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EKCO MDI SYSTEMS
By Tim Davis – August 2007
One of the more interesting projects I was involved in during my years at EKCO was the development and support of MDI (Miss Distance Indicator) systems on behalf of MOD. These were systems to score missile and gunnery practice firings in real time. There were two systems; the Radioactive system (RMDI) and the Acoustic system (AMDI).
Until the advent of RMDI, guided weapon test firings were scored using high-speed photography, radar data, kine theodolites, Doppler techniques and other methods. The results from all of these had to be processed and interpreted by skilled personnel. In the case of air-to-air gunnery a banner target was commonly used and the score was not known until the banner was recovered and the holes in it could be counted. However, in the case of the RMDI and AMDI systems the score could be transmitted to whoever was interested with minimum delay. Also it did not require the setting up of specialist equipment. EKCO technical literature of the time claimed an operational cost advantage of some 10x over then existing systems.
RMDI (E245) towing aircraft installation
The development of both RMDI and AMDI was controlled by T (GW) 2 of MOD. - Initially led by Wally Newman - with technical support provided by Doug McIlroy and a small group based at the old Fleetwood Golf Club house that was part of the RAE, Farnborough establishment. (Incidentally, it was McIlroy who decreed that we should not use printed circuit boards in the MDI systems. As a result all circuit boards had to be pinned and back-wired - this made assembly very expensive.)
Work on both systems started in the early sixties and development, production and support contracts helped to support EKCO for twenty plus years.
Close up of Rushton winch and (dummy) target - Photo courtesy Cobham PLC
Rushton Target Film
Both systems could be fitted into the Rushton target, which was supplied and operated by Flight Refuelling Ltd. through a small team led by Phil Bunn. The Rushton target comprised a metal cylinder about 8 inches in diameter and about 8 feet long. It had fins at the rear, which housed remotely fired flares to provide a heat source for heat-seeking missiles, or smoke as a visual marker. It was towed on a C. of G. tow at up to 10 miles behind the towing aircraft -well; one didn't want an errant missile to mistake the tug for the target!
High intensity IR flares being fired – Photo courtesy Cobham PLC
Information on miss distance provided by the RMDI or AMDI, (depending on which was fitted) was telemetered in real time back to the tug where further processing of the information from the target provided a score in terms of miss distance in feet, in the case of RMDI, or as the number of rounds passing through predetermined zones, in the case of AMDI. The score could then be relayed by the tug to whoever was interested.
MDI indicator units as fitted into towing aircraft
The RMDI system, for which I was responsible - initially under Peter Harvey was intended for use against guided weapons such as Sea Dart, Sparrow and Rapier. A gamma emitting radioactive source was fitted to the weapon in such a way as to provide a near isotropic radiation pattern around it. In the case of Rapier this was a simple, cone shaped, insert clipped into a recess in the weapon's nose (There is a Rapier Missile on display at the 'Military Museum' in Maldon which has a dummy source cone fitted to it) In the case of heat seeking weapons, such as Sparrow, a small source had to be fitted to each of its four fins in order to obtain a suitable radiation pattern.
The sources were supplied by AEA (Atomic Energy Authority) Amersham and, in order to obtain consistent results the precise activity of each one had to be known. So each was supplied with a number representing its actual activity and the date of measurement so that the decay of the source could be accounted for. This number had to be set into the Display Unit before firing. (See RMDI Display Unit illustration above)
Test firings were always conducted out to sea so that the spent missile with it source sank to the bottom of the ocean. But you can't leave radioactive sources scattered all over the place, so we devised a bimetal capsule to house the radioactive source which ruptured within about ten minutes of coming in contact with sea water. The source, in the form of a soluble salt, dissolved in the sea and was widely dispersed.
The RMDI target equipment was housed in a cylinder about seven inches in diameter and a couple of feet long, which slid into the Rushton target. It comprised a plastic scintillator, which detected the gamma radiation from a nearby radioactive source, suitable processors and a telemetry transmitter to send the detected count to the towing aircraft.
