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Aerial Lighthouses.


Extract from the 1929 Encyclopaedia Britannica.

Aerial Lighthouses. - "Light signals are needed by aircraft in night flying, just as they are required by the mariner. Aircraft travel in three dimensions and also at higher velocities than a ship. Light signals for the guidance of an airman must therefore be at short intervals and must be visible from the horizon up to the zenith. One form of optical apparatus for an aerial lighthouse comprises a lower section similar to the portion below the focal plane of a marine revolving light; above this is a section of a fixed light optic with its axis horizontal instead of vertical as in a marine fixed light. The lower revolving lens emits a high?powered beam of light of a small angle with its axis just above the horizontal while the upper segment throws a narrow band of light of low power from the horizontal to the vertical. Although an airman would pick up the main beam emitted by such an apparatus at, say, 30 miles, he would be above it (if flying at a height of 6,000 feet), when at a distance of about 20 miles and not near enough to pick up the weaker beam. To compensate for this the lower lens and the illuminant are made of such dimensions and power that the main beam is stronger than is actually required in the direction of its axis and a portion of the rays from this beam is bent upwards by means of refracting prisms placed in front of the panel, thus reinforcing the light in the direction where additional power is required. The optical apparatus is rotated on a mercury float or on ball bearings as in a marine lighthouse.

In some aerial apparatus, as at Cranbrook in Kent, reflecting mirrors are used as well as refractors in front of the lower part of the lens, and refracting prisms are employed instead of the fixed light lens in the upper portion of the apparatus. Lanterns containing the apparatus of aerial lights have glazed roofs as well as the side glazing usual in marine lighthouses.

In Great Britain and France the guiding principle of airways lighting is to provide powerful lights at comparatively long distances apart, which can be picked up by airmen at long range flying either low down or at comparatively high altitudes.

In the United States and in Germany the practice is to lay a series of comparatively low power lamps at short intervals along the air route, the airmen being expected to follow the line marked out."

Inland aerial lighthouses or beacons were established as early as 1922 on high ground at Tatsfield, Cranbrook, Lympne and later at Brenchly on the Croydon to Paris air route. Their duty was to aid airliners flying at night.

By day the airplanes usually followed railway lines and many of the railway stations had their names painted on the roof in large letters but at night this was of no navigational benefit. Even today the tall water towers on the approach route to London Heathrow bear the international Heathrow airport code to identify themselves during daylight to incoming air traffic.

The Paris air route from Croydon passed over Tatsfield first, then Brenchly (near Tunbridge Wells), next Cranbrook and finally Lympne (an airfield near Hythe on the Kent coast) before crossing the English Channel.

Trinity House gave much help and advice in the construction of these lighthouses and each had a self contained light unit. The light was illuminated by dissolved acetylene stored in cylinders on site and turned on and off by a 'sun valve' allowing the light to be lit during the hours of darkness only. As the gas passed through the lens mechanism it caused the lens to revolve. The incandescent mantle was capable of being changed automatically if it became defective.

Coloured lights had been tested but not used as it was found that the coloured glass absorbed too much of the light thus reducing its effectiveness. On an average an aerial lighthouse cost £ 20,000 each.

Tatsfield

The picture of Tatsfield Airways Lighthouse is dated April 21st 1931. Tatsfield is 8 miles south east of Croydon and lies in the extreme east of Surrey running along the border with Kent. It is one of the highest villages in Surrey with the highest spot at Botley Hill at 876 feet above sea level.

This Air Ministry lighthouse was located on Tatsfield Hill, 223 feet NNW of the BBC Receiving Station and was a flashing beacon made by Plessey. Some local historians say it was still in place in 1941 but unused; others say it was dismantled at the outbreak of war. However no trace of it survives today.

The Cranbrook lighthouse was at Hartley, a part of Cranbrook on one of the highest points of the Weald in Kent and was about 32 miles south east of Croydon. It was an open iron work structure erected by the London firm of Morris and was 50 feet tall with a lantern on top.

