Originally Posted by
mcoates
Let's say a solar system on an aircraft weighed 40 kg (the nano panels weigh 2.8 kg/m2 + inverter etc) then we would actually be going backwards because it would use more electricity than the system can produce to actually carry around the extra weight.
Please don't think we have not been down this road already, many times
It seems like a better option might be a solar charger kit that can be sold with the plane - but maybe it's cheaper to just install a regular solar power system and plug the charger into that. Hangars do tend to have no shortage of roof space, and the panels don't need to be anything fancy.
Originally Posted by mickjoebill
Is there a rule of thumb where x hours of endurance in a ICE aircraft equals Y hours in a electric aircraft?
I did a few calculations a while back while pondering whether a conversion would be possible. The answer is "no, don't even think about it".
Consider a PA28 with an O-320 engine. The engine alone weighs about 125 - 130kg and produces up to 160hp. From the Warrior handbook, you'd expect to burn 5.5 GPH at 55% power (88hp, 66kW). With 48 gallons of usable fuel, you get just about 8:60 endurance (never mind reserves, ground handling, climb, etc).
I'll assume that an electric motor of the same power (160hp or about 120kW) would weigh about 25kg (a bit over twice what the Pipistrel one does, for a bit over twice the power). This leaves us with 100kg of batteries where the engine used to be, and with current lithium-ion power density (about 250Wh/kg for commercially available cells) this translates in to 25kWh of energy. 25kWh being used at 66kW gives you only about 23 minutes endurance, which is hopeless. However, this is just replacing the engine - not the fuel tanks. If you fill the Warrior's fuel tanks with batteries to achieve the same weight (original 50 gallons weighs 136kg) then that gives an additional 34Wh (31 minutes), for a total endurance of almost an hour.
You could fill the baggage compartment and maybe the rear passenger seats with batteries too. Reducing the available load to 200kg (440lbs) means that you can put another 500lbs or so of batteries in the Warrior (57kWh), which raises the endurance to a whole 1:45. Realistically this would be similar to the Pipistrel's one hour once reserves, taxi, etc are added. Of course, you're now hauling around an exceptionally heavy Warrior (it'll be very close to MTOW all the time due to the batteries) which is no longer a four-seater (back seats are full of batteries). Overhauls cost a fortune (you're replacing out four massive battery packs), probably much more than having the old O-320 done.
The only real advantage over the Pipistrel is the speed - cruising at between 92kts and 105kts depending on altitude. Of course, you won't be doing a whole lot of cruising with only an hour's cruise endurance.
Realistically, it looks like an electric plane has to be designed for the task, and a practical electric plane (at this stage) is probably only going to be a trainer. Pipistrel appears to have hit a pretty good spot, with an endurance just long enough for basic training, a cost low enough for flying schools to find it attractive, and a size/weight comparable to many other light sport aircraft.