Expert highlights deficiencies in Saras flight control system

Bangalore: Did the National Aerospace Laboratories (NAL), the designers of the indigenous Saras light transport aircraft — a prototype of which crashed on March 6 killing its three-man Indian Air Force (IAF) crew — err in flying the aircraft?
A senior NAL official told The Hindu that an independent, but a brief review in last December of the design aspects, including the Saras’ flight control system by an aviation specialist from Germany, had brought out deficiencies in the aircraft’s existing controls and “recommended modifications, changes and further reviews to address existing problems.”
On the aircraft’s rudder control, the specialist had even gone as far as stating: “On one of the quadrants in the empennage of the Saras, the cable guard limits the rotation of the quadrant. By rotating the quadrant, the cable will be stretched and it causes a load increase in the cable tension and may limit deflection angle of the control surface. In addition, this changes the kinematics. This should be investigated and corrected prior [to] next flight.”
During his four-day visit, the expert had discussed with officials connected with the Saras programme, “aerodynamic issues, especially on the balanced and trim tab, control forces in the rudder control system during single engine operation, centring of the aileron control [and] loads on the flap system.”
The expert then provided NAL with an executive summary of the individual issues which were discussed, explaining that while in some areas recommendations could directly be given, in other fields more detailed investigations would have to be performed.
The twin-engine prototype went down as its IAF test crew were involved in verifying for the first time on the Saras an engine relight (shutting off and restarting, in sequence the engines in mid air).
The ill-fated prototype was fitted with new Pratt and Whitney engines that were not only larger in size, demanding modifications to the aircraft’s stub wings and the strengthening of the rear fuselage, but also produced a higher thrust (1,200 shaft horsepower) compared to the engines (850 shaft horsepower) that are flying the Saras’ first prototype.
Though they acknowledge the German expert’s findings, NAL officials were tight-lipped on whether the highlighted design deficiencies were investigated or corrected.
23/03/09 Ravi Sharma/The Hindu

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Categories: Indian Aviation- In General Mar 2009, New Mar 2009, Safety Mar 2009