TTT designed for the Northern Tools 5x8 trailer

[jfbrubaker1969]

A friend of mine expressed interest in buying a TTT (Tiny Travel Trailer) and asked me about it. I took a look at products out on the market and thought "I could come up with something better." I love a challenge, I love problem solving and I love finding a better way to do something more efficiently/cost effectively.

My design criteria was pretty simple:
1. A DIY design with the comforts and amenities of a travel trailer
2. Lightweight
3. Strong
4. Easy construction
5. As inexpensive as possible

I started with the trailer frame, looking at what is commercially available, and the Norther Tools 5x8 trailer seemed like a perfect choice. Using that trailer as my foundation I then began to think through the 'Want' list of amenities that I would want to have in a TTT.

1. A reasonable size wet bath
2. Queen size bed
3. Functional kitchen
4. Comfortable and spacious seating/dining area
5. A good amount of storage.

After a lot of head scratching, sketching, CAD drawing and revising, I think I have finally come up with a really good design. I'm calling it the Tiro (pronounced Tee-Roe), it's Latin for 'novice' (since it's my first design). I have a background in engineering and construction but I've never applied it to a TTT before! The Tiro has the following amenities:

1. A 32x32 wet bath
2. A large U-shaped dinette that will comfortably sit four people
3. Dinette converts to a double OR a queen size bed
4. Spacious kitchen area with a sink, refrigerator and lots of counter space
5. Lots of storage

A couple of notes on construction. The floor, walls and roof are laminated construction with wood framing, 1.5" rigid foam insulation core and ply inner and outer skins. The ply skins are glued to the wood framing and the rigid foam insulation to create a strong and light shell.

 

[jfbrubaker1969]

A couple more images

 

[Tomterrific-TNT]

You have designed much in a small space. Good job. My only critique is the height and width will make towing at freeway speeds tough. A longer narrow camper will be easier to tow. Have you thought of a collapsible design?

I tow with 4 cylinders so torque is at a premium. A V8 will have less problems, of course.

Tt

 

[jfbrubaker1969]

You have designed much in a small space. Good job. My only critique is the height and width will make towing at freeway speeds tough. A longer narrow camper will be easier to tow. Have you thought of a collapsible design?

I tow with 4 cylinders so torque is at a premium. A V8 will have less problems, of course.

Tt

Hi TT,

Thanks for the compliment and the critique. There is definitely a trade off between interior headroom and increased wind resistance. The most significant source of drag is the low pressure area created at the back of the trailer. Something like Airtabs should make a noticeable improvement in that regard.

 

[Pmullen503]

All that cabinetry and framing will add weight. I'd suggest less framing with foam board infill. Keep that cabinetry as light as possible. Thinner wood with tab and slot construction instead of thicker wood with fasteners. You can get away with foam board for some of the internal dividers which will also save some weight.

You've done a good job packing a lot in a small space. I'd also suggest you mock up the interior with cheap wood or even cardboard boxes to see what it will be like in terms of space. You may want more space with less storage.

 

[Tony Latham]

That's a serious chunk of planning.

You may want to make sure that the front overhang isn't so much that it may make contact with the tow vehicle while backing. Since you've got all of that CAM work done, it'll be an easy thing to do from a top-camera view.



Tony

 

[jfbrubaker1969]

All that cabinetry and framing will add weight. I'd suggest less framing with foam board infill. Keep that cabinetry as light as possible. Thinner wood with tab and slot construction instead of thicker wood with fasteners. You can get away with foam board for some of the internal dividers which will also save some weight.

You've done a good job packing a lot in a small space. I'd also suggest you mock up the interior with cheap wood or even cardboard boxes to see what it will be like in terms of space. You may want more space with less storage.

Hi PMullen,

Thanks for the comment. I haven't actually 'designed' the cabinetry yet, whats drawn is just to show the concept. The cabinetry exterior face will be constructed of 3/4" thick wood framing with a 1/8" ply facing. Interior cabinet partitions will be kept to an absolute minimum to reduce weight. In regards to the shell framing, it's drawn up as 2x2 construction for the concept, but much of it can be reduced to 1x2 construction to reduce weight.

 

[jfbrubaker1969]

That's a serious chunk of planning.

You may want to make sure that the front overhang isn't so much that it may make contact with the tow vehicle while backing. Since you've got all of that CAM work done, it'll be an easy thing to do from a top-camera view.



Tony

I've already considered that, the tongue would need to be extended a little. I did that once with an old popup I used to have.

 

[jfbrubaker1969]

I did a 3-View study with the trailer tongue extended 12".

 

[OP827]

This looks a little high to be safely towed at higher speeds, at least to me. I had a light fiberglass trailer called Boler, a longer 17' version and it would start waging its tale at speeds over 65mph although the tongue weight was substantial and it had a good compound aerodynamic shape similar to Airstream. And my trailer was longer and lower than this one.

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[OP827]

Please don't get me wrong, I really appreciate your design and effort and will follow your progress, but having high CoG and wide body over a relatively narrow positioned wheels is somewhat inherently unsafe. The reason I am getting sensitive to this kind of shape, this pretty much reminded me my neighbor's home build. He put his wide camper that he later said that he did not like carrying in and out the bed of his truck and installed his camper on a utility trailer similar in size to your model. I had no knowledge at that time whether it was a good idea or not. Then one day I saw his truck in a driveway with all one side and roof badly damaged. I asked him what happened and he said that he lost control of his homebuilt trailer on a highway. Trailer was destroyed and the truck got damaged... Since then I started thinking that building a trailer with a low CoG and low air drag is a really good idea.

