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Distribution authorized to U.S. Gov't.agencies only; Foreign GovernmentInformation; 04 FEB 1963. Other requestsshall be referred to British Embassy, 3100Massachusetts Avenue, NW, Washington, DC20008.

AUTHORITYDSTL, AVIA 18/2035, 1 Aug 2008; DSTL, AVIA18/2035, 1 Aug 2008

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MINISTRY OF AVIATION

(:0

AEROPLANE AND ARMAMENTC5 EXPERIMENTAL ESTABLISHMENT

SOSCOMBE DOWN

"H~w~:-~: OF 'ML' I 1171W! FLIIT;T 3Y3Tpr:r: IT7TA:JL TTO T! :'-F' 7'JLC? B.L

W FlT.L'r 2 . 7TLLB,:SR.A.F.

MINISTRY OF AVIATION

THIS DOCUME NT IS THE PROPERTY OF H.M. GOVERNMENT ANDATTENTION Is CALLED TO THlE PENALTIES ATTACHING To

ANY INFINGEMENT Of THE OFFICIAL SECRETS ACT. ll~liS

Is klhm" fi t, -s FS If~l t 0- o "I . nd t , i - -om st t, oo lsn t.r r~

doIt.. TMe P.6k. ... cId.1nE thl Fet F -lmuIe o mletbI. tbis Ltook hibiwssis, Il sissst4 hel -u essisls .14 1WY.. A, y'p- Mi b-e i.eke ..eb.ieedsis bMid., uiswe ebtolmilo potleno l Itadoo . by fledol ng

*t .F wwIkeea d it, Itoetther wlish hi, ti d O d ....t. .e . o.d ... ow1 2 6THE SECRETARY, MINISTRY OF AVIATION. LONDON, W.C.2

Lm pi sto ,O - bo p-14al. other Pe.. wnill bonao. All p- .......ism" isre. thi tk somste#oOOatel. t on dotu , hlt docomn It,,

3rxc~ub Fftom AUTOMATICAAE w 1. II,#* R~ I boo Din 5200.10

Dom HW APPLY

RT, o . E/Te oh/222/lav.

AEROPLA1 ANJD AiM BN]T MXPERIbIRHTAL EfSTAaliBSIA] T-

An Asse:oment of the ilitar, Flight SystemCompass Installation in the Vulcan B. 14k,. 2

Pere.rented by

Flt.1t. B. -. Wiilliams i.d.F.

lavigation Soctiori

A. & A.E.E. Ref: ATTR 25/01

Summary

The 1,11ilitary Flight System Compass installation in the Vulcan B. 1k. 2provides a satisfactory gyro-magnetic compass system for navigational use..The Track Control Unit provides a useful and accurate navigation aid.. Thelarge amplitude Northerly phugoid instability, and the l:oass of gyro datum in

turns, reduces the usefulness of the system and could degrade weapons systemaccuracy. Modifications to overcome these deficiencies are recommended.

OThis document containo information affectin-1g ths Ntiozal

Defense of t .- U. . s , . , efling of t2

ES ..- tis 793 and• . c f its contents

prohibited

by iaw.

This Report is issued with the authority of

Air Commodore,Commandant, A. & A.E.E.

SECRET

I.-~ ~ ~ ~ In(-Dl 'IJo

3. roourld c'ulro'ioolo of CcsIII W-::

4.. -air Cs~ibra-Wc2 o )r of oinp-ar,, fyro- s

5.. ,-t~io/oi~as {abj-iJ.'ty

6.. Thr2~nsor AzdanofJi CyoIn Yrr.e, Mcdto 5

7.. A on'n;of -ehc 'fras-Lck 'Cortro23 1.Jdt

8.,. Concl wlorao

9.. 'Rc ommerida-ai onos 7

List of Apmmno-oc

Ai-,r 'Ce2ill-atiorl of' S. i.. .C m s

loz-clliatior of Comr)aso Deviation. f-Iu to IUo'-rthr2-y 2sbU

M,..:S. -A=irnuth -ro T-D't 3atez -C

-:EffeotL- of -uerrm on 33'ee M.R.r, §yro -D

list of TsbaezTab-le

Malmetic Survey Thesuits .

