System and method for alleviating structural loads on a pivoting main landing gear of an aircraft in a pivot turn maneuver

There is provided a pivot turn load alleviation (PTLA) brake system for alleviating structural loads on a pivoting main landing gear of an aircraft in a pivot turn maneuver. The PTLA brake system includes a brake control system operatively coupled to at least two main landing gear, each having two or more wheels. The PTLA brake system further includes a PTLA brake inhibit subsystem coupled to the brake control system. The subsystem inhibits braking of one or more of the two or more wheels of the pivoting main landing gear, in the pivot turn maneuver, so that at least one wheel of the two or more wheels is in an unbraked state, and a remaining number of the two or more wheels are in a braked state. The PTLA brake system alleviates structural loads, and reduces wear on the at least one wheel that is in the unbraked state.

FIELD

The disclosure relates generally to systems and methods for braking aircraft, and more particularly, to systems and methods for braking pivoting main landing gear of aircraft in and during a pivot turn maneuver.

BACKGROUND

Large transport aircraft, both commercial and military, typically include a main landing gear arrangement that supports most of the aircraft weight, along with a nose gear for stability and steering. The main landing gear usually includes a left main landing gear and a right main landing gear, each having multiple wheels, and each wheel including one or more brakes.

The wheel brakes on the main landing gear are controlled by the pilot after landing to assist in the ground deceleration of the aircraft. The wheel brakes can also be controlled by the pilot during ground taxi maneuvers, and pivot turn maneuvers or 2-point turn maneuvers performed on the ground. The large mass of an aircraft and the high landing speed results in very high momentum, which can translate to very high structural loads during braking maneuvers, for example, when the brakes are applied suddenly.

Known systems and methods exist for braking main landing gear during a pivot turn maneuver. However, such known systems and methods brake all of the wheels on a pivoting main landing gear. Braking all of the wheels on the pivoting main landing gear during a pivot turn maneuver may result in excessive wear on the wheels and tires, and increased structural loads and braking loads on the pivoting main landing gear. Moreover, known systems and methods may require the use of heavy and bulky main landing gear assemblies and components to withstand the high structural loads and braking loads experienced during a pivot turn maneuver.

Accordingly, there is a need in the art for systems and methods that avoid braking all of the wheels on a pivoting main landing gear and that allow certain wheels on a pivoting main landing gear to roll freely during a pivot turn maneuver, and that reduce structural loads on a pivoting main landing gear during a pivot turn maneuver, and that reduce the weight of main landing gear assemblies and components designed to withstand high loads during a pivot turn maneuver, and that provide significant advantages over known systems and methods.

SUMMARY

Example implementations of this disclosure provide systems and methods for braking pivoting main landing gear of aircraft in and during a pivot turn maneuver. As discussed in the below detailed description, versions of the systems and methods may provide significant advantages over existing systems and methods.

In one exemplary version, there is provided a pivot turn load alleviation (PTLA) brake system for alleviating structural loads on a pivoting main landing gear of an aircraft in a pivot turn maneuver. The PTLA brake system comprises a brake control system operatively coupled to at least two main landing gear. Each of the at least two main landing gear has two or more wheels. The brake control system controls braking of the at least two main landing gear.

The PTLA brake system further comprises a pivot turn load alleviation (PTLA) brake inhibit subsystem coupled to the brake control system. The PTLA brake inhibit subsystem inhibits braking of one or more of the two or more wheels of one main landing gear comprising the pivoting main landing gear, in the pivot turn maneuver, so that at least one wheel of the two or more wheels is in an unbraked state, and a remaining number of the two or more wheels are in a braked state. The PTLA brake system alleviates the structural loads on the pivoting main landing gear of the aircraft in the pivot turn maneuver, and reduces wear on the at least one wheel that is in the unbraked state.

In another version, there is provided an aircraft. The aircraft comprises a fuselage, one or more wings attached to the fuselage, and a plurality of landing gear attached to the fuselage. The plurality of landing gear comprises a nose landing gear, and at least two main landing gear. Each of the at least two main landing gear has two or more wheels. During a pivot turn maneuver by the aircraft, one of the at least two main landing gear comprises a pivoting main landing gear.

The aircraft further comprises a pivot turn load alleviation (PTLA) brake system. The PTLA brake system comprises a brake control system operatively coupled to the at least two main landing gear. The brake control system controls braking of the at least two main landing gear.

The PTLA brake system further comprises a pivot turn load alleviation (PTLA) brake inhibit subsystem coupled to the brake control system. The PTLA brake inhibit subsystem inhibits braking of one or more of the two or more wheels of one main landing gear comprising the pivoting main landing gear, during the pivot turn maneuver, so that at least one wheel of the two or more wheels is in an unbraked state, and a remaining number of the two or more wheels are in a braked state. The PTLA brake system alleviates structural loads on the pivoting main landing gear, during the pivot turn maneuver by the aircraft, and reduces wear on the at least one wheel that is in the unbraked state.

In another version, there is provided a method for alleviating structural loads on a pivoting main landing gear of an aircraft in a pivot turn maneuver. The method comprises the step of initiating the pivot turn maneuver with the aircraft. The aircraft has a pivot turn load alleviation (PTLA) brake system. The PTLA brake system comprises a brake control system operatively coupled to at least two main landing gear. Each of the at least two main landing gear has two or more wheels. The brake control system controls braking of the at least two main landing gear. The PTLA brake system further comprises a pivot turn load alleviation (PTLA) brake inhibit subsystem coupled to the brake control system.

The method further comprises the step of activating a pivot turn load alleviation (PTLA) brake inhibit command of the PTLA brake inhibit subsystem, to one or more brake control units of the brake control system, upon meeting one or more brake inhibit conditions. The method further comprises the step of inhibiting braking of one or more of the two or more wheels of the pivoting main landing gear, in the pivot turn maneuver, so that at least one wheel of the two or more wheels is in an unbraked state, and a remaining number of the two or more wheels are in a braked state. The PTLA brake system alleviates the structural loads on the pivoting main landing gear of the aircraft in the pivot turn maneuver, and reduces wear on the at least one wheel that is in the unbraked state.

The Figures shown in this disclosure represent various aspects of the versions presented, and only differences will be discussed in detail.

DETAILED DESCRIPTION

Disclosed versions or examples will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed versions are shown. Indeed, several different versions may be provided and should not be construed as limited to the versions set forth herein. Rather, these versions are provided so that this disclosure will be thorough and fully convey the scope of the disclosure to those skilled in the art.

Now referring to the Figures,FIG. 1Ais an illustration of a perspective view of an aircraft10having a pivot turn load alleviation (PTLA) brake system12configured in accordance with a version of the disclosure, andFIG. 1Bis an illustration of a top plan view of the aircraft10and the PTLA brake system12ofFIG. 1A.FIG. 2Ais an illustration of a functional block diagram showing the aircraft10with an exemplary PTLA brake system12of the disclosure.

The blocks inFIG. 2Arepresent elements, and lines connecting the various blocks do not imply any particular dependency of the elements. Furthermore, the connecting lines shown in the various Figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements, but it is noted that other alternative or additional functional relationships or physical connections may be present in versions disclosed herein.

As shown inFIGS. 1A-1B, and 2A, the PTLA brake system12comprises a brake control system14and a pivot turn load alleviation (PTLA) brake inhibit subsystem16coupled to the brake control system14. As shown inFIGS. 1A-1B, the aircraft10includes a fuselage18with one or more wings20coupled to the fuselage18, and a tail21. The aircraft10can be supported at multiple points via landing gear22(seeFIGS. 1A, 1B, 2A), including main landing gear (MLG)24(seeFIGS. 1A-1B, 2A) and a nose landing gear26(seeFIGS. 1A-1). As shown inFIGS. 1A-1B, the main landing gear24is positioned aft of the nose landing gear26, and the main landing gear24includes a left main landing gear24aand a right main landing gear24b.

In one version disclosed herein, there is provided the PTLA brake system12for alleviating loads28(seeFIG. 2A), such as structural loads28a(seeFIG. 2A), on at least one main landing gear24comprising a pivoting main landing gear32(seeFIG. 2A) of the aircraft10in a pivot turn maneuver30(seeFIG. 2A), or during a pivot turn maneuver30, that is executed or performed by the aircraft10. During the pivot turn maneuver30, for example, if the aircraft10has two main landing gear24, one main landing gear24comprises the pivoting main landing gear32(seeFIG. 2A) and the other main landing gear24(seeFIG. 2A) comprises a non-pivoting main landing gear34. The pivoting main landing gear32is closer to a turn center33(seeFIG. 2A) of the pivot turn maneuver30, or pivot turn, than the non-pivoting main landing gear34. The pivoting main landing gear32is closest or nearest to the turn center33of the pivot turn maneuver30, or pivot turn. Torsion is high when pivoting near the center of the pivoting main landing gear32. During the pivot turn maneuver30, one main landing gear24is braking and being pivoted about, and the other main landing gear24is moving circumferentially about the braked main landing gear24. Typically there are two brake pedals64(seeFIG. 2A), such as a left brake pedal64a(seeFIG. 2A) and a right brake pedal64b(seeFIG. 2A), with each brake pedal64commanding a different main landing gear24, and each brake pedal64may be operated by different pilots154(seeFIG. 2B).

