The infamous Vokes Air Filter

[Fatboy Coxy]

Hi all

I'd like to know more about the British infamous Vokes Air Filter, used in the North African Campaign from 1941. I say infamous, because I've read that it had a negative impact on the speed and maneuverability of aircraft it was fitted to, but operating in the sand and dust environment of that theatre of war, something like it must have been needed. I'll provide what little I know, or have read, and hopefully people can fill in the missing bits, correct me or confirm my 'facts'.

Vokes was (is I believe still) a developer and manufacture of engine filters, and was asked to provide a special 'tropicalised' filter to deal with large amounts of sand and dust in the air, and so save on excessive engine wear. What they produced was a large dust filter that fitted over the carburettor air intake under the nose, and was in service from mid 1941 in North Africa. All well and good so far, however the size of the 'air scoop' underneath caused considerable drag, affecting performance. They were fitted to both the Hawker Hurricane and Supermarine Spitfire, but I don't know if the American P40 series of aircraft were fitted with them or a different dust filter, as it had the ability to bypass the filter once having taken off.

Performance figures I have read suggest the Spitfire lost 16 mph due to its air filter, the Hurricane lost 20-25 mph, and I'm unaware what performance was lost on the P40s.

A RAF MU (Maintenance Unit) based at Aboukir, Egypt, worked on refining the Vokes Filter, reducing lost performance, but was only made in small number, this was called, not surprisingly the Aboukir Filter.

Hurricanes and Spitfires sent to the Far East (Singapore, Burma, Australia and India) also used the Vokes filters.

However at some stage I think the original Vokes filters disappeared, this may be with the change up of model of aircraft being operated and a better filter being introduced, or an acceptance of a shorter engine life time, in exchange for retaining that potential life saving speed.

And that's it, all very shaky info to be honest.

 

[Juha3]

Some info about Vokes Volkes filter - what's inside?

Spit Mk. IXs and VIIIs fitted with tropical filter had instead of the Vokes a Supermarine tropical air intake with integrated filter element working in the same princible than the filters on Merlin Mustangs and Bf 109s. Incoming air could be directed through the filter when needed, otherwise it bypassed the filter.

 

[MIflyer]

When RAF Typhoons were deployed to Normandy they found the dust on those rough airfields was a problem. So they had a representative from a UK filter company come over and in short order he devised a way to install filter cloths in the existing engine hardware and this proved to be effective.

Now, why were US aircraft never seen with filters? That is, except for the Spitfires flown by the USAAF in the Med? Well, for one thing the Allison V-1710 was a downdraft intake engine, where the air came in through the top of the cowl, requiring a long duct that was suitable to carry air filters. The RR Merlin was an updraft intake engine and so the air intake came right off the bottom of the fuselage. On the Merlin Mustang the air intake was located right under the prop, once again providing a long intake duct that could be used for a filter.

 

[GreenKnight121]

We just had a thread where this was discussed..... the "Pink FR/PR Spitfires" thread - many posts about both the Vokes and Aboukir filters: Pink FR/PR Spitfires

And an earlier one "How good a plane was the P-40, really?", which has scattered discussion of air filters on P-40s and other aircraft: How good a plane was the P-40, really?