FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1956
1956 - 1684.PDF
846 FLIGHT, 30 November 1956 AIRBORNE PROXIMITY INDICATOR . . . use may be made of such echoes in the hemispherical systemfor ground-proximity indication. The receiver-transmitter unit is built up of modular components using printed circuitry and,where possible, transistors. A meter and meter switch permit easy checking of circuit operation and power-supply voltages.The unit is designed for installation in the pressure cabin. One of the more difficult components of the system is the aerialarray. Four quadrant aerials are needed, each with a horizontal beam-width of 90 deg and a vertical beam-width of 15 deg. Twofurther aerials cover the upper and lower hemispheres. By using a square waveguide behind each of the aerials, cross-polarizedtransmitter and receiver probes achieve the necessary isolation between transmitter and receiver to allow a single aerial struc-ture to be used for both functions in each aerial element. The cross-polarization also considerably reduces echo from denserain. The aerial switch is a co-axial unit mounted close to the aerials; it switches the transmitter and one of the three receiverssimultaneously to each of the four quadrant aerials for 0.5 sec per quadrant. It turns at 30 r.p.m. and has no wiper contacts.The hemisphere aerials operate continuously with their own receivers.Because it is not practical to use aerials of the size required to give ideal area coverage, there is an inherent overlap in thequadrant coverage at the upper and lower surfaces of the lobe formed by the 15 deg included angle over each quadrant. Whenan intruder is in an overlap area an indication on two of the quadrant warning-light lines will appear. The length of time for which this double indication occurs is partly dependent onthe radar cross-section area of the particular intruding aircraft; but Collins state that under average circumstances an overlaparea is not likely to be more than ± 7 deg. Though such a dual indication from one intruder is undesirable, the case of a secondintruder in exactly the right position to give a combined indica- tion similar to that caused by lobe overlap is considered by thedesigners to be most unlikely. It is also stated that intruders at a range of one or two milesbetween 200 and 400ft below the protected aircraft may be indicated simultaneously by the hemispherical and quadrantcoverage. The 15 deg vertical angle of the quadrant coverage has beenchosen as a good compromise in ensuring long-range detection of climbing or descending aircraft having relatively high speeds ofapproach. The hemispherical aerials cover the areas immediately above and below the protected aircraft, and here also a dualindication may appear on quadrant and hemisphere indicators as in the overlap zones. Collins are making efforts in the designof the aerial to reduce such duplication to the minimum. Collins expect no major problem to arise when two aircraftequipped with PI-101 approach each other. Cross-polarization used in the aerial system assists in rejecting interfering signalsand the F.M.-C.W. system itself strongly rejects unsychronized signals. The equipment is being designed to give a satisfactoryindication of small, clean aircraft with a small radar cross-section area. The completed equipment, less aerials and cables, isexpected to weigh about 68 1b and to include seven electronic valves, 32 transistors, a magnetron and a klystron. BLACK BOX FLYING CONTROLS (continued from page 844) by means of a long system of rods, cables, levers, torque shafts,etc., is a clumsy way of achieving a simple object; the inherent reliability of such a system, however, has been proved and cannotbe ignored. If electrical position signalling is to achieve a com- parable degree of reliability, then at least duplicate signalling mustbe provided, with automatic means of coping with failures— although it is then questionable whether in themselves theadvantages of electric signalling would be sufficient to justify the complication involved. "The problem becomes quite different, however, the momentone begins to deal with the design of inherently unstable aircraft [a concept to which we refer in a leading article]. An automaticstabilization system and its associated signalling channels would then be required to function at all times and with an extremelyhigh degree of reliability; and a case for retaining a mechanical linkage would practically disappear, since the aircraft could notbe controlled by it alone. "Under such conditions the most likely solution to be adoptedis that in which the computor reinterprets the pilot's demand signals; for instance a sideways movement of the stick may beinterpreted as a demand for given rate of roll, which in high speed aircraft may require large aileron motion in one direction followedby some opposite aileron, and the computor