Aircraft Wheel Research Articles

Aircraft wheel testing with machine-cooled HTS SQUID gradiometer system

For eddy current detection of deep-lying flaws in large aircraft wheels, an automated airplane wheel inspection system using a HTS SQUID gradiometer sensor is being developed. Wheel drums made of aluminum alloys have to be tested frequently since they are subject to enormous dynamic loads and very high braking temperatures at landing. For economic reasons, testing should be performed from the outside without removing the inner ferromagnetic keys which fit the brake system. In order to operate the sensor in hostile environments such as airport maintenance hangars, a planar rf double hole SQUID gradiometer was used. SQUID cooling is performed by a closed cycle Joule-Thomson cryocooler, equipped with flexible plastic gas lines. The wheel testing is being performed on an automated test stand with the wheel slowly rotating and a robot with the SQUID enclosure scanning stepwise along the wheel axis. Additional signals due to inner cracks of 10 mm length, penetrating 25 percent of the 10 mm thick wall, are easily identifiable in the periodic signal background due to the presence of ferromagnetic keys. In comparative measurements, the prototype SQUID system clearly exhibited advantages over conventional techniques, with optimization reserve still at hand.

Inspection of aircraft parts with high remanent magnetization by eddy current SQUID NDE

We have developed an eddy current NDE system based on HTS rf SQUIDs as magnetic field sensors. Due to their high field sensitivity even at very low frequencies, SQUIDs are especially suitable for applications where a large eddy current penetration depth is required. We have used 3 GHz rf SQUIDs in our system made from YBCO thin films with a field resolution of about 1 pT//spl radic/(Hz) and a high dynamic range, more than 140 dB//spl radic/(Hz) in unshielded environment. With this system we could detect deep lying (up to 26 mm) cracks in test samples and original aircraft parts. Measurements made on the same sample showed an improvement in the signal to noise ratio of up to 3 orders of magnitude for cracks deeper than 13 mm, when comparing a conventional eddy current NDE unit with our SQUID system. Test objects containing ferromagnetic structures with a high remanent magnetization (often more than 1 mT), like aircraft wheels or steel bolts in part of the aircraft wing, very often cause instabilities of the flux locked loop operation of the SQUID. To prevent unlocking, we have developed a new background field compensation scheme. Special compensation electronics takes care of slowly varying magnetic fields of up to 1 mT/s and enabled us to perform eddy current measurements in presence of slow (<30 Hz) background field variations of up to 5 mT.

Influences of KBE on the aircraft brake industry

A general review has been conducted to describe the situation of the aircraft wheel and brake industry and to describe possible applications of knowledge based engineering (KBE). The latest books and publications available to the authors have been reviewed during the survey to identify the latest thinking on the topic. The paper investigates tools to increase productivity in general, explains the way a KBE tool works, and describes possible KBE applications in the wheel and brake industry as design tools and as diagnostic tools. The relationship of KBE to existing IT systems is considered and put into the context of restructuring process. A case study describes the formulation of rules and the code that can be used with the ICAD software. Possible pitfalls are described. An outlook into future trends is included.

Apparatus for rotating an aircraft wheel prior to landing

Apparatus for rotating an aircraft wheel prior to landing

EFFECT OF TEMPERATURE ON THE BEHAVIOUR OF ASPHALTIC CONCRETE MIXTURES UNDER REPEATED Lams

In the recent years an important trend has been established towards the use of heavier highway md aircraft wheel loading. The high axle loads lead to excessive permanent deformation in asphalt pavements, especially at high temeratures in hot regions. The main objective of this research is to study the effect of test temperatures on the creep behavior of asphalt concrete mixtures. Dynamic creep test was used for this purpose. Creep strain, mix stiflkess modules and rate of deformation were obtained as a function of axial applied stress and/or test temperature. It is concluded that the creep strain, rate of deformation 'and mix stiffness modules depends upon the bitumen stifhess, and influenced proportionally by variation of test temperature.