Detail of telemetry unit and aerial as fitted into Rushton target
The approach of a tagged missile resulted in an increasing output from the detector and the peak output was interpreted by further processors in the tug aircraft as the miss distance in feet.
The RMDI system had a maximum range is 50 feet with a probable error of + or - 10% and could cope with closing velocities of Mach 5. It was assigned forces equipment number ARI-23189.
Several hundred of the systems were made over a few years, mostly used against Rapier in the Hebrides, until 'Radioactive' became a dirty word and the system was quietly dropped as evidenced by the reply by DEFRA to a parliamentary question tabled by the MP for Delyn recorded in Hansard (the proceedings of the House of Commons) in November 1997, where a Mr. Rooker stated:
Our records show that 112 radioactive miss-distance indicators were dumped in the Holyhead Deep in the second half of 1974. The Ministry of Defence has advised that the dumpings took place on 14-15 August 1974. The disposals were authorised by the Ministry of Defence and the records show that the Ministry of Agriculture, Fisheries and Food was informed. I am advised that these disposals do not have any significance for human health or the environment. Nevertheless, as I explained in my earlier reply to my hon. Friend the Member for Delyn (Mr. Hanson), I have passed the details to the National Radiological Protection Board for an independent assessment, the results of which I expect to announce shortly. I have today placed in the Library of the House copies of the one original archive document identified by this Department, which relates to these disposals.
Rapier firing on RA Range Hebrides on the island of Benbecula - Photo by
Peter Russell
The AMDI system was Eric Fielder's baby - again under Peter Harvey and operated on a completely different principle. The AMDI system was intended for scoring air-to-air and ground-to-air practice gunnery, which tended to be multiple shot, so the readout was displayed in terms of the number of shots passing through three pre-set zones. The system operated by measuring the amplitude of the characteristic N shaped pressure wave generated by the passage of a supersonic projectile. This amplitude is a function of the size and shape of the projectile as well as its distance from its trajectory. A precision microphone, capable of coping with the high sound pressure levels (in the region of 130dba) was fitted in the nose of the Rushton target and the processed information from passing rounds was telemetered to the tug and displayed as the number of rounds which passed through each zone. There were three zones, Inner, Middle and Outer; the boundary settings were determined for each type of round using static guns and were set with controls on the Display Unit. (See photo above). To obtain consistent results the sensitivity of each microphone and its amplifier had to be standardised using a Pistonphone. This was a battery operated device with a couple of pistons, driven by a small motor, which provided a standard sound pressure level in a sealed cavity when a microphone was inserted.
The AMDI system could detect the passage of rounds at up to about 100 feet, depending on the type of round, at a rate in excess of 3000 rounds per minute, and classify them with a probable error of about + or - 10%. The system had forces equipment number ARI-23190.
One of the good things about working on the MDI project was that, after Peter Harvey left, Eric Fielder and I were left more or less alone to get on with the job with no interference from higher management or from Sales/Marketing. We reported progress to MOD at regular meetings. In the early days these meetings were held at the EKCO London office. At that time the London Office was a second floor flat in Gower Street. It was run by Jack Rogerson, a friend of Gerry Brunker, with a secretary. It comprised a sitting room, which doubled as Rogerson's office, a smaller room for the secretary, a bedroom which top EKCO brass could use when caught short in London, a small kitchen and a large dining room with a large and magnificent table, used for meetings. (When the office closed this table, and eight matching chairs, ended up in Bill Thompson's office at Southend - WE was very proud of that table and woe betide anyone who put a mark on it - as Eric once did. He was never forgiven! (Bill Thompson was usually referred to as 'W.E'. to distinguish him from 'E.B'. who was one time Nucleonics Sales manager.)
These meetings were chaired by Wally Newman and were attended by Doug McIlroy, Phil Bunn from Flight Refuelling and representatives from Inspection, the navy, RAF and, occasionally, the army. The drill was that at about 12.30 we paused, I unlocked the well-stocked drinks cupboard and we had a drink or two (McIlroy, being an ex- naval man always had a pink gin) before going round the corner to a hotel for lunch. We resumed the meeting about 2 o'clock. Occasionally Rogerson, who was quite a good cook, produced a three-course meal for us and served it at the table.