-Aut-o-ilot/ roass Heinading St abi ity7 2

Effecet of turns on Freie- Yf.F..S'.. T4yrco iatumr 3

SBURPFT

BE MIT

Duin Havcin io

herin2 7avi.etion tceceoer trials caOrrie d Out at; this EstablishmtW~on heanB. Yh.2 W.53 the oPOrtulity 'wIas tkpm to in staeth

per nce f the miltarY, Ilight ZoYcten ~ osacinstallation.Thiz rerrt sersch ru of th11,t investiga-on.

The trial i.d4azzezzsnent of ithe, foflotwing aspects:

a A zwmntic ourvey of the aircraft.

(b A ;'round calibration of the 1,%F.Z. compasses,

AT, air caliration of the 14FZ comrasses.

(4)~ An azzezent of At-lo/orasstability.

(e n azzeoment of the yerforma-pre of the Azimuth gyro used in theIfree'o ;ode.

(f) A z azzssent of theP nerfornan-ep of the T'rack Control Uit.

ou f the irforcation cbtaired durinE these trials has bean progressively

reverte iin letter renrorts fron this Establishwmnt.

2. Magnetic &Zurvey

Te folsigcoeffic ients wrea eptaincad from a Fourier analysis of themeasicred atinrs obtained Jf1ror a "We lve T oint sming of the aircraft ith

+tefezass aetectors relled by dirpec± redirg srvey compasses. These

A31 -10I7 SUFNEY pBE2ULTS

50-' ErrorsfonasIoto Coeffcin-s

De-iat ion B -E

II r - A -po i-n % -. CL .+L 9

starbaardL aetec t:r zositizn -. .7 j I -C6 07~ LO 2-

No significant effect was ntoted at the dete ctoar rcsitions froms runningthe aircraft engilnes or thle cnaratian of controls and electrical services,either si nslv or- iyn tobi2-ati on. it is concluded that the ~ES. commassEetector rsositiostisfy the rendiremnents of Av, .P.970, Charter 7117 and areaiczeQtable-_ for ase in, the 3.hla . __ __

3. ron.Calibratiom Ef the Coctazs Systens

Ina-ing the ii:,tial groluad calibration of the compass systenms it asf candt that siecr a-ors rare introduced by the acolicat-ion of de-viation

coreian pLtecrasz! resolver unilts. Subsce uent Investigation at ti71stab~dshment showed that this effect was due to the large 2,LOQ cycle ripplecontenlt of the naircrat D).C. suzoly to the deviation corrector circuits.agacitive coveing between the corrector circuits and- the detector output

lteads a 'aced a, false Signal At the concass resolvers which was manifested as

/an incorrect ...

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-4-

an inc-orrec,-t hcadlinr'. A modification was -,ub3'u11cntly introduced, to overcorcethiz def'iciency ty scr:enring th- de tclo-r output leads be-twour,,n thcr compassdetectors arnd thru re-ol-vur unit: (Vulcan. mod. 1 C'72) , lire compass calibrationswere carried out on YH.536 aftcur the incorporation of this modification andthe quality as- foun, to be Poodl, the man 5'deviation error being q-0.080.

An ascuratw calibratior of' thu B arnd C deviation corrector after Mod. 1072was incorporateAl, oill 3howeird some departurre from linearity and it was concludedthat this ca rodu-codF by asmall anmoint of irduct-ive coupling between thedeviation corrector coils and the earth inductor coils within the detector units.The comass mraufa-tur,:rs prof osed a modification to -overcome this effect byintroducingi some :7tra circuitry in the compas s amlifiers to smooth andstaoilisme, th(- L.S. suorly to the deviation corre ctor circuits. A prototypemodification -was roxamined at t'his Establishment and was found to be comletelyeffective in eli;iet-ing all rcesidual cross coucling effects betwteen thedeviation correctcr circu-its ard the_ rest o:_, the comroass system. It wasrecomo,.ended that this modification,- should be arrlied to all M.F. S. compassarxlif'iers (A7.. c.6 ated , 7th june , 1S6i1 reers) . It is-holed3 that actionis -now in hand~ to i-7plement this rrecommenrieticn.

