The relatively gentle stopping before the end position prevents a strong impact as well as springback and also protects the actuator and the machine parts from wear or irreparable damage. Preliminary design of aircraft landing gear strut paper title font. An emphasis is placed on the function and calculation of loads acting on oleopneumatic shock absorbers, which are the main type of shock absorber considered. Multiobjective optimization of passive shock absorber for. Not only do oleo struts have a higher efficiency and dampingtoweight ratio than any other type of shock absorber, they also dissipate energy in a more optimal way, storing and releasing energy at controlled rates during the compression and. Multiphysics based simulations of a shock absorber sub. An oleo strut is a pneumatic air oil hydraulic shock absorber used on the landing gear of most large aircraft and many smaller ones.
The mixture of oil and gas mode which is known as hydro pneumatic shock absorber, created a revolution in landing gear growth in the. Singleobjective optimization of passive shock absorber. The innovation behind the original design, patented by vickers armstrong in 1915, was recoil control by forcing oil through orifices in a positive manner. An oleo pneumatic shock absorber for use as a loadbearing element in a vehicle wheelsuspension arrangement. Numerical investigation of oleo pneumatic shock absorber. A1 is a diagram of high speed and low propelling force. This paper deals with the active control of a nonlinear active landing gear system equipped with oleo pneumatic shock absorber. Runway induced vibration can cause reduction of pilots. The mc 9 to mc 75 model range has a very short overall length and low return force. The oleo pneumatic shock absorber of the present invention is shown operatively connected between the main support strut 14 and each wheel axle through a crank arm 15. It was also used on berliet trucks and has more recently been used on mercedesbenz cars, where it is known. This thesis is based on the construction of a realistic analytical model of an oleo pneumatic shock absorber for a combat aircraft. A steel coil spring stores impact energy from landing and then releases it, while an oleo.
Equations of state in fighter aircraft oleopneumatic shock absorber modelling arttu heininen1, jussi aaltonen1, kari t. Parker pneumatic b shock absorbers actuator products shock absorbers miniature shock absorbers mc 9 to mc 75 selfcompensating miniature shock absorbers are selfcontained hydraulic units. The shock absorber stops the moving load in a much shorter time. By providing this extra motion about a horizontal axi thse two wheels can be kept in. The shock absorber shown here is to model the leakage in the recoil chamber which is a common type of fault observed in most of the shock absorbers. The principles illustrated by the successful use of hydropneumatic suspension are now used in a broad range of applications, such as aircraft oleo struts and gas filled automobile shock absorbers, first patented in the u. In the equation defining pneumatic force the effective polytropic. Oleo struts are critical elements of aircraft landing gear, connecting an aircrafts wheels to the airframe to provide the main path through which load forces are transmitted. An oleo pneumatic strut is an air oil hydraulic shock absorber used on the landing gear of most large aircraft and many smaller ones. It dissipates the kinetic energy produced by impacts arising when an airplane lands at high speed but also offers a comfortable ride to passengers when the airplane taxies at low speed. Hidracar oleo pneumatic shock absorbers linear decelerators decelerate masses in reciprocating, linear, circular and other movements. Study of interaction between shock absorber parameters.
The inerter is a recently introduced mechanical element, in which the. The first innovation to the oleo pneumatic shock absorbers was the metering pin, which modulated. The absorbers can be used as a suspension of light airdrop system as well as a part of landing gear of small uav. A shock absorber of the oleo pneumatic type comprising. Oleo pneumatic type most of todays aircraft use oleo pneumatic shock absorbers. Oleo pneumatic technology was subsequently reused by the manufacturer to produce several other products, including hydraulic railway buffers and industrial shock absorbers. Figure 1 shows a simple oleo pneumatic shock absorber construction. Principles of passive vibration control shock absorber. It dissipates the kinetic energy produced by impacts arising when an airplane lands at high speed but also offers a comfortable. An oleo pneumatic shock absorber has both a gas charge, typically nitrogen or dry air is used, and a hydraulic oil. Comparison of all shock absorber types based on a weight normalized efficiency calculation. These have a high damping to weight ratio and are used in most modern. Lifting a platform or structure and, at the same time, work as a shock absorber with an oleo pneumatic accumulator attached.
