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GENERAL PRACTICES MANUALNOT AI RCRAFT WHEELS

101102103104105106

201202203204205206207208

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GENERAL PRACTICES MANUALNDT AI RCRAFT WHEELS

DescriptionSystem OperationInterpretation

DescriptionSystem OperationInterpretation

201

201

201

202Systems Using a Meter DisplaySystems Using a Chart RecorderSystems Using a Storage Oscilloscope

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GENERAL PRACTICES MANUALNDT AIRCRAFT WHEELS

This General Practices Manual contains information on detailed examination ofaircraft wheels for cracks using Non-Destructive Testing Techniques as laiddown by Dunlop Aviation. This manual will be updated as and when new typesof equipment become available. If further information is required contactDunlop Aviation Division, Holbrook Lane, Coventry.

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Page

Wheel Preparation 202

Flange Rim/Tyre SeatPeripheries of Bolt HolesRadii in Nut and Bolt Head SeatsPeripheries of Ventilation/Lightening Holes·0· Ring Seal GrooveRadii Under Drive Block AbutmentsWeb RadiiLock Ring GrooveInner Wall Radii in Centre Flange

NDT Specified Inspection Areas Main Wheel (Typical)Typical Circumferential Scan PatternTypical IIMetoptic EM1211 Test Set UpTypical IIlnspection Instrument Eddyprobe 411 Test Set UpTypical Circumferential Scan PatternTypical Sinusoidal Scan PatternTypical Scan Paths Peripheries of Bolt HolesTypical Scan Path Nut and Bolt Head Seat RadiiTypical Scan Path Peripheries of Ventilation/

Lightening HolesTypical Scan Path '0· Ring Seal GrooveTypical Scan Pattern Radii Under Drive Block AbutmentsTypical Scan Path Web RadiiTypical Scan Paths Lock Ring GrooveTypical Scan Patterns Inner Wall Radii

Fig.

1101102103201202203204

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205206207208209210

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GENERAL PRACTICES MANUALNOT AI RCRAFT WHEELS

1. Description

In the 'Check' section of the Component Maintenance Manual for an aircraftwheel a sectional illustration details the areas in which NOT inspection isrequired. A large number of these areas can be covered by the commoninspection techniques outlined in this manual. Areas specific to a particu-lar wheel only will be covered in the relevant wheel Component MaintenanceManual.

It is the object of this manual to detail techniques that will reveal fatiguecracking of aircraft wheels in the order of 2 mm (0.08 in.) long 0,25 mm(0.01 in.) deep.

A. Flange rim/tyre seat: critical area, preferred method of inspectionSemi-Automated Eddy Current.

Particular care must be paid to the inspection of the flange rim/tyre seat area (reference area A) as small cracks and defects inthis area may result in rapid crack propagation, causing a sec-tion of flange to becomedetached. It is important that the tech-niques employed are capable of finding defects of the order des-cribed in para.2 Object.

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Semi-Automated Eddy Current inspection is the preferred method of inspec-tion for the flange to tyre seat area. A number of test sets and techniquesare available, examples of which are described. Reference should also bemade to test set manufacturers instructions.

The scan pattern used in a semi-automated eddy current technique is nor-mally circumferential, as illustrated in Figure 101. The pitch of the scanpath being determined by the type of test set and probe used. The com-plete barrel area of the wheel may be scanned, on large wheels the mini-mum amount of tyre seat area scanned is to be 50 mm (2 in.).

SCj~P'T(:H,J·..R.··.·.··.R··.·.·••R•••·.~·I;'~:R-:-_-I·.·.·.·.E· ••··E-B.· ••••_•..•...; R 1~....~••..~."~•••••.~it"",( )

Clean the area to be inspected as detailed in 'Cleaning' section of Compo-nent Maintenance Manual. Remove loose paint and tyre rubber in theflange rim radius and tyre seat area.

