Between 265 & 485 SQ/FT The 12-Gauge Garage

[404]

Re: Teardrop Camper -- Structural Thoughts

As you are going to all this work and trouble, I suggest a different shape. Pic shows Cd of different shapes.

One can have the overall drag force by making a raindrop shape that the canned ham shape would fit INSIDE of. So much more inside volume/space and same drag. The compound curves over the entire shape adds much stiffness.

 

[Mr.N]

Re: Teardrop Camper -- Structural Thoughts

As you are going to all this work and trouble, I suggest a different shape. Pic shows Cd of different shapes.

One can have the overall drag force by making a raindrop shape that the canned ham shape would fit INSIDE of. So much more inside volume/space and same drag. The compound curves over the entire shape adds much stiffness.

Nice of you to thinking about making it more efficient.
However, That model doesn't account for ground affect, turbulence of the vehicles drag and it affect on stability. Stability is much more important than gas mileage.


I can hardly wait to see what you're going to do with the inside Jack. Post your ideas up.


.

 

[Jack Olsen]

Re: Teardrop Camper -- Structural Thoughts

I suppose I could always add a spoiler of some kind to the rear of the trailer.



(Click on the image for video.)

 

[404]

Nice of you to thinking about making it more efficient.
However, That model doesn't account for ground affect, turbulence of the vehicles drag and it affect on stability. Stability is much more important than gas mileage.


I can hardly wait to see what you're going to do with the inside Jack. Post your ideas up.


.

Very good point and thanks for bringing it up. For stability the center of mass must be in front of the center of drag. Add fins.

 

[Keel]

Re: Teardrop Camper -- Structural Thoughts

I think a almost 5 foot tall, 10 foot long unit at 750-800 lb will be way to light..
Why are you looking at making it light weight? it won't make it tow better, or save you any mpg.. at least not in that shape. maybe if you build a baby airflow, but not a teardrop..
your comment on the fact that
"In one respect, trailer gets the same amount of pressure from the wind whether it's light or heavy. Its resistance to changing direction is more when it's heavy, but that applies to getting the thing back in line as well."

is all well and good, but it take more wind to move a heavier unit.. and I'd be looking at resistance to changing directions by force than the light weight making it somewhat easier to recover.. won't matter as it drags you into a ditch,, or oncoming traffic..

I doubt this is going behind the 911.. so there is no real reason to make it light and make it the winds whipping boy that will cause white knuckle driving.
if really thinking of towing with a 911, I'd rethink this, the airflow over the car will be going straight under the teardrop as it'll be wider or as wide as the car and with the roof forward shape of the trailer, all that air going under the unit, will only make it lighter and more prone to crosswinds
What is the thinking behind the weight??

 

[rowerwet]

Re: Teardrop Camper -- Structural Thoughts

Picture of me torture testing my EPS foam/fabric skinned kayak, 12' long 15 lbs.
I built it to learn how to work with foam, preparing to build a foamie camper.

 

[Jack Olsen]

Re: Teardrop Camper -- Structural Thoughts

600-900 pounds is not all that light, for one of these. I rented a commercially made teardrop for a camping trip with my son. I pulled it up mountain roads to 7000 feet. It rained. There was wind moving over the summit. No drama with the the thing at all.

It weighed 490 pounds.

Guys have been making foam trailers that are standing height inside for decades. I've never driven one, and I'm not condoning the practice. But I haven't heard about anyone being blown into oncoming traffic yet.

 

[Rudyjr]

Re: Teardrop Camper -- Structural Thoughts

I watched Dave design and build the Atma Travalear that you have pictured in your thread Jack over at Tiny Tavel Trailers. He is a designer I believe and did an unbelievable job with the design and build of that trailer. I think it is probably one of the finest homebuilt teardrops I have seen. I don't think you could go wrong with that design, I know he has links to all of his drawings on that site.Here is the link to his build.
ww.tnttt.com/viewtopic.php?f=50&t=35081#p637721

 

[Jack Olsen]

Teardrop Camper -- Structural Thoughts

Yes. The drawing I posted is based on his, but with a higher roof, a leading-side curve down below, and a 'leaned-forward' distortion to the basic shape.

