Embed Size (px)
Citation preview
ARL/Struc. Note 424 ARL/Struc. Note 424
/2!
I
DEPARTMENT OF DEFENCE
DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION
z AERONAUTICAL RESEARCH LABORATORIES
MELBOURNE VICTORIA
Structures Note 424
THE PERFORMANCE OF AIRCRAFT
CONTROL CABLESUNDER SERVICE CONDITIONS
by
M. B. BENOY, R. A. FELL and P. H. TOWNSHEND
LUL
Cm COMMONWEALTH OF AUSTRALIA 1977
A MONWEALTECHNUALI APRIL 1976INFORMATION SERVICEU. S. DEPARTMENT OF COMMERCE
SPRINGFIEL!D VA. 22161
3 .!
IJ
DOCUMENT CONTROL DATA
I. Security Grading/Release Limitation 2. Document Type/Number
(a) Document Content Unclassified Structures Note 424
(b) This Page Unclassified 3. Dociment DateApril 1976
4. Title and Sub-Title h
The Performance of Aircraft Control Cables under Service Conditions
5. Personal Authois: M.B. Benoy, R.A. Fell & P.H. Townshend
6. Corporate Author(s): AERONAUTICAL RESEARCH LABORATORIES
Abstract
Investigations w.ere conducted on the adverse effects of service conditions on theper/forman' o/flexihle steel wire ropes used in aircraft controlsysterms with particularreference to the A uster aircraft. i
S8. Computer Prugr:mn(s) -- Titles and Language
9. l)escriptors I1. Cosati Classifications
Aircraft 0103, 1402, 1106, 1309Control EquipmentWire RopesService Life
RD 73 50-4
10. L.ibrarv Distribution (Defence Group) 13. Sponsoring Agency Reference
Central LibrarySTIB.110ARI.CS -IMRI.., Vic, NSW, South Aust. 14. Cost CodeWRI-
Air Office. ARDU, AMTS 7100Army Office, EDE, Bridges Library
15. Imprint
MELBOURNE AERONAUTICAL RESEARCH LABORATORIES 1976
"i L--:':"/ I; -• " ...¥ ' •••- '' .. . . ..
DEPARTMENT OF DEFENCE
DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION
AERONAUTICAL RESEARCH LABORATORIES
- .!~~~/ . .... ..... ...... ..... ! ",." .. • .'
STRUCTURES NOTE:424
THE PERFORMANCE OF AIRCRAFTCONTROL CABLES
UNDER SERVICE CONDITIONS,
SM. BBENOY, RAFELL 0 P. H. TOWNSHEND
• ...... /"SUM M A R )Y,4iter e.xaminationa oaircraft control cahles broken or wornt in service together
with mechanical tests antd theoretical analysis the.fillowing /actors were found tocontribute, to f.ailure:
(a) Abrasion ofthe cahles onpullevs orfairleads causing a much more serious loss ofstrength than is apparent from surface wear.
"(B) lBrinelling" oft he individual wires in the strands due to.fluctuating cable tensioninducing high contact stresses between helicall' wound wires. This causes strain-hardening fdiohwed hi brittleness in the hard-drawn wires leading to theformation .0/' sur/ace cracks.
(c) F'atigue of wires due to flexing around pulehys and fairleads.(d) ('nobserved/failure of'the core strand due to the combined effects of(h) and (c).
Subsequent to the investigations a review was made of the published work onaircrafl control cables and covers the development oJfstandards and air-worthinessrequirements. A bibliography, which includes wvire ropes in general engineering hasalso been added.
/ ._
(ONTENTS
Page No.
1. INTRODUCTION 3
2. INVESTIGATION OF SERVICE CONDITIONS AND CABLE DAMAGE 3
2.1 Examination of Cables Damaged in Service 3
2.2 Inspection of control cable installations 4
2.3 Measurement of cable loads in service 4
3. INVESTIGATION OF THE FACTORS AFFECTING CABLE STRENGTH 53.1 Determination of the mechanical properties of cables 5
3.2 Effect of cable wear on ultimate strength 5
3.3 Evaluation of nylon covered cable 5
4. ANALYSIS OF CABLE STRESSES 6
5. DISCUSSICN 7
5.1 Historical 7
5.2 (ab'ts 7
5.3 Pulleys 8
5.4 (able Standards 8
6. ('ON('ICUSIONS 9 A
6.1 Cables 9
6.2 Nylon covered cables 9
6.3 Pulleys 9
6.4 Rudder control circuit 9
6.4.1 Rudder limit stop 9
6.4.2 Circuit tensioning 9
6.4.3 Fairleads 9
7. RI:VIEW OF STANI)ARi)S AND RELATED INVESTIGATIONS 9
7.1 (able Standards 10
7.1.1 Nylhr. covered cables II
7.2 Pulleys
7.2.1 Pulley groove profile
A(KNOWLEDI) EM ENTS I
RE F ER EN(CE;S 12
APPENI)IX I: Analysis of stresses in a 7 x 7 cable
DISTRIBUTION
DOCUMENT CONTROL DATA
TABI.ES
FIGU !R ES
IBBIIOGRAPlHY
I,
* =,j~
I. INTRODU nTION
Following the occurrence of service failures in rudder cables of Auster aircraft aninvestigation was undertaken at the request of ).C.A. asi rer'rted in Reference 1. As a result ofthis work the problem of progressive deterioration of aircraft control cables in service wasconsidered to be of sufficient importance to warrant extending the A.R. I.. investigations.
Examination of worn control cables froim small civil and military ,ircraft and glidersindicated that a substantial reduction in strength could occur with little or no visible evidence ofdeterioration. An experimental programme, including sonic theoretical analysis, was thereforeplanned to investigate the Iactors contributing to the reduction of ultimate strength of controli cables if) service.
[he following threc types of cables were considercd:
(i) 7 x 7 aircraft cable (i.e. 7 strands of 7 wires) miinimutmn breaking load I(cwt., (4,98kN)made to an Auster specification (Relf. 2)
(ii) 7 x 14 aircraft cable (i.e. 7 strands of 14 wires) nurnimtum breaking iad 10 cwt., (4.98kN) made to British Standard Spciciication W9. (Ref. 3).
(iii) 7 x 19 aircraft cable (i.e. 7 strands of I) wires) minimtumn breaking load 17601bf (7.83kN) made to American Military Specilication MIi.-I'-5424. (Rel. 4).
Mhe layout of the wires in the cables is illustr;tcd in Ifigs. I ald 2.
Fatigue tests were also carried out on samples of galvanised steel cable (5 cwt. (2.49kN)minimumil breaking lo0ad, 7 x 7 construction to B..S. W.90) s.peci; lly prepared with i a nylon coveringto resist abasion.
It should be noted that t his report is based onl %% ork %% hii'h was carried out in t lie early 1960'sand was tie 1CSubject oflt wo i nternal A. R. I.. report s. I'cause of delays in vetting etc. due to higherpriority tasks, it has only now been consolidated into one report with the addition of laterdeye lopmernts.
The investigatio oIS, experimental %olrk aind restilts are as presented in (le earlier reports but inthe I )iscussioi allItusions aer made to t lie i nfl tie ices of ad v,•lices ii i cable design, current technologyard standards. An up-to-date hibliography is included at the end of the report.
2. I VESTI(CATION OF SERVICE (CONI)ITIONS ANI) (CABLE DAMAGE !
hi order to detcrmnine thlie factorS that cauSetd dteLrioratiOll Of Control cables a number of0cables damaged in service were examined and the control cable installation was inspected in anumber of Auster aircraft.
2.1 Examination of (aibles I)amuiged in serfie
A numnber of cables worn or broken in servicc \k as e xanmined byh nicroscope. The rudder cablefailures frot tnlhe Atustcr aircralt (reported in Ref. I ) arc includcd. The aircraft have been given anarbitrary designation f1or the purposes of this repor'. i.e. VIIA. VII II. VfI(., V\IE.
I tit lie A uster rudder cables most of t lhe kk Or ia rd distorted sect ions of ca hle occurred at 254-305mrm (10 - 12 i nches) from t lie rudder pedal eve attachnient and 356mmni (14 inches) from thehorn turnbuckle attachment (Fig. 3). [he wear tor the flormner condition was at a change ofdirection pulley and the liater where the cable rubbed on the [abric fairlcad oru emerged from therear fuselage. It was at this latter location where sonic ol t ecables \ere corroded and the positionwhere VIIC had severe internal corrosion which was not detected by external visual inspection.
[he wires of the 7 x 14 cable from VIIA were heavilv abraded, the abrasion marks beingclearly visible and laying approximately at right angles to the cable. This abrasion had occurred onone side of the cable only (approximiately halt the circu~mferen~ce) and extended about 57 mm (2'i4
inches) each side of the failure. rhe individual wires were each examined at the point of fracture bymicroscope and this revealed no clear evidence olf atigue failure but showed that most of the wireshad failed by static-tensile load. A photograph of the failure showing the extent of abrasion isshown in Fig. 4.
