Paris - From their roots in spying and stealth military attacks, unmanned planes are spreading into the civilian sphere and could soon be put to work in tasks as diverse as inspecting oil pipelines, catching rhino poachers and even flying travellers.
According to the European Commission, there are more than 400 projects across 20 European countries to develop civil unmanned aerial vehicles (UAV) ranging from some weighing just a few grams to others the size of an Airbus A320 jet.
More than 80% of the companies working on these projects are small and medium-sized businesses or start-ups.
"The market is growing very rapidly, especially this year," Johanna Claussen, chief executive of one such company, German manufacturer MAVinci, told Reuters.
MAVinci, based in Leimen near Heidelberg, makes UAVs with a wingspan of 1.6m that take aerial images for land surveys conducted for infrastructure projects, mines or applications in the building industry.
"The market holds huge potential, and we can't even make as many systems as our customers would like to buy," Claussen said.
Aviation and aerospace industry research firm Teal Group has estimated that annual spending on UAVs around the world will almost double to $11.4bn by 2022.
Almost all the money is currently still going toward military applications, but the European Commission says it is highly likely that a real market for civil applications will emerge over the next decade.
For that to happen, though, legislation will need to be developed dictating how, where and when UAVs are allowed to fly in public airspace, and advocates of the new technology still face concerns over safety and privacy.
US lawmaker Rick Larsen, a Democrat from the state of Washington, said privacy concerns continued to surface, even in states like his that are closely tied to the aerospace industry, and needed to be addressed head on.
"Local law enforcement, state and federal government as well as the companies involved do have a responsibility to explain how they see the balance between the privacy issues that we have and the use of unmanned aerial systems. That is what is going to make this happen," Larsen told Reuters at the Paris Airshow.
UAVs come in two basic shapes, those that look like cockpit-less aircraft - such as the ones made by MAVinci - and those that have helicopter-like rotor blades allowing them to hover and take off and land in restricted spaces.
German rail operator Deutsche Bahn is testing the use of multi-rotor UAVs equipped with infra-red cameras to catch vandals spraying graffiti on trains parked at its vast depots.
Those UAVs, made by German firm Microdrones, have a diameter of about 1m and cost €60,000 each.
Smaller UAVs can be had for as little as a few hundred euros, such as the Phantom quad-copter made by US-based DJI Innovations. It weighs less than 1gk, can be carried in a backpack and comes with a mount for an outdoor sports camera.
"The possibilities are limitless," said Stefan Eichhorn, sales chief of Munich-based Ascending Technologies, which makes multi-rotor UAVs for aerial photography and video. His company's flagship model, the AscTec Falcon 8, starts around €18 000.
UAVs have also recently been trialled to spot rhinoceros poachers, and even to deliver pizzas and burgers in the UK.
Oil and gas companies are hoping to use them to detect pipeline faults in the Arctic once regulators open up airspace for the commercial use of unmanned aircraft, and EADS unit Eurocopter has been developing a helicopter that can fly with or without a pilot.
Some even hope UAVs will revolutionise air travel. French university Ecole Polytechynique Federale de Lausanne is presenting an idea at the Paris Airshow for a wing-shaped UAV to which several capsules that look like rail cars could be attached to carry passengers.
"My grand-father would never get in an elevator unless there was an operator in it. But today you and I would take an elevator and would not think twice about it," said Tom Captain, Global Aerospace & Defence Sector Leader at consultancy Deloitte Touche Tohmatsu Limited.
"The same goes for flying. People say, 'I'm not getting in the aircraft if there is no pilot'. The truth is many flights are run by computers anyway, with automated take-off and landing."