AD-A122 IIMANUFACTUJRE OF A HOT.WIRE TARGET ELEMENT FOR A CLOD 1/LIOU ID WATER CONTENT METER(U) AERONAUTICAL RESEARCHLARSMMEL ROURNE (AUSTRALIA) N 0REPACHOL MAR 82

UNCLASSIFIED ARL MEC H-ENS -M41 A/ 2/ .

flE~h E jfflfllfl_ ET.

132.

1.1 ~1.8

iii1 *= 1

MICROCOPY RESOLUTION TEST CHART

NATIONAL BUREAU OF STANDARDS- 1963-A

DEPARTMENT OF DEFENCE

DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION

AERONAUTICAL RESEARCH LABORATORIES

MELBOURNE, VICTORIA

Mschaical Eqngiering Technical tHorandum 412

MANUFACTURE OF A HOT WIRE TARGET ELEMENT FOR ACLOUD LIeCiIC IATER CONTENT METER

N;.J. RRO=

Apved - or Public Relase

D

©s COMMONWEALTH OF AUSTRALIA 1981 18

UNCLASSIFIED

DEPARTMENT OF DEFENCE AR-002-348

DEFENCE SCIENCE AID TECHNOLOGY ORGANISATION

AERONAUTICAL RESEARCH LABORATORIES

Mechanical Engineering Technical Memorandum 412

MANUFACTURE OF A HOT WIRE TARGET ELEMENT FOR A

CLOUD LIQUID WATER CONTENT METER

Neil 3. REPACHOLI

SUMMARY

An Instrument has been developed to measure the liquid watercontent of artificially generated and naturally occurring icing cloudsduring ground and flight anti-icing trials of the Nomad N24 aircraft.

This report describes the techniques employed in the manufactureof the hot wire target elements used in the liquid water contentmeter. S

POSTJ ADDRESS: ChLef Superintenoent, Aeronautical Research Laboratories,P.O. Box 4331, Melbourne, Victoria, 3001, Australia.

CONTETS

PAGE NO.

1. INTRODUCTION 1

2. DESCRIPTION OF THE HOT WIRE TARGET PROBE 1

3. MANUFACTURING PROCEDURE FOR THE TARGET PROBES 4

3.1 Insulation between coil and tubing 4

3.2 Slave winding - First half 4

3.3 Master winding S

3.4 Slave winding - Second half 5

3.5 Protective external coating S

3.6 Earth connection for master and slave windings 7

3.7 Probe connector assembly 7

4. PROBE REPLACEMENT 12

5. CONCLUSION 12

DISTRIBUTZON

DOCUMENT CONTROL DATA

Accession Fr

NTIS GRA&IDTIC TAB yUnannounced 0Justificatio

Distribution/

Availability Codes__.

Avail and/or .x S

1. INTRODUCTION

Anti-icing trials were conducted in 1979 with a Nomad 324aircraft, (see Atkins, 19811. In-flight measurements were requiredof the liquid water content in the airstream entering the engines whenoperating in natural or in artificially - generated icing cloudconditions.

While developinq instrumentation to measure airstream liquidwater content (MC), some problems were encountered in the manufactureof suitable hot-wire target probes. The probes had to be robust,easily replaced and, for repeatability of results, the response ofindividual probes to airstream LWC was required to be very similar.Full details of the LWC instrumentation are given in Skidore et al.,(1982). The method employed to manufacture the probes is describedin this Report.

