Analysing Helicopter Landing Gear

Analysing Helicopter Landing GearThe Landing gear, an important part of a helicopter, assists the helicopter to land. So, when the helicopter is in land condition, the arrive gear should withstand the whole weight of the helicopter. Apart from this, it should also withstand the thrust while arrive operation is on.The come gear of a helicopter can be of three typesSkid typeWheel typeThe skid type come gear is the simplest unrivalled and cheaper to manufacture. Some skids allow the helicopter to land even on water. If the helicopter need to land on hard surfaces ( want runway) regularly, then nigh special kinds of shoe need to be attached to the skid. The shoe can be replaced upon wearing. The most commercial helicopter has the skid type landing gear.The rhythm type landing gear is little complicated and costlier as compared to the skid types but the wheel type landing gear gives easier ground handling and expedient while rough and crush landing.In our case, we befool to env ision a landing gear suitable for landing on an air craft carrier. The landing condition can become really bad due to the vertical motion of the aircraft carrier. Considering this severe landing condition I attain chosen to go ahead with the wheel type landing gear for this appointment.I exact utilise ADAMS/View for creating the invention models, ADAMS/Vibration for running the vibration digest and ADAMS charge processing for analyzing and diagramting the results.Design of Landing Gear MechanismResearch on Existing Landing GearFrom the earlier days of the aviation history, many concepts of the landing gears are used. I volition explain few of them hereLanding gear with leaf rebounds The uses of aluminum leaf take shapes are possible for the very easy weight helicopter (around 300kg). The concept looks attractive.Fig.1 Showing the concept of aluminum spring landing gearThe concept of the heavy duty composite leaf spring is being experimented by some of the commercial ai rcraft manufacturer including AIRBUS. The main advantage of leaf spring concept is its reduced part count.Landing gear with stupefaction absorber Most commercial applications use jarful absorbers for the flesh of the landing gears.Fig.2 Showing a typical shock absorber bottomd landing gear design ground on the numbers and the positions of the tires, this type of landing gears are typically classified in nine configurations as shown in the below figure (fig.3).Fig.3 Showing classifications of shock footd landing gearI have used the Twin configuration of tires for each of the landing gears and used total of three landing gears in my final design. However, before selecting the final design, I have studied whiz concept with both twin configuration landing gears at rear and one single configuration landing gear at front as well.Design InputsFew of the design inputs were given along with the assignment and for others, either I googled out from the manufacturers specifications or ass umed. All together I have used the following design inputsWeight of the helicopter = 5126 KgLength of the helicopter = 15.16 mSpacing between the two rear landing gear = 2.5 mSpacing between the front and the rear landing gear = 5 mYoungs modulus of steel = 2.7E11 N/m2Density of steel = 7801 kg/m3Poissons ratio of steel = 0.29Youngs modulus of rubber = 5E6N/m2Density of steel = 1100 kg/m3Poissons ratio of steel = 0.3Possible design optionsAfter doing the preliminary study of the existing available designs, two aspects had come to my mind before proceeding further one, covering all the assignment tasks and two, simplicity. I was looking for coming out few design concepts, which are good enough to cover all the assignment tasks and simple enough to finish the assignment in time. And I came out with the following two conceptsDesign option -1 In this concept, I have used two twin-configured rear landing gears and one single-configured front landing gear.Fig.4 Showing a real life example of the Design option-1The three landing gears (one front and two rears) are attached to a angulate crest put made up of steel. The top steel frame in turn is bolted with the fuselage.Design option-2 In the second concept, I have used three twin landing gears. One, in front and two are at rear. Please not that I have used two wheels (twin) in front (in design option-1, I have used a single nose wheel in front). The three landing gears are connected with the triangular top frame. The top frame is bolted with the fuselage.Creations of the ADAM modelsADAMS is a tool, develop by MSC and used extensively for simulating different types of mechanisms. It has different modules, out of which I have used the ADAMS/View here. I also used the ADAMS Vibration plug-in for simulating the action of the ocean waves on the stationary helicopter on the aircraft carrier.I have used the block option for creating the infantry (aircraft carrier platform), torus option for creating the wheels , the li nk option to realize the axels, cylinder option to create the top frame (which will be bolted to the fuselage) and the spring option for creating the shock absorber springs . Also, I have made used of the options like point, contacts, joint, describe, input channel and output channel. How? I will explain in details little later, while explaining each of the design concepts separately.Fig.5 Showing MSC ADAMS toolsADAMS model for the design option-1Start ADAMS/View.In the main toolbox right click the Rigid body and click the Point to create the points each at the wheel centers, at the three vertex of the frame, at the top left corner of the base.Again in the main tool box, right click the Rigid body bar and click the Box to create the base. check off on the Torus of the Rigid