As shown inFIG. 1A, the main landing gear24is a 2-main landing gear configuration36(see alsoFIG. 2A). Although the main landing gear24shown inFIG. 1Ais a 2-main landing gear configuration36, the PTLA brake system12may also be used with a 3-main landing gear configuration38(seeFIG. 2A), a 4-main landing gear configuration40(seeFIG. 2A), or another suitable main landing gear configuration.

As shown inFIGS. 1A-1B, each main landing gear24can include a post42carrying a truck44. The truck44can include multiple wheels46(seeFIGS. 1A-1B, 2A) that are selectively or collectively braked to reduce the speed of the aircraft10during taxi maneuvers and post-landing rollout. The aircraft10has at least two main landing gear24, and each of the at least two main landing gear24have two or more wheels46. For example, each main landing gear24may have two wheels, four wheels, six wheels, or another suitable number of wheels. Where the at least two main landing gear24comprise the left main landing gear24aand the right main landing gear24b, each of the left main landing gear24aand the right main landing gear24bmay have two pairs48(seeFIG. 2A) of wheels46. Each pair48of wheels46is disposed on an axle49(seeFIG. 2A), such as a common or single axle. As discussed in further detail below, during the pivot turn maneuver30, one or more wheels46, such as one or more of the two or more wheels46, may be in the form of one or more unbraked wheels46a(seeFIG. 2A) in an unbraked state52(seeFIG. 2A), and a remaining number54(seeFIG. 2A) of the wheels46, such as the two or more wheels46, may be in the form of braked wheels46b(seeFIG. 2A) in a braked state56(seeFIG. 2A). In one version, as shown inFIGS. 3A-3C, each main landing gear24comprising the left main landing gear24aand the right main landing gear24b, may include two forward wheels46cand two aft wheels46d, and further comprises two inboard wheels46eand two outboard wheels46f.

Each wheel46has one or more brakes58(seeFIGS. 1A-1B, 2A) coupled to the wheel46, or located at the wheel46. As shown inFIGS. 1A-1B, the brake control system14is operatively coupled to the at least two main landing gear24, and is operatively coupled to the brakes58. The brake control system14is configured to control, and controls, braking of the at least two main landing gear24. The brake control system14can direct the application of various combinations of brakes58, depending upon one or more aircraft characteristics or parameters, as will be discussed in greater detail below. The brake control system14can also disable braking of selected brakes58, also depending upon these characteristics or parameters.

Accordingly, the brake control system14can receive pilot inputs60(seeFIGS. 1A-1B, 2A) (e.g., command signals62(seeFIG. 2A) received via brake pedals64(seeFIG. 2A) at a flight deck66(seeFIG. 2A) of the aircraft10), threshold values68(seeFIGS. 1A-1B, 2A), and aircraft data70(seeFIGS. 1A-1B, 2A). In particular, with versions of the PTLA brake system12of the disclosure, the aircraft data70and the threshold values68may be used to determine which brakes58to apply and which brakes58to inhibit, as is also described in greater detail below.

As shown inFIG. 2A, the brake control system14comprises a brake controller72with a plurality of brake control units74. The brake control units74comprise electronic control units that control command signals62representing brake commands76. The brake control units74may be implemented with the brake controller72, such as in the form of a processor, microprocessor, or other suitable controller device. The brake control units74may be used with suitable hardware components, suitable software or programmable logic, memory elements, and the like, which may carry out a variety of functions under the control of the brake controller72, or other suitable control devices. In one version, one or more of the brake control units74may be implemented with a computer processor that hosts software and provides external interfaces for the software.

The brake control system14may further comprise a plurality of controls78(seeFIG. 2A), such as one or more of, wheel speed controls, fluid temperature controls, wheel temperature controls, valve controls, brake controls, parking brake controls, wheel power controls, anti-skid controls, taxi brake release controls, or other suitable controls. The brake control system14may be powered by a power supply80(seeFIG. 2A), for example, an electrical power supply, or another suitably power supply.

As further shown inFIG. 2A, the brake control system14comprises a plurality of brake control valves82. Each brake control valve82has a first end84a(seeFIGS. 3A-3C) and a second end84b(seeFIGS. 3A-3C). The first ends84aof the brake control valves82are coupled to one or more brake control units74, via electronic connector elements86(seeFIGS. 3A-3C), such as wires, or other suitable connector elements. The second end84bof each brake control valve82is coupled to the brake58or brakes58on each wheel46, via a hydraulic connector element88, such as a hydraulic line, or other suitable connector elements. One or more of the plurality of brake control units74generate or generates one or more brake commands76(seeFIG. 2A) to one or more of the plurality of brake control valves82. Those skilled in the art will appreciate that versions of the PTLA brake system12may be practiced using different aircraft brake control systems and aircraft configurations, and that the brake control system14described herein is merely one exemplary version.

As further shown inFIGS. 1A-1B and 2A, the PTLA brake system12comprises the PTLA brake inhibit subsystem16coupled to the PTLA brake system12. The PTLA brake inhibit subsystem16is configured to inhibit, and inhibits, braking, and is configured to inhibit, and inhibits, the brakes58, of one or more of the two or more wheels46of the one main landing gear24comprising the pivoting main landing gear32, in and during the pivot turn maneuver30by the aircraft10, so that at least one wheel46of the two or more wheels46is in an unbraked state52(seeFIG. 2A), for example, a rolling state53(seeFIG. 2A) or an inhibited state57(seeFIG. 2A), and a remaining number54(seeFIG. 2A) of the two or more wheels46are in a braked state56(seeFIG. 2A).

The PTLA brake inhibit subsystem16is configured to generate, and generates, a pivot turn load alleviation (PTLA) brake inhibit command90(seeFIG. 2A). The PTLA brake inhibit subsystem16inhibits braking and inhibits the brakes58, of one or more of the two or more wheels46of the pivoting main landing gear32, in and during the pivot turn maneuver30, via activation92of the pivot turn load alleviation (PTLA) brake inhibit command90, to one or more brake control units74of the brake control system14, upon meeting one or more brake inhibit conditions94.

As shown inFIG. 2A, the one or more brake inhibit conditions94may comprise an on ground state of the aircraft96, indicated when the aircraft10is in an on ground position98, that is, the aircraft10is positioned at, and moving on, a ground location rather than in the air. If the aircraft10is in the on ground position98, the brake inhibit condition94is met or satisfied. If the aircraft10is in the air, the brake inhibit condition94is not met or satisfied. The on ground state of the aircraft96may be determined with the aircraft10being in the on ground position98, may be determined with an aircraft on ground indication or sensor input, may be determined with a main landing gear fully extended indication or sensor input, may be determined with a tilt of the truck44of a main landing gear24indication or sensor input, may be determined with a shocks strut squat switch or oleo pressure indication or senor input, or may be determined with another suitable indication or sensor input.

As shown inFIG. 2A, the one or more brake inhibit conditions94may further comprise an acceptable aircraft ground speed100, indicated when an aircraft ground speed101of the aircraft10is less than a pivot turn load alleviation (PTLA) speed threshold104. In one exemplary version, the PTLA speed threshold104is 10 (ten) knots or less than 10 knots, and if the aircraft ground speed101is 11 (eleven) knots, the aircraft ground speed101exceeds the PTLA speed threshold104of 10 knots, and the brake inhibit condition94is not met or satisfied. If the aircraft ground speed101is 9 (nine) knots, the aircraft ground speed101is less than the PTLA speed threshold104of 10 knots, and the brake inhibit condition94is met or satisfied. The acceptable aircraft ground speed100is preferably less than 2 (two) knots. The aircraft ground speed101for determining the acceptable aircraft ground speed100may be estimated or determined from an average wheel speed102(seeFIG. 2A), where average wheel speed means averaging all aircraft wheel speeds, may be estimated or determined from an Inertial Reference System (IRS) ground speed or acceleration, or may be estimated or determined using another suitable system or means.

As shown inFIG. 2A, the one or more brake inhibit conditions94may further comprise a pivot turn load alleviation (PTLA) active flag command indication106, generated by a monitoring logic108of the PTLA brake inhibit subsystem16, to monitor brake pedal positions110, to detect initiation31of the pivot turn maneuver30, according to one of a plurality of pivot turn brake pedal profiles112. For example, the monitoring logic108monitors both the left brake pedal64aand the right brake pedal64bto detect and to determine whether or not the pivot turn maneuver30is being initiated or attempted by a pilot or pilots. A monitoring logic output108a(seeFIG. 2A) is determine based on the plurality of pivot turn brake pedal profiles112, discussed in relation toFIGS. 4-7below. If the monitoring logic108of the PTLA brake inhibit subsystem16detects the initiation31of the pivot turn maneuver30, based on one of the plurality of pivot turn brake pedal profiles112, the brake inhibit condition94is met or satisfied.

