Spillage drag occurs when an aircraft engine receives more airflow at its inlet than the engine's compressor can ingest at a given power setting. This causes excess airflow to spill back out of the engine inlet into the free stream air and results in a drag penalty. This can result in significant spillage drag in some flight conditions, particularly at high speeds. This phenomenon becomes more problematic with increasing airspeed.
Embodiments are directed to systems and methods for controlling aircraft engine inlet geometry. A flight control computer or similar system may determine a required engine power based upon current aircraft parameters, determine a desired engine air mass flow based upon the required engine power, calculate an optimum engine inlet area based upon the desired engine air mass flow, a current airspeed, and an air density, and provide a command to one or more actuators to adjust the aircraft engine inlet to conform to the calculated optimum engine inlet area. The optimum engine inlet area is calculated to cause minimum spillage drag and thereby optimize aircraft performance.
The aircraft parameters may comprise one or more of outside air temperature, altitude, airspeed, and humidity. The required engine power may be determined from aircraft performance chart data. The desired air mass flow may be determined from engine performance model data. The flight control computer may further determine a relationship between air mass flow and airspeed based upon the aircraft performance chart data and the engine performance model data.
In a tiltrotor aircraft, the flight control computer may determine a current engine inlet angle, then calculate the engine inlet area based upon the current engine inlet angle, and/or adjust the command to the one or more actuators based upon the current engine inlet angle.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the system to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present application as defined by the appended claims.
Illustrative embodiments of the system of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.
Propulsion system 105 includes a pylon 109 that is configured to rotate along with other rotatable pylon structure to improve aerodynamic airflow. Moveable pylon 109 can be mechanically coupled to an actuator system used for moving the proprotors 108 between airplane mode and helicopter mode. During the airplane mode, vertical lift is primarily supplied by the airfoil profile of wings 104, while rotor blades 108 provide forward thrust. During the helicopter mode, vertical lift is primarily supplied by the thrust of rotor blades 108. It should be appreciated that tiltrotor aircraft 101 may be operated such that propulsion systems 105 are selectively positioned between airplane mode and helicopter mode, which can be referred to as a conversion mode.
Control surfaces 110 on wing 104 are used to adjust the attitude of tiltrotor aircraft 101 around the pitch, roll, and yaw axes while in airplane or conversion mode. Additional stabilizers or control surfaces 111 may be required when tiltrotor aircraft 101 is in airplane mode. Control surfaces 110 and 111 may be, for example, ailerons, flaps, slats, spoilers, elevators, rudders, or ruddervators.
Propulsion system 105 for a tiltrotor aircraft 101 typically features a power train, drive shaft, hub, swashplate, and pitch links within pylon 109. The drive shaft and hub are mechanical components for transmitting torque and/or rotation from the engine 106 to the rotor blades 108. The power train may include a variety of components, including a transmission and differentials. In operation, the drive shaft receives torque or rotational energy from engine 106 and rotates the hub, which causes blades 108 to rotate about the drive shaft. A swashplate translates flight control input into motion of blades 108. Rotor blades 108 are usually spinning when tiltrotor aircraft 101 is in flight, and the swashplate transmits flight control input from the non-rotating fuselage 102 to the hub, blades 108, and/or components coupling the hub to blades 108 (e.g., grips and pitch horns).
The geometry of the engine inlet 306 is determined by the size and position of engine intake walls 307a,b along with the top and bottom (not shown) of the engine inlet.
Spillage drag occurs when the forward-facing inlet duct 306 intakes more airflow than the engine compressor 301 can ingest at a given power setting. This excess airflow 402 spills back out of the inlet 306 into the free stream air and results in a drag penalty. While an engine inlet is often sized for maximum airflow conditions, which is typically during hover for a rotorcraft, this can result in significant spillage drag in other flight conditions and particularly at high speeds.
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In an embodiment, an algorithm utilizes aircraft parameters and existing models and relationships to determine the optimal inlet area to minimize spillage drag as a function of airspeed and engine power setting at the current ambient conditions, such as altitude and air temperature. Control over the inlet geometry provides improved aircraft performance in cruise flight, including specific fuel consumption (SFC), range, and maximum airspeed capability.
In step 604, for the required power as determined in step 602, the corresponding required engine air mass flow is determined from an engine performance model. The engine performance model may provide plots 605, for example, illustrating air mass flow versus SHP. The engine model may be a thermodynamic performance model from an engine manufacturer, for example, that predicts air mass flow for a specified power setting and for a given temperature, altitude, and airspeed. The engine performance model may take other factors into consideration, such as RPM, measured gas temperature (MGT), and/or exhaust gas temperature (EGT).
