Automatic Controls for Airplane Take-Off and Landing Modes

Airplanes traditionally take off and land with flaps fixed in an extended position. The extended flaps impart high lift characteristics to the aircraft even at low speeds. During take-off, the throttle is opened and the flaps are retained in an extended position for a considerable distance above the runway. The high thrust while at low altitudes create considerable community noise. During an approach, the flaps are extended while on the glide slope angle at a position several miles from the threshold. The extended flaps present high drag as well as imparting high lift and require substantial engine power to effect a constant configuration steady state approach; which creates a high community noise level. In U.S. Pat. No. 2,350,751, there is disclosed an automatic flap control system to adjust the flaps from extended to flight position when a predetermined speed is reached during take-off and to extend the flaps from normal flight position when airspeed falls below a predetermined value. This is essentially a safety device to extend flaps when the airspeed is low, and retract when airspeed is too high.

It is known to utilize a decelerating approach extending the flaps and cutting back on the engine thrust both as a function of time. This has the disadvantage of not allowing for wind direction and velocity near the ground. It was discovered that significant noise reduction benefits may be gained with the control arrangement as disclosed.

In a take-off mode the extended flaps are automatically retracted to a predetermined position which may be fully retracted to flight position. The retraction is in response to reaching a sensed predetermined and preset airspeed. A command signal is generated which will be entered only after the landing gear has been raised and stowed away after take-off. The command signal actuates a power source to retract the flaps. Take-off also provides distance measuring a predetermined point from brake release and an indicator to notify when said distance has been reached.

In the approach mode, the disclosure provides for a decelerating approach with the flaps automatically extending during part of the approach as a function of distance from touchdown, the throttle is automatically cut back to a predetermined level during the same period as a function of flap position, and the stabilizer is automatically trimmed as the flap position changes.

It is an oject of this invention to provide noise reduction during take-off and landing modes of an airplane by automatic control of flaps, engine thrust and stabilizer trim.

FIG. 1 shows a block diagram of automatic control of an airplane during take-off mode.

FIG. 2 shows a block diagram of automatic control of an airplane during a decelerating approach.

In FIG. 1, take-off system 10 has a central air data computer 12 which senses airspeed. Pilot's control panel 14, among other items, has speed reference select dial 16 and distance indicator light 18. Summing junction 20 receives input from the sensed and the referenced speed and imparts a signal to the level detector 22 which transmits a signal once the indicated level has been reached. Switch 24 is located in the landing gear doors. When the gear is stowed, the switch activates summing switch 26 to allow the signal from level detector 22 to pass through to the servo-amplifier 28 for the transfer valve 30 which allows hydraulic fluid to pass through the flap position valve 32 thence to the hydraulic motor 34 which retracts the flaps 36. A longitudinal accelerometer 38 signal is integrated first in integrator 40, then integrator 42 to convert accelerometer information into distance of the airplane from brake release. A summing junction 43 receives the distance signal along with a predetermined distance from brake release as set in the distance select switch 44 of the pilot's panel. This generates a signal--once the preselected position has been reached--which enters comparator 46, amplifier 48, thence into distance indicator light 18.

In operation, the flaps 36 are extended into high lift configuration. The flap handle 50 is moved to the position to which one wishes the flaps to automatically retract, the predetermined airspeed at which the flaps will retract is entered in speed select dial 16 and the preselected distance from take-off or brake release is entered in distance select switch 44 and the take-off initiated. Once airborne, the landing gear will be stowed and a signal transmitted. The flaps will automatically retract in response to the sensed airspeed once said speed exceeds the preselected airspeed, provided the gear is stowed. A voltage proportional to sensed airspeed from the central data computer is summed or compared with voltage proportional to the preselected speed to generate a command voltage which is amplified to actuate the transfer valve and thence the flaps. The flaps will be retracted to the point allowed by the flap handle setting. A voltage proportional to longitudinal acceleration is obtained from the auto-throttle accelerometer 38 which is integrated twice to derive a voltage proportional to distance. This voltage is compared at 43 with voltage proportional to preselected distance and imparts an indicating signal 18 to notify that thrust may be cut back. Thus, during the initial segments of the climb-out, flaps are retracted automatically when speed and gear conditions are met to reduce the drag and improve climb-out capability and increase altitude or thrust cutback. Upon receiving the signal that the preselected distance has been met, the engine thrust is cut, the airplane pitches over and a positive rate of climb is maintained at the reduced thrust. The increased height and reduced thrust reduces the community noise level of the climb-out.

