I should perhaps say firstly that I am no expert on FIDO but knowing what an important part it played during the wartime years at RAF Hartford Bridge / Blackbushe and with my own knowledge of its use I decided to research further. Using mainly the internet and some magazine articles I have been able to put together this short history of its development and how its use proved so important.
Losses of Allied aircraft had reached unacceptable levels by early 1943 and it wasn't only due to enemy action. As our aircraft flew out to undertake operations over enemy occupied Europe it was often the case that on their return they found their home bases could not accept them for landing for one reason or another and diversion to another airfield was called for. However, that was not always easily achieved due to adverse weather such as low cloud, mist or mainly fog which might well be covering the whole of southern England. Another problem was damaged aircraft or those low on fuel which had to be directed to an airfield where it was known that they would be able to land, whatever the weather conditions.
The understanding at that time was that any aircraft not being able to make a safe landing should head for the coast where it would be placed on a heading out to sea. The crew were to bale out while it was still over land and parachute to safety. Providing all went according to plan the aircraft crew would survive but another aircraft would be lost. It was therefore necessary in some way to ensure that aircraft returning to this country from operations could be directed to an airfield where a safe landing would be possible - but how? In particular bomber losses were huge and Air Chief Marshal 'Bomber' Harris recognised the problem and decided that something needed to be done urgently. It was initially Arthur Hartley, a Yorkshire man and ex WW1 fighter pilot, who had more recently been working as a civil engineer for Anglo Persian Oil that was given the task. He had been seconded to the Petroleum Warfare Department in 1940 where he was appointed the Technical Director, and set about developing the FIDO system. FIDO was officially known by the RAF as standing for 'Fog Intense Dispersal Of' but more commonly elsewhere as 'Fog Investigation and Dispersal Operation' or 'Fog Intense Dispersal Operation'. It was being devised as a system that by means of heat would clear fog over a runway to allow aircraft to use that runway.
The device was initially devised and worked upon at the Department of Civil Engineering at the University of Birmingham. Later Dr J D Main-Smith an ex Birmingham University resident, became the Principal Scientific Officer in the Chemistry Department at RAE Farnborough where development was continued. As the FIDO system was designed for use at RAF bomber stations, RAF Hartford Bridge could be considered for such an installation and being so close to Farnborough it would be ideally placed for trials work to take place. There followed a visit in August 1943 by the Director of Aircraft Safety accompanied by a Senior Member of the Petrol Warfare Department. They came to assess the suitability of installing a fog dispersal system at the airfield and shortly afterwards it was decided that this work should be put in hand. The corresponding orders were issued for the work to proceed almost immediately on what was to prove a very valuable asset in the future. Following urgent installation of the system and following much experimental work at both the University of Birmingham and at RAE Farnborough the first operational use of FIDO at RAF Hartford Bridge was on 19th November 1943.
Meanwhile back at Farnborough development work was proceeding. Dr Ramsbottom, the Chemistry Department Head, as a courtesy was to share the joint patent of FIDO with the Ministry of Supply. This was quite usual at the time and it also covered development of support equipment and most importantly the burner itself. It was important that the fog that the device was being designed to remove was fully understood. There are two distinct types of fog found in this country which might have been encountered at Hartford Bridge being Radiation or Avection. Far the most common was Radiation fog which tended to be much thicker in those days than we experience today. It was not unusual for the fog to be so dense that you would not be able to see more than a yard in front of you. There were a lot more dust particles in the air that fog formed on in the 1940's than we find today, thanks to the Clean Air Act of 1956.
For the record Avection fog usually occurred when warm air met cooler air over a cold surface, for example at a coastal airfield where the ground had cooled at dusk and therefore the air was also cooler but the wind coming in off the sea remained warmer. Fog is described as being formed when the temperature falls below the dew point and water vapour condenses on particles of dust in the atmosphere. As the land surface rapidly lost heat, especially on calm nights, the air temperature was cooled below its dew point and condensation took place. Thus with more particles of dust in the air in those days, the more water droplets there would be, and the denser the fog would be.
So if the temperature could be raised again then the fog should disappear?
Being so close to Farnborough where development work continued to take place, Hartford Bridge and later Blackbushe were used for experimental work as the wartime years progressed.
A typical installation consisted of two above ground pipes, with interspersed burners at regular intervals. These were positioned to be parallel to the runway edges and laid down on either side of the full length of the main runway. They were set back on the grass from the runway edge and had another single pipe supported over the top forming a triangle with downward facing nozzles.
Each of these tanks was protected by brickwork designed to resist damage from bomb splinters or enemy fire and was surrounded by a brickwork bund to contain any fuel leaks. Each bund also had four foam ports built in to add additional protection in case of fire.
When the fuel reached the burners it was pumped through nozzles to form a mist of the petrol which mixed with fuel dripping from the top pipe. This was ignited by a taper carried by a man, walking in the early days, but later on a bicycle. Later still a vehicle was used with an ignition source lashed to the back.