Host Atma is pretty great. Mine will be pretty crude by comparison.

 

[theoldwizard1]

Re: Teardrop Camper -- Structural Thoughts

Square (aluminum) tubing is great for side-to-roof or side-to-floor joints. Use a good caulk and rivet with extra large heads. A thin 1x1 angle over the outer seam, caulked and riveted should keep water infiltration to a minimum.

90° are terrible in shear. TRIANGULATE ! Us 1x1 or 1.5x1.5 square tubing. Spray glue the inside and then press in per-cut solid foam insulation.

One secret is attaching the bottom rail to the trailer frame. Press fit hardwood inserts into the bottom square tube. Now you can through bolt without crushing the tube.

 

[bczygan]

Re: Teardrop Camper -- Structural Thoughts

Very good point and thanks for bringing it up. For stability the center of mass must be in front of the center of drag. Add fins.

Man......That's "The Bomb!"

 

[kerrynzl]

Re: Teardrop Camper -- Structural Thoughts

Jack, do yourself a favour and buy the lightest sprung torsion axle available.
The reason I suggest torsion is it eliminates "roll steer" by design [basically trailing arm]

With a leaf spring, the axle moves rearward in an Arc when compressed.
This is actually roll oversteer which is quite unstable, it will dart off into the direction that is compressed and transfer weight to the other side [compressing that side, and starting oscillations]

Back to back leaf springs on a tandem cancel each other but on a single axle they can make towing unpleasant.

There are other methods to turn roll oversteer into understeer. Having the front spring eye at the same height [or lower] than the axle centreline is one of them [ the Chrysler method ]

A torsion axle is cheap and will fix all these handling problems in one simple unit

 

[bczygan]

Re: Teardrop Camper -- Structural Thoughts

I think a almost 5 foot tall, 10 foot long unit at 750-800 lb will be way to light..
Why are you looking at making it light weight? it won't make it tow better, or save you any mpg.. at least not in that shape. maybe if you build a baby airflow, but not a teardrop..
your comment on the fact that
"In one respect, trailer gets the same amount of pressure from the wind whether it's light or heavy. Its resistance to changing direction is more when it's heavy, but that applies to getting the thing back in line as well."

is all well and good, but it take more wind to move a heavier unit.. and I'd be looking at resistance to changing directions by force than the light weight making it somewhat easier to recover.. won't matter as it drags you into a ditch,, or oncoming traffic..

I doubt this is going behind the 911.. so there is no real reason to make it light and make it the winds whipping boy that will cause white knuckle driving.
if really thinking of towing with a 911, I'd rethink this, the airflow over the car will be going straight under the teardrop as it'll be wider or as wide as the car and with the roof forward shape of the trailer, all that air going under the unit, will only make it lighter and more prone to crosswinds
What is the thinking behind the weight??

A real lightweight trailer CAN be a problem.

I once moved an ultralight airplane with a borrowed homemade trailer. The trailer was about 7'wide and tall and 24' long. It had a standard heavy axle and wheels and springs and deck. The enclosing structure was steel tubing covered with aluminum lap siding.

When you carry something light like a 400 pound ultralight, the heavier a trailer, the more it beats up the cargo. In addition, this trailer was light enough, with a single axle, and a lot of side area, that whenever we passed a break in the trees, the wind tried to move it sideways.

Bill

 

[bczygan]

Re: Teardrop Camper -- Structural Thoughts

This is pretty aerodynamic!

 

[bczygan]

Re: Teardrop Camper -- Structural Thoughts

For shorter low speed trips:

 

[kerrynzl]

Re: Teardrop Camper -- Structural Thoughts

A real lightweight trailer CAN be a problem.

I once moved an ultralight airplane with a borrowed homemade trailer. The trailer was about 7'wide and tall and 24' long. It had a standard heavy axle and wheels and springs and deck. The enclosing structure was steel tubing covered with aluminum lap siding.

When you carry something light like a 400 pound ultralight, the heavier a trailer, the more it beats up the cargo. In addition, this trailer was light enough, with a single axle, and a lot of side area, that whenever we passed a break in the trees, the wind tried to move it sideways.

