sábado, 11 de junho de 2016

Why no PTLU on Airbus 340-500/600 or Reason for a PTLU on Airbus 330/340

Yaw Maneuver Criteria

• “Sudden Pedal Input till pedal stop” (one way) must be structurally possible from VMCA to VD

• “Sudden pedal release from full pedal input” once in steady side slip state, must be structurally possible from VMCA to VD.

Yaw Maneuver Criteria

• In case of an engine failure, the pedal deflection required for the corrective action from the pilot after 2 sec recognition time must be possible.

Loads and Rudder Travel Limitation Unit

• In other words, the structure and the load limits are dimensioned so as to match the yaw maneuver criteria with adequate rudder deflection limited by a judicious RTLU.

• However, the RTLU is not designed to protect the Rudder Structure for any “unrealistic” action of the pilot on the rudder pedals.

• Finally, the Certification Criteria do not address “all” possible asymmetry cases for load considerations (typically 2 same side engine out configuration on a quad, sharp roll maneuvers with rudder deflected …)

Typical Cases including high loads

• Engine failure case:

If, once the pilot has centered the ß target, he then commands a sharp turn unto the live engine, the side slip increases rapidly.

Thus the Yaw Damper abruptly reacts, which induces high loads.

Typical Cases including high loads

• Engine failure case

– Be aware that there is no restriction to roll the aircraft with an engine failure (no additional rudder input required)

– Furthermore with an engine failed, the maximum roll rate is limited to 7.5 o / sec (on FBW A/C at low speed, typically 160 knots).

– At VMCA and V2 min, the certification requires to demonstrate adequate roll capability, with full roll input; the maximum ß reached is around 10 o and loads are Ok.

Reason for a PTLU on A330/A340

• The “Yaw Damper” has a great authority in terms of rudder deflection and rudder deflection rate, on A330/A340 as compared to A310/A320.

• Thus, in case of a steady state side slip maneuver, the Yaw Damper decreases the initial rudder deflection so as to minimize the Side Slip.

• The PTLU is the Pedal Travel Limit Unit which limits the pedal deflection as a function of the A/C CAS.

Reason for a PTLU on A330/A340

When the pilot releases the rudder pedals suddenly to neutral, as requested by certification criteria, a peak of high loads can be reached (since the rudder pedal release is equivalent to a mechanical rudder movement of same amplitude) leading to a rudder deflection on opposite side.

Why no PTLU on A340-500/600
• The rudder channel is fully electric on the A3456

• Thus the rudder pedal directly commands the amount of rudder as a function of the IAS and pedal deflection

• At a given IAS, the rudder pedals are able to command a maximum rudder deflection, as per TLU. Any additional pedal input has no effect on the rudder (PTLU and RTLU built in the lateral law).