Plane crash blamed on 'turbulence' from wind farm

[N707ZS]

Copied and pasted from BBC News
Beverley plane crash blamed on 'turbulence' from wind farm - BBC News (https://www.bbc.co.uk/news/articles/c193278vlypo)

Have flown in a couple of balloons near them and you get the feeling they pull you towards them which is the obvious effect, then up and over the top.

[meleagertoo]

How could a turbine which is being driven by the wind possibly "pull" you towards it? Indeed the opposite must be true, the turbine must be offering an (infinitessimally small) impediment to the airflow upwind of it or else it wouldn't be turning.
As to producing enough 'turbulence' to cause an aircraft to crash...
"could not be ruled out" indeed! Presumably neither could the Bermuda Triangle or intervention by little green lizards.
What a fatuous weasel excuse!

[treadigraph]

https://assets.publishing.service.gov.uk/media/620bb596e90e0710aa4b69f3/Piper_PA-22-150_G-ARDS_03-22.pdf

[sablatnic]

They seem to create some turbulence in this photo.


https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/259x194/images_2_4ffaa336d197d40e54401516fec06ec7a366f2b7.jpeg

[blind pew]

I launched off mount leinster and flew off towards the coast deciding that there should be a nice thermal source from the next hill with a turbine on top. The turbulence was so bad that I immediately headed to Bunclody, landed then spent the next couple of hours on a perfectly good soaring day sitting in the sun and drinking Guinness.
The turbulence from the turbines has had a documented effect on crop growing times by raising the average air temperatures.

[SimonPaddo]

How could a turbine which is being driven by the wind possibly "pull" you towards it? Indeed the opposite must be true, the turbine must be offering an (infinitessimally small) impediment to the airflow upwind of it or else it wouldn't be turning.
As to producing enough 'turbulence' to cause an aircraft to crash...
"could not be ruled out" indeed! Presumably neither could the Bermuda Triangle or intervention by little green lizards.
What a fatuous weasel excuse!
Isn’t the wind that is powering the turbine just causing you to drift? If the turbine is into wind you would be blown towards it. Nothing to do with it pulling you towards it.

[N707ZS]

Isn’t the wind that is powering the turbine just causing you to drift? If the turbine is into wind you would be blown towards it. Nothing to do with it pulling you towards it.
It's an imaginary thought that it's dragging you in as you travel towards it! If you haven't done it you will not know.

[340drvr]

It's an imaginary thought that it's dragging you in as you travel towards it! If you haven't done it you will not know.
OK, I'll buy that, for your balloon, not unlike the way the ground looks when you cross a ridge while in a crab for a crosswind (in a plane).
Just to clarify, neither the BBC report nor the official accident report mention anything about being pulled into turbines, The plane was 1400m downwind from the nearest windmill.

[blind pew]

I have no doubt that there is an explanation for the drift but the problem is that the subject is extremely complex and very few if any understand the forces involved.
Many moons ago I was sat in Tom Crean’s pub, the South Pole in, he of Shackletons expedition, having a discussion with a meteorologist who lectured on the world circuit. He obviously knew the theories of wave propagation but not the realities.
50 years ago I was taught to forecast from station reports, draw synoptic charts and predict the weather around the globe; I soon found out that theoretical weather is not local weather. I asked our aerodynamicist how a two channel model could perform an axial roll on rudder alone; reply with high Reynolds number aerodynamics does strange things.
From there I’ve re learnt aerodynamics and aerology from gliding and again with paragliding with combined 4000 plus hours. The atmosphere does stuff that the textbooks do not cover..there is now upwind influence, wave flow from wind shear associated with temperature inversion and interference patterns to name a few.
Morning flights in Ballons are generally influenced by temperature inversions, shear associated with them and wave.
I tried flying a drone with an anemometer to measure this phenomena before I paraglide having been caught out. Balloonists release toy helium balloons to obtain an approximation of the conditions.
We have come a long way from my first glider which did the first 300km uk flight where the designers got the wing, brakes and rudder wrong; we now have a world record of over 3,000km and paragliders have gone from 5 km to 600 plus. Catamarans have gone to incredible speeds as have model gliders at over 300kph in ridge lift using wind shear. A spin off of these back shed technology is wing tip design.

[SimonPaddo]

Who would have guessed ?

Apparently, a spinning propeller causes air to be at a lower pressure in front of the propeller and higher pressure behind.

So lower pressure, compared with the surrounding air-stream, must represent a slight suction force whilst higher pressure is a propulsive force.

Its what stops all of us going backwards for Christmas !

N
True for a power driven propeller, but for a wind turbine driven by the wind?

[Pilot DAR]

I believe that the presence of the wind farm, relative to the 119 hour PPL flying a short wing Piper could have been a 1% factor in the accident, so yes, it could have been a factor, many other things could have been much greater factors.

[TRENT210]

Thinking outside the box maybe ?

