Grish Brothers made a Nylon Tornado prop 9 X 4 that I would use on my OS 25 AX PBF for combat flying. They would hit the ground or other planes and never break. You could actually take the tip of the blade and double it back to the hub and would not break. They have since been dis-continued, company went out of business.

But- look at the prop while running from above and you could see the prop flex considerably from idle to full power. This had to have bad tracking !!