The height and intensity of the flames depended on the pressure of the petrol being pumped through the pipes.
As the vapour caught fire banks of flames were produced to a significant height which dispelled the fog as the temperature was raised. FIDO was operational at Hartford Bridge by 19th November 1943 and caused some consternation amongst personnel initially before they realised what it was. Several thought that there had been an incendiary raid by the enemy due to all the flames and someone went a step further and called out the local fire brigade!
There was no doubting, however, the role that FIDO played during the war as it was used on numerous occasions to help diverting aircrews, unable to land at their home bases to make safe landings.
One drawback was, however, that two lines of flame beside the runway was without doubt a hazard to incoming and damaged aircraft if they happened to swing off the runway on landing and got nearer the flames than was intended. The FIDO section consisted of one sergeant, three corporals and seventeen airmen. Whenever the system was in use there was a manned watch tower with personnel keeping a look out for potential problems and a team on the ground that could quickly remedy a problem by use of strategically placed valves which would quickly close the fuel to a particular section. There were also personnel in the pump room while the system was in use. Throughout the time it was installed the provision of the system to disipate fog was a godsend to many a pilot who had been running out of options as to where a safe landing could be made. It was doubtless responsible for saving the lives of many aircrew and their valuable aircraft but at a high financial cost as petrol to run it was not a cheap commodity. The estimated 11000, lives that the invention has been credited as saving would however, make the running cost seem insignificant. General Eisenhower, Supreme Commander Allied Expeditionary Forces, visited the airfield on the 18th April 1944 and as it was a foggy morning was given a demonstration of FIDO in action. Although he was very impressed, on asking how much it was costing to operate he expressed horror at the cost and the amount of valuable petrol it was using. He promptly ordered that the demonstration be stopped immediately and that the very valuable commodity be saved for future emergency use!
During July/August 1944 updating of the system was taking place which turned out to be the installation of an entirely new type.
This was constructed in trenches on either side of the runway into which the pipes were placed with what were known as slot burners placed at regular intervals. The top of the trenches were covered and protected by a thick mesh through which the flames would rise. The burners themselves looked rather like giant safety pins stood on edge with small jets along the upper and lower surfaces. The new system pumped fuel through the underground pipework via five Sulzer centrifugal pumps, coupled to Ford V8 engines, and under pressure into the new design burners. Fuel in the lower pipe of the burner was ignited automatically, which in turn generated sufficient heat to vaporise the fuel in the top pipe of the burner. This once ignited, provided the flame which came up through the grill. As the majority of the system was located underground it proved much less of a hazard to the aircraft than previous systems which had stood above ground. The older above ground system formed a barrier which could stop an aircraft in the flames in the event of an accident causing it to run into the FIDO line. In addition, the flush to the ground heavy mesh, of the new system was able to support an aircraft if it did run through the flames. Unfortunately, however, it didn't prove popular with the service crew!
There was one real problem with this system which was the build-up of residue from the leaded petrol being used to fuel it. To prevent the nozzles becoming fouled there was the laborious task of pricking out the jets, which was a filthy and back-breaking task that found no favour with the crew allocated to maintain it, but at least they didn't have to light it any more by hand as an electrical ignition system was now in place.
This system was still active when the airfield closed in November 1946 (and still there and visible in 2006 whenever there was a dry period of weather. In fact I uncovered a section at one time and having removed the grass that had grown over the paving slabs covering the trench, found some of the pipework still in situ. Unfortunately, the burners were no longer in place though). It seems that the older above-ground system was also reintroduced for a period at a later date. RAF Blackbushe, as the airfield was by this time known, continued to keep FIDO available until the time that the airfield closed and passed into civilian hands.
The Ministry of Civil Aviation who had taken over the running of the airport post RAF days continued to have FIDO available but only for emergency use. It was also chargeable if deemed not to qualify as 'justified emergency' status - and it was expensive.
I have no record unfortunately of charges made at Blackbushe, but as an example at Manston, the only other airfield equipped with FIDO at this time charges were in the region of £500 for the 15 minutes warm-up period and then each subsequent minute £250 which was a huge cost in those days. During May 1948 a test burn of part of a newly installed Haigill Mk5 system was used to demonstrate the operation to airline personnel and other interested parties. The approach end and western half was lit and included intersection burners. This system was very similar to the above ground type used previously by the RAF during the wartime years. In November 1952 a demonstration 'burn' was carried out by the MCA prior to closing down the facility and placing it on a care and maintenance basis. Flights were made available in a BEA Elizabethan and Viking, an MCA Dove and a BOAC York. Although the demonstration was successful initially, there was a lot of thick smoke as the flames set fire to sections of the grass. The flights were, however, considered successful but some on board the aircraft were concerned that the air over the runway was quite bumpy, caused when fresh air was drawn in to replace that displaced by the heat produced by FIDO. This was believed to be the last time FIDO was ignited at Blackbushe.