Normally people blame needing the toilet for a crash landing 🤪

[rnzoli]

https://assets.publishing.service.gov.uk/media/620bb596e90e0710aa4b69f3/Piper_PA-22-150_G-ARDS_03-22.pdf
thanks, this has all the details I was curious about :)
The airfield management has never heard of the effect from other pilots, and suggested that "there can be some shadowing from the trees to the west of the clubhouse".
Studies of wind turbine turbulence estimate that the effect dissipates within the distance of 5-8 times of the rotor diameter.
The runway was 15-17 times of the rotor diameter away in this case.

[averow]

In Medicine, when an operator (Surgeon) starts blaming their equipment and the help in the room for their (frequent) procedural struggles we like to bring up the concept of "operator error in technique".

[biscuit74]

This is an aircraft with an aileron rudder interconnect, left still operational in this machine. Many folk disabled this - it can be overridden but presumably would be felt as pressure on the controls. With only 27 hours on type at the time of accident, it's possible the pilot hadn't previously found this to be an issue. At the flare, with possible, turbulence and crosswind, the use of aileron and rudder are not likely to be co-ordinated, (especially when I fly) so this system will be adding adverse pressures. Not what you really need ; a time when it's important to make the aircraft do what you want, not what it wants !

As for the estimate of turbulence impacts dissipating within 5-8 time rotor diameter, I'd really like to see the link to that, or some citation, please. Intriguing. It may be true in some ideal conditions, but certainly isn't true where I often fly. We have a windfarm a couple of miles upwind - for the prevailing wind, and it can be impressively rough if you pass through the direct wind track on climb out. I am certainly well outside the 8 lengths of the turbine blades distance !

[rnzoli]

As for the estimate of turbulence impacts dissipating within 5-8 time rotor diameter, I'd really like to see the link to that, or some citation, please
There you go, Sir, please let us know what you think. https://www.liverpool.ac.uk/media/livacuk/flightscience/projects/cfd/wakeencounter/caa_wind_turbine_report.pdf
As in many fields of science, this is the current best thinking, but there is always a possibility to refine and improve the models, the LIDAR wind speed measurements etc.
I personally find it challenging the separate turbulence caused by wind turbine blades and other turbulence caused by terrain, or low-level wind shear near the ground due to tree-lines and buildings.
Some interesting parts of the study, highlighted by me:
The statistical LIDAR data indicated that for this particular wind turbine the wake mean velocities recovered to the free stream speed at a position about five rotor diameters downstream. The LIDAR measurements were compared with the results of a full CFD simulation conducted for the MEXICO wind turbine with a similar tip speed ratio, and also compared with the velocity deficit wake models. In general, reasonable agreement was found.

The WTN250 wake induced velocity fields generated by the Kocurek wake vortex model, were integrated into an aircraft flight dynamics model based on a GA configuration to simulate the wind turbine wake encounter scenario of a light aircraft approaching an airport. Piloted flight simulations were carried out to study the severity of this type of wake encounter. The flight simulation results suggest that the WTN250 wind turbine wake mainly generated yaw disturbances on the encountering aircraft and caused a yaw angle deviation less than 10 deg.

[biscuit74]

Thanks 'rnzoli', I shall have a look at that. 117 pages will take me a while !

I understand what you mean about the difficulty of identifying what is causing specific turbulence - I have flown both sailplanes and tug aircraft into wave conditions frequently; the turbulence conditions at low level can vary greatly during a single day, or some days from one tow to the next.

In the case of the windfarm nearby us, we have from time to time encountered notable turbulence while climbing out downwind of the windfarm in wind directions varying from West through SW to due South, which suggests to me that the most likely cause is blade turbulence from the windfarm. It is variable and unpredictable, sometimes completely absent when anticipated and then occasionally surprisingly strong. I suspect that atmospheric conditions influence its propagation and likely 'longevity' downwind, just as with other effects, like wave. I know one pilot who reported being rolled rapidly through more than 90 degrees flying just downwind of the farm, which must have been exciting. I don't know how close that aeroplane was.

For the airfield case described in the accident report, I'd have thought ground interference would rapidly diminish or decay the rotor, though I think wing wake rotors can last for quite a long time and track a fairly long way. Interesting.

[xrayalpha]

We at Strathaven Airfield are just under 5,000m from the eastern boundary of Europe's largest onshore windfarm - the Whitelee/Browncastle complex. Each turbine higher than the Blackpool Tower.

And surrounded by bigger and smaller turbines to all the other points of the compass.

With around 32 LAA-type light aircraft and microlights based here, and an active microlight school, we have probably more practical experience of operating close to wind turbines.

The classic model of wake turbulence is that it sinks and spreads. But we find turbulence in certain conditions on climbout up to 350ft higher than the top of the Whitelee turbines. The is a slight hollow in the ground in between us and them - so is there some sort of wave? Or is it that the ground rises from the Clyde Coast to Whitelee (at c 800ft AMSL) and that creates a sort of wave that carries the turbulence with it?

Flying from Prestwick to Strathaven with a northerly with component and low cloudbase - say 1200ft AMSL as you follow the A71 and you are in the valley at Darvel - you can't climb out and maintain VFR and you can't head south because of the high ground. It can be like a washing machine in there. Most pilots here avoid that area in those conditions. The ones that don't haven't listened to their comrades tales!

