Patent Application
20170121012
The present invention relates generally to movement of an aircraft during ground-based operations. More particularly, the invention relates to an electric taxi system (ETS) for moving an aircraft away from a terminal gate.
In traditional commercial aircraft operations, an aircraft may be positioned at a terminal gate for discharging and loading of passengers. After completion of loading, a ground-based tractor or tug may be employed to push the aircraft in a reverse direction away from the gate and to move the aircraft into a position from which the aircraft may begin taxiing under its own power. Use of such tugs contributes to increased operational costs. In some instances a tug and its operator may not be readily available at a desired aircraft-departure time and such unavailability may result in operational delays.
Comprehensive electric taxi systems (ETS) are currently being developed for modern aircraft. Such systems may employ multiple electric motors to drive landing gear wheels during aircraft ground movement and taxiing. An aircraft equipped with such a comprehensive ETS may be able to move away from a gate under its own power without a need for a tractor.
In a typical comprehensive ETS, electrical power for the motors may be supplied from an auxiliary power unit (APU) of the aircraft. Main engines of the aircraft may remain off while the aircraft is propelled on the ground by the electric motors, thus saving the expense of fuel. Substantial weight may be added to an aircraft by installation of a comprehensive ETS. This added weight may result in added in-flight fuel consumption.
Consequently, not every commercial aircraft is a good economic candidate for a comprehensive ETS because of an economic trade-off, between ground-level fuel savings, added in-flight fuel cost and the cost of installing an ETS. An aircraft that makes many short flights in a day may realize overall fuel cost savings because it may spend much of its work day performing ground level movement. The cost of installing an ETS in such an aircraft may be economically justifiable. An aircraft that is employed in long-haul routes may suffer added overall fuel cost by carrying the weight of a compressive ETS over its long routes. Such an aircraft may not be a candidate for a comprehensive ETS.
Thus, even though the development of comprehensive ETS systems may result in some reduction of tug use for some aircraft, there may remain many aircraft for which a comprehensive ETS is not economically justifiable. These aircraft without a comprehensive ETS may still require tug use.
As can be seen, there is a need for system that will allow an aircraft to depart from a gate and move at low speed into a position from which the aircraft may begin taxiing under its own power without use of a tug. More particularly, there is a need for such a system that may be installed on an aircraft at a low enough cost and with a low enough weight so that it may be economically justifiable for a wide range of aircraft, irrespective of utilization patterns of the aircraft.
In one aspect of the present invention, a gate departure system for an aircraft comprises an electric traction motor for driving a wheel of a main landing gear assembly of the aircraft on only one side of the aircraft; and a controller selectively connected to a starter-generator of an auxiliary power unit (APU) and to the traction motor to control flow of electrical power to either the starter-generator for starting of the APU or the electric traction motor for driving the wheel.
In another aspect of the present invention, apparatus for moving an aircraft comprises. a traction motor for driving a wheel of a main landing gear of the aircraft on only one side of the aircraft; and a steering system to counteract rotational force imposed on the aircraft by the traction motor during forward or reverse movement of the aircraft, the steering system including; a direction sensor for sensing direction of forward or reverse movement of the aircraft and a nose wheel angle error indicator coupled to receive and integrate signals from the direction sensor.
In still another aspect of the present invention, a method for moving an aircraft away from a gate comprises the steps of driving a wheel of a main landing gear assembly on only one side of the aircraft to produce forward or reverse movement of the aircraft; and orienting a nose wheel of the aircraft to counteract rotational force imposed on the aircraft during the forward or reverse movement.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Various inventive features are described below that can each be used independently of one another or in combination with other features.
The present invention generally provides an on-board wheel driving system for an aircraft. More particularly, the invention provides a low-cost and lightweight system that is capable of driving a wheel of an aircraft at a relatively low speed suitable for pushback and movement into a position from which the aircraft may begin taxiing under its own power during departure from a terminal gate.
Referring now to
The gate-departure system 100 may be less costly and may have a lower overall weight than a comprehensive electric taxi system (ETS), such as that shown in US Patent Publication 20120104159 and incorporated herein by reference. As compared to a comprehensive ETS with multiple traction motors and controllers, the present system may include only one traction motor 104. The traction motor 104 may be provided with controlled electrical power through a starter-generator control unit (SGCU). The SGCU may be selectively connected to a starter-generator of the auxiliary power unit (APU) and to the traction motor 104 to control flow of electrical power to either the starter-generator for starting of the APU or the electric traction motor for driving the wheel 106. In that regard, the traction motor 104 may be controlled with an SGCU that would otherwise be installed on the aircraft to control starting of an auxiliary power unit (APU). In other words, the traction motor 104 may be controlled without incurring additional cost and weight associated with a separate, dedicated traction motor controller.