In one version, the one or more of the brake inhibit conditions94comprises one brake inhibit condition94being met or satisfied, where the one brake inhibit condition94comprises the on ground state of the aircraft96or an equivalent indication or sensor input, or the acceptable aircraft ground speed100or an equivalent determination or estimation, or the PTLA active flag command indication106. In another version, the brake inhibit conditions94may comprise two brake inhibit conditions94being met or satisfied, where the two brake inhibit conditions94comprise the combination of the on ground state of the aircraft96and the PTLA active flag command indication106, or the combination of the acceptable aircraft ground speed100and the PTLA active flag command indication106, or the combination of the on ground state of the aircraft96and the acceptable aircraft ground speed100, or another suitable combination. In another version, the brake inhibit conditions94may comprise three brake inhibit conditions94being met or satisfied, where the three brake inhibit conditions94comprise the on ground state of the aircraft96or an equivalent indication or sensor input, and the acceptable aircraft ground speed100or an equivalent determination or estimation, and the PTLA active flag command indication106.

Thus, when one or more of the brake inhibit conditions94are met or satisfied or detected, the PTLA brake inhibit subsystem16generates and activates the PTLA brake inhibit command90(seeFIG. 2A) to the one or more brake control units74of the brake control system14, and the one or more brake control units74enable the PTLA brake inhibit command90to send the PTLA brake inhibit command90to a wheel selection50(seeFIG. 2A), for determining which of the two or more wheels46of the pivoting main landing gear32are to be inhibited, and to inhibit braking of the wheels46in the wheel selection50. Preferably, the PTLA brake inhibit command90is activated very rapidly after one or more of the brake inhibit conditions94are met or satisfied, for example, within 100 ms (one hundred milliseconds) of the one or more brake inhibit conditions94being met or detected. The plurality of brake control units74receive the PTLA brake inhibit command90from the PTLA brake inhibit subsystem16and inhibit generation of at least one brake command76(seeFIG. 2A) corresponding to at least one of the plurality of brake control valves82coupled to the at least one wheel46that is in the unbraked state52. Preferably, the selection of one or more wheels46(seeFIG. 2A) to be inhibited changes to the next wheel46, in sequence, whenever either left or right commanded brake pedal effort transitions from above 12% (twelve percent) to 8% (eight percent) of full brake pedal travel.

In one version, the wheel selection50may comprise one axle pair48aof wheels46on the pivoting main landing gear32, for example, one axle pair48aof forward wheels46c(seeFIGS. 3A-3C) or one axle pair48aof aft wheels46d(seeFIGS. 3A-3C), on either the left main landing gear24a, when the left main landing gear24ais the pivoting main landing gear32, or the right main landing gear24b, when the right main landing gear24bis the pivoting main landing gear32. With this version, one axle pair48aof wheels46shall be inhibited at a time.

Preferably, the wheel selection50comprises a pair48of wheels46, either forward wheels46c(seeFIGS. 3A-3C) or aft wheels46d(seeFIGS. 3A-3C) that share an axle49(seeFIG. 2A), on a four wheel46, two axle49, pivoting main landing gear32, and that are in an unbraked state52(seeFIG. 2A) during the pivot turn maneuver30, and the other pair48of wheels46of the four wheel46, two axle49, pivoting main landing gear32are in a braked state56(seeFIG. 2A) during the pivot turn maneuver30. With this version, for each subsequent pivot turn maneuver30a(seeFIG. 2A), the wheel selection50of the one axle pair48aof wheels46changes, in a sequential order51(seeFIG. 2A), to a different axle pair48b(seeFIG. 2A) of wheels46, such as another axle pair48aof wheels46. Preferably, the selection of inhibited axle pairs48c(seeFIG. 2A) changes to the next axle pair48aof wheels46, in sequence, whenever either left or right commanded brake pedal effort transitions from above 12% (twelve percent) to 8% (eight percent) of full brake pedal travel. This percentage value corresponds to a normalized full brake pedal travel, for example, 0% is fully off the brake pedal, and 100% is the brake pedal fully depressed.

In another version, where the pivoting main landing gear32has four wheels46, the PTLA brake inhibit command90of the PTLA brake inhibit subsystem16may inhibit braking of one wheel46, that is, one wheel46in the unbraked state52and three wheels46in the braked state56on the pivoting main landing gear32, in and during the pivot turn maneuver30by the aircraft10. In yet another version, where the pivoting main landing gear32has four wheels46, the PTLA brake inhibit command90of the PTLA brake inhibit subsystem16may inhibit braking of three wheels46, that is, three wheels46in the unbraked state52and one wheel46in the braked state56on the pivoting main landing gear32, in and during the pivot turn maneuver30by the aircraft10. In yet another version, where the pivoting main landing gear32has four wheels46, the PTLA brake inhibit command90of the PTLA brake inhibit subsystem16may inhibit braking of two wheels46that are not axle pair48awheels46, for example, one forward wheel46cand one aft wheel46d, either inboard wheels46e(seeFIG. 2A) or outboard wheels46f(seeFIG. 2A), or two diagonal wheels46i(seeFIG. 2A) such as two opposite corner wheels, in and during the pivot turn maneuver30by the aircraft10.

For the axle pair48acombination of wheels46of two diagonal wheels46i, such as two opposite corner wheels, where one pair of two diagonal wheels46iare in the braked state56and the other pair of two diagonal wheels46iare in the rolling state53(seeFIG. 2A), the estimated reduction in torsional load reaction28b, or torque load, is about 9%. For the axle pair48acombination of wheels46with one forward wheel46c(seeFIG. 2) and one aft wheel46d(seeFIG. 2) in the braked state56, and the other forward wheel46cand the other aft wheel46din the rolling state53, the estimated reduction in torsional load reaction28b, or torque load, is about 18%. For the axle pair48acombination of wheels46with two forward wheels46c(seeFIG. 2) in the braked state56and the other two aft wheels46d(seeFIG. 2) in the rolling state53, the estimated reduction in torsional load reaction28b, or torque load, is about 13%. This alternate wheel pairing enables integration with the taxi brake release function130(seeFIG. 2A).

The PTLA brake inhibit command90acts as a pivot turn assist function114(seeFIG. 2A), and may be implemented in one brake control unit74(seeFIG. 2A) or more than one the brake control units74.

Further, the PTLA brake inhibit subsystem16may be configured such that no single loss of function results in an erroneous brake inhibit on both trucks44, that is, the left truck and the right truck. Moreover, no single loss of function, except power loss to the brake control units74of the brake control system14, shall result in loss of function on one main landing gear24.

As shown inFIG. 2A, the PTLA brake inhibit command90may undergo deactivation116and be removed, when one or more brake inhibit deactivation conditions118is/are met or satisfied. As shown inFIG. 2A, the one or more brake inhibit deactivation conditions118may comprise the aircraft ground speed101of the aircraft10exceeds the pivot turn load alleviation (PTLA) speed threshold104, for example, the aircraft ground speed101exceeds, or is greater than, 10 (ten) knots. As shown inFIG. 2A, the one or more brake inhibit deactivation conditions118may further comprise both brake pedal commands120, including a left brake pedal command120aand a right brake pedal command120b, exceed a pivot turn load alleviation (PTLA) triggering brake pedal command threshold122, for at least a predetermined time period124. In one version, the predetermined time period124may be one (1) second after both the left brake pedal command120aand the right brake pedal command120bexceed the PTLA triggering brake pedal command threshold122, for example, above a 50% command threshold. The predetermined time period124, such as the one (1) second delay, is to ensure both brake pedal commands120(seeFIG. 2A) are consistently above the PTLA triggering brake pedal command threshold122, for example, above the 50% command threshold, indicating that the pilot154(seeFIG. 2B) is requiring the need to stop the aircraft10rapidly or come to a complete stop. Once the predetermined time period124, such as the one (1) second timer, is up and both brake pedal commands120are above or exceed the PTLA triggering brake pedal command threshold122, for example, above the 50% command threshold, then the remaining two brakes58which were inhibited will return to the commanded braking level.

As shown inFIG. 2A, the one or more brake inhibit deactivation conditions118may further comprise the aircraft10entering into an active parking brake state126, that is, a parking brake128of the aircraft10is engaged, or becomes active.

In one version, the one or more of the brake inhibit deactivation conditions118comprises one brake inhibit deactivation condition118being met or satisfied, where the one brake inhibit deactivation condition118comprises the aircraft ground speed101of the aircraft10exceeds the pivot turn load alleviation (PTLA) speed threshold104, or both brake pedal commands120, including the left brake pedal command120aand the right brake pedal command120b, exceed the PTLA triggering brake pedal command threshold122, for at least the predetermined time period124, or the aircraft10enters into the active parking brake state126. In another version, the brake inhibit deactivation conditions118may comprise two brake inhibit deactivation conditions118being met or satisfied, where the two brake inhibit deactivation conditions118comprise the combination of the aircraft ground speed101of the aircraft10exceeds the pivot turn load alleviation (PTLA) speed threshold104, and both brake pedal commands120, including the left brake pedal command120aand the right brake pedal command120b, exceed the PTLA triggering brake pedal command threshold122, for at least the predetermined time period124; or the combination of the aircraft10exceeds the PTLA speed threshold104, and the aircraft10enters into the active parking brake state126; or the combination of both brake pedal commands120, including the left brake pedal command120aand the right brake pedal command120b, exceed the PTLA triggering brake pedal command threshold122, for at least the predetermined time period124, and the aircraft10enters into the active parking brake state126. In another version, the brake inhibit deactivation conditions118may comprise three brake inhibit deactivation conditions118being met or satisfied, where the three brake inhibit deactivation conditions118comprise the aircraft ground speed101of the aircraft10exceeds the pivot turn load alleviation (PTLA) speed threshold104, and both brake pedal commands120, including the left brake pedal command120aand the right brake pedal command120b, exceed the PTLA triggering brake pedal command threshold122, for at least the predetermined time period124, and the aircraft10enters into the active parking brake state126.

