Automatic attack angles and overload alarm , AUASP - an element of the flight-navigation complex in an airplane , designed to control the current angle of attack and alert the crew in case of reaching a critical or critical angle of attack. The danger of exceeding the permissible angle of attack is a possible disruption of the flow and the subsequent dumping of the aircraft in a tailspin .
The principle of operation of AUASP is based on continuous measurement of the current angle of attack, local critical and overload with built-in sensors and their comparison with the maximum allowable for this type of aircraft. In case of reaching a critical level, an audible alarm is triggered and the light panel lights up.
There are several options for the execution of the system, fundamentally not having large differences. Structurally, it consists of an angle of attack sensor α (ДУА, a weather vane on the side of the aircraft), a critical angle sensor α cr (ДКУ), a vertical overload sensor n y (ДП), and a two-pointer pointer UAP on the instrument panel in the cockpit. The signals from the sensors are amplified and converted to mechanically move the two arrows (current angle of attack and overload) and the moving sector of the pointer, covering part of the scale. When the aircraft enters critical mode on the UAP pointer, the arrow of the current angles of attack approaches the edge of the red sector of the critical angle of attack or the arrow of overloads reaches the limit value and a warning signal is issued - the red lamp on the indicator lights up and an audible signal (bell) is issued. AUASP alarm system is registered by means of objective control, in the presence of a voice informant - it is duplicated in the control system.
If the AUASP alarm is triggered, immediately turn the helm column away from you and increase the engine operating mode.
The performance and composition of AUASP on different types of aircraft are very different. So, in AUASP-12, standing on the An-26 , Tu-95MS , Tu-154 and other old Soviet types of aircraft, there is one DUA-9R sensor operating at a constant current voltage of 27 V - it is fed as a weather vane heating element, so and variable resistors that provide a signal to the system. The complex of altitude and speed parameters of the IKVSP, in various versions, standing on the An-72 , An-124 , An-140 and other Antonov Design Bureau aircraft, includes two DAU-72 aerodynamic angle sensors, the heating of which is powered by a single-phase alternating voltage of 115 V, and as sensors applied contactless selsyn . If the DAU signals are different, the “DAU - Disagree” panel lights up, and the average value is displayed on the UAP. On airplanes of the Airbus A320 family , three DAUs are installed, which allows, according to the majority principle, to identify a faulty DAU.
The critical angle sensor can also have a completely different design. As a rule, the critical angle is calculated from the position of the wing mechanization (based on the signal from the limit switches on the transmission of the flaps and slats), the speed or the Mach number (α cr decreases with increasing speed), often the signal from the icing indicator is also taken into account when calculating α cr - when icing, the critical angle readings are reduced by 1-2 °.
Turning off the AUASP alarm can be one of the causes of the disaster: for example, in 1985 the crew of the Tu-154 , which crashed in Uzbekistan , did not realize in time that the plane was going to stall, because the AUASP alarm either failed (the AUASP could be turned off, subsequently automatic its inclusion when unclenching the front landing gear ), or was not perceived correctly. It is interesting that on many types of foreign-made aircraft such an indicator is not installed in the cockpit, and also on some domestic (for example, An-22 ) AUASPs are not available. [one]