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Send your letters to The Editor, E&T, Michael Faraday House, Six Hills Way, Stevenage, Herts SG1 2AY, UK, or to engtechletters@theiet.org. We reserve the right to edit letters and to use submissions in any other format.

Aircraft tracking problems

Roger Forster (Letters, May 2014) is surprised that pilots have the ability to turn off their aircraft’s SSR transponder from within the cockpit, suggesting that it should not be possible to do this while engines are running.

Unlike a mobile phone, which communicates with one basestation while monitoring the power of the neighbouring ones, the SSR transponder is replying to many ground transmitters as part of a country-wide network of radar systems. Aircrew are asked to switch off the SSR (strictly they switch it to standby) when the information becomes a hindrance to controllers; for example when the aircraft has landed and the now out of date information is a distraction or causes clutter on the radar screen.

While I can think of other solutions to these problems, there is a much more important reason why the crew can switch the SSR off. Imagine being over the Atlantic when there is a fire in the wiring. Imagine the crew smell smoke coming from the one system they cannot switch off. According to a 2010 study by the Royal Aeronautical Society, more than two-thirds of aircraft fires between 1992 and 2000 were electrical, and the FAA reported that there are more than 900 smoke or fume-related incidents in the US every year.

Smoke, fumes and fires are a lot more common than one might expect. Aircraft are complex and the bigger safety picture must be examined when proposing solutions to very rare events.

Dr Tony Kirkham CEng MIET
By email


The suggestion by geostrategist Azmi Hassan that only the US has the technology to detect objects in the deep ocean (http://bit.ly/1otuEj4) is incorrect. British and European scientists have also been locating instrument packages laid on the sea floor for periods up to at least a year’s duration for many years. Also, long-range sonars and deep-towed instruments with higher resolution sonars have created images of the seabed.

There are two surprising features of the acoustic beacons on Malaysia Airlines Flight MH370’s flight data recorder: the reported frequency of 37kHz and the fact that it pinged for only 30 days. The circle of detectability by a surface ship over a 37kHz beacon in ocean depths to 6,000m is very small and unreliable due to the high absorption of sound at that frequency. Ocean scientists have used frequencies in the range of 8-12kHz for this purpose. The circle of detectability radius at 10kHz would approach the water depth, corresponding to ranges around 10km and transmission angles up to 45° from the vertical. (Shallower transmission paths become unreliable due to variable refraction).

If the transmissions are at regular intervals, most of the battery energy will be wasted if there is no ship near enough to hear them, so it makes more sense for the beacons to be transponders, only transmitting when an interrogating surface ship is within range. The listening receiver on the transponder needs very little power, so battery power should last much longer than 30 days. The aviation regulatory agencies might reconsider the specifications for the underwater elements of the FDR.

Brian McCartney FIET
By email


Shifting to LEDs

One way of reducing the high-cost disadvantage of LEDs (Letters, May 2014) may be to separate the lightbulbs from the energy convertors. Those wishing to replace low-efficiency lighting with LEDs could then supply an entire lighting circuit from a single source, and avoid additional wiring costs by reconnecting the existing wiring. The conversion becomes a matter of replacing fittings, and reducing the supply voltage instead of the current.

Combing the energy conversion with the LED chip is convenient, but is wasteful since the whole unit is discarded when the chip fails. The assumption that the answer to cost is to make the energy converter cheaper, and design it for the shorter life of the chip, encapsulates the philosophy of the throwaway lifestyle we take for granted.

John Carpenter, FIET


In a house move four years ago I inherited a five-lamp luminaire on which I wanted CFLs with dimming. Being advised that it was not possible, I did some tests which astonished me. Installing five CFLs and a dimmer switch, and connecting my popular-make multimeter measuring AC Volts across the lamps, I duly found that at any voltage above 150V the lamps stayed steady with no noticeable dimming effect, and at any lower voltage the lamps started flickering.

On replacing three of the CFLs with three of the original tungsten-filament lamps (having similar rated lumen outputs) and retaining just two CFLs, I found that the CFLs retained their full brightness without any flickering down to a meter reading of around 30V. And at this voltage there wasn’t, of course, any light from the filament lamps. The result was that the dimmer switch gave a smooth range of light output from around one-third to full brightness - with effectively all the dimming being on only the filament lamps. This has now been in daily use for four years with no failures of any CLFs or the dimmer switch - just two of the filament lamps.

Can a lighting expert throw any ‘illumination’ on these surprising characteristics?

Geoffrey White MIET
Port Appin, Argyll


One of the LED don’ts in your May article (http://bit.ly/1jLGxy0) was “Don’t have LED sources directly within the line of site… as this can cause visual discomfort if the source is in view.” If only this had been thought of by the powers that be who decreed that new cars should have these wretched daytime running lights. Up until recently if a car so fitted approached me while driving I either had to close my eyes or look away. Not good for safety. I now wear sunglasses while driving, whatever the weather, and find that I can tolerate the approaching lights.

