I've long known that wind turbine blades can cause massive interference to radar systems, so much so that wind power generation is usually banned within a reasonable distance of things like airports. Now there may be a novel solution. The Telegraph reports:
Defence and technology group QinetiQ has built 'stealth’ wind turbines which barely show up on radar.
The company has applied knowledge built up over 40 years in military applications to make a French windfarm consisting of 35 turbines each 400ft high appear to radar systems as if they were just 4ft high each.
EDF, the French state-owned power giant, turned to FTSE 250-listed QinetiQ for help after being refused permission to build the country's most powerful wind farm at a site near Perpignan, southern France, because the giant towers and spinning blades of the turbines would interfere with radar systems used to predict weather.
. . .
Military stealth works to defeat radars using multiple frequencies while weather radar is narrow band so on the face of it producing a stealthy turbine should have been simpler than most military applications.
However, Mr Moore said it turned out to be extremely challenging.
“The aerodynamic shape of the turbines blades couldn’t be altered significantly because they would become inefficient and we couldn’t put a stealthy coating on because it would be thick and heavy, which would also make them inefficient,” he said.
In the end the company designed blades made out of composite materials which absorb radar waves and turn it into heat, while a special cladding was put on the towers and the generators themselves to make them disappear to radar.
There's more at the link.
I find this fascinating, for two reasons. First, if turbine blades (and their supporting towers) can be made less visible to radar, will they pose a greater risk of collision to low-flying aircraft? I can see military planes, flying nap-of-the-earth, running slap into one if they can't see it coming on their electronic systems. Second, can the same technology be applied to helicopter rotors? Rotors are one of the most visible parts of any helicopter on radar systems. If they can be made radar-invisible, a full 'stealth helicopter' can't be far away - and that has huge implications for Special Forces infiltration and exfiltration operations.
Most interesting . . .