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Aviation History
1946
1946 - 1551.PDF
AUGUST 8TH, 1946 FLIGHT Redueiog Aircraft Losses Maclaren AntUstrike Coolant Protection System : Automatic Isolation of Damaged Sections ^MONG the many developments about which little or/•% nothing was told during the war period, one of the '«-£••• more interesting was a system for automatic anti-smke coolant protection in aircraft. The experimental and production woik on Mr. O. F. Maclaren's original lay-out was completed by his firm at Heston, and only the diffi- culties involved in the quantity production of the variousitems, and in their installation without disturbing the normal flow of airciaft manufacture, prevented the systemfrom being more extensively used. Mr. Maclaren will be remembered as the designer of a " steerable" under-carriage system which permitted drift landings and was successfully applied on test to various types, including theOxford and the Mustang. It is undoubtedly true that by far the greatest proportionof aircraft losses during the war were the result not so much of personal casualties in combat or from anti-aircraftfire, but of forced landings following damage to coolant systems. As far as single-engined fighters are concerned,it has been impossible to obtain reliable figures, since the resultant damage nearly always prevented the aircraft fromreturning to base, and no records could consequently be compiled. But a number of figures were obtained fordamage to multi-engined air- craft—and, in particular, forthat suffered by Mosquitoes. It was found, for instance,that in twenty-eight cases of strike damage, fourteen ofthese involved complete or partial loss of coolant fromthe system actually outside the engine nacelle itself. The degree of importanceattached to such coolant pro- tective measures is indicatedby an extract from Air Publi- cation 970, which, amendedearly this year, reads: '' On single-engined aeroplanes adevice shall be incorporated to ensure that, in the eventof a single strike in the radia- tor, at least sufficient coolantwill be retained in circulation to enable the aeroplane tocontinue in straight and level flight." It does not requirea great deal of imagination to realize that a similar sys-tem can be applied with equal value to items such aslubrication circuits, and might even be developed fortypes of military air- lift power unit. Simple Principle In principle the Maclarensystem is quite simple. When a strike is suffered in or neara radiator, that part of the coolant system is instantan-eously isolated, thus prevent- ing loss of glycol and engine failure. Naturally enough, the system can only beapplied successfully in cases where two separate radiators are fitted—but this is the rule rather than the exception in fighter design. The surfaces of the radiator sections areenclosed in screens consisting, in effect, of wire circuits, connected in series and carrying a small electric current.If a bullet, shell or shell-splinter pierces the area, it must necessarily pass through one of the screens, and thus breakthe circuit. This breakage causes a solenoid to operate which, in turn, closes a full-power circuit. This " blows "high tensile steel fusible links. A trigger mechanism then allows the closing of each of the spring-loaded valves inthe coolant system. Simple as the principle may be, the detail design workand the organization of comparatively easy methods o\ manufacture "of the various parts involved the exercise otconsiderable ingenuity. The "contact areas" are of two kinds. The internally placed screens must, of course, tutof sufficiently thin section to be capable of installation be- tween the radiator block and the enclosing fairing, and tobe fully insulated. Those in front of, and behind the honeycomb itself must, additionally, permit free passageof air and be robust enough to be resistant to the impact of stones thrown up while taxying and taking off. Whereas the construction of the steel grids is a com-paratively straightforward affair, apart from the very critical tempering of the steel ribbons, that of the screenswas considerably complicated by manufacturing difficulties. The method finally used for producing the breakable con- A semi-diagrammaticsketch of the Maclaren system as applied tolater marks of the Spit- fire. On the left is anexample of the intern- ally placed screening,and on the right a sec- tion of the honeycomb-covering grid. Below, on the left, is a section-ed view of the automatic valve and its fusible link; notice how the " snap " valve and its fixed fairing normally form astreamline shape in the coolant pipeline.
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