5. Problem definition
When one of the engine out (EO), a yaw torque exist so few things
happened like:
large magnitudes of the yaw rate, the sideslip angle and the roll rate
occur.
A high stress arise on the structural of the aircraft
the aircraft deals with stability issues
A design goal is to prevent the energy resulting from the unbalanced
engine after the EO from being transferred from the yaw motion into the
roll motion.
6. Aircraft Load Alleviation in case of an
Engine Out by Robust Yaw-lateral
Decoupling
Here, we investigate whether the aspects of structural dynamics (load
alleviation at the vertical tailplane) and thereby of the static aircraft
structure design can be integrated into the design of an EO controller
One third of the structural dynamic simulation time is spent on this case
because the changing mass and mass distribution and the uncertain
aerodynamic properties in particular due to variations of the velocity,
the altitude, and the flap/slat-setting, have to be covered.
7. How to deal with EO
1. The pilot reaction
According to the Joint-Aviation Requirements JAR 25.367 the pilot
begins to react at the first maximum of the yaw rate.
Large sideslip angle has built up. Because the pilot react after 2
from the EO happened.
The pilot reaction is then to reduce the yaw rate by the maximal
rudder deflection rate until the derivative of the sideslip angle
passes zero.
Afterwards,
the pilot reduces the rudder deflection angle to a value that is
approximately required to maintain
2. The RUD control
We will disuse it later
8. Robust Unilateral Decoupling
In the controlled system, there is only a coupling from the lateral
acceleration to the yaw rate, but not vice versa. The system is
unilaterally decoupled in the sense that the yaw rate is made non-
observable from the lateral acceleration at the decoupling point.
EO controller has to be combined with a prefilter generating the
reference yaw rate from the pilot command (𝑟𝑟𝑒𝑓) In order to
distinguish between a yaw rate that has been commanded by the pilot
, and a yaw rate in consequence of an EO
9. The system analysis
The state of the system (x) is:
𝑥 = 𝐵 𝑟 𝑇
We can define a pair of forces affected the system:
A. The wing, fuselage, pods force ( the uncertain function)
B. The tail force (the uncertain function)
10. The system analysis
the desired balance of torques would be achieved by choosing the
rudder deflection angle ∂𝑟. Such that
And because the forces and the disturbance torque unknown , so its
impossible to implement this control law
Therefore define a decoupling point DP in a distance 𝑙𝐷𝑃from the CG
so that 𝐹𝑌,𝑤𝑓𝑝 does not enter into the lateral acceleration 𝑎𝑌,𝐷𝑃 at the
decoupling point.
11. The system analysis
The differential equations are expressed in terms of 𝐹𝑌,𝑤𝑓𝑝 and 𝐹𝑌,𝑡𝑎𝑖𝑙
13. The system analysis
By the previous two equations we can said that the yaw rate (r) has no
influence on both 𝐹𝑌,𝑡𝑎𝑖𝑙 and 𝑎𝑌,𝐷𝑃
Since the variations of the aerodynamic derivatives of the tail 𝐹𝐵,𝑡𝑎𝑖𝑙 ,
𝐹𝑟,𝑡𝑎𝑖𝑙 And𝐹∂𝑅
can be expressed in terms of the variations of the
velocity, the altitude and the flap/slat-setting , and as 𝑙𝐷𝑃 is assumed
to be constant, a gain-scheduling is only required in the velocity, the
altitude and the flap/slat-setting, which can be easily measured.
The controller essentially achieves the robust decoupling of 𝐹𝑌,𝑡𝑎𝑖𝑙
from the yaw rate. By doing a state transformation from 𝐵 𝑟 𝑇
to
𝑎𝑌,𝐷𝑃 𝑟
𝑇