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DRIVE DOGABUTMENTS(BRAKE SIDEHALF HUB)

'O'RING SEALGROOVE(BRAKE SIDEHALF HUB)

VE~TILATION ILIGHTENING HOLES(BOTH HALF HUBS)

To carry out adequate and effective crack detection using EddyCurrent Equipment a trained operator should be available andthe limitations of the techniques and test equipment appreciated.

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GENERAL PRACTICES MANUALNOT AIRCRAFT WHEELS

000\=UCRACK DETECTOR ANDRECORDER UNIT

PROBE ARMPROBE ARMGUIDERAM

/: 000 Ii 000 I

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CONTROL PANEL PROXIMITY SWITCHES

This system is designed for use with a trace recorder having twopaper speeds. Two probe types are utilised, one contoured to fitindividual tyre seat radii and containing two scanning cores to coverthe flange to tyre seat radius and the tyre seat radius to the startof the tyreseat area. It is important that the profile of this probematches that of the bead seat radius of the hub being inspected. Airgaps between the probe and hub will result in a loss of sensitivity.The other probe has a flat section to cover the tyre seat and barrelarea. This probe has a scan area of 9 mm (0.35 in.) coupled with acircumferential scan path of 2 mm (0.08 in.) pitch, thus any defectwill be scanned at least three times. To facilitate setting up of thesystem a calibration block containing a real or artificial crack 0,5 mm(0.02 in.) deep approximately 0,1 mm (0.004 in.) wide is required.

The inspection probes described to cover the flange rim andtyre seat radius can be employed manually using a simpleturntable.

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This system incorporates a chart recorder with a fixed paper feed andutilises an inspection probe with a spherical tip that is sensitive overa full 360 degrees at its contact point. The system gives a circumfer-ential scan of approximately 1,6 mm (0.062 in.). To facilitate settingup of the system a calibration block containing a real or artificialcrack 0,5 mm (0.02 in.) deep approximately 0,1 mm (0.004 in.) wideis required.

(1) Adjust lift off control to give minimal test meter needle movementwhen probe is lifted slightly from test block.

(2) Adjust meter sensitivity to give a signal trace height of 15 mm(0.6 in.) on recording paper for the 0,5 mm (0.02 in.) deepdefect in the calibration block.

(4) Set upper and lower proximity switches to pre-determined posi-tions (X and Y Figure 102) ensuring lower switch is set to givea scan start at the outer edge of the flange area (point X Figure102) and upper switch to give a scan at least 50 mm (2 in.) intothe tyre seat area (point Y Figure 102).

Scan may be extended to include complete barrel area ofwheel if desired.

C. Interpretation

(1) View recording trace, investigate any signal trace of 5 mm (0.2in.) height or greater using a hand held probe and a high fre-quency test meter.

(3) Corrosion is not permitted, dress out corrosion as detailed in'Repair' section of Component Maintenance Manual.

(4) Dress out physical damage as detailed in 'Repair' section ofComponent Maintenance Manual.

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(1) With cable connected to one connection of the contoured probe,adjust trace sensitivity to give a signal height of 15 mm (0.6 in.)on the recording paper for the 0,5 mm (0.02 in.) deep defect inthe calibration block.

It is recommended that a series of hubs or hub sectionsbe obtained with tyre seat radius profiles to match thecontoured probes being used and contain known fatiguecracks in the tyre seat radius. Spark eroded or milledslots 0,5 mm (0.02 in.) deep 0,1 mm (0.004 in.) to0,2 mm (0.008 in.) wide, 6 mm (0.25 in.) to 8 mm(0.3 in.) long may be used. At the start of eachwheel batch these hubs should be used to calibratethe test equipment ..

(2) Select turntable speed to 1, trace recorder speed to high, turn-table/recorder synchronisation to 'ON'. Place probe in tyre seatradius, depress auto zero button, switch turntable on. Scanhub for two full revolutions.

(3) Connect cable to the opposite connection of contoured probe.Repeat steps (1) and (2).

