Landing gear [1] is one of the important parts of an aircraft; often referred [2] to as undercarriage. Landing gear is a structure which is installed on the aircraft for the purpose to support the weight of the aircraft while it is on the ground and also allows the aircraft for smooth maneuver such as takeoff and landing. Landing gear also provides mobility to the aircraft on ground or water. It is capable of reaching the largest local load on the plane. The landing gear’s main function is to control the rate of compression/extension and to prevent further damage to itself as well as other parts of an aircraft when a load is applied. Loads can be either static or dynamic in both cases the structure must withstand applied loads and deformation and continue to do its purpose. Among the available configuration the most common type of landing gear arrangement is tri-cycle arrangement. Considering the nose landing gear configuration of a tri cycle the stress distribution and deformation [3] is noted for an executive jet aircraft for applied loads.

Landing gears are located on the under carriage of aircraft . The front landing is called as nose landing gear while main landing gear [4] is located on rear side of aircraft. Nose landing gear consists of actuators to retract and extension; drag brace to lock the pins metering pin extension; trunnion; rotation lock pins; aft braces; oleo cylinder; oleo piston; brake assembly; tires and wheels which is shown in Figure 1.

Figure 1: Nose Landing gear nomenclature.

Operational Requirement showed in Table 1

Table 1: Operational Requirement.

(1)

C= s/b (2)

= 1.2 + 1.9

=3.1

(3)

=26.883m

(4)

V_R = 1.1V_s (5)

(6)

=6267. 4 N

Based on the design requirement and as per the need of the project the nose landing gear dimensions are altered and are designed in CATIA V5 R19. Since only nose landing gear is concern of this project nose landing gear is designed along with nose cone as shown in Figure 2.

Figure 2: Designed Landing Gear in CATIA.

In order to analyze the fluid flow, the geometry is spilt into number of elements. If the number of elements is high the accuracy of results is high [5]. TRIA surface mesh is used to mesh the geometry. Auto mesh is used to mesh the curved surface and edges.

The geometry is subjected to flow analysis. It is done by assigning flow properties to the geometry within the domain. The body was tested for five different conditions by varying its angle of attack from -5º to15º with the equal increments of 5º and by maintaining flow speed constant at 0.2 mach.

The domain properties are as such that the outlet from the geometry is 5 times when compared to inlet. The flow is assumed to be continuous which is also non buoyant. The static temperature assigned is 300 K. It is also found that there are 468848 nodes and the number of elements in the domain is 1599260. The meshed geometry shown in Figure 3.

Figure 3: Meshed body in domain.

The landing gear is checked for its stability and stiffness by assigning it two material properties Aluminum alloy and Structural steel [6]. The material properties of steel and aluminum alloy are given in below Table 2.

Table 2: Material properties.

A. Flow analysis-pressure contour

From Figure 4a; a flow analysis has been carried out for the landing gear assembly and nose cone. The geometry is placed in the domain and fluid is allowed to flow over aircraft portion with a Mach number of 0.2 with an angle of attack of -5°. Variation of pressure is obtained for a range of -10742.89 Pa to 3364.05 Pa. Pressure distributions at 0° angle of attack is explained in Figure 4b. The maximum pressure variation is 3333.33 Pa. There is an increase in pressure distribution with the increase in angle of attack. Similar analysis is carried for 5°, 10° and 15° angle of attack as given in Figures 4c-4e respectively. In all the cases it is noticed that the maximum pressure acts on front portion of landing gear and nose cone.

Figure 4: Pressure Contour at different angle of attacks.

From the pressure plots using dynamic equations, coefficient of lift and drag can be calculated and are tabulated in Table 3.

Table 3: Lift and Drag Coeffiecient.

Using the values from Table 3 coefficient of lift and drag values are plotted against angle of attack.

Graph for C_L v/s Angle of attack is shown in Figure 5. It is known that with the increase in angle of attack lift coefficient increases and after reaching a certain angle it tends to decreases which is known as stall angle. From the Figure 5 at 15º angle of attack there is higher lift coefficient which would fall down if the angle of attack is increased further.

Figure 5: C_L v/s Angle of attack.

Figure 6 is a graph for C_D v/s Angle of attack. At an angle of attack -5° greater amount of drag is experienced by landing gear. With the increase in angle of attack from 0 to 15° drag reduces gradually to minimum value because thrust is more than drag.

Figure 6: C_D v/s Angle of attack.

B. Flow analysis –temperature contour

Temperature plots for geometry subjected to flow analysis at mach 0.2 are given in Figure 7. Figure 7a-7e shows geometry at -5º, 0º, 5º, 10º and 15º. In all the cases there is a slight variation on temperature for changing angles and maximum temperature is found at the tip of nose cone and front portion of landing gear.

Figure 7: Temperature plots at different angle of attack.

C. Mechanical analysis

The landing gear assembly has undergone a deformation, when a constant load is applied on the assembly which is at static condition. From Figure 8 maximum deformation of 0.78 mm which is indicated in red color region, and a minimum deformation of 0.000087 mm as shown in blue color region for applied loads. And landing gear assembly is suggested to be safe for a given material and load.

Figure 8: Static Deformation for Steel.

The landing gear assembly has undergone a deformation, when the aircrafts lands on hard runway. An impact load is induced on landing gear which is then transferred to axle and then to strut. From Figure 9 maximum deformations of 4.1 mm which is indicated in red color region, and a minimum deformation of 0.46 mm as shown in blue color region for applied loads. And landing gear assembly is suggested to be safe for a given material and load.

Figure 9: Impact Deformation for Steel.

Table 4 explains the results of static analysis. The maximum deformation occurs in case of aluminum alloy and a maximum stress distribution is for steel.

Table 4: Static Analysis results.

During impact test at a given loading condition a maximum deformation occurs for aluminum alloy and stress distribution is maximum in case of steel which is tabulated in Table 5.

Table 5: Impact Analysis results.

D. Aero acoustic results

An initial approach has been carried out to study the noise generated [7] by landing gear by dwelling its surface. The obtained results were of noise in terms of frequency and azimuth angle. It was compared with the available data [8] which closely matched with the result which is given in Figure 10.

Figure 10: Acoustic Results.

CFD analysis has been carried out to study flow around nose landing gear and nose cone, where the flow has been considered into 3 regions on nose landing gear and nose cone namely upper region flow, mid region flow and lower region flow. The upper region flow has its effect on strut while mid region flow effected axle and slightly on wheel. The effect of lower region flow was experienced on wheel.

Sudden application of load deforms the structure. The static deformation and stress distribution are tabulated in Table 4 and impact deformation and stress distribution are tabulated in Table 5.

Stress and deformation value which is obtained for applied loads on structure are found to be within design range and hence the nose landing gear is suggested to be safe.

A possible solution to reduce landing gear noise is streamlining the flow field through the use of fairings. However, streamlining of the entire landing gear structure is difficult due to its size and function (wheels must rotate, brakes require cooling) and a more complicated weight trade-off analysis becomes necessary to determine potential benefits.