In the 7 x 7 cable VHB the wires showed no marked external abrasion but were heavilydamaged consistent with high pressure between wires. There was considerable deformation and insome strands the core wire had assumed a hexagonal cross-section tinder pressure, which was
3
A
probably comihined wit h rubbing, fromni fhe surrounding wir es. Fig. 5 shows ,r photo of the failurein which the damage to the ssrres call be ckcarly seen,
The difficult v of* detect ing inter nalI wire damage was cnmphasised w he n thle operat or of' V HELremoved both 7 x' 14 rudder cables two Iliing hoursa Iter a ('ertificate of A irworthiness beca use of'a broken wire f'ound in one of* the cables. 'I hese cables were examined in the laboratory and onewas f'ound to have a completely hroken core strand. each side of- the f'racture was corroded adistance of' about 12.7 mim 1'., inch) and indications were that f'ailure had existed f'or some timeprior to the inspection.
[he 7 x 7 cable hrorm V IIC had worn approximately 0.051 mim (0.W02 inch) where it hadrubbed onl the fabric but had no othter abnormal change in appearance. However, extremely closeinspect ion revealed a sli, ilt discolouration at the point of the strands. Cutting of' the cable andsubsequent inrspect ion with at microscope showed that a considera ble area of the strand in contactwith the core strand had( corroded and bri nell ing oft the wires of adjacent strands bad alsooccurred. [his damage was at tribhuted to the continualI haminmering and rubbing between the wiresofIti hecahle under Ii rictuating tension arising f romn cable vibrationi due to rudder buffetting f'romthe propeller slipstream. Ilioweser. thre samelI State Of Corrosion and brinelling was l'ourd in a 7 x 14cable rcnmosed from aI gl ider where vi bration could occur dute to self excitation or running overtinevenl ground surf'aces. It wais, interestin rigto note that this glider cable. while showing outer wearof appnrox. (1.05 1 rum1 (t).t002 j ich,) had seseral core strand wires failed as shown in Fig. 7. In anotherglider cable wires III seseratl strands had failed in ftilgue at %arious locations but little or no wearwais C\ x lveident ( Fig. 8), It ssais only alrci scveral Iinspect ions of the cable that these wireswere ribsers ed beca rise II, r ctiics rc of stuch at nature that the "'clothI method"' of detection(Ref. (f did lnot indicate airs tailc IL' ires.
2. ., Inspection of control err hie inistallations
Ifrere a rc four f'act ors I n conitrol cable I Irst il Il~ritIor[is whItich cani be recogrii/ed as contri buti ngto cable damrrage. I liesc arc.
(I) (abl v \i hn'lrt Ion irgarils puilleys, and tairleads. I Iris is, particularly inmportarit in ruddercarhcs nrrr sinall Illropeller driseiiaircraft due fto tire effects of slipstream on the rudder.
(iii Cilt~hlc' bendingp Stres-ses (fle to f'Clexig of1 tIre cable ar rmund pulleIYS.
liii) D ariiage ito urnproteecite cables.6\s ) (orrosrori, dute in) r'eirrisal of lirntecfis couitirngs by rubhinig oft wires against each
of hier.I Ire COIrIrIrl Lir'cirirt tf Ire Arist c is described ii soriemcdriila~s it is tv (ica Iof small propeller
drisr'ri aircrirtt arnd illustratres Minnie: ot the ardscisc conditions III which'cables operate.In some nIl I lie Auster airicrf At Cx~airiii ted I lie ca bles were slarck ri thIle unloaded condition while
ri ni t hers file.\ were tenrs~ioned fri 2.27 kg (5 lb.) h by brrimpcccord. I lie cable was linked directly to theruidder pedal. f ire load f rrir which iN subject fit a lcser rat it) of 1.5: 1. [hle cable is deflected throughapproix. IS- bya 3.Xmi1.2ri)daii'rprlc sir uated at I lie forward lower corner of' thecabin entry door. I Iilsis thIre unv pulleyv (iii the pr srde. \k hrill onr the starboard side there are twopuilleys oneif )1 . .X iran 1 1.25 in. lnliaiietcu iiu anritl oif57 - miii (2.25 in. Idiamecter. the targer- pulleyappearinig no be piIMs L 1d 0 lii aecrirurndate a Ii IIgCIr an1gularl deflectionr.
lIn the A.1. series aircraft thle cable runs arc uiritriulcened thirmnughout the cockpit area, while inthe .1,5 series, shiroudinig is provided aft of* thre pulleys. However the pulleys are in all casesvulnerable fto dam rage [rorm personnelri ernterinrg oir Iea\ irg thre crick pit and to contamination. F'romthe pulley thle cable runs af't via two block and tw wi nirg fairleads down the fuiselage and emergesthrough a rei riforced h ole in thle la brie in tthe side of thle fuselage. thle tinral 610 mm (24 in.) of thecable to the rttdder being exposed. [hle cable %%as subject tor about 3" deflection at the aft fairleadand the exit hole [~rnin thre fuselage. at the former filie a irlead was worn to a bout 3014 of the cablediameter arid slight wear arid corrorsiomn was evident at tlie exit hole. The adjustment and stop
limiting rudder miovemlent were located inr the rudder honii.
2.3 Measurement oIf cable loads In service[he majority of cables exmirninc were from Auster .15 aircraft and to investigate the reasons
f~or cable fa3ilures in service typical cable generating loads were measured.
4
LI
A type .156 Auster was modified to enable the insertion of an A. R,.. loop transducer of 2.23kN (500 lIl.) capacity. Ihe aircraft was hiown under various conditions, and the loads at thetransducer were rceorded automatically by a S. F.I.M. recorder. A series of ground manoeuvre Cloads were also recorded using this equipment, These conditions and results (shown in Tables Iand II) where the manoeuvre of full "left" and -'right" rudder at 80 knots straight and levelproduced a roacasured load of 0.98 kN (2201bf*), while a maximum toad of 1.95 kN (440 Ibf) wasrecorded for a ground manoeuvre when the instruct or appl'ed opposite rudder control to over-ridethat being applied by the pupil (Rcf. 5 relates to a cable failure during dual instruction).
The ultimate design load requirements for the various types of Auster aircraft are set out inTable III to give an indication oftypical control forces that can be expected in small aircraft olth.s
3. INVESTIGATION OF THE FACTORS AFFECTING CABLE STRENGTH
A number of investigations were carried out to determine the causes of cable damageobserved in FPara. 2.
3.1 Determination of the mechanical properties of cables
As previously stated some cables removed from service were found to have a broken corestrand while the outer strands appeared intact. Tensile tests were therefore made on cables, corestrands from the cable and wires from the core strand.
Ile specification and test data for the three types of cable are shown in Table IV. Tensileproperties and dimensions of single wires from the cable are shown in Table V. Curves of directtensile stress versus extension are shown in Fig. 9. for the centre wire and outer wire of the corestrand of a 7 x 7 cable. Since the wires were preformed it was not possible toexpress theextensionin terms of strain since a large part of the extension for an outer wire occurs in straightening of thehelical twist. Slight crimping of the core w;re may also be present due to the effect of the contactforces of the outer wires.
However. these graphs give the average tensile stress and an indication of the plasticelongation at failure. It is interesting to note that both the ultimate stress and the plasticdeformation of the outer wire appear to be significantly less than the centre wire, It is possible thatthis effect is due to the superimposed bending stresses applied in straightening the preformed outerwire. hn such very hard drawn wires these stresses are likely to be quite significant.
3.2 Effect of cable wear on ultimate strength
To investigate the effect of wear in service, the minimum diameter of the worn cables takenfrom service was measured and the failing load determined in a tension test. New cables were alsoabraded using fine ema-rv cloth and rubbing the cable by hand in a longitudinal direction over alength of three inches and around one third of the circumference. This corresponded to the extentof the worn area observed on cables fromn service. The failing load of the cable was then determinedin a testing machine, the overall length of the cable being 610 mm (24 inches).
By microscopical examination of each cable tested the area of the failed section of each wirewas measured to within an estimated 50'i. This enabled the failing load to be plotted againstpercentage reduction of area in Fig. 10. and against reduction of cable diameter in Fig. II. There isa considerable variation in results but curves have been drawn through average values. Thepercentage reduction of area was estimated by the microscopic examination of abraded cabiesthat had failed in service and an estimate of the expected failing load could be obtained from Fig.10.
3.3 Evaluation of nylon covered cableWear and abrasion had been cited as one of the principle causes of cable failure, Ref. I.
Therefore, in conjunction witf, D.C.A. it was decided to carry out fatigue tests to evaluate theperformance of nylon jacketed cable in comparison with standard cable.
