Page 7 - Volume 17 Number 2

& HartzellUp for NewKing Air PropStaff ReportFinding ways to get more performance out of an ex- isting airframe is what Raisbeck Engineering has always been about. The Seattle-based modifier hasgrown to dominance in its field by enhancing Beech King Air and Bombardier Learjet aircraft. Putting more engine power to work, boosting performance and resale value, is at the heart of Raisbeck’s methodology. And when it comes harnessing an engine’s horsepower, it makes sense to take a look at propeller improvements. That’s just what Raisbeck and Hartzell Propellers have done, as they recently announced their new Swept Turbofan propellers for the BeechKing Air 200 series.Now, propeller design is as much art as science--unless radical breakthroughs are undertaken. One can increase the blade count, tweak the airfoil or enlarge the diameter--all methods that can work, with various advantages and disadvantages. A larger prop, as any seaplane pilot knows, pushes more air, but when tip speeds approach the speed of sound at takeoff rpm, there’s a huge noise penalty to be paid, often more than regulatory or customer interests will accept.A Breakthrough ConceptEnter the new Swept Turbofan Propellers, developed over the past three years by a cooperative effort between Raisbeck and Hartzell. It’s well known that sweeping an airfoil’s chord line delays theonset of drag rise from compressibility. Swept-profile propellers have been used on Lockheed C-130J Hercules cargo planes for some time. By sweeping the quarter-chord measurement, by almost 30 degrees in the case of the new Raisbeck/HartzellFEBRUARY 2013TWIN & TURBINE • 5