Eddy current nondestructive material evaluation based on HTS SQUIDs

High Temperature Superconductor (HTS) Superconducting Quantum Interference Devices (SQUIDs) are promising sensors for applications in eddy current nondestructive evaluation (NDE). Due to their high field sensitivity at low frequencies, they are especially suitable for applications, where a large penetration depth is required. We have investigated two different SQUID-based NDE systems, one of which is optimised for testing felloes of aircraft wheels. The second system allows for testing planar structures using a motorised x-y-stage, which moves the cryostat above the planar samples. As sensors 3 GHz rf SQUIDs made from YBCO were used, having a field noise of about 1 pT/√Hz. This results in a dynamic range of our SQUID system of about 155 dB/√Hz. In most cases, the SQUIDs have been cooled by immersing them in liquid nitrogen. We have however also developed a cryosystem, which allows for cooling the sensors by a Ne-gas flow. In planar test structures we could detect flaws with lengths of 10 mm, having a height of 0.6 mm in a depth of 13 mm. In aircraft felloes, flaws located at the inner surface of the felloe (thickness 8 mm) were easily detectable despite a high static background field of up to 0.5 G caused by ferromagnetic structures inside the felloe. For flaws in a depth of 5 mm, the spatial resolution of both systems was about 8 mm without applying image postprocessing.

Experiments on eddy current NDE with HTS rf SQUIDS

HTS SQUIDs are promising sensors for applications in eddy current NDE. Due to their high field sensitivity at low frequencies, they are especially suitable for applications, where a large penetration depth is required. We have set up two SQUID systems for low frequency eddy current NDE. 3 GHz rf SQUIDs made from YBCO are used as sensors with a field resolution of about 1pT//spl radic/(Hz). One system, where the SQUIDs are cooled by immersing them in liquid nitrogen, is optimised for testing fellows of aircraft wheels. The fixed cryostat is mounted close to the outer surface of the rotating fellow. The second system uses a cryocooler for SQUID cooling. A motorised x-y stage is used to move the SQUIDs above the plane specimen to be tested. Due to the high slewrate of the SQUID electronics, both systems can easily be operated in an unshielded environment. A double-D shaped coil is used to reduce the excitation field at the location of the SQUID. We report on first results of measurements on aircraft parts.

In-flight Airflow Measurements of a Cessna AgHusky Agricultural Aircraft

A measurement system based on pressure probe techniques was developed and used to survey airflow speed and direction near the trailing edge of the wings and under the fuselage of a Cessna AgHusky agricultural aircraft. The main feature of the system was an airflow measuring rake comprised of eight, 5-tube probes designed to measure total pressure and airflow direction and two stream pressure probes to measure static pressure. The probes were encased in a 0.74-m long airfoil that was positioned vertically at numerous lateral positions 0.23 m behind the trailing edge of the aircraft wing and horizontally at several locations beneath the aircraft fuselage. The test flight protocol included three aircraft loadings (0-, 227-, and 454-kg hopper loads) and two airspeeds (145 and 185 km/h) at an aircraft wheel height of 1.5 m. The measurements indicated that air velocity, airflow yaw angle, and airflow pitch angle were all significantly affected by variations in aircraft loading, aircraft speed, and measurement locations. The air velocity ranged up to 195 and 235 km/h in the propeller slipstream at indicated airspeeds of 145 and 185 km/h, respectively. Velocities of 64 to 97 km/h were recorded near the underside of the fuselage where the airflow was blocked by spray system hardware. Outboard from the propeller slipstream, the air velocities were lowest in the area directly behind the trailing edge of the wings and highest either 0.203 m above or 0.305 to 0.475 m below the trailing edges of the wings. Airflow yaw and pitch angles were largest for the 145 km/h indicated airspeed with the 454-kg load and in the area below the fuselage and aft of the spray system hardware. Outboard of the propeller slipstream, the yaw angles did not exceed 6. The airflow pitch angles ranged up to 7 at the wing measurement locations with the largest downward angles occurring 0.102 to 0.203 m above the wings and the largest upward angles occurring directly behind the trailing edges of the wings. These results provide a basis for selecting and locating spray delivery equipment on agricultural aircraft in order to minimize the effects of airflow on the production of small droplets that are most subject to spray drift.

An investigation of tire-wheel interface loads using ADINA

Aircraft wheels are designed to exhibit a fail-safe point so that a crack in the wheel can be detected before any catastrophic failure occurs. Presently, engineers use intrusive instrumentation to directly measure the tire-wheel interface pressure distribution. The goal of the current research is to demonstrate a nonintrusive methodology for using experimental displacement data in conjunction with the finite element method to back calculate this pressure distribution. The result is a well calibrated and credible finite element model which can be used to investigate the structural performance of the wheel.