Bill

That is because a lightweight trailer is usually over-sprung [ they are like a tuning fork when empty ]

I built a tandem car hauler that weighed 400kg [880lbs] when empty, when I loaded my Corvette on it the weight went up to 1600kg
That is 400% of the tare.
So you need to spring it to the intended usage.

A teardrop [or most campers] don't have this dramatic weight increase from empty to loaded so it is easier to get a compromise.

 

[OldmanB]

Re: Teardrop Camper -- Structural Thoughts

Jack, do yourself a favour and buy the lightest sprung torsion axle available.
The reason I suggest torsion is it eliminates "roll steer" by design [basically trailing arm]

With a leaf spring, the axle moves rearward in an Arc when compressed.
This is actually roll oversteer which is quite unstable, it will dart off into the direction that is compressed and transfer weight to the other side [compressing that side, and starting oscillations]

Back to back leaf springs on a tandem cancel each other but on a single axle they can make towing unpleasant.

There are other methods to turn roll oversteer into understeer. Having the front spring eye at the same height [or lower] than the axle centreline is one of them [ the Chrysler method ]

A torsion axle is cheap and will fix all these handling problems in one simple unit

Wow, all these years of owning a single axle sprung trailer and never had this problem, must be different where you live?

 

[SRX]

Re: Teardrop Camper -- Structural Thoughts

I found this DIY site. Seems legit

http://doityourselfrvcom.c.presscdn.com/wp-content/uploads/2014/01/porsche_rv.jpg

 

[Charles (in GA)]

Re: Teardrop Camper -- Structural Thoughts

Knowing Jack, I can see some sort of wing or spoiler in this campers future.

 

[kerrynzl]

Re: Teardrop Camper -- Structural Thoughts

Wow, all these years of owning a single axle sprung trailer and never had this problem, must be different where you live?

The problem is there, but you are probably not aware of it.
In fact it's not a problem when you tow a HF trailer behind an F350 or similar [which is the USA fix]

Jack wants to tow behind a lightweight Porsche.
If you got a single axle leaf spring utility trailer and towed it behind a lifted up truck ,it will sway badly when empty! Put it behind a vehicle with a low hitch and the sway will disappear

In the 70's when I was a kid, our roads were plagued with single axle caravans with 20+ cars backed up behind them [usually towed behind a POS Pom car like a Hillman Hunter, or Morris Marina]
Speedway people were just as bad with overloaded homemade single axle trailers swaying to the track.

A pair of 500lb torsion ends [250lb each] is only $150 and eliminates the problem ,and can be mounted to allow the floor to be lower


http://www.northerntool.com/shop/tools/product_200649002_200649002

 

[mikegt4]

Re: Teardrop Camper -- Structural Thoughts

Jack
Here is an old blog about building a composite camper with Nidacore (polypropylene honeycomb sandwiched with fiberglass). The designer/builder was an engineer at Robinson Helicopter so he knows his composites. Unfortunately most of the photos no longer come up but it is still worth a read.

And of course you have already been reminded about http://tnttt.com/

http://thesupercamper.blogspot.com/2006/09/super-camper-inspiration-concept-and.html

http://www.merrittsupply.com/products/32038-3m-nida-core-structural-honeycomb-plain-h8pp.aspx

 

[DocRocket]

Re: Teardrop Camper -- Structural Thoughts

Unless you are sold on Aluminum honeycomb panels, you could also look at these:
https://dragonplate.com/ecart/categories.asp?cID=207

They have lots of carbon fiber/foam composite honeycomb panels, different ratings, etc...
Prices are not cheap by any means, but how much is cool worth?

 

[Krash Kadillak]

Re: Teardrop Camper -- Structural Thoughts

Jack wants to tow behind a lightweight Porsche.

Did he say that? Must have been kidding. His daily is a Jeep. Don't know what his wife's vehicle is.......

 

[Jack Olsen]

Re: Teardrop Camper -- Structural Thoughts

My main tow vehicle will be my BMW sedan. The Jeep was my first thought, but of my three cars, the old Jeep has the least power, poorest brakes, and is (laterally) least stable (with its old Rancho, lifted) suspension. If I was going off road, it would be another story. But this is California camping, which means you pull up to the parking spot and camp.

