Taking a private aircraft can be a surprisingly cheap way of travelling.
The flight I took from the small aerodrome of Benavente, near the Portuguese capital Lisbon, to Braga, a city 300km further north, took around one hour and twenty minutes. The cost for a single passenger in the tiny two-person aeroplane: €35 (£25) return.
That was a demo flight arranged by Skyuber. The Portuguese company has developed a mobile application to allow private pilots to find passengers for their flights and share costs with them. It works in much the same way as carpooling websites.
Despite its name, Skyuber has no connection to the popular taxi-hailing Uber app that allows users to book a car and driver. And the founders say they don't want to compete with private jet companies and low cost airlines.
"It's a booking service, matching pilots with empty seats to people wanting to fly," explains co-founder Carlos Oliveira, a 38-year-old entrepreneur and investor, who sold his first start-up to Microsoft. His business partner is Joao Paulo Girbal, a 53-year-old former Microsoft manager, who now owns a pilot school.
In the narrow niche it operates in, Skyuber is another example of how the sharing economy offers a new way for people to monetise excess resources, such as seats in their cars or rooms in their houses. Just like Uber and Airbnb have changed traditional industries, Skyuber's founders would like to give many more people access to flying.
"We want to have the largest aircraft fleet in the world without owning the planes", says Mr Oliveira.
'Uber of the skies'
There are plenty of companies being dubbed the new "Uber of the skies" as apps offering the opportunity to book a plane ride proliferate, though most are not adopting the traditional car-pooling model.
Among them JetSmarter, Ubair and Rise in the US, and Victor, a European company that flies globally, allow you to book a private jet and travel in style, some even market their service at transporting pets. It's less expensive than owning your own plane, but the services are still aimed at the well-heeled.
Other companies such as Surf Air charge fixed monthly fees for Californians hoping to avoid the local ground level traffic.
If you prefer to travel by helicopter, that's available too in places. Blade offers helicopters for hire in New York and even Uber itself - the firm that runs the car app - has trialled helicopter-pooling at the Cannes film festival this year.
But America's Federal Aviation Authority has grounded Flytenow and Airpooler, US services that were operating a similar service to Skyuber's cost-sharing model, citing regulations on carrying paying passengers.
Skyuber is targeting people who may need to do a short flight, but also those who just want the experience of flying in a small plane in the seat next to the pilot.
"It is for enthusiasts and for everyone else who up until now didn't have access to this," says Mr Oliveira.
Peter Foggin, a long time pilot and director of Kairos Aviation, a UK company that sells planes, acknowledges "flight costs are always an issue, so cost sharing is a great idea". However, he notes, "the challenge is to be able to create journeys that suit the pilot and the passenger".
Others have tried before to establish similar businesses, including in the US, but none have really taken off, in part due to regulatory hurdles.
Some other online services and apps allow users to book private planes and a pilot. Those flights, even if done in private jets, are considered commercial flights and may legally transport passengers for profit. Pilots on Skyuber, however, may only share costs with people they fly with.
This means individual pilots, rather than the firm itself, are responsible for safety and insurance. Skyuber asks pilots for a copy of their license and medical certificates, and it also reviews each aircraft's legal documents. But the company states that, being just a booking platform, it's up to pilots to observe all safety and aviation rules, and to decide whether, and how, to operate each flight.
The flight from Benavente to Braga cost approximately half the price of a return train ticket. But passengers still have to find a means of transportation from the city centre out to the tiny airport where this kind of light aircraft takes off and lands. And there is unlikely to be much choice over a return flight.
Passengers also need to be prepared for a trip with fewer amenities than in a train or on a commercial flight: no air conditioning, which was definitely a problem for my trip on a hot afternoon (flying at a higher altitude and opening a tiny window were the two options suggested by the pilot to cool down the cockpit). When flying low, there was a lot of bumping, which caused some nausea. The engine was loud and communication with the pilot had to be done through the radio system, in spite of the fact we were sitting very close. Of course, there's very little space and no toilets. The view is much better, though.
Moreover not all flights would be as cheap as the one I took. Aircrafts with capacity for up to six people can be registered on the platform. But the larger the aircraft, the more fuel it will consume and some of the aircraft operate on more expensive fuel. Some airfields charge planes for taking off and landing, which can add €10 or €20 to the price.
There are no transactions between pilot and riders. Users pay through Skyuber's platform. The company charges a 20% fee (plus VAT) of the payment the pilot receives.
Just as in other parts of the sharing economy, the app enables users to rate pilots. Pilots can also rate their passengers and turn down anyone troublesome. Mr Oliveira says this is for safety reasons, as the pilot always makes the last call regarding whether to take off or not. If a flight is cancelled, nothing is charged.
The company says there are currently around 1,400 pilots signed up, and around 7,000 would-be passengers.
Paulo Almeida, a flight instructor who signed up to use Skyuber, sees it as "an opportunity to share the emotion of flying". But he also says it may bring safety benefits, as it makes it cheaper for amateur pilots to maintain their skills. "When fuel prices and taxes went up, some pilots stopped flying as many hours as advisable", he says.