Re: Wind Turbines and stealth

[Arved Sandstrom]

"David McArthur" > wrote in message
om...
> Interesting piece on Radio 4 this morn (UK): Wind turbines apparently
> play havoc with ATC radars.
> Qinetiq, the UK defence research agency is looking at a solution:-
> Adding 'electromagnetic elements' between some of the layers of the
> glass fibre.
> The chap they were interviewing from Qinetiq said that the result was
> "Destructive Interference" causing the cancelling out of the radar
> energy.
>
> ...I wonder if this is some military stealth concepts making the jump
> to civilan applications.
>
> Comments?

A quick Google shows that there is a fair amount of comment on the general
problem: http://www.qinetiq.com/casestudies/2003/case_study.html and
http://www.countryguardian.net/modradar.htm , for starters. This is probably
the best report I found on the Web:
http://www.bwea.com/aviation/ams_report.html (Incidentally, this last has a
three-part PDF report and an excellent HTML summary).

Some of the problems evidently have been solved using existing (known)
techniques - filtering through electronics and software. The Doppler return
from a wind turbine resembles that of a/c (more to the point, apparently
most ATC radars just pick up Doppler; they don't do fine analysis of the
Doppler, though), but the object itself is not moving, so they simply do
so-called "plot" or "track" filtering.

As an aside, it makes me wonder if a helicopter hovering would then not also
completely get filtered out by an ATC radar? It's been 2 decades since I
took antenna theory and electronics, so I have no idea. But it's an
interesting speculation.

I think the remaining problem that they are trying to solve is the possible
large radar cross-section of a wind-turbine. Add in the fact that one
actually typically has entire wind-farms, and one has such a large return
that discriminating out a much smaller Doppler signal in the vicinity
becomes quite difficult. I don't grok the actual scope of the problem, but
according to what I gather from the articles, solving this problem by
modifying radar installations is much more labour-intensive and costly than
mitigating the Doppler return problem. So I am not surprised to hear that
they are looking at using turbine material mods to reduce RCS.

AHS

[Urban Fredriksson]

In article >,
David McArthur > wrote:

>...I wonder if this is some military stealth concepts making the jump
>to civilan applications.

Stealthing bridges and buildings isn't something new and
from this little information it's hard to tell if the
suggested solution is something suitable for aircraft,
ships or vehicles.
--
Urban Fredriksson http://www.canit.se/%7Egriffon/
Just because something is obvious doesn't mean it's true.

[Anonymous]

Urban Fredriksson wrote in message ...
>In article >,
>David McArthur > wrote:
>
>>...I wonder if this is some military stealth concepts making the jump
>>to civilan applications.
>
>Stealthing bridges and buildings isn't something new and
>from this little information it's hard to tell if the
>suggested solution is something suitable for aircraft,
>ships or vehicles.

Well if you can make the blades of a wind generator less visible to radar, then surely the same techniques could be applied (or have
already been applied) to reducing the Radar Cross-Section (RCS) of propellor-driven aircraft such has the Hercules or Osprey..?

[Howard Berkowitz]

In article >, wrote:

> In article >,
> David McArthur > wrote:
>
> >...I wonder if this is some military stealth concepts making the jump
> >to civilan applications.
>
> Stealthing bridges and buildings isn't something new and
> from this little information it's hard to tell if the
> suggested solution is something suitable for aircraft,
> ships or vehicles.

Look to elementary education for stealth -- invisible playmates,
homework-eating dogs, often the homework itself, etc.

[David McArthur]

"Arved Sandstrom" > wrote in message >...
> "David McArthur" > wrote in message
> om...
> > Interesting piece on Radio 4 this morn (UK): Wind turbines apparently
> > play havoc with ATC radars.
> > Qinetiq, the UK defence research agency is looking at a solution:-
> > Adding 'electromagnetic elements' between some of the layers of the
> > glass fibre.
> > The chap they were interviewing from Qinetiq said that the result was
> > "Destructive Interference" causing the cancelling out of the radar
> > energy.
> >
> > ...I wonder if this is some military stealth concepts making the jump
> > to civilan applications.
> >
> > Comments?
>
> A quick Google shows that there is a fair amount of comment on the general
> problem: http://www.qinetiq.com/casestudies/2003/case_study.html and
> http://www.countryguardian.net/modradar.htm , for starters. This is probably
> the best report I found on the Web:
> http://www.bwea.com/aviation/ams_report.html (Incidentally, this last has a
> three-part PDF report and an excellent HTML summary).
>
> Some of the problems evidently have been solved using existing (known)
> techniques - filtering through electronics and software. The Doppler return
> from a wind turbine resembles that of a/c (more to the point, apparently
> most ATC radars just pick up Doppler; they don't do fine analysis of the
> Doppler, though), but the object itself is not moving, so they simply do
> so-called "plot" or "track" filtering.
>
> As an aside, it makes me wonder if a helicopter hovering would then not also
> completely get filtered out by an ATC radar? It's been 2 decades since I
> took antenna theory and electronics, so I have no idea. But it's an
> interesting speculation.
>
> I think the remaining problem that they are trying to solve is the possible
> large radar cross-section of a wind-turbine. Add in the fact that one
> actually typically has entire wind-farms, and one has such a large return
> that discriminating out a much smaller Doppler signal in the vicinity
> becomes quite difficult. I don't grok the actual scope of the problem, but
> according to what I gather from the articles, solving this problem by
> modifying radar installations is much more labour-intensive and costly than
> mitigating the Doppler return problem. So I am not surprised to hear that
> they are looking at using turbine material mods to reduce RCS.
>
> AHS

Thanks for the links - it sounds like an intriguing problem.
The bit that caught my attention on the interview was the specific
reference to destructive interference - I'm curious to know what sort
of materials (or arrangement of materials) would be able to produce a
phase difference(?) that would nullify the incoming radar signal?

David

[Stephen D. Poe]

David McArthur wrote:
>
....snipped...
> Thanks for the links - it sounds like an intriguing problem.
> The bit that caught my attention on the interview was the specific
> reference to destructive interference - I'm curious to know what sort
> of materials (or arrangement of materials) would be able to produce a
> phase difference(?) that would nullify the incoming radar signal?
>
> David

There were several consumer-oriented stealth-related books that were
published at the end of the 1980s. They should have sufficient general
details. Try:

- Stealth, Doug Richardson, Orion Books, NY, 1989.
- Stealth Aircraft, Bill Sweetman, Motorbooks International, 1986.
- Stealth Technology, J. Jones, Aero, 1989.

Or for something a bit more detailed, see:
- Radar Cross Section, Eugene F. Knott, John F. Shaeffer, Michael T.
Tuley, Artech House Radar Library, 1993, 2nd ed.

[EndX]

A certain David McArthur did scribble:

> Thanks for the links - it sounds like an intriguing problem.
> The bit that caught my attention on the interview was the specific
> reference to destructive interference - I'm curious to know what sort
> of materials (or arrangement of materials) would be able to produce a
> phase difference(?) that would nullify the incoming radar signal?
>
> David

The use of dielectric materials with a reflective backing with an overall
quarter wavelength thickness would suffice. For total destructive
interference you want it in antiphase, or a half wavelength out of phase. A
RAM with quarter wavelength thickness would give you this property. The
stealth books Stephen Poe listed will have a more full explanation.

--�
rgds

BMFull