To save money, I build new ones from the stubs of the broken ones. In this Instructable, I'll show you how to do that.
In addition to saving money, I found my new blades to be both more durable and to lead to a more stabilized hover (at the expense of high rotor speeds).
Step 1: What's Needed?
You need the stubs, because they have the mounting hubs formed in them and they help set the correct pitch of the blades. Once the new blades are cut and shaped, we'll cover them with Monokote for a sleeker finish and to add additional strength.
(2) Plastic blade stubs, cut to the same length (about 1" or so of blade remaining)
(4) Pieces of 1/16" balsa wood (or 3/64" if you can find it)
Glue - CA or Gorilla Glue
Monokote covering or similar material
Covering iron or a small household iron
Step 2: Cut Everything to Size
Step 3: Glue and Clamp Sheets to Stubs
It's important the the blade be glued securely and clamped well, especially at the stub end to get good adhesion of balsa to the stub.
You should end up with a nice curvature at the stub end, that becomes less curved at the tip end.
Step 4: Cut Balsa Blade Down to Original Blade to Size
I cut my new blades a bit shorter than the originals, but left the chord (width) of them be a bit wider. I found that the design resulted in requiring high rotor speeds for hovering, but was more stable in the hover as well.
You will need to experiment for your particular helicopter. For first blades you can cut them larger and longer and mount them uncovered. You can then adjust the size down until you reach optimum size for your machine and flying style.
Step 5: Sand to Make an Airfoil Shape
During this step, you'll also want to make sure that you end up with two blades that have the same weight and balance. If not, you'll get a disturbing vibration when flying.
Step 6: Cover Your Blades
Using your iron, follow the directions with your covering, but make sure the covering is absolutely smooth. Also, make sure you keep the amount of covering used consistent, else you will affect the balance of your blade pair.
Step 7: Finished!
I hope you enjoyed this Instructable and found it easy to follow.