Patent Description:
Conventionally, various types of aircraft utilize shock strut assemblies to assist in reducing and managing energy transmitted from landing gear to the structure of an aircraft to which the landing gear is attached. Such shock strut assemblies often feature a piston that compresses a fluid within a sealed chamber. The fluid typically includes a gas segment and a liquid segment. <CIT>, <CIT> and <CIT> relate to indicators for weighing and locating the center of gravity of an aircraft. <CIT> relates to automated calculation of the center of gravity of aircraft on the ground.

This application discloses a method for estimating a center of mass of an aircraft via a shock strut system according to claim <NUM>.

In various embodiments, the takeoff phase may be determined by sensing at least one of the first gas pressure, the second gas pressure, the third gas pressure, being less than a threshold pressure. The landing phase may be determined by sensing at least one of the first gas pressure, the second gas pressure, the third gas pressure, rises and then remains substantially constant over a predetermined period of time. The method may further comprise: receiving, by the processor, a first stroke of the first shock strut from the takeoff phase to the landing phase of the aircraft from a first position sensor; receiving, by the processor, a second stroke of the second shock strut from the takeoff phase to the landing phase of the aircraft from a second position sensor; receiving, by the processor, a third stroke of the third shock strut from the takeoff phase to the landing phase from a third position sensor; and determining, by the processor, the takeoff phase by receiving a fully extended (or near fully extended) stroke measurement from at least one of the first position sensor, the second position sensor, and the third position sensor. The method may further comprise determining, by the processor, the landing phase by receiving the near fully extended stroke measurement and a minimum stroke below a stroke threshold over a predetermined period of time from at least one of the first position sensor, the second position sensor, and the third position sensor; receiving for a first period time in the predetermined time period the minimum stroke; and receiving in a second period of time in the predetermined time period the near fully extended stroke measurement. Determining the center of mass of the aircraft may further comprises averaging, by the processor, a first force of the first shock strut, averaging a second force of the second shock strut, and averaging a third force of the third shock strut from the takeoff phase to the landing phase. The center of mass may be determined in a horizontal plane.

This application further discloses a center of mass estimation system according to claim <NUM>.

The controller is operable to receive a first pressure from the first pressure sensor, receive a second pressure from the second pressure sensor, and receive a third pressure from the third pressure sensor from a takeoff phase to a landing phase of the aircraft. The controller may be operable to average a first measurement of the first pressure from the takeoff phase to the landing phase, average a second measurement of the second pressure from the takeoff phase to the landing phase, and average a third measurement of the third pressure from the takeoff phase to the landing phase. The controller may be operable to determine a center of mass lateral distance from the wheelbase axis and a center of mass longitudinal distance from the wheel tread axis. The controller may be operable to determine the takeoff phase based on at least one of the first pressure, the second pressure, and the third pressure dropping below a takeoff pressure threshold. The controller may be operable to determine the landing phase based on at least one of the first pressure, the second pressure, and the third pressure rising and remaining substantially constant for a predetermined period of time. The center of mass estimation system may further comprise a first position sensor of the first shock strut, a second position sensor of the second shock strut, and a third position sensor of the third shock strut, wherein the first position sensor, the second position sensor, and the third position sensor are in electrical communication with the controller. The controller may be operable to determine the landing phase based on at least one of receiving a stroke measurement from at least one of the first position sensor, the second position sensor, and the third position sensor being near fully extended for a first period of time in a predetermined time period; and receiving the stroke measurement from at least one of the first position sensor, the second position sensor, and the third position sensor being a minimum stroke below a stroke threshold in a second period of time in the predetermined time period.

This application further discloses an article of manufacture according to claim <NUM>.

In various embodiments, the operations further comprise determining, by the aircraft center of mass estimation system, the takeoff phase from the measuring of at least one of the first pressure, the second pressure, and the third pressure. The operations may further comprise determining, by the aircraft center of mass estimation system, the landing phase from the measuring of at least one of the first pressure, the second pressure, and the third pressure. The operations further may further comprise beginning measuring the first pressure, the second pressure, and the third pressure in response to determining the takeoff phase. The operations may further comprise ending measuring the first pressure, the second pressure, and the third pressure in response to determining the landing phase has ended.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration and their best mode. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized, and that logical and mechanical changes may be made without departing from the scope of the appended claims.