4. Air Oalibration of' the CnasSse

A calibration of' the comrass system was carried. out in the air in orderto assess the mean change of' deviation durir- flight. Twvilve thirty-minuteleezs rare flow n or. -u± spaced h 1 -ins an on- each leg 30 simultaneous-whotog rawuhic oceerl.va-ions were- macia o', the Sun's relative omarane ard theco:atYass rcvr il.From tl ese dbs -vaons mean flight leg deviationsw7ere calculated and s-Yb.4ected to Fourir analysis. The results of thiscalibra-tion are show~n an forh cl 'm a.. Avendi:, 'A' and compared -with therrevi-jouc and tne suc un rou-,na saorwbraons. No abnormal results -wererevealed by th- s,' clira~ion and it is concluded that, from the magneticasneet, the cc-sste in the -Vulcan B. Mk. 2 is acce-otable.

5. Aatc-PilctAr /C-- Stahilit

The stabil - th aircraft while under -. to-cilot control was assessed-by ref'erence c' -C F-7ror,-r rac record-_r<-Z of' relevant aircraft~ manoeuvreand attitude "_ ,an -cmaas inforntion. Table 2 gives a summary ofthe r- s-uLs ir for i re1 & ar7 it-ies of the oscillati one of theaircrff ''rtf csiinscstne -ra.

2 Ai-T0-PILOT CCI.'PASSS HEA:IUP1 STAB ILITY

Dieto _EiEh Compas ,1o0de iHdS. Stability

Tth LO) X- (L"agnetic Compass Ste~ering)_

CLOGS I . 10

South L-.--- i

BEas t L )(I~ I ..jo

'We st 50 .C-')'" ' :0

I 10

11 L COC (Gyro Compass Steering)_

/TIhis table ...

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-5.

This Table clearly illustrates the magnitude of the phugoid instabilityexperienced on a heading of 14agnetic North, and it also indicates that thisoscillation increases in amplitude with increase of altitude. This effectis attributed to slackening of the aerodynamic response to control, withreduction of' indicated airspeed, as altitude is increased. The period ofthis oscillation is approximately 4.minutes at 40,000 ft. increasing to5 minutes at 514,000 ft.

To illustrate the compass error due to Northerly instabilityAppendix 'B' shows the oscillation of compass deviation obtained by comparingthe oscillation, of M-.F.S. heading with that of a high grade free gyro. Thisgraph indicates the probably accuracy of instantaneous compass heading duringthis condition of instability. It is concluded from these results that the Auto-Pilot/'i.FS. compass combination provides an unstable platform response on aheading of Magnetic North. This instability will seriously degrade the accuracyof astro sighting and of radar bombing, particularly when long range offsetsare being employed. It is recommended as an interim measure that, for astrosight taking or bombing, the free gyro mode of the MI.F.S. compass system isemployed on headings within 450 of Magnetic North.

In an attemot to overcome the problem of instability on Northerlyheadings, the compass manufacturer has produced a prototype partial-integratingamplifier, the fnction of which is to effectively increase the compass monitoringtime constant on susceptible headins. This prototype amplifier is currently

undergoing assessment at this Establishment and a separate report on the resultswill be issued in the near future. Preliminary results indicate that this

amplifier produces a marked improvement in compass performance on headings about

North. If this finding is confirmed in detailed analysis a recommendation willbe made to introduce the modified aoplifier for use in Vulcan and Victor aircraft.

