BBK I know where you are coming from.
And again that's the reason for that particular type. They grow huge very quickly. And the foliage is a key factor as well it needs to be the thick drooping type which layers not the branches stick out at 90degrees type.
If you think about sound proof rooms the walls aren't solid they are foam with shapes in them. Line of trees with a fence in the middle of them with a shaped latex form for the problem frequency's up to 12ft may also be a solution. The trees would protect the latex fence, while also giving their noise reduction.
And the height required would be a function of how close you can get them to the apron in question.
The out of sight out of mind may have a huge effect on the complaints. It goes from they are running those bloody engines and not going anywhere to oh something must be moving. And trees are good a bloody great wall isn't
As test goes its a relatively easy one to organise. You just need to recce out some lumps of woodland and then speak to your rotary colleagues and organise them to visit on a day during training with the sound monitoring gear set up.
Another solution which would be more expensive would be a huge PA system which would pump out and actively cancel noise towards the village. But you would more than likely need a new power line into the base for it to be any use. Which is why I didn't mention it before.
Surely you must have some Engineery types in holding that could be given a project to have a look at it.