Standard 5 cwt. (2,49kN) 7 x 7 cable to B.S.S. W9covered with nylon was available in onlylimited quantity so only four test specimens were available. Two specimens of nylon covered cable
"As the max. speed for this type ofaircrai ..- 120 knots it was estimated that flight loads may exceedI. Ilk N (250 INf) for a similar manoeuvre.
, 5 4..M' A,
and two specimens of standard cable were tested on hardened steel and "Micarta' pulleys (at atemperature of 53'C ( 1200 F.) Although, as expected, the nylon jacketed cable on the steel pulleywas far superior to the standard cable the results using a Micarta Pulley were inconclusive. Theresults of these tests are summarised in Table VI.
4. ANALYSIS OF ('ABLE STRESSESSome of the wires of the core strand under contact from the wires of the outer strands showed
evidence of rlastic deformation. Evidence of freuting was also present. In the tests to failure on new"cable,: described in Para. 3. I there was also evidence of the wires in the core strand having beenindented by wires from the outer strands, In a cable the outer strands are arranged in a helixaround the core strand. When tension is applied to the cable the outer strands close on the corestrand resulting in pressure between adjacent strands in the rope. In a similar way contact forcesoccur between wires within the core strand. Forces at contact between strands also arise due to thecable passing around a pulley, the most heavily loaded strand being the inner strand bearingagainst the pulley,
A theoretical analysis ofthe contact forces between wires ofa 7 x 7 cable was therefore carriedout by applying the theory of Ref. 7.
The following equations for this case are derived in Appendix L.
In a 7 wire strand the load in the strand is given by:
I - I, (I f 6cos I3) ... (I)/I'Whcre I, is the tensile load in the core wire and I, is the helix angle.
Similarly lotr the cable the axial load is given by:
P 0-: l), f1 0 Cos AB,) ... (2)
Whete 11, is the load in the core strand and /3, is the lay angle.
Considering now the radial force where the outer strands contact the core strand we have:
trr I cos 13 sin (39 ( - 6 Cos 1/3)
Applyiog thc generl equations in Ref. 8 for elastic contact stresses between two cylinders, anexpression for conta.t stresses between the wires of' adjoining strands has been obtained inAppendix I. !he contact stresses as a function of cable load have been calculated and the resultsare presented in Table VI.
Considering the core stiond the radial loading on the core wire exerted by an outer wire is:, 2 1,, sin' 3, in the st:,ind
d
where d is the wire diameter and L, the load in the outer wireand , . 2 R,. sin' (, in thiý cable
I)
where 1) is the strand diameter and P.. is the. load in the outer strand -.'ith the assumptions of'Appen:d::.: 1.
This leads to an expression for the contact stresses on the core wire of:
where A is a function oft he wire diameter and contact angle and may be obtained graphically fromRef. 8.
The experimentally determined failing loads of a 7 wire strand have been compared with thosepredicted from the strength of a single wire using equation (i) which assumes that all wires behaveelastically up to failure. In the same way the ultimate strength of each of two cables has beenpredicted from the measured failing load for a single strand. All these results are presented in TableVilla which shows that there is reasonabhe agreement between predicted and measured values ofultimate strength.
6!I
i "
lests were also conducted on cables in which the core strand had been cut. The predictedfailing load in this case is:
P = 6 V,, Cos ,,
assuming that all the outer strands carry equal tensile loads. The test results are compared with thepredicted values in fable VIlIb.
5. DISCUSSION
5.1 Historical12 With the limited documentation available an attempt has been made to piece together thehistory of the Auster rudder control circuit.
[he Auster was the product of laylorcraft Aeroplanes (England) L.td. a company formedabout 1940 to manufact Lire the American Tavlorcraft light cabin monoplane under licence. Theaircraft was used during t he war as a light utility and observation aeroplane. The company laterbecame Auster Aircraft L.td. It is presumed that the rudder control circuit was originally designedwith an American cable to MII.-C-1511, probably a 2.38 mm (3,32 in.) diameter cable of 7 x 7construction and an ultimate breaking strengt h of 4.09k N (920 lbf). (This was the cable the Belgian I
authorities used as a replacement for the British cable in 1949 and reported no further defects in1961). [he nearest British cable would have been the 10cwt. (4,98kN) 7 x 14cable of 3.05 (0.120in.) diameter to BS.S. W2 (not preformed: W9 did not appear till 1946).
In 1945 duc to failure of cables then in use (presumably the 7 x 14 Britishcable) British Ropescarried otit a series of testS using an oscillator to reproduce the hammering and conse luentabrasioi and fraying of the cable on pulleys. The hammering was due to the slipstream over therudder. (para 2.2). he conclusions reached in these tests was that a 7 x 7cable was more resistantto abrasion than the 7 x 14 due to the larger diameter of the wire. 7 x 7 cables were thereforeadopted. In 1952 anot her "crop of troubles" was experienced resulting in a further series of tests byBritish Ropes, in this case comparative fatigue tests. I he existing 7 x 7cable was compared with "aconiparable American' cable" and a 7 x 7 cable "manufactured to a new technique", (probably
pref.rnmed as in W9), [he new 7 x 7 cable had a life 2'.: times the American cable and 5 times theexisting 7 x 7 cable. This new 7 x 7 cable subsequently became Auster Standard .Il 264 and wasadopted for all Austers and is one of the cables which is the subject of this investigation.
One of t lie ot her cables investigated was of 7 x 14construction and this would appear to be the
result of I).C.A. Air Navigation Order which reqiestLd replacement of all 7 x 7 cables with 7x 14or 7 x 19 construction, (Ref. 9).
5.2 Cables
('able of 7 x 14constrtiction is more flexible than 7 x 7cable and hence has higher resistance tohatigue. It follows that the cable of 7 x 19 construction is superior to both the 7 x 14 and the 7 x 7giver similar conditions and materials. The 7 x 19 cable. to MI 1.-C5425 is 50% stronger (static
tensile strength) for the same diameter as the 7 x 7 and 7 x 14 and is superior in fatigue to the cablemade to British Standards (See Refs. I0 and II).
[he investigation revealed that the cable of 7 x 14 construction was an inherently unstable
configuratio,; prone to internal abrasion and a tendency to ovality. l)ifficulty was experienced in
service in checking the uniform diameter of the cable witha micrometer because of ovality of up to
0. 15 mm (0.(),6 in.). The tendency to instability is well illustrated in Fig. 2, where a length of 7 x 14
cable has been set in Araldite and the ends of 'he cable polished to show the wire layout in the
strands. thc mobile four wire core is adequately illustrated leading to a variety of other than
circalar strand shapes. ['he comparatively orderly arrangement of 7 x 7 and 7 x 19construction isshown in the sketches in Fig. I.
It may be of interest to note that the daughtsman who prepared these sketches was unable tofind any illuNiration of 7 x 14 cable despite a thorough search of references and the literature onaircraft and commercial cables. [here was also no mention of 7 x 14 cable except in the BritishStandards rciated to aircraft cables.
The comparative fatigue tests on standard and nylon covered cable (5 cwt. (2.49kN)capacity7 x 7 construction) on steel pulleys demonstrated the superiority of the covered cable, 2.7 times the
endurance of the standard cable. However, the results using an aircraft pulley (Micarta material)
7
were inconclusive due to the limited number of specimens available at that time. It was noted thatthe nylon jacket tended to interlock the broken strands o, the .;.ble and thus prevent total failureunless the failure was entirely at one cross section. One se-rious disadvantage of the nylon coveredcable is the difficulty in detecting broken wires, an important azpect of maintenance inspection in Nservice.
Other characteristics noted were the tendency to local bending' the cable at the site of cracksin the nylon cover and the increased resistance to bending ca):- u by the nylon cover on smalldiameter cable.
5.3 PulleysThe existing "sheave ratio" (Pulley diameter, cable diameter) for the Auster rudder circuit is
11.8 for the 31.75 mm (1.25 in.) diameter pulley and the 7 x 7 cable. If this pulley was the samediameter in the American design then the sheave ratio using the MIL-C-151I cable of 2.38 mm(3:32 in.) diameter would have been 13.3. For a satisfactory fatigue performance for 7 x 19galvanised cable loaded to 20% of its breaking strength Ref. 12 recommends a minimum sheaveratio of' 16, and states "less than 16 rope diameters falls within a critical region in which cable life isrelatively low". Reference 13 recommends a sheave ratio of 18 for 7 x 19 galvanised and stainless,ables and a ratio of 28 for 7 x 7 cables.
In Ref 14 F.T. Hill states "A minimum pulley diameter is suggested by the BritishAirworthiness Authorities as not less than 20 times the diameter of the cable".
