PIQUA, Ohio — July 14, 1994 — Hartzell Propeller is nearing certification of a new lightweight, three-bladed composite propeller system designed for use on aerobatic aircraft. The new propeller system will initially be certified on the Aviat Pitts Special S-2B.
The system will be available to additional experimental aircraft category aircraft as a Hartzell Top Prop™ High Performance Propeller Conversion Kit on a Supplemental Type Certificate (STC) basis. A two-bladed version will be certified at a later date.
Hartzell’s aerobatic system consists of composite blades incorporating high performance aerobatic airfoils, a brand new shank design, a nickel erosion shield bonded to the leading edge to provide impact and erosion resistance, an aluminum hub, a new spinner, and an oil accumulator system to provide engine overspeed protection.
The accumulator system consists of a valve pad assembly between the engine oil supply and the governor. When the valve senses an oil pressure loss from the engine, the accumulator takes over, continuing to supply the governor with oil, and the pilot with effective propeller pitch control.
The new composite three-bladed design offers aerobatic pilots superior low speed thrust with only a minimal gain in weight. The new composite three-bladed kit weighs only 5.66 lbs. (2.57 kg) more than a comparable two-bladed aluminum system. Additional benefits of the composite system include improved tip clearance due to a shorter prop diameter, better reparability due to the easily workable composite structure, and a stronger warranty (3 Years/3000 Hours).
Pilots can also expect a reduction in vibration. Two-bladed props generate two large pulses of thrust compared to a three-bladed prop’s greater number of smaller, smoother pulses. As a result, the extra blade reduces overall aircraft vibration. Hartzell’s composite aerobatic prop also has a lower polar moment of inertia which puts less load on the engine crankshaft and helps reduce the risk of crankshaft breakage in severe aerobatic maneuvers.
Flight performance results are impressive. Ken Hadden of Columbus, Ohio and President of the local International Aerobatic Club has performed the initial flight testing. He noted that “…vertical penetration is fantastic and more time can be spent on down lines because of the braking effect of the three wide-chord blades.” In addition, “… topping off a line from vertical to horizontal is easier because of the added low-speed thrust of the propeller and the dramatic reduction in torque effect at high power settings.” During the flight test program, the oil accumulator system worked exceedingly well and the pilot was unable to overspeed the engine.
The new propeller system has successfully completed vibration testing throughout the entire flight envelope of the Pitts S-2B test aircraft, including a vibration survey of the Lycoming AEIO-540-D4A5 engine. The new system was also analyzed during high stress maneuvers such as power on spins, snap-rolls, torque-rolls and lomcevaks. One of the first applications of the new system is on the B. F. Goodrich Extra 300 flown by well known airshow pilot and national aerobatic champion Patty Wagstaff. To date, Patty has flown more than 250 hours on the new Hartzell system.
Certification is expected in the fall of this year and the prop will meet the same criteria as other Hartzell composite props that have now undergone millions of flight hours on the Cessna Caravan, Beech 1900 Commuter, Shorts 360, CASA 212 and the Porsche Mooney PFM.
Hartzell Propeller Inc. is the world’s leading manufacturer of propeller systems enjoying 60 percent market share on turboprop airliners and 85 percent market share on corporate turboprops. The 76-year-old company is also well known for its design leadership having introduced the industry’s first full-feathering propeller for light twins, the first fully reversing propellers for corporate turboprops and the industry’s first composite structure blades.