The name 'CRANBROOK' was carved out in 20 feet long letters in the chalk for daylight identification but as the Second World War approached the letters were dug up and the land ploughed over. The lighting mechanism was removed and the tower dismantled shortly afterwards.

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Cranbrook Aerial Lighthouse

No trace of it survives today but for many years after the war the name Cranbrook was still clearly visible from the air as the corn grew a different colour on the barren remains of the letters.

Lighthouse optics were also used during the Second World War as airfield beacon lights when they were mounted on trailers so that they could be used on temporary airfields.

It seems likely that all the inland aerial lighthouses were dismantled and removed at the outbreak of war. By the time the war was over in 1945 the advent of radar and radio made them redundant and the need to re-erect them never occurred.


Andrew writes on 25th June 2006 :-

Good morning!. I was pleased to discover your interesting website as air lighthouses are a subject that fascinates me. Between Croydon and the coast up to 15 intermediate beacons were made by Aga and ran on acetylene gas, which is noted for its brilliance. Later, during the 1930s they were converted to electric operation. The first site out from Croydon was known as Tatsfield, located north of the B2024 road, just east of Botley Hill at the top of Titsey Hill, and it is believed that this lighthouse is the one now preserved at North Weald airfield museum. Other sites included Merle Common (near Oxted, due south of Tatsfield), Merstham, Brenchley (south of Paddock Wood), Hartley (near Cranbrook) and a site near Folkestone (possibly Lympne). Clearly this list is well short of 15 and I'm not sure if the Tatsfield site that he notes accords with yours. I know he is right because the air lighthouse is marked at this site on a map on page 11 of the book 'A Detective in Surrey' by Donald Maxwell (published 1932). It's possible that the Tatsfield beacon moved location subsequently. Other information I have garnered includes: At Croydon the distinctive flashing red light of a giant light beacon with 6,080 candle-power guided airmen for up to 80 miles to the landing place, whilst the Mont Valerien beacon, just outside Paris, boasted an amazing 1,000,000 candle-power, obtaining its magnification from two six-foot reflectors. On a clear night it was visible to a pilot flying 1,000 feet above Croydon. If this prompts any thoughts I'd be delighted to hear from you!


Paul writes on 15th July 2008 :-

I have just returned from finding a 1941 OS map to study which (rather surprisingly given the wartime date) shows the location of the beacon. See photo. Having investigated the area suggested - 223NNW of the listening station - I can vouch for the fact that there is an interesting rectangular area now very overgrown with trees 35 x 17 metres approximately, marked out with bricks in the ground which might just have been the place. On a hunch last night, I thought to check certain dimensions and was rather pleased with myself today for being able to confirm that as I had thought quite possible, that site was in fact once a tennis court presumably for the amusement and exercise of the listening station staff. !

In fact the marked point is approx 240 metres SE of the entrance to the listening station where to this day there is a lattice radio mast which I remember having existed there since the 1961 when as a child we moved here from Croydon. The size of the fenced enclosure in the photo on your site appears very similar to the existing site although the boundary is well over grown but I shall investigate tomorrow. This is between Beddlestead Lane and Tatsfield Approach road and is a marked high spot of 865 feet ASL on some OSmaps. This location would also seem to far more sensible than the suggested NNW of the listening station as it is in a treeless area unlike the other which is next to a copse that is clearly marked on maps dating far earlier.

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Paul writes again on 17th July 2008 :-

I think your comment that '...no trace of it survives today.' could be updated to note that the fence in the early picture appears to have survived - almost intact within the hawthorn that has taken over the boundaries of the site and it is in remarkably good condition considering its age!

To be fair, It is hard to be 100% certain that it really is the original although by the nature of the way the trees have grown intertwined with the bars, the fence is certainly no more in its first flush of youth than am I!

Judging by the lie of the land I think it is as I have presented it in the attached photo which means the camera is looking North East with Croydon Airport being almost exactly 8 miles to the North West of the site.

