In the past few years, the excitement around electric airplanes has made it hard to separate the hype from the facts and even harder to separate the serious aviators from the fast-talkers out to get rich on government grants and venture capital. But rejoice! We finally have a real electric airplane to anchor the discussion in facts, not wishes. This airplane is not just a marketing prototype for airshows. It’s actually for sale. It flies at real airports. And it’s built by a manufacturer who’s been in the business for decades. Writer and pilot Sarah Deener describes flying the Pipistrel Velis Electro in the January 2024 edition of AOPA Pilot magazine. If you can’t find a copy in your local library, check out your local municipal airport (the little one with flight schools, not the big one with commercial airlines). Look in the stack of magazines beside the comfy chair in the lobby. The article won’t take long to read and provides many of the numbers I discuss below.

Before we get into it, I need to review three key engineering points. The first is that batteries aren’t “gas tanks for electricity.” Gasoline tanks are simple, inert containers. Use them over and over and they last for decades. Batteries are expensive chemical reactors that decay each time they’re drained and recharged. They have limited lifetimes and need artificial cooling in high power applications.

The second point is that batteries are heavy. Seriously heavy. It takes a 50-pound lithium battery to match the energy in a single pound of gasoline (which is just enough to fill a McDonald’s medium drink cup). But since electric motors are 3 to 4 times better at converting energy into usable work, it takes 3 or 4 pounds of gasoline to do the same work as a 50-pound battery. That reduces lithium’s weight disadvantage from 50-to-1 down to about 14-to-1. As a rule of thumb, gasoline will power a vehicle roughly 14 times longer and take it 14 times farther than the same weight of lithium batteries. To compensate for that disadvantage, electric cars carry lots of batteries. The batteries in an electric car typically weigh from 800 to 1700 pounds, far more than the 100 pounds of gasoline in a typical car. That weight difference leads directly to the final engineering point.

Adding batteries to an airplane is nothing like adding them to a car. The weight of a car is supported by the road beneath it. You can pile on as many batteries as the suspension will carry (and as much weight as the motor can pull uphill). But the weight of an airplane is strictly limited to what the wings and power plant can lift into the air. If you want to extend an electric airplane’s range by adding batteries, you have to leave something else behind, either passengers or cargo.

With that understood, let’s look at the actual airplane.

The Pipstrel Velis Electro is a light, two-seat, high-wing aircraft. Its two liquid-cooled batteries weigh 150 pounds each (300 pounds total). The pilot and passenger together cannot weigh more than 378 pounds, and that’s all the Electro can carry. There’s no provision for cargo, not even an overnight bag. On the demo flight described in the magazine article, the pilot did four takeoffs/landings and flew some common training maneuvers. The entire flight lasted 29 minutes, during which the battery went from Full down to 27%. (In other words, the flight used up 73% of the battery capacity.) In round numbers, that’s 30 minutes of flying for 3/4 of the battery, which means a full battery could fly for 40 minutes. The Electro’s advertised flight duration is “up to 50 minutes,” which I’m guessing they can achieve with only one person on board, a single less-than-full-power takeoff, and gentle flying—the aviation version of hypermiling.

How much does an hour of flight cost? The Electro flew level using 30 kilowatts of power. (That number will be slightly higher or lower depending on air density and airspeed, but 30 kilowatts is close enough for a reasonable estimate.) In the everyday world, 30 kilowatts is 16 blowdryers running on High, all at the same time. On average, the electricity cost (minus the cost of charging hardware) would be $6/hour in the USA. The batteries also need to be replaced every 500 hours. The article didn’t give a price, but other sources in the trade press say it will cost around $20,000. Divide that by 500 hours and you get another $40/hr for a total of $46/hr.

How does that compare with gasoline? The Electro’s nearly identical cousin–the Pipistrel Velis Club–has a combustion engine that burns 5 gallons an hour of unleaded automotive gasoline. That costs about $20/hr where I live. Regular oil changes and spark plug replacement raise the cost to $24/hr. Both gasoline and electric aircraft engines need occasional teardowns/rebuilds, and I don’t have enough data to say whether those two costs are a wash.