Thus, the detailed description herein is presented for purposes of illustration only and not for limitation. For example, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option.

Aircraft landing gear systems of an aircraft in accordance with the present disclosure comprises a shock strut. Estimation of a center of mass of the aircraft is determined through the shock strut by measuring certain variables through the shock strut, including gas pressure, and/or stroke of the shock strut at various points during operation of the aircraft, and calculating the center of mass from the variables.

Accordingly, with reference to <FIG>, a perspective view of an aircraft <NUM>, in accordance with various embodiments. The aircraft <NUM> is configured for vertical takeoff (e.g., a helicopter, or the like). The aircraft <NUM> includes a landing gear arrangement <NUM>. The landing gear arrangement <NUM> includes at least three landing gear assemblies. In various embodiments, a mass estimation system including each landing gear assembly may be configured to calculate a force during a landing event. Each landing gear assembly in the landing gear arrangement <NUM> may include sensors configured to measure various variables and may use the variables to estimate a center of mass of the aircraft <NUM> along a horizontal plane.

Referring now to <FIG>, a schematic plan view of a landing gear arrangement <NUM>, in accordance with various embodiments. The landing gear arrangement <NUM> includes a right hand side (RHS) landing gear assembly <NUM>, a left hand side (LHS) landing gear assembly <NUM>, and a center landing gear assembly <NUM>. In various embodiments, the center landing gear assembly <NUM> may be disposed after or forward of the RHS landing gear assembly <NUM> and the LHS landing gear assembly <NUM>. Although illustrated as including two-wheel landing gear assemblies, any number of wheels is within the scope of this disclosure. For example, each landing gear assembly (e.g., landing gear assemblies <NUM>, <NUM>, <NUM>) may include one wheel, two wheels, four wheels, eight wheels, or any other number of wheels and be within the scope of this disclosure.

In various embodiments, each landing gear assembly (e.g., landing gear assemblies <NUM>, <NUM>, <NUM>) may include a center contact point of the wheel(s) of each landing gear assembly. In various embodiments, a wheel tread (A) may be a distance between the center contact point <NUM> of LHS landing gear assembly <NUM> and the center contact point <NUM> of RHS landing gear assembly <NUM>. Similarly, a wheelbase (B) may be a distance between the center contact point <NUM> of the center landing gear assembly <NUM> and a line from the center contact point <NUM> of the RHS landing gear assembly and the center contact point <NUM> of the LHS landing gear assembly <NUM>, the distance being measured in a perpendicular direction to the wheel tread (A) measurement. The wheel tread (A) is measured along a lateral axis (e.g., X-Axis) and the wheelbase (B) is measured along a longitudinal axis (e.g., Y-Axis).

With reference now to <FIG>, a side view of the landing gear assembly <NUM> is illustrated, in accordance with various embodiments. In various embodiments each landing gear assembly from <FIG> (e.g., RHS landing gear assembly <NUM>, LHS landing gear assembly, <NUM>, and center landing gear assembly <NUM>) may be in accordance with landing gear assembly <NUM>. In the various embodiments of the invention, landing gear assembly <NUM> comprises a shock strut <NUM>. Shock strut <NUM> may be mechanically coupled to a wheel assembly <NUM>. In various embodiments, shock strut <NUM> may be configured to absorb and dampen forces transmitted by wheel assembly <NUM> to an aircraft.

Shock strut <NUM> may comprise, for example, a piston <NUM> and a cylinder <NUM>. Cylinder <NUM> may be configured to receive piston <NUM> in a manner that allows the two components to telescope together and absorb and dampen forces transmitted by wheel assembly <NUM>.

