Aeronautics and astronautics – Aircraft power plants
Reexamination Certificate
1999-09-14
2001-04-03
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Aircraft power plants
C060S200100, C060S039240, C137S015200
Reexamination Certificate
active
06209821
ABSTRACT:
BACKGROUND OF THE INVENTION
As the demand for travel to distant destinations has increased, the need for faster and more efficient supersonic aircraft has grown. This need is no longer limited to military applications, as demand for improved civilian supersonic transports has greatly increased. Although past generation supersonic aircraft have been operating for decades, they have always been limited in their efficiency. The efficiency of supersonic aircraft affects their range and operating costs. One approach to increasing efficiency has been to improve the engine operation. This has been achieved in part by using air inlets which are designed to be adjusted in flight to control the airflow and optimize engine performance. Although this approach has resulted in increased operating efficiency, it has come at the cost of increased occurrences of inlet “unstarts” and engine compressor stalls, which risk passenger safety and reduce efficiency and engine output.
When the shock wave is maintained at the throat of the inlet, the inlet is defined as being “started”. When the shock is not positioned at the throat, the inlet is “unstarted”. During an unstart condition there is a greater loss of pressure over the shock wave, which dramatically lowers the efficiency of the inlet. An unstart may cause excess air to spill out from the front of the inlet and produce significant drag. Further, the change in airflow and pressures can cause the engine's compressor to stall, which greatly reduces the engine's power output. Those aboard a supersonic aircraft which experiences an unstart, experience a sudden jolt as the aircraft lurches backwards when the engine thrust abruptly drops. While such a jolt may be acceptable in military applications, it is definitely unacceptable for civilian transports.
To try to solve this unstart problem, various devices have been developed which attempt to limit the occurrence of unstarts. One approach has been to maintain the location of the shock wave by using a series of sensors placed longitudinally along the inlet to measure pressures within the inlet. These pressure measurements are then compared to a fixed set of pressures, which are indicative of proper placement of the shock wave in the inlet throat. In the event the shock wave is improperly positioned a control system takes corrective action by moving a bypass baffle to a more open or closed position, to move the shock wave forward or aft in the inlet.
Since these prior devices sampled the airflow at the inlet, and since they required time to react to changes in the airflow, a built-in lag unfortunately exists. This lag allows relatively sudden changes in the airflow to cause unstarts. Increasing the response speed of the control system has been attempted to reduce unstarts. However as the response speed is increased the control system becomes subject to unacceptable stability problems. Attempts have also been made to use trends of airflow conditions to predict changes to the conditions, so that the control system begins to “react” before the need for it is certain. However, these predictions have not been sufficiently reliable to adequately anticipate future temperature changes. Another approach to the lag problem has been to add an attitude anticipator system to the control system. The attitude anticipator measures the rate of change of attitude and adjusts the inlet geometry and bypass baffle positioning to avoid unstarts. However, this system was limited to changes in attitude of the aircraft, and as such could not anticipate changes in the airflow itself.
Therefore, a need exists for a device which is able to accurately anticipate changes in airflow conditions so as to avoid unstarts in supersonic aircraft engines. The device must be able to sense changes in the airflow conditions prior to arrival of the changes at the inlet, to allow the control system to reposition the bypass baffle in a timely manner.
SUMMARY OF THE INVENTION
The present invention employs remote sensing instrument to measure the temperature of the air at a sufficient distance ahead of an aircraft, to allow time for an inlet/engine assembly to be adjusted by a control system to conform to changes in the engine inlet temperature. For supersonic capable aircraft which have a variable engine inlet designed to retain a shock wave within the inlet, the invention takes an air temperature measurement a distance ahead of the aircraft, to provide enough time so the engine inlet can be repositioned to avoid inlet unstart and/or engine compressor stall. In so doing, the invention provides the inlet control system sufficient time to make the necessary inlet changes, without having to force the control system to become unstable by overly increasing its response speed. Also, by providing a measurement of the actual temperature ahead of the aircraft, the invention avoids the need to use unreliable temperature trend analyses or predictions based upon the airflow conditions measured at the aircraft or upon the aircraft's attitude.
The apparatus of the invention is embodied in an air vehicle having a variable airflow inlet and/or engine. The apparatus includes a remote sensor, for measuring the air temperature ahead of the aircraft, and an inlet control system for varying the inlet and/or engine to conform to the measured air temperature. The air temperature measurement is made by the remote sensor a sufficient distance ahead of the aircraft to allow time for the inlet and/or engine to be adjusted at or near the arrival of the measured air in the inlet and/or engine.
During supersonic flight, the inlet can retain a shock wave within it. In such a flight condition, the remote sensor measures the air temperature ahead of the vehicle and provides the measurement to the inlet control system. In turn, the inlet control system varies the inlet to control positioning of the shock wave within the inlet. The remote sensor can be a radiometer, such as a passive microwave radiometer. The control system is connected to the inlet and to the remote sensor to receive the measurement of the air temperature ahead of the vehicle. As such, the inlet control system can vary the inlet to maintain the position of the shock wave during the arrival of the air having a measured temperature entering the inlet and thus prevent the unstart condition.
In one embodiment, the apparatus includes a microwave radiometer and an inlet control system. The microwave radiometer determines a change in air temperature value (AT) and transmits it to the inlet control system. The inlet control system uses the change in temperature value to vary the inlet (e.g. a bypass baffle) so that the position of the shock wave in the inlet is maintained, or otherwise kept within an acceptable range, during the arrival of air in the inlet which corresponds to the measured temperature change. The radiometer is mounted to the vehicle and orientated to allow measurements to be taken along the flight path of the vehicle. The radiometer includes a sensor unit and a data unit. The sensor and data units measure air temperature at at least one “applicable range” ahead of the vehicle. The data unit determines the change in temperature value by comparing present and past temperature measurements made by the sensor unit. In its simplest form, the change in temperature value is determined by the data unit finding the difference between a current temperature measured at the applicable range and a past temperature measurement of air which currently corresponds to the location of the vehicle. However, the data unit can provide a more precise form of determining the change in temperature value by using the current temperature measurement and a series of past temperature measurements. The data unit is in communication with the sensor unit. The data unit is also in communication with the inlet control system so as to provide the control system with the change in temperature values. In turn, the inlet control system is in communication with inlet pressure transmitters and uses the pressure measurements ob
Jordan Charles T.
Kusmiss John H.
Steele George L.
The United States of America as represented by the Administrator
LandOfFree
Apparatus and method for measuring air temperature ahead of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for measuring air temperature ahead of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for measuring air temperature ahead of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513179