At present, most aircraft uses a passive oleopneumatic shock absorber due to its high strut efficiency compared to. The oleo story leading world experts coventry and shanghai. Singleobjective optimization of passive shock absorber for. A single leg of the halffork type connects the shock strut and the axle. The basic structure of an oleo pneumatic shock strut is outlined in figure 7 below. The basic function of the shock absorber is to absorb and dissipate the impact. History the internally sprung wheel george dowty 19011975 gloster gladiator 1934.
Shock absorber series rbrblrbq smc pneumatic cylinders. Each shock absorber is designated 16 since they are identical one to the other and the extension and retraction thereof serves to move each pair of associated wheels 12 independently relative to the strut 14 about an axis 17. Swedish society of aeronautics and astronautics ftf. Rainbow aviation services oleo pneumatic oilgas shock struts, or oleo struts, are shock absorbers that cushion forces associated with aircraft landings and ground maneuvers such as taxiing.
Shock absorbers absorb the energy of a moving actuator. Comprehensive design of an oleopneumatic nose landing gear strut. Quiri hydromecanique is a manufacturer of hydraulic devices and especially dampers and shock absorbers. This plot shows the significant advantage of using an oleopneumatic. It is undesirable for an airplane to bounce on landing as it could lead to a loss of control, and the landing gear should not add to this tendency. The answer was the oleopneumatic or air oil shock strut, originally introduced in the late 1920s by the cleveland pneumatic company. This design cushions the impacts of landing and damps out vertical oscillations. The purpose of the shock strut is to alleviate load on the airframe and. The multiphysics nature of the problem is tackled by conducting a range of validation cases in the base areas expected to be of relevance.
Pdf design and analysis of modified oleo strut shock. A shock absorber, as defined in claim 4, wherein a second air chamber is separated from the lowpressure section by a movable third piston. The diagram below shows how this double function is implemented by the insertion of an ordinary valve or an oleo hydraulic distributor, becoming a single effect cylinder when both its oil inlet and exit ports are. An automobile shock absorber contains springloaded check valves and orifices to control the flow of oil through an internal piston. Clevelands aerol strut quickly gained acceptance in the 1930s, and was the landing gear technology of choice by the time aviation exploded in the 1940s, transforming cleveland pneumatic aerol into one of the nations largest wartime industrial. Young 2 presented the development of conventional landing gear with respect to the design, energy absorption characteristics, landing gear geometry and types from 1940 to the present. The objective of the project was to design an oleo pneumatic shock absorber for the main landing gear of a commercial aircraft, boeing 737200, taking into consideration passenger comfort during takeoff and landing. The improved model for landing gear dynamic a acm digital. For any application involving a combination of high aircraft weight, high sink speed or minimum gear space an oleo pneumatic strut should be considered for its obvious gains in performance, small size and low weight. Pdf nonlinear vibration analysis of oleo pneumatic. Pdf nonlinear vibration analysis of oleo pneumatic landing. Such a double acting oleo pneumatic shock absorber, especially intended for use in, respectively aircraft landing gear is described in landing gear shock absorber design criteria and the assessment of tirewheel configuration by j. Optimal inerterbased shockstrut configurations for landing gear touch. Conceptual design of singleacting oleopneumatic shock.