As further shown inFIG. 2A, the aircraft10may optionally include a taxi brake release function130. In the case where the aircraft10already includes the taxi brake release function130, the PTLA brake inhibit subsystem16may be integrated with the taxi brake release function130, to obtain a taxi brake release function integration132. The taxi brake release function130may limit the brakes58to one or more but not all of the wheels46. In one example, the taxi brake release function130may limit the brakes58to a pair48(seeFIG. 2A) of wheels46. The taxi brake release function130selects a wheel selection50(seeFIGS. 3A-3C) for the PTLA brake inhibit command90(seeFIGS. 2A, 3A-3C), to inhibit braking of one or more but not all of the wheels46of the pivoting main landing gear32. In one example, one or more but not all of the wheels46, such as a wheel pairing, as shown in the left main landing gear24ainFIGS. 3A-3C, and discussed in further detail below, may be selected, as it optionally enables integration of an existing taxi brake release function130, also referred to as a taxi brake select function, and the PTLA brake inhibit command90function under the same PTLA brake inhibit subsystem16algorithm or programmed logic.

The PTLA brake system12alleviates loads28(seeFIG. 2A), such as structural loads28a(seeFIG. 2A), on the pivoting main landing gear32during the pivot turn maneuver30by the aircraft10, and reduces wear136(seeFIG. 2A) on the at least one wheel46that is in the unbraked state52, that is, the at least one unbraked wheel46a(seeFIG. 2A) with inhibited brakes, and reduces wear136on the tire of the wheel46. Further, the PTLA brake system12inhibits braking on one or more brakes58on the pivoting main landing gear32, in order to reduce torsional load reaction28b(seeFIG. 2A) exerted on the pivoting main landing gear32. The PTLA brake system12may also reduce cornering forces134(seeFIG. 2A), which, in turn, also reduce wear136. The PTLA brake system12may also provide U-turn optimization138(seeFIG. 2A), when the inboard wheels46eare released. The PTLA brake system12may also reduce the overall weight of the main landing gear24, because with reduced structural loads28aand reduced cornering forces134, various components and materials on the main landing gear24may be reduced or eliminated, for example, a smaller, reduced weight scissor link, a smaller, reduced weight torque link, or another downsized structure on the main landing gear24, such as the pivoting main landing gear32. The potential to reduce weight of the main landing gear24of the aircraft10may be at least a weight savings of twenty-five pounds (25 lbs.) or more.

Now referring toFIG. 2B,FIG. 2Bis an illustration of a functional block diagram showing the aircraft10and the PTLA brake inhibit subsystem16ofFIG. 2Awith a plurality of PTLA enter scenarios140and a plurality of PTLA exit scenarios142. As further shown inFIG. 2B, the PTLA brake system12includes the brake control system14and the PTLA brake inhibit subsystem16that monitors the PTLA enter scenarios140and PTLA exit scenarios142. The various pivot turn brake pedal profiles112(seeFIG. 2B) monitored and sensed by the monitoring logic108(seeFIG. 2A) to detect and determine the initiation31(seeFIG. 2A) of the pivot turn maneuver30(seeFIG. 2B), as shown inFIGS. 4-7, and discussed in further detail below, each represent one of the PTLA enter scenarios140and one of the PTLA exit scenarios142. Each of the PTLA enter scenarios140and each of the PTLA exit scenarios142include an initial state144(seeFIG. 2B), a state change146(seeFIG. 2B), and a result148(seeFIG. 2B).

Three (3) exemplary PTLA enter scenarios140are described below using a Side A150(seeFIG. 2B) and a Side B152(seeFIG. 2B) of one main landing gear24(seeFIG. 2B) entering into a pivot turn maneuver30(seeFIG. 2B) or pivot turn, to become a pivoting main landing gear32(seeFIG. 2B), with brake pedals64(seeFIG. 2B) to the one main landing gear24, and four wheels46(seeFIG. 2B) with brakes58(seeFIG. 2B) of the one main landing gear24. The three (3) exemplary PTLA enter scenarios140are summarized as follows:

(1) A first PTLA enter scenario140a(seeFIG. 2B) includes: (a) an initial state144of no brakes58are on/applied on Side A and no brakes58are on/applied on Side B, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102(seeFIG. 2B), below the PTLA speed threshold104(seeFIG. 2B); (b) a state change146of a pilot154(seeFIG. 2B) applying the brake pedal64on Side A, and the brake pedal64on Side B is not applied, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; and (c) a result148with one or more brakes58on Side A are on/applied and one or more brakes58on Side B are inhibited brakes58a(seeFIG. 2B) in an inhibited state57(seeFIG. 2B), and no brakes58on Side B are on/applied, and with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104.

(2) A second PTLA enter scenario140b(seeFIG. 2B) includes: (a) an initial state144of brakes58are on/applied on Side A and brakes58are on/applied on Side B, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; (b) a state change146of the pilot releasing the brake pedal64on Side B, and the brake pedal64on Side B is still on/applied and held down, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; and (c) a result148of one or more brakes58on Side A are still on/applied, and all brakes58on Side B and one or more brakes58on Side A are released, so that the one or more brakes58on Side A that are released are inhibited brakes58ain an inhibited state57, and with the aircraft ground speed101(see FIG.2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104.

(3) A third PTLA enter scenario140c(seeFIG. 2B) includes: (a) an initial state144of brakes58are on/applied on Side A and no brakes58are on/applied on Side B, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, above the PTLA speed threshold104; (b) a state change146of the aircraft10decelerating so that the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, is below the PTLA speed threshold104, and the brake pedal64on Side B is still on/applied and held down, and the brake pedal64on Side B is not applied; and (c) a result148of no brakes58on Side B are on/applied, and one or more brakes58on Side A are released, so that the one or more brakes58on Side A that are released are inhibited brakes58ain an inhibited state57, and with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102below the PTLA speed threshold104.

Three (3) exemplary PTLA exit scenarios142(seeFIG. 2B) are described below using the Side A150and the Side B152of one main landing gear24entering into the pivot turn maneuver30or pivot turn, to become a pivoting main landing gear32(seeFIG. 2B), with brake pedals64to the one main landing gear24, and two or more wheels46, for example, four wheels46, with brakes58of the one main landing gear24. The three (3) exemplary PTLA exit scenarios142are summarized as follows:

(1) A first PTLA exit scenario142a(seeFIG. 2B) includes: (a) an initial state144of one or more brakes58on Side A are on/applied and are inhibited brakes58ain an inhibited state57, and no brakes58are on/applied on Side B, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; (b) a state change146of a pilot releasing the brake pedal64on Side A, and the brake pedal64on Side B is not applied, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; and (c) a result148with no brakes58on/applied on Side A and no brakes58on/applied on Side B, and with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104.

(2) A second PTLA exit scenario142b(seeFIG. 2B) includes: (a) an initial state144of one or more brakes58on Side A are on/applied, and are inhibited brakes58ain an inhibited state57, and no brakes58are on/applied on Side B, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; (b) a state change146of a pilot applying the brake pedal64on Side B, and the brake pedal64on Side A is held down, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; and (c) a result148with all (full) brakes58on/applied on Side A and all (full) brakes58on/applied on Side B, and with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104.

(3) A third PTLA exit scenario142c(seeFIG. 2B) includes: (a) an initial state144of one or more brakes58on Side A are on/applied and are inhibited brakes58ain an inhibited state57, and no brakes58are on/applied on Side B, with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, below the PTLA speed threshold104; (b) a state change146of the aircraft10accelerating so that the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, is above the PTLA speed threshold104, and the brake pedal64on Side B is still on/applied and held down, and the brake pedal64on Side B is not applied; and (c) a result148with all (full) brakes58on/applied on Side A, and no brakes58on/applied on Side B, and with the aircraft ground speed101(seeFIG. 2B), for example, as determined with the average wheel speed102, above the PTLA speed threshold104.

With the above discussed plurality of PTLA enter scenarios140and plurality of PTLA exit scenarios142, the brakes46may be limited to one or more but not all of the brakes46based on the taxi brake release function130(seeFIG. 2A), and the no brakes applied may mean brakes below a certain pedal threshold, such as a minimum PTLA triggering brake pedal command threshold122a(seeFIG. 4), for example, 25% pilot brake pedal effort (seeFIGS. 4-7). In addition, with the above discussed plurality of PTLA enter scenarios140and plurality of PTLA exit scenarios142, the apply or applied pedal may mean the brake58passes above a certain pedal threshold, such as a maximum PTLA triggering brake pedal command threshold122b(seeFIG. 4), for example, 27% pilot brake pedal effort (seeFIGS. 4-7), and the release pedal may mean the brake58passes below the minimum PTLA triggering brake pedal command threshold122a(seeFIG. 4), for example, 25% pilot brake pedal effort (seeFIGS. 4-7). In addition, differential wheel speeds between the left main landing gear24aand the right main landing gear24bmay be considered to obtain a more precise activation criteria. Moreover, a secondary threshold may be used to ensure the pivot turn command was intended or not intended, and a delay function may be used to ensure the brake pedal command120was intended to execute the scheme, i.e. a pivoted turn. The percentage values correspond to a normalized full brake pedal travel, for example, 0% is fully off the brake pedal, and 100% is the brake pedal fully depressed.

