Balsa Dust and Rotor Blades...  It`s all part of the fun....

If you don`t mind making a little balsa dust,  it`s not that difficult to make good rotor blades with just a wood file,  a couple sanding blocks,  sandpaper, and of course a small Shop Vac...   
What you see here is the making of balsa rotor blades with a reasonably close Clark-W airfoil.    Why the C-W?   Well it is relatively thin, much more so that the standard C-Y, it`s easy to form by hand,  and the in-flight performance (for the small models) has been excellent!

These blades here are for a small rotor of about 35"  (less than one meter) ,   Select a good grade of balsa sheet of the correct thickness  (here it is 5 to 6 mm),  and cut the blanks to slightly oversize.    I have generally used an aspect ratio of about 10 : 1 ,  which was also the ratio used and found to be excellent in the recent (Feb 2000) Garber/Friedlander wind tunnel test.    I decided to test a slightly wider chord with a ratio of 8:1... which is what you see here.     You need to cut out a template  of your  Airfoil   to make sure the curvature is accurate.    

Place the larger sanding block on the edge of your work bench/table, which gives you a solid  non-slip  foundation for sanding.   I use a wood rasp/file with a medium side, go one step at a time with each blade to insure each blade gets equal shaping with the others.    File one section on one blade, and do the others exactly the same before going on to another section... this helps in keeping all blades identical , which is important.     It is good idea to make an extra blade.     After each step, check with the template.




Note that prior to the filing I glued a basswood (or spruce) leading edge stick,  that is filed to shape along with the balsa.   Leading edges can be of wood such as this,  or you can groove the edge slightly after the shaping for a Carbon Fiber rod ( which works very well ) or even use a piece of music wire.    As you can see,  the high lift point along the chord,  is about the 33% point,  which is an excellent place to align the mounting bolt(s) to the Hub.





In the next photo note that I have shaped no less than six identical blades, all from the same sheet of balsawood.   Being able to cut all your blades for a particular rotor set from the same sheet assures you a set of blades that will weigh virtually the same, which is also very important.




Next, I CA glue Carbon Fiber (Iron-on type) strips to give the blade critical shear strength, and then glue the mounting plates of 1/64 plywood.   Note:  these are aligned along the 33% chord point !








Small weights (lead, solder,  steel, etc.)   are placed flush with the underside,  near the blade tips.  With this set I elected to epoxy thin steel washers into cut-outs you can easily make with an XACTO #11 knife blade.   embed the weights so that the airfoil surface remains smooth.    Please click on this photo for a better view...






Now cover the top with bright contrasting colors...   Strips at least 2" (50mm) wide aid greatly in making the top of the rotor visible.    Without this the rotor may tend to vanish and be difficult to see.   When you can see the rotor,  you know the model is turning toward you,  not away.


Jim Baxter,  August  2000





Key things to remember:

(1)  Whenever possible use the same sheet of light to medium balsa for each set of blades.  All blades need to be of equal weight.
(2)  Use a block of wood covered in sand paper for a slip free filing surface.
(3)  A 1" wide (25mm) medium cutting grit wood file works best for filing.   A medium to course sanding block, as a substitute for the file will work, however I find it is much more difficult to use.
(4)  USE A TEMPLATE  of your desired airfoil to insure uniformity and accuracy !
(5)  Some sort of solid leading edge is a virtual necessity.  A supporting strip or spar along the 33% chord line is important,  and recommended,  but not critical.
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