Landing Gear.Pdf

Study of Evolution and Details of Landing Gear INDEX CHAPTER 1 1.1.1 INTRODUCTION 3 1.1.2 EVOLUTION 3 CHAPTER 2 2.1 DIFFERENT TYPES OF LANDING GEARS 6 2.1.1 TRICYCLE LANDING GEAR 7 2.1.2 CONVENTIONAL LANDING GEAR 7 2.1.3 UNCONVENTIONAL LANDING GEAR 8 2.2 DIFFERENCE BETWEEN MAIN AND NOSE LANDING GEAR 9 2.3 SHOCK STRUTS 10 2.3.1 TYPES OF SHOCK STRUTS 1. METERING PIN TYPE 10 2. METERING TUBE TYPE 11 3. NOSE GEAR STRUTS 12 4. DOUBLE-ACTING SHOCK ABSORBER 12 2.4 OPERATION OF SHOCK STRUTS 13 CHAPTER 3 3.1 HYDRAULIC SYSTEM FOR AIRCRAFT LANDING GEAR 15 3.2 LANDING GEAR EXTENSION AND RETRACTION 15 3.2.1 LANDING GEAR EXTENSION AND RETRACTING MECHANISMS 15 3.3 EMERGENCY SYSTEMS 16 NIMRA INSTITUTE OF SCIENCE & TECHNOLOGY, A.E - 1 - Study of Evolution and Details of Landing Gear CHAPTER 4 4.1 BRAKING SYSTEM IN LANDING GEAR 18 4.2 DIFFERENT TYPES OF BRAKES AND THEIR EVOLUTION 4.2.1 CARBON AND BERYLLIUM BRAKES 18 4.2.2 AUTO-BRAKE AND BRAKE-BY-WIRE SYSTEM 19 4.3 DESCRIPTION OF A HYDRAULIC BRAKING SYSTEM 20 4.4 ADVANCED BRAKE CONTROL SYSTEM (ABCS) 21 4.5 PNEUMATIC BRAKING 21 4.6 DIFFERENTIAL BRAKING 22 CHAPTER 5 LUBRICANTS USED IN LANDING GEAR 23 CONCLUSION 24 REFERENCES 25 FIGURES FIG. 1 LANDING GEARS IN THE INITIAL STAGES 26 FIG. 2 BASIC TYPES OF LANDING GEARS 26 FIG. 3 TU-144 MAIN LANDING GEAR 27 FIG. 4 TRACK-TYPE GEAR 27 FIG. 5 THE ITALIAN BONMARTINI TRACK GEAR 28 FIG. 6 THREE COMMON TYPES OF LANDING GEARS 28 FIG. 7 TRICYCLE LANDING GEAR 29 FIG. 8 LA-4 AIR CUSHION GEAR 29 FIG. 9 MAIN LANDING GEAR 29 FIG. 10 NOSE GEAR ASSEMBLY 30 FIG. 11 SHOCK STRUT WITH A METERING PIN 31 NIMRA INSTITUTE OF SCIENCE & TECHNOLOGY, A.E - 2 - Study of Evolution and Details of Landing Gear FIG.12 SHOCK STRUT WITH A METERING TUBE 32 FIG. 13 SIMPLE NOSE GEAR STRUTS 33 FIG. 14 DOUBLE-ACTING SHOCK ABSORBER 33 FIG. 15 OPERATION OF SHOCK STRUT 34 FIG. 16 OLEO-PNEUMATIC SHOCK STRUT TYPES 35 FIG. 17 BASIC HYDRAULIC SYSTEM 35 FIG. 18 THE HYDRAULIC LANDING GEAR SYSTEM INSIDE THE WHOLE AIRPLANE 36 FIG.19. TYPICAL BRAKE AND ITS RELATIONSHIP TO THE LANDING GEAR 37 FIG. 20 BERYLLIUM BRAKE 38 FIG. 21 CARBON BRAKE 39 FIG. 22 ESTIMATED NUMBER OF STOPS VS. KINETIC ENERGY PER POUND. 39 FIG. 23 BRAKE MATERIALS: SPECIFIC STRENGTH VS. TEMPERATURE 40 FIG. 24AUTO-BRAKE AND BRAKE-BY-WIRE SYSTEM 40 FIG. 25 EMERGENCY HYDRAULIC BRAKING SYSTEM 41 FIG. 26 PAIRED WHEEL HYDRAULIC BRAKING SYSTEM 41 FIG. 27 INDIVIDUAL WHEEL HYDRAULIC BRAKE CONTROL SYSTEM 42 TABULAR FORM TABLE 1 PROPERTIES OF DIFFERENT HEAT SINK MATERIALS 42 NIMRA INSTITUTE OF SCIENCE & TECHNOLOGY, A.E - 3 - Study of Evolution and Details of Landing Gear CHAPTER 1 1.1 INTRODUCTION The landing gear is that portion of the aircraft that supports the weight of the aircraft while it is on the ground. The landing gear contains components that are necessary for taking off and landing the aircraft safely. Some of these components are landing gear struts that absorb landing and taxiing shocks; brakes that are used to stop and, in some cases, steer the aircraft; nosewheel steering for steering the aircraft; and in some cases, nose catapult components that provide the aircraft with carrier deck takeoff capabilities. The landing gear is the principle support of the airplane when parked, taxiing, taking off, or when landing. The most common type of landing gear consists of wheels, but airplane0s can also be equipped with floats for water operations, or skis for landing on snow. [Figure 1-9] The landing gear consists of three wheels—two main wheels and a third wheel positioned either at the front or rear of the airplane. Landing gear employing a rear mounted wheel is called conventional landing gear. Airplanes with conventional landing gear are sometimes referred to as tailwheel airplanes. When the third wheel is located on the nose, it is called a nosewheel, and the design is referred to as a tricycle gear. A steerable nosewheel or tailwheel permits the airplane to be controlled throughout all operations while on the ground. 