In various embodiments, a liquid, such as hydraulic fluid or oil, is located within shock strut <NUM>. Cylinder <NUM> and piston <NUM> may, for example, be configured to seal such that liquid contained within shock strut <NUM> is unable to leak as piston <NUM> moves relative to cylinder <NUM>. Further, shock strut <NUM> may be configured to contain a gas. The air may be positioned above the gas (referred to as an "air-over-oil" arrangement) or vice versa. Similarly, cylinder <NUM> and piston <NUM> may be sealed such that gas is unable to leak as piston <NUM> moves relative to cylinder <NUM>. As such, shock strut <NUM> may comprise a pressurized environment within cylinder <NUM>. Although described as an "air-over-oil" arrangement," any shock strut configuration is within the scope of this disclosure. For example, the shock strut configuration may be a single stage separated air-oil, a dual stage separated air-oil, a dual stage mixed air-oil pressure activated, or a dual stage mixed air-oil stroke activated configuration and be within the scope of this disclosure.

Shock strut <NUM> may further comprise, for example, a gas pressure sensor <NUM>. In various embodiments, gas pressure sensor <NUM> may be capable of measuring the pressure of the gas within shock strut <NUM> at a desired time. For example, gas pressure sensor <NUM> may measure the gas pressure within shock strut <NUM> before, during, or after take-off, or at any point during the duty cycle of shock strut <NUM>.

In various embodiments, shock strut <NUM> may further comprise, for example, a gas temperature sensor <NUM>. Gas temperature sensor <NUM> may be capable of measuring the temperature of the gas within shock strut <NUM> at any point during the duty cycle of shock strut <NUM>.

Shock strut <NUM> may also comprise a position sensor <NUM>. In various embodiments, position sensor <NUM> may be capable of measuring the position of piston <NUM> relative to cylinder <NUM>, which is conventionally referred to as the stroke or stroke, of shock strut <NUM> at a desired time. Position sensor <NUM> may be configured to measure the position indirectly, for example, by measuring the orientation of one or more shock strut torque links <NUM> (or other components). For example, position sensor <NUM> may measure the stroke of shock strut <NUM> at any point during the duty cycle of shock strut <NUM>.

With reference to <FIG>, a method <NUM> for determining a center of mass of an aircraft is illustrated, in accordance with various embodiments. Method <NUM> may, for example, comprise utilizing data from a flight cycle (e.g., from just after takeoff and just after landing) to estimate a center of mass of an aircraft (e.g., aircraft <NUM> from <FIG>).

In various embodiments, method <NUM> may comprise determining a take-off event (step <NUM>). The take-off event may be determined utilizing measurements from position sensor <NUM> or gas pressure sensor <NUM> from <FIG>. For example, typically, a shock strut should extend to a fully extended position during take-off of an aircraft. As such, the position sensor <NUM> may determine the take-off event by measuring an extension of the shock strut and determining the shock strut is at or near fully extended. In various embodiments a take-off event may be determined solely from the gas pressure sensor <NUM>. For example, the gas pressure sensor <NUM> may determine the take-off event by measuring a gas pressure below a threshold gas pressure. The threshold gas pressure may be slightly greater than a minimum pressure of the shock strut <NUM>. In various embodiments, in response to determining the take-off event (e.g., step <NUM>), at least one of pressure data and stroke data may begin being recorded for each landing gear assembly.

In various embodiments, at least one of the gas pressure and the stroke measurement for each shock strut may be measured from just after take-off (e.g., determined from step <NUM>) to just after landing. For example, the method <NUM> further comprises determining a landing event (step <NUM>). In various embodiments, only a single strut may be analyzed to determine take-off (step <NUM>) and landing (step <NUM>). The landing event may be determined utilizing measurements from position sensor <NUM> or gas pressure sensor <NUM> from <FIG>. For example, shock strut may transition from a fully extended position to a stroke near zero during landing. As such, the position sensor <NUM> may determine the landing event by measuring an extension of the shock strut and determining the shock strut is at or near zero. For example, the position sensor <NUM> may determine a landing event has occurred when an array of position measurements (e.g., <NUM> seconds of measurements) shows a minimum stroke is less than <NUM> inches (<NUM>), a maximum stroke is greater than <NUM> inches (<NUM>,<NUM>), a stroke for the first five seconds of the array is less than <NUM> inches (<NUM>), and the maximum stroke in the first ten seconds of the array is greater than <NUM> inches (<NUM>). These parameters may be varied based on a given application. The first two criteria ensure that the set of data is associated to a landing, or a takeoff, or any other event that has caused shock strut <NUM> to travel between <NUM> inches (<NUM>) to <NUM> inches (<NUM>). The third criterion ensures that the set of data is associated with a landing event, because in the first five (<NUM>) seconds the shock strut has been fully extended. The fourth criterion ensures that the chosen set of data also includes five (<NUM>) seconds of measurement after compression. If the data array meets all these criteria, it is categorized as a landing event.

