the road. Like you said, I don't recall any documented examples and one might assume if there were any.. we'd read about it here.

But, as we strive to build a lighter "cabin" of balsa, foam or composites...I have concerns that there is a critical point where the combination of square inch surface area of the sides, cabin weight and chassis weight will not tolerate typical driving conditions. I'd add wheel-to-wheel "footprint" width also. That question can be answered by engineers and is worthy of exploring, I think, before one of our members/builders suffers a tragic accident. That's where I'm coming from. If that question has been answered by any design engineers on this site, I'd be interested in their review.

[doug hodder]

Poplar is also a viable material to use. While not good on exposure to the elements, in a sealed composite wall, it would be fine. Takes a screw well, glues up easily, relatively light weight, typically straight grained and easy to work, (it does like sharp tools however). Depending on where you are...spruce may not be available in some areas without really paying for it. Poplar is relatively inexpensive and can be found easily. Just an idea. Doug

[Oldragbaggers]

Thank you all so much for your replies. I was just thinking, and you have all redirected my thoughts a bit with your comments.

Grant, you brought up a great point, and I am surprised it didn't occur to me sooner (water saturation) because after I read your post I remembered why we were replacing that balsa deck in the first place. And you're right, rigid foam would do the job too, with less weight and no chance of rot. I was just thinking how you could laminate the plywood skin to the balsa with epoxy and it becomes basically one solid piece. It's overkill, I'm sure. I'm always thinking though and sometimes I have no idea where my mind is going to go until after it's already there.

Gary, you didn't hijack the thread at all. I was talking lightweight and so were you, it's all one and the same. And I appreciate your thoughts, although I also think that if the cargo trailers, which are not too aerodynamic, can fly down the road unloaded with no problem, then a teardrop should fair better since it will not have as much wind resisitance if designed with a curved front. Most teardrops do not have as much "sail area" as a square, higher sided cargo trailer.

Larry, you say your floor is only 1/8" ply on BOTH sides, with foam. Your foam is only 1" thick? Wow, how solid does it feel when you sit on it? How far apart are your stringers?

Lots of great ideas and information. Thank you all, again, for taking the time to comment.

[StPatron]

Gary, you didn't hijack the thread at all. I was talking lightweight and so were you, it's all one and the same. And I appreciate your thoughts, although I also think that if the cargo trailers, which are not too aerodynamic, can fly down the road unloaded with no problem, then a teardrop should fair better since it will not have as much wind resisitance if designed with a curved front. Most teardrops do not have as much "sail area" as a square, higher sided cargo trailer.

Thanks, Becky. I enjoy batting these ideas around, too. The "what if" questions seem to be second nature for this crowd, all good.

As I type this, this part of the country is experiencing high wind warnings. It's brutal outside. The warnings specifically address cargo vans, semi-trailers, etc. Semi-trailer blow-overs aren't unheard of here when straight-line winds blow and the semi-trailers have the advantage of a beefy undercarriage and a broader wheelbase. Granted, they have a larger "sail" but it demonstrates that the blow-over possibility exists. My "teardrop and TTT" mind can't help but question the possibility of danger from large truck generated wind shear and whether it's a valid concern or not.

I don't understand how a more aerodynamic design is advantageous in my "oncoming semi on a two-lane" example... with regard to blow-overs. In my experience, the worrisome force is not the initial hood-lifter, but instead the blast hitting the vehicle or trailer sides. In comparison with an ultra-lightweight foamy, for example, I'd venture to guess that cargo trailers are carrying more weight in the roof and associated framing materials.. a stability advantage.

Design engineers can provide the numbers for us, they calculate wind shear forces in the design of numerous structures.
Based on our design elements...
1. What is the wind shear force that's necessary to cause a topple?
2. Can that force be generated in the truck passing scenario?

I'll keep researching. Thanks for your thoughts, I'm enjoying your remarks and enthusiasm. Always delightful.

[angib]

Becky, balsa core is used in fiberglass to increase its strength without adding too much weight - but this is for decks and cabin roofs that you can walk on, so these are structures far stronger and heavier than any teardrop needs to be. Just the skin on one side of those decks is stronger than a teardrop needs to be.

All sandwich structures suffer from the problem that once you've made the outside skin tough enough to withstand minor impacts, like on a dirt road, it's tough enough to be all the skin the teardrop needs. I think Steve Wolverton used the best lightweight construction for a small trailer body:
- 4mm (3/16") plywood outer skin - preferably marine plywood;
- minimal 3/4" deep (ie, 1x...) framing;
- foam insulation between the framing, if required for heat control;
- fabric inner surface glued/stapled in place.

You can argue that 1/8" plywood is enough for the outer skin, but I think it is a bit fragile on its own.

Some folk might like to research balsa sandwiches as I think they haven't realised it is end-grain balsa that is being discussed - quite different from cross/side-grain balsa which would be fairly weak. Here is an offcut of 1/4" end-grain balsa (stuck to a scrim backing to make it a flexible sheet material until laminated in place):

[Oldragbaggers]

Gary, I do see your concern and I too would be interested in hearing some data on that. At first blush it didn't seem to be anything to be concerned about, but I have to admit, there are times when driving over the Key Bridge here in Baltimore in a strong wind that even my little Hyundai, which sits pretty low to the ground, feels like it is going to set sail. I should think the risk would be greater with a minimal frame, such as the pico light frame.

Andrew, thank you for clarifying, I was indeed talking about end grain balsa. You have raised a lot of good points and I always appreciate hearing your point of view. It sounds like foam, lightweight 1x1 framing, 4mm marine ply and a layer of light fiberglass cloth is the way to go. Do you think that method is adequate for the floor also, and if so, how close together do the stringers need to be?

This thread has already given me a lot of good ideas. Keep them coming!

[Larry C]

I think the blown off the road risk is a myth. The axle, wheels, tires, and frame are the lowest point and weigh the most. Teardrop's are mostly aerodynamic, and if built strong enough, should not suffer the fate of being blown off the road. Has there been a documented incident that anyone knows of?
I would think an unloaded cargo trailer with it's tall straight sides would
be more prone to the wind blowing it around.

??
Larry C

Thanks for your comments, Larry. And, my apologies for the side-topic hijack, Becky.

I don't think a teardrop (with the "standard" construction methods that have been used) are in "blown over" danger while on the road. Like you said, I don't recall any documented examples and one might assume if there were any.. we'd read about it here.

But, as we strive to build a lighter "cabin" of balsa, foam or composites...I have concerns that there is a critical point where the combination of square inch surface area of the sides, cabin weight and chassis weight will not tolerate typical driving conditions. I'd add wheel-to-wheel "footprint" width also. That question can be answered by engineers and is worthy of exploring, I think, before one of our members/builders suffers a tragic accident. That's where I'm coming from. If that question has been answered by any design engineers on this site, I'd be interested in their review.

Gary,
You may be right, especially in the western states. I have carried very light weight kayaks hundreds of miles over many years, and I know the feeling of a big truck passing. It would cause the light weight boats to shake violently, and try to lift. I too think it would be interesting to here from the engineers what is considered "too light" for a Teardrop Trailer.

Larry