It would seem that sufficient information was available at that time to enable reasonablesheave ratios to he specified, although the figure of 11.8 could possibly have been condoned on thebasis of the small wrap angle of 18'. Again, in the elevator circuit a 57.15mm (2.25 in.) diameterpulley is fitted apparently to accommodate a larger wrap angle. There seems to be littlejustification for this as Ref. 15 finds there is no significant varation in fatigue life above a wrapangle of 200.
5.4 ('able StandardsThe relevant British Standards for aircraft cables at the time were: -
6W2 (Sept. 1946) Steel wire rope and straining cords (not preformed)W9 (Sept. 1946) Preformed steel wire rope.WIO Non corrodible steel wire rope (not preformed)W II (1946) Preformed non corrodible steel wire rope.
The American standards were:MIIL-C-151 I (Nov. (1949) ('able: steel (carbon) flexible, preformed.MII.-C-5424 (Aug. 1948) Cable: steel (corrosion resisting) flexible preformed for aeronauticaluse).
The specification drawn up by Auster Aircraft for 10 cwt. (4.98 kN) cable called for wire inaccordance with BSS W9.
In assessing the relative merits of the various cables it is difficult to make a direct comparisonbecause of the differences of so-called equivalent cables. The British method of designation of thecable is by ultimate breaking load whereas the American system is by cable diameter. If theAmerican and British cables happen to have the samr' breaking load then the cor struction may bedifferent. For example Reference 10 finds that the cable to MIL-C-5424 is superior to the Britishcable but this finding is qual;fied by the fact that the tests were carried out over the same diameterpulleys for cables for cables of different diameters, viz.:...18mm (0.125in.)and 3.64mm(0.143in.) ard 15 cwt. (7.47 k N) capacity. Generally, the only obvious differences between the Americanan i Brii;sh specifications are:
(i) The American specification calls for an endurance test.(ii) The American specification calls for lubrication of the cable during manufacture.
The Auster specification, incidentally, called for an endurance test of 2.400 cycles with thecable loaded to I 3 of the breaking load and a sheave ratio of over 20.
If we now examine the Standards for cables in the Auster category we find the followingcomparison:
8
Construction Diameter Min. Specificationsmm (inches) Breaking Load kN (Ib)
7 x 7 2.38 4.09(920) (MIL-C-1511(0.094) (M IL-C-54242.69
7 x 7 (0.106) 4.98 (1,120) Auster JB 2643.05
*7 x 14 (0.120) 4.98 (1,120) (BS W9! (as W1II
3.187 x 19 (0.125) 7.83 (1,760) MIL-C-5424 (1957)
7 x 19 (0.125) 8.90 (2,000) MIL-C-1511 (1948)
3.81*7 x 19 (0.150) 7.48 (1,680) B.S.W9- WII
* Also available not preformed BS W2 and WIO.
6. CONCLUSIONS
6.1 Cables
The performance of the 3.18 mm ('I/ in.) diameter cable of 7 x 19construction to MIL-C-1511or MI1.-C-5424 is superior to cables of 7 x 7 or 7 x 14 construction.
6.2 Nylon covered cables
No conclusion is possible on the performance of the nylon covered cable due to the limitednumber of specimens available. However, inspection for broken wires is likely to be a majorproblem for this type'of cable.
6.3 PulleysPulley diameters should be as large as practicable and at least 20 times the cable diameters.
6.4 Rudder control circuit
6.4.1 Rudder limit stopThe rudder limit stop should be situated at the pedal rather than at the rudder horn. Many
aircraft later than the Auster feature stops at the pedal as well as on the control surface itself.
6.4.2 Circuit tensioningThe rudder control circuit needs to be "closed" and tensioned. (Ref. 16)
6.4.3 Fairleads
More direct routing of the cable (particularly at the fuselage exit) is required to avoidabrasion due to fairleads. Protective covering over exposed cables in the cockpit area aredesirable.
7. REVIEW OF STANDARDS AND RELATED INVESTIGATIONSWith the passage of time some of the findings and recommendations from this investigation
have been over'aken by the updating of standards in the light of experience, increasingseverity ofoperating conditions and improvements in manufacturing techniques. For example theInternational Organisation for Standardisation (ISO) has played an increasingly important role inthe formulation of standards through Committee ISO/TC 20 (Aircraft and Space Vehicles).
In 1957 ISO/TC 20 had asked the Italian Member Body to draw up a proposal on theinternational standardization of pulleys for flight controls. This proposal was based on a revisionof the American standards for pulleys at that time, AN 219. AN 220 and AN 221 (now MS 20219,MS 20220 and MS 20221) where it was permitted to use several cable diameters for a given pulleydiameter and vice versa e.g. M.S. 20220 (Ref. 17) for cable diameters of 3.18 mm( /K in.). 3.97mm(5/32 in.) and 4.76 mm (3/16 in.) permits the use of pulley diameters 31.88 mm (1.255 in), 63.63
9
-L .. ....
mm (2.505 in.), 95.38 mm (3.755 in.) and 127.13mm (5.005 in.). The design parameters are thepulley maximum operating loads and the cable maximum operating loads and no reference ismade to the minimum sheave ratio. Thus it is possible to specify a pulley /cable combination with asheave ratio of less than 10.
Meanwhile, in 1966. British Civil Airworthiness Requirements (Ref. 18) laid down rules forcontrol system installations and gave recommendations for pulley sizes. This was presented ingraphical form with the number of wires in the cable as abscissa and the sheave ratio as theordinate and a family of curves with the sheave ratio increasing for a given cable according to theload (expressed as a percentage of the breaking strength) in the cable. Within practical limits thisstandard has set a sheave ratio of 20 or above.
In Reference 19(1971) the U. K.. commenting on the Italian proposals and other internationalinvestigations, pointed out that the U.S. were still discussing pulley standardisation and plannedto conduct additiona! tests. The U.K. recommended that one cable should be used for two pulleysizes, one with a minimum sheave ratio of 25 to be used where space was limited and the other withan ideal sheave ratio of 40 for use wherever possible. The Italian Member Body was again invitedto recommence a study of aeronautical pulleys and so far as can be ascertained no ISO standard[-as yet been agreed upon.
7.1 ('able Stmndards
Of the British Standards issued in 1946. viz. 6W2, W9, WI0. and WI I, 6WE and WI0 wererendered obsolescent in 1964 because the S.B.A.C. indicated a preference for preformed cables.W9 was replaced by 2W9 in 1965 and 2WI I superseded WI I in l;67. These two specificationsrecognised that "there has been a marked increase in the severity of conditions under whichflexible wire ropes operate in aircraft flying control systems", and introduced correspondingimprovements. Lubrication during manufacture was introduced (U.S. practice), the wire fromwhich the rope was made was more fully specified, dimensional tolerances and ranges of tensilestrength were specified. The issue of British Standard W12 in 1968 showed the effects of I.S.O.with :he in.roduction of the specification of the cable by diameter (U.S. practice) instead of bybreaking strength. lVhp cable of 7 x 14 construction was discontinued.
W 12 was followed by W 13 in 1973 specifying the corrosion resisting equivalent of W12. Thesituation can be well summarised by quoting from the Foreword to W13 viz.:
"This British Standard specifies the requirements for preformed corrosion-resisting steel wirerope to comply with ISO Recommendation R 564 'Designations, diameters and brea4kingstrengths of preformed stranded steel cables for aircraft controls' and International Standard ISO2020 'Technical Specification for flexible steel wire rope for aircraft controls'.
ISO, R 564 specifies the dian!,ter, construction and minimum breaking strength of the rope,all of which are in accordance with RgCommendation Nu,. 3310ofl'Associatiou Internationale desConstructeurs de Materiel Aerospatia!e .'A.I.C.M.A.) and with the United States MilitarySpecification MII.-C-5424A. Sizes of rope. larger than 6.4 mm (,4 in.) diameter, though includedin M I LC-5424A. are seldom used in mode: n aircraft, and have been omitted from this standard".
Recapitulating. it is int&estingto note that in 1965 in 2W9 a sentence inthe Foreword stated"An endurance test is being formulated and will be added to the specification by amendment assoon as possible". In 1973, eight years later, the same statement appears in the F-oreword of W13.Evidently, some difficulty was being experienced in the formulation of an endnirance test.Moreover, in 1969, at the ISO meeting, the U.K. and French delegates were charged with theresponsibility of producing recommendations for an endurance test. Investigations on this matterhad been in progress for some time and a test programme designed to compare the scatter ofresultsbetween a proposed U.K. method and the U.S. MI I.-Spec. method showed a considerable scatterbetween three nominally identical machines built to the MIL-Spec (Ref. 20).
The issue of the ISO Technical Specification for flexible steel wire ropes for aircraft controlsISO 2020 shows that the problem of the endurance test has still not been resolved. A footnote tothe specification states: p
"While awaiting the publication of an ISO test ,rocedure --- an endurance test can be carrieddout in accordance with a relevant national specification". The United States, incidentally, hasexpressed its disapproval of ISO 2020.
