GB818291A - Improvements in or relating to warning devices on rotary wing aircraft - Google Patents

Abstract

818,291. Warning devices on rotary wing aircraft. WESTLAND AIRCRAFT Ltd. May, 13, 1957 [May 14, 1956], No. 14896/56. Class 4. A rotary wing aircraft includes rotor speed and engine speed tachometer generators connected to give an audible signal when the rotor speed approaches a preselected limit. In the embodiment described, three phase signals from the rotor speed tachometer generator 9, Fig. 1, are fed directly to a full wave rectifier W2 shunted by a capacitator F5, and through three equal capacitors F1, F2, F3, to a full wave rectifier W1 shunted by a capacitor F4. One coil of relay A/1 and one coil of relay B/1 are connected in series across the output of rectifier W1, and a second coil of each relay is connected across the output of rectifier W2 through trim resistors VR1 and VR3 or VR2 and VR4 respectively, depending on the position of contacts EE1 and EE2. The two coils of each relay are connected to give flux opposition, the result being that when the frequency of the tachometer generator signals approaches a maximum value, determined by the setting of resistor VR1 or VR2, relay A/1 is operated, and when the frequency approaches a minimum value determined by the setting of resistor VR3 or VR4, relay B/1 is operated. Closure of contact A1 or B1, Fig. 3, energizes a relay slugged by a capacitor F6, and thus opens a contact C1, de-energizing the relay and closing contact C1. This cycle is repeated at a frequency depending on the value of resistors R1 or R2 and capacitor F6, and if relay is energized, the frequency may be ten cycles per second, and if relay is energized, three cycles per second. Closure of contact C2 of relay C/2 energizes relay D/1, opening contact D1, de-energizing the relay and closing contact D1. The resultant wave-form is filtered by capacitor F8, and the output actuates an aural alarm, e.g. in headphones. A three-phase output from the engine speed tachometer generator 10 is fed to a full wave rectifier W3 shunted by capacitor F7, which normally energizes a relay E/1 through a trim resistor VR5. If the engine fails relay E/1 is de-energized, closing contact E1 and energizing relay EE/2. Thus if autorotation is established, the frequencies at which relays A/1 and B/1 change over are altered since contacts EE1 and EE2 substitute the trim resistors VR2 and VR4 for VR1 and VR3.