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 back up and 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 (that’s one 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. So in general, gasoline will power a vehicle 14 times longer and take it 14 times farther than the same weight of lithium batteries. How do electric cars compensate for that disadvantage? A typical gasoline car carries around 100 pounds of gasoline, but electric cars carry 800 to 1700 pounds of batteries.
The final engineering point is that 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 much weight as the suspension will carry. But the weight of an airplane is limited to what the wings and power plant can lift. If you want to add battery weight to an airplane, you must 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 liquid-cooled batteries weigh 300 pounds. 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 suggests that a full battery could fly 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 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. In a flight school, that’s roughly once-a-year and would probably be combined with the annual inspection. 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 there’s not enough data yet to say whether those two costs are a wash.
Does the Electro meet the 14-to-1 rule of thumb for gasoline vs. electric range? 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 almost 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 to the rule of thumb.
What about using solar panels to extend the range? The Electro’s wing area is 10 square meters. Solar panels covering that area can produce up to 2 kilowatts of power, but it takes 30 kilowatts to keep the Electro flying. On a good day, solar panels could only add 2 minutes to a 30-minute flight, and only in direct sunlight. At any other time, solar cells can’t help much. They could even reduce the flight time because the extra weight always consumes power. [The same is true of adding solar cells to land vehicles. It looks great in futurist cartoons, but even with perfect solar cells, the sunlight striking a vehicle doesn’t contain anywhere near enough energy to move the vehicle.]
How far can the Electro go? The airplane is intended to fly in the immediate vicinity of an airport. Period. Pipistrel is very clear that if you want to fly from one airport to another, you can’t use the Electro. 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 I think they’re forcing the airplane into that niche. Having recently been a student, a 30 minute flight isn’t 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. And since recharging takes one to two hours, the number of lessons per day is limited.
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 cool but you can’t do much with it. A truly 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 having less than 12 minutes before the engine quits. Lots of things can go wrong that close to the ground, and many of them are completely out of your control. Even if you’re on a stable approach and on the glide path, an unexpected gust of wind can blow you to the side at the last second, forcing you to go around and try again. 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 shaving that margin to create the appearance of almost-practical flight times. I might as well say it out loud: “What could possibly go wrong?”
