I went looking for the 5 rotor diameter wake turbulence study and found several things.
1. The document I recall I am sure was this one from the University of Liverpool in 2006 "Wind Turbine Wake Encounter Study". Their study used the East Midlands turbines for the Lidar analysis and then used that to check theoretical models of turbulence from the turbines and they make the 5 rotor diameter spacing assessment.
https://www.liverpool.ac.uk/media/li...ine_report.pdf
As FB mentions the East Midlands turbines are not as big as Cobden's proposed ones but it uses that actual measured data to compare with theoretical models of turbulence.
2. The UK CAA then put out a CAP about wind turbines that referenced the above study and they say it is valid for rotors up to 30m but beyond that size there was not enough information to know exactly the effects but that there was ongoing research being done on larger sizes and there is an urgent need for this to be done. They state that as the results about larger turbines become known they would be updating their recommendations.
https://publicapps.caa.co.uk/docs/33...INAL%20Feb.pdf
That was in 2006. I could find no further updates despite the ongoing research they said was being done. It is possible I looked in the wrong place and there may be more recent stuff. Curious though any further research is not easily found. Maybe they decided it wasn't urgent
3. I found a web page of a consultancy "Pager Power" company that does research on the impacts of turbines on things like radar, navigation and communication etc, that said they have been researching the aviation impacts since 2006 and have flown drones, aircrafts and helicopters close to turbines up to 80m diameters to assess turbulence and have found " In all cases, turbulence thought to be caused by the turbines was apparent, but the size of these effects was considered less than the normal turbulence effects experienced in day to day flying".
They have no published reports on this that I could find though so not sure how much weight to put on that.
https://www.pagerpower.com/news/turb...wind-turbines/
All the above is from my quick scanning - I may have missed or misunderstood things so feel free to read the above.
Like I said - I have no dog in this fight but am curious - if there is significant danger from turbulence at long distances (say > 1 nm) it is an issue I would like to know for my own benefit.
Other than anecdotes, is there any verified reputable data on turbulence beyond the immediate location for wind turbines?