I'm just a layperson but surely the 'planes cannot fly in those "blank spots" because there would be wind turbines in the way.

reminds me of objections by RAF for wind farms in areas of N England where they do low altitude traing. Given that people near airports tend to object to the planes as do many people in rural areas in the low altitude training areas then are we going to see an IMBY campaign for windmills to ward away the greater evil of planes or vice versa

"Earlier this year the Ministry of Defence objected to planning applications for proposed wind farms over fears that they would create blank spots in its low-level radar coverage"

Not that I'm a eco-warrior, or anything, but if all of the WWF/ClimateChange commentry turns out to be true, would these blank spots be the expanded Channel/Atlantic Ocean?

Mines the one with the 15 day old mouldy cheese and wheatgrass sandwich in the pockets, and the faux leather elbow pads.

civilian radar is notoriously crap at spotting low level craft anyway - read as "can't" (and some would say our military gear is just as bad and in some cases worse...)

just out of curiosity - when did they start building wind turbines several hundred feet tall?

Recall that radar is a send-and-return system, so any blank area would extend radially from that area out to the limits of the system.

I'm not familiar with the geography around that area, but if there is something behind that area they want on radar then it's a Bad Thing.

RADAR or 'radar' BTW?

cash or clean air? Seems like its the cash every time.......

What the hell were pilots doing studying this? They know how to fly planes, for sure, but what do they know about ATC and radar?

Can anyone explain this bizarre piece of logic?

>> I'm just a layperson but surely the 'planes cannot fly in those "blank spots"

>> because there would be wind turbines in the way.

I am just a lay person too, but I think "cast shadows" might be a better term than "create blank spots". Depending on the angles and proximity, I imagine the turbines could effectively block the radar's view of the sky - it is likely the shadow cast would be much larger than the turbines themselves.

They're a waste of time - they produce a miserable amount of electricity, look crap, don't produce a steady stream of power, mess up the grid and need a proper power station to provide backup support.

Which is why Denmark scrapped their windfarm program a few years ago.

Actually, it's "windpower versus hundreds of people dying in airliner crashes". Air safety must come first, and if there is even the slightest chance that a radar shadow could cause an airliner to be lost from the sight of air traffic control then I'm all for the windfarm being moved somewhere else. Having said that, I would have thought Rushy Mead was far enough out to be below the flight-path for Heathrow, unless they're worried the spinning blades will somehow produce false echoes? And how would five create less of a problem than six, unless we're talking a very narrow beam which sounds more like an ILS radio beam than general radar? After all, there is already a single big windmill on the North side of the M4's junction 11 at Green Park.

>> just out of curiosity - when did they start building wind turbines several hundred

>> feet tall?

Not sure when the first one was, but the wind farm near me (Kentish Flats) was completed in 2005. BTW the hub heights are 70 metres (above mean sea level) or 230 feet, the rotor diameters are 90m or 295' - giving a total maximum height approx of 115m or 377 feet (i.e. several hundred feet). HTH.

One solution might be to install a secondary radar on the other side of the wind farm which could illuminate the shadows.

..it's already crashed.

Not sure when they started building them several hundred feet tall but the tower of the GreenPark turbine just up the M4 from this site is 85m tall and the blades are 33m long making it nearly 400 foot high.

1. Civil ATC radar is active - it listens to signals transmitted by aircraft. It works for any aircraft with a transponder switched on. It is unlikely to be disrupted by electromagnetic noise, short of deliberate jamming or a nuclear war.

2. Military radar is passive - it broadcasts a pulse and listens for the echo - so it is in principle rather vulnerable to electomagnetic noise. Its purpose is to detect aircraft that are not using a transponder, such as invading foreign powers, errant light aviation pilots, terrorists and so on. It is generally agreed that these sorts of aviators should be kept well away from major airports and from centres of civilisation in general.

3. Wind turbines are indeed hundreds of feet high - say 250ft hub height with a 1 MW electrical generator on top. It seems believeable that such a device broadcasts a fair amount of electromagetic interference and could disrupt passive radar over a wide area.

4. Adding this nuisance to the general inconvenience, cost and unsightliness of wind turbines, might it be better to build an single always-on 1.2 GW nuclear power station, rather than 4000 wind turbines (1MW at 30% load factor) that stop working when the weather is calm?

You got 1 and 2 the other way around. Active radars transmit pulses and listen for returns. Passive radars simply listen for ambient radiations. The military uses passive radars, sonars, etc. because they don't give away your position.