As shown inFIGS. 1A-1B and 2A, in another version of the disclosure, there is provided the aircraft10comprising the fuselage18(seeFIGS. 1A-1B), and one or more wings20(seeFIGS. 1A-1B) attached to the fuselage18, and a plurality of landing gear22(seeFIGS. 1A-1B) attached to the fuselage18. The plurality of landing gear22comprising the nose landing gear26(seeFIGS. 1A-1B), and at least two main landing gear24(seeFIGS. 1A-1B, 2A), each of the at least two main landing gear24having two or more wheels46(seeFIGS. 1A-1B, 2A), wherein during a pivot turn maneuver30(seeFIG. 2A) by the aircraft10, one of the at least two main landing gear24comprises a pivoting main landing gear32(seeFIG. 2A). Each main landing gear24may have, for example, two wheels, four wheels, six wheels, or another suitable number of wheels.

The aircraft10further comprises the PTLA brake system12comprising the brake control system14operatively coupled to the at least two main landing gear24, wherein the brake control system14controls braking of the at least two main landing gear24. The PTLA system further comprises the PTLA brake inhibit subsystem16coupled to the brake control system14, wherein the PTLA brake inhibit subsystem16inhibits braking of one or more of the two or more wheels46of one main landing gear24comprising the pivoting main landing gear32, during the pivot turn maneuver30, so that at least one wheel46of the two or more wheels46is in the unbraked state52, and a remaining number54of the two or more wheels46are in the braked state56. As discussed above, the PTLA brake system12alleviates the structural loads28aon the pivoting main landing gear32, during the pivot turn maneuver30by the aircraft10, and reduces wear136on the at least one wheel46that is in the unbraked state52.

The PTLA brake inhibit subsystem16inhibits braking, via activation92(seeFIG. 2A) of the PTLA brake inhibit command90, to one or more brake control units74(seeFIG. 2A) of the brake control system14, upon detection of one or more of the brake inhibit conditions94(seeFIG. 2A). As discussed above, the one or more brake inhibit conditions94comprises one or more of, (a) the on ground state of the aircraft96(seeFIG. 2A), indicated when the aircraft10is in the on ground position98(seeFIG. 2A; (b) an acceptable aircraft ground speed100(seeFIG. 2A), indicated when an aircraft ground speed101(seeFIG. 2A) of the aircraft10is less than the PTLA speed threshold104(seeFIG. 2A); or (c) the PTLA active flag command indication106(seeFIG. 2A), generated by the monitoring logic108(seeFIG. 2A) of the PTLA brake inhibit subsystem16, to monitor brake pedal positions110(seeFIG. 2A), to detect initiation31of the pivot turn maneuver30, according to one of the plurality of pivot turn brake pedal profiles112(seeFIG. 2A).

The PTLA brake inhibit command90is deactivated when one or more of the brake inhibit deactivation conditions118(seeFIG. 2A) is/are met or satisfied. The brake inhibit deactivation conditions118may comprise one or more of: (a) the aircraft ground speed101of the aircraft10exceeds the PTLA speed threshold104; (b) both the left brake pedal command120a(seeFIG. 2A) and the right brake pedal command120b(seeFIG. 2A) exceed the PTLA triggering brake pedal command threshold122(seeFIG. 2A), for at least a predetermined time period124(seeFIG. 2A); or (c) the aircraft10enters into the active parking brake state126(seeFIG. 2A).

In one version, the aircraft10may further comprise the taxi brake release function130, and the PTLA brake inhibit subsystem16is integrated with the taxi brake release function130, which executes the PTLA brake inhibit command90on behalf of the PTLA brake inhibit subsystem16, to inhibit braking of one or more but not all of the wheels46of the pivoting main landing gear32.

Now referring toFIGS. 3A-3C,FIG. 3Ais an illustration of schematic drawing of a PTLA brake system command logic diagram156ain a pivot turn maneuver30by the aircraft10,FIG. 3Bis an illustration of schematic drawing of another version of a PTLA brake system command logic diagram156b, andFIG. 3Cis an illustration of schematic drawing of yet another version of a PTLA brake system command logic diagram156c.

FIG. 3Ashows the PTLA brake system command logic diagram156awhere the brake inhibit condition94comprises one brake inhibit condition94comprising the PTLA active flag command (CMD) indication106activating the PTLA brake inhibit command90, to result in a PTLA brake inhibit command (CMD) enable function158, where a brake control unit74of the brake control system14(seeFIG. 2A) enables the PTLA brake inhibit command90. The PTLA active flag command indication106is generated by the monitoring logic108(seeFIG. 2A), which determines whether or not the pivot turn maneuver30is being attempted by the pilot154(seeFIG. 2B), and the monitoring logic output108a(seeFIG. 2A) is determined based on one of the pivot turn brake pedal profiles112(seeFIGS. 2A-2B, 4-7).

FIG. 3Bshows the PTLA brake system command logic diagram156bwhere the brake inhibit conditions94comprise two brake inhibit conditions94comprising either, (a) the on ground state of the aircraft96and the PTLA active flag command (CMD) indication106, or (b) the acceptable aircraft ground speed100and the PTLA active flag command (CMD) indication106, where either combination activates the PTLA brake inhibit command90. This results in the PTLA brake inhibit command (CMD) enable function158, where the brake control unit74of the brake control system14(seeFIG. 2A) enables the PTLA brake inhibit command90. The PTLA active flag command indication106is generated by the monitoring logic108(seeFIG. 2A), which determines whether or not the pivot turn maneuver30is being attempted by the pilot154(seeFIG. 2B), and the monitoring logic output108a(seeFIG. 2A) is determined based on one of the pivot turn brake pedal profiles112(seeFIGS. 2A-2B, 4-7).

FIG. 3Cshows the PTLA brake system command logic diagram156bwhere the brake inhibit conditions94comprise all of, (a) the on ground state of the aircraft96, (b) the acceptable aircraft ground speed100, and (c) the PTLA active flag command (CMD) indication106, to activate or generate the PTLA brake inhibit command90. This results in the PTLA brake inhibit command (CMD) enable function158, where the brake control unit74of the brake control system14(seeFIG. 2A) enables the PTLA brake inhibit command90. The PTLA active flag command indication106is generated by the monitoring logic108(seeFIG. 2A), which determines whether or not the pivot turn maneuver30is being attempted by the pilot154(seeFIG. 2B), and the monitoring logic output108a(seeFIG. 2A) is determined based on one of the pivot turn brake pedal profiles112(seeFIGS. 2A-2B, 4-7).

As shown inFIGS. 3A-3C, the PTLA brake inhibit command (CMD) enable function158is carried out where the brake control unit74of the brake control system14(seeFIG. 2A) enables the PTLA brake inhibit command90, to result in a PTLA brake inhibit command (CMD) enable160sent to a wheel selection function162. As further shown inFIGS. 3A-3C, the PTLA brake inhibit command90may optionally be integrated with the taxi brake release function130if it is present and existing on the aircraft10(seeFIGS. 1A-1B, 2A), to obtain the taxi brake release function integration132. As shown inFIGS. 3A-3C, a current taxi brake release selection164may optionally be selected, when it already exists and is present on the aircraft10, to select Wheel X166in a number1position168corresponding to a forward outboard wheel position number1168aof the wheels46of the left main landing gear24awhich, in this case, is the pivoting main landing gear32. As shown inFIGS. 3A-3C, the current taxi brake release selection164further selects Wheel Y170in a number2position172corresponding to a forward outboard wheel position number2172aof the wheels46of the left main landing gear24a.FIGS. 3A-3Cshows the left main landing gear24awith four wheels46and the right main landing gear24bwith four wheels46. Wheel X166and Wheel Y170are an axle pair48a(see FIGS.3A_3C) of wheels46. The PTLA brake inhibit command90inhibits the braking of Wheel X166and Wheel Y170, and a Wheel X, Y inhibit command (CMD)174(see FIGS.3A_3C) is sent to a brake control unit command (CMD) generation176. As shown inFIGS. 3A-3C, the brake control unit command generation176also receives a pilot pedal command (CMD)178and a hardware (HW) enable command (CMD)180.

As shown inFIGS. 3A-3C, the brake control unit command generation176then sends a Wheel X inhibited command (CMD)182and a Wheel Y inhibited command (CMD)184to the brake control valves82. One brake control valve82is coupled, or connected to, Wheel X166, via a first hydraulic connector element88a, to inhibit braking of Wheel X166on the left main landing gear24a, and another brake control valve82is coupled or connected to Wheel Y170, via a second hydraulic connector element88b, to inhibit braking of Wheel Y170on the left main landing gear24a. As shown inFIGS. 3A-3C, the PTLA brake inhibit command90, along with the brake control units74and the brake control valves82, result in inhibited paired wheels46hon the pivoting main landing gear32. As shown inFIGS. 3A-3C, no wheels on the right main landing gear24b, which is a non-pivoting main landing gear34, are inhibited.

