Mr M D MAKSIMOVIC bsc

LANDING GEAR in PPT Serbia

The landing gear is one of our main products manufactured for the first time in 1949 for the airplane S-49, piston trainer, since when we have designed, developed and manufactured the landing gear for 14 types of airplanes.Today, we produce the landing gear for the aircraft: Galeb, Jastreb, Kraguj, Utva-75, Super Galeb, Orao, Lasta 2 and Lasta 3.

LANDING GEAR DESIGN

The company's design office house over 30 highly qualified personnel of which approximately one third is engaged on work with aircraft landing gear. The SDRC software system I-DEAS at PPT Landing Gear Division was selected specifically to embrace the requirement of landing gear design and is capable of:

2D drawing Wire framing Solid modeling

CAD/CAM techniques are employed to explore design alternatives then to supply optimum production configurations.

Design work on landing gear covers the following: aircraft requirements suspension options shock absorber techniques materials ethnology steering controls retraction mechanisms associated hydraulics

DESIGN APPROACHLanding gear design is dependent, not only on the type of aircraft, but also on the requirements for its usage and intended operational role. The choice of suspension and the shock absorber arrangement

The determination of the pivot axes for three-dimensional geometry

often result from the matching of runway conditions with those of aircraft structure leading to optimum passenger comfort.

DYNAMIC ANALYSIS

The design of aircraft landing gear equipment involves the application and dissipation of energy within the various mechanisms, not only for the main function-that of landing-but also for retraction, lowering, steering and other associated mechanisms.Over the year Landing Gear Division has developed comprehensive analytical techniques to determine the performance of such mechanisms.These analyses insuring that loads generated are well within the strength and performance parameters. Upon request the airplane manufacturer we are able to suggest the solution with the most suitable kinematics, minimal weight, minimal space requirement, simple maintains and long life-time.SHOCK ABSORBER

Nose L.G. Main L.G.-right Aircraft Lasta 3

The oil-air

shock-absorbers are designed to absorb the vertical component of the kinetic energy of the airplane with high efficiencies approved by the drop test. We are producing double stage, single stage and shock absorber with use of needle.

Aircraft Lasta 3 - Nose L.G.

MATERIALSThe basic material used for the main elements of the landing gear is high strength steel and high resistance aluminum alloys.The landing gear components manufactured of these high resistant materials are permanently under control during the entire manufacturing procedure starting from forging, machining, heat treatment, final surface treatment and installation.Typical aluminum alloys include 3.4354, 3.4364, 2024, 7010 and 7075, while the steels cover 300M, 4330 and 4340, also 35NCD THQ.RESEARCH AND DEVELOPMENT PPT carries out all its research and development on landing gear units and associated actuation system.Test applicable to landing gear include:

element testing of mechanisms stress evaluation dynamic testing of prototype units qualification testing for certification

PPT is capable of meeting all test requirements as laid down by the relevant civil and military authorities.LANDING GEAR TEST The engineering development department covers every aspect of landing gear qualification and is fully equipped for:drop testingstrength testingfatigue testingfunctional testingvibration testingenvironmental testing

PPT has

available test equipment designed in compliance with MIL specifications for testing of landing gear of aircraft.The testing facilities available at PPT for the Landing Gear Division consist of: drop test, strength test, fatigue test, durability test and impact test machinery.In PPT testing Facilitates is possible to test the landing gear of the wheel vertical force up to 25t.The PPT landing gear test facility is computerized so that results are available for engineering assessment.

DROP TESTThe PPT possesses two towers for testing of landing gears to vertical reaction on the wheel of 25t.Measuring of vertical reaction on the wheel is carried out by three-axial force indicator while acquisition and processing of the measuring results are computed. It is possible to acquire testing data on 32 channels.Shutting of wheels is carried out by a mobile equipment that can rotate two wheels at the same time to 400km/h.

DURABILITY TESTThe durability test system carries out simulation of the runway profile.Both horizontal and vertical actuators can be used simultaneously.The horizontal actuator can attain the force of up to 10t and the vertical one 25t.

IMPACT TEST EQUIPMENTThe system enables duplicating of the drop test by application of the simulation system.The hydraulic impact simulation system uses the basic hydraulic system with a shoot loop operating on the shifting control unit. The control signal to servo actuator is realized with an analog computer known as collision simulator. The test parameters such as simulated

Aircraft Lasta 2: Main L.G. Drop test result

mass, wing lift and impact speed are electronically adjusted on calibration dials.The collision simulator duplicates the ideal mathematical impact model between two masses. It determines the shifting links as a function of an unknown shock absorber run and controls SHA to move toward the appropriate shifting in #t# time.It is possible to simulate smaller drop of 100 to 5000 kg wing lift from 0 to 100%, and the impact speeds up to 4.5 m/s.

