Posted by: Wayne | April 9, 2010

Rudder – Day 4

Over the past two days I had finished shaping the outline of the rudder blade using a combination of jigsaw, block plane, rasp, and sandpaper.

Final outline for the rudder blade.

The next step is to convert a rectangular block of wood into something resembling a foil.  There are many ways of going about this, from the TLAR (that looks about right) method to highly precise jigs and routers.  I chose to use the method outlined in http://www.duckworksmagazine.com/09/howto/foilcuts/index.htm.  This involves drawing guide lines on the edges and faces and planing a series of facets which closely approximate a NACA 00xx series foil.  Actually, I decided to slightly modify the shape by going with a larger radius on the leading edge.  This should allow the rudder to “fly” at a higher angle of attack before it stalls.  After some simulations using xfoil, I arrived at a set of numbers I think will work well.

The most difficult set of lines to draw are on the edges, as they need to be quite precise.  I used a combination of a pencil, a block of wood, a drill, and a table to accomplish this.  Simply drill a hole in the block at the appropriate elevation, stick a pencil through the hole, and then scribe by laying the board flat on the table and sliding the block with pencil along the edge.

My high-tech method for marking a straight line along the edge of a board.

After this, I simply used a tape measure and ruler to mark the lines along the face of the rudder blade.  I also used a saw to connect the lines from the trailing edge to the forward edge of the salient facet.  Then it was time to use a plane to turn vast quantities of wood into shavings.  This is only partly done at this point.

Quite a ways to go.

Now I get to keep planing away anything that doesn’t look like a rudder.

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Responses

  1. Very nice. I remember playing with xfoil in high school.

    For removing a lot of material, a bigger plane is really nice. I might have something lying around that I can bring out in July.

    • I am also thinking that the rasp we have should work well. It is about 8″ long by 2″ wide, with fine and course sides. It should also avoid tear-out on some of the more difficult grain.


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