If we now turn to the American scene we find that the U.S. Military Specifications MIL-C-
10
- . -
X
151 1 (1949 and M IL-C-5424 (1949) have continued through to 1973 witsh a few minor amendmentssuch as specification of the chemical composition of the steel, wire tolerances and tensile strengths.
In IS73 Mli,-W-83420 was issued zuperseding MIL-C-1511 aii, 5424 and combining in onespecification carbon steel and corrosion resisting steel cables and their nylon jacketed equivalents.I-is specification is now entitled "wire rope", flexible instead of "cable" flexible.
7.1.1 Nylon covered cablesBecause of'reports of excessive wear on control cables in F-5 and T-38 aircraft extensive tests
on nylon covered cables were carried out by Wright Patterson Air Force Base in 1967-68. Thenylon cover, or jacketing, is extruded over the cable to completely enclose the cable with aprotective coating. The cables tested were nylon covered stainless steel cables to MIL-C-5424 andtests were made at normal temperature and ai -40°C(-4.00 F). (Ref. 2i). The results of these tests"showed that the life of the cables was significantly increased by the wear protection afforded by thenylon covering and in addition assisted in vibration damping, protection against sand, grit, fluidsand otner harmful elements. However Ref. 22. commenting on the tests, again emphasised theserious problem of cable wear detection on this nylon covered cable and states that, to date, no 14satisfactory solutions have been found to solve this problem. Reference 22 also i idicates that in the11.S. carbon steel cables are being replaced by stainless steel cables. Results o' endurance tests atlow temperature show that the stainless steel cables are far superior t,; the carbon steel product.(Ref. 23).
7.2 Pulleysl)uring the course of the ISO sponsored investigati, ,is already mc:ntioned in Paras 7 and 7.1
other significant factors in cable wear have been discovtr-d. (Ref. 23). One of these is theconsiderable w'ear sustained by a cable where it passes over a pulley. at a small wrap angle. * (This isrelevant to the Auster see paras. 2.2 and 5.3). There was a marked difference in the wire wear andfailure at pulleys in which the angle of wrap was only 15' compared with those of a wrap angle ofover 90'. It appears that the rope with the small wrap angle, due to the lack of support from thepulley groove, has a transverse scrubbing action imposed upon the wires in contact with the pulleywhich leads to abrasiont and early fatigue failure, However these findings do not appear to agrecwith the investigations in Italy (lab. Centre FIAT. Ref. 24) where it was found that cable lifedecreases with increase of wrap angle from 0" to 450.
7.2.1 Pulley grooe profile
In 1971 the United Kingdam ISO l)ocument (Ref. 19) still indicates some disagreement withI SO proposals on groove profiles and favours a groove to give maximum support to a cable and toprovide for regular proportional increases in pulley groove dimensions as the cable size increases.Some U.S. investigations in this area are described in Ref. 26.
In conclusion it seems there is still much work to be done to arrive at agreement on standardsand international acceptance of design criteria to ensure the satisfactory performance of aircraftcontrol svstems and cables.
ACKNOWIEDGEMENTS
Ihe advice and assistance of I)r. A.0. Payne in the planning of the investigation and duringcompilation of the report is gratefully acknowledged.
The author wishes to express his appreciation for the willing co-operation of A.R.L. Librarystaff in the procurement of extensive reference material.
"Thanks are also due to the Department of Transport, Air Transport Group ('ormerlyDepartment of Civil Aviation) for discussions and assistance with reference material.
*1The angle subtended, at the pulley centre, by the arc of contact of the cable.
II
S. ..... •-- " .. . .. • ... .. '= • . dz~ ii • • . .• h .. ...
R EFER ENCES
1. R.A. Vell. Preliminary report or the f'ailure of -Atster" rudder cables.C.A. patching and Aero. Research Labs.A.O. Payne Structures and Materials Tech. Merril 88 July 1960.
2. Specificat ion f'or 7 x 7. 10 cwt. cont rol ce bes X' type) AJ.!3 264.Auster Aircraft L~td.Rearsbv L~eicester. Jan. 1959I,3. Pref'ormed stec! wire rope. British Standard Specification W9.Brit ishi Standards Institution. Sept. 1946,
4. C'able: Steel (corrosion resisting). Flexible. Preformed (f'oracrona iiiical Lise). MIilitary Specification MIF.-C-5425 Anidt 1.3
5. Rudder C'ont rol Ca ble FaiIlure,I .( 'A. Aviation Safety D)igest No. 121 Dec. 1957 p. 26.
6. ('ontrol (*ab le Inr1poct ionI .('.A. Aviation Satetv D)igestMarch 19621. 11.24.
7. \VI., Starkev and /iAn A nlvsis of ('n-tical St resses andt M odeof F'ailure of wire rope.N.IA. Cress I alls. A.SM.F. Nov. 1959 pp. 307 - 3 11.
8. I'. . Seeleyv anId Ad va ICed MCI ehariics Of M teiaS.J.. Smith JIohn %Wikv\ & Sons Inc, Ne\% York, N.Y. 1952 p. 342 et seq.
9. C'ommonwealthi of Austtalia. I epartilctit of('ivil Aviation. AirNavigation Orders, Section I105,I. 3. o. 1. 5.A,.0N. P~art 105 21st August 1953.
1t). ( .R1. lar-ratt , Fatigue tests of aircraft control cables.C'ommonwealth Aircraf't Corporation Ptv. Ltd.Report AG 410) 1961.
II. (.14. Banra:c Long-term fat igue tests of control cables to Spec MI I-('-5424Commonwealt h Aircraft Corporation P.' L.Recport A6 417 196 1
12. "D ata fom aircraft control cables"American C hamn anid C'able Co.P~.6 1942.
13,.. F{. IF i kll'!i "Wire Rope Assemblies''MIachine IDesign Vol. 33 No. 16p. 88 1961.
14. 1.. I1. HIill Materials Of Aircia!t ('ons(truct ionP'itman London Ist. Uditionl.p. 129 1933.
IS, I .1. ( jod Irev [hle corrosion fat igue of' aircralft control ca bles. Fatigue testsA.H~. Fleury under service loads.lDartrey Lewis John A. Roebling's Sons Company, for Office of Scientifie
Research and IDevelopment.OSRI) 4543. NRC-IS M-439.
I16. ILetter to C'ivilI Aviation Liaison Officer. Australia H ouse fromF'. Watkin. Head of' Design D~ept., Auster Aircraf't Ltd.. Oct.I 1959.
17. Pulley, groove. flight control, aircraft U1.S. Military StandardMS 20220 Mar. 1965.
is. British C'ivil Airworthiness Requirements Chapter 1)4-8.Appendix Sub Section D)4 para. 5. Control System InstallationsFeb. 1966. 1
BIBIOG(RAPHV
I lie preparat ion al' this report has entailed a Illa'rly extensive literature search and has revealedat number of publications which, while not directly associated with this investigation may.nevertheless, be of' incidental interest to those involvecd with wire ropes.
Ihlis bibliography with the refecrences cited and the references f'rom this report should formthe basis of a reasonably comprehensive int'ormation source on wire ropes.
I. Hlaigh. HI.PWire Rope Problems. S. 'ale~s Insvitut h' a//igitteers., Provs.Vol. 52 No. 5. 1937 pp. 327 - 357.
2. Cables and ('able Terminals f'or Aircraf't, American Chain and (Cable Co. C'onn. U.S.A.1940.
3 1-114t .. Calculation of stresses inwr rpsIir 1;:' Wmire Prodlucts. Vol, 26 Sept.'
6. ole A.. Iell. R.A.. and JIohnstone W.W, Tensile and E~ndurance Tests onl preformedstanlssstelcables. Aero Research Labs. Melbourne. Structures and Materials Note 206
7. Aircraft Inspection and Repair A('43 - 13 - I Chapt. 4. Control cablesand terminals FederalAviation Agency 1965.
8. lDang, R.(i. and Steidel., R+ . Contact Stresses in Stranded C'able, Ev~perimentaI Alec/junktis.Vol. 5 May 1965 pp. 142 - 147,
9. Senior Ii .A. and Spear, .1A.N, [rndUranee! tests onl flexible wire rope for aircraft flyingcont rols, Report All) I) 000002 68 Part 1.Aer-onautical1 Inrspection D irectorate Minist ry oflTechnology U.K. Jan. 1968.
It). (ianihrell. S.C. St uidv low cycle Fatigue otf wire rope. Wiire andi Wire Products Oct. 1969 pp.127 - 1 30 (Commnnctts oin effects of pulley material onl fatigue life of 'cables).
11. Wood IHerbert I ., A surve * of* publications dealing with corrosion in wire rope. Report 71-3I.O.S, . I hie (Cat holic U niversity of' Amnerica Washing I .C, J une 1971.(A collect ion oft bothIiJournal and report literature dealing with corrosion and prevention of*corrosionl of wkire ropes. Forty-one references are cited including other suirveys).