David A Hall CEng MIET


The greatest drawback in replacing incandescent lamps with LEDs is that they often cause interference to portable radios and other equipment, to such an extent that they become unusable. Interference covers quite a wide frequency range from below 100kHz to around 300MHz. All devices in this range seem to be affected and include LW, FM, DAB and even Wi-Fi and one’s Internet connection speed.

It’s claimed that this may be due to foreign manufacturers omitting ‘unnecessary’ filter components from their LEDs’ internal switched-mode driver circuits after submission for approval, to save money.

Anthony Harrison CEng FIET
North Yorkshire

If it ain’t broke

David Parsons (Letters, May 2014) writes about how he is still using the battery charger he made as a ‘home office’ job while working at laboratories in north London in the early 1960s. I worked at GEC East Lane Wembley from 1940 to 1949 and in 1941 made a battery charger, winding the mains transformer using a coil-winder that was in a local workshop in one of the labs. I also still use my charger, which is now some 70 years old. Isn’t this a truly remarkable coincidence?

Keith Taylor
Bransgore, Dorset


In 1961 I joined what I suspect was the same company as David Parsons as a sandwich-student on a four-year course. While in a development laboratory during one of the industrial periods of the course, I built a 12V 1A-regulated power supply to use with various pieces of amateur radio equipment. Most of the components were parts that I had salvaged from surplus wartime radio equipment, but all the transistors were old development samples.

A few years later I modified it to operate at 6V or 12V and added a voltage control that allowed the output to be increased enough to use it as a battery charger. Until a few years ago it was in regular use for charging my motorcycle batteries. I then changed the type of battery in my pre-war motorcycle to a small, sealed lead-acid type with only 6Ah capacity. To give the correct charge rate for this smaller battery, I added a switch to select between a current limit of either 1A or 0.6A. Other than this modification, the power supply/charger has functioned faultlessly for over 50 years. It is still in use every two months to refresh the charge in my two motorcycle batteries.

John Beddows CEng MIET


In my garage is a rather dusty white metal box, the size of a large biscuit tin, embossed ‘Property of Walls’. It houses a well-earthed homemade 6V/12V car battery charger that is no longer used for health and safety reasons. Made around 1955, the components were obtained from RAF National Service surplus items and second-hand kit bought in the Charing Cross Road. What a recycling nation we used to be!

Dr Peter Burville FIET
St Margaret’s Bay


Give buses the hard shoulder

A few weeks ago I travelled by Megabus coach from Manchester to London. A mere £5 and four and a half hours - and not much slower than a car as the bus sped through the London traffic by virtue of the bus lanes. It arrived just two minutes behind schedule.

There is currently ‘improvement’ of the motorway system to allow cars to use the hard shoulder during busy periods. This does reduce journey times slightly, but the net effect is to create shorter, wider traffic jams with little advantage, as experience has shown that traffic expands to fill the space available.

A far better solution would be to allocate the hard shoulders as bus and coach lanes. This would be a win-win situation. With dedicated lanes, buses would have even speedier journeys, particularly at peak times when they would be an attractive option. This would attract more users from their cars, thus also easing car congestion.

The system could be further improved by having bus interchanges at motorway junctions - providing a high-speed national network. With comfortable modern coaches and the use of hard shoulders, maybe the time is ripe for this. At a fraction of the cost of the HS2 proposal, this could make a significant improvement to our transport system.

We need to act fast. Once allowed, the motoring community would be reluctant to give up the use of hard shoulders.

Rob Basto


Making smart meters workable

The term ‘smart meter’ seems to be the answer to everything these days and the UK specification tries to do everything - it is effectively a billing system built into the meter complete with prepay functionality and a cut-off switch. It is so complex that the rollout programme has been delayed and delayed as more and more issues emerge. Having the cut-off switch means it is part of the critical national infrastructure, which means there are security issues, which means new secure protocols are required, which means new key management services have to be set up and so it goes on and delays continue.

Smart metering is rather different where, as in France, the meter is simply a sensor on the network providing consumption data. Pricing information can be easily downloaded from the Web and costs calculated using half-hour metering data either locally on a device in the home or online and cost considerably less than the £12bn quoted by DECC for the British roll out.

Perhaps if this approach had been adopted in Britain we would have had smart-metering systems being deployed by now rather than facing another six-month delay.

Smart meters in themselves will not save energy but a smart-metering system that feeds into home energy-management systems with built in controls would - as being deployed in Japan.