Determination of tire-wheel interface loads for aircraft wheels

A numerical tool is developed for determining the pressure distribution at the tire-wheel interface of an aircraft wheel from experimentally obtained strains. The methodology employs an axisymmetric finite element model which is subjected to asymmetric loading. The loading is represented as a double Fourier series, and the components are determined by a least squares fit using the experimentally determined strains. A finite element code was developed to perform this analysis. Sample experiments are presented to illustrate the validity and the robustness of the algorithm. Finally, the limitations of this type of analysis are discussed and future directions are indicated.

Durability evaluation for components by simulating fatigue test and extreme value analysis

A simulating fatigue testing method and requirements are explored to evaluate quantitatively the durability of components which cannot be conveniently and economically tested. Three requirements for analogies are necessary, i.e. the geometry and manufacturing quality of critical detail, stress and stress gradient at the expected cracking plane, and the crack initiation position and crack propagation path. The initial fatigue quality (IFQ) of components may be described by using the simulation test results and the extreme value theory. The distribution of time to reach any given crack size and the probability of crack exceedance, which is the measurement of componental damage in service, are then obtained. Taking aircraft wheel hubs as an example, predictions resulting from simulation tests are verified by a full-scale component fatigue test, and would be acceptable for durability evaluation.

Automated aircraft wheel inspection

Automated aircraft wheel inspection

Computer-aided aircraft wheel inspection uses eddy current technique

Computer-aided aircraft wheel inspection uses eddy current technique

The dynamic response of an aircraft wheel to variations in runway friction

Experimental and analytical techniques are presented for the determination of the response characteristics of a scale-model aircraft wheel to changes in runway friction. Results obtained from tests using these techniques are given. The wheel spin-up acceleration is shown to be proportional to wheel load and to the magnitude of the surface friction coefficient after surface change. It is also found to be inversely proportional to brake torque, but is largely independent of speed. An increase of speed is shown to increase the distance required for spin-up of a locked wheel as it encounters surfaces of higher friction coefficient. Good correlation of these trends is obtained analytically.The effects of tyre flexibility are indicated by the results of both the experimental tests and the analytical simulations. These effects may degrade the performance of aircraft antiskid braking systems. It is recommended, therefore, that simulations used in the development of such systems take proper account of tyre flexibility when modelling the dynamics of the wheel and tyre.

Aircraft Wheel Design and Proving

Aircraft manufacturers now demand wheels which are not only light but also have a long life capability. A typical civil aircraft project such as the Boeing 757, requires a fully approved wheel with a demonstrated life of 50,000 roll miles which equates to approximately 10,000 landings.

Dunlop Commissions £1M Aircraft Wheel Roll Machine

Dunlop Aviation Division has put into operation a new aircraft wheel roll machine at its Coventry site, a project which is valued at nearly £1 million.

Aircraft Wheels and Tyres

The need for drastic standardisation of aero wheels and tyres in England is long over‐due. The U.S. Air Services have standardised five sizes of tyres for their needs, and these five sizes use only four axle diameters. In contrast, the English standards, covering the same range, list nineteen standard tyre sizes and fifty‐two axle diameters and length combinations.

Semi‐automatic Aircraft Wheel Testing

Why, people may ask, should you worry about aircraft wheels — wings and engines yes — but wheels?

Compaction

Compaction of soils is a complex process in which several soil properties as well as compactor characteristics interact. General rules have been developed through years of experience in construction and through a need, in the recent past, to increase the sub-base and base strength of runways to accomodate higher aircraft wheel loads. General guidelines are adequate when there is no need for an accurate prediction of the number of compactor coverages required to effect a given level of soil compaction. During the conduct of a recent program, it was necessary that an estimate be made of the time required to compact soil to a certain strength. A review of the literature indicated that little recent work has been done on compaction and on the modelling of the compaction process. Similitude modelling has been used to predict the trafficability of soft soils. Although the soil compaction criteria are different from those of trafficability, it was felt that similitude modelling could also be applied to compaction. This paper describes the basis for CBR and density models and some indications of their form and prediction ability.

On the tones and pressure oscillations induced by flow over rectangular cavities

Experimental measurements of the frequencies of discrete tones induced by flow over rectangular cavities were carried out over a range of low subsonic Mach numbers to provide a reliable data base for (aircraft wheel well) cavity noise consideration. A mathematical model of the cavity tones and pressure oscillation phenomenon based on the coupling between shear layer instabilities and acoustic feedback is developed to help in understanding the tone generation mechanism. Good agreement is found between discrete tone frequencies predicted by the model and experimental measurements over a wide range of Mach numbers. Evidence of tones generated by the cavity normal mode resonance mechanism at very low subsonic Mach numbers is also presented.