At one of these meetings Wally announced that a trial of RMDI against Sea Dart was to take place at RAE Aberporth on Monday 18 May (or whenever). So, on the Sunday Phil Allen and I went to Aberporth with duplicate receiving equipment, and Eric and Rodney Davis went to RAF Llanbedr to support Flight Refuelling who supplied the target and tug. In my innocence I thought that Monday 18th meant Monday 18th; it didn't! It meant at some indeterminate time after that date. In the event we spent several weeks, on and off, between Aberporth and Llanbedr. The trials were pronounced successful in the end but we never knew the actual result as it was all rather hush-hush at the time; even McIlroy was told 'you don't need to know' in answer to a question - he was cross!
There was another set of trials over Lyme Bay. I think that might have been against Sparrow. RAE had a caravan full of equipment on the cliffs overlooking Charmouth, which they used to monitor trials over Lyme Bay. Phil Allen, Rodney and I spent several weeks, on and off, at RAE Boscombe Down. Incidentally, the TSR2 project had just been cancelled and they were taking printed circuit boards out of the redundant aircraft and giving them away as souvenirs before using the aircraft as targets for air-to-ground practice firing. Everybody said 'what a shame'.
In 1965 Wally Newman and I went to America to sell AMDI and RMDI to the Americans, as they had no comparable system. We went to Washington and thence to Los Angeles, Albuquerque, Dallas, Boston and a few other places in between visiting various contractors and air force bases on the way. In Washington we went to the Navy Building; a huge, sprawling place built along a central corridor about half a mile long and at least 30 ft wide with bicycles rushing up and down. At the air force base in Albuquerque we were met by the British Liaison Officer, Col. Latham, who introduced us to the base commander; I have never seen two such stressed men in my life; Latham was sweating and almost incoherent and the base commander was speechless and did nothing but sit behind his desk and knead a ball of worry putty; I found it quite distressing. Latham recovered his composure after a short while. I can't remember anything else about that visit except that Latham invited us to his home for dinner that evening - the most enjoyable meal we had the whole time we were there and I made a pig of myself!
The overriding impressions I have of the visit are
- The awful food which always seemed to have to be eaten in the dark so that one couldn't see what one was eating and
- The masses of expensive machine tools and instrumentation, none of which looked as if it had ever been used, and the low level of expertise of the majority of the people we met. At one base a senior officer said that he envied the professionalism of the British armed forces.
On another occasion we went to Brussels to make a presentation to a NATO committee. Alan Theile who was Marketing Manager for Avionics set up this visit. Eric, Alan and I went, with Phil Bunn and 'Jock' from Flight Refuelling. We took a set of RMDI units and Flight Refuelling took a Rushton target so that we could set up a display and demonstration. When we arrived at the NATO building we discovered that Eric's name had been omitted from the list for security clearance and so he was not allowed into the main building. Eventually, as a concession, he was allowed into a small room at the end of a long corridor where the packing for our equipment was stored. Alan did the presentation to the committee - following a long and boring, presentation by a fellow from Shorts about the development of some missile or other - all with simultaneous translation into five languages.
The French expressed an interest in RMDI but insisted that they should conduct their own trials; they had a tracked, rocket-propelled vehicle on which a source could be mounted to represent a tagged missile, with the RMDI mounted on a stand at a variable distance from the track. This seemed a simple arrangement and the French agreed to pay an engineer's expenses for two weeks. Eric went with a set of RMDI units. He spent two weeks at the range doing absolutely nothing and nobody would talk to him or tell him what was going on. After two weeks he gave up and came home in high dudgeon. No sooner had he got back but they said 'We are ready now' and he had to go out again; this time all went well - except that we had to pay for this second visit; WE. was cross and blamed Eric - probably because Eric had marked his precious table!! Six months later a French company had the temerity to send us a brochure describing a RMDI system virtually identical to ours. Perfidious French!!
