For those of you that would like to know what I've posted about extruded aluminum blades, here is one of the posts:
Thread; Extruded Blades
04-11-2007, 09:17 AM
My only problem with aluminum extruded blades are that they are not a composited metal structure, besides the spar. Meaning, that like a Bensen or Rotordine blade, if a stress crack occurs, there is more than one layer of material that should hold the blade together until the next flight, where the crack should be discovered during inspection. If a crack would occur on an extruded blade, it is possible that it would crack all the way in one flight, not ever giving the pilot a chance to find it.
But..... I agree that if properly assembled the blades seem to be holding up to customer use. As Mike said, he has been using them for 9 years. How much flight time that translates into I have no idea. Even if it was hundreds of hours, thats nothing compared to the time as a fleet that we have put onto composited metal blades over the years.
To that end, I also use extruded aluminum blades on the UAV helicopters I build with great success, but limiting the life to 250 hours. I use the fully symmetrical 6.750" cord blade. I tried to buy they from Vortec, lucky I didn't send my money, ended up they didn't have any in stock and he would have kept my money until he received more orders so he could afford to extrude a new run, which turned out to be never.
So I had to have my own extrusion dies made, and I found a good place that could extrude short runs and had them made myself. Only cost around $14,000.00 for dies and all, including a run of blades, forward spar, middle spar and flat caps.
I'm looking into fiberglass "Pultruded" blades for my next project.