High Speed Wind Tunnel for KidWind

 

This post is going to cover the development and evolution of the shroud design to increase wind velocity in the standard KidWind tunnel. After considerable testing and experimentation it was determined that the best way to increase the velocity was to reduce the inlet opening of the wind tunnel. Pictured here is the simplest of designs, a 32" diameter opening made out of flat cardboard! This brought the wind speed up from 4.5 m/s in the standard KW wind tunnel to a whopping 8.5 m/s! The early resulting out put of a turbine placed in this wind speed was considerable and approached 400 Joules of energy in 30 seconds with a 30 ohm load.

Could this "plain Jane flat cardboard" be the best design?  All the professional wind tunnel designs were more elegant and looked more scientific. So I began my improvements. Not so much for velocity but for the "looks".

I would go for a radius inlet opening. This was modeled after the successful larger tractor tire inner tube testing that was done earlier in the year. After deciding on using styrofoam for the material and solving the technical problems as to how I would cut and shape it with a hot wire construction began.

The optical result over the flat cardboard was impressive. The wind velocity still below the flat cardboard by about 1 m/s. To address this it was suggested that an extension tube (shown in pink) be added to the exit side of the radius. This was done and various lengths were tried. The longest length, about 12" was best. Test wind speeds were measured with a standard anemometer on the end of a stick. This got me  thinking about the testing method and I decided to shift to Joule output. I would keep the blades and generator the same for all testing. To my surprise the Joule output with the flat cardboard and radius opening shrouds were the same! My guess is that the turbulance caused by the flat cardboard design was the cause. This seemed to be demonstrated visually and graphically on the Vernier voltage display screen. So this radius would be the final design.

 

 Since the idea is to use the standard KW wind tunnel for regular KW Challenge testing and then add on the shroud for some "serious fun" testing at higher wind speeds after the main KW challenge I needed to keep the same dimensions inside the standard KW tunnel when the radius shroud was in place. A 3/4" plywood with a 32" diameter hole was hinged to the entrance of the standard KW wind tunnel. It was hinged on one side to allow it to be swung open so teams could  get inside and set their turbine for testing. 2x6 extensions were added to hold the radius portion of the design.

2X6 extensions and plywood hinged in place. You can see the turbine inside through the 32" diameter opening.

Important to note is the tight fit of the 3/4" plywood to the opening of the standard KW wind tunnel as shown here. No gaps mean fewer losses in wind speed.

The final step was to build the tube between the 3/4" plywood and the radius shroud opening. I choose to us light gauge metal coil stock.

The end results from the outside looks impressive and has the desired "cool factor".

What it looks like from the inside of the tunnel.

And with the high velocity shroud swung open allowing team access to the turbine for placement and set up.

The results

The Joule output numbers tell the story. 6 blades (110 mm wide, 520 mm long with 15 degree twist) NACA 2415 airfoil connected to a 30 watt generator with 1:30 gear ratio and a 45 ohm load.  Output: 35.957 volts, .753 amps, 27.075 watts and 807.51 Joules in 30 seconds! Sweet

Cabin Doors Made and Hung

 This was the last of the windows. The center window is fixed and the two side ones open to the inside of the cabin. These windows face the West but will be well shaded by the 3 foot roof overhang.

The glass for the doors needed to be tempered and took a bit longer to get. The challenge of making the frames for the doors was a little more complicated as there was no center post and I wanted the doors to interlock. With three layers of material this required some serious planning. First I made a "story stick" for the exact width and height of the 6 x 6 door frame.

In the sketch you can see the stack-up of the three layers. The yellow side door would be the door least often used and would be pinned in place at the bottom and top. The pink side door would be the primary door and the interlock needed to be constructed accordingly. The 11/16 inch glass would allow for a foam seal on each face. Stock 3/4" thick would be used to surround the glass. It would be cut to be flush with the frame on three sides. The mating side of the doors would need to be staggered as in the sketch. The 1 x 6 cedar material would make up the frame and hold the glass in place. All this was drawn full size on the "story stick" and made the job possible.

