By John Croft
Raisbeck Engineering has achieved a drag reduction of up to 12% with its ZR Lite performance enhancement programme for the Bombardier Learjet 31/31A/31ER series. The tests were run on a modified Learjet 31A-136 at cruise speeds up to Mach 0.81.
Key to reducing drag on the aircraft was minimising the transonic shock build-up between the engine nacelle, wing, pylon and fuselage, where local Mach numbers can reach M1.6 during normal cruise. Raisbeck addressed this by installing new trailing-edge flaps with span-wise twist that ranges from -6º at the root to +2º at the tip.
Two years ago, Raisbeck certificated a ZR Lite package with trailing-edge flaps, horizontal winglets and wing leading edge "vortilons" for the Learjet 35/36. Performance gains included 25% less time to climb, higher cruise altitude, greater range and faster cruise speeds.
Raisbeck says US Federal Aviation Administration certification testing for the Learjet 31 modifications, expected to cost under $100,000, is 60% complete and the company will begin selling kits in January.
Source: Flight International