1.2 EVOLUTION The first wheeled landing gears appeared shortly after the Wright Brothers' maiden flight in December 1903. Santos-Dumont's "No. 14 bis" had a wheeled landing gear; this airplane made the first flight in Europe in October 1906. This was followed quickly by wheeled aircraft designed. Then came World War I, by which time the configurations had more or less settled down to tail wheel types, employing fairly rugged struts attached to the fuselage and landing gears that had some degree of shock absorption through the use of bungee cords wrapped around the axles, as illustrated in figure 1. The Sopwith Camel was shown in fig. 1(a), SE5 shown in fig. 1(b) and SPAD VIL shown in fig1. (c) Were typical World War I fighter/scout aircraft. Both the Camel and SPAD had axles that pivoted from the spreader bars, the main difference being in the location of the bungee that restrained the axle from moving . The Camel's bungees were at the extreme ends of the spreaders and permitted 4 in. of wheel travel. The SPAD's shock cords permitted NIMRA INSTITUTE OF SCIENCE & TECHNOLOGY, A.E - 4 - Study of Evolution and Details of Landing Gear 3–4 in. of travel (depending on the model), but were located inboard of the gear support struts. In the 21 years between World Wars I and II, landing gear design developed as fast as airframe design. The latter changed from braced wood and fabric biplanes to aluminum alloy monoplanes and the landing gears became retractable, employing a variety of shock- absorbing systems. Increased shock absorption became necessary in order to accommodate the constantly increasing aircraft weights and sink speeds. Although the shock absorber stroke is not a function of aircraft weight, it was important to increase that stroke in order to lower the landing load factors and thereby minimize the structure weight influenced by the landing loads. Larger-section tires provided some of the desired shock absorption, but size limitations and relatively low (47%) efficiency prevented a major contribution from this source. Therefore, shock-absorbing support struts were devised. These ranged from rubber blocks and compression springs to leaf springs, oleo-pneumatic struts, and liquid springs . To decrease drag in flight some undercarriages retract into the wings and/or fuselage with wheels flush against the surface or concealed behind doors; this is called retractable gear. The earliest retractable landing gear is that used on the Bristol (England) Jupiter racing aircraft of the late 1920's. In the United States, Lockheed's Model 8D Altair, which first flew in 1930, had a fully retractable landing gear. The landing gear consists of two dual wheel main gears and one dual nose gear, each main gear is equipped with Disk brakes, anti skid protection and thermal tire deflators (fusible plugs). The landing gear is positioned hydraulically as selected by the landing gear lever in the cockpit on the center instrument panel. Door and gear sequencing is automatic. Except for the nose gear, which is mechanically opened and closed by the movement of the gear, there is a door release handle in each main gear well for ground access. NIMRA INSTITUTE OF SCIENCE & TECHNOLOGY, A.E - 5 - Study of Evolution and Details of Landing Gear CHAPTER 2 2.1 DIFFERENT TYPES OF LANDING GEARS Airplanes require landing gear for taxiing, takeoff, and landing. The earliest airplane Wright Flyers used skids as their landing gears. Soon, wheels were attached to the skids. Since that time, various arrangements have been used for wheels and structures to connect them to the airplane. Landing gears are generally categorized by the number of wheels and their pattern. Figure 2 illustrates the basic types. This terminology is rapidly gaining worldwide acceptance. For instance, the USAF/USN Enroute Supplements define the strength of 11 a given field as T-50/TT-100, indicating that the airfield is cleared to accept aircraft weighing 50,000 lb with a twin-wheel gear or 100,000 lb with a twin-tandem gear. There are also hybrid arrangements such as the 12-wheel arrangement used on the Soviet TU-144 supersonic transport depicted in the figure 3 and the track gears that were tested on the Fairchild Packet, Boeing B-50, and Convair B-36 the latter is illustrated in the figure 4. The objectives of the track gear were to reduce the weight and size attributable to the tires and to improve flotation by having a larger contact area. Track gears did have higher flotation by keeping the contact pressures as low as 30 psi, but there was no weight reduction. In fact, aircraft weight was increased by about 1.8% (1.78% on the Packet and 1.87% on the B-36). Maintainability and reliability were also degraded substantially because of the complicated mechanism (multiple shock absorbers in the track bogie), low bearing life, low belt life, and high spin-up loads. The Italian Bonmartini track gear was also tested successfully, but it too was heavier than a conventional gear. It used a pneumatic belt to encompass the two wheels, as shown in the figure 5. Today, there are three common types of landing gears namely conventional landing gear shown in figure 6(a), Tricycle landing gear shown in figure 6(b), and Unconventional Landing Gears as shown in figure 6(c).

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