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.
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).
