Mandan, an aerodynamic 6x10 foamie

[skyl4rk]

A 2" sheet of R250 will bend 6" to 8" along it's length without excessive pressure.

Thank you, that is the information I am looking for, and I hope to go to the store and do the in-store bending tests this weekend. I can adjust the hull design to fit the amount of bend that the material will allow.

I have been thinking about the hot wire cove strip planking idea that you brought up. That idea can be used to create some very aerodynamic boat hull type shapes, easily and quickly.

[ghcoe]

I have been thinking about the hot wire cove strip planking idea that you brought up. That idea can be used to create some very aerodynamic boat hull type shapes, easily and quickly.

What was said before, The glue is harder to sand than the foam so you will get a ridge at the glue line. On my build I cut back the glue line into the foam some and then sanded the foam. Once I got the foam faired to where I wanted it I then painted the foam with Gripper. I still had a void at the glue line so I filled it with light weight spackle and then sanded it down to the surface of the foam/Paint. By painting the foam it makes it hard to sand into the foam so you can get a nice fairing at the cut line. Prior to figuring out this it was a real pita to get that glue line perfect. I was fighting that ridge and then I could not tell how far I was sanding into the foam. This process worked out pretty good.

I do not have a picture of how it looks now, still working on that.

Here is a shot of the foam lay up for the rear hatch radius using hot wire cut sections glued together.

glue up

DSCF1993 small.jpg (184.81 KiB) Viewed 652 times

[GPW]

George, that’s one SOLID looking hatch !!!!

Sky , although I’ve been interested in Mandan/Hidatsa archery for a long time , never knew about these lodges ... Pretty smart folks !!! ...

[Pmullen503]

.............

I have been thinking about the hot wire cove strip planking idea that you brought up. That idea can be used to create some very aerodynamic boat hull type shapes, easily and quickly.

Might be worth the effort to make the tool to bead and cove the foam strips for tight bends. The wire would have to hold it's shape when hot. If you cut slowly enough, you should be OK. Maybe gravity feed?

The piece would hold it's shape without supporting structure. A judicious application of glue should keep the glue away from the area you need to sand. If you cover with canvas, that will hold the pieces together.

[skyl4rk]

I did a quick test at Menards, bending a piece of pink 2" 250 foam. I would estimate that the center can be easily deflected about 6" when each of the ends of the 8 foot length are held in place. More bending is possible but it starts to take a lot of force.

[skyl4rk]

I changed the design to no more than 8" of bend over a ten foot length. I also made the body symmetrical.

https://drive.google.com/file/d/0B6-YuMVYi0dodWhFS083OE02bkR1R20yanM4bXZsSVp6blQ4/view?usp=sharing

The Hull Designer software will show you a model of the hull, which you can manipulate, then when you save it, it will save dxf images of the unfolded panels. I opened the dxf files in a CAD program (LibreCAD) and did some moving and mirroring to make the panels full size. Unfortunately I have not figured out how to dimension them yet in CAD, so I printed them out and hand wrote the dimensions on the panels. I recommend modeling the panels to see how well they fit together.

The symmetric body design should fit the 2" foam's ability to bend. I'm not sure how aerodynamic it is, but it should be a little better than a box, in any case. The size of the panels means they will have to be pieced together from a number of 48x96 foam sheets, which complicates things. However, the design provides a 6 foot x 10 foot trailer body. The ends are narrower, and the slope of the walls reduces usable space compared to a 6x10 rectangular trailer body.

What do you think? Will this design provide enough improvement in aerodynamics to make the complicated construction worth it?

[Pmullen503]

..............What do you think? Will this design provide enough improvement in aerodynamics to make the complicated construction worth it?

Depends what "worth it" means.

As for aerodynamics, rounding all the corners, especially up front, is important. Nice thing is that foam is easy to shape.

Then you have to think about the interior layout. Where will you put the doors, the galley, the windows? I think you should build a model of the basic shape and figure out where everything will go and whether you think it looks good.