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[troubleScottie]

Just a point on the air resistance. Although the flat/square rear of the trailer will add drag, the major factor is the cross sectional resistance. Anything not covered by the cross sectional area of the car is adding to the drag.

Drag = 1/2 * rho * C * A * V **2

Rho is fluid density
C is drag coefficient
A is cross sectional area
V is velocity.

Your vehicle is already handling its cross sectional area and any drag for its shape. Towing is adding in the trailer's effect.

There are other considerations : the flow or turbulence between the tow vehicle and trailer, flow under the trailer, fenders, shape of the trailer.

The drag coefficient (C) is dependent on the shape of the object in this case the trailer shape. For instance, a box has the worst at 1.0. A half wing eg the classic tear drop design is 0.09. A short cylinder is worse than a cube (1.15). A long cylinder is better than a cube (0.84). A trailer with rounded leading, side and rear edges is better than the simple box. I have not seen what is good enough rounding eg 1" radius or 1' radius or 1 meter radius.

As others have stated, the center of gravity (CoG) with the cabinets is pretty high. To go higher, one needs a wider base. How much -- no idea. Also the weight is on one side. Not sure if that affect it much. Most designs have their weight low, at floor level or below the trailer frame and the weight is distributed across the width or centered.

 

[jfbrubaker1969]

Please don't get me wrong, I really appreciate your design and effort and will follow your progress, but having high CoG and wide body over a relatively narrow positioned wheels is somewhat inherently unsafe. The reason I am getting sensitive to this kind of shape, this pretty much reminded me my neighbor's home build. He put his wide camper that he later said that he did not like carrying in and out the bed of his truck and installed his camper on a utility trailer similar in size to your model. I had no knowledge at that time whether it was a good idea or not. Then one day I saw his truck in a driveway with all one side and roof badly damaged. I asked him what happened and he said that he lost control of his homebuilt trailer on a highway. Trailer was destroyed and the truck got damaged... Since then I started thinking that building a trailer with a low CoG and low air drag is a really good idea.

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Sorry for the delayed response, I haven't had a chance to get on to the forum for a while. You are making valid points and I have actually taken them into consideration already. As I had stated earlier, the framing shown in the images was basically just a quick conceptual draft. What I drew is 2x2 but much of it can be done with 1x2. Interior skin/sheeting would be 1/8" ply. Cabinets would be constructed of 1x wood framing with an 1/8" ply exterior skin, so they would be pretty light weight. If I were to pursue this I would be making every effort to keep the CG down as low as possible. One good thing about designing this in 3D in CAD is that I can easily calculate the CoG.

 

[jfbrubaker1969]

Just a point on the air resistance. Although the flat/square rear of the trailer will add drag, the major factor is the cross sectional resistance. Anything not covered by the cross sectional area of the car is adding to the drag.

Drag = 1/2 * rho * C * A * V **2

Rho is fluid density
C is drag coefficient
A is cross sectional area
V is velocity.

Your vehicle is already handling its cross sectional area and any drag for its shape. Towing is adding in the trailer's effect.

There are other considerations : the flow or turbulence between the tow vehicle and trailer, flow under the trailer, fenders, shape of the trailer.

The drag coefficient (C) is dependent on the shape of the object in this case the trailer shape. For instance, a box has the worst at 1.0. A half wing eg the classic tear drop design is 0.09. A short cylinder is worse than a cube (1.15). A long cylinder is better than a cube (0.84). A trailer with rounded leading, side and rear edges is better than the simple box. I have not seen what is good enough rounding eg 1" radius or 1' radius or 1 meter radius.

As others have stated, the center of gravity (CoG) with the cabinets is pretty high. To go higher, one needs a wider base. How much -- no idea. Also the weight is on one side. Not sure if that affect it much. Most designs have their weight low, at floor level or below the trailer frame and the weight is distributed across the width or centered.

Back in my younger days I actually spent a year studying aeronautical engineering. So, while I am not an expert, I do have a pretty good grasp of aerodynamic principles. The box end of the trailer is probably the largest source of parasitic drag (i.e. form drag). One option is the rounded corners you mentioned, but you end up with construction complexities. A much simpler and effective solution would be to use AirTabs.

 

[jfbrubaker1969]

He put his wide camper that he later said that he did not like carrying in and out the bed of his truck and installed his camper on a utility trailer similar in size to your model.

I'm assuming this was a typical truck bed camper? If so, then yeah, that would have been a recipe for disaster as Cog would have been pretty high.

I'd have to brush off my college physics books to do the calculations but a quick and simple graphical illustration shows it would have to tip almost 30 degrees to roll over. The actual computations would be WAY more complex than that! Just for graphical purposes I placed the center of mass in the middle of the trailer (in reality the trailer frame would add enough weight to lower the center of mass a decent amount). Once the mass and center of mass are calculated the centripital force required to cause a roll over could be calculated which could then be used to determine a maximum speed/turning radius ratio.

 

[OP827]

Yes, that was a typical stick built truck camper with cabover bed, so pretty high CoG and biger surface area at the trailer upper half. That is a dangerous combination with strong side wind, speed and other large vehicles turbulence or sharp turn manuevering. There is a certain speed and wind speed limit for any design and figuring that limit could be a real indicator of stability in comparison to other designs.

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