Some of these parameters are investigated independently by researchers to understand the influence on an oleo pneumatic shock absorber in order to meet the undercarriage performance requirements 4. Conventional oleo struts employ orifice dampers in the interests of providing. Optimization of an oleopneumatic shock absorber for main. Failure analysis of a broken support strut of an aircraft. Optimization of passive shock absorber for landing gear. Presented general approach to optimal design of the semipassive devices can be applied for design of different types of fluidbased absorbers, e. The mixture of oil and gas mode which is known as hydro pneumatic shock absorber, created a revolution in landing gear growth in the united states in 1950 bauer,2011. A twostage oleopneumatic shock absorber incorporating two pneumatic air pressure chambers, a high air pressure chamber and a low pressure air chamber, separated by a hydraulic fluid oil pressure chamber. The oleo pneumatic shock absorber has a high efficiency under dynamic conditions both in terms of energy dissipation and return to normal static conditions 1. This invention comprises a shock absorber of the oleo pneumatic type comprising a cylindrical oil chamber separated by a movable orifice plate into high and lowpressure chambers, with a hollow tapered metering pin passing through the orifice plate to provide a fluid passageway connecting the high and lowpressure chambers, and incorporating a relief valve which comprises a highpressure air. This type of shock absorber contains two integral components.
Every traditional aircraft has a shock absorber in its main landing gear. The oleo pneumatic shock is the most common type of shock absorber landing gear system used in aircrafts. By installing the shock absorber the machine wear and maintenance can be drastically reduced. Apr 29, 2019 oleo pneumatic shock absorber technology has continued to be refined, for example with us patent us2959410 a, jarry hydraulics, in 1960. The dynamic characteristics of a nonlinear main landing gear.
This invention relates to oleo pneumatic shock absorbers such as those employed on mechanical equipment for example vehicles especially aircraft undercarriages, and more particularly to such a shock absorber wherein the rate of compression is programmed separately as for example in the case of aircraft landing gears for the landing impact and for rollout subsequent to the impact. Selfcompensating shock absorber is suitable for unvaried operating conditions and available in the range of effective weight for the best deceleration. Characterization of a piezoelectric valve for an adaptive. Oleo pneumatic shock struts are the most common type of shock absorber used on modern aircraft. Double acting oleo pneumatic shock absorber fokker b. Selection of applicable model in order for the shock absorbers to operate. By installing a shock absorber cycle times are reduced giving much higher production rates. The shock absorber comprises a cylinder attachable at its lower end to the wheel hub, a drowned piston housed in the cylinder and connected by a piston rod to the vehicle body, and flowdetermining means determining fluid flow past the piston during operation of the shock absorber. The most common shock absorber type is an oleo pneumatic shock absorber.
The presented work was a part of study aimed at the development of a new concept for a. Jan 01, 2018 shock absorbers shock absorbers designed to absorb and damp shock impulses during taxi, takeoff and landing. Each shock absorber is designated 16 since they are identical one to the other and the extension and retraction thereof serves to move each pair of associated wheels 12. Nonlinear vibration analysis of oleo pneumatic landing gear at touchdown impact. Automation technology and mechanical engineering, tampere university, tampere, finland 2. A twostage oleopneumatic shock absorber incorporating two pneumatic air pressure chambers, a high air pressure chamber and a low pressure air. They also work as shock absorbers of weights in free fall, as suspension of vehicles and wagons, for the tightening of chains, conveyor belts, rollers, etc. However, classical passive pneumatic absorbers have an ef. This type of strut is currently the most advanced type being used in. Finnish defense forces logistics command, tampere, finland ft2019, 8. Equations of state in fighter aircraft oleo pneumatic shock.
A dynamic system model of the shock absorber is used to generate physically consistent boundary conditions. Examples of applications military and offroad vehicles oleo pneumatic shock absorbers tank gunposition dampers nuclear submarine periscope dampers wind turbine chassis dampers snubbers for dynamic piping or heavy devices support. For the different level of oil servicing the shock absorber efficiency and maximum load. The oil chamber contains an orifice and metering pin, which orifice and metering pin control the rate of collapse of the low pressure air chamber. Equations of state in fighter aircraft oleo pneumatic. The wheel is fitted with a 27inch smoothcontour tire which is inflated to normal operating pressure of 32 pounds per square inch. History oleo pneumatic shock absorbers george messier 18961933 messier oleo pneumatic landing gear farman 190 1927. Adjustment type shock absorber is for the optimum deceleration to turn and set properly adjustment dial to the impact conditions. Nov 01, 2020 understudy nose leg assembly has an oleo pneumatic shock absorber system which dampens a part of landing impact energy whereas the remaining is transferred to the aircraft structure. A shock absorber takes the brunt of the shock imparted to the landing gear, absorbs it and dissipates the kinetic energy. Sep 26, 2020 conceptual design of singleacting oleo pneumatic shock absorber in landing gear with combined method download pdf advanced technology helicopter landing gear preliminary design investigation. Shock absorbers and dampers testing solutions special shock. The barrel is generally made out of aluminum forging. Including inerters in aircraft landing gear shock strut to improve the.