12. Starr. I .J. ( orrosion prevention and Control in Steel wire ropes in the mineral industry..111strala.sian Co rrosion hDrgin'erinrg Nov. 1971 pp. 7 - 12.
13. Inspect ion of' Coant rol C'ables. A1irccorihim'sAN ,'11'sor[ C'icular NVo. 61. D ept, of' CivilAviation Australia Feb. 1972.
14, Hecker. Karl. On the latigue strength of steel wires. Stahldawi l:'iven Vol 18. August 1972 pp.87.3 - 88(0 (In G erma n).
I5. M achida. S., and I 11urelli. A.J Response of a strand to axial and torsional displacements.JIournal of Mechanical Frngineering Science. Vol. 15 No. 4 1973 pp. 241 - 251.
l6. Wire rape lubrication and corrosion Protect ion. Indlustrial ILuhri'afion tii nI riholiogyI Ian I-eb. 1973 pp. 7 - 12.17. P1hillips. lamies W., and Costello. George A. Contact stresses in twisted wire cables. .ournal
of Engineering Mechanics D~ivision. Proc. of Amer. Soc. of* C. Engrs. April 1973 pp. 331 -
341.
18. Australian Wire Ropes. Australian Wire Industries Newcastle n~d. (A comprehensive and upto date handbook prepared by A.Wl. f'or the guidance of' engineers, operators and ropeusers.)
19. Co~mments by the United Kingdom on D~ocument 20 N 1276 -.
Control PulleysISO TIC 20 (Secretariat 807) 1305 Nov. 1971.
20. FI.A. Senior A Technical Report covering the exarninat ion ol'threc AmericanJ.F. Stoddart type flexible steel wire cable testing mnachines.
Report No. A.Wl) 2 70 AQI)ILaboratory Ministry of' Technology Mar. 1970.
21. Perry L.. Smith Evaluation of' nvo and polyolefin Jacketed aircraft conirolca blesV Technical Report ASD-TR-68-30 W-P.A.F.B Ohio. August1968
22. W hv contitrol cabhies of* stain less steel give A merica n aircraft greatreliabhility.Wirc and Wire Products June 1969pp. 62-64
213. Perry I., Smith Breaking Stre:,gth aind Endurance lest ing of' Aircraft controlcablesTechnical Report SF.(-*FR-67-l9
24V .Sno SEFIl Wright-Patterson Al-KB. Ohio May 1907.~Endurance tests on flexible wire ropes f'or aircralt flying controls
R. Everard Report No, All) L)EV 92 66. Aeronautical InspectionD~irectorate, Ministry of' Aviation August 1966.
25. Second lDraf't proposcd by Italian Member Body f'orStandardisation of' Aircrafýit Control PulleysI SO IC 20 (Italy-16) 1276 Oct. 1971
26. Werner Gi K roggel Evaluation of' Aircraft Puilley Groove Effects on Jacketedcontrol cable li fe.I ccl. Menmo ASDI) N [I ;rM-74-lWright-Patterson A.l'.lt Ohio, August 1974,
Postal Addrless: Chief Superintendent,Aeronlkwtical Research labor101atories.P.O. Box 4.31.1MEII LB)I RN I. Victoria 3)001
-lif
APPENDIX I
by
Patricia D)iamond & Sue Vanderhorght
(i) Notation
#I Angle of lay of the axis of an outer wire of a strand to the core wire.
0B. Argle of lay of the axis of an outer strand of a cable to the core strand.
V Angle between the line of contact of outer wire and axis of core wire
D. d Diameter of strand and wire respectively, inches
T,,, P Load in outer wire and outer strand respectively. lb.
T,, P, Load in core wire and core strand respectively, lb.
T. P Load in strand and cable respectivespcl lb.
FI, Radial loading between wires at parallel wire critical region lb/in.
F, Radial force between wires at crossed wire critical region, lb.
b. Semi minor axis of ellipse of contact.
x Axial co-ordinate, inches.
y Tangential co-ordinate, inches
SCo-ordinate radially inward from cylindrical surface, inches.
A. B Terms dependent in geometry of contacting bodies.
4 Term dependent on material and geometry of.contacting bodies.
"E Modulus of elasticity, p.s.i.
M Poisson's ratio.
(, Normal stress in axial direction in core wire of strand, p.s.i.
0,. Normal stress in axial direction in outer wire of strand, p.s.i.
(,, Critical normal stress, psi. •
(i11) Analysis of stresses in a 7 x 7 cable 4
Consider six wires wound round a centre wire at helix angle , to form a strand and six strandswound round a core strand at a lay angle of `8..
The load T in a strand is given by:
T = T, + 6 T,, cos 13, ... (i)
where T, and 1,. are tensile loads in core and outer wires respectively.If wires are elastic, compatibility of strain gives:
cos (3, .1. (2)
r Cos3,I +6 cos' 3, . . . (3)
and T= T, (I + 6 cos' fl) .. (4)Similarly the load in the outer strands of the cable is given by:
P" Cos (,1+ 6 cos' (3, ''(5)
and P P, ( + 6 cos' ,)
where P. and P,, are loads in the core strand and outer strands respectively and P is the load in thecable.
"! ......'5
There are two important critical regions of contact stress in a cable subjected to a tensile force.The first of these, called the parallel wire critical region is located at the line ofcontact between thewires of the strand. Whether the regiot, is between an outer wire and core wire of a strand orbetween two outer wires is dependent on the diameter of the core wire. The critical stresses arehigher when the contact is between the outer wire and core wire of a strand (Fig. 13 (al). Thesecond critical region, called the crossed wire critical region, is located between the wires ofadjacent strands.ta) Parallel wire critical region
The most serious case of :n outer wire wrapped round the core wire results in a radial loading
•'Fp = 2 T,, sin' , 3 ... (7)
where . (L (Fig. 1.3 (N)
However the outer wire makes contact with the core wire at an angle iwhere tan =,s=,½tanf(Fig.13 (C))
Hence the contact loading per inch is given by:
F,, =- 2 I, sin' 13 cos (/13 - 0. . (8)
IT Cos* 6Sin' 1 Cos (/30- ') (9)
d1 Co f 6 cos' fl)
where v artan ( tan /1)
Contact Stresses
From Ref. H L1,,.-2 ( Q l I L].. .1 o. (10)
h A
,,A .....J h ,
where h is one hall tihe width of the rectangle area ot|contact and A is a function of the geometry ofthe contact region.
h-- v' 22 1 ,, Arr ... (13)
and d( - ) . . (14)F
The principal stresses o,, ,, :.. have their maximum Valuies at 0 0, that is, at the surface ofcontact.
(ritical Stresses
The critical normal stress, n,,, is given by substituting equations (9), (13) and (14) intoequatifn (12).
b 411! c,,s_,:/ si.- J3 cos (1.- v)]":. . •5"A ti--d' ,• ( I +- 6 cos-'• /3"1) ( -- ,
(b) Crossed Wire Critical Region
' ~ The radial force, F_, between two wires of' adjacent strands is given by:
K --FI dr To sin: /
3tan(? 9 tanf, (16)
A - "
Critical Stresses
The critical normal stress in the crossed wire critical rvgion is given by:e,., = - c, (h: A) . . . (17)
where b = ch (F, A)" (Ref. 7) ... (18)
where'Ch and ca are functions ot, the angle fP and are presented graphically on pages 356 and 357 ofRef. 8. plotted against a quantity Bi A where
B1A = (I +sin" P) + (I -sin'fi) cos2/3 3
+ (l+n j -( l-si-n.6) cos2f3 ., (19)3 3
1 ,
•o,• ~~~~~~~~~~~~~~. .. .............,• ,: :,,.••, . .. •• • . . .. . ... ,••.,•, ..
TABLE I
CABLE LOADS RESULTING FROM FLIGHT MANOEUVRES
Manoeuvre Speed - Knots Cable Load Pedal
_ _ kN (lb.) Force kN (lb.)
Straight &Level
Full L. & R. 50 0.712(160) 0.472 (106)Rudder 60 0.890 (200) 0.592 (133)Rudder 70 0,935(210) 0.623 (140)Rudder 80 0.9,9 (220) 0.654 (147)Estimated 120 1.1 (250)1 0.743 (167)
Steep TurnsL. & R, 0.312 ( 70) 0.209 ( 47)
Side Slip R -. 0.579 (130) 0.383 ( 86)1, -- 0.668 (150) 0.445 (100)
'.evel MediumTurns 0.312 ( 70) 0.209 ( 47)
Taxying with 0.445 (100) 0.298 ( 67)applicationof brake
*The load for the manoeuvre at the m,,ximum design cruising speed of 120 knots was obtained by
extrapolation.