The doors were quite heavy, weighing in at about 75 pounds each so I transported them to the cabin on a sled since I could not drive up to the cabin with all the snow.

Doors hung. Mission accomplished. Very nice light and good view.

Looking at the cabin from the S.W. 

Looking at the cabin from the N.E.

Well this just about wraps up the cabin work for this year. May experiment with sizing up the BTU's needed for the propane fireplace that will be used for heat. Will have to think about that for awhile.

Gable Ends and Windows

 

A window was added to the South end to let in more light. Then the gable end was insulated and covered with salvaged barn board.

The North end of the loft was insulated and then covered with 1 x 8 tongue and groove pine to match the ceiling. In both ends the boards were set back to expose the 6 x 6 post and mortis and tenon brace work.

With the interior pretty much in hand it was time to move on to the windows. Thermo pane glass panels with interior dividers were ordered. The planning for this required a considerable amount of measuring and thinking.

The glass panels would be sandwiched between two layers of cedar. These layers had to be the correct size so as to fit into the cabin window framing. The inside of the layer had to be large enough to keep the glass in the frame. Lastly there needed to be a spacer the thickness of the glass between the two layers. This spacer had to be just the right size to fit the glass on the inside and be flush to the edge of the top and bottom layers to make the sandwich. Also the corner Lapp joints had to be alternated to provide the needed strength. Pocket screws were used to assemble the first layer. Then the spacers were nailed and glued in place. The glass was inserted and then the top layer was screwed on to finish the sandwich.

After a couple of hours the first two windows were framed and turned out well. Now it was out to the cabin to hang them.

Everything in the cabin is built heavy and oversized and the windows are no different. Locating and  inletting the hinges of these heavy windows would be a challenge. Getting them to hang and not bind would the the goal.

Mission accomplished ! Two down, with another three panel window and the doors to go. Should be an interesting next couple of days in the workshop and out at the cabin.

   

Roof is on. Cabin buttoned up for winter

 It took a few months but the electric service power is finally in. 

I have a new appreciation for electricity coming from the grid. Although a lot of time and effort went into planning the circuits, running the wires and hooking up the outlets, switches and lights it will be well worth it. No more noisy, polluting generator. Multiple convenience outlets to plug into with minimum extension cords. Very nice. Those against renewable energy power should have to go a few days with just a generator to power their house or business. 

So with 100 amp service and 6 circuits way over kill for a tiny 12 by 16 cabin with a loft but fun.

After some serious measuring and planning the roof tin and trim was ordered and shipped out in some nice protective box pallets (that they charge for but can be returned for credit) from Menards. Full length 16 foot sheets. Requiring 3" long screws because of the 2" of Styrofoam on the roof for insulation.

Pre-drilling the sheets for screws and using the half of the extension ladder with the hooks made the process of putting on the sheets tolerable. But roofing is still a "younger mans" job! 

Pictures of the cabin roof from the back and the front. Turned out very well. After putting on the ridge cap I now know what a turkey wishbone feels like. 

To help keep the snow and weather out over the winter I wrapped the cabin in plastic. This way I can heat it to take off the chill while I install the windows and door and do some trim work on the gable ends.

Happy Thanksgiving 

The Cabin is in the details

 With the stairway to the loft complete and the loft floor in I had a platform to work off from to close in the area between the top of the cabin walls and the roof.

Note: The blue outlet boxes are for the circuits that will be ran to the 100 amp fuse box. This will be the next step in the process and some new learning as to how to recess the boxes and make the wire runs for the 6 individual circuits to power up the cabin.

The gap between the roof and top logs is the width of the 6x6 rafters and needs to be sealed and insulated well. Wiring to loft outlets and light fixtures will also be run in this space.