Does the Electro line up with the 14-to-1 rule of thumb for gasoline vs. electric range? The TL;DR is Yes. The gasoline-powered Club can fly 5.5 hours on a full tank (26 gallons, 156 pounds). Scale that up to the weight of the Electro’s battery (300 pounds) and the gasoline flight time is 10.6 hours. That’s nearly 16-to-1 over the Electro’s 40 minutes. If we accept the Electro’s marketed duration of “up to 50 minutes,” the ratio might be 13-to-1. Either one is close.

Can we extend the range with solar cells on the wings, something like the Solar Challenger? The TL;DR is Not Really. Solar Challenger was a specialty aircraft built from high-strength, lightweight materials designed to fly one person at about 30 mph in good sunlight and tame weather conditions. The designer, Paul MacCready himself said, “I do not pretend that a solar aircraft is a practical alternative for air travel, but we wanted a dramatic flight to get people thinking about solar power.” In terms of hard numbers, Solar Challenger produced about 3.8 kilowatts of power in direct sun. The Electro is sturdier, heavier, faster, and has smaller wings. It requires nearly 8 times as much power (30 kilowatts) just to fly level. Modern solar cells on the Electro’s 10 square meter wings could provide (at most) an extra 2 kilowatts in direct sunlight, less than 7% of the necessary power. And some of that 7% would be consumed just to lift the extra weight of the solar panels and related electronics. In low-light or nighttime conditions, the dead weight of the solar panels would probably reduce the overall flight time.

How far can the Electro go? Almost nowhere. The airplane is only intended to fly in the immediate vicinity of an airport. Pipistrel is very clear that if you want to fly from one airport to another, you can’t use the Electro. In the US, airplanes must carry at least 30 minutes of extra fuel to deal with unexpected emergencies, but the Electro only has 40 minutes of “fuel” to begin with. Even when flying close to an airport, the Electro is supposed to land once the battery is down to 30%, just like the pilot did in the magazine article. An airplane that can’t leave the immediate vicinity of its home airport isn’t good for much except demonstration flights. Some people are using the Electro for flight training, but having recently been a flight student, I don’t believe 30 minutes is long enough for an effective lesson. There are too many logistical details in simply getting airborne and landing again without trying to squeeze an effective learning experience into the little time that’s left. [Aside: The battery is wired in, so you can’t swap batteries and take off again. The Electro takes an hour or two to recharge.]

All in all, the Electro’s 40-minute range didn’t surprise me because I’ve been doing the battery math ever since I considered electrifying my first Subaru in the 1990s. And these limitations aren’t unique to the Electro. Any airplane with the same size and payload would need the same amount of power to stay airborne, and any decent 300-pound lithium battery would deliver that power for around 40 minutes. Like the jet packs of the 1960s, the Electro is very cool, but it can’t stay in the air long enough to be useful. A practical electric airplane will have to wait for the next big breakthrough in battery technology–either that or Mr. Fusion.

And that was supposed to be the end of this post. Then I thought again about landing with 30% of the battery. It gave me the wiggins, because landing is stressful enough without knowing that you have less than 12 minutes before the airplane turns into a glider. Lots of things can go wrong that close to the ground, and many of them are completely out of the pilot’s control. Even if you’re on a stable approach to the runway and heading for a perfect landing, a gust of wind can blow you to the side at the last second, forcing you to go around and try again. Going around takes precious minutes and consumes extra energy since you have to climb back to up pattern altitude. Complicated things can go wrong, too. If you’re second-in-line for landing and the airplane in front of you blows a tire on the runway, the runway is closed until the obstacles have been cleared. You can’t land beyond the wreckage, and even if you think you can, you shouldn’t. You stay in the air. You might even have to go to another airport, which is one of the reasons that airplanes are required to carry an extra 30 minutes of fuel (more for commercial and night flights). But an airplane on its last few minutes of battery can’t go anywhere else. The pilot would have to make a forced landing while there are emergency vehicles and personnel on the ground.

That’s the crux of it: The lithium batteries in the Electro can barely fly the plane long enough to provide the mandatory 30-minute safety margin, and people are gaming that margin to create the appearance of almost-practical flight times. I might as well say it out loud: “What could possibly go wrong, Stockton?”