PARIS (Reuters) -Opportunities in defence, emergency healthcare and cargo could help make flying taxis a reality in the next few years after the sector recently received backing from the Trump administration, executives in the industry said at the Paris Airshow.

President Donald Trump this month told regulators to speed up certification to accelerate the development of electric vertical take-off and landing aircraft (eVTOLs), aiming to secure a U.S. lead over Asia in the technology.

The executive order gave fresh impetus to an industry that has struggled to win over critics and regulators.

"We take a lot of spears, people are like 'batteries are too heavy'," said Kyle Clark, founder and chief executive of BETA Technologies, at the show. "But the reality is, if you put the airplanes in the right places, the benefits are real."

Flying taxis - seen in predictions of the future for decades - need to shake off the idea that they are just for the rich to become viable at scale.

Their manufacturers say emergency medical services, cargo and defence could help, where they offer a cheaper and quieter alternative to helicopters in areas from passenger and goods transport to rescue missions.

BETA, Joby Aviation and Archer Aviation are in the U.S. Air Force Agility Prime Program, which aims to develop technologies for autonomous cargo and hybrid-electric aircraft.

Joby and Archer have previously signed military contracts worth $131 million and up to $142 million, respectively. 

"We have two aircraft at Edwards Air Force Base, and we are really grateful for all the support and all the learning we've gotten out of that," Joby Aviation's founder and chief executive JoeBen Bevirt said. "We think there's incredible opportunities on the defence side."

BETA's Clark, who flew its conventional takeoff and landing aircraft in Paris, said the company had a clear position in defence: reliable aircraft that showed up to every mission.

"We've gone to somewhere near 10 bases," he said. "We've done 1,000s of takeoffs and landings with the military, we've had an exceptional dispatch rate.

"We didn't just dabble in there. We've got contracts. I think that, like, we've got hundreds of millions of dollars of actual, tangible dollars flowing into us with defence."

The three companies, along with Wisk Aero, said Trump's order was a big deal in boosting the sector's prospects.

U.S. Transportation Secretary Sean P. Duffy and acting FAA Administrator Chris Rocheleau announced a U.S.-led alliance with Britain, Canada, Australia and New Zealand to streamline the certification of eVTOLs globally at the Paris show on Tuesday.

Wisk Aero, owned by Boeing, differs from its rivals in that it is focused on launching fully automated services.

"We have the political support, we have the industry support and then we have the money to make it happen," CEO Sebastien Vigneron said.

Public concern over automated driving systems in cars suggests fully automated flying could have some convincing to do to gain wider acceptance.

BETA's Clark said once the aircraft were in the hands of customers, the business case would be clear.

He said he had flown passengers from the Hamptons to JFK airport in New York using only $7 of electricity.

"You basically flip opex and capex on its head for recurring costs, and it just tells you what type of customers and applications you want for these airplanes," he said.

"It's not a once-a-week flyer, it's a three, four, 10 times-a-day flyer where you exploit the benefits of electric propulsion."