Asymmetric TACS Failure With Centering Strips Installed
Tamarack SB1475 adds centering strips to the Tamarack Active Camber Surface (TACS) of ATLAS.
The TACS were initially designed to be aerodynamically over-balanced to provide low TACS hinge moments and load alleviation effectiveness. In the event of an ATLAS fault, the system removes electrical power from the TCU and actuator. The actuators can be back-driven when unpowered, so in certain circumstances it was possible for the TACS to aerodynamically move to an un-faired position. During certification, it was shown that any combination of un-faired TACS positions is recoverable and safe, at the time of failure and for continued safe flight and landing.
Tamarack, in the interest of continual product improvement, designed “centering strips” to mitigate the aerodynamic over-balance of the TACS and reduce the severity of TCU failures. This was approved by Cranfield Aerospace Solutions as SB1475, prior to EASA’s EAD.
Flight testing was conducted to verify the performance of the TACS centering strips. Testing included a sample of simulated ATLAS failures to check the TACS centering strip performance in actual flight conditions. A proprietary ATLAS manual control module was installed to override normal ATLAS function and introduce simulated ATLAS failures (asymmetric TACS deployments) followed by simulated ATLAS faults.
Flight testing with the centering strip modification included simulated dual asymmetric failures in level flight, at high speed, with autopilot ON. The first video below was taken during a flight trail simulating a dual asymmetric failure condition with the TACS centering strips installed. The video clearly shows that this failure condition with centering strips is not severe. For example, the autopilot remains engaged, and returns the airplane to level flight without pilot intervention.
Centering strips are now included in all new ATLAS installations.
In the second video below, you will see a flight trial video of the right hand TACS, fully deflected up, when the power is removed, simulating a system fault, the TACS returns to the faired position.