Patent Application
20150375854
The present invention generally relates to steering an aircraft during ground-based operations. More particularly, the invention relates to control of main landing gear wheel speeds to facilitate and improve nose wheel steering when an aircraft is propelled with an electric taxi system (ETS).
Conventional engine thrust taxiing uses the nose gear exclusively to steer the aircraft (at low speed). Turning requires the massive aircraft to accelerate in the yaw axis. This is precipitated by creating and sustaining a side load at the nose gear which arises after the nose gear is turned. It is generally too cumbersome to differentially control engine thrust for this purpose (the engine response is relatively slow compared to the steering response). Aside from yaw acceleration, turning wheels themselves cause a resisting torque. A loaded rolling wheel even produces resistance since the contacting surface has to continually deform as it loads and unloads (surface spreading). A turning wheel is subject to even more deformation since the outboard fibers must travel farther than the inboard fibers. This effect is called “scrubbing”, “scuffing” or “creep”.
All these actions require power to sustain. The relationship between speed, load, inflation and turning radius can be determined by test. A simple electric taxi system operates like an engine system where equal torque is applied to one designated wheel of the left and right main gear.
As can be seen, there is a need for an improved taxi control system to provide for steering of an aircraft with reduced lateral loading of a nose wheel resulting from yaw acceleration.
In one aspect of the present invention, an aircraft taxi control system may comprise: a left main gear (MG) motor; a right MG motor; a first motor drive controller configured to produce a left motor torque signal responsively to nose gear angle (NGA) and nose wheel speed (NGS); and a second motor drive controller configured to produce a right motor torque signal responsively to the NGA and the NGS, said left motor torque signal and said right motor torque signal being coordinated to reduce lateral loading of the nose wheel during a turning maneuver.
In another aspect of the present invention, a method for turning an aircraft during taxiing may comprise the steps: driving a left MG motor at a first speed; driving a right MG motor at a second speed; and varying the first speed relative to the second speed responsively to NGA and NGS to reduce lateral loading of a nose wheel resulting from yaw acceleration of the aircraft during a turning maneuver.
In still another aspect of the present invention, a method for controlling an aircraft during ground based operation may comprise the steps: producing a motor torque command (MTC) from a nose gear speed command (NGC); producing a nose gear angle command (NGA); applying the MTC and the NGA to a speed ratio table to produce a left torque command (LTC) and a right torque command (RTC) as a function of aircraft geometry; producing a left MG torque application command; producing a right MG torque application command; driving a left MG motor responsively to the left MG torque application command; and driving a right MG motor responsively to the right MG torque application command, so that the aircraft turns responsively to the NGA command with reduced lateral loading of the nose wheel resulting from yaw acceleration of the aircraft.
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 aircraft taxi control system in which differential torque may be applied to main gear wheels in order to impart yaw torque on the aircraft and reduce side loading on a nose gear wheel. More particularly, torque compensation may be derived from knowledge of the nose gear steering angle and landing gear geometry.
Referring now to
The system 100 may employ the NGC 120 and the NGA 122 to develop and apply a left main gear (MG) torque signal 124 to a left MG drive motor 128. The system 100 may also develop and apply a right MG torque application signal 126 to a right MG drive motor 130. As explained later hereinbelow, the signals 124 and 126 may be developed and applied so that the aircraft 102 may be steered with minimal lateral loading of the nose wheel(s) 118 and with minimal energy imparted to main gear drive wheels 132 and 133.
In operation, the summer 104 may receive NGC 120 and a main gear speed signal (MGS) 134 and produce a speed error signal (SER) 136. The SER 136 may be applied to the PID filter 106 and the PID fitter 106 may produce a motor torque command (MTC) 138. The speed ratio table 108 may be employed to determine a left turning torque command (LTC) 140 and a right turning torque command (RTC) 142. The LTC 140 and RTC 142 may be derived from the table 108 as functions of the NGA 120, the MTC 138 and various parameters relating to aircraft geometry. The LTC 140 and the RTC 142 may account for basic turning torque (as explained later hereinbelow). The LTC 140 may be applied to the PD filter 110 and a left drive signal 144 may be provided from the filter 110 to the left motor drive controller 114. Similarly, the RTC 142 may be applied to the PD filter 112 and a right drive signal 146 may be provided from the PD filter 112 to the right motor drive controller 116. The drive signals 144 and 146 may account for aircraft yaw acceleration and tire scrubbing (as explained later hereinbelow).
Responsively to the drive signals 144 and 146, the motor drive controllers 114 and 116 may provide the MG torque application signals 124 and 126 to the motors 128 and 130. The MG torque application signals 124 and 126 may vary as needed so that the aircraft 102 may be steered with minimal lateral loading of the nose wheel(s) 118 and with minimal energy imparted to main gear drive wheels 132 and 133.
It may be noted that aircraft speed is referenced at the nose wheel 118. This has two advantages. One is that the pilot can relate best to nose wheel speed since that is near where he or she operates, and the other is that a singularity is avoided for the case of 90 degree nose gear angle where ground speed becomes zero even though the nose wheel and the pilot are in motion.
Referring now to
Referring now to
Referring now to
The relationships illustrated in the graph 200 may be characterized with the expressions:
RMG speed ratio=AMP*sin(ZCA+NGA); and (1)
LMG speed ratio=AMP*sin(ZCA−NGA) (2)
Where ZCA=90°−a tan(D/L/2); (3)
AMP (amplitude)=1/sin(ZCA); (4)
It may be noted that under prior art operating procedures aircraft steering is limited to a nose gear angle of 60 degrees. Employment of the steering system 100 may safely allow sharper steering. In fact, 90 degrees of steering angle may allow for rotation or pivoting of the aircraft 102 about the point that is midway between the left and right main gear wheels 132 and 133. The system 100 may also allow for reverse aircraft motion while still achieving reduced lateral loading on the nose wheel 118 because a neutral nose gear angle is considered to be plus or minus 180 degrees according to the speed ratio table 108.
Referring back to
dYaw_rate/dt=d(steering angle*velocity)/dt=d(NGA*NGS)/dt=dNGA/dt*NGS+dNGS/dt*NGA (5)
Where:
NGA=nose gear angle; and
NGS=nose wheel speed.
Additionally, aircraft fuel load, passenger count and cargo weight can be accounted for in a yaw inertia term which may be incorporated as a factor in differential torque required to accelerate and decelerate the aircraft 102 in the yaw axis. This factor may be applied as a scalar multiplier of the differential term of the PD filters 110 and 112. The PD filters 110 and 112 may account for continuous changes in nose gear speed and turning angle.
The motor drive signals 144 and 146 may be continuously provided to the controllers 114 and 116 so that the MG drive wheels 132 and 133 impart most of the torque required to perform a turning maneuver. It may be noted that if the motor drive signals 144 and/or 146 produce power demands that exceeds power availability, the commanded power may be scaled back to such a degree as to no longer exceed the available supply power.
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.