6. Performance of the Azimuth Gyro in the Free Mode

Two sorties were flown to assess the drift of the unmonitored compassgyro on a straight flight leg of three hours duration. The results wereobtained by comparing sumultaneous photographic records of the relative

bearing of the Sun and the compass resolver dials, with the compass selected

to free gyro mode. The results are shown at Appendix 'C' as the resultantdrift rate after correction has been made for transport rate and the difference

of Earth rate from thc latitude of mass balanc2 compensation (570 N). The results

indicate that the compensated free gyro drift rate did not exceed 50 per hourand this supports other evidence which suggests that the mean free gyro driftrate is apopoximately 40 per hour at the one sigma level. The drift ratesshown at Apendix tC, were measured over twenty minute intervals as the

condition of the trial dId not allow the rates over a shorter period to beassessed. Thus it is possible that there may be short period drift ratesconsiderably exceeding 5

0/hr. but no evidence was found to support this

suggestion when the aircraft was flying a constant heading.

This gyro performance is adequate for use in a compass system utilising

magnetic monitoring, but would be inadequate in conditions where magnetic

monitoring was not available and frequent astro heading checks unobtainable.The maximum observed gyro wander rate could produce a hang-off error in amonitored compass system of 0.120.

The trial also included an assessment of free, gyro performance during

and after turns. In these cases gyro heading before and after the manoeuvre was

compared with true heading obtained from astronomical observations. Theaccuracy of this method is assessed at 0.20 (S.D.). In all cases the turnwas carried out at 250 bank at an altitude of 38,000 ft. and an indicated

Mach Number of 0.85. The results are shown in Table 3 which demonstrates a

marked tendency for the gyro to lose datum during a turn.

A/ABLE 3 ...

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-6-

SE CRFET

TABLE 3 - EFFECT OF TURNS ON FREE IF.S. R0 DATUM

Direction and mount of Shift of DatumTurn PotCyo Sa:or yoJDiff of Datum shiftTunPort Gy r o Starbjoard Gyro

0!

180°S 6.0's 08 I 3.50oo 0 08

5L5°P 7-4°P 6. 0 P.80

105'P .9,P I .3P .4o

31.0S 7.5 S 6.40 s .10

1 60'P 2.8P 3.8P 1.0 °

9002 0 1 .8 0 S . 0

1 80°S LLS , .5 0 S 2.9°o 0 o

2700 7-.7 P 5.3 p 2.L°

1000 S 1.60- 2.60S 1.00

3700P 7.00P 6.7 P .3

17502 3.L0 S 2.5'S .90

3900P 8,70P 7.1 OP

560°S 6.30S 6.5°S 3

This table shows that the 1 .F.S. gyro tends to lose datum in the directionof a turn by an amount which varies with the amount of turn. This result isclearly demonstrated by Appendix 'DI which presents these results in graphicalform by plotting the amount and direction of datum shift, against the amountand direction of turn. An analysis of the data from which these results werecomoiled indicates that there is no tendency for the gyro to nrecess back toits pre-turn detum when the turn is completed. Further ex.eriments haveshown that the datum shift appears to be related only to the amount of turnand is not affecterl by altitude, speed, or rate of turn.

No explanation can b, o1ffrred for the systematic nature of these error:s.Nutation drift, caus. d by vibraticr. :,hen the 7ymbal axs are not orthogonal,does not ariear to satisfy the obvious symmetry of thc findings. It is under-stood that the cor, ass manufactur r is currertly inv stigating this effect inar. attempt to jroviIe - physical oerlanation and to determine what remedialaction mieht be possible . The loss of gyro datum during' turns is a seriouslimitation of th .. 3. comeass system and is likely to dcprade weanons system

accuracy, ynoticularly :hc n offset bombine t-cliniqurs arc employed. Tt isrecommended that this eff. ct should be fully invstigated., and appropriatemodification action tkrr. to climinate this souce of Prror.