I t
I :
TABLE I!CABLE LOADS RESULTING FROM STATIC GROUND MANOEUVRES
T]
Manoeuvre "A" j..B" Average Average PedalkN (lb.) kN (lb.) Force kN (lb.f)
Instructor applying 1.56 1.96 1.70 1.099opposite rudder to (350) (440) (385) (247)pupil
Applying parking 0.445 0.623 0.534 0.356brake (100) (140) (120) (80)
Releasing parking 0.579 0.623 0.600 0.401brake (130) (140) (135) (90)
Shifting position 0.890 0.592in seat (200) (133)
Full rudder tolimit stop against 1.56 1.037horn (350) 233
"A" and "B" were different combinations of "Instructor and Pupil"*For safety reasons this test was not made during flight.
TABLE IIIAUSTER RUDDER CABLE DESIGN PROOF LOADS
IType Pilot Effort Cable Load ReservekN (lb.) kN (lbf.) factor
1.335.5F (300) 1.962 (441) 1.9
J5K
.151,
All others
Incl. JSA 1.780 (400) 2.621 (589) 1.43J5R1
The above information was obtained from the Auster Type Record and assumes an ultimateload for the cable of 840 lb. based on a splice efficiency of 75% for the 10 cwt. cable.
tI
CC
ViIci.
-t -
KA--- N-
OW,
I
TABLE V
TENSILE PROPERTIES AND DIMENSIONS OFSINGLE WIRES
Wire Location Meas. l)ia. Max. Load Approx, Max. Stress Spec.Cable in strand mm (inch) kN (Ib) 0.2% P.S Wire
kPa (ps.i.) kPa (p.s.i.) Dia.
('ore of 'entre 0.325 (0.0128) 0.167 1.722,560 2.039,440 0.33 (0.013)(Core of outer 0.300 (0.0118) (37.5) (250.000) (296,000) 0.305 (0.012)
7 x 7 Outer of centre 0.305 (0.012) 0.125 1,894,750 2,032.550 0.305 (0.12)Outer of outer 0.279 (0.011) (28.0( (275,000) (295.000) 0.2K5 (0.0112)
Core of centre 0.216 (t).(Xis) 0.076 1.722.500 2,067,000 0.203Core of outer 0.216 (0.0085) (17.0) (250,000) (300,000) (0.(X)8)
7 x 14 Outer o1. centre 0.203 (0.00q) 0.065 1,825.850 1,99H,100 0.229Outer of outer 0.203 (0(.0)) (14.5) (265.00)) (290.000) (u. '%Y)
Core of centre 0.295 (0.0116) 0.142 1,79140X) 2.067,000(ore of outer 0.229 (0.(X)9) (32.0) (260.000) (300.000)
7 x 19 2nd row. of centre 0.229 (0.(X)9) Not2nd row of ot;.er 0.216 tO.tX)85) SpecifiedOuter of centre 0.216 (0A()85) 0.076 2.135.9(X) 2.342.600Outer of outer 0.203 ((.(X)95) (17.0) (01 ),0()00 (340,0(X))
I
- - : r-'.
IIN
- C O*• -
,,.1
IP
u t=
V3~ 00*00 0
-~ __<
TABLE VII
LOADS AND STRESSES(a) PARALLEL WIRE CRITICAL REGION
o cr T PPascal (psi) N. (Ib) N (Ib)
-6.59 x 10'(-9.57 x 10') 962.0 (216,09) 6008(1350)-1.52 x 10'
(-2.2 x I10) 8.18(1.8385) 51.1 (11.486)-1.65 x 10'(-2.4 x 10) 8.55 (1.9203) 53.4 (11.997)
(b) CROSSED WIRE CRITICAL REEGION
o cr T PPascal (psi) N (Ib) N (Ib)
-1.79 x IOW(-2.6 x IO() 8793 (197.6) 6008(1350)-1.52 x 10'
(-2.2 x 10) 0.549 0.1233 3.748 (0.8423)- 1.65 x 10'(-2.4 x IOL) 0,713 0.1602 4,870 (1.0943)
00
000
0 00 0o
STRUC. NOTE 424FIG. 1
' Ih
7x7
I.i
7 19
AE O4
I
I , ARRANGEMENT OF WIRES IN 7 X 7 CABLE AND 7 X 19 CABLEL~. __________________..-
STRUC. NOTE 424FIG. 2
(ýI AS ul t 01c n
(b) Polished at the other cnd
ARRANGEMENT OF WI RES IN A 4D8 kN (10 CWT) 7 x 14 CABLE TO BSW 9(Set in araldite)
STRUC. NOTE 424Cable deformations FIG. 3
6.4 mm
[~C~F 5~---.-~%~'Stbd cable366mm51mmHorn, attachment end
Abrasion Starts
27 m Cable JA 2393X279mm6 m Port cable
(11(1346m Horn. attachment end
6.4 mm
(1/4
267 mm - Port cable(10.5')Rudder pedal attachment end
318 mm(12.5")
CABLES ON VHD
Corrosion 38 mm (1.5"1) long.i i Cable JA 2393X
(14")
~~ ' orrosion 25.4 mm (1.0"1) long
305mmCable JA 2394X
__254 mm
318 mm- -
(12.5") Mx. abrasion measured 0.05 mm (0.002") on dial
CABLES FROM VHC.
1L. i
STRUC. NOTE 424FIGS. 4 & 5
FIG. 4 CABLE FAILURE IN VHA SHOWING ABRASION OF STRANDS.
FS
FIG. 5 STRAND FAILURE IN VHB SHOWING DAMAGE BETWEEN WIRES.
1.o
STRUC. NOTE 424FIG. 6
iL
:1I
Neg. no. 5409
INTERNAL WIRE DAMAGE IN CORE STRAND VHE
STRUC. NOTE 424 1
FIG. 7 FAILURE OF CORE- sTF'8AND WIRES.
(a)
"--tom
Worn and fretted cable 7 x 14removed two fiymig hours after a C. of A. inspection
FIG. 8 (VISIBLE DAMAGED WIRES PRIOR TO UNRAVELLING)
STRUC. NOTE 424FIG. 9
1'2.07(0.3) E
E 2
1.72 .... 01(0.25)
- 1.03 C4 ,-(10.15) .. . ... . ... -,
/ ~E~
0.69(0.1) E . ..-
0.34(0.05)
0 .01 .02 .03 .04 .05Strain
STRESS-STRAIN CURVES FOR TWO WIRES OF A 10 CWT (498 kN)7 X 7 GALVANIZED CABLE.
3/
STRUC. NOTE 424FIG. 10
Abraded in laboratoryu 7 x 14 Aircraft cablesA 7 x 7 Aircraft cables
6.23 _ I L11400)
6.34 _
11200)
4.45 ___ __(1000)
z. 3.5$
(800)
Measured dia reductionof 0.203 mm (0.008")
2.67 -- ... _ _(600) Core strand load + max A '1
manoeuvre load
1.78(400)
Core strand failing load
0.89 _ _,(200)
0 20 40 60 80 100
% Reduction of area by abrasion
VARIATION OF FAILING LOAD WITH REDUCTION IN AREA OF CABLE.
(Extracted from ref. 1) 32-
m, m *tt. . • • - ft ~ m • .. .. ... . .. ..- - • , -. .
STRUC. NOTE 424IOFIG. 11
(8.00) Abraded in lab. Abraded in service(100o nil 9 x. 9aircraft cables0 a 7 x14 to
(1200)
S(1000) 71
(1200)0
(6000)X _7x1
(200)7x7
6.893- *, (200)
0.0(2 (0104 0.5s .0()-2()03(2
STRUC. NOTE 424FIG. 12
0. 15 mm (0.006") wear line
wire dia. 0.28 mm (0,011 H"cable dia. 2.59 mm (0,102")
0.15 mm (0.006") wear line.
7 x 14
wire dia. 0.23 mm (0.009")cable dia. 2.90 mm (0.114")
0.15 mm (0.006") wear line
7 x19
wire dia. 0.20 mm (0.008")cable dia. 3.35 mm (0.132")
WEAR ON INDIVIDUAL WIRES OF VARIOUS CABLES.
STRUC. NOTE 424FIG. 13
Point of wire contact
Radial interstrand loading
Core strand wire
b)dIlei
/ *-. * Lay of extreme fibre of a wire
______. Line of contact betweenouter and core strands
Inside
wirew,,o ' •",,,
SDevelopment of wires
'and strands
d 7.1-5d
GEOMETRY OF 7 X 7 CABLE.
