Nicely conserved WWII Tiger Moth airplane near the Gold Coast in Queensland, Australia. I got to experience the communications system from those days. The helmets are mounted with plastic tubes, which connect to a funnel in front of the pilot in the back seat. His helmet in turn, was connected to a funnel in front of the passenger seat at the front. I failed to yell loud enough through the sophisticated communications system. My best effort to communicate with him? Raise thumbs up above my head to indicate I was doing fine. The aerobatics added a plenty of fun to the ride. According to the pilot, it pulled about 3-4 Gs.