Here is a sequence of photos showing each major step in the building of the small rotor blades used on the "MINNIE" autogyros. These procedural steps would be basically the same for larger rotor blades with changes in materials, etc., as would be required for the larger blades.
Assemble all the materials. Blade blanks, Leading edge strips, Carbon fiber strips, Ply mounting plates, and wire for the leading edge... If you have selected nice balsa, your blade blanks should not only weigh the same, but only a couple grams.
Epoxy the spruce strips to the leading edge. Be sure that the bottom edges of each are flat/flush against the board. Again, check the weight, each blade should weigh the same.
File & sand the blanks to an airfoil shape, checking constantly with the template for accuracy. Check the weights again.... to insure each blade weighs the same as the others. We do this to make sure we have not made a mistake with any single blade.
Mark the location of the chord-wise balance line (25-33%) and tack-iron the "iron-on" strips of Carbon Fiber in place. Then use thin CA to secure them in place.
Using the chord balance line for alignment, epoxy/clamp the mounting pads in place on both top & bottom. The blades should still weigh only a few grams (less than 1/3 ounce?) at this time.
Cut the wires to size, bent a 1/4" "L" in each end, pin drill in the leading edge for the "L" hooks. Using a small vice to hold in the blade in place, spread a bead of epoxy along the spruce leading edge. Place the wire down, and hold until dry with strips of scotch tape.
Smooth out the epoxy bead with your fingers, then add a few more strips of scotch tape, and allow to cure completely. The blades should now weigh perhaps 1/3 ounce (10 grams?) Once the glue is cured, this would be a good time to drill for the mounting holes. USE CAUTION: these holes must be aligned/placed accurately. While you`re at it, trim the edges of the blades as per the plans, and if desired you can "harden" the ends & edges with thin CA.
At this time we need to balance each blade span-wise by "teetering" each blade on a round cylinder such as a # 11 XACTO knife handle. Place the blade on the handle, rotate the handle left/right until the blade balances. Then mark the location on the blade. Do this with each blade, and compare them to each other. If you have done your work well,
they should all agree to within 1/8". In the situation here, with these blades, three agree
exactly, and one is off by 1/4". This means we will place the balance lead in the same location for three blades, and move the lead bead on the fourth blade parallel to the leading edge just enough to teeter this blade at the same location as the remaining blades.
At the position determined in the previous balancing procedure, cut a small hole, and insert/epoxy a lead "split shot" sinker in place near the tip, just forward of the end of the CF strip. If you look closely, you can see the lead weights in place in the upper right ends of the blades, with the top blade having the lead about 1/8" further toward the tip of the blade than the others. After applying the epoxy, place a strip of scotch tape over the spot to not only hold the lead in place, but to smooth out the glue surface. There are several reasons for the lead beads. (1) Allows for span balancing, yet keeping the blades at equal weight. (2) Adds "tip" weight to each blade, which improves performance.
Double check the balance of each blade, both chord-wise and length-wise, and you are now ready to cover the blades! If you have done your work well, each blade should still weigh less than 1/2 ounce! NOTE: You might want to apply "Balsarite" before covering with Monokote, and if you do, THIN the Balasrite 50/50 with Acetone to keep the weight down.
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