Somewhere along the way we built a couple of prototypes of a 'mini' RMDI. The detector (a plastic scintillation) had to remain about the same size as the original to maintain sensitivity (about a 6 in. right cylinder) but the electronics were compressed to about a quarter of the volume of the original. It so happened that Avionics, at that time were setting up a 'thin film integrated circuit' facility at the EKCO Rochford factory with Joe Phelan in charge. A 'thin film integrated circuit' was a sort of forerunner of the IC's we know today. It comprised a glass substrate about 2 ins. square on which were deposited the circuit plus resistors, by a photographic/vacuum deposition process with transistors and capacitors soldered on afterwards - I can't remember how. We used several of these 'boards', each housed in a metal case about half an inch thick. This version didn't get very far because the process was very expensive and Avionics decided not to continue. At about the same time the Rochford factory closed and Avionics moved to Crawley and became part of MEL.
A later development of the AMDI system was the Air-to-Ground version. This was for scoring air-to-ground practice firings. The established method of scoring was to set up a 15 ft. square Hessian screen (the Americans used a 20 ft. square screen) on steel scaffolding as a target. Then an aeroplane came along, fired a short burst and withdrew. Then a couple of men ran out and counted the holes in the screen and marked each with a blob of paint. The number of holes in the screen was relayed to the pilot of the aircraft who then returned to try again. The unmarked holes were counted and the whole procedure was repeated until the target was destroyed.
Complete Air to ground system – author's collection
System being installed behind ground target at Pembrey ranges – author's collection
In the air-to-ground AMDI system a microphone was set up in front of a suitable target or marker and protected by a small sand bank. The attack aircraft fired a short burst, as before, and the Information from the microphone was transmitted to a receiver in the adjacent control tower and classified in zones as in the original AMDI system. The score was relayed to the pilot of the attack aircraft who could then have another go with minimum delay.
During the trials phase the Hessian screen was used as a reference. It was really frightening to see the damage these guns could do to the scaffolding - one round could chop a standard steel scaffold pole in half - and these were only practice rounds. The trials were mostly against the 30 mm Aden gun, which could fire up to 600 rounds per minute, and the American 20 mm Gatling type gun, which could fire at up to a mind boggling 3000 rounds per minute.
On one famous occasion we were told that it had been arranged that three American A10s, which were fitted with the fearsome Gatling gun would be available at 10 in the morning at the range at R.A.F. Cowden, in Yorkshire. So Phil Allen and I and a couple of blokes from RAE, Farnborough (Terry Chubb and ??? I know them well but I can't for the life of me remember his name) rushed up early in the morning and set up the system and waited. At 10.30 there was a call to say that the aircraft had been delayed but would be along at 11.00. We waited again; another call announced that there would only be one aircraft. Eventually this one aircraft turned up, did a couple of dry runs then came in, fired a single shot and the gun jammed. I can't remember whether he scored or not! .... So that was that. We all packed up and went home.
After the Air-to-Ground system came the Sector Acoustic Miss Distance System - SAMDI. This was a rather half-hearted development because MOD changed their policy of awarding cost-plus development contracts about this time (1983) and EKCO would have to pay their own costs, which they couldn't (or wouldn't) afford. However, we did a small amount of work.
The system was to be part of a banner target being developed by Flight Refuelling. The system was intended for air-to-air practice firings, mainly in a tail attack, and was to classify rounds in sectors - high, low, left and right - as well as in miss distance zones. The miss distance was to be measured by a miniaturised AMDI using the original B&K microphone but the sector information needed four cheap pressure transducers disposed around the periphery of the unit (The B&K microphones were hideously expensive). So we devised a form of transducer, which comprised a pressure sensitive plastic film, which produced a small signal when subjected to pressure. These could be made to be flush with the target body. RAE gave us a shock tube with which to test the arrangement and we built a prototype, which appeared to work.
Prototype S.A.M.D.I (with case off) – author's collection
We took this prototype to Farnborough and tested it against a static gun. The system worked in most situations but in one attitude suffered from interference from the shock wave travelling along the length of the target body. I was convinced that this defect could be corrected but we went no further because EKCO Management decided it was all too risky so they persuaded Graseby to take it on. Phil Allen (who was due to retire in six months) went with it. I don't know what Graseby did with it - I lost sight of MDI at that stage.
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