In step 606, the data from the performance charts 603 and the engine model 605 are combined to provide a relationship between the air mass flow and airspeed, such as plot 607. Knowing the current airspeed, the current air mass flow can be calculated as illustrated in plot 607. In step 608, the optimal engine inlet area may be calculated by dividing the air mass flow by the product of the airspeed and air density. The air density may be calculated by the flight control computer using the observed or estimated OAT, air pressure, and humidity, for example. The equation in step 608 may be used to create a plot 609 of engine inlet area versus airspeed for a particular air mass flow and air density.
In step 610, the flight control computer sends a command to adjust the engine inlet geometry to match the area calculated in step 608. The command may be, for example, a signal to an actuator 310 (
In some tiltrotor aircraft, the engine inlet rotates with the engine from a horizontal position facing into the airstream for airplane mode to a vertical position for hover in a helicopter craft mode. For aircraft in which the engine inlet rotates, in step 611 the flight control computer may adjust for the angle of the engine inlet relative to the airstream. The engine inlet area calculation in step 608 may be adjusted to compensate for the engine inlet angle, such as by modifying the required engine inlet area in proportion to a parameter based on the cosine of the engine inlet area. Alternatively, or additionally, the commands sent by the flight control computer to the engine inlet actuators may be modified in step 610 based upon the engine inlet angle and the calculated engine inlet area.
In an example embodiment, a method for controlling an aircraft engine inlet comprises determining a required engine power based upon current aircraft parameters, determining a desired engine air mass flow based upon the required engine power, calculating an optimum engine inlet area based upon the desired engine air mass flow, a current airspeed, and an air density, and providing a command to one or more actuators to adjust the aircraft engine inlet to conform to the calculated optimum engine inlet area. The aircraft parameters may comprise one or more of outside air temperature, altitude, airspeed, and humidity. The required engine power can be determined from aircraft performance chart data. The desired air mass flow can be determined from engine performance model data.
The method may further comprise determining a relationship between air mass flow and airspeed based upon the aircraft performance chart data and the engine performance model data.
The method may further comprise determining a current engine inlet angle, and calculating the engine inlet area based upon the current engine inlet angle.
The method may further comprise determining a current engine inlet angle, and adjusting the command to one or more actuators based upon the current engine inlet angle.
In an example embodiment, an aircraft comprises an engine having an inlet section with variable geometry, a flight control system configured to: determine a required engine power based upon current aircraft parameters, determine a desired engine air mass flow based upon the required engine power, calculate an optimum engine inlet area based upon the desired engine air mass flow, a current airspeed, and an air density, and provide a command to one or more actuators to adjust the inlet section geometry to conform to the calculated optimum engine inlet area. The optimum engine inlet area causes minimum spillage drag to optimize aircraft performance. The engine inlet section is configured to tilt between a helicopter mode position and an airplane mode position. The aircraft parameters may comprise one or more of outside air temperature, altitude, airspeed, and humidity. The required engine power may be determined from aircraft performance chart data. The desired engine air mass flow may be determined from engine performance model data.
The flight control system may be further configured to: determine a current engine inlet section angle, and calculate the optimum engine inlet area based upon the current engine inlet section angle.
The flight control system may be further configured to: determine a current engine inlet section angle; and adjust the command to one or more actuators based upon the current engine inlet section angle.
The flight control system may be further configured to: determine a relationship between engine air mass flow and airspeed based upon aircraft performance chart data and engine performance model data.
In an example embodiment, a flight control computer comprises one or more processors, and one or more computer-readable storage media having stored thereon computer-executable instructions that, when executed by the one or more processors, causes the processors to: determine a required engine power based upon current aircraft parameters, determine a desired engine air mass flow based upon the required engine power, calculate an engine inlet area based upon the desired engine air mass flow, a current airspeed, and an air density, and provide a command to one or more actuators to adjust the aircraft engine inlet to conform to the calculated engine inlet area. The computer-executable instructions may further cause the processors to: determine a relationship between engine air mass flow and airspeed based upon the aircraft performance chart data and the engine performance model data. The computer-executable instructions may further cause the processors to: determine a current engine inlet angle, and calculate the engine inlet area based upon the current engine inlet angle. The computer-executable instructions may further cause the processors to: determine a current engine inlet angle, and adjust the command to one or more actuators based upon the current engine inlet angle.
Embodiments of the present disclosure are not limited to any particular setting or application, and embodiments can be used with a rotor system in any setting or application such as with other aircraft, vehicles, or equipment. It will be understood that tiltrotor aircraft 101 is used merely for illustration purposes and that any aircraft, including fixed wing, rotorcraft, commercial, military, or civilian aircraft may use an engine-exhaust suppressor system as disclosed herein.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.