Lockheed Martin is completing final tests of a stick-pusher system designed to beat unexpected stall characteristics with its C-130J Hercules II.
The discovery of unusual stall behaviour has delayed delivery of the first aircraft to the Royal Air Force and Royal Australian Air Force (RAAF), and forced Lockheed Martin into fitting a stick pusher after various aerodynamic solutions were tried unsuccessfully.
The company spent five months attempting to analyse and cure the stall problems, thought to result from the high-energy vortices created by the six-bladed Dowty Aerospace R391 propellers and more-powerful Rolls-Royce Allison AE2100D3 turboprops.
More than 20 aerodynamic solutions, ranging from wing fences to vortex generators, were tested over more than 1,000 stalls during the period before Lockheed Martin resorted to the stick-pusher. Initial analyses of the pusher by RAF and RAAF test pilots suggest that the system is "about 90% OK", with a few more "tweaks" still expected to be made. Meanwhile, US Federal Aviation Administration tests of the system have been completed with no problems, says the company. More aerodynamic solutions will be tested in 1998, it adds.
The problems occurred because the high-energy vortices caused flow to attach, detach and re-attach at different areas of the upper-wing surface at different flap configurations and varying angles of attack. In some cases flow would attach to one wing surface and not another.
Lockheed Martin says that it has completed test and development of an automatic asymmetric thrust-control system which compensates for failure of an outboard engine by automatically reducing the thrust on the opposing engine.
Source: Flight International