Now referring toFIG. 4,FIG. 4is an illustration of a graph186showing a pivot turn brake pedal profile112, in the form of an exemplary first pivot turn brake pedal profile112a, where entry is made into a pivot turn maneuver30, in the form of a left pivot turn maneuver30b, for an entry in left pivot turn maneuver188with a both pedals depressed initially and at the end scenario190. As shown inFIG. 4, the graph186includes a first portion192with a pilot brake pedal effort193in percent (%) on the y-axis, and time194in seconds (s) on the x-axis. This percentage value corresponds to a normalized full brake pedal travel, for example, 0% is fully off the brake pedal, and 100% is the brake pedal fully depressed. As further shown inFIG. 4, the graph186includes a second portion196with a pivot turn flag198on the y-axis and also time194in seconds (s) on the x-axis, and a first not active portion200, an active portion202, and a second not active portion204along the x-axis. As further shown inFIG. 4, the graph186includes a third portion206showing brake states208of wheels46on the left main landing gear24aand the right main landing gear24b. As further shown inFIG. 4, the brake states208include no brakes210, brakes on212, and inhibited brakes-no brakes214.

As shown inFIG. 4, the first portion192shows a left pedal plot216for a left pedal218and shows a right pedal plot220for a right pedal222, through the first not active portion200, the active portion202, and the second not active portion204, as the entry in left pivot turn maneuver188transitions into and out of a braked pivot turn. The first portion192further shows hysteresis224with a minimum PTLA triggering brake pedal command threshold122aand a maximum PTLA triggering brake pedal command threshold122b. As used herein, “hysteresis” refers to an output selection in which an output command changes at different thresholds depending on the direction of an input command travel. Such hysteresis is used in control functions to avoid limit cycling effect in the output command, if the input, for example, the brake pedal command, signal oscillates from one fixed threshold to another.

As shown inFIG. 4, during the first not active portion200, the left pedal218and the right pedal220are both initially depressed and the wheels46of the left main landing gear24aand the right main landing gear24bare in the brakes on212brake state208. As further shown inFIG. 4, during the active portion202, the left pedal218is held down, and the right pedal222is released and the wheels46of the right main landing gear24bare in the no brakes210brake state208. As shown inFIG. 4, when the right pedal plot220falls below the minimum PTLA triggering brake pedal command threshold122atransitioning from the first not active portion200to the active portion202(and the average wheel speed102(seeFIG. 2A) is less than the PTLA speed threshold104(seeFIG. 2A)), the PTLA brake inhibit command90is activated and PTLA is entered, and the PTLA brake inhibit command90(seeFIGS. 2A, 3A-3C) is sent to the brake control unit74(seeFIGS. 3A-3C) and the wheel selection50(seeFIGS. 3A-3C), to inhibit brakes58(seeFIG. 2A) on a pair48of wheels46on the left main landing gear24a. As shown inFIG. 4, during the active portion202, the pair48of forward wheels46con the left main landing gear24ais in the inhibited brakes-no brakes214brake state208, and the pair48of aft wheels46don the left main landing gear24ais in the brakes on212brake state208. It is noted that the pair48of aft wheels46dcould be inhibited instead of the pair48of forward wheels46con the left main landing gear24a, or other combinations of wheels46, for example, diagonal wheels46i(seeFIG. 2A), one wheel46, three wheels46, or another suitable number of wheels.

As shown inFIG. 4, when the right pedal plot220goes above the maximum PTLA triggering brake pedal command threshold122btransitioning from the active portion202to the second not active portion204, the PTLA brake inhibit command90is deactivated, and in the second not active portion204, the left pedal218is still held down and applied, and the right pedal222is applied, so that an all brakes applied state226results at the PTLA exit. As shown inFIG. 4, during the second not active portion204, all of the wheels46on the left main landing gear24aand on the right main landing gear24bare in the brakes on212brake state208.

Now referring toFIG. 5,FIG. 5is an illustration of a graph228showing a pivot turn brake pedal profile112, in the form of an exemplary second pivot turn brake pedal profile112b, where entry is made into a pivot turn maneuver30, in the form of a left pivot turn maneuver30b, for an entry in left pivot turn maneuver188with a both pedals depressed initially and released at the end scenario230. As shown inFIG. 5, the graph228includes the first portion192with the pilot brake pedal effort193in percent (%) on the y-axis, and time194in seconds (s) on the x-axis. This percentage value corresponds to a normalized full brake pedal travel, for example, 0% is fully off the brake pedal, and 100% is the brake pedal fully depressed. As further shown inFIG. 5, the graph228includes the second portion196with the pivot turn flag198on the y-axis and also time194in seconds (s) on the x-axis, and the first not active portion200, the active portion202, and the second not active portion204along the x-axis. As further shown inFIG. 5, the graph228includes the third portion206showing brake states208of wheels46on the left main landing gear24aand the right main landing gear24b. As further shown inFIG. 5, the brake states208include no brakes210, brakes on212, and inhibited brakes-no brakes214.

As shown inFIG. 5, the first portion192shows a left pedal plot216afor the left pedal218and shows a right pedal plot220afor the right pedal222, through the first not active portion200, the active portion202, and the second not active portion204, as the entry in left pivot turn maneuver188transitions into and out of a braked pivot turn. The first portion192further shows hysteresis224with the minimum PTLA triggering brake pedal command threshold122aand the maximum PTLA triggering brake pedal command threshold122b.

As shown inFIG. 5, during the first not active portion200, the left pedal218and the right pedal220are both initially depressed and the wheels46of the left main landing gear24aand the right main landing gear24bare in the brakes on212brake state208. As further shown inFIG. 5, during the active portion202, the left pedal218is held down, and the right pedal222is released, and the wheels46of the right main landing gear24bare in the no brakes210brake state208. As shown inFIG. 5, when the right pedal plot220afalls below the minimum PTLA triggering brake pedal command threshold122atransitioning from the first not active portion200to the active portion202(and the average wheel speed102(seeFIG. 2A) is less than the PTLA speed threshold104(seeFIG. 2A)), the PTLA brake inhibit command90is activated and PTLA is entered, and the PTLA brake inhibit command90(seeFIGS. 2A, 3A-3C) is sent to the brake control unit74(seeFIGS. 3A-3C) and the wheel selection50(seeFIGS. 3A-3C), to inhibit brakes58(seeFIG. 2A) on a pair48of wheels46on the left main landing gear24a. As shown inFIG. 5, during the active portion202, the pair48of aft wheels46don the left main landing gear24ais in the inhibited brakes-no brakes214brake state208, and the pair48of forward wheels46con the left main landing gear24ais in the brakes on212brake state208. It is noted that the pair48of forward wheels46ccould be inhibited instead of the pair48of aft wheels46don the left main landing gear24a, or other combinations of wheels46, for example, diagonal wheels46i(seeFIG. 2A), one wheel46, three wheels46, or another suitable number of wheels.

As shown inFIG. 5, when the left pedal plot216agoes below the minimum PTLA triggering brake pedal command threshold122atransitioning from the active portion202to the second not active portion204, the PTLA brake inhibit command90is deactivated, and in the second not active portion204, the left pedal218is released, and the right pedal222remains released, so that all of the wheels46on the left main landing gear24aand on the right main landing gear24bare in the no brakes210brake state208at the PTLA exit.

Now referring toFIG. 6,FIG. 6is an illustration of a graph232showing a pivot turn brake pedal profile112, in the form of an exemplary third pivot turn brake pedal profile112c, where entry is made into a pivot turn maneuver30, in the form of a left pivot turn maneuver30b, for an entry in left pivot turn maneuver188with a no pedals depressed initially and both pedals depressed at the end scenario234. As shown inFIG. 6, the graph232includes the first portion192with the pilot brake pedal effort193in percent (%) on the y-axis, and time194in seconds (s) on the x-axis. This percentage value corresponds to a normalized full brake pedal travel, for example, 0% is fully off the brake pedal, and 100% is the brake pedal fully depressed. As further shown inFIG. 6, the graph232includes the second portion196with the pivot turn flag198on the y-axis and also time194in seconds (s) on the x-axis, and the first not active portion200, the active portion202, and the second not active portion204along the x-axis. As further shown inFIG. 6, the graph228includes the third portion206showing brake states208of wheels46on the left main landing gear24aand the right main landing gear24b. As further shown inFIG. 6, the brake states208include no brakes210, brakes on212, and inhibited brakes-no brakes214.

As shown inFIG. 6, the first portion192shows a left pedal plot216bfor the left pedal218and shows a right pedal plot220bfor the right pedal222, through the first not active portion200, the active portion202, and the second not active portion204, as the entry in left pivot turn maneuver188transitions into and out of a braked pivot turn. The first portion192further shows hysteresis224with the minimum PTLA triggering brake pedal command threshold122aand the maximum PTLA triggering brake pedal command threshold122b.

