Introduction to Landing Gear System:
Landing gear system is the most important system in the aircraft which works with the hydraulic system and without which an aircraft cannot land on the runway. The landing gear consists of a nose gear, left and right landing gears under the wing. The main role of landing gear system is the energy absorption during landing, braking and taxi control. The components of the system are as follows: * Strut
* Shock Absorber
* Extraction/retraction mechanism
Diagram showing how each component is linked:
How The System Works?
Some small aircrafts such as Cessna 152 have fixed landing gear because it is a light aircraft and landing gear does not affect the flight. The larger aircrafts such as C-130 or fighter jets have retractable landing gear. The retractable landing gear helps the aircrafts in climbing into the higher atmosphere and also it reduces the drag in the flight. The image shows the components of a type of landing gear system. Some aircrafts are equipped with skis for landing in snowing conditions or floating on the water. A retractable gear is the mechanism by which undercarriages retracts or flush into wings or fuselage to decrease drag in flight. In aircrafts, retractable gear mechanism is controlled by hydraulic fluids and in some aircrafts electrical system is used as well. The first retractable gear was designed by French pioneer of aviation named, Alphonse Penaud in 1876. The system gets the pressure required from the pump which is driven by hydraulic fluid system. During landing, when the landing gear extracts, the hydraulic valves which controls the hydraulic fluid, releases the hydraulic pressure to unlock or open the doors holding individual landing gear. When the doors are opened, hydraulic pressure is sent down to the hydraulic actuator which is present in each gear which pushes the gear to extract allowing aircraft to land. The next most important step is the braking control once the undercarriage is down, the control valves releases the hydraulic pressure to the braking valve on the left and right gear whereas, the hydraulic fluid travels to steering valve on main gear or nose gear. The landing gear also has components known as shock absorber. Once the aircrafts touches the surface of earth, the potential energy of the undercarriage is converted to kinetic energy. The shock absorbers play an important role in absorbing or dissipate the kinetic energy. The hydraulic shock absorber consists of a long cylindrical shaped body with a sliding piston inside which releases pressure on the hydraulic fluid in hydraulic systems and releases pressure on air in pneumatic systems. When the landing gears are fully extended, a locking mechanism works by locking all the gear down in the position so that they can tolerate the weight of the structure (aircraft). All landing gear have latches which is a device used to hold landing gear in certain position during extraction and retraction. The landing gear doors also have a latch which helps the door to open and close during extraction and retraction. In larger aircrafts such as Boeing 727, each landing gear is equipped with self-adjusting multi-disc hydraulic brakes. The controls of these brakes are either in the feet of pilot (brake pedals) or pneumatic brake handle. The system has pressure sources which come from brake accumulator and nose brake power. In case of loss in the pressure of hydraulic system, the check valves control the flow of fluid. The tyres of aircrafts are different from other automobiles and have nitrogen inflated in them and also tyres are tubeless. The tubeless tyres give the advantage of smooth landing and no chance of tyre puncture which could cause serious accidents.
Compare Hydraulic system with Pneumatic System
The difference or similarities between hydraulic system and pneumatic system can be...