2. DESCRIPTION OF THE HOT-WIRE TARGET PROBE

The hot wire target probe was based on a design, shown in

figure 1, developed by the Commonwealth Scientific and Industrial Research

Organisation, (CSIRO) (see King et al. (1978)). The airstream LC ismeasured by using, as a target, a constant temperature hot-wire elementwhich forms one arm of a Wheatstone Bridge circuit. The power requiredto maintain the wire at a constant temperature, thereby balancing the

heat transfer loss from the wire to the airstream, gives a measure ofthe LWC. However, in order to meet Department of Transport (DOT)standard airworthiness acceptability tests, further development ofthe CSIRO probe was necessary. Operation of the UsC sensing head and

metering instrumentation under the following conditions was requiredby DOT:.

a) ENVIRONMMIALOperating temperature: -350C to +400CRelative Hunidity: up to 100% with heavy condensationVibration: a power spectral density of

O.01g3/Hz in the bandwidth of0 to 2 KHz.

Altitude: 0 - 20,000 feet.

b) MECHANICALThe equipment must remain secure in the event of a

10 g deceleration and be as small as practicable.

The CSIRO probe uses a double ended configuration (figure 1)with electrical connections beina taken out through simple plugs of anon-aiaft design. This probe was difficult to remove from the housingand ice build 4p tended to occur not only on the unheated Araldite endfillets but ulso on the "flying leads" around the outside of the probe

FIG.1 csIRO DESIGNED TARGET ELEMENT 4

FIG.2 ARL DESIGNED TARGET ELEMENT

-4-

housin. These leads were needed to electrically connect the outboardplug.

To overcome these problems a ncw design based on a singleended configuration was adopted. This is shown in figure 2. It allowed

elimination of the outboard plug, termination of all windings in arecessed Cannon connector and provided a simple means of support forthe outboard end of the probe.

The actual target consists of a coil of double enamelledcopper wire 0.102 mm in diameter (42 STAG), closely wound on a 1.6 mmdiameter cupro-nickel supporting tube of 0.16 mm wall thickness. Themain element was 38 mm long with a 19 mm slave or guard winding ateither end. The purpose of the slave windings was to minimise axialheat losses from the target element. Nominal resistances were 3.75 ohmsfor the target element and 1.87 ohms for each slave winding.

This design was more robust than the CSIRO probe, interchangeof probe elements was easier and most of the areas causing ice buildupwere removed. In addition, it permitted the insertion of a smallthermocouple into the bore of the support tube to provide a measure ofthe preset element winding temperature during calibration.

3. MANUFACTURING PROCEDURE FOIP THE TARGET PROBES

Using 1.6 mm diameter cupro-nickel tubing and 0.102 (42 SWG)diameter double enamelled copper wire, the recommended procedure formanufacturing the probe and probe head assemblies is as follows.

3.1 Insulation between coil and tubing

The cupro-nickel tubing forns part of the earth return circuitof the master and slave windings and so insulation between tubing andwindings is necessary. Five Minute Araldite is used as the insulatoras it is capable of withstanding the heat generated by the surroundingcopper coil. The procedure is:-

Ci) Coat the cupro-nickel tube with a thin smear of Five MinuteAraldite epoxy resin.

(ii) Apply mild heat to thin the Araldite and ensure a smoothfinish of uniform thickness.

3.2 Slave windin2 - First half

This winding is 19 mm long with about 160 turns (see figure 3)and sufficient leadout to reach the connector end of the tube. Theprocedure is: -

-5-

(i) Carefully wind the first half of the slav coil ensuringthat the insulation of the copper wire does not crack andthat the turns are placed neatly against each other.

(ii) Use a small dot of polyurethane lacquer to secure thestart of the winding and the lead-out. Allow about 5minutes for the lacquer to dry.

Best results were obtained by winding the wire slowly byhand to avoid overlapping turns or gaps, then temporarily securingthe leads while the master and second half of the slave coils werebeing wound.

3.3 Master Winding

This winding is 38 mm long with 320 turns. Sufficient wireshould be allowed for the lead-in to reach the non-connector end, andfor the lead-out to reach the connector end. The procedure is: -

i) wind the master coil, beginning hard up against the endof the first half of the slave winding.

(ii) Secure the leads with a dot of lacquer.

