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Sometimes it's hard to separate Robert Downey Jr from his famous Avengers character, Tony Stark.

In the films (and comics) Stark is a rich inventor and technology genius.

In real life, not only has Downey Jr assembled an organisation than plans to use robots to tackle climate change, the group, called the Footprint Coalition, is also helping to pay for flying car technology.

The company called Whisper Aero, is developing tech for air taxis which they say will make vehicles much quieter than other flying cars currently in development, which are basically small planes with between four and twelve noisy propellers.

Explaining his involvement, Robert Downey Jr said that creating noise pollution for the sake of new flying vehicles "is a problem".

"The future needs to be as considerate as it is compelling," he added.

Speaking to media company, Bloomberg, Mark Moore, Whisper Aero's founder and a former Nasa engineer said they have come up with a thruster design that will mean quieter drones and flying cars that will blend into the background sounds of a city.

"Half the people think drones are cool, and half of them are so annoyed," Moore says. "They're annoyed because there is this really aggravating noise source that should not be there."

Moore says about 400 companies are currently making flying cars and thinks that the noise they will make will limit their success. Explaining that although they're quieter than helicopters, the aircraft will still produce a bee-like buzz.

With the help of Downey Jr.'s Footprint Coalition, Whisper has now raised $7.5 million (£5.4m) from investors.

The company plans to start selling its first products, which will probably be quieter drones, by 2023.