Details of Some Components Used for Subsidiary Services in Aircraft Radio Compass adverse effects of moisture. (The container is sealed in the presence of a dry neutral gas to ensure that no A small and light radio compass for use in the M.F. moisture is enclosed in it). Higher power ratings, such band has recently been produced by Marconi's Wire as that mentioned above, are obtained when the EW54 less Telegraph Co. Ltd. It weighs less than 10 kg. is mounted in small cooling fins. Even higher ratings and is suitable for all types of aircraft. can be obtained if oil or forced air is used for cooling. Intended primarily for pilot operation, the compass The device has a high rectification efficiency, has a fixed receiving aerial in the form of a sealed arising from its very low forward resistance, and this, iron-cored crossed loop with no moving parts, and combined with its small size, makes it especially with a maximum height of under ¾ in. The makers suitable for vehicle and aircraft applications. Used claim that by this arrangement a low drag loop instal with a.c. generators the new junction rectifiers pro lation can be achieved without recourse to full sup vide a medium power d.c. supply which is unaffected pression. Alternatively the aerial may be fully recessed by the brush gear trouble sometimes experienced with into the fuselage. d.c. generators. A Bellini-Tosi type of direction finding system is reduce jet noise at the source. The requirements for At an ambient temperature of 20 deg. C. the employed, the goniometer being embodied in the such devices are that they must give a useful noise typical EW54 rectifier passes a current of 8·0A at bearing indicator. Bearing presentation is by means reduction with no effect on engine performance. +0·5V and 6mA at — 100V. Any increase in tempera of a scale pointer, driven directly from the shaft of After some preliminary work on silencing systems, ture results in an increase in both the reverse and the goniometer search coil. There are two sizes of Rolls-Royce designed a corrugated nozzle. This re forward currents at specified voltages. The rise in the indicator, 3⅛ in. and 2½ in. diameter, to allow for places the usual convergent propelling nozzle of a reverse current means greater power dissipation, but variations in available cockpit space. Any suitable jet engine, and consists of a nozzle with longitudinal the corresponding increase in forward current reduces bearing indicator, however, may be used in conjunc corrugations or flutes. A range of nozzles with dif the forward resistance and thus provides some slight tion with the compass. For this purpose a coupling ferent numbers of corrugations from 60 to 4 was made compensation. In practice, the absolute maximum unit is provided which includes a synchro element for and tested. As a result jet noise was reduced and, with operating ambient temperature is 55 deg. C. and the transmission of the bearing indication to the slave careful design, the nozzle did not affect the engine maximum storage temperature 70 deg. C. indicator on the pilot's instrument panel. Transfer of performance. The pitch of the noise affected by the It follows that cooling fins, by increasing the heat the slave indicator from other equipment to the radio corrugations was found to depend on the number of dissipation of the device, step up the output power of compass and vice versa is accomplished by remote corrugations, and a nozzle with 6 corrugations caused the rectifiers. The following figures relating to a full switching. the largest reduction in the loudest part of the jet wave bridge arrangement operating into a resistive The receiver circuits of the compass are contained noise. load with a smoothing choke illustrate this point: in two rack-mounted units and are remotely operated The latest nozzle to be tested gives a noise reduc from a single control unit. Plug-in sub-units are used tion of 11 to 12 decibels, which means that the loud for ease of replacement. The frequency coverage is Output at Output at ness is reduced to less than half and corresponds to 200 to 1,700 kc/s. covered in three ranges. The ambient ambient the difference in noise heard on the ground from an 28 V d.c. aircraft supply is used directly for H.T. temperature temperature aircraft flying overhead at 1,000 ft. and one flying A portable test set for checking the main units and of 20 deg. C. of 55 deg. C. at 3,000 ft. Development work is continuing, and each of the sub-units has been designed specially for when the optimum point is reached production will this equipment. V A V A be arranged and engines fitted with the nozzles made Without cooling 50 6·8 50 2·4 available. With cooling 50 24·4 50 4·0 The work has been done on a specially-designed Medium Power Germanium Junction Rectifier engine test stand, but a set of nozzles has now been The General Electric Co. Ltd., has introduced the made for the De Havilland Comet and will be flight If the EW54 exceeds its maximum dissipation first germanium p-n junction rectifier for use in tested in the near future. Since the noise heard on the rating the reverse current can rise further which medium voltage and current circuits to become ground from a jet-engined transport aircraft taking again increases the dissipation; this cumulative effect commercially available in this country. A 50 c/s a.c. off is about 9 decibels more than that from a com can cause a condition known as 'runaway' which will full wave bridge, using four of the new Type EW54 parable piston-engined aircraft, it is hoped that the result in permanent damage to the device. rectifiers, will provide a maximum output power of fitting of corrugated nozzles to jet aircraft will mean The efficiency of a full wave rectifier circuit working 1 kW (50V at 20A) with an input voltage of 50V that they will be no noisier than propeller types. into a resistive load has been defined as the product r.m.s. of the mean d.c. output voltage and current divided by The EW54 rectifier is only 1½ in. long and has a the product of the r.m.s. a.c. input voltage and current. maximum diameter of ⅝ in. Careful attention has been R-Theta Computer The maximum theoretical efficiency for any type of given to the hermetic scaling of the unit so that the rectifier is then 81 per cent when using a sinusoidal in A navigation aid which indicates the distance and sensitive p-n junction is completely shielded from the put wave form. The EW54 rectifiers, used in a circuit bearing of an aircraft from a given point instead of of this type, have a rectification efficiency of over its position in terms of latitude and longitude, has 95 per cent of the limit value. been invented by a Canadian, W/C. T.C. Wright, and In addition to high rectification efficiency the EW54, developed by PSC Applied Research Ltd. of Toronto. because of its low forward resistance, also exhibits very Called the R-Theta computer the instrument can be used in most types of aircraft, and weighs 37 lb. The good regulation. Thus, when a 50V r.m.s. input is name is derived from the concept of reporting posi applied to a full wave bridge arrangement, the output tion by polar instead of Cartesian co-ordinates. voltage drops from a value of 45V at zero d.c. output current to 44V at an output current of 20A. This small Basically the computer consists of an automatic voltage drop corresponds to an internal forward machine for calculating how far and in what direction resistance of about 0·05 ohm. the aircraft has moved from its starting point, and a The EW54 is suitable for operation at a.c. input set of gears and electrical circuits for computing the frequencies of up to a few kc/s but, due to the 'hole distance and bearing of the aircraft's destination, storage' effect, the efficiency is reduced at the higher allowing for wind. Calculations in the computer are performed automatically, independently of radio frequencies; this means that the output ratings must transmissions. Distance and bearing of an alternative also be reduced. destination can be set into the device by turning two When the EW54 is used in a two phase circuit, the knobs and depressing a switch. Distance is indicated output voltage has to be reduced, although a high out on a counter in the face of the instrument and direc put current is permissible. This is because the peak tion is shown by a double arrow. A single arrow in inverse voltage in such an arrangement is approxi the display panel indicates the aircraft's track over mately twice that in the full wave bridge circuit. As a the ground. When the aircraft is turned so that the result the maximum output voltage in a two phase single arrow lies over the double one it is flying to circuit is 25V. wards the destination. Should the pilot wish to return to base, he lifts a lever marked 'vector-add' and the Corrugated Jet Nozzle double arrow swings round to the direction of the base from him. The device is fitted with a 'memory' For about four years several aero engine manu which remembers the aircraft's heading and speed facturers have been engaged under contract to the while the navigator is adding or subtracting vectors. Ministry of Supply, on the development of means to October 1955 351
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Oct 1, 1955
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