Abstract
Asymmetry limitation requirements between left and right wing flap surfaces play an important role in the design of the implementation of the secondary flight control system of modern airplanes. In fact, especially in the case of sudden breaking of one of the torsion bars of the flap transmission line, the huge asymmetries that can rapidly develop could compromise the lateral-directional controllability of the whole aircraft (up to cause catastrophic occurrences). Therefore, in order to guarantee the aircraft safety (especially during take-off and landing flight phase in which the effects of asymmetries could generate uncontrollable aircraft attitudes), it is mandatory to timely detect and neutralize these asymmetries. The current monitoring techniques generally evaluate the differential angular position between left and right surfaces and, in most the events, limit the Flaps Control System (FCS) asymmetries, but in severe fault conditions (e.g. under very high aerodynamic loads), unacceptable asymmetries could be generated, compromising the controllability of the aircraft. To this purpose, in this paper the authors propose a new active monitoring and control technique capable of detecting the increasing angular error between the different flap surfaces and that, after stopping the whole actuation system, acts on the portion of the actuation line still connected to the PDU to minimize the FCS asymmetries.
Highlights
Flap actuation, in most commercial and military aircraft, is composed by a centrally located Power Drive Unit (PDU), a transmission and a number of actuators
This work aims to propose a new active monitoring and control technique capable of detecting the increasing angular error between the different flap surfaces and that, after stopping the whole actuation system, acting on the portion of the actuation line still connected to the PDU in order to minimize the Flaps Control System (FCS) asymmetries
In several real application, the flaps asymmetry monitoring technique is commonly based on the detection of the differential position between left and right flap surfaces [2]; its use generally slightly reduces the asymmetry, but in some cases, it may have unacceptable behaviours
Summary
In most commercial and military aircraft, is composed by a centrally located Power Drive Unit (PDU), a transmission and a number of actuators. As described in [1], the mechanical transmission generally consists of torque tubes connecting PDU output with the actuators; high-speed, flexible drive shafts are used in small commercial aircraft. Final actuators are usually linear-type, reversible screw actuators (e.g. ballscrew or rollerscrew) though some solutions still use less efficient components like the acme and lead screws; some solutions are based upon rotary type systems. Such systems must prevent asymmetries between the left and right wing flaps in case of shaft failure (detected by a dedicated asymmetry monitoring system), and to hold the surfaces in the commanded position following the shutoff command given when no actuation is required. If the actuators use an irreversible screw, the aforementioned requirements are intrinsically accomplished; otherwise, as shown in [2], if the actuators are reversible (i.e. higher efficiency) a brake system is necessary: controlled wingtip brakes (one for each wing), engaged in order to slow down the system after a failure has been positively identified (Figure 1); self-acting irreversibility brakes within each actuator, activating when the actuator output overruns the input shaft (Figure 2)
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