Skunkworks MAKING THINGS BEND AND BREAK The FAA sets out broad specifications of what a propeller must be able to do to pass certification testing, and each manufacturer must create its own test plan. A significant portion of Hartzell's certification plans go through the Engineering Test Lab, a dedicated facility with only five employees. The lab is an engineer's playhouse. Each new blade and hub is sent through numerous tests. Sections of composite blades are pulled with 50,000 pounds of force out from the shank and then pushed up and down thousands of times to simulate in-flight loading. Hub pistons are exercised up and down millions of times, and even deice boots are put through a wind machine-affectionately called the Blowmaster-to determine its impact on airflow. All but a few of the machines in the lab are homemade. Sticking with Hartzell's focus on experienced machinists designing and running the processes, a technician manages the lab, and workers who used to build blades now operate the machines that test them. If all goes well at the lab, the blades are wired with sensors that can detect stress and sent to an aircraft for test flying. -IJT ERIC HUBBARD EXAMINES results from a blade stress test (top). Hartzell is incorporating more digital, independent measuring of parts in the quality control section of its metal manufacturing facility. 66 | AOPA PILOT July 2017