A weed-spraying contractor is the latest Canberra businesses taking to the skies with an unmanned aircraft.

Greg Harris is leasing a 3.36 metre-long helicopter, which carries two eight-litre containers of spray.

This will bring a new dimension to weed control, which costs the ACT government $1.9 million annually and billions of dollars across Australia.

The Civil Aviation Authority has approved 41 operators of unmanned aircraft across Australia and the listing is climbing fast.

The Canberra Times reported last month on the first aerial vehicle to get approval to operate commercially for photography.

CASA's director of Aviation Safety, John McCormick, told an industry forum in February numbers had doubled in 12 months and their rapid growth would challenge regulators.

Mr McCormick said right to privacy was a matter for the Australian Privacy Commissioner.

''Another evolving topic is environmental issues; again, while acknowledging that it is not part of CASA's role, like manned aircraft, RPA (remotely piloted aircraft) operations will have an impact on the environment.''

Mr Harris said his unmanned helicopter would reach remote areas, opening the way for more economic weed control, for example in steep terrain in the Brindabella Mountains clearing blackberries from under power lines, a job that could require hauling a bulldozer into the bush.

''We can get into ravines, crevices, insane places where people just can't go, but we can put that machine in,'' Mr Harris said.

''We can stand on a hill and fly down into gully lines, or big, deep creeks. That's its advantage.''

Bushfires, a bad back and curiosity led Mr Harris to becoming the first contractor for Yamaha to use the RMAX technology.

A truck driver until he injured his back, Mr Harris helped a mate spraying weeds and, when he finished that job, was called to do more, which led him to buy a boom spray and go into business for himself.

He became a preferred contractor for Urban Services after the 2003 Canberra firestorm, when weeds erupted across the territory's burnt areas.

''A long time ago, doing contract work for Environment ACT, we were hanging off the side of hills, spraying St John's wart. It was terribly hard work and dangerous, trip hazards, snakes, and the boys whingeing to me. The only thing I could think of was something remote. Bigger helicopters cost too much money, not practical, plus they take out a lot of the non-target species as well.''

So began years of research and, more recently, calls to and from Japan and a franchise agreement with Yamaha.

He expects to fly mostly at two metres above the ground to avoid spray drifts, covering three times the amount of ground in the same time conventional weed spraying takes.

Mr Harris said the aircraft was not noisy and had been tested for noise.

''If you are in your home, and it is on an oval 150 metres away, you would not hear it,'' he said.