Its almost a truism that aircraft performance numbers are a smoke-and-mirrors act where best-case scenarios are pushed forward as simple facts. Looking at the numbers we have to remind ourselves that real-world compromises-no, you cant fill the tanks and the seats-are kept off the table. Were beginning to smell the distinct aroma of aviation optimism, spiked with a twist of marketing, in the new arena of electric aircraft. With an opportunity for those potential buyers to put deposits down on kits or power systems within the next 12 months, its time to take a close look at where this new industry stands. 
The Good News
Electric flight in enclosed light airplanes is practical with todays technology. Yuneec International and Electric Aircraft have both flown proof-of-concept aircraft on battery power for dozens of hours. Sonex has a couple of years invested in systems development. None of these companies have hit the two-person, two-hour, 85 MPH mark, but they are close enough that we can believe its within the grasp of incremental improvement.
The bad news is that we have no solid way to benchmark these designs. This is a new arena where we can only make educated guesses.
Risks and Compromises
Anyone who has seen YouTube video of lithium battery fires should wonder about fire risk with electric airplanes. The short answer here is that the odds are on our side. Batteries will overheat and potentially ignite when being overcharged or over-discharged. Overcharging is only likely to happen in the hangar, while youre not in the airplane. Were going to let this dog lie, perhaps pointing to how many laptop batteries are getting charged right now and how few of them are on fire.
A much bigger concern is fire during discharge-e.g., in flight. There are two risks here: too high a power draw from the whole battery pack and a simple short circuit. Companies we spoke with are all are developing smart systems that precisely manage the charge and discharge of individual cells. The occupants safety may rest largely on that controller. This could be a non-issue, but we have no data on reliability, so we don’t know. In evaluating a design, however, protection and isolation of that controller from heat and water should be high on the list.
Shorts at the batteries themselves are probably a non-issue. These tend to be sealed systems with few opportunities for exposed wire. Chafing exposing a 300-volt cable somewhere in the airframe 2000 hours into its life may be more of an issue. Designs that make annual inspection of these runs easy would be a plus. Randall Fishman, President of Electric Aircraft, actually had a cell fail in his prototype because a loose cable bouncing while the aircraft was being trailered cut into a cell (it was a big cable). The result was only a small overheat and minimal damage.
Perhaps this is why Electric Aircrafts Electraflyer X will house its batteries in stainless steel. Were not sure that would make a difference if a cell went nuclear. The box might not melt, but it would be so hot that other aircraft components probably would. “Isolation” is going to be a crucial term when it comes to safety in electric aircraft.
Heat is probably more of an issue with battery life. LiPo batteries heat up when charged or discharged. A temperature of 90-100 degrees is ideal, but hotter than that and their lifespan is reduced. Of the designs weve seen so far, we like the Electraflyer Xs design with controllable airflow through the battery boxes. Were skeptical of designs that pack several cells together tightly. Hotter cells in the middle might not last.