FATIGUE TEST EQUIPMENTThe fatigue test system with three channels is available including three actuators for the vertical, lateral and horizontal inlet as required servo-regulators.Servo-controls possess both force and run indicators. The equipment can test the landing gear with a vertical force on the wheel to 25t.

AIRCRAFT WHEELSAll our wheels are virtually of the same type as that illustrated here.

The various existing alternatives differ in size only.To make tire mounting and removal esier, these wheels consist of two wheel halves assembled by tie bolts and self locking nuts of

1. Control Room 2. Landing Gear Durability/Impact Test Equipment 3. Small Drop Tower 4. Tyre/Brake Test Machine 5. Large Drop Tower

1

3

2

4 5

high strength steel. The two wheel-halves are interchangeable. They are made of die forged aluminum alloy and they are protected by anodizing and hot polymerized paint resisting to shocks, oxidation and hydraulic fluids.The wheels are fitted with taper roller bearings protected from external projections by flanges. They are provided with fuses preventing tires from bursting in case of abnormal overheating.All our wheels can accommodate the tachometer driving device used in our brake control systems.BRAKESThese brakes have been designed for the simplest possible maintenance, at the most reasonable price and for the best possible weight. Aircraft manufactures have been attracted by the ease with which faulty parts can be replaced. The brakes consist of three main parts:THE BRAKE SUPPORT mounted freely on the wheel axle and remaining fixed to it. THE HYDRAULIC UNIT which provides pressure for the disc linings, by means of its pistons, whose backward movement is controlled by automatic wear compensation devices. These devices are incorporated in brake cylinders, and there fore retain the same efficiency at all times, and are impervious to outside conditions. THE OPERATIONAL UNIT, integral with structural parts, by means of serration in the torsion tube, which makes it possible to transmit the braking torque to the brake bar. This torsion tube and its functional components which include rotary discs and supports carrying the friction linings. Supports and rotary discs are segmented to prevent thermal distortion. Our brakes are characterized by:

short braking path long life-time simple maintenance

EQUIPMENT FOR TESTING WHEELS, TYRES AND BRAKESMachines for testing of small diameters of tires and wheels are available. The machine can be used for development testing of tires and brakes for airplanes with the wheel dynamic load of up to 10 000 kg and the maximum speed up to 400 km/h.

ACTUATION MECHANISMSFor lowering and retraction of landing gear, Landing Gear Division offers suitable equipment to provide a total system. Depending on the geometry, most our landing gears are capable of emergency free fall lowering. Typical system components are:

hydraulic actuators folding stays up/down locks door locks

Hydraulics is a PPT specialty and the company is ideally suited to produce hydraulic system coordinated with the landing gear.

INTERNAL LOCKING ACTUATORSThe hydraulic actuators produced by PPT may be provided with mechanical locking system of the claw-type.

Aircraft G-4 Main L.G. Retracting Actuator

The most attractive features of this device are, on the one hand, its compactness i.e. its capability of taking up significant loads when compared with its reduced overall dimensions and, on the other hand, its extreme reliability proven by forty years of experience in aviation.The automatic locking of the actuator rod at the end of travel is made possible by the #claw# flexible fingers trapped between a rod shoulder and locking piston.Consequently, locking is achieved through the effect of the actuating pressure, other wise, through a low external load. Unlocking is hydraulically controlled, the locking piston moving back under the effect of the pressure. These actuators are used for landing gear leg bracing, for door and air brake.They include mechanical switches which allow to know whether the mechanism is locked or not.

According to the applications required, locking can be achieved with rod retracted or extended as well as in both positions in a few cases.

UPLOCKSOur uplock units, the design of which is based on a common

principle are intended for various installations. They ensure the automatic uplocking of a landing gear unit. They consist of a box incorporating a switch and a hydraulic actuator. The box encloses the locking device mainly consisting of a hook and a link connected by an extension spring which during locking holds the link roller on the hook path. These uplock units incorporate switches of different types (microswitches or proximity switches) which indicate whether the landing is locked or not. The single or double piston actuator ensures the gear hydraulic unlocking with NORMAL or EMERGENCY system.