Referring now to
An SGCU and an ATRU may be pre-existing components of a typical commercial aircraft with an APU. In accordance with the present invention, these pre-existing components may be selectively connected through various contactors so that they may also be employed to control the traction motor 104. Thus, an APU-equipped aircraft may be provided with an on-board gate departure system of the present invention without incurring a cost and weight penalty that might otherwise arise from providing separate power conditioning and control devices for a traction motor.
Dual use of the SGCU 116 and ATRU 118 may be implemented by positioning and operating various contactors in the control assembly 110. An external power contactor (EPC) 120 may be interposed between an external power source 121 and the ATRU 118. A starter contactor (SC) 122 may be interposed between an output 124 of the SGCU 116 and a starter-generator 114 of the APU 112.
With the EPC 120 and the SC 122 closed, a controlled-power path 126 may pass from the external power source 121, through the ATRU 118 and the SGCU 116, and into the starter-generator 114. In that context, the SGCU 116 may control starting of the APU 112.
With the EPC 120 open, a power contactor (PC) 128 closed, the SC 122 open, and a traction contactor (TC) 130 closed, a controlled-power path 132 may pass from the starter-generator 114, through the ATRU 116 and the SGCU 118, and into the traction motor 104. In that context, the SGCU 116 may control operation of the traction motor 104.
Referring now to
Referring now to
In an exemplary embodiment of the gate-departure system 100, a combination of size of the traction motor 104, size of the starter-generator 114 and the sequences of instructions provided by the instruction blocks 138 and 140 may be selected so that:
∫0t1Isdt>∫0t1Itdt (1)
where:
Is=current to starter generator 114 of APU 112;
It=current to traction motor 104;
t=time; and
t1=elapsed time to APU ignition.
It may be seen that the left half of equation 1 may characterize a degree to which the power control block 134 may experience load-related heating during APU starting within a time period t1. The right hand side of equation 1 may characterize load-related heating of the power control block 134 during movement of the aircraft within the time period t1. Current provided to the traction motor 104 during initial acceleration may be greater than a maximum current provided to the starter-generator 114 during APU stating. Nevertheless, overall heating of the power control block 134 during use of the traction motor 104 may remain within design limits established for block 134 in the context of the SGCU 116 being employed to control starting of the APU 112.
In other words, the SGCU 116 may be sufficiently robust so that it may be effectively employed to control the traction motor 104 even if the traction motor 104 has a momentary current draw that may be higher than a maximum current draw of the starter-generator 114. Indeed, the SGCU 116 may perform effectively even if the traction motor 104 has a current rating higher than a current rating of the starter-generator 114. The gate departure system 100 may be retrofitted into any aircraft with pre-existing SGCU for an APU; and such retrofitting may be made without a need to modify the power control block 134 of a preexisting SGCU. Such retrofitting may only require introduction of software to produce requisite instructions for operation of the traction motor 104.
The gate departure system 100 may be implemented with only one traction motor. As compared to a comprehensive ETS with multiple traction motors, advantageous cost and weight savings may result from utilizing only a single traction motor to propel the aircraft 102 during gate departure maneuvers. These savings arise from a combination of factors. First of all, a single motor has a lower overall cost and weight than multiple traction motors. Secondly, a single traction motor may be controlled with only a single controller, whereas an ETS with multiple traction motors requires multiple motor controllers. In the system 100, the SGCU 116 may be used as the requisite single controller for controlling the single traction motor 104.
The single traction motor 104 may be selectively coupled, through a clutch 152 (See
Such a rotational force may be counteracted by orienting a nose wheel 150 (See
But a counterintuitive or non-obvious design choice has been made in the context of the gate departure system 100 of the present invention. The gate departure system 100 may be employed to slowly move an aircraft. from a gate (e.g., at a speed of 2 knots or less). When the aircraft 102 moves slowly, the nose wheel 150 may subjected to relatively low stress even if the nose wheel is oriented at a high angle relative to an axis of the aircraft. Thus, the aircraft 102 may be moved away from a gate with a single motor driving a wheel on only one side of the aircraft and steered in a straight line without exposing the nose wheel to excessive stress.
Referring now to
Referring now to
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