3.4 Slave winding - Second half

This winding was identical to the first half of the slavewinding except that both leads required sufficient length to reach theconnector end of the probe. The manufacturing technique for thiswinding is the same as that given in section 3.2.

3.5 Protective external coating

coating of polyurethane lacquer is applied to hold thewindings firmly in place and to provide target and slave windings withsome protection against solid particles, such as ice fragments, whichcould be encountered in some operating conditions. A thin coating oflacquer about 5Unm thick or less is recommended by King et al. (1981)because excessive coating thickness causes premature saturation of thetarget element. The coating thickness is also directly related to thethermal lag of the instrurtent. A low thermal lag allows rapid responseto changes in liquid water contet. Using a polyurethane lacquer,the ARL target element had an average coating thickness of llm. Thecompleted master and slave windings are shown in figure 4. Thepolyurethane coating thickness measurements are shown in figure 5.

FIG.3 COIL AFTER FINISH OF FIRST SLAVE WINDING

3.6 Earth conection for master and slave windinas

A solder joint (figure 6) between the winding leads and thecupro-nickel support tube at the non-connector end allows the tube toact as an earth, thereby eliminating the requirement for two connectors.The procedure is;-

(i) Run the lead-out wire of the master windinq and the lead?-inwire of the second half of the slave winding along the backface of the probe to the non-connector end and fix withAraldite.

(ii) Remove an area of Araldite from the non-connector end ofthe tube to provide a clean surface suitable for soldering.

(iii) Carefully burn the insulation off the ends of the two wiresand soft solder to the tube as close to the windings aspossible, leaving at least 1cm clear at the extreme end ofthe tube for end support of the probe in the housing assembly.

The following points should be noted:

(i) Use as little Araldite as practicable and ensure thatnone of it encroaches onto the front surface of the probe.

(ii) Ensure while soldering, that the heat does not burn theinsulation on the windings.

(iii) Use the minimum amount of solder practicable because anuneven or bulging surface tends to attract ice build-up.

(iv) Take particular care to avoid dry joints when soldering asthis extra resistance is in addition to the sensing resistanceand decreases the sensitivity of the LWC meter.

3.7 Probe connector assembly

The probe assembly was completed by terminating in a Cannontype 407 CEAKPTO6A8-4P connector. A short length of 0.71 m (22 SWG)tin coated copper wire, soldered at one end to the inside of the probetube and to terminal D of the Cannon plug at the other, provided ahandy support between the probe and the connector to hold it in placewhile connecting the other wires. This arrangement also provided themeans for aligning the probe axially with the connector and for adjustingthe overall length of the probe assembly to the required length of100 M.

FIG.4 THE COMPLETE MASTER AND SLAVE WINDINGS

440

'-i

U0

4 0

.4.)4)

0 > 0--4- E-u~ 4 ) o

00

E EE E-

CILM 0.

0c

OD£N cc

N N -t H-* '0

I 44

FIG.6 SOLDER JOINT FOR THE EAATH OF MASTER AND SLAVEWINDINGS

Terminal connections at the Cannon plug were:-

(a) master winding lead-in to terminal A.

(M) lead-in of first half of the slave winding to terminal B.

(c) lead-out of the first half of the slave winding and lead-inof the second half of the slave winding to terminal C.

d) probe connector supporting wire (earth] to terminal 0.

To complete the probe assembly at the connector end the followingsequence is recommended.

(i) Run the remaininq leads, i.e., those in a, b and c above,along the back face of the probe to the connector end and

fix with Araldite.

(ii) Solder one end of the supporting wire to pin D of theCannon plug and, adjustinq for alignment and probe length,

solder the other end to the inside of the probe supporttube.

(iii) Solder the slave and raster leads to the connector terminalsas in a, b and c above, takinq care to avoid dry joints anddamage to the wires. The insulation is removed from the endof the wires by burning with a match and wiping away theresidual carbon.

(iv) Carry out a resistance test between the connector pins toverify that there are no short circuits between master andslave windings and to check for correct resistances of the

windings.