But it is not consistent! And no-one knows why. And that is the issue with simulations. As pilots, we need to know what is predicted to happen on that day. And at £2-3 million each installed, no-one is going to dismantle even one turbine just to please me. Would be cheaper to buy the airfield and close it!


ps The WTN 250 wind turbine used for the research model has a 30m rotor diameter, and a 250kW A far cry from the Browncastle turbines with 100m rotor diameter and 2.5mW output !

And a larger rotor diameter will then be more in the upper air and away from ground effects (even just bushes and trees), just by its size.

[Mechta]

If a wind turbine rotates at constant speed and this is speed is related to the average wind speed seen by the full rotor disc, then perhaps it is possible that the slower moving air at the bottom of the blade disc (and wind gradient) is actually accelerated by the blades?

[markflyer6580]

Not posted on here for a while but though I would add some context from the wind turbine side of things. As a day job I run an offshore windfarm. We have been doing quite a bit of work around the effects on turbulence and such so that when we are covering such big areas the turbines don’t adversely affect each other and we can get them to yaw slightly out of the way of their neighbours to increase production,they are roughly 1km apart with a 154m rotor diameter, so at full chat there is some wake from them but not as much as you would think. We are talking marginal gains (worth ££) with what the boffins get up to.

From a flying point of view we hoist on to the top of them via heli. Only once in my 7 years of heli hoisting ops has the turbulence from other turbines been too much (at a smaller windfarm with the same turbines), this was however in 50kt winds and even then it was safe enough to hoist, just a bit wild and we like to be cautious. I appreciate turbine helis are different to vintage pipers and as a 150hr lapsed PPL, I haven’t experienced it from the controls myself, but living within a couple of miles of the airfield in question I really can’t see how this incident had anything to do with local wind effects from a small onshore windfarm.

Just my 5p worth.

[NorthSouth]

The NLR aviation research group in the Netherlands published a report in 2020 (https://reports.nlr.nl/server/api/core/bitstreams/1ff6ede3-a52b-4314-ba93-0cb750e1cb04/content) which found that - for offshore helicopters - problematic turbulence was unlikely to be encountered beyond 6 turbine rotor diameters downwind of a single turbine. They proposed a safety factor of eight rotor diameters downwind of a multiple-turbine wind farm.
NS

[ATC Watcher]

In Germany , where I fly a lot, we have high concentration of Windmills ,in some cases very close to the landing circuit. Never heard or experienced any such "wake turbulence" nor ever heard of anyone complaining about it.
How to bring down a beautiful old PA22 like this is a shame , as with 150 HP you should be able to overcome any downdraft on a flat countryside. ..

[Albrecht0803]

In smaller planes, ultralights, you can feel the downstream turbulence. But it is not severe in a reaonable distance. Upstream, there is no effect on a plane. I tried it myself, flying in the height of the hub around a windmill.

[Cedrik]

Sprayed and flown around them a bit, never a problem with turbulence. Flown the Tri and Pacer a bit as well, the Piper Shortwings normally handle turbulence well.

[FlexibleResponse]

There is a lot to learn on the subject of wind turbines and the effect on airflow downwind. It stands to reason that a wind turbine that generates 2-3 MW (1500 average households) must drag quite a large amount of energy from the movement of the mass and velocity of the air. Removal of energy in the relatively small area of the wind turbine rotor rotational area must have a profound fluid dynamics energy interchange with the free-flow airstream outside the rotor.

In turn the preservation or otherwise dissipation of these effects would depend on numerous factors such as size of rotor area, height of rotor, steadiness of wind velocity, gusts, vertical temperature gradient and stability of same, ground friction effects, geography and proximity of other wind turbines…to name just a few.

Yes, a lot to learn…much as we did learning about wake turbulence and persisting characteristics under some conditions that research and tests eventually revealed. We lost a few aircraft and folks prior to gaining a good understanding of the characteristics of the phenomenon was learnt the hard way.

The jury is still out…

[fdr]

the condensation in the wake of the wind turbine is stated as being due to expansion cooling of the mass in the wake. I'm not sure I buy that argument but it has been made. The condensation is also possible just from the slight mixing that is necessary to get coalescence to occur, in perfectly still conditions condensation is delayed.

As energy is extracted from the airmass by a wind turbine, there will be a velocity deficit in the wake compared to the free stream flow that is not affected by the actuator disk of the turbine, and that will give a slight shear on transitioning from one condition to the other. The turbine does give a rotation to the mass flow in the wake which also results in loss of velocity in the free stream direction, and it gives some shear out of plane which would be dependent on entry height relative to the core, angle of entry, and flow/blade velocities.

[FlexibleResponse]

This Applied Physical Sciences Research Article indicates that wind speed loss behind a wind turbine working at operating conditions is in the order of 50% velocity. The included graphs give some visualization to the subject:

​​​​​​https://www.pnas.org/doi/10.1073/pnas.1602253113#:~:text=This%20limit%20is%20associated%20wit h,balance%20of%20the%20lower%20atmosphere.


https://www.pnas.org/action/downloadSupplement?doi=10.1073%2Fpnas.1602253113&file=pnas.1602253113.sapp.pdf