As shown inFIG. 6, during the first not active portion200, the left pedal218and the right pedal216are both initially not depressed and the wheels46of the left main landing gear24aand the right main landing gear24bare in the no brakes210brake state208. As further shown inFIG. 6, during the active portion202, the left pedal218is applied and depressed, and the right pedal222is not applied and depressed, and the wheels46of the right main landing gear24bare in the no brakes210brake state208. As shown inFIG. 6, when the left pedal plot216bgoes above the maximum PTLA triggering brake pedal command threshold122btransitioning from the first not active portion200to the active portion202(and the average wheel speed102(seeFIG. 2A) is less than the PTLA speed threshold104(seeFIG. 2A)), the PTLA brake inhibit command90is activated and PTLA is entered, and the PTLA brake inhibit command90(seeFIGS. 2A, 3A-3C) is sent to the brake control unit74(seeFIGS. 3A-3C) and the wheel selection50(seeFIGS. 3A-3C), to inhibit brakes58(seeFIG. 2A) on a pair48of wheels46on the left main landing gear24a. As shown inFIG. 6, during the active portion202, the pair48of forward wheels46con the left main landing gear24ais in the inhibited brakes-no brakes214brake state208, and the pair48of aft wheels46don the left main landing gear24ais in the brakes on212brake state208. It is noted that the pair48of aft wheels46dcould be inhibited instead of the pair48of forward wheels46con the left main landing gear24a, or other combinations of wheels46, for example, diagonal wheels46i(seeFIG. 2A), one wheel46, three wheels46, or another suitable number of wheels.

As shown inFIG. 6, when the right pedal plot220bgoes above the maximum PTLA triggering brake pedal command threshold122btransitioning from the active portion202to the second not active portion204, the PTLA brake inhibit command90is deactivated, and in the second not active portion204, the left pedal218remains depressed and applied, and the right pedal222is depressed and applied, so that an all brakes applied state226results at the PTLA exit. As shown inFIG. 6, during the second not active portion204, all of the wheels46on the left main landing gear24aand on the right main landing gear24bare in the brakes on212brake state208.

Now referring toFIG. 7,FIG. 7is an illustration of a graph236showing a pivot turn brake pedal profile112, in the form of an exemplary fourth pivot turn brake pedal profile112d, where entry is made into a pivot turn maneuver30, in the form of a left pivot turn maneuver30b, for an entry in left pivot turn maneuver188with a no pedals depressed initially and then both pedals released at the end scenario238. As shown inFIG. 7, the graph232includes the first portion192with the pilot brake pedal effort193in percent (%) on the y-axis, and time194in seconds (s) on the x-axis. This percentage value corresponds to a normalized full brake pedal travel, for example, 0% is fully off the brake pedal, and 100% is the brake pedal fully depressed. As further shown inFIG. 7, the graph232includes the second portion196with the pivot turn flag198on the y-axis and also time194in seconds (s) on the x-axis, and the first not active portion200, the active portion202, and the second not active portion204along the x-axis. As further shown inFIG. 7, the graph228includes the third portion206showing brake states208of wheels46on the left main landing gear24aand the right main landing gear24b. As further shown inFIG. 7, the brake states208include no brakes210, brakes on212, and inhibited brakes-no brakes214.

As shown inFIG. 7, the first portion192shows a left pedal plot216cfor the left pedal218and shows a right pedal plot220cfor the right pedal222, through the first not active portion200, the active portion202, and the second not active portion204, as the entry in left pivot turn maneuver188transitions into and out of a braked pivot turn. The first portion192further shows hysteresis224with the minimum PTLA triggering brake pedal command threshold122aand the maximum PTLA triggering brake pedal command threshold122b.

As shown inFIG. 7, during the first not active portion200, the left pedal218and the right pedal220are both initially not depressed and the wheels46of the left main landing gear24aand the right main landing gear24bare in the no brakes210brake state208. As further shown inFIG. 7, during the active portion202, the left pedal218is applied and depressed, and the right pedal222is not applied and depressed, and the wheels46of the right main landing gear24bare in the no brakes210brake state208. As shown inFIG. 7, when the left pedal plot216cgoes above the maximum PTLA triggering brake pedal command threshold122btransitioning from the first not active portion200to the active portion202(and the average wheel speed102(seeFIG. 2A) is less than the PTLA speed threshold104(seeFIG. 2A)), the PTLA brake inhibit command90is activated and PTLA is entered, and the PTLA brake inhibit command90(seeFIGS. 2A, 3A-3C) is sent to the brake control unit74(seeFIGS. 3A-3C) and the wheel selection50(seeFIGS. 3A-3C), to inhibit brakes58(seeFIG. 2A) on one or more but not all of the wheels46, for example, to inhibit brakes58on a pair48of wheels46, on the left main landing gear24a. As shown inFIG. 7, during the active portion202, the one or more but not all of the wheels46, for example, the pair48of aft wheels46d, on the left main landing gear24ais in the inhibited brakes-no brakes214brake state208, and the one or more but not all of the wheels46, for example, the pair48of forward wheels46c, on the left main landing gear24ais in the brakes on212brake state208. It is noted that the one or more but not all of the wheels46, for example, the pair48of forward wheels46c, could be inhibited instead of the one or more but not all of the wheels46, for example, the pair48of aft wheels46d, on the left main landing gear24a, or other combinations of wheels46, for example, diagonal wheels46i(seeFIG. 2A), one wheel46, three wheels46, or another suitable number of wheels.

As shown inFIG. 7, when the left pedal plot216cgoes below the minimum PTLA triggering brake pedal command threshold122atransitioning from the active portion202to the second not active portion204, the PTLA brake inhibit command90is deactivated, and in the second not active portion204, the left pedal218is released, and the right pedal222remains released, so that all of the wheels46on the left main landing gear24aand on the right main landing gear24bare in the no brakes210brake state208.

Now referring toFIG. 8,FIG. 8is an illustration of a flow diagram showing an exemplary version of a method250of the disclosure. In another version of the disclosure, there is provided the method250(seeFIG. 8) for alleviating structural loads28a(seeFIG. 2A) on a pivoting main landing gear32(seeFIG. 2A) of an aircraft10(seeFIGS. 1A-1B, 2A) in and during a pivot turn maneuver30(seeFIG. 2A).

The blocks inFIG. 8represent operations and/or portions thereof, and lines connecting the various blocks do not imply any particular order or dependency of the operations or portions thereof.FIG. 8and the disclosure of the steps of the method250, set forth herein, should not be interpreted as necessarily determining a sequence in which the steps are to be performed. Rather, although one illustrative order is indicated, it is to be understood that the sequence of the steps may be modified when appropriate. Accordingly, certain operations may be performed in a different order or simultaneously.

As shown inFIG. 8, the method250comprises the step of initiating252the pivot turn maneuver30with the aircraft10. The aircraft10has a pivot turn load alleviation (PTLA) brake system12(seeFIGS. 1A-1B, 2A). As discussed in detail above, the PTLA brake system12comprises the brake control system14(seeFIGS. 1A-1B, 2A) operatively coupled to at least two main landing gear24(seeFIGS. 1A-1B, 2A). Each of the at least two main landing gear24has two or more wheels46(seeFIGS. 1A-1B, 2A). For example, each main landing gear24may have two wheels, four wheels, six wheels, or another suitable number of wheels. The brake control system14controls braking of the at least two main landing gear24. The PTLA brake system12further comprises the pivot turn load alleviation (PTLA) brake inhibit subsystem16(seeFIGS. 1A-1B, 2A) coupled to the brake control system14.

The step of initiating252(seeFIG. 8) the pivot turn maneuver30with the aircraft10, may further comprise initiating252the pivot turn maneuver30with the aircraft10having the PTLA brake system12with the brake control system14including a plurality of brake control units74(seeFIG. 2A) and a plurality of brake control valves82(seeFIG. 2A), wherein one of the plurality of brake control units74receives the PTLA brake inhibit command90(seeFIG. 2A) from the PTLA brake inhibit subsystem16, to inhibit generation of at least one brake command76(seeFIG. 2A) to the at least one wheel46.

As shown inFIG. 8, the method250further comprises the step of activating254a pivot turn load alleviation (PTLA) brake inhibit command90(seeFIG. 2A) of the PTLA brake inhibit subsystem16, to one or more brake control units74(seeFIG. 2A) of the brake control system14, upon meeting one or more brake inhibit conditions94(seeFIG. 2A). The step of activating254(seeFIG. 8) further comprises activating the PTLA brake inhibit command90, upon meeting one or more of the brake inhibit conditions94comprising one or more of: (a) an on ground indication of the aircraft96(seeFIG. 2A), when the aircraft10is in an on ground position98(seeFIG. 2A); (b) an acceptable aircraft ground speed100(seeFIG. 2A), when an aircraft ground speed101(seeFIG. 2A) of the aircraft10is less than a pivot turn load alleviation (PTLA) speed threshold104(seeFIG. 2A); or (c) a pivot turn load alleviation (PTLA) active flag command indication106(seeFIG. 2A), generated by a monitoring logic108(seeFIG. 2A) of the PTLA brake inhibit subsystem16, to monitor brake pedal positions110(seeFIG. 2A), to detect initiation31(seeFIG. 2A) of the pivot turn maneuver30(seeFIG. 2A), according to one of a plurality of pivot turn brake pedal profiles112(seeFIGS. 2A, 4-7).