(v) Encapsulate the leads and pin connections in Araldite(ensuring appropriate separation between the leads) to forma secure conical shaped support as shown in figure 7. Apresentable cone form may be obtained when shaping the fiveMinute Araldite by slowly rotating the probe and turning itend on end, as required, to prevent the Araldite from eitherrunning down the face of the probe or from overflowing ontothe connector.

(vi) Slip the securing cover nut over the body of the probe andscrew to the Cannon connector.

(vii) Eliminate the possibility of earth loops by placing eomWlon tubing, 1.5 mm inside diameter by 5 mm long, over thefree end of the support tube to provide insulation from theprobe housing at the outboard end of the probe.

-12-

4. PROBE REPLACEJNT

The sensing head assembly, i.e. probe and housing, used inthe Nonad aircraft anti-icino trials is illustrated in figure 8. Thecompleted unit shown mounted on a Nomad N24 aircraft in figure 9, wasdesigned to enable probes to be easily changed in the event of windingdainaqe or failure.

Probe interchange was simply accomplished by removing thecap nut shown in the assembly (figure 8), withdrawing the probe fromthe Cannon connector socket and the probe housing, then replacing witha spare.

A further requirement necessary to preserve instrumentsensitivity when using different probes, was that the effective electricalresistances of individual elements agree within 12.5%. Lead resistancebetween probe and instrument, junction resistances at connections andthe resistance of the element winding itself all contributed to thetotal probe resistance. As the instrument worked by sensing changes inresistance it was important that all resistances other than the masterwinding had to be kept to a miniumn. Lead resistances were kept toless than 1% of the effective element resistance by using 36 x 0.33 UMTeflon coated cable and taking special precautions to ensure successfulsolder joints. Individual element resistances were checked accuratelyto 10.01 of an ohm and varied between 3.75 and 3.95 ohms. A separateresistance card located in the instrument box was required for eachelement so that the operating temperature of the wire could be accuratelyet at 91C. Thus, when an element was replaced its resistance card

was inserted into the liquid water content meter instrument box.The complete circuit diagram for the LWC meter is shown in

figure 10.

5. CONCLUSION

The completed target probes were used in over one hundredflight trials in the Nomad N24 aircraft anti-icina program; only oneelement was damaged. A test program carried out in the icing tunnelfacility at ARL showed less tendency for ice to accumulate on the ARLprobe than on a CSIRO type. This was important as ice accumulationaffected the airstream velocity passing over the tarqet element andhence altered the accuracy of the meter.

An external protective coating was applied to the targetelement to reduce its susceptibility to damage by ice fragments. ItIs Important to keep the coating thickness to less than 50pm to avoidJTweam tSaturation of the target element and unacceptable thermal lags.Mae WE 2 most important features of this probe was the achievement ofa a thickness of only l2.m using a polyurethane lacquer. The

I

t

I

I.

PIG.7 THE COMPLETED PROBE LESS THE SECURING NUT

-14-

coating thickness is a compromise between probe susceptibility todamage by ice fragments on the one hand and probe sensing range andreaction time on the other (see Kina et al. 1981).

Another feature of this design was the reduced amount of icebuild-up on the probe compared with the original CSIRO double endedprobe. This resulted in less disturbance to the airstream passingover the target area and hence greater accuracy.

