One of the innovations at this year’s Paris Olympics was supposed to be an electric flying taxi service.

Germany’s Volocopter promised its electric-powered, two-seater aircraft, the VoloCity, would be ferrying passengers around the city.

It never happened. Instead the corporation ran demonstration flights.

While missing that deadline was embarrassing, behind the scenes a more solemn issue was playing out – Volocopter was urgently trying to raise fresh property to keep the firm going.

Talks to borrow €100m (£83m; $106m) from the government failed in April.

Now hopes are pinned on China’s Geely, which is in talks to receive an 85% stake in Volocopter in profitability for $95m of financing, according to a Bloomberg update. The deal could cruel that any upcoming manufacturing would be moved to China.

Volocopter is one of dozens of companies around the globe developing an electric vertical receive-off and landing (EVTOL) aircraft.

Their machines commitment the flexibility of a helicopter, but without the expense, noise and emissions.

However, faced with the massive expense of getting such novel aircraft approved by regulators and then building up manufacturing capabilities, some investors are bailing out.

One of the most high-profile casualties is Lilium.

The German corporation had developed a radical receive on the EVTOL theme.

Lilium’s aircraft uses 30 electric jets that can be tilted in unison to swing between vertical lift and forward flight.

The concept proved attractive, with the corporation claiming to have orders and memoranda of understanding for 780 jets from around the globe.

It was able to demonstrate the technology using a remote controlled scale model. Construction had begun on the first packed-sized jets, and testing had been due to commence in early 2025.

As recently as the Farnborough Airshow in July, Lilium’s COO Sebastian Borel was sounding confident.

“We are definitely burning through money,” he told the BBC. “But this is a excellent sign, because it means we are producing the aircraft. We’re going to have three aircraft in production by the complete of the year, and we have also raised €1.5bn”.

But then the money ran out.

Lilium had been attempting to organize a loan worth €100m from the German advancement lender, KfW. However, that required guarantees from national and state governments, which never materialised.

In early November, the corporation put its main operating businesses into insolvency proceedings, and its shares were removed from the Nasdaq ownership swap.

For the instant, work on the recent aircraft is continuing, as the corporation works with restructuring experts to sell the business or bring in recent property. However, getting the recent e-jet into production is looking more challenging than ever.

The high-profile British player in the eVTOL economy is Vertical Aerospace. The Bristol-based corporation was founded in 2016 by businessman Stephen Fitzpatrick, who also set up OVO vigor.

Its striking VX4 design uses eight large propellers mounted on slim, aircraft style wings to generate lift. Mr Fitzpatrick has made ambitious claims about the aircraft, suggesting it would be “100 times” safer and quieter than a helicopter, for 20% of the expense.

The corporation has made advancement. After completing a programme of remote-controlled testing, it began carrying out piloted tests earlier this year. Initially, these were carried out with the aircraft tethered to the ground. In early November, it carried out its first untethered receive-off and landing.

But there have also been solemn setbacks. In August last year, a remotely-piloted prototype was badly damaged when it crashed during testing at Cotswold Airport, after a propeller blade fell off.

In May one of its key partners, the engineering giant Rolls Royce pulled out of a deal to supply electric motors for the aircraft.

Ambitions remain sky high. Vertical Aerospace says it will deliver 150 aircraft to its customers by the complete of the decade. By then, it also expects to be capable of producing 200 units a year, and to be breaking even in money terms.

Yet financial strains have been intensifying. Mr Fitzpatrick invested an extra $25m into the corporation in March. But a further $25m, due in August if alternative property could not be found, has not been paid. As of September, Vertical had $57.4m on hand – but it expects to burn through nearly double that over the coming year.

Hopes for the upcoming appear to be pinned on doing a deal with the American financier Jason Mudrick, who is already a major creditor through his firm Mudrick pool Management.

He has offered to invest $75m into the business – and has warned the board of Vertical that rejecting his schedule would inevitably navigator to insolvency proceedings. But the shift has been resisted by Mr Fitzpatrick, who would misplace control of the corporation he founded.

Sources close to the talks insist an agreement is now very close. The corporation believes if a deal can be done, it will unlock further donation collection opportunities.

Amid the turbulence, one European assignment is quietly on track, says Bjorn Fehrm who has a background in aeronautical engineering and piloted combat jets for the Swedish Air Force. He now works for aerospace consultancy Leeham.

He says that the EVTOL assignment underway at Airbus is likely to survive.

Called the CityAirbus NextGen, the four-seater aircraft has eight propellers and a range of 80km.

“This is a technology assignment for their engineers, and they’ve got the money, and they’ve got the recognize how,” says Mr Fehrm.

Elsewhere in the globe, other well funded commence-ups stand a excellent transformation of getting their aircraft into production. That would include Joby and Archer in the US.

Once the aircraft are being produced, the next test will be to view if there’s a profitable economy for them.

The first routes are likely to be between airports and city centres. But will they make money?

“The biggest issue area when it comes to the expense of operation is the pilot and the batteries. You require to transformation the batteries a couple of times per year,” points out Mr Fehrm.

Given all the uncertainty and expense, you might wonder why investors put money into recent electric aircraft in the first place.

“No one wanted to miss out on the next Tesla,” laughs Mr Fehrm.

pursue BBC Technology of Business Editor Ben Morris on BlueSky

pursue BBC Business Correspondent Theo Leggett on BlueSky