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Aviation History
1959
1959 - 0537.PDF
264 FLIGHT, 20 February 1959 FLYING AIDS . . . - : M.RG MKI ' 'I " Above, the Mk 1 and 2 Master Reference Gyros made by S. G. Brown Ltd. Below, the miniature, integrating-type Decca Navigator installa- tion for small aircraft 4*i*^ (i) be capable of integration with long-distance navigationaids so as to accommodate additional equipment pro- pressively as the requirements develop; (j) be easy to site and maintain; (k) require no regular air calibration checks; and (1) provide a high coverage/cost ratio. Significant developments are now taking place in Decca air-borne equipment and some of these have already been mentioned in Flight during recent weeks. Both the Mk 10 andthe Mk 8 receiver are being miniaturized. The first Mk 10, designed for S.B.A.C. racking, retains existing constructionalpractice as far as possible in order to reduce the number of new features to the practicable minimum. The Mk 10A, which is nowgoing into production, is basically the same but contained in a long 1| ATR case. In anticipation of the requirement forduplicated receivers, Decca are now working on the miniaturized Mk 10B which will fit into a long | ATR case. It will be largelytransistorized and, since the power requirements will be greatly reduced, the power unit will be incorporated in the Flight Logcomputer case. An additional 150 cu in of space will be saved by more than halving the size of the 50 coil cans in the Mk 10.The combined computer and power unit of the Mk 10B will be housed in a long | ATR case. Further circuit refinement in thecomputer will lead to the elimination of the three Decometer movements now used. The stud switch which is the basis of thepresent scale-changing facility will be replaced by a printed circuit disc. Both the present and the miniaturized computerscan handle Decca and Dectra inputs. It is not considered desirable to reduce the surface area of theFlight Log, but the new Type 860 display head, which is now available, has a depth of only ljin compared with the 5|indepth of the current Type 331 head. The Dectra receiver corresponding to the Mk 10B will becontained in a long £ ATR case. In this form it will have many more stages and components than present Dectra receivers whichare designed for use only with the North Atlantic Dectra chain. Most sections of the receiver lend themselves well to the applica-tion of transistors, but a small number of sub-miniature valves may be retained in miniaturized versions. A new Mk 8 receiver, making full use of the available patternsensitivity, is being produced for special purposes such as survey- ing, and a version of this known as the Mk 8A and housed in along £ ATR case is to be introduced. The miniature RF channels and other relevant transistorized sections of the Mk 10B will beavailable for other receivers and one of these will be a Mk 8B in a long \ ATR case. Decca receivers have been designed for use in helicopters,business aircraft and small military aircraft such as fighters. There are two types, the Mk 9 which consists of five units includ- ing an aerial amplifier and weighs 20£ lb and a Bendix/Deccareceiver consisting of three units weighing altogether 21 lb. The Mk 9 has been in production for a number of years and has hadextensive operational use. It employs the principle of lane integra- tion for the resolution of pattern ambiguity, the small size of thereceiver being made possible by the omission of the lane identifi- cation facility. It is highly accurate and employs a specialminiature Flight Log weighing 4 lb and measuring 3£in x 6iin x 4^-in. Later versions of the Mk 9 will be transistorized and, inthe smallest aircraft, the Flight Log could be eliminated with a saving of 4 lb. The Decometers alone, the Flight Log alone orboth together could be used. The Bendix-Decca light aircraft receiver uses die Mk 10 chainsand derives a pair of position line readings three times per minute in terms of coarse hyperbolic patterns generated by theMk 10 transmissions. There are only two R.F. channels in this receiver and two Decometers, the latter built into the receiveritself. They are switched to whichever two of the three available hyperbolic patterns have the best angle of cut at the user'slocation. Readings derived from the brief Mk 10 transmissions are held stable until the next transmission. This Bendix-Decca receiver contains only zonal ambiguity, theeffect of which will be negligible at the airspeeds involved. The pilot need only be able to set the correct zone letter for eachpattern and the receiver will set itself up of its own accord. Either the two Decometers or a combined Flight Log and com-puter, now being prepared by Bendix, may be used. The Decca Mk 9 and the Bendix-Decca light aircraft receiver use powersupplies respectively at 24 V D.C., 7 A and 28 V D.C., 2 A. While the Mk 10 receiver can be easily set up for operationand chart characteristics can be simply changed, a fully self- setting facility is to be incorporated in a Mk 3 Flight Log whichis now in an advanced stage of practical development. In this case a different computer system incorporates digitizing discswhich derive binary code quantities from the incoming red, green and purple angular values. The digital computations produceX and Y outputs, still in terms of the binary code, which are fed to the appropriate co-ordinate of the Flight Log. Six tracks printed along the edge of the Flight Log chart areilluminated by miniature lamps and the output from six corre- sponding photo-transistors then records the binary code quantityrepresented by the markings intercepting the light at any instant. The number of digits, and therefore of lamps, can be increasedto eight or nine. The output of the phototransistors is compared with the digitized output of the receiver in the correspondingco-ordinate and the resulting error signal is made to turn on the paper-drive motor until the difference is zero. Because slippingof the paper over the rollers is no longer important the sprocketed drive is eliminated. The pen is driven across the Flight Log in asimilar manner although a printed track system obviously is not Assembling a floated inertial-quality gyro in a dust-free, air-con- ditioned room at the Autonetics division of North American Aviation
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