1/2 Scale "model" windmill

[Merlinn]

I was just kidding. I never lobbed a round at a windmill. Always loved them and wanted one. I finally had the perfect place for one and now my dreams are fulfilled.

[Merlinn]

Having trouble replying with a picture. What am I doing wrong?

[Merlinn]

I was just kidding! I never lobbed a round at a windmill. I always wanted one and now I have the perfect place for one so an Aermotor A702 now resides in my front yard!

[Merlinn]

Sorry for the duplicate posts. Slow internet here!

[Windcatcher530 Dan]

That's ok merlinn when you get older including me every post and day is a new one. Over and over and over and over see what I mean

[arizonian]

Another question that has reared it's head: What is the maximum sustained wind velocity before the tail starts to self-furl. What is the maximum allowed before the operator should furl the tail from the ground.

[arizonian]

Having trouble replying with a picture. What am I doing wrong?

At the bottom, click on Attachments and just drag your picture into the text or click on Add Files.

[Windcatcher530 Dan]

As far as self furling that depends on what hole you use on the tailbone to put your spring in.closer to the mill it will furl quicker. I usually self furl my mills if the winds are going to be around 35 miles and hour just to cut down on wear and tear.

[arizonian]

Tilting at Windmills
I am documenting my windmill build project for any one that wants to follow along. There will be multiple photos, and there will be gaps and out of sequence shots, so please bear with me. Don’t pay attention to the dates on the photos as they will be all over the place. This project was started in earnest at the end of September with the first piece of material that was bought.

The first thing needed is to size the windmill. A one-half scale seemed plausible, so that is the direction this is going. This is not a true model in the sense of copying down to the last bolt a vintage Aermotor windmill, but the operating mechanisms and principles are based on the general Aermotor design. Also, I do not have access to a foundry so any and all castings in the original mill will be fabricated steel to mimic the design intent rather than the actual dimensions.
The Sail:
To calculate the sail (wheel) several photos were taken and printed and then drawn on to map out the curvature of the blades, the openness of the wheel and the angle of attack to the wind. The chord angle of the curved blade coupled with the percent openness of the wheel, the number of blades and the scaling factor and some rudimentary trigonometry gave a pretty fair estimate of the blade geometry. As seen in the photos below, the sail is not solid wheel but has a roughly ~38% openness.

The chord angle is about 35°. Once the size of the sail blade and chord angle was determined, the actual dimensions of a half scale blade could be calculated. The wheel in my windmill will be forty-eight inches in diameter with a blade length of fifteen inches and a flat width of six and five-eights inch. The angle of attack to the wind depends primarily on the speed of the wind. As this is a fixed pitch turbine, the angle of attack will change over time depending on wind velocity and the RPM of the sail.

The curvature of each of the blades required a wooden buck for final forming. Each blade was formed with a slip roller. The buck was created using a router with a pivot to mimic a part of a cone at the appropriate geometry. Since there is always springback when cold forming steel and the slip roll in use only duplicated approximately, the buck and hammer was used to bring the final form. The buck was reinforced on the bottom when repairs to the buck were made necessary. The last photo is the soldering fixture to attach the bottom clip and middle clip to each vane.

Yes, I did take a photo of a photo. We'll see how that turns out later.

More to come.

[arizonian]

Center Hub and Sails: The center hub presented numerous challenges. A dividing head, a 20 inch sine plate and the appropriate number of turns that were mathematically correct to place the spokes in their intended position. There are twelve spokes, six on each hub face, with three leading and three trailing spokes on each face. There is a one and a half inch gap between the leading and trailing spokes on opposing hub faces. The spokes cross each other at the inner ring and have a separation of two inches at the outer ring. The spokes also lean in toward each other so they are in a staggered alignment at the outer ring. The first set of three holes for the leading spokes were milled, drilled and tapped an each face without a hitch, but a mathematical error placed the trailing spokes in the wrong position. A bit of welding to plug the mistakes and a correction was made to the formula.

The sine plate was posted about earlier, but in brief, it is fabricated from a short length of S4x7.7 S-beam and a three-eights by five by twenty-one inch cap plate. The sine length is twenty inches between centers. The twenty inch length of the sine plate was required to allow the mounting of the dividing head and tail stock at the appropriate angle to drill and tap for the spokes in the hub.

The inner and outer rings were cut to length, drilled and rolled with a cheapie Harbor Freight ring roller. Spokes are from 1/4" hot rolled and threaded on each end.

I have to admit that the spokes are not exactly what I hoped for. I learned that there are two threads almost exactly the same but off by .008". The desired thread is 1/4-20 UNC, but the die I used is a #14-20 die. Turns out that there used to be #14-20 (.242") standard that is no longer in use today.

The last shot is hammer forming the inner (bottom) clips. Thanks, Three Piece!

More to come.