7. Asseosment nf the Track Control Unit ('.C.u.)

The Track Control Unit provides ar output of true track to the ]%%F.S.Beam Compass, when 'RE-0TE' is sIoctd at the pilot's kIF.S. selector, and.thus controls the auto-wilot when this is enrgaged. True heading is alsoprovided both to N.B.S. and to th, 'round Position Indicator. Current valuesof drift and variation may be, se-t in either manually or automatically, fromGOre n Satin in the case oi irift, and. from a can in the Navigation Panel 14k. IA(N.P.I .A.) in the case of variation. A direct icasurc.ient of true headingaccuracy is difficult to mak. as no suitable mceans of proesenting the informationis normally available, bidt the error in this quantity must be the sum of theerror in the basic compass loop, thc error in ac applicati on of variation andresidual deviation, and the accumulated transmission errors between the compassresolver and the output. Taking the knowo vaeuc s of these quantities it cn

Ae shown ...SE~reET

SECRET

-7-

be shown that the instantaneous true heading accuracy over the U.K., or anarea where variation is known to a similar accuracy, is +i .5 ° at the onesigma level. This figure is supported by measurements made during this trialwhich also indicated that the mean true heading accuracy over a period ofapproximately three minutes was about +10 at the same level of probability.

Due to the extreme accuracy of the drift output of Green Satin the truetrack output of the 'oC.U. has a probable error aporoximately equal to that ofthe true heading output. A smoothing time constant is introduced in theapplication bf drift at the T.C.U. which provides a stable output of track,allowing accurate and simple tr-ack steering. This track steering facilitywas assessed on two long flight legs between Boscombe Down and Idris. Onboth occasions variation was set to 'AUTO' but the current value checked againstcharted values, and reset if necessary, at 30 minute intervals. Drift wasselected to 'AUTO' except for two short periods when Green Satin unlocked.On each flight two small alterations of heading were made, based on monitoringfixes, and the maximum measured deviation from the preplanned track was 3 N.M.The track steering facility of the M.F.S. was found to bo a most useful andconvenient aid to routine navigation and ap-reniably reduced the work loadon the Naviator/Plotter.

The variation setting control of the T.C.U. can be used to applycori~ections for residual compass deviation, but accurate checking is madedifficult by the oscillation produced in the auto-variation system. At thisEstablishment's suggestion the manufacturers have produced a prototype modifiedT.C.U. which includes a large scale deviation trimmer oermitting accuratesetting of corrections up to +30. This was found to be a most useful modi-fication providing means for applying deviation corrections and also F.M.A.corrections derived from the measured cross track error in the aircraft D.R.position. It is recommended that the modified T.C.U. is introduced for servicein all Vulcan and Victor aircraft.

S. Conclusions

The Military Flight System compass installation in the Vulcan B. Mk. 2provides a satisfactory manetic compass system for navigation usc. The tracksirring facility of the Track Control Unit Erovides a useful end accuratemeans of navigatir-e the- aircraft and reduces the work load on the Navigaior/Plotter. The basic compass systec was found to meet the requirements ofAv.P.970 Charlter 7,17 and the accuracy of t ho true heading and true trackoutputs was found to be approximately fl .50 (S.D.) instantaneous or +10 (S.D.)averaged over about 3 minuts. The aircraft/compass combination was found tosuffer from severe phugoid instability on Northerly headings with a maximummeasured amplitude of j4l at 54,000 ft. at 0.35 I .1..

The yerformance of the azimuth gyro was found to be adequate for use in amagnetically monitored system on constant headings, but would be of little usein a 'free' morle unless fre.uent Astro heading checks were available. Thegyros were found to exhibit a disturbing loss of datum in turns, the magnitudeof which appears to hav a linear relationship with the amount of turn. Thiseffect is likely to degrade the weapons system accuracy when offset bombingtechniques are employed. No explanation can be offered for this error.

9. Recommendations

The following recommendations are made as a result of this trial:-

(i) Magnelically, the .F.S. compass system is satisfactory for use inthe Vulcan B. Mk. 2.

/(ii) ...

SE CRE T

SECRET

(ii) A modification should be applied to all M.F.S. compass amplifiersto improve the smoothing and stability of the D.C. supply to. thedeviation corrector circuits.

iii) Action should. be taken to eliminate the instability of the Auto-Pilot/Compass combinations on headings about Magnetic North.