would automatically provide this. This type of control is not really new, and corres-ponds more or less to 'manoeuvre stick control' [an auto-pilot actuated by an articulated control column; described in Flight,February 18, 1955], which has been popular in the United States for some time. The difference is that, from being an added facilityof the auto-pilot, this system becomes the basic means of control- ling the aircraft, and may therefore require considerableelaboration. "All electric components involved would have to be duplicatedat least, but there is also the question of reliability of hydraulic ABOUT COMPUTERS A USEFUL, non-mathematical introduction to the principles**• and applications of computers employing valves and other electronic devices has recently appeared. With the title ElectronicComputers: Principles and Applications, it has been edited by T. E. Ivall and is published by Iliffe and Sons, Ltd., DorsetHouse, Stamford Street, London, S.E.I, at 25s (postage 9d). Though primarily written for engineers and students it willalso be found useful by business executives, for the treatment has been made as general as possible in order to give a broadbackground picture of the whole field of computing. Those wishing to do so can then pass on to more specialized studies.The book deals comprehensively with both digital and analogue computers, comparing the two types, describing their circuitryand construction, and outlining their rapidly developing applica- tions in commerce, industry and science. Considerable emphasisis placed on their application to automation techniques, and also on the use of analogue computers as simulators of control systems.In the final chapter the future evolution of computers is discussed. components and supplies. One way of solving both of theseproblems at once is for each control surface to be driven by three actuators in parallel [as shown in Fig. 5]. Each has its ownhydraulic supply, electric signalling devices, wiring, and networks, and each also has certain basic instruments of its own—possiblyrate gyros. The system would then be such that—in manual control at least—any single failure would affect only one channel;whatever the cause of the fault, the actuator in the faulty channel would be overpowered by the other two. Systems of this typecould not stand two failures in general, but can be arranged to stand certain combinations of two failures; if any combination oftwo failures is to be tolerated, quadruplication would seem to be inevitable. [Quintuplication has already been suggested elsewhere.]As electrical components, wiring, fittings, etc., become more reliable, we may find that such extreme measures will become un-necessary. There are of course difficulties in synchronizing three actuators—let alone four—but in some respects all-electric signal-ling facilitates actuator design. Firstly, a valve which needs electrical actuation only is obviously going to be simpler than onewhich has to accept both electrical and mechanical inputs; secondly, there is no need for mechanical differentials or movingcylinder arrangements, both of which are a nuisance; thirdly, there is far less likelihood of instability due to structural feedbacks[distortion of the structure under aerodynamic or jack reaction loads causing relative movement of the input linkage which willmove the control valve] through the signalling system." In conclusion, the author made it clear that integrated controlsystems are dictated by the problems associated with high speed flight: "They may range from a relatively simple combinedpowered control/auto-pilot to a highly sophisticated system with all-electric signalling and probably triplicated actuators, bristlingwith automatic safety devices. Whatever the type of system, reliability is likely to remain the central problem." CURING TV TROUBLESM ANY television viewers do not get the best out of their sets,either because they do not know how to use the controls, or are afraid to adjust them for fear of making things worse or causingdamage. To readers with families or friends suffering from this form ofTV-itis, we would suggest that a book called Improve Your Television Reception, by John Cura and Leonard Stanley, wouldprove an appropriate Christmas gift. The authors explain what each control is intended to do, and how it should be used; theydescribe the different kinds of interference and suggest how these may be overcome; and in a series of 136 questions and answerscover almost every imaginable television trouble and provide a remedy.All this information is given in simple, non-technical language and illustrated by "tele-snaps" showing exactly the conditionsdescribed. Improve Your Television Reception is published for Wireless World at 5s (5s 4d by post) by Iliffe and Sons, Ltd.,Dorset House, Stamford Street^ London, S.E.I.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