(4) Connect cable to the tyre seat/barrel probe, calibrate as perstep (1). Select turntable speed 4, trace recorder speed to low,position probe to overlap scan area of contoured probe. Switchturntable on. Scan tyre seat/barrel area for at least 50 mm(2 in.). Switch off.

Scan may be extended to include the complete barrelarea of wheel if desired.

(1) View recording trace. Investigate any signal trace of 5 mm (0.2in) in height or greater using a hand held probe and a highfrequency test meter.

(2) Reject a cracked half hub.

(3) Corrosion is not permitted, dress out corrosion as detailed inIRepair' section of Component Maintenance Manual.

(4) Dress out physical damage as detailed in •Repair' section ofComponent Maintenance Manual.

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/[]0

]0 0I 0 0/0 0

CONTROL PANEL

1

0 0 0 C

g C 0 CI ,

i, I I CJ r_I \l= ~CRACK DETECTORAND RECORDER UNIT

SCANOVERLAPSCAN

SCAN

SCANOVERLAP

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Manual eddy current inspection can be applied to all areas listed, includingthe flange to tyre seat area when semi-automated eddy current techniquesare not available, providing the hubs are fully disassembled apart fromremoving the bearing outer races. A wide range of test sets are availablefalling into two main categories; high frequency sets operating with a signalfrequency above 1 MHz, low frequency sets operating below 1 MHz. Inaddition to the following procedures reference should also be made to testset manufacturers instructions when inspecting wheel hubs.

A. Various inspection probes are utilised during manual eddy currentinspection, the most commontypes are:

(1) Non ferrous point probes, used in conjunction with fixed highfrequency test sets. The standard forms of the probe are:

(a) 'pi type (pencil)

(b) 'KI type (knife)

(2) Differential probes used in conjunction with low frequency testsets operating at approximately 30 KHz. These probes may takethe following forms:

(a) 10 mm (0.39 in.) long with a 2 mm (0.08 in.) radiused tip,used to inspect tyre seat radii.

(b) 10 mm (0.39 in.) diameter flat probe, used to inspect tyreseat area.

(c) Probes moulded to the form of the flange rim to tyre seatarea. These probes will contain separately wound coreswhich give an extended area of coverage.

(3) Non ferrous point probes used with variable frequency test setsat around 200 KHz. These probes are held in probe guides con-toured to fit into the scan area.

A. To allow setting up of a test set a calibration sample is required.This may be one of the following types.

(1) Standard non ferrous test block containing a slot 0,5 mm (0.02in.) deep 0,1 mm (0.004 in.) wide.

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(2) Hub or hub section containing a known fatigue crack 0,5 mm(0.02 in.) deep and 2 mm (0.08 in.) to 4 mm (0.16 in.) long inthe flange rim/tyre seat area.

(3) Hub or hub section containing an artificial defect in the flangerim/tyre seat radius. This should take the form of a spark eroded or milled slot 0,5 mm (0.02 in.) deep and 3 mm (0.12 in.) to4 mm (0.16 in.) long with a maximumwidth of 0,2 mm (0.008 in.).

A. Systems Using a Meter Display

Obtain a full scale deflection from the 0,5 mm (0.02 in.) deep, realor artificial defect in calibration sample. Set the audio/visual alarmto trigger at half scale deflection.

Some test sets have an audio/visual alarm which triggersat a fixed position e. g. 40%of scale deflection. In this in-stance the 0,5 mm (0.02 in.) deep defect should be set to80%of scale deflection. Test equipment with other fixedtrigger levels should be adjusted accordingly.

Adjust the sensitivity so that the 0,5 mm (0.02 in.) deep real orartificial defect produces a signal height of 15 mm (0.6 in.) on therecording paper.

Adjust the equipment so that the 0,5 mm (0.02 in.) deep real orartificial defect, produces at least a half screen height image.

