With regards the "helicopter" sound it is actually the sound of a mounted machine gun.
For the whole shooting of the show out in the open, the crew didn't actually shoot in Turkey itself. They actually stayed at home, in Melbourne. The crew managed to find a secluded hill range and a local gun range to film on, and even built trenches there. While they did go to Gallipoli, the scenery was altered too much to actually create the impression of the landscape.