Body bar to create all the five wheels.Click on the Link of the unbendable body bar to create the three axels.Click on the Cylinder of the Rigid body bar to create all the three sides of the top frame.Use the Merge two bodies of the rigid body bar to merge all the three sides of the top frame into one. infra Joint bar, select Revolute to connect the wheels with the respective axels.Under Forces bar, select translational Spring-Damper to connect the axels and the respective vertices of the triangular top frame.Create sliding joints between the base and back ground and between the top frame and back ground.Under Forces bar, select Contact to create the contact between the wheels and base.Finally, the design option-1 ADAMS model should look like belowFig.6 present the ADAMS model of design option-1ADAMS model for the design option-2Following the similar procedure as described for creating the ADAMS model for design option-1, I have created the Design option-2 (with twin in front). The ADAMS model of the design option-2 looks like belowFig.7 Showing the ADAMS model of design option-2Comparisons of the design optionsAfter finishing the ADAMS model for both the design concepts, I run the Nor mal landing epitome on both design option models. The data used for the Normal landing digest for both the design options are as below tumid descent speed of the top frame = 0.5 m/secVertical upward speed of the base = 0 m/secSpring awkwardness coefficient= 30 N/mmSpring damping coefficient =1 Ns/mmSpring preload = 17000 NI got the following resultsFig.8 Showing the acceleration plot of the top triangular frame for Design option-1 and the Design option-2.The above plot (fig.8) is showing that the acceleration of the top frame for the design option-1 is higher than that for the design option-2.Fig.9 Showing the Z- accusation reaction force plot of the joint between the top frame and the back ground (space) for Design option-1 and the Design option-2.The above plot (fig.9) is showing that the design concept-1 is producing lots of Z- direction force, the force that can affect the stability of the helicopter.So, on the basis of the above analysis, I have chosen the Design option-2 fo r further study.Results and CalculationsSpring CalculationsSprung mass = 5126 kgMaximum acceptable acceleration = 0.3 m/s2Preload on each spring = 5126*(9.81+0.3)/3 = 17274 NDynamic Analysis ResultsNormal landingNormal landing analysis is performed based on the following conditionsVertical descent speed of the top frame = 0.5 m/secVertical upward speed of the base = 0 m/secSpring Stiffness coefficient= 30 N/mm, 50 N/mm, 70 N/mmSpring damping coefficient =1 Ns/mmSpring preload = 17274 NFig.10 Showing normal landing analysis of the design option-2 for different spring rateHard landingHard landing analysis is performed based on the following conditionsVertical descent speed of the top frame = 3 m/secVertical upward speed of the base = 3 m/secSpring Stiffness coefficient= 30 N/mm, 50 N/mm, 70 N/mmSpring damping coefficient =1 Ns/mmSpring preload = 17274 NFig.11 Showing hard landing analysis of the design option-2 for different spring rateCrush landingCrush landing analysis is performed based on the following conditionsVertical approach speed of the top frame = 15 m/secVertical upward speed of the base = 0 m/secSpring Stiffness coefficient= 30 N/mm, 50 N/mm, 70 N/mmSpring damping coefficient =1 Ns/mmSpring preload = 17274 NFig.12 Showing crush landing analysis of the design option-2 for different spring rateThe acceptance criteria of the above analysis are as followNormal landing Minimum accelerationHard landing 50 m/sec2Crush landing 300 m/sec2In golf club to fulfill all the acceptance criteria, I have chosen the spring stiffness as 30 N/mm and proceed further for the vibration analysis.Vibration Analysis ResultsFig.13 Showing frequency response of the design option-2The pick of the frequency response curve is indicating the resonance frequency, which is around 2.5 Hz for our case.Fig.14 Showing PSD plot of the design option-2The above plot is showing the transmitted power from all the inputs used in the analysis as a function of the frequency. Again, the pick (2 .5 Hz) is showing the resonating frequency here.DiscussionTask 1For the Task-1 , I have developed two design options (as shown in section 3.1 and 3.2) and compare the two design options on the basis of normal landing analysis (section 3.3). The result has shown that the design option-2 is better in terms of acceleration and z-direction reaction force. Hence I have selected the design option-2 for the further study.Task 2For the task-2 , I have run the normal, hard and crush landing analysis (section 4.2) on the design option-2 for different spring stiffness and choose the best spring stiffness to ensure that all the acceptance criteria is met.Task 3For Task-3, I run the vibration analysis for the design option-2 (section-4.3) and find out the resonating frequency for the mechanism on response to the sea wave.Task 4For the task-4, I have discussed (section 3) how I have used the ADAMS/View for creating the ADAMS model and also, I have discussed how I simulate the mechanism.Conclusion The emphasis is given to come out with a simple but somewhat good landing gear mechanism, which will be able to pass all the test conditions specified in the assignment. The hand calculations are used for selecting the spring preload however, the selection of the spring stiffness is done on the basis of hit and trial.ADAMS/View and ADAMS Vibration plug-in are used for the whole analysis for getting the pronto and easily interpretable results.I believe that the design of the mechanism can be further improved by incorporating the torsion springs along with the compression springs.