(iv) The loss of azimuth gyro datum in turns should be fully investigatedand action taken to eliminate this source of error.

(v) A modified Track Control Unit incorporating a large scale deviationtrimmer should be introduced for service in all Vulcan and Victoraircraft.

Circulation List

A. D. Nay. 2 Copies I for action.d..D. (R.i.F.) B. 2 Copies (for information of D.P.O.)Nay. '(a) I CopyNav. (b) IR.D.T.3 IT. T. L. 50 CopiesR.A.E., Farnborough 5 CopiesR.A.E., Bedford. 2

SECRET

SECRET APP A.*~E~EAD rR CALIS RATION.

- -- -PREVIOUS GIRROuNO CALISRATIOC'J

-SUB6SEQ~UENT GiROUND CALIBRgrTION.

-1 - -------

V-

7I---- --l . . . . ,.--- I- .-

013c 120 15O 0~ ;6IS0 ?I 40. ?'70 -IS0 330 31E0

E A D IN Gr 50AR P OD OMPASS,

.- . -.4 - -.. . . .

3 Pr 030 0 r 090 ?o SC 3QO 210 24.0 270 300 55(l 3c.'

w -1I HEADNG01 ~P COMRASS

ITHE ABOV/E GRAPHS ARE A p..OT op CALCULATED ODE'T)ON

C8-TAU'..ED BY FOURIER ANA'~SOF OBSERVED DE'IIATriCIN11

2 inHE ANLNSSSHOV./ED TI-.E F0LOIVOIN7, 50% DEVIATION ERRORS

.3 SO '/. DEVIATION ERRORST'Y'E OF= SINO4 A DATES

PORT COMPASS STS0 COMPASS

GROUND -7T SEPT i8E0 .0, 0s

t.R IO5~I6"SEPT .960 140 ,3N

ITI

hr3 ALLOWANCE [5 MADE. r-OR CORIOLIS ACCELERATION ON THE

PENDUILOUS DETECTOR

SECRET.

AIR CALIBRATION OF THE COMPASSES(VULCAN MK.2)

Lnl

oAPP. S.

I I ~ I

t*NJ Iot

0 01

I 0 0

7~1 S CRET.A P P. C .

LEGEN.O

9 ASE.DR 6 2719-60-6 IO.IS -BASE 29960

140

AIN

Ml NS- _ _ _ _

z ~20--K

20 10 0 o e o 6 a

M.F.S. AZIMUTH GYRO DRIFT RATES

SECRET. APP. D.

+ PORT GYRO0 STARBORD GYRO

I 4 0P -----------------

I I

_____....._--_-___- I i t I _____ _________ ________ --

i P 8P 7P, 6P 5P 4P 3P 2P IP Is a ~ 4 5 6 7 5 92 - 70P

3' Lsso osu -*------ _ _ _ _ _ _ _ _ _

i..

IJ

9P SPSECRET.

LOSEFFECTS OF TURN ON I. GYRO

dstl1

[dstl P.'

Defense Technical Information Center (DTIC)8725 John J. Kingman Road, Suit 0944Fort Belvoir, VA 22060-6218U.S.A.

AD#: AD339998

Date of Search: 1 August 2008

Record Summary: AVIA 18/2035Title: An assessment of the military flight system compass installation in the Vulcan B Mk IIAvailability Open Document, Open Description, Normal Closure before FOI Act: 30 yearsFormer reference (Department) AAEE/TECH 222/NHeld by The National Archives, Kew

This document is now available at the National Archives, Kew, Surrey, UnitedKingdom.

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Access to UK public records is governed by statute, namely the PublicRecords Act, 1958, and the Public Records Act, 1967.The document has been released under the 30 year rule.(The vast majority of records selected for permanent preservation are madeavailable to the public when they are 30 years old. This is commonly referredto as the 30 year rule and was established by the Public Records Act of1967).

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