I'm going to look into torsion axles. 500# seems low, but maybe it would be better than 1000#? I'll have to do some weight calculations when I've got a clearer picture of what the materials are going to be.

On materials, I would like to find something lighter than the Aluminum Composite Panels -- but it's got to be relatively cost-effective. I really like the polypropylene sandwiched between aluminum (it's lighter than the ACP panels I've been looking at), but it's too expensive. The polypropylene with FRP sounds great, but again, the cost is high.

I also need 5x10 sheets. A lot of this stuff isn't available larger than 4x8.

 

[whyNick?]

Re: Teardrop Camper -- Structural Thoughts

Knowing Jack, I can see some sort of wing or spoiler in this campers future.

And a green interior with lots of built-in storage.

Cool idea Jack, I predict this will be an interesting thread...

 

[kerrynzl]

Re: Teardrop Camper -- Structural Thoughts

Did he say that? Must have been kidding. His daily is a Jeep. Don't know what his wife's vehicle is.......

In his drawing you can quite clearly see the Carrera RS ducktail,
This drawing gives away his true intentions, even though he may deny it

 

[DocRocket]

Re: Teardrop Camper -- Structural Thoughts

My main tow vehicle will be my BMW sedan. The Jeep was my first thought, but of my three cars, the old Jeep has the least power, poorest brakes, and is (laterally) least stable (with its old Rancho, lifted) suspension. If I was going off road, it would be another story. But this is California camping, which means you pull up to the parking spot and camp.

I'm going to look into torsion axles. 500# seems low, but maybe it would be better than 1000#? I'll have to do some weight calculations when I've got a clearer picture of what the materials are going to be.

On materials, I would like to find something lighter than the Aluminum Composite Panels -- but it's got to be relatively cost-effective. I really like the polypropylene sandwiched between aluminum (it's lighter than the ACP panels I've been looking at), but it's too expensive. The polypropylene with FRP sounds great, but again, the cost is high.

I also need 5x10 sheets. A lot of this stuff isn't available larger than 4x8.

In all seriousness, you may find yourself doing some layup on the curved parts. I suspect that commercially available flat pieces of thick foam-core board are not going to be friendly to bend to produce your teardrop shape. The 1/4" stuff for your model may be OK, but the 1" may be beyond making nice bends in. As someone said earlier, fiberglass will be waterproof, and fairly narrow slats on the curves should be stiff enough laterally, while allowing you to make the curves.

If larger pieces are not available in whatever you decide to use, you may want to look at incorporating "I" or "H" section metal as rails to join smaller panels. It may also be a convenient way to frame in your doors/windows. You should be able to slide the panels in to the channels of the "I" or "H" and bond them in place with appropriate epoxy for both waterproofing and structural strength.

 

[zmaxmotorsports]

Re: Teardrop Camper -- Structural Thoughts

For shorter low speed trips:

I remember riding bikes like that back in the day,no way in hell would I want to travel more than a few miles on it on flat land let alone 1200 miles cross country!

 

[d.mcfarland]

Re: Teardrop Camper -- Structural Thoughts

What if the floor was aluminum square tube frame with inexpensive pine slats, just like a bed basically. If the top and side are waterproof, the water won't be sitting on the wood. If/when the wood is in need of replacement it costs $30 bucks or whatever for full replacement.

 

[Jack Olsen]

Re: Teardrop Camper -- Structural Thoughts

Knowing Jack, I can see some sort of wing or spoiler in this campers future.

Oddly, I'm at a campground north of Ventura right now, and there's a full height teardrop that has a ducktail-type spoiler on it. It makes me wonder if lift is an issue with these things, and if a slight forward rake with the bottom surface -- and even a spoiler -- or vortex generators -- on the top might help.

In all seriousness, you may find yourself doing some layup on the curved parts. I suspect that commercially available flat pieces of thick foam-core board are not going to be friendly to bend to produce your teardrop shape. The 1/4" stuff for your model may be OK, but the 1" may be beyond making nice bends in.

But I think the think stuff from my model would be plenty strong enough for the full-sized trailer. And with a layer of foam and corrugated plastic laminated onto it (on the inside), it will be much stronger than it needs to be.

At least, that's my current thinking. The aluminum composite stuff is VERY easy to work with -- and to form into curves. It's not as light as some of the alternatives, but it's much lighter than plywood construction.