John Cowburn CEng FIEE
Director, Smart Energy Networks


Smart meters may be useful in industry if you have one for each production area, say, but for domestic use they are an overkill - over complex and therefore largely a waste of money. All that is needed of a domestic smart meter is to provide consumption figures remotely without someone having to call to read it.

Richard Wilson


Benefits of space exploration

I find it incredible that E&T readers question the need to investigate the possibility of colonising Mars (Letters, May 2014). Ignoring the impact that space exploration has already had on technology and society, many of the big issues that plague the human race today can be alleviated, if not solved, by increased space exploration, not less. Exploration always leads exploitation and subsequent development.

The exploitation of resources known to exist on the Moon alone could provide material to build solar satellite powerstations and space habitats. The sunlight energy available for harvest in space is of the order of ten times that on the planet surface, and it doesn’t suffer from night-time and poor weather. The habitats can produce large quantities of food without pesticides.

All this has been looked at in studies as far back as the mid-1970s. It is a combination of mental inertia, the influence of interest groups and lack of political will that has kept us back from realising the great benefits of space exploitation.

RJ Ringrow MIET


‘Vanity’ of DSLR users

It was entertaining to see the For & Against debate in the May 2014 issue of E&T (http://bit.ly/debate-1404 )on whether smartphone cameras pose a serious threat to the DSLR market. From the point-and-pray of the old box Brownie with its pathetic prism viewfinder, cameras evolved via the Rollei twin-lens to try to show the user what the photograph would look like. The single-lens reflex was the final step for film cameras, with a mirror to show the exact view.

Every digital camera shows the exact image that will be captured, whether it be a mobile phone or an expensive DSLR. The DSLR is the ultimate vanity product, shaped to proclaim “Look, I’m a real photographer” with its clumsy bulk, when many more ergonomic designs would be better.

John Billingsley CEng FIET
Toowoomba, Australia


Vacuum cleaner mystery

Why is the efficiency of domestic vacuum cleaners so low? The question arises from my retirement research project, the Coanda disk aircraft (www.coanda.co.uk), which is intended as a small unmanned aerial vehicle for urban area use.

This has involved studying fluid dynamics, a new field to me. The Coanda disk aircraft uses a turbine-like fan similar to the type commonly used in ordinary domestic vacuum cleaners but required to deliver induced air power of the order of 70W for an all up vehicle weight of about 2kg.

To help understand the problems of designing a power unit I have investigated the common vacuum cleaner and found that whereas the input electrical power might be of the order of 1kW; the induced air power at the business end is typically less than 0.5W.

Bob Collins
Wimborne Minster, Dorset


Electric vehicles

I would like to draw attention to really good example of consumers working with manufacturers and distribution network operators to understand how electric vehicles will affect our demand profiles and technology to manage their demand.

My Electric Avenue (http://myelectricavenue.info/) has demonstrated that consumers do care and want to be involved in developing innovation. It is also an excellent way to enthuse the next generation of engineers.

Dr Mary Gillie CEng



Recently I had to replace several 13A sockets in a newly purchased residence because they offered undue resistance to the insertion of standard 13A plugs. One of these sockets had a broken neutral contact. Investigation showed that a previous occupant had used plastic socket covers in the belief that they would guard against accidents to children.

I wholeheartedly endorse the letter from Peter Munro in your May 2014 issue. The general public are largely unaware that BS1363 socket outlets have built-in safety shutters. They are also unaware that the widely available ‘safety’ covers are potentially dangerous and do not have to conform to any established safety standards.

I pointed out the dangers to a national accident-prevention organisation and suggested that stricter regulation should be introduced. The reply was that whilst they do not recommend the use of such devices, “there is considerable merit in the use of socket covers as part of wider efforts by new parents to recognise and respond to everyday domestic hazards.”

The same reply contained the incredible statement that, “Whilst it is conceivable that poor design of socket covers might cause damage and shorting within electrical sockets, this is more likely to be the result of wear and tear using ordinary 13A plugs with their hard metal contacts rather than plastic socket covers.”

David G Buckley C Eng MIET
Milton Keynes


In April this year, South Africa adopted a new standard for socket outlets based on IEC 906. For decades, South Africa has used a 15A round pin design which was abandoned in UK when the 13A rectangular pin design was adopted.

Because of the way the sockets are recessed, it is impossible to touch the pins when putting in or taking out a plug. For this reason, it is regarded as the safest design available. Yes, the shutters over the live and neutral sockets can be opened by using something to insert into the earth socket; there’s no practical way to prevent this. But the compact design will make it impossible to design socket covers which can be used to do this.

It has one other great advantage: the compactness means that multiple sockets can be installed in one conduit box, making it easier to avoid the sort of electrical spider’s webs that adorn many offices and kitchens.

Mike Young
Sedgefield, South Africa

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