As for #4, ins't nuclear power still more a NIMBY or even NIABY issue than wind turbines?

How low are these planes coming in over Reading?

It can't be much of a hazard to planes if they're suggesting going for five windmills instead of six.

> I'm not familiar with the geography around that area,

> but if there is something behind that area they want on

> radar then it's a Bad Thing

Its going to be Aldermaston

Its not that they will effect the planes, but the blades of the turbines are known to scatter the RADAR waves and can produce ghosts.

So this could be a problem when you have a stack of 747s landing

Kimbie

I've always wondered about this "windmills are ugly" argument. Personally, I think they're a beautiful example of minimalist engineering. I love the look of windmills turning in the breeze. There are some perfectly valid arguments against wind farms on the grounds of efficiency and capacity, but IMO the aesthetic argument is hugely in favour.

And, yes, I would be most happy for a wind farm to be built by my house.

Same reason there is no nuclear power station on the Thames!

This is to justify not having to build the unpopular things in urban areas....."Sorry, has to be rural, other wise the planes will crash...."

What will they say when they build a windmill near a rural raf base! : ..."ah, yes, but that radar is totally different...... etc,etc"!

@Steve Evans - The planes over Reading are direct flightpath for Heathrow, they are sometimes also circling to wait for landing. They are pretty low, by comparison to cruising altitude.

@whoever else it was: The problem with wind turbines is that they (if I understand this correctly) can create a scattering of RADAR signals, this is fairly well understood and (last I heard) the CAA have a project to develop software that can correct for this on the screens of the ATC personel. This is probably the reason that five are better than six, because of the nature if the interference.

Incidentally, I hope they are as cool at the turbine up at Green Park, it makes a great landmark, when you come down the M4 after a long journey and see it, it's a bit of a "Yay, I'm home now" Then you remember that you live in Reading...

At least it's not Slough.

I fly into Amsterdam fairly often -there are hundreds of windmills on the approach path

>just out of curiosity - when did they start building wind turbines several hundred feet tall?

http://www.geograph.org.uk/photo/761096

>Turbine details: Tower Height: 60m

>Blade Length: 40m Total Max Height: 100m

About 300 feet.

"Turbine No 9 on Scout Moor has a commanding view of the town of Rochdale in the valley below."

"Commanding" doesn't truly describe the utter dominance of the hill as you come on on the motorway..

Maybe plastic blades would help?

The problem with Radar and wind turbine is NOT EMI (electromagnetic interference) but shading and reflection of the signals.

Have you ever heard your voice through the blades of a fan? Like a fan, the turbine blades will "chop" the signal and cause weird reflections of the signal. If the radar pulse is delayed or distorted, the distance reading will be incorrect. If there is a reflection of the signal, the direct reading will be incorrect.

As to the question of 5 versus 6 wind turbines, it might be a function of allowable signal loss being exceeded with 6 but not with 5.

"4. Adding this nuisance to the general inconvenience, cost and unsightliness of wind turbines, might it be better to build an single always-on 1.2 GW nuclear power station, rather than 4000 wind turbines (1MW at 30% load factor) that stop working when the weather is calm?"

Can't we crank it up a touch to 1.21GW? If you get the reference, come join me back in the 80's...

The GE 3.6MW Turbines have a rotor diameter of 104m and that doesn't include the site dependent tower height: http://www.gepower.com/prod_serv/products/wind_turbines/en/36mw/index.htm

If the craft are in a landing pattern over *Reading* at 500 feet they are already fooked.

> Which is why Denmark scrapped their windfarm program a few years ago.

Nope, we did it because our current gubmint has shit for brains. If it's not big business as grandfather did it, we won't do it. New technology? Pshaw!

Ok, I feel compelled to wade into this, especially since in the not too distant past I used to be responsible for a whole bunch of RAF radars, and am qualified up the hill and back for discussing some of the intricacies.