Oleo pneumatic shockabsorber hidracar oleo pneumatic shock absorbers linear decelerators decelerate masses in reciprocating, linear, circular and other movements. The original oleo pneumatics shock absorber was developed from the vickers gun recuperative gear design which was first applied to an aeroplane by the french company breguet aviation. When the strut is compressed, the uid is forced through the ori ce producing a damping force. Nonlinear vibration analysis of oleo pneumatic landing gear.
The commonly adopted geometries for modem landing gear structures are telescopic. Dec 21, 2017 these bumps appear when runway maintenance is due. A comprehensive design cycle of a nose landing gear strut having an oleo pneumatic shock absorber for a lightweight aircraft is proposed. The oleo pneumatic shock strut is the most common type of shock absorber landing gear system used in aircrafts. The shock absorber analyzed in this thesis is the most current and modern type of shock absorber available. Oleo pneumatic shock absorbers, namely passive shock absorbers are commonly used in mediumlarge aircraft landing gears, and can be optimally designed for specific conditions. The simulation of an oleo pneumatic shock absorber is discussed focusing on the solver validation and high fidelity case setup. However, passive shock absorbers cannot function optimally under conditions that differ from their specified conditions. The oleo pneumatic s hock absorber consists of an upper chamber and a lower chamber of crosssectional area a. Pneumatic and hydraulic shock absorbers include cushions and springs. Oleo pneumatic shock absorber is considered the safest and the most efficient modern shock absorption type with efficiencies up to 90%. The combination of multibody dynamics and matlabsimulink. The hydraulic uid is within the lower chamber of the strut and the pressurized gas is contained in the upper chamber. Pdf in this paper, nonlinear vibration analysis of a typical aircraft oleo pneumatic landing gear has been done.
These shock absorbers for having both fluid and gas flow can benefit from the advantages of both previous states. Nonlinear vibration analysis of oleo pneumatic landing. Spring steel leg oleo pneumatic strut rubber cord shock absorber rubber pad absorber rubber cord is used on old and light, cheap airplanes spring steel as part of fixed main landing gears. The high gear and weight efficiencies associated with the oleo pneumatic shock absorber make it the preferred design for commercial transports 2.
They have the highest efficiencies of all shock absorber types and also have the best energy dissipation. Based on the analysis procedure as outlined in this chapter, algorithms were developed to determine the required stroke and piston length to meet the given design conditions, as. Coil springs easy to fit the shock absorber inside the spring much lighter than leaf springs smaller packaging volume breakproof, no maintenance no lateral guidance possible, hence it is necessary to make use of a combination of guidance bars and lateral restraints they require to be combined with certain suspension systems the natural frequency of the suspension decreases when the. Support strut is a component attached to the nose landing gear leg and assists it to remain in the extended position during taxi, takeoff and landing phases. Oleo pneumatic 406 oleo pneumatic sizing 4 refinements 416 real gas model 416 inflation gas solubility in oil 417 design for realworld operation 422 example single stage oleo pneumatic shock absorbers 422 multiple stage oleo pneumatic shock absorbers 427 active shock absorbers 434 shock absorber design considerations 442 seals 442. Shock absorbers and dampers testing solutions special. Us4381857a programmed oleopneumatic shock absorber. Landing gear shock absorbers, usually oleo pneumatic shock absorbers, are intended for the reduction of forces transmitted to the aircraft from the impact during landing. The movement of the drive piston is brought to a standstill by rubber elements andor hydraulically. Nowadays, passive oleo pneumatic shock absorbers are widely used in aircraft 3.
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