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Aviation History
1935
1935 - 1299.PDF
MAY 30, 1935 31 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT 583^ gressive throttle opening and a fine degree of control over engine speed. (2) He cannot run on mixture strengths that will be either too weak or wasteful, need not alter his mixture control lever with changes of altitude, and need not judge mixture strength by watching his thermometer, boost gauge and altimeter. On the other hand, it is possible, through forgetfulness or if the pilot's attention is engaged elsewhere, for him '.o fly with his throttle lever fully open whilst the mixture control is in the "weak automatic" position, and the Hobson Pilot's Cockpit Control was designed to prevent this. This particular device so interlocks the pilot's throttle and mixture levers that the '' weak automatic '' setting can only be used with the throttle lever in the safe cruising range, any movement of the latter outside of this safe range of cruising speeds either to the full-throttle or slow- running positions automatically shifting the mixture lever to the "rich automatic" position. Two views of this control are shown in Fig. 11. A third position of the pilot's mixture lever is the " over-ride " position, which keeps the mixture control at the " auto matic rich " setting, but over-rides the boost control and opens the enrichment jet valve. This is the position in which the pilot sets his mixture lever for take-off. Fig. 11. Two views of th* Hobson cockpit control. The pilot also has an emergency throttle position, which can only be reached by going through a gate protected by a seal. Should, in a grave emergency below rated height. the pilot want maximum power output, even if it may badly strain the engine, movement of the throttle lever through the gate over-rides the boost control, and, in addi tion, mechanically opens the carburetter throttle to its wide-open position; but to minimise the possibility of damage, the rich mixture jet is automatically opened. As damage if any, may not show up until some later period, it is intended that the breakage of the seal shall be recorded in the log-book, and the engine examined before it is put into service again. Cruising on Ultra-weak Mixtures The subject of a further patent is the use of mixtures weaker than is normally used for cruising, in conjunction with considerable extra ignition advance. It is so arranged that the interconnection between the Hobson P'lotS Cockpit Control gives retarded ignition for slow running, an extra degree of advance during the cruising range on ultra-weak mixtures, some retardation at full boost and further retardation for take-off boost and emer gency over-ride. It will be seen, therefore, that a scheme has been evolved which renders it impossible for the pilot to so mishandle his controls that he can damage his engine, or make a mistake which might endanger his life or the machine. He is relieved of all responsibility for the welfare of the engine, and it enables him to give his un divided attention to flying and navigation. The psychological effect of such a " robot " scheme on a pilot, particularly in aerial warfare, which may be taking place at rapidly varying altitudes, needs no lively imagination. Automatic Ignition Control In multi-engine machines it is not feasible to hand- operate the ignition timing—which requires a fast-moving cam—owing to slogger and springiness of the machine control. The Hobson Automatic Ignition Control device (shown in Fig. 12) which operates to time the ignition in accord ance with induction pipe pressures, is devised for use on multi-engine machines. In these circumstances, and act ing in consonance with boost pressure changes, it can be made also to operate the carburation heat control and other engine adjuncts. Fig. 12. The Hobson Automatic ignition control. The device is intended to operate so as to retard the ignition for regular idling and starting without kick-back, when the throttle is more or less at the idling position. It should then rapidly advance the ignition to the maximum when cruising conditions aie present. It should again somewhat retard the ignition for normal full-load running, and further retard it for take-off boost or when the emergency over-ride boost is in action. It contains a device which prevents a continuous advancement of ignition timing as height is gained above the rated height, or alternatively reduces the rate of in crement of advance as height is gained above the rated height. In addition, it can also be used to bring the power and rich-mixture jets into operation. Carburation Heat Control It is very desirable to give extra heat to the carburetter when cruising at less than normal boost, not only to prevent freezing, but also to secure more economical running. The ignition control can be used to govern the heat input to fefle carburation system in accordance with boost pressure, and to obtain this effect, it may operate
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