Imagine a typical training flight. The student and an instructor start up the airplane, taxi out, take off and proceed to, let's say, practice ground reference maneuvers before returning to the airport to do a few touch-and-goes and before calling it an hour. Afterward, the two repair to a briefing room to briefly go over the day's flight and cover the next lesson. During that 20- to 30-minute time period, the airplane is being charged. By the time the instructor is ready to take to the sky with his next student, the airplane is ready to go.
With two hours' range, even the long cross-country requirement for the Private would be easy to accomplish, with no need to "refuel" at any of the three required legs along the way (that is, as long as there's minimal time spent getting lost and then found again). At least for the Private, it seems as though the training role would work well for an electric-powered 172. In fact, until battery life improves as storage technology advances, it might be one of the only realistic roles.
Skyhawk vs. Skyhawk
While it might look that way at first glance, upon closer inspection it's clear that Bye's electric Skyhawk isn't a 172 with an electric motor bolted on the nose and some batteries thrown in.
The biggest difference in the illustration of the electric Skyhawk supplied by Bye Energy is that strange prop. The six-blade prop is very light in weight and is designed to be the perfect complement to the electric motor. (Note: Though usage varies widely in general, an electric power plant is not referred to as an engine, a term that is usually reserved for some kind of combustion device. In fact, "power plant" is certainly off target, as well.) More on the motor in a bit.
There might be a few other outwardly noticeable differences between your father's Skyhawk and George Bye's. Bye's wings could very likely at some point be fitted with solar panels, to help recharge the batteries, even in flight. The panels would be located on top of the wings, except, presumably, for aerobatic models. This is another reason the Skyhawk is an excellent candidate; it is a high-wing airplane, so the solar panels are out of harm's way, unlike with, say, a Cherokee. They will also be light and will add little additional drag, Bye says.
There are also going to be, at some point, small generators at the tips of the wings. These mini turbines will capture the energy of the wingtip vortices and turn that energy back into electrical power, to be used by the airplane to enhance endurance.
Another source of power is the prop, which would generate electricity when in descent, for instance, or even while the airplane is sitting on the ramp on a particularly windy day. It's like free gas. Bye isn't saying, at least at this juncture, just how much free "gas" these systems will provide.
Weight vs. Weight
Figuring out the weight differences between the two airplanes is an interesting exercise, because how they derive their power is so fundamentally different.
The electric motor in the Bye Energy Skyhawk will weigh just 45 pounds, the same as just 7½ gallons of avgas. This is compared with the approximate 350-pound weight of a four-cylinder Lycoming power plant. In addition, with the Lyc you need to add the weight of fuel, which is 42 gallons times 6 pounds per gallon, for a fuel weight of 252 pounds, which, added to the engine's weight, gives you a grand power-system total of around 600 pounds. There are small additional savings in the removal of fuel drains, tanks and lines as well.
If it weren't for the fact that the electric motor needs batteries to run, the swap would be a major win in terms of weight. But it does need batteries, and those batteries, while getting lighter and more energy dense all the time, are still heavy.
The current battery of choice is the lithium polymer (sometimes referred to as a lithium-ion polymer) battery, often called LiPo. LiPos have the advantage of being much lighter than the lithium-ion batteries they have largely replaced because instead their electrolyte is not held in an organic solvent but in a solid polymer, allowing the cells to be housed in thinner, more flexible and much lighter housings, while also allowing the batteries to be shaped in a variety of ways.
The downsides for LiPo batteries are significant. Their recharge cycle characteristic, that is, the number of times they can be recharged before degrading, is improving but is still marginally workable for airplanes. Recharge figures are approaching a thousand cycles before the batteries can no longer hold 80 percent of their charge.
Bye's design will not feature removable batteries, as some other emerging electric-powered airplanes have. Instead, Bye says that the design will be optimized for recharging. In fact, if recharging times do get down to 15 minutes to half an hour, the slight time difference between swapping batteries and charging them will make the issue moot. It might even be faster just to charge them.