The first step was to cut and fit the bottom piece as shown on the right side in the picture. This required a bevel cut at an angle that matched the roof pitch. Next the vertical piece was fit so that it butted up against the bottom piece and also was beveled to match the pitch of the roof. The triangle area behind these two pieces will be filled with insulation and make a nice seal to keep out the cold.

View from the loft looking at the stair well. The gable end will be insulated and covered will 1x 6 tongue and groove pine boards.

 

Here is a picture looking up from the main cabin floor toward the bottom of the loft floor. There will be a railing along this edge but this area will be left open to the roof. A ceiling fan will hang down in this area and help move the air down from the ceiling.

Next, wiring, windows, doors and roof steel.

Roof and Loft - That's a lot of wood!

The first order of business was to surface all the rough sawn boards that would make up the floor of the loft so they were the same thickness.

This was one of the two piles of shavings that came off the loft boards (imagine doing this with a Jack plane by hand). Note: When mixed with a little fuel oil this stuff make a great fire starter for wood fires.

This was a process to say the least. As the boards were various thickness from two inches + down to 1 - 1/2" the boards had to be sorted out from thickest to thinnest and ran through the surfacer in order of thickness to avoid constant height re-adjustment. After a couple of hours the job was done. With all the loft floor boards at just a bit over 1 - 3/4" in thickness.

The next steps in the process required a bit of multi-tasking. I decided that it would be easiest to stain and finish all the roof and loft boards before they were put up. It is a lot easier to do this when they are down on the ground and not overhead. So it was off to Menards to get the 16' long 2 by 8's and 2" styrofoam insulation. Here again a bit of engineering was required to get everything loaded for the 25 mile trip to Darlington. One thing that made the trip possible was the sheet of OSB plywood that I placed in the area  between where the two piles of 2 by 8 overlapped so that when the truck turned the upper pile did not catch on the lower pile on the boat trailer. Looks a bit like some of the load pictures you see on You Tube.

That's a lot of roof! Had to improvise a bit to build racks the would hold all 63 of the roof boards so they could be stained and finished. First the boards were stained using a roller and then two days later coated with a clear coat of gloss polyurethane.

While I was at it I thought it would be best to stain out the cabin logs as well. The week before I had bleached the logs to brighten them up and then wire brushed them to remove any loose material and smooth them out. Then using my Wagner airless sprayer went to town on the inside and outside of the cabin logs as well as the roof beams and supports. The Honey Gold stain really brought out the grain and color of the pine logs. Later I will also give the inside a coat of the gloss polyurethane to shine them up. When the sun is on it make it look like a picture out of the log cabin magazines.

With all the boards and cabin walls stained it was time to set some scaffolding and begin putting on the roof boards. This has gone pretty well so far. The 2" styrofoam will go on next and then the steel roof.

Here is a shot of what the roof is going to look like when finished. You may notice some dark 2x4's in the picture along side of the roof rafters. These were required to support the roof boards on the edges until the proper 6 be 6 beam extension pieces could be cut and attached to do the job.

So things continue to progress and soon the cabin roof will be on and any rain kept out so the inside work can begin, loft floor, loft stairs, gable end insulation, wiring, window and door frames... 
  

Gable Ends and bleaching

 So now with the Rake end boards set in place it was time to frame in the Gable ends. I practiced on the solid end and then went on to frame in the window and air conditioner openings.

Next on with the 1/2" sheathing. This will seal off the wall and provide a nailing surface for the rough cedar boards that will be run vertically.

The exposed wood discolors a bit as you can see in the first picture. To brighten it up some a 50/50 mix of bleach and water is sprayed on the surfaces and just like that the wood looks fresh and the grain stands out more. Now with a coat of finish it will stay this way if protected from the elements. More on that later after the roof is on.

So another step along the journey of building Cabin #6 taken. If the weather cooperates I will stain out the cabin and maybe even cut in some outlet and switch box openings next. Or maybe work on surfacing the loft floor boards. Plenty of things to work on.