5. Wheel Preparation

Clean all areas to be inspected as detailed in ·Cleaning' section of Compo-nent Maintenance Manual. Remove loose paint and tyre rubber from flangerim radius and tyre seat area, ensure nut and bolt head seat radii are freefrom jointing compound.

To ensure a satisfactory scan pitch is maintained a coating ofdye penetrant developer can be sprayed on to the scan area.During inspection the scan pitch will be traced in this coatingallowing it to be monitored.

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(1) Two scan patterns may be used in this area, circumferential andsinusoidal. Either is acceptable providing complete coverage isachieved.

(2) Using a pencil probe inspect flange rim and tyre seat area usinga circumferential scan as illustrated in Figure 201. Amplitude ofscan IA1 should be 50mm (2 in.) minimum, scan IB1 15 mm (0.6 in.)minimum. The pitch of scan IC' will be determined by the fre-quency of the probe and test set used, e.g. 1 mm (0.04 in.) forhigh frequency equipment operating at 1 MHz or over, 2 mm(0.08 in.) for lower frequency equipment operating at 200 KHz.It is recommended that whenever possible an indexing device andturntable be employed to ensure an even scan pitch.

Typical Circumferential Scan PatternFigure 201

(3) Using a pencil type probe inspect flange rim and tyre seat usingsinusoidal scan patterns as illustrated in Figure 202. Amplitudeof scan IA1 should be 50 mm (2 in.) minimum, scan IB1 15 mm(0.6 in.) minimum. The pitch of scans ID1 should be 2 mm (0.08in.) maximum.

ISCAN PATHOVERLAP

Typical Sinusoidal Scan PatternFigure 202 20-00-01

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Using a pencil type probe inspect the peripheries of bolt holes onboth sides of half hub as illustrated in Figure 203. The distance ofscan from bolt hole should be 1 mm (0.04 in.).

If the probe is allowed to veer on to the edge of bolthole meter needle deflection will occur. These deflec-tions should not be confused with those caused by adefect.

To ensure a satisfactory scan at the required distancefrom holes, locally produced non-metallic bungs witha lip of appropriate size may be used as a probe guide.

Using a pencil probe inspect the nut and bolt head seat radii asillustrated in Figure 204.

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Using a pencil probe inspect the peripheries of ventilation/lighteningholes on both sides of half hub as illustrated in Figure 205. Thedistance of scan from edge of hole should be 2 mm (0.08 in.).

Typical Scan Path Peripheries of Ventilation/Lightening HolesFigure 205

Using a knife type probe inspect the '0' ring seal groove with bothsinusoidal and circumferential scan patterns as illustrated in Figure206. The minimum scan pitch for both scan patterns should be 2 mm(0.08 in.) .

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Typical Scan Path '0' Ring SealFigure 206

Groove

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Usng a pencil probe inspect the radii under drive block abutmentsusing a sinusoidal scan pattern as illustrated in Figure 207 the pitchof scan X should be 2 mm (0.08 in.) with an amplitude of 5 mm(0.2 in.). Scan should extend 5 mm (0.2 in.) beyond the edges ofdrive block abutment.

This inspection is only feasible when drive blocks and heatshields are removed.

Typical Scan Pattern Radii Under Drive Block AbutmentsFigure 207

Using a miniature pencil probe inspect the web radii as illustrated inFigure 208. c'--"""

Typical Scan Path Web RadiiFigure 208

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Using a special miniature knife type probe inspect the lock ring grooveusing sinusoidal and circumferential scan patterns as illustrated inFigure 209. The scan pitch for the sinusoidal scan should be 2 mm(0.08 in.) for the circumferential scan 1 mm(0.04 in.).

'O'RING SEAL GROOVEREFER TO FIG 206

Using a pencil probe inspect the inner wall flange radii using sinu-soidal and circumferential scan patterns as illustrated in Figure 210.The pitch for both scan patterns should be 2 mm (0.08 in.).

FlANGEITYRE SEAT AREAS ...REFER TO FIG 201/202------... .. ~

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