July / August 2004 - CSIR

16Close-up view of theDAP flutter exciterMkII mounted on anMk 82 bombcarried underan aircraftdevelops unique flutter exciterCSIR Defence Technology hasdeveloped a novel flutter exciterto excite aircraft during flutterflight testing. Flutter flight testingis aimed at demonstrating that theaircraft flight envelope is flutterfree.Response measurements fromdeliberate excitation of the structureare used to identify and trackfrequency and damping valuesagainst velocity, and to identifyflutter conditions without actuallyencountering flutter. Flutter is aself-sustaining oscillation that canlead to structural failure and theloss of an aircraft, and should beavoided at all costs.The DAP flutter exciter Mk II can provide aflutter flight test capability to any militaryaircraft carrying an external store. Theflutter exciter is installed into or onto theexternal store, thus requiring no structuralmodifications to the aircraft. No dedicatedwiring is needed and the exciter is controlledby the normal store signals availablein an aircraft such as “fire” or “jettison”.The flutter exciter has a mass of7.5 kg, diameter of 127 mm and is 460 mmlong, which makes it easy to install ina variety of external stores. The flutterexciter is pre-programmed to executea frequency sweep and generates anoscillating rectilinear force using contrarotating,aerodynamically unbalancedimpellers. The device is driven by the airflow and the power requirement is minimal.The DAP flutter exciter Mk II was demonstratedin flight in March 2004 at the TestFlight and Development Centre (TFDC) ofThe South African Air Force. The exciterwas mounted to the nose of a Mk 82 bombcarried under a Cheetah C test aircraft.The exciter performed according to expectationat altitudes of 10 000 and 35 000feet, at Mach numbers up to 0.96 andspeeds up to 540 knots equivalent airspeed (equivalent to 1 000 km/h at sealevel).The flutter exciter has been marketed internationallyat exhibitions such as theAerospace Testing Exposition 2004 inHamburg where it generated considerableinterest. It will also be on show at theCSIR Defence Technology stand at theAfrican Aerospace and Defence 2004 showat Waterkloof Airforce Base in Septemberthis year.The CSIR provides a complete flutterprediction and aeroelastic analysis service,including ground vibration testing, finiteelement modelling-based structural dynamicanalysis, unsteady aerodynamic analysis,flutter calculations and support of flutterflight tests through near real-time dataanalysis.Enquiries:José MartinsTel: +27 12 841 4890Fax: +27 12 349 1156Email: jmartins@csir.co.za