As shown inFIG. 8, the method250further comprises the step of inhibiting braking256of one or more of the two or more wheels46(seeFIGS. 1A-1B, 2A) of the pivoting main landing gear32, in the pivot turn maneuver30, so that at least one wheel46of the two or more wheels46is in an unbraked state52(seeFIG. 2A), and a remaining number54(seeFIG. 2A) of the two or more wheels46are in a braked state56(seeFIG. 2A). The PTLA brake system12alleviates the structural loads28aon the pivoting main landing gear32of the aircraft10in the pivot turn maneuver30, and reduces wear136(seeFIG. 2A) on the at least one wheel46that is in the unbraked state52.

The step of inhibiting braking256(seeFIG. 8) may further comprises inhibiting braking256of one of, one wheel46, two wheels46, or three wheels46, in the pivot turn maneuver30by the aircraft10. The step of inhibiting braking256may further comprise inhibiting braking256of an inhibited wheel selection50(seeFIG. 2A) of one or more but not all of the wheels46, for example, one axle pair48a(seeFIG. 2A) of wheels46, on the pivoting main landing gear32, and with initiation31of a subsequent pivot turn maneuver30a(seeFIG. 2A), the inhibited wheel selection50of the one or more but not all of the wheels46, for example, the one axle pair48aof wheels46, changes, in a sequential order51(seeFIG. 2A), to a different one or more but not all of the wheels46, for example, a different axle pair48b(seeFIG. 2A) of wheels46.

As shown inFIG. 8, the method250may further optionally comprise, after the step of inhibiting braking256, the step of deactivating258the PTLA brake inhibit command90, upon meeting one or more brake inhibit deactivation conditions118(seeFIG. 2A). As discussed above, the one or more brake inhibit deactivation conditions118comprise one or more of, (a) the aircraft ground speed101(seeFIG. 2A) of the aircraft10exceeds the pivot turn load alleviation (PTLA) speed threshold104(seeFIG. 2A); or (b) both a left brake pedal command120a(seeFIG. 2A) and a right brake pedal command120b(seeFIG. 2A) exceed a pivot turn load alleviation (PTLA) triggering brake pedal command threshold122(seeFIG. 2A), for at least a predetermined time period124(seeFIG. 2A); or (c) the aircraft10enters into an active parking brake state126(seeFIG. 2A).

As shown inFIG. 8, the method250may further optionally comprise, initiating252the pivot turn maneuver30with the aircraft10having a taxi brake release function130(seeFIG. 2A), and integrating260the PTLA brake inhibit subsystem16with the taxi brake release function130already present and existing in the aircraft10, so that the taxi brake release function130selects a wheel selection50(seeFIGS. 3A-3C) for the PTLA brake inhibit command90(seeFIGS. 2A, 3A-3C), to inhibit braking of one or more but not all of the wheels46of the pivoting main landing gear32.

Now referring toFIGS. 9 and 10,FIG. 9is a flow diagram of an embodiment of an aircraft manufacturing and service method300, andFIG. 10is an illustration of a functional block diagram of an embodiment of an aircraft316. Referring toFIGS. 9-10, versions of the disclosure may be described in the context of the aircraft manufacturing and service method300, as shown inFIG. 9, and the aircraft316, as shown inFIG. 10. During pre-production, the exemplary aircraft manufacturing and service method300(seeFIG. 9) may include specification and design302(seeFIG. 9) of the aircraft316(seeFIG. 10) and material procurement304(seeFIG. 9). During manufacturing, component and subassembly manufacturing306(seeFIG. 9) and system integration308(seeFIG. 9) of the aircraft316(seeFIG. 10) takes place. Thereafter, the aircraft316(seeFIG. 10) may go through certification and delivery310(seeFIG. 9) in order to be placed in service312(seeFIG. 9). While in service312(seeFIG. 9) by a customer, the aircraft316(seeFIG. 10) may be scheduled for routine maintenance and service314(seeFIG. 9), which may also include modification, reconfiguration, refurbishment, and other suitable services.

As shown inFIG. 10, the aircraft316produced by the exemplary aircraft manufacturing and service method300may include an airframe318with a plurality of systems320and an interior322. As further shown inFIG. 10, examples of the systems320may include one or more of a propulsion system324, an electrical system326, a hydraulic system328, and an environmental system330. Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the automotive industry, including automotive vehicles, the marine industry, including watercraft, ships, and submarines, and other suitable industries.

Methods and systems embodied herein may be employed during any one or more of the stages of the aircraft manufacturing and service method300(seeFIG. 9). For example, components or subassemblies corresponding to component and subassembly manufacturing306(seeFIG. 9) may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft316(seeFIG. 10) is in service312(seeFIG. 9). Also, one or more method embodiments, system embodiments, or a combination thereof, may be utilized during component and subassembly manufacturing306(seeFIG. 9) and system integration308(seeFIG. 9), for example, by substantially expediting assembly of, or reducing the cost of, the aircraft316(seeFIG. 10). Similarly, one or more of method versions, system versions, or a combination thereof, may be utilized while the aircraft316(seeFIG. 10) is in service312(seeFIG. 9), for example and without limitation, to maintenance and service314(seeFIG. 9).

Disclosed versions of the PTLA brake system12(seeFIGS. 1A-1B, 2A), and the method250(seeFIG. 8) alleviate loads28(seeFIG. 2A), such as structural loads28a(seeFIG. 2A) and torsional load reaction28b(seeFIG. 2A), or torque load, on a pivoting main landing gear32(seeFIG. 2A) of an aircraft10, in and during a pivot turn maneuver30(seeFIG. 2A), by an aircraft10, and reduces wear136on one or more wheels46of the pivoting main landing gear32having brakes58inhibited by the PTLA brake system12, and reduces wear136on the tires of such wheels46. Further, the PTLA brake system12inhibits braking on one or more brakes58on the pivoting main landing gear32, in order to reduce torsional load reaction28b(seeFIG. 2A) exerted on the pivoting main landing gear32. The loads28(seeFIG. 2A), such as structural loads28a(seeFIG. 2A) and torsional load reaction28b(seeFIG. 2A), or torque load, on the pivoting main landing gear32(seeFIG. 2A), are reduced because only a portion of the brakes58, such as half of the brakes58, are applied, and the other portion of the brakes58, or other half of the brakes58are inhibited or unbraked. The PTLA brake system12provides load alleviation for 2-point turn maneuver or pivot turn maneuver30.

Moreover, disclosed versions of the PTLA brake system12(seeFIGS. 1A-1B, 2A), and the method250(seeFIG. 8) may also reduce cornering forces134(seeFIG. 2A), which, in turn, also reduce wear136. The PTLA brake system12may also provide U-turn optimization138(seeFIG. 2A), when the inboard wheels46e(seeFIG. 2A) are released. An additional advantage of the PTLA brake system12may also be to reduce the overall weight of the main landing gear24because with reduced structural loads28aand reduced cornering forces134, various components and material on the main landing gear24may be reduced or eliminated, for example, a smaller, reduced weight scissor link, a smaller, reduced weight torque link, or another downsized structure on the main landing gear24, such as the pivoting main landing gear32. Moreover, the PTLA brake system12reduces brake load during a brake pivoting maneuver, or pivot turn maneuver30, by an aircraft10having a 2-main landing gear configuration36(seeFIG. 1A) to take advantage of individual wheel brake control.

In addition, disclosed versions of the PTLA brake system12(seeFIGS. 1A-1B, 2A), and the method250(seeFIG. 8) provide for integration with a taxi brake release function130(seeFIG. 2A) that may be already existing or present on an aircraft10, to obtain a taxi brake release function integration132(seeFIG. 2A). The taxi brake release function130selects a predetermined one or more but not all of the wheels46, for example, a pair of wheels46, when making a wheel selection50(seeFIGS. 3A-3C), and the PTLA brake inhibit command90uses that wheel selection50to assist the brake control unit74, to inhibit braking of one or more but not all of the wheels46, for example, the pair48of wheels46, of the pivoting main landing gear32.

Further, one disclosed version of the PTLA brake system12(seeFIGS. 1A-1B, 2A), and the method250(seeFIG. 8) provides for an axle pair48aof wheels46that are side-by-side and share a common axle49(seeFIG. 2A) between them. A paired axle release approach having two wheels46that share an axle49, on a four wheel46, two axle49main landing gear24, is one exemplary scheme or arrangement, where half of the wheels46are unbraked and inhibited by the PTLA brake system12, and the other half of the wheels46are braked during the pivot turn maneuver30. The PTLA brake system12logic may alternate between the pair48of forward wheels46cinhibited and the pair48of aft wheels46dinhibited on the pivoting main landing gear32(seeFIG. 2A). It is noted that the PTLA brake system12may also inhibit braking of one wheel46, two wheels46, three wheels46, or another suitable number of wheels46in the pivot turn maneuver30performed by the aircraft10.

Many modifications and other embodiments of the disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. The embodiments described herein are meant to be illustrative and are not intended to be limiting or exhaustive. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Any claimed embodiment of the disclosure does not necessarily include all of the embodiments of the disclosure.