Using an LWC meter based on a CSIRO design and target elementsas described in this report, LIC's up to 3 gm/M 3 at air velocities upto 66 m/s (see Skidmore & Pearce 1982) were measured.

|

Insulating 100mm diameterbush stainless steel

KPT 06A8-4P tube adspot

eleen anwsivrwr

eleetrina

connectorcoretinshpd ri

V.8TA S tuF SEndN sEDASML O IupotRCOTT METEReemn adslv wr

FIG.9 A.R.L. -G.A.F. SENSING HEAD ASSEMBLY

I AVERAGING CIRCUIT -22Cil RV20.31 lOOK

3-.~vOM 320v 1 1

470K '03 6

NOTE IRESISTORS SELECTED TO SET H W LM 112TEMPERATURE AT 90-C ICO* 2

2 PROVISION FOP SCALING NETWORK 68~r 4 C12If REQUIRED 1000 Pf

3 Ri £R2 PROVIDE BIAS FOP START- f 0vUP

22 VOLT REGULATOR 3-20VIC2

LM317o2V VIN~ vOUT *21, PIS 7R'.7

5 I ALL. 4 7K [2'

R19 T POINTS

C7 6 C 2N22220.,l P20 6 8,L 0D1 f 1K

3 9K R16

POWER PANEL 3-20V___

-20 VOLTS IA Fj.SE 20j3-20 vZ 75 ERROR AMPLiFIEP 9 NOTE1

VOLTS __lMO SO0T.;09 RESIST

IZL PANEL 02 01 jf* LIGHT l R1

'6K .. 100K 1 24- 6V 13 Ri.__ TI 2 R6On 2.00

3-,20VJI 2N3053 '.-20V - - Cl2 R2 6 L 1 C 1 ? lOOPf 24-16V 2.4-

1 1 R7 101D1 R1004 rC3. 100 K 15011

02 270 pf 00601 02T *TO WIT1 N37 T 100p 0.25%LTO ALLOTHEREA RTHSS14 15

FIG. 10 LWC METER CIRC

an.

RV2

7 100K( SCALING DAA05E

+ 18 61 12 NETWORK] SEE NOTE 2 I 1NPw

LM11I 15K 0 LWf -0 0C'? I4.7K r 0C1 R24 A AOv AVE1000 pf IIM

INDICATOR Ci~t 32 I2AE E

31 3V~ HIGH DIP T.M

3-20 V

ALL 4 7K 270n 270n

NTS 03301 2V PANEL LEO

VT? IN4001 10 OV LOW GIP2N2222 SEE NOTE 2

16 R25 15K

P16I SCALING NETWORK 47K

3-20 V 2?P2

NOTE 1 23 ILZ E

C9 RESIS TORS R2 2 -t

lOOK 11 R) IS BALLAST _

2.4 -16V A13 RAPO ,. 0 TSAEITR2 6 loon 2.4-16V 4 18 h ~-1100 P8 2.4-16V 2.4 -16V 2 _________________

R5 R3 16 IsRloan R0 82K *2NOTE 3 1 AIPCPA$T :ABLE

100Kx 150n 36 K -

*TO) WITHIN 12 ovSPAPEPf0.25% NC ~N:

14 15is__ _

CENTRAL EARTH POINT

r C METER CIRCUIT DIAGRAM COPIED Flom r AF ORAWIN~ WO N-I8 SEET 2 ISSUE 1

Lmm T~qtmp rWINS'5S7 A I

REFERENCES

ATKINS PB, (1981). Experientalinvestigations of intake icing.ARL Mech. Eng. Report (in publication).

KING WD, DA PARKIN and RJ RAWDSWORTH, (1978). A hot wire liquidwater device having fully calculable response characteristics.Journal of Applied Keteorology, Vol. 17, 1809 - le13.

KING WD, GT MAYER and GA HEPBURN, (19el). Further performance testson the CSIRO liquid water probe. Journal of Applied Meteorology,Vol. 20, No. 2, 195 - 202.

SKIDMORE 7V and GF PEARCE, (1982). Cloud liquid water contentmeasuring equipment for the Nomad N24 aircraft flight icing trialsof 1978-1979. ARL Mech. Enq. Note (in publication).