What if the floor was aluminum square tube frame with inexpensive pine slats, just like a bed basically. If the top and side are waterproof, the water won't be sitting on the wood. If/when the wood is in need of replacement it costs $30 bucks or whatever for full replacement.

Well, there is water incursion from below, because of towing. But I don't think I will need any meaningful framing below the floor at all -- even if it's corrugated plastic. I think having the floor sit on angle-stock that's adhered to the walls will be plenty. As I understand it, it doesn't serve much of a structural role at all. It just has to hold up to road vibration/impacts and not fall through when people are sleeping on it. The real structure goes from the axle to the walls to the roof.

(I think.)

 

[bczygan]

Re: Teardrop Camper -- Structural Thoughts

Oddly, I'm at a campground north of Ventura right now, and there's a full height teardrop that has a ducktail-type spoiler on it. It makes me wonder if lift is an issue with these things, and if a slight forward rake with the bottom surface -- and even a spoiler -- or vortex generators -- on the top might help.

But I think the think stuff from my model would be plenty strong enough for the full-sized trailer. And with a layer of foam and corrugated plastic laminated onto it (on the inside), it will be much stronger than it needs to be.

At least, that's my current thinking. The aluminum composite stuff is VERY easy to work with -- and to form into curves. It's not as light as some of the alternatives, but it's much lighter than plywood construction.

Well, there is water incursion from below, because of towing. But I don't think I will need any meaningful framing below the floor at all -- even if it's corrugated plastic. I think having the floor sit on angle-stock that's adhered to the walls will be plenty. As I understand it, it doesn't serve much of a structural role at all. It just has to hold up to road vibration/impacts and not fall through when people are sleeping on it. The real structure goes from the axle to the walls to the roof.

(I think.)

The floor might have to support 400 pounds of people.....at least at my house.

 

[HOTFR8]

Re: Teardrop Camper -- Structural Thoughts

Jack, have you had a look at any plans that are available on the net ?

 

[DocRocket]

Re: Teardrop Camper -- Structural Thoughts

The curved upper surface is going to produce some lift, not much in comparison to the drag, but the lighter the construction, the more it will likely matter. The Lift force will act, much like on a wing, at about 25% back from the front most likely, so it will be acting to reduce tongue weight directly, and that might make towing interesting if it all adds up wrong.

 

[markviii]

Re: Teardrop Camper -- Structural Thoughts

Plans look great! Try looking up Grizz1963's thread Mixed Grill - from London, England. He has a detailed description with pictures of his teardrop build. Or try to pm him because he may not have seen your thread in Free Parking.

Chris

 

[Hinrix6]

Re: Teardrop Camper -- Structural Thoughts

I don't mean to get off the topic of designing a camper, but if anyone in the Omaha area is interested in a free teardrop camper that needs a ton of TLC, I came across this gem this morning.

http://omaha.craigslist.org/zip/5144110892.html

 

[Charles (in GA)]

Re: Teardrop Camper -- Structural Thoughts

I like good stout frames on trailers. I would think a welded aluminum box tubing or channel structure with the lighweight body attached to the top would be best. You want really decent support under you, good solid connection between the suspension and the tongue and the heavy frame will help immensely with keeping the body square and preventing it from flexing. You gotta have something solid to attach the suspension to.

I really like the Timbren suspension packages and after seeing them on the web site, I would not consider anything else.

 

[ez-duzit]

Re: Teardrop Camper -- Structural Thoughts

...I'd like to avoid (as much as I can) a traditional frame for it...

Huge elementary mistake.

Use a frame, like virtually all trailer builders do.

 

[stanleyoutdoors]

Re: Teardrop Camper -- Structural Thoughts

Consider using aluminum honeycomb, especially for the floor. It's cheaper than you think if you have a local company. Also consider 3m vhb foam for adhesive. Can accommodate lots of misalignments and vibrations

Sent from my XT1058 using Tapatalk

 

[Jack Olsen]

Re: Teardrop Camper -- Structural Thoughts

I like good stout frames on trailers. I would think a welded aluminum box tubing or channel structure with the lighweight body attached to the top would be best. You want really decent support under you, good solid connection between the suspension and the tongue and the heavy frame will help immensely with keeping the body square and preventing it from flexing. You gotta have something solid to attach the suspension to.

