Jet-setters hoping to catch a ride on a Tesla-of-the-sky will have to be patient.

Early investors are pouring tens of millions of dollars into electric, autonomous and vertical-takeoff-and-landing (VTOL) concepts like Zunum Aero, Volocopter and Aurora Flight Sciences. But Jim Harris, aerospace and defense partner at Bain & Company, says consumers will have to wait longer than some of those companies say.

“2022 feels early to me,” Harris said. “We’re likely 15 to 20 years out for something like an electric aircraft used for commercial passenger transportation.”

Boeing, which last week acquired Aurora and is one of Zunum’s main investors, represents one of many legacy aerospace companies aiming to keep up with an industry-wide push to evolve electric technology.

“The legacy in aerospace is hardware with a little software. Now software is becoming a much bigger part of this,” Harris said, before adding that legacy aerospace companies will have to move to a model based on software.

When it comes to electric, autonomous and VTOL, Harris believes each technology will progress independently. He says that all three “are squarely in the development phase” but, as they have separate engineering obstacles, each will “have its own timeline.”

Electric jets face the same battery challenges as automobiles and utilities: efficiency, risk of fires and more.

“If problems with battery technology get solved, they’ll get solved in automobiles and utilities,” Harris said.

Aerospace is far more conservative testing new commercial products than the automotive industry, Harris noted. It will take a few years to develop even small electric aircraft, Harris says, and “the degree of testing that will be required will be very extensive.”

The same precautions go for autonomous, even though commercial aircraft today already have limited self-flying capabilities already. Harris defined autonomy on a gradient scale of mild-, some- and full-autonomy. He predicts airplanes with some autonomy will debut in four or 5 years, saying that “it will be more than 10 years until we see full autonomy.”

UBS analysts Jarrod Castle and Celine Farnaro largely agree with Harris, writing in a note on August 7 that “remotely controlled planes carrying passengers and cargo could appear by 2025.”

“You don’t get a second chance if something happens midflight,” Harris said. “Development for autonomous aircrafts involves copious testing and due diligence, which slows the speed to market, even more so than autonomous automobiles.”

No matter which technology blooms first, Harris says infrastructure will need to change a lot to support autonomous .

“The level of maintenance required is going to be significantly higher than on automobiles and you’ll need the infrastructure to do that,” Harris said.

Harris thinks general aviation facilities, currently in limited use for small, private aviation, are the first place these regional-catering technologies will look to grow. Municipal airports may also be used.

Electric automobiles and alternative fuel trucks alike required serious investment to build out the infrastructure to refuel and service. Harris thinks there is an exponential benefit that comes as networks scale and more service areas emerge.

“How much of existing facilities can be repurposed? An awful lot,” Harris said.

Harris named several established aerospace players who are ready to jump into one or all of these three emerging technologies.

“Everyone’s playing catch up in the legacy aerospace,” Harris said, adding that General Electric and Pratt & Whitney “see this as the future.”

UBS tacks on several more suppliers, saying both Rockwell Collins and Honeywell are also poised to benefit from advancements in autonomous technology.

Another giant, Airbus, claims its quadrotor flying taxi is on track to make its first flight by the end of 2018, with plans to start flying the craft in cities by 2023.

“The vast amount of investment in these areas is taking place outside of the traditional aerospace areas,” Harris said. “This industry is going to see a lot more investment, and a lot of M&A activity, over the coming years.”

Harris warns that, regardless of the resources behind these projects, the first-generation projects probably aren’t going to change aviation. Progress is more likely to come through applying these technology advances to legacy aircraft.

“That will change how Americans, and people globally, get around,” Harris said.