I have a lot of experience with electric aircraft, although in the model form. It’s true that they are clean, quiet, powerful, reliable and vibration free.
I fly precision aerobatics in contests and electrics have almost completely taken over. I will never go back to fuel-powered aircraft for those reasons.
But
Battery technology places severe limits on flight time, and thus range in a full scale application. A typical model aerobatic sequence takes six or seven minutes to fly and the aircraft returns with 20% of its battery capacity remaining. That’s as far down as you can drain a modern lithium chemistry battery without severely affecting its lifespan. A fuel tank of size similar to the battery packs we use, carrying a lighter load of fuel, would allow flights of 20 minutes or more.
Someone mentioned that a charged battery weighs no more than a discharged one…well, we look at it the other way…a dead battery is just as heavy as a full one! Our competition models are limited by rule to a ready to fly weight of just over 11 pounds (5kg) and our battery weight makes up around 2 1/2 pound of that.
I love my electric models, but it’s going to take a lot of advances to make electric practical for full-scale use.
Well, there is 24M. A long-awaited battery that would cut electric-vehicle costs may finally be close | MIT Technology Review The problem is that the trip from the lab, to industrial scale-up, to aviation certification is a long and twisty path. If, and it’s a big if, they can get this to work then it addresses a lot of the range issues we are discussing.
Last time I checked (haven’t flown for over 10 years) it was a air reg that every aircraft flight plan ensure the craft had a 45-minute reserve. the logic was that if your destination was inaccessible (weather being the typical issue -visibility from fog low clouds, or thunderstorms) this should normally be sufficient for making an alternate airport. While landing out on the open water (or in a field or on a road, for land aircraft) is an option to save lives, it’s never as safe as a proper airbase landing. Worse with a seaplane - how would you recharge, you can’t just pour a couple of jerrycans into it.
I assume for Vancouver, the alternate would be Boundary Bay. if the alternate airport is more than 45 minutes, then you needed that much more fuel.
the reserve is on top of your alternate. So you have to enough fuel for your destination, Plus alternate, plus reserve.
But the electric motor is far lighter than a regular motor, at least in cars. A Tesla Model 3 weighs pretty close to a comparable gasoline car in weight, and nowadays car companies do care about weight. (Just not as much as aircraft) The Tesla Model 3’s 70KWh packs the 4,416 cylinder cells (2170) in to four modules that weigh around 1054 lbs / 478 KGs combined. But then there are other factors - a car needs to be more rugged due to road bouncing and needs a serious steel road hazard protection bottom plate.
Turbo Beaver - 680hp, seats 9-11 people, 186 US Gal fuel (1170lb.) gross weight 6000lb useful load 2973lb (2100lb on floats)
I think an electric plane has a long way to go to compete with a kerosene or gasoline aircraft.
Another interesting point is battery use rate - there are several YouTube videos about driving the autobahn with a Tesla. The Tesla battery pack is regulated by the computer; these guys are running their car full throttle (almost) in the 120mph to 145mph range (200 to 250 km/h) to provide this level of power (i.e. drain the batteries that fast). The computer monitors the battery pack and after a while backs it down (their car drops to 90kmh - 55mph) for the batteries to cool. Also, Tesla battery packs are flooded with antifreeze coolant circulating to help prevent hot spots - excessive heat-cool cycles wreck batteries. Whereas with aircraft, unlike cars on highways with speed limits, the engine at cruise is typically running at well over 50% power. (meaning you need more batteries - more weight - to compensate) It’s a different design paradigm.
This is either because Tesla installed too small a radiator for these kinds of extended high speeds (it makes sense - a bigger radiator lowers the car’s efficiency and thus range per watt-hour, and thus requires Tesla to install a bigger battery in order to get the same range) or because the battery cell types they are using are too thick for the heat to reach the cooling tubes.
I think it’s the former. This part is fixable, the batteries for an aircraft would be designed for the need which would mean water cooling if necessary and thinner cells if necessary.
But yes, the energy density in Watt-hours/kilogram is the real showstopper.
I think it’s because they did not intend for their vehicles to be driven for extended periods of time over twice the legal speed limit in most countries. (Not just electric cars. Recall the scene, I think it was Gumball Rally or Cannonball Run, where the one team is driving across the desert in the west at full speed with the cabin heat blasting, because the engine will overheat with just the radiator )
Water cooling would add additional weight, which is a major concern for aircraft.
But it may not be necessary: ambient temperature at cruising height is -40ºFºC to -60ºF/-33ºC – air cooling may be enough for that. (Though much energy is needed at takeoff and to slow down at landing; those happen at much higher temperatures. Extra cooling may be needed only at those times.)
Sounds good. But because of its low density, transferring heat to air at airliner cruising altitudes is quite challenging. Basically, the size of the necessary heat exchanger is a show-stopper.
A case in point is the problem of cooling the avionics on fighter jets. It turns out the best way to do this is to dump the heat into the jet fuel.
That’s also needed to keep the fuel from freezing.
That may be true in the winter or at much higher altitudes but float planes aren’t going to be going much above 5000 ft in most cases and without supplemental oxygen for the pax almost never above 10000 ft. With an adiabatic lapse rate of 3C/1000 ft you’re only looking at 15-20 degrees off sea level temp at cruise. The trade off then becomes aerodynamic efficiency for liquid cooling vs weight savings using air cooling or some combination of the two.
The actual engineering solution used is going to depend on all of the parameters. However, nominally the obvious solution would be to design the battery pack with air channels between the modules (which would probably be shaped like thin plates for greater peak current). And redundant servo driven door somewhere along the forward side of the aircraft to allow in air, pushed by the aircraft’s own motion, through the battery pack as needed.
Essentially, air cooling and in a very similar way to the air cooled piston engines that small planes use.
Note that this causes additional drag.
Correct