Firstly, next time you are at an airport, have a look at the radar heads. Note one very key thing about them - they only rotate in 1 axis. The radar head does not pitch up and down. You will also notice that the radar is very wide, but not very tall. This is the same for both Airfield Surveillance Radars (ASR) and the Secondary Surveillance Radars (SSR). I'll explain the difference between the 2 later. Now, with a little bit of basic physics we can understand the consequences of these features. Basically, the wide but not very tall radar means that the beam is tuned very narrow when viewed from the top, but not very narrow when viewed from the side. The fact that the radar is rotating in only 1 dimension implies that dimension is the only one we can distinguish features in. So every feature is projected into a single plain. Now, the final point is that seeing something nearby can stop you from seeing something further away. Usually with most radars, the existence of large buildings a long way off just creates shadows. If large metal structures are a lot closer they can have the worse effect of bending the radar beams (think of the diffusion patterns you get from a Young's double slit experiment). Now finally, most modern skin paint radars rely on doppler shift to pick up moving objects. The problem with a wind turbine in particular is that it is moving fast enough when in operation to appear as an object on a doppler shift radar.

Now, the reality is that, despite having both ASR and SSR at Heathrow, Air Traffic Control will rely much more on SSR which works with a transponder in the aircraft "replying" to an interrogation request from the SSR radar head. Unfortunately, you are not required to have a working transponder in order to fly, so you still need skin paint radar to make sure no muppet in a light aircraft is about to fly into the middle of your stacks being scheduled for landing.

Finally, in certain locations things get considerably worse. The Instrument Landing System (ILS) used at pretty much every airport in the world is even more susceptible to problems. This system pushes out 2 sets of radar energy. One very tall and thin, the other very small and wide. They are transmitted out on a line that the aircraft can use to detect whether it is on the centreline and correct glide slope for landing. It is the system that all modern auto-pilots use for automated landings. These can also be affected (and bent) by large metal objects protruding into the area the beam is used in.

Now, the way you prevent this being a problem is two-fold. A bunch of research has been done to identify areas around modern flying aids where you don't want big objects. These are plotted into manuals which airports will use to object to planning permission. If something absolutely has to be sited in an area which has shown to be at issue in the past, then you will potentially consent to it being sited, and flight-test the system afterwards. This is very high risk though, since you can end up having to pull structures down, or close down a runway if you get it wrong.

Finally, I've regularly seen situations where simply scaling down the size of the project has taken it out of the at risk tables. I know it's unlikely that if 5 turbines in an area are ok then 6 won't be, but these sorts of things do happen. And in the manuals you have to include cut-off points. Sometimes these cut-off points will be rather conservative, but that is what it sounds like they are applying.

Wind flow at low levels is a fraaction of that available above 50 feet. Ground objects and just turbulent flow near the surface trash the amountof energy extractable from the wind. The higher the better.

50 feet is considered minimum to get th ebulk of the wind energy so then you have to add the blade diameter onto that. which takes you up to 200-300 feet for a commercial installation.

BTW That is also why all of these "home" windmills that mount on roofs or 20 foot poles are a scam. Air flow is badly restrited at that level. I have some 50 foot trees around my house and ariflow will be dead still at or near gound level, but tops of those trees are swaying like crazy.

Thanks for that. I understood it , wish more posts gave us useful information.

I did fly a bit some time ago in NZ, before we had to use radio in light aircraft , and radar had still to arrive here.

All this technology takes the fun out of flying !

Could also be that one of the proposed turbines was just in a worse spot than the rest, so it had to go. You can't get them too close together, so 6 would probably cover a decent amount of ground, and thus a decent amount of radar area.

And to whomever suggested plastic blades... You probably underestimate the various forces on a rotor blade. Some people have mentioned blades 40m long, and wind pushes against the whole length of the thing, which causes a hefty tendency towards tip deflection. To maintain maximum efficiency, the contour and angle of attack of the blades has to be controlled, and if the ends of your blades are busy flapping around, you're probably not going to generate anything but entropy.

Plus they get spinning rather fast and you really, really don't want one of them breaking. That'd throw the whole thing out of balance at a high speed, which would completely destroy the turbine, at a minimum, plus huge chunks of machinery falling from 100m would be fun.

A composite blade would probably work, but many composites have conductive fibers, which would do allll sorts of fun things to photons. Think polarization and diffraction.

People have already addressed the radar concerns pretty well (AC's 'Radar theory' - good post, thanks). So I'll just answer one of the other questions raised:

Angus - it's 'radar'. Acronyms and abbreviations that are treated as actual words in common use - laser and sonar are other examples - don't need to be capitalised. In cases of the abbreviation being a proprietary name, say of a specific organisation, then you can capitalise the first letter. This is why the BBC usually refer to Nasa and Nato (although with those two I think they look better capitalised in full).

