Aircraft landing gear system - Essay Example

? AIRCRAFT LANDING GEAR SYSTEMS Introduction The aircraft is a heavier than air machine and making it land and take off is facilitated by what is termed a Landing Gear mechanism. The landing gear in most aircraft consists of a tricycle configuration. This has a landing wheel that retracts into the nose (forward fuselage) of the aircraft and a set of two wheels that normally retract into the wings of the aircraft.. The National advisory Committee for Aeronautics (NACA) by testing in a wind tunnel in 1927 came to the conclusion that the aircraft landing gear made a significant contribution to the drag of an airplane. The retractable landing gears thus became a priority. Landing Gear and Avionics Modern aircraft design incorporates the Landing gear system with the aircraft. This is an entire process of engineering and is referred to as Multi Disciplinary Optimization (MDO). Landing gear is a part of MDO and incorporates flight mechanics, stability, control and performance. . This is a part of Avionics, which allows an aircraft system to transfer analog or digital data with the help of a wireless, data line or any other medium. Aircraft systems components and connectors will also form part of this module. This is often referred to as Flight Management System (FMS). The FMS is very versatile and outputs for automatic control of the aircraft right from take off to the final approach and landing are provided. This data is displayed through electronic flight instruments as well as aircraft monitoring and navigation systems. The undercarriage and the landing gear mechanism form part of this FMS. Flight Management System and ARINC 429 The key part of any FMS element is a Flight Management computer and a display unit. The entire information is displayed through a system of data buses. The word Bus is short form of Omnibus and in computer and digital systems it means a free data exchange between all components of a computer system. One of the important bus systems in vogue for commercial aircraft is ARINC 429. ARINC stands for Aeronautical Radio Inc. and the purpose of this organization is to standardize all equipment used in aircraft. This system makes use of a unidirectional bus standard called the Mark 33 Digital Information Transfer System (DITS). The ARINC 429 is a two wire differential bus. This connects a single transmitter to one or more receivers. The ARINC 429 will send or transmit data in packets of 32 bits at a speed of 100 kilobits per second. This will make the information appear in real time to the pilot, who really needs this information. This system is installed in most modern airliners like Boeing 737,747,757 and Airbus A 310, 320 and 330. A diagram of the ARINC 429 is given on the next page. The ARINC 429 Line Receiver converts the bipolar (Differential) data TTL/CMOS compatible outputs. Each receiver channel is lightening protected and operates independently. Line Receiver Diagram of ARINC 429 A Block Diagram ARINC 429 Transceiver is shown. It Provides an Interface between standard Avionics type serial digital data bus and a 16 bit wide digital data bus. A single transmitter with an 8X32 bit FIFO buffer facilitates the interface. Two independent receiver channels, and a host programmable control work together. The options are selected by them. A self test option is also available where data is internally wrapped around from the transmitter to the receivers. The ARINC 429 Parameters are tabulated below. . ARINC 429 Parameters Parameter High Speed Low Speed Bit Rate 100 K bps 12.5 K to 14.5 K Bit Time (Y) 10 us ± 5% 1/bit rate us ± 5% High Time (X) 5 us ± 5% Y/2us ± 5% Rise time 1.5 us ± 0.5us 10us ± 5us Fall time 1.5 us ± 0.5us 10us ± 5us ARINC, Data Format and Error ARINC messages generally consist of 32-bit data word. These data words are always 32 bits and consist of five field parity, SSM, Data, SDI and Label. ARINC 429 has two speeds of data transfer, a low speed (12-14.5 Kb/s ) for low critical applications and high speed bus for transferring large and critical data. Another point that must be mentioned is that ARINC429 has no means of error correction and can only communicate error detection. An error once observed will require manual or other methods for correction. Comparison With ARINC629 And 1553B The ARINC 629 and MIL 1553B is a refinement of over the ARINC 429. Whereas the ARINC 429 operated from a single source and multiple sinks, the ARINC 629 like the MIL 1553B operates from multiple sources and multiple sinks. In addition the highest rate of data transfer for an ARINC 429 is 100 K Bs/ sec. This is bettered by the ARINC 629 which operates at a speed of 2 Mbytes/sec and in real terms is 20 times faster than the A429. In addition the A629 can service 131 terminals on a data bus. ARINC 629 is used on the new Boeing 777 Aircraft. It uses a high-speed bi-directional bus capable of either regular or irregular transmissions. The MIL1553B is basically for military aircraft and the latest stealth fighters and bombers incorporate this technology. As safety measures for military and civil aircraft are different, the military standardization is MIL-STD, while for Civil it is ARINC. ARINC Data Transmission ARINC 429 protocol uses a point-to-point format, transmitting data from a single source on the bus up to 20 receivers. The transmitter is always transmitting, either data words or the NULL state. ARINC 429 data words are 32 bit words made up of five primary fields: Read More