Huge elementary mistake.

Use a frame, like virtually all trailer builders do.

This is exactly why I'm posting the questions. I appreciate the input, but I'm hoping I can learn more specifics about what pieces would be no longer essential or beneficial in the move from plywood (which has its own set of strengths and weaknesses) to a material like aluminum composite products.

Again, I'm untrained. But a wooden frame doesn't seem to have much strength on its own. The one in this picture could be pushed over pretty easily. Wood flexes and has limited strength to hold onto fasteners. It makes great sense when you're then adding thin wood panels, since the frame pieces strengthen the edges of the panels. But with ACP, I can make an adhesive bond along the full length of the joined panels that doesn't seem like it would be weak in a way a similar joint would be with plywood.

There are very few examples of structural failures with teardrops online. Rotten wood is the one easy thing to find, but that's not the issue here.

I can strengthen the wall-to-roof seam with square tubing and I can strengthen the wall-to-floor seam with square tubing. But does one of those offer more benefit than the other? I know angle-stock is less resistance to shear than square tubing, but with the wrap-around-and-down front wall (from the roof) providing lateral strength, combines with shear-type walls fore and aft, would square tubing at the seams be doing any appreciable amount of work?

I wouldn't be surprised if they are. But I wish there were a way to find out with more certainty so I can avoid unnecessary pieces in this thing.

Consider using aluminum honeycomb, especially for the floor. It's cheaper than you think if you have a local company. Also consider 3m vhb foam for adhesive. Can accommodate lots of misalignments and vibrations.

Thanks. I'm looking around. Finding 5x10 sheets of any of these composite/laminate/structured materials is the trick. I've got sources now for aluminum composite panels and corrugated plastic. But I'm also looking into other options.

And I've already done a bunch of testing with about a dozen different adhesives, including (for structural bonds) the 3M VHB tapes, Dow 995, and 3M ScotchWeld structural epoxy adhesives. I think flexibility is important, considering the vibration the thing will be subject to.

As I continue with this project, I hope to learn enough about Sketchup to be able to post illustrations of what I'm planning in order to get feedback from people who have a better understanding of how this works. I don't mind overbuilding, in and of itself, but I'd rather be able to find the stuff that offers no benefit up front.

 

[MoonRise]

Re: Teardrop Camper -- Structural Thoughts

Jack,

re:

I can strengthen the wall-to-roof seam with square tubing and I can strengthen the wall-to-floor seam with square tubing. But does one of those offer more benefit than the other? I know angle-stock is less resistance to shear than square tubing, but with the wrap-around-and-down front wall (from the roof) providing lateral strength, combines with shear-type walls fore and aft, would square tubing at the seams be doing any appreciable amount of work?

I wouldn't be surprised if they are. But I wish there were a way to find out with more certainty so I can avoid unnecessary pieces in this thing.

If you want a detailed engineering structural analysis, sure it could be done to evaluate angle iron versus hollow square tube corner joint reinforcement. But I don't think you really want to go and hire an engineering firm or consultant to do such an engineering analysis. $$$$$, after all.

Want strong and light weight and a monocoque type construction? Then use some sort of thin panel (wood or composite) and fiberglass the whole exterior. Just like making a fiberglass boat skin (power boat or canoe or kayak). Want more high-tech and possibly even lighter weight? Then go for a carbon fiber 'skin'.

Even 'stronger"? Thin lightweight panels and 'skin' them inside and outside. Thicken the panels but keep them lightweight and with the two skins ('glass or carbon) you have made a strong and relatively 'stiff' composite panel.

Just how 'strong' are you trying to make this teardrop trailer? Wooden framework and the thin wooden or composite 'skins' is usually plenty strong enough for 'normal' use.

Want to turn it into almost a 'roll cage' structure? It can certainly be done. Might not be needed for 'normal' conditions though.

Wood is used for a lot of 'homebuilt' project because it is relatively easy to get and cut and attach and not to expensive (ignoring exotic hardwoods and such) and often strong enough for the job.

Heck, they even build houses out of wood.