I'm usually all for the Reg's entertaining subtitles - but can I ask why the apparent sarcasm in this one? Maybe I'm just reading too much into it, but - "nothing must interfere with Heathrow"? Gives Heathrow that evil-all-controlling-corporation spin, don't you think? Sounds as though you think it unreasonable that air traffic be kept as safe as possible around the country's busiest airport in the country's most populated area.

Have you ever seen a large wind farm? There is a large farm about 20 miles off the road between Santa Rosa and Fort Sumner (New Mexico, USA). Twenty freaking miles away (aka: 32km for the Imperially challenged) this forest of white "sticks" out there is just plain ugly.

You are in country with fairly little development (mostly graising land and open prairie) and just not much man made other than the road you are driving on. And then out there there at the edge of the mesa is this blight that stretches for MILES. Talk about an EYE SORE!

Of course, they have finished up a new wind farm about 20 miles West of Santa Rosa that is only about 10 miles (16 km...) off the road. Thankfully, it is only a blight for about 10 miles because there are enough hills around there to block the view of the think when you are West and East of it, other than that 10 mile stretch of road.

Personally, I would MUCH rather see a GW class nuclear plant out there instead of that wind farm.

In the UK we allow the use of a single capital letter, or no capitalisation, I believe in "American English" there are different rules.

As for the radar issue, I understand that the distance between 5 wind turbines could be further than 6 causing less diffraction, or that they might have a risk assessment form where they've predetermined 5 as acceptable, but it's a little disappointing. We're coming up to a massive energy shortage, we need every ounce of power from wind, tidal, and nuclear (ie non-fossil based fuels), and even relatively small projects are being cut back by planning permission.

If we don't build nuclear soon it'll be too late, they take so bloody long to build we'll be caught short when coal supplies slow. Without renewable to bridge the gap I might have to start stockpiling candles

Large moving structures in radar feild of views cause moving ghost returns and completely destroy the phase relationships of the returned signal. Generally just making post processing a modelling nightmare and your results somewhat error prone. Without return stability you have no chance of telling if it's a civillian craft or a similar sized, bomber of choice flown by you enemy until it's all a bit too late. But that's a probalm for tomorrow.

The met office used to have a service where you paid a small fee for them to tell you the best place to put your wind turbines. Unfortunately, after a few years, they realised that these 'best places' were also the best place to put your weather radars. Weather radars that they had installed through a similar exercise but for a much larger fee!

Paris - She'd never be caught out by an unexpected blow.

Pit we can't have more airports, they are significantly less polluting than wind turbines when you take into account all the (usually fossil fuelled) reserve capacity required for times when there is a static area of high pressure over the UK.

"Personally, I would MUCH rather see a GW class nuclear plant out there instead of that wind farm."

Personally, I can't say I'd be a great deal happier with a landscape covered in nuclear plant than with one covered in wind turbines. You, though, would "MUCH rather" a nuke plant than a wind farm. So if aesthetics is the only issue here - as suggested by the bulk of your post, because you didn't mention any other factors - then what,I wonder, leads you to prefer one eyesore over another?

..there is not much point in building wind turbines in Reading. The one that is already there hardy moves because of the lack of wind. On the other hand shutting down Heathrow has it's attractions. So I say go for it!

PS. I have a licence to use exclamation marks, so there!!

Ok, the wind isn't blowing and the windmills are still. How often does that happen across the entire country (plus surrounding water)?

So I guess you are a nuke man then? So tell me where does the electricity come from when your nice shiney GW unit is offline for refuelling, for 3 months every 3 years? Or are you suggesting we should build inefficient gas reactors or use the wonderful Soviet RMBK design?

Where does the power come from when the reactor SCRAMs at full load and takes a couple of days to come back online?

Where does your power come from when then is a large increase in demand (say an ad break) and your reactor cannot repond quickly enough to stop the grid frequency dropping and the generating network collapsing (eg Sweden 1983). Dinorwigg is not the answer btw as that is designed to fill in for relatively fast responding fossil fuel plant.

@RRRoamer: Get a life. Beauty is in the eye of the beholder and people have a remarkable propensity to live with eyesores.

@Tim: Given that the majority of the time needed to build a new nuke plant is taken up by public enquiries and the government has already promised that the public won't get a choice (national security and all that...) then new nuke plant can be built pretty quickly. Additionally, the government has promised to reduce the burden of building and safety regulations so that is another speed gain, doesn't that leave you with a nice warm feeling inside?