The block diagram of FIG. 1 shows switch 52 to indicate the signal from a servo-amplifier may be used in a different embodiment to energize an electric motor 54 which in turn positions the flap handle and thereby retracts the flap. In the same manner, switch 56 is used to show that other embodiments may use other means of measuring distance to generate a voltage signal to compare with voltage proportional to the preselected distance. An Inertial Navigation System (INS) 58 may be used for determining distance or onboard Distance Measuring Equipment (DME) 60 may be used for determining distance. The DME would include an antenna 62 and a DME interface 64.

In FIG. 2, approach system 66 defines a decelerating approach with automatic control of flaps, engine thrust and stabilizer trim. The flaps 36 are extended over a preselected portion of the approach as a function of distance from touch down. A continuing flap command is transmitted to servo-amplifier 28, thence transfer valve 30, flap control valve 32, and hydraulic motor 34 to automatically extend the flaps over the preselected portion of the approach. The flap command may be generated by monitoring horizontal slant or vertical distance. Switch 68 may be used to select the type of control. Using distance monitoring, a computer 70 measures horizontal distance from touchdown. This computer, when used in conjunction with ground distance measuring equipment gives excellent accuracy. A signal proportional to horizontal distance is summed at 72 with a signal proportional to preselected horizontal distance at which the flaps will be fully extended as set in pilot control panel 14 to give a summed signal for inputting into a function generator 74 to convert the distance signal into a flap command signal for inputting to the servo-amplifier. A vertical distance control has a sensed height signal from a central air data computer 12 and a predetermined final height signal from the pilot control panel summed at summing junction 76 to give a command signal to a function generator 78. The function generator converts the signal proportional to height to flap command signal. Sensor 80 indicates flap position and sends a feedback control signal to function generator 82 for throttle control and to function generator 84 for stabilizer trim control. When using vertical distance as the control means for the flap, it is preferable to utilize pressure altitude to generate the required signal than to use radio altitude. Field elevation system and field temperature corrections are entered in the control panel and pressure altitude and static air temperature sensed by the central air data computer to obtain the vertical distance signal. The flaps may be actuated by use of electric motor 54 to move the flap handle 50, and thus the flap control valve 32, in response to the command signal from the servo-amplifier instead of using the transfer valve 30.

The sensed flap position is converted by the function generator 82 to a signal proportional to speed differential which is summed by summing junction 86 with a signal proportional to a final preselected speed as set in the control panel 14 to give a speed command to auto-throttle 88 which, in turn, imparts a throttle command through the throttle handle 90 to engines 92 to impart thrust to the airplane.

The flap position feedback to function generator 84 converts flap position to a trim signal. At the point of starting into the decelerating approach initial stabilizer position 94 as modified by bias 96 as set in the control panel 14 is summed at 98 to impart a signal. This signal, along with the trim signal, goes into multiplier 100 where it is multiplied into a trim command signal which combines with a signal from the auto throttle in summing junction 102, then is transmitted to trim coupler 104 thence trim motor 106 to automatically trim stabilizer 108. A sensor 110 imparts feedback to initial stabilizer position 94.

In operation, the glide slope is entered with landing gear down but with flaps in an intermediate position. The automatic decelerating approach is armed with preselected final distance, speed and the stabilizer bias set in the control panel. The flap handle is removed from a detent to permit movement of the flap control valve. The flap is automatically extended during the preselected distance, and airspeed is automatically reduced to a predetermined amount as the flap is extended. Pitching moments resulting from flap extension and speed reduction are trimmed automatically as flaps extend. The effect of center of gravity variations on the trim requirements is accounted for by using the initial stabilizer position as modified by bias to adjust the input. Upon reaching the preselected distance, which preferably may be about one mile horizontally or about 300 feet vertically from the runway, the flaps are extended and the engines will be spooled-up and the balance of the approach will be in the conventional manner.