* U A6, -
DISTRIBUTION
Copy No.AUSTRALIA
DEPARTMENT OF DEFENCE
Central OMce
Chief Defence Scientist IExecutive Controller ADSS 2Superintendent -Defence Science Administration 3Superintendent -Assistant to Executive Controller ADSS 4Controller -- Service Laboratories and Trials
Division 5Controller -. Military Studies and Operational
Analysis Division 6Controller -Programme Pianrý,g and Policy Division 7Central Library 8S.T..B. 9J. 1. D. 10
Aeronautical Research LaboratoriesChief Superintendent IISuperintendent Structures Division 12Structures Divisional File 13M.B. Benoy ) 14R.A. Fell ) Co-authors 15P.H. Townshend ) 16C.A. Patching 17A.O. Payne 18Library 19
Central Studies EstablishmentLibrary 20
Materials Research Laboratories
Library, Victoria 21l~ibrary, New South Wales 22Library, South Australia 23
Weapons Research EstablishmentLibrary 24
Air OfficeD. Air Eng 25Air Force Scientific Adviser 26Library, Engineering (AMTS) Canberra 27SJ.S.O., Support Command, H.Q. 28Library, A.R.D.U., Laverton 29SQN. L[DR. Brock Bryce, Air Eng. 5B 30-40
Army Office
Army Scientific Adviser 41Mr. Gardiner, Engineering Design Establishment 42Library, Engineering Design Establishment 43The Bridges Library, Royal Military College 44U.S. Standardisation Group 45
Navy Office
Naval Scientific Adviser 46Superintendent, R.A.N.R.L. 47
DEPARTMENT OF MANUFACTURING INDUSTRY
Government Aircraft Factory
Library 48-49
DEPARTMENT OF TRANSPORT
AIR TRANSPORT GROUP
Director - General/Library 50-80Mr. P.S. Langford 81
QANTASLibrary 82
TRANS-AUSTRALIA AIRLINES
Library 83
ANSETT AIRLINES OF AUSTRALIA
Library 84
GLIDING FEDERATION OF AUSTRALIAEssendon Airport 85-105
STATUTORY AUTHORITIES AND PkIVATE INDUSTRY
Hawker de Havilland Pty. Ltd.Hawker de Havilland Pty. Ltd. (Tech. Librarian) Bankstown 106-107Hawker de Havilland Pty. Ltd. (Manager) Lidcombe 108Commonwealth Aircraft CorporationCommonwealth Aircraft Corporation (Manager) 109Commonwealth Aircraft Corporation (Manager of Engineering) 110Rolls-Royce of Australia Pty. Ltd.Mr. Oliver IH]Library of New South Wales,Acquisition Librarian 112Edmund Schneider Ltd., South Australia 113
Universities
Adelaide Barr Smith Library 114Canberra Australian National Library 115La Trobe Library 116Melbourne Library, Engineering School 117Monash Library 118Newcastle Library 119New England Library 120New South Wales Library, School of Mechanical
Engineering 121Queensland Library 122James Cook (QId.) Library 123Sydney Professor G.A. Bird, Aeronautics 124Tasmania Library, Engineering Department 125West Australia Library 126Royal Melbourne Institute of TechnologyLibrary 127
CANADANational Research Council of Canada, Library 128-129
II
* -. . . . .. . -. . ". ..
U niversities
McGill Library 130Toronto Institute of Aerophysics 131C.A.A.R.C. Co-ordinator Structures - Dr. G.R. Cowper 132
FRANCE
A.G.A.R.D. Library 133O.N.E.R,A. 134Service de Documentation et d'lnformation 135
GERMANY
Z.LD.l. 136-137
INDIA
Ministry of Defence, Aero Development Est. 138Department of Civil Aviation, Director 139Hindustan Aeronautics Ltd, Library 140Hindustan Aeronautics Ltd, Helicopter Factory, Library 141Indian Institute of Science, Library 142Indian Institute of Technology, Library 143National Aeronautical Laboratory, Director 144-145C.A.A.R.C. Co-ordinator Structures
Professor P.N. Murthy 146-150C.A.R.C. Co-ordinator Materials 0
D)r. S. Ramaseshan 151
ISRAEL
Technion Israel Institute of Technology, Professor J. Singer 152
ITALY
Aerotcchnica Editor 153
JAPAN
National Aerospace Laboratory, Library 154
U niversities
lohuku (Sendai) library 155Tokyo Institute of Space & Aero. Science 156
NETHERLANDSN.L.R. Director, Amsterdam 157Central Technical Institute, T.N.O. Appledorn 158
NEW ZEALAND
Air Department, R.N.Z.A.F. Aero. Documents Section 159Department of Civil Aviation. Library 160University of Canterbury. Library 161
SWEDEN
Aeronautical Research Institute 162Kung. Tekniska Hogscholens 163Library of Chalmers Institute of Technology, Gothenburg 163S.A.A.B. Linkoping, Library 165S.F.A.B. Troilbatten 166
UNITED KINGDOMDepartment of Manufacturing Industry,
Senior Representative 167Defence Research Information Centre 168-169Aeronautical Research Council, N.P.L.. Secretary 170Royal Aircraft Establishment, Library, Farnborough 171-172Royal Aircraft Establishment, Library, Bedford 173Aircraft & Armament Experimental Establishment 174National Physical Labs., Aero. Divn. - Superintendent 175British librarv, Science Reference Library
Holborn I)ivn. 176British Library, Lending Division, Boston Spa 177C.A.A.R.C. Co-ordinator Structures
Mr. A.J. Sobey. R.AE. 178
IndustryAircraft Research Association. Librq,'y Bedford 179
Rolls Royce (1971) Ltd, Aero. [)ivn. Chief Librarian. Derby 180Rolls Royce (1971) ltd, 1i istol Siddeley Div. T.R. & 1.,
I ibrarv Services 181Aircraft Companies
Hlawker Siddeley Aviation ltd., !3rough 182Hlawker Siddeley Aviation lI.td., (ircengate 183Hawker Siddeley Aviation Ltd., Kingston U pon Thames 184Hawker Siddeley Aviation ltd., iHatfield 185British Aircraft Corporation ILtd.
Commcrcial A c. Divn. FiltonBritish Aircraft Corporation Ltd,
Military A: c. Preston 186British Aircraft Corporation ltd,
Commercial Aviation I)ivn. Weybridge 187British Ilovercraft Corporation ltd., E. Cowes 188Fairy E'nginecring I.td, Hydraulic l.ivn, tleston 189Short Biros. & Harland, Queens Island, Belfast 190Westland Helicopters ltd, Yeovil 200
Universities
Bristol Engineering Department. Library 201Cambridge Lngineering Department, Library 202Liverpool Fluid Mechanics D)epartment,
Prolessor .1.H. Preston 203London Queens College, Professor A.D. Young 204Manchester Professor of Applied Mathematics 205Nottingham library 206Shelfield I)epartment of Fuel Technology.
ILibrary 207Southampton Library 208Strathclyde Glasgow. Professor D.C. Pack 209
INTERNAIIONAIL COMMITTEE OF AERONAUTICAL FATIGUE 210-232
UNITED STATES OF AMERICACounseller l)efence ScienceAerospace Research Labs.,
Wright Patterson A.F.B. Ohio 233Airforce Flight Dynamics Lab.
Wright Patterson, A.F.B. Ohio 234Arnold Engineering Development Center,
€ I." .. '_ - - -. 7-,-
Arnold Airforce Station, Itennessee 235National Technical Information Service.
Springfield 236Library of Congress, Gift & Exchange Decpt.
Washington D.C. 237Library, National Bureau of' Standards,
Washington D.C. 238iiN.A.S.A. Scientific & Information F-acility,
College Park 239N.A.S.A. Research Center. Cleveland. Mr. S. Leiblein 240American Institute of' Aeronautics & Astronautics 241Applied Mechanics Reviews 242Allis Chalmers Inc. Milwaukee, D)irector 243 HBoeing Co, Seattle, Head Office 244Boeing Corn Seattle, Industrial Plroductio.,. Div;.ion 245 i~Cessna Aircraft Co': Mr. l).W. Mallinee Executive Eng. 246General Electric, West I v',n, Mass.
'Xircraft Engine Group 247
Palo Alto orr 248t
Mc'onnell Doga Ioprthca S. Lois Diihrtor 257
Uloitd Aicrf Corp.nt Fpt Haitrard 258
Iarioan Depiarimint of' Cinil & g Appie Mah.Bronofuestso A.ison Lib(rari y 253
CoaniHorkias Iouet ihtGeerlibar 260Ioll mino a I i rarv 265
U iversitties.olSi.& ec.
NC orkelNcA YoirkarvrAro as 2564Notrnel Ithaca Librr ar 2657Florinda on~iet Iept iibrary 266
Stanrd I' Dipvrsion of Fi.&Aeroauics, Libaryh268(ic. Wshigto Professor I-'ruedentier 269
WiJohnHpin Sras I~ prt t Memorial26IliosLibrar'ý 270
Intttsofa Teaehnologyci &Teh.BrookiGn Kotc. Aekro.las. irr 262
Massachuset ts I ibrar v 274
Spaes okEhaý 27524
Nor a eLirr 6
Prnctn 'fiav 6
