Interesting wooden propeller link

http://mission.base.com/pedal-power/pp_prop1.html

From viewing other messages i have started to work on the above paper. Like John Moore, i am stuck on page two which describes the lamination sizing diagram. How do you know how many to use? How do you interpret this diagram for actual use? I cannot get mt head around the expalnation.

Thanks

 

Consider the photo on page 1. If you were to move the point of view forward a bit so you were looking side-on to the prop, what you'd see is essentially the same as the lamination sizing diagram (fig. 3). The 5" separation he shows for each stack is arbitrary - it has nothing to do with the blade pattern, and its only function is to keep the stack graphics from overlapping. If you were to sight down the trailing edge of the blade, the heavy dots he shows on the bottom line for each stack would actually be lined up on top of each other.

In the diagram, the axis of the prop runs up and down. The three stacks he shows in the figure represent the blade at three different radii - at the hub, at the maximum width of the blade, and at the tip. Each station has its own pitch angle, corresponding to the helical shape such that each section will advance the same axial distance per revolution.

You have to use enough lamina to accommodate the maximum width of the blade, shown as 4" on his diagram. The height of the stack is then max_width * sin(pitch_angle@max_width), rounded up to the nearest whole layer. Another way to calculate it would be max_width/sqrt(blade_pitch^2+2*pi*(radius@max_width)^2)*blade_pitch, and round up.

The trailing edge of his blade design is a straight line. This means that at each spanwise section, the trailing edge will be on the bottom layer where he has the heavy dot. The width of the arms in each layer has to be able to accommodate the thickness of the blade at each station. So you come up the pitch line at that station the width of the blade there and mark the location of the leading edge, then draw in the section shape and draw another line at the pitch angle tangent to the top of the section. Draw vertical lines from these parallel pitch lines to the neighboring layers and you'll have the width of the spoke at that location.

Once you have the width of the spoke at the three spanwise locations, you can lay out a pattern like Fig. 4, using the spoke width at the hub, max width radius, and tip.