The site now has some fairly modern Microwave equipment installed although various redundant concrete fixtures indicate that there have been a few changes over the years. But for pathways to the relevant equipment the remainder of the site is very overgrown and concealing among other things what appears to be a ROC Post in the very centre. Given its relative position within the square, the picture of the item labelled 'Base' may perhaps have been the leftmost corner of the original structure.

As an incidental consideration, the site itself has no security features whatsoever and nor is there much in the way of restriction to the surrounding field. It is good soil however, this year sprouting a very healthy crop of beans and I am sure it would be appropriate and of course respectful to the landowner to mention that the site is on private land.

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Photo of fence - photo of base - photo of beacon site


Paul writes again on 25th July 2008 :-

With a view to going to see the beacon in North Weald I contacted the museum there to be assured that the beacon they have was from Hatfield (Hertfordshire) not Tatsfield. Hatfield is clearly not going to be a guide for planes to and from Croydon but was the location of the de Havilland aircraft factory. I found a picture on the web of what remains of the beacon as it is today and am intrigued to note that the design is identical to the picture of the Tatsfield one so it presumably was also manufactured by Plessey. The name plate as far as I can make out in the picture reads "Hatfield Airfield Beacon 192? - 1941"

The fence in the Tatsfield site is however surely the same. It has the same variation of posts and the dimensions match visually. Being able to now see the landscape more clearly I am also sure - for what's its worth - that the original shot is taken looking north east.

I have also found a document about the Tatsfield listening station which includes a picture of the same site in the early sixties with an arrangement of direction finding antennas. I realise that it was actually this that I remember from my childhood and back then with a considerable discomfort about the desolation of this little hut with a red light on top surrounded by mysterious aerials way out in the darkness of the adjacent open fields.

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Frank writes on 10th February 2009 :-

I have been reading the correspondence concerning the aerial lighthouse at Tatsfield and I have been endeavouring to uncover a little of the history of the network of aerial lighthouse in the U.K. I enclose a brief note of some of the information I have found which may be of interest.

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Air Lights (image on the left) is a list of the light patterns used by the aerial lighthouses and airfield light beacons. This comes from an RAF map of 1934. Airways 1936 (middle image) shows the air route between London and the coast and has the aerial lighthouses marked. This comes from a publication dated 1936. Tatsfield (image on the right) comes from a postcard and you can just make out the sunvalve on the top.

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Hatfield (image on the left) shows the beacon in situ at Hatfield aerodrome which is now preserved at North Weald. This picture comes from the 'Flight' archive which encourages the use of their material. Hounslow (middle image) is a picture of the Hounslow light in 1920. This too comes from "Flight". Merstham (image on the right) is the beacon that used to be on the brick sighting tower over Merstham railway tunnel. This is also from 'Flight'. I believe that Brenchley, Bethersden and Merie beacons may have been of a similar design. I have seen a reference in "Hansard" to the new Merstham beacon as the "first of a new type of beacon".

Here is Frank's research;

During the early years of civil aviation visual markers were used by airmen to navigate. This generally meant following railway lines and looking for other indicators (towns etc). During the day markers such as the railways were easy to follow. Many railway stations had their name painted in white on the roof for the benefit of passing airmen. At night, or in poor visibility, some other means of marking the way was needed. Hence, drawing on maritime experience as well as experience gained with night flying in WW1, it was decided that a system of lights should be installed.In the 1920's and 30's aircraft used a designated route when flying between London and Paris.

The airway to Paris ran from the aerodrome at Croydon (prior to this from Hounslow) and followed the Kenley valley (and the railway line from Purley to Oxted) to Woldingham where it passed over the North Downs at Botley hill, the site of the first aerial lighthouse to be built in Britain. Once over the Downs the route turned left to follow the railway line from Redhill to Ashford. A second aerial lighthouse was built to the south of the airway at Cranbrook as a marker. At Ashford the route turned right to the airfield at Lympne on the coast (there was a light on the airfield as a beacon), once again within sight of the railway line (from Ashford to Folkestone) before crossing the Channel. Coastal maritime lighthouses and the Channel lightships also provided valuable guidance for aircraft crossing to and from France and their positions and lighting patterns came to be marked on aviation maps.