I like it. I'd put fake rivets on it and steampunk details.

[ghcoe]

If you angled the side walls like that it will really make for some complicated joints. I do like the side walls bowed like that and the roof. If you left the side wall angle out I think it would be a pretty easy build with the roof and side bows. windows and doors would be a pain to try and make water tight too, with angled side walls. just some food for thought.

[Pmullen503]

If you angled the side walls like that it will really make for some complicated joints.............

Actually, since you could build it like a boat on a temporary frame, you could make the panels over-sized and hot wire or saw the angles into the panels as you cut them to size.

[skyl4rk]

The way that I would angle the edges to fit the curved and angled panels is to bevel them with an orbital sander.

For example, to bevel the top of a side panel to fit the roof panel:

Set both side panels on a jig that represents the correct location of the panels.

If you imagine holding a straight edge from panel to panel, this represents the angle that the edge needs to be beveled to, to match the roof panel. As you move forward and aft, the angle may change. Keep the straight edge running perpendicular to the opposite panel and the bevel angle will stay correct.

Now take an orbital sander, and clamp a broomstick so that it is parallel with the sanding disk face. Use the broomstick in place of the straight edge in the example above. Lay the broomstick on the opposite panel, and it holds the angle of the sanding disk to make the correct bevel.

The operator will need to know when he has cut away at the edge enough, so it takes a certain amount of skill.

I have done this in smaller scale using a hand plane and a piece of wood, to bevel plywood prior to joining it with epoxy. I think beveling the foam will be easy and fast.

[ghcoe]

The good thing about foam is that if you mess up it is easy to fix. I would still worry about keeping the water out. Most windows are designed to be mounted vertical and will not drain properly when tilled back. I had a travel trailer that the front window was angled like that and it constantly was a problem until I used a lot of silicone. Stopped the leak, I think, but look terrible. Also, If you mount the door on the side it will want to wick water into your dry spot more than if the door was horizontal. I don't think you will gain any aerodynamics by angling in the walls like that. Although it would add style point .

[ghcoe]

You can read up on everything aerodynamic for fomies here.

viewtopic.php?f=55&t=49036

[skyl4rk]

Here is the tow vehicle, and an older aero experiment...

http://ecomodder.com/forum/showthread.php/nissan-versa-base-1-6-a-7489-3.html#post97821

Unfortunately, it disintegrated during a high speed run.

[ghcoe]

It probably fell apart do to turbulence. Here is a good read on the Kammback. http://en.wikipedia.org/wiki/Kammback

While the realities of fluid dynamics dictate that a teardrop shape is the ideal aerodynamic form, Kamm found that by cutting off / flattening the streamlined end of the tear at an intermediate point, and bringing that edge down towards the ground, he could gain most of the benefit of the teardrop shape without incurring such a large material, structural, and size problem. The airflow, once given the suggestion of the beginning of a turbulence-eliminating streamlined teardrop tail, tended to flow in an approximation of that manner regardless of the fact that the entire tail was not there. This is called the Kamm effect.[9]

Remember that a trailer towed behind the TV is already in turbulence from the TV and aerodynamics of the trailer is diminished considerably. Frontal area is probably the best place to eliminate drag, outside of that shape probably does not matter too much. This is all discussed in the above mentioned thread.

[angib]

As for aerodynamics, rounding all the corners, especially up front, is important. Nice thing is that foam is easy to shape.

Yes, the most important thing is to round the vertical and horizontal (well, top only) front edges.

Pram dinghies do not run immersed up to their gunwhales which is why they can get away with a boxy shape - and why there is no guarantee that shape is aerodynamic. But if it is the tow vehicle's shadow, it shouldn't be too bad, providing the flow can stay, if not attached, at least fairly smooth - which is where the front corner rounding is so important.

The rear vertical and horizontal edges should not be rounded - sharp edges here will have lower drag (and a bit better stability).