FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1944
1944 - 0404.PDF
2'J8 FLIGHT FEBRUARY 241H, 1944 AIR FILTRATION FOR AIRCRAFT ditions. Makeshift airfields would have to be used fre quently, and even good airfields would be subjected to disruption by enemy attacks. Moreover, it would never be possible, always to have fully staffed maintenance units on hand at all the right places at the right times, with adequate supplies of spares and equipment. Aircraft would most certainly be lost through unavoidable causes; it was of the highest importance that as few as possible should be lost through avoidable causes. If really efficient filters could be provided, engine life would be considerably lengthened, the morale of the crews would be correspondingly benefited, and the output of the aircraft factories would increase in value, because fewer of the new machines would be needed to replace losses. But their requirements amounted to an enormous prob lem which called for rapid solution. They demanded a high standard of filtration efficiency, which in itself necessi tated an enormous filtering area; they insisted that the filters should be small, light, dependable, easily serviced, of patterns to fit the various types of machines, and, of course, they were not to have any appreciable adverse effects upon speeds and altitudes. It was a tall and urgent order. Engines clogged-up in Few Minutes Furthermore, the dust conditions actually encountered were unfortunately far worse than had been envisaged. In the battle over Europe in the earlier days of the war in Holland, Belgium and France, engines were wearing out after about fifty flying hours, and even on some of our airfields in this country engine wear and high oil consump tion were observed, on occasions, after as little as ten hours. In the Western Desert, conditions were appalling. Sand storms, often rising to a height of 18,000 feet, buried every thing, and aircraft on the ground were lost to sight at only a few feet distance. Engines were clogged up in a few minutes; even in '' normal desert conditions,'' aircraft taking off fed many ounces of sand into their engines by airscrew action during the warming-up period, and this was especially so when they were taking off in formation, each aircraft taking the full force of the sand swept up by the machines in front. All these problems have been overcome by two types of filter which we have now been producing in great numbers —the Vokes Aerovee and the Vokes Three-ply. The Aerovee is a dry type filter, constructed of non- inflammable material and very light in weight. It is made in five layers; two of wire gauze between which there are two layers of fabric, with a centre layer of cottonwool. The Vokes Three-ply is a viscous type of filter fitted on air- cooled engines. This picture shows the inner assembly for a Bristol Blenheim. The Vokes Aerovee is a dry type of filter, fitted on liquid- cooled engines. This one is from a Whitley. These layers are stitched together and are then corrugated into deep folds, so that in relation to the air inlet, an enormous filtering surface is created. The ratio is, in fact, about 200 to 1. The filter element is housed in a light fibre frame and tilted at such an angle that dust particles in the incoming air tend to fall gravitationally from the filtering surface. This type of filter is largely self-cleaning engine vibration shaking it free from accumulated di/^J when servicing does eventually become essential, it is only necessary to take out the ele ment and tap it sharply a few times against a dry flat sur face. When the Aerovee was first introduced, although it passed the severest filtration tests, doubts were expressed thai because of its construction it might catch fire from exhaust flames. It was, however, proved conclusively by special tests, in which engines were deliberately back-fired for approximately one hour, that far from this being the case, it was an excellent flame-trap. Especially built to fit into the design of the aircraft, the Aerovee is installed with in line engines. It is now pajrt " Tropicalised " aircraft of an Australian Spitfire squadron in the Western Desert, fitted with Vokes filters.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