Ih

DISTRIBUTION

AUSTRALIA

Deartment of Defence

Central Office

Chief Defence ScientistDeputy Chief Defence Scientist ) copy)Superintendent, Science and Technology ProgrammesController, Projects and Analytical StudiesDefence Science Representative (U.K.) (Doc Data sheet only)Counsellor, Defence Science (U.S.A.) (Doc Data sheet only)Defence Central LibraryDocument Exchange Centre, D.I.S.B. (17 copies)Joint Intelligence OrganisationLibrarian H Block, Victoria Barracks, Melbourne

Aeronautical Research Laboratories

Chief SuperintendentSuperintendent - Mechanical EngineeringDivisional File - Mechanical EngineeringAuthor: N.J. RepacholiG.F. PearceW.H. Schofield

Materials Research Laboratories

Chief Superintendent/Library

Defence Research Centre

Library

Central Office

Director General - Army Development (NSO) (4 copies)

Central Studies Establishment

Information Centre

RAN Research Laborator

Library

Navy Office

Navy Scientific Adviser

.../cont.

DISTRIBUTION (CONT.)

Army Office

Army Scientific Adviser

Encvineerinq Development Establishment, Library

Air Force office

Aircraft Research & Development Unit, Scientific Flight Group

Air Force Scientific AdviserLiry

Technical Division LibraryDirector General Aircraft Engineering-Air ForceDirector General Operational Requirements -Air Force

Department of Indutr and Commerce

Government Aircraft Factories

ManagerLibrary

Department of Science & _T.chnoloqL~y

Bureau of Meteorology, Library

q Trans o~e Australia

LibraryFlying Operations and Airworthiness Division

statutory & State Authorities and Industry

CSIRO

Division of Cloud PhysicsLibraryDr. W.D. King

Trans-Australia Airlines, LibraryCoimonwealth Aircraft Corporation, LibraryHawker do Havilland Aust. Pty. Ltd., Bankatown, Library

GERMIANY

Deutsche Forschungs- und Versuchsanstalt fur Luft- und Raumfahrt e.V.XKP. Schickel

SPARES (5 copies)

TOTAL 60 copies

DOCUPXLNT CON1TROL DATA

l~a.R N l~.~2tabishnen .~ 2.ocuentDate 3.Task NoAR-002-348 ;ARL-NECH-EN7G-TECH-?!ENO-412 March, 1982 AUS 78/069

.Titie5.secu~rity .No PagesMANUFACTURE OF A HOT 'TIRE TARGET ELEMENT~ a.documeit 17FOR~ A CLOUD LIQUID U-ATER CONTEI1T I UTER I MICLASSIrIED 7.oRe

ib.title c.abstrac 4ei

8 .Athor9.DongraingInstructionsN.J. REPACHOLI

10.Cr7-'o rtAthradAres1.uthority (as appropriate)

Aeronautical Research Laboratories a. sponsor b. Security c .Dowrhgrading

G.P.O. Box 4331, t1ELBOURNE VIC. 3001 dAproa

12.Secondary Distribution (of this docurent)Approved for public release.

overseas enquirers outside stated limitations should be referred throughASDIS, Defence Information Services Branch, Departnent of Defence, CampbellPark, CANiBERRA ACT 2601.

13.a.This docu.ent ray be AIINOUNCED in catalogues and awareness services

available tot No limi~tations.

13.b.Citation for other purposes (i.e. casual announcement) may beunre~stricted.

14 -Desciptorsi' l.COSATI Group4Ice formation indicators 0401

Meteorological instruments 1402Precipitation (meteorology)Hot wire anemometersCloud physics

16.Abstriact -

This report describes the design and manufacturing techniques of a hotwire target element for a liquid water content meter, based on a c.S.I.R.O.design. which was used durincr monad icing trials in Australia and theUnited Kingdom.

17. ImprintAeronautical Research Laboratories, Melbourne

IS.Docurnent Series and Number 19.Cost Code I 20.Type of Report and PeriodMechanical Engineering 425260 CoveredTechnical memorandum 412

21 .Computer Programs Used

22.Establiahment File Ref(s)