Even the most ardent wind farm supporter would not want to be accountable for an air accident and would agree that the responsible siting of wind farms was imperative.
A modern wind turbine will create disturbed air flow (turbulence wake) for up to 20 rotor diameters. For an 82 metre turbine, such as the ones proposed in Stoke Goldington, turbulence wake will affect aircraft up to 1,640 metres away from the rotors.
Additionally, the CAA’s guidance for obstacles is that "no obstacles greater that 150 feet should be within 2,000 metres of an airfield".
A responsible response to the "turbine wake created by wind farms" and the 'CAA guidance for obstacles near airfields" means that Stoke heights wind farm is not viable. This wind farm proposal is just 900 metres from a helipad and 500 metres from an airstrip.
Further information regarding turbulence wake
Wind turbines consist of aerofoil shaped blades arranged in a vertical plane. The effect of removing energy from wind passing through the blades is to reduce the wind speed behind the turbine. This along with tip losses creates vortices or wake turbulence. Wake turbulence is well understood for aircraft, it has been documented that there have been serious and fatal accidents in the UK to light aircraft because pilots were unable to maintain control after being caught in the wake vortex generated by heavier aircraft. The Civil Aviation Authority have published a “Safety Sense” leaflet providing information for pilots concerning the dangers of wake turbulence and how to avoid it:
The following text is extracted directly from the above leaflet:
“The heavier the aircraft and the slower it is flying, the stronger the vortex. Among other factors, the size of the vortex is proportional to the span of the aircraft which generates it, for instance a Boeing 747, with a span of 65 metres trails a vortex from both wingtips each with a diameter of around 65 metres.
The proposed wind turbines have a blade diameter of 82 metres – greater than the above mentioned Boeing 747. It can therefore be safely assumed that they will generate vortices of considerable magnitude.
Further CAA documentation regarding turbulence wake at airfields
A further CAA publication “Aeronautical Information Circular (AIC) P 18/ 2009 Wake Turbulence” details the minimum spacing between aircraft in order to avoid problems of wake turbulence.
From this document it can be seen that the combination of “heavy” to “light” results in a requirement for a spacing of 6 to 7 nautical miles.
Below is a scale comparison diagram showing the size of a wind turbine against a Boeing 747 aircraft and Hughes 500 helicopter.
Even if we assume that the magnitude of the blade-tip vortices of wind turbines are less than that of a 747, we must put air safety first and take a cautious approach when developers propose these obstacles next to airfields.
The CAA has confirmed that no trials have yet been conducted to measure the effect of wind turbine wake on aircraft.
However, the CAA’s guidance for obstacles is that "no obstacles greater that 150 feet should be within 2,000 metres of an airfield”.
The developer at Stoke Goldington wants to place 400ft turbines within 1000ft of a helipad. That is an unreasonable proposal which cuts the CAA’s obstacle guidelines in half and takes no account of turbine wake effects.