From the information I have discovered so far a partial chronology of aerial lighthouses seems to be roughly as follows; A system of aerial lighthouses first used in Germany to guide airborne Zeppelins. At least fourteen were built by 1914. Small mobile aerial lighthouses were used in France by the Allies during WW1 to guide aircraft returning from missions (this idea would be repeated in the U.K in the Second World War as the "Pundit" or "Landmark" beacons and the 'Occult' network. Both systems used mobile aerial light beacons of different designs).

Tests began in the U.K on developing aerial lighthouses and other lighting equipment for use in civilian aviation at Andover in Hampshire in 1919. A lighthouse was built at Hounslow airfield in 1919, replacing an earlier small light beacon. This only remained in service until March 1920 when the airfield closed. A second lighthouse was constructed at Croydon aerodrome in 1920. Croydon had by then replaced Hounslow as the aerodrome for London although it was not yet officially "London Airport". The lighthouses at Croydon and Hounslow were both built by the Gas Accumulator company of Brentford. Both were powered by acetylene.

A series of trials were carried out to test the effectiveness of the light at Croydon and further lighting at Lympne airfield using the R33 airship. A lighthouse was erected at Biggin Hill aerodrome for a temporary period. The lighthouse beacon only remained in operation at Croydon for two years. On the 27th January 1922 it was removed from the airfield prior to it's installation at the top of a steel lattice tower on the North Downs at Tatsfield Hill to form part of the new network of lighthouses marking the London - Paris route. Light beacons (known as cone lights) were installed at Croydon and Lympne airfields. Lighthouses were constructed at Tatsfield in Surrey and Cranbrook in Kent.

Until the permanent beacons were erected temporary structures were put in place.Tatsfield was built on top of 30 foot steel lattice tower. The light output was around 60,000 candle power although this was increased fairly early on.Cranbrook was a more powerful light (90,000 candle power) built on top of a 50 foot steel lattice tower. The light flashed with this pattern: Period. 7 sec. Characteristics; light 0:1 sec. eclipse 0 :5 sec. Light 0:1 sec. eclipse 0:5 sec. Light 0:1 sec. eclipse 5:7 sec. The pattern the light showed was altered at one point (in 1931) but was returned to the original scheme after only a few months.Tests carried out by, among others, Alan Chobham to test the new system of airway lighting.

A beacon was built at Merstham in Surrey in 1931, powered by electricty. This marked an alternate route over the North Downs following the London to Brighton railway line between Purley and Merstham. Aircraft then turned on to the original route. The light seems to have been built on top of a 36 foot high brick "sighting tower" (which still stands) built around 1834 to facilitate the surveying of the Merstham railway tunnel. The tower stands directly above the first Merstham tunnel near Merstham Village to the east of the M25.Merstham beacon only remained in use for about eight years (the entire beacon network was taken out of use, and possibly completely dismantled, on the eve of war in 1939). The description of the beacon below comes from Flight (April 1932), the beacon was never run on acetylene gas as at Tatsfield or Cranbrook but instead was electrically powered from the start using a voltage of 100V, illumination was provided by three-filament 3 K.W. 100 volt G.F. lighthouse lamps which gave out a beam of 85,000 candle-power. The light flashed the Morse letter 'M' for identification. Tatsfield, and any other remaining early beacons, were probably converted to use electricity during the 1930's. 'Flight' reported on the new beacon;

