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Aviation History
1946
1946 - 0710.PDF
FLIGHT APRIL IITH, 1046 De-icing for To-day The T.K.S. Fluid System Described ; Ingenious Distribution and Regulation Methods : Automatic Protection IT has become customary nowadays to consider thataircraft de-icing will eventually be done by thermalmeans, and certainly one or two projected civil designs, both here and in America, have been planned with theuse of this system in view. Nevertheless, and whether or not thermal methods of protection eventually become theaccepted practice for large aircraft capable of economically carrying the necessary equipment, a good deal of experi-mental work is still necessary before they can be con- sidered to have "arrived." In the meantime a considerably improved version ofan blder system is being fitted to nearly all the British civil transports now in course of prototype development orproduction. The ptesent Air Registration Board regula- tions virtually require that all civil aircraft must be fittedwith some form of aerofoil, airscrew and windscreen de- icing system, and, though the method to be used has beenleft to the discretion of the manufacturers, the latter are naturally going ahead with the installation of equipmentwhich is now available and which has the capacity to do the job. This equipment, the T.K.S. (ofwhich the letters are made of the names Tecalemit. Kilfrost andSheepbridge Stokes, thus indicat- ing something of the origin of thecomponents), can, as a matter of history, be fairly considered to bethe direct heir to the Dunlop sys- tem, which was originally devel-oped and tested by Farnborough. In it a special de-icing and ant-lcing lluid was fed to porous over- shoes in the leading edges. Endurances The same principle is used to-day in the T.K.S. system, though the methods of distribution and regulation have been very muchimproved, and the fluid itself has been modified in its constituency to permit greater economy and endurance in operation. So much so that the equipment in an air-craft ol the Tudor size has ar endurance, at the normal rate ofteed, oi something like five hours or, with heavy icing emergency delivery, of more than an hour.Since the object of all meteorological reports and of all- weather flying is that of avoiding icing conditions as faras possible, such endurances should be more than ample. Incidentally, the total weight of the equipment carried isless than halt that of the fluid, so it is obvious that, for shorter-stage journeys, the total figure concerned may bereduced accordingly. In the case of the Viking installation, lor instance, the equipment itself weighs 1451b, while thefluid, when a maximum supply is carried, weighs i6olb. Two major problems have had to be overcome in thecourse of development of the T.K.S. system. The first being that of regulating the flow at the surfaces so thatthe fluid will quickly reach all essential points and yet not be wasted, and the second that of initial regulation foidifferent conditions. The regulation and accurate dissipation at the surfacesis completed by special distributors which are built into the leading-edge structures in positions and in numbers accord- The T.K.S. dis-tributors and control panel intheir latest form. The porous"spreader'" is flush with theleading edge. ing to the particular requirements, A large aircraft, forinstance, might have triple lengths of distributor inboard, two at the mid-section, and one near the tip; while asingle strip only might be required for the tailplane and fin leading edges. The construction and operation of the distributor maybest be followed from a study of the sketch on this page. It consists briefly of a radiused square-section metal tubewhich is divided into two longitudinal compartments by a central web. As the distributor is installed the rearmostcompartment forms the primary feed. From this the fluid is led by capillary control tubes to the second compartment,into which a porous metal "spreader" is sintered. This porous distributor becomes, after the sintering process,actually part of the tube and forms part of the leading edge. The de-icing fluid—which may roughly be described asbeing a compound of alcohol, glycerine, glycol and glucose —seeps through the spreader evenly and runs over thesurface at a known and controlled rate. The relative viscosity of thefluid is of considerable import- ance and has been the subject ofmuch development. In earlier attempts to obtain an even film offluid on the wing surface, low- viscosity liquids were used be-cause these were more easily dis- tributed. Though adequate forthe purpose, these earlier fluids were extravagant because the pro-tective film could only be 'main- tained by using high rates of flow ;development of the present distri- butor enables a more viscous (andeconomical) fluid to be used. Automatic Control The pressure feed is main-tained by means of an electrically- driven Tecalemit micro-pump,which is controlled automatically and is mounted directly below thefluid supply tank. In the latest version of the T.K.S., the electri-cal flow controller has been separ- ated from the control panel itselfand can be installed in any posi- tion in the aircraft, while thepanel, which is now only a matter of four or five inches square, canbe situated in the most convenient dashboard or other mounting, where it can be in continuous view. There are three different "standards" of de-icing con-trol, and these can be selected by three switches on the panel. The fiist can be described as being directly manual,since the supply is switched on or off at the will of the pilot, though there is a degree of automaticity since the initialsupply of fluid is regulated to provide an ample and quickly-formed film. The second "standard" is automatic. In this case theswitch concerned is left on during flight, and a Smith auto- matic ice-detector brings the pump into action when icingconditions are met. This detector briefly consists of a small tube, mounted in the direct airflow, with the num-ber of microscopic holes; at the first sign oi ice formation, and long before any deposits appear on the aircraft struc-ture, these holes are plugged by the formation and pressure- change causes an electric contact to be made. The de-icing
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