In various embodiments a landing event may be determined solely from the gas pressure sensor <NUM>. For example, the gas pressure sensor <NUM> may determine the landing event by measuring a gas pressure when an array of gas pressure measurements (e.g., <NUM> seconds of measurements) shows a plateau of gas pressure. For example, in accordance with various embodiments, the pressure measurements of the first five seconds of the array may be separated by <NUM>%, <NUM>%, or <NUM>%. In various embodiments, in response to determining the landing event (e.g., step <NUM>), pressure data may stop being recorded for each landing gear assembly and a center of mass may be calculated for the aircraft.

The method <NUM> further comprises measuring gas pressure of a first shock strut of an aircraft (step <NUM>), measuring gas pressure of a second shock strut of the aircraft (step <NUM>), and measuring gas pressure of a third shock strut of the aircraft (step <NUM>). The shock struts may be in accordance with the shock strut <NUM> from <FIG>. The shock struts may be arranged in a landing gear configuration in accordance with landing gear arrangement <NUM> from <FIG>.

In various embodiments, a static measurement upon stabilization of the values just after landing may be determined from steps <NUM>, <NUM>, and <NUM>. In this regard, after the pressure values from the gas pressure sensors have stabilized just after landing, the values may be transmitted to a center of mass estimator. The center of mass estimator may estimate a center of mass based on the stabilized values.

The method <NUM> further comprises estimating a center of mass of the aircraft (step <NUM>). For example, if a pressure is measured and recorded of a shock strut from at least three landing gear assemblies from just after takeoff until just after landing and a cross-sectional area of the shock strut along with the gear rake angle are known, a force for each shock strut may be calculated and a center of gravity may be determined for a horizontal plane of the aircraft as a lateral distance (a) from wheelbase (B) and a longitudinal distance (b) from wheel tread (A) from <FIG>. For example, step <NUM> may comprise calculating the horizontal coordinates of the center of gravity of the aircraft based on the data collected during steps <NUM>, <NUM>, <NUM> and utilizing the following equations:
<MAT>
<MAT>
<MAT>.

In the above set of equations, WA/C is the weight of the aircraft, FCLG is the load applied to the aircraft by the center landing gear, and mean(PCLG(t - T:t)) is average center landing gear pressure over a period of T seconds, and ACLG is a piston cross-sectional area of center landing gear. Lateral distance (a) from wheelbase (B) and longitudinal distance (b) from wheel tread (A) are unknowns and solved for. It is of note the formulation showed above assumes a zero rake angle for all gears. For non-zero rake angles, the equations will be modified to determine the vertical component of the shock strut load.

<FIG> shows a block diagram of a center of mass estimation system <NUM>. System <NUM> includes gas pressure sensor <NUM>, and position sensor <NUM> mounted on shock strut <NUM>, and digital processor <NUM>. Pressure sensors <NUM>, <NUM> and can be in the form of individual sensors or can be in the form of a combined pressure/temperature sensor. The servicing algorithm executed by processor <NUM> comprises the following sub-algorithms: recorder <NUM>, landing/takeoff detector <NUM>, counter <NUM>, center of mass estimator <NUM>, and data logger <NUM>.

Recorder <NUM> acquires the gas pressure from pressure sensor <NUM> and the stroke parameter from position sensor <NUM>. In various embodiments, recorder <NUM> records the two parameters in an array or circular buffer that keeps the readings for a set period of time, for instance <NUM> seconds. New set of recordings is added to top of the array and the oldest set of data is eliminated from the bottom of the array to keep the length of the array equivalent to <NUM> seconds of data. At any instant, recorder <NUM> exports the array which comprises the latest <NUM> seconds of data to landing/takeoff detector <NUM>. At startup, when the length of the array is not equivalent to <NUM> seconds, recorder <NUM> sends a "false" detection state discrete signal to landing/takeoff detector <NUM>, so that landing/takeoff detector <NUM> avoids using data from an incomplete array. Once <NUM> seconds of measurements is available in the array, the detection state discrete signal turns into "true" and allows landing/takeoff detector <NUM> to use the measurements.

Once landing/takeoff detector <NUM> receives the array of data, it checks the array against the following set of criteria:.

The first two criteria ensure that the set of data is associated to a landing, or a takeoff, or any other event that has caused shock strut <NUM> to travel between <NUM> inches (<NUM>) to <NUM> inches (<NUM>). Upon detecting a landing, the landing/takeoff detector may active the center of mass estimator. In this regard, since the system <NUM> has identified a change in landing gear shock strut stroke, the system may estimate a center of mass upon landing. Upon detecting a landing (after detecting a takeoff previously), the landing/takeoff detector may feed a stroke measurement from the position sensor <NUM> and the parameters from the gas pressure sensor <NUM> to the center of mass estimator just after landing. The third criterion is used to determine that the set of data is associated with a landing event, because in the first five (<NUM>) seconds the shock strut has been fully extended. The fourth criterion ensures that the chosen set of data also includes five (<NUM>) seconds of measurement after compression. In this regard, data is fed to the center of mass estimator <NUM> just after landing (approximately <NUM> seconds or the like). If the data array meets the first two requirements, but not the second two requirements, the data is classified as a takeoff and the center of mass estimator will not be activated. In this regard, a landing data arrays is fed to the center of mass estimator just after a landing is detected. If all these criteria are met, it is categorized as a landing event and the landing event is the data array fed to the center of mass estimator <NUM>. Counter <NUM> is also started to prevent landing/takeoff detector <NUM> from receiving any new array for five (<NUM>) minutes (a selectable parameter). This relaxes the need for a high speed processor as data acquisition and center of mass estimation will not be performed simultaneously.

Center of mass estimator <NUM> utilizes real-time measurement of gas pressure, and/or shock strut stroke from a landing event. Center of mass estimator <NUM> determines an average force applied to each shock strut during the period of interest. Center of mass estimator <NUM> estimates the center of mass by calculating a distance in a horizontal plane (e.g., X-Y plane from <FIG>) from a lateral distance (a) from the wheelbase (B) and a longitudinal distance (b) from the wheel tread (A).

Data logger <NUM> records the outputs of center of mass estimator <NUM> for output to a display device <NUM>. In various embodiments, display device <NUM> may be disposed in a cockpit of an aircraft (e.g., aircraft <NUM> from <FIG>). Gas pressure, and shock strut stroke for every flight cycle (e.g., take-off through landing) is recorded by data logger <NUM>. Data logger <NUM> can provide indications to the display device <NUM> where the center of mass of the aircraft is (based on the center of mass estimation from the center of mass estimator <NUM>). In various embodiments, the data logger may just communicate values or communicate code to an alternate device for further use.

In various embodiments, the period of interest may occur prior to a full flight cycle. For example, a pilot may wish to know the center of mass of the aircraft prior to flying. In such an instance, the pilot may takeoff vertically, hover for a few seconds, and then land within the time period outlined above. In this regard, a pilot may know an estimation of the current center of mass of the aircraft prior to a full flight cycle.

The following nomenclature corresponds to various equations and parameters described in the present disclosure:.

Claim 1:
A method for estimating a center of mass of an aircraft (<NUM>) via a shock strut system comprising:
receiving, by a processor (<NUM>), a first gas pressure of a first shock strut from a takeoff phase to a landing phase of the aircraft from a first gas pressure sensor;
receiving, by the processor, a second gas pressure of a second shock strut from the takeoff phase to the landing phase of the aircraft from a second gas pressure sensor;
receiving, by the processor, a third gas pressure of a third shock strut from the takeoff phase to the landing phase of the aircraft from a third gas pressure sensor;
determining, by the processor, the center of mass of the aircraft based on the first gas pressure, the second gas pressure, the third gas pressure, a wheel tread distance along a wheel tread axis, and a wheelbase distance along a wheelbase axis; and
transmitting, by the processor, the center of mass of the aircraft to a device; and
wherein the takeoff phase includes a vertical takeoff, the landing phase includes a vertical landing, and the takeoff phase to landing phase occurs within a predetermined period of time.