THE MERSTHAM BEACON

The beacon which has been installed at Merstham utilises a special three-filament 3kw. lamp. It has a dioptric fixed-type lens giving a beam which, it is maintained, obviates the disadvantages of the horizontal beam given by the Marine lighthouse type of beacon, it being considered that as an aircraft moves in three dimensions, light from the horizontal and vertical is necessary in order that the pilot may not lose sight of the beacon from the time he comes within its range. The lamp, the light from which is intensified by a spherical silver mirror mounted on the door, is placed a little below the centre of the belt of a 500mm. diameter dioptric lens in order to tilt the beam slightly. This lens is built up of two parts ; the lower part of the lens (A) consists of three upper and five lower refracting prisms and a central belt covering a horizontal angle of 180 deg. The part of the lens system which provides the highest vertical rays (B) is fitted in 180 deg. of the lantern roof and consists of four prisms of special section designed to give the correct distribution.The candle-power of this beacon is 85,000 in the main beam, the range being approximately 31 miles ; in countries where the air is clearer, the range increases by about 30 per cent. The beacon rotates and a flashing character is obtained by means of shutters (C) fixed in front of the lens and rotating with it about a vertical axis, thus any Morse character can be given by arrangement of these shutters. The revolving drive is taken through a free-wheel to permit turning the beacon for cleaning purposes.

Further beacons were installed at Merle Common, near Oxted in Surrey and at Brenchley and Bethersden in Kent. These were all built in 1934 and were electrically powered, the lights came into operation in August of that year. Cranbrook seems to have been taken out of use at around this time. The purpose of the new beacons seems to have been to place lights at closer intervals and nearer the air route (Cranbrook was some distance from the actual airway, both Brenchley and Bethersden were much closer) The beacon at Merle seems to have marked the point at which the airway joined or left the line of the Redhill to Ashford railway and also indicated the point at which the alternative air route via Merstham rejoined the main route. At some point during the period lighting was used to guide aircraft airfield beacons were installed on emergency landing grounds along the route at Penshurst, Marden and Littlestone, all these landing grounds were in Kent and were used in case of poor weather or mechanical problems.

If Cranbrook was taken out of use at this time this brought the total number of airway lighthouses on this side of the channel to five (this does not include beacons located on airfields such as Lympne, Littlestone, Penshurst, Croydon etc).'Flight' recorded:New London-Continental BeaconsLuminous beacons have been established at Merle (2 ½ miles N.W. of Edenbridge), at Brenchley (6 miles E. by N. of Tunbridge Wells) and at Bethersden (six miles W. by S. of Ashford), and these will be operated until further notice. Each exhibits a flash of 0.12 second every three seconds, and has a clear weather range of 45 miles. Red identification lights, having a three second period and a range of eight miles, are allotted to each, the code letters being "T" for Merle. "M" for Brenchley, and "O" for Bethersden. Not everyone was pleased with the presence of the beacons. Local residents often objected (sometimes strongly) to these new flashing lights which disturbed the night and it is hard not to have some sympathy with this view.

Coastal lighthouses shine their beams out to sea, away from houses, the aerial beacons, although less powerful, were extremely bright and shone their light many miles inland, where people lived (Merstham had a quoted range of 50 miles!). Inevitably some people took matters into their own hands and it was not unknown for bricks and so on to be hurled through the glass beacons, damaging the lights. The loss of a beacon could cause serious danger to unsuspecting airmen, of course, and early on it became a specific offence to interfere with an aerial lighthouse.

AIR NAVIGATION REGULATIONS:

AMENDMENTS 1923Article 15 of the principal Order : " (2) A person shall not wilfully or negligently injure or interfere with any aerial lighthouse established or maintained with the approval of the Secretary of State or any light exhibited from any such lighthouse."Even as early as 1934 the lights were already becoming an anachronism, navigational equipment was improving rapidly, aircraft now flew higher and did not need to rely so much on visual landmarks. As aircraft became more powerful and reliable the old airway to Paris was being used much less than hitherto in preference to more direct routes and one correspondent to "Flight" went so far as to claim that providing more lights was rather like putting street lights along the Pilgrim's Way! In spite of this, even in 1935, experiments with new lighting equipment were still being undertaken: An Experimental Beacon Every night between 10 p.m. and 6 a.m. an experimental luminous beacon of the track-indicating type will be operated 1 ½ miles E.S.E. of Crowborough railway station. The beacon exhibits a white group-flashing light every five seconds, and the track indicated is that between Croydon and Le Bourget. Networks of aerial lighthouses were built right across Europe and in many other parts of the World. It was intended by Britain that the "Imperial routes" to India and as far as Australia should all be marked by a network of such lights.

The U.S developed a trans-continetal network for use by it's airmail service. The following article comes from "Flight" and describes the new lighting network then being installed in the U.K. Before long it should be possible to carry on night air services between Airways London and Paris with almost as great facility as they are now operated during the hours of daylight. The foundations of a new aerial lighthouse have been laid at the summit of Titsey Hill, near Woldingham, and within the next week or two the steel lighthouse tower will have been erected and the lights installed. Another and more powerful light is to be erected on high ground at Cranbrook, in Kent, which, when it is completed, will finish the chain of lights between London and the Kent coast. There is already a powerful light at Lympne and another at the terminal aerodrome at Croydon.

The whole of the lighting scheme of the London-Paris airway is to be finished this winter, in readiness for the spring air traffic, and with its completion the stretch of airway between London and the coast will be the first in the world to be so illuminated. Pilots of night flying machines will be in sight of at least one of the lights throughout the whole of the journey, and at times no less than three will be visible. The lights themselves are quite unmistakable in their character, as they will be visible as a brilliantly lighted triangle, impossible to mistake for anything else, at a distance of at least twenty miles.This is only a step in the great work of lighting the world's airways. In the time to come, there will be chains of such lighthouses girdling the earth, and the airways will be even more effectually lighted than the world's seaboards. It must come because under existing conditions air transport is handicapped against its rivals by reason of the fact that without these guiding lights it can only operate by day. Night flying for commercial purposes is merely a question of direction-finding, and until it is possible for the night pilot to be certain of his direction and his exact whereabouts, it is out of the question to successfully operate night services. The lighting of the airways, therefore, is a work that must be pushed along with all possible speed.


Thanks to both Andrew, Paul and Frank for their interesting additional information on this fascinating piece of history.


In Octcober 2010, Henry commented "Yesterday we searched the highest part of Merle Common for 4 concrete bases that my friend who lives nearby remembers seeing 20 years ago when he moved into the house down the hill. No luck, what was open common is now overgrown with fern and bramble. He spoke to Mr. Hillier today (the warden for at least 40 years) and he confirmed that we were in the right area. Mr. Hillier also said that there was a photo of the tower in a book titled "Boy's book of Flight"?????? or something similar. The photo was Merle Beacon because his relative is in the pic with a bicycle. Can you confirm the exact location and recall any photo reference of the Merle Common beacon. Was it a Plessey device?'


Later Henry reports "Merle Common Airway Light, update 28/10/2010; In the last few days I've found and uncovered the concrete foundation pads for the Merle Common tower. 51 deg 13' 29.40" N : 0 deg 00' 51.04" E. They are approximately 43/45" square, slightly domed concrete with the remains of large steel fixings in the centre. There are traces of orange paint.

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Merle Common Airway Light

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Left -North pad; Center - West pad; Right - South pad with traces of paint.


John - November 2010 :-

I stumbled across your website whilst looking for information on an Ariel beacon we are currently about to restore at our works. The Beacon we have is the old Dehavillands Beacon which was donated to North weald some years ago. The University of Hertfordshire has now purchased the beacon and we are currently about to start restoration. If you are interested you are welcome to come down to our works to see it before work commences on it .


Steve; the Project Engineer; March 2015:-

It took us approximately 9 months to fully restore it and also along with this time the University was applying for planning permission to have the piece on a constructed plinth. We have been informed it's the last remaining one of its kind left in the country. And doing some research there was a map that we found where you could fly from Biggin Hill to the William Wallace memorial in Scotland all navigated by these light beacons. The Beacon was dropped when it was transported to North Weald from Hatfield in 1984 so when we received it at our works nearly every pane of glass was smashed or cracked. The most costly part was the glazing of the piece as its quite hard to find someone who can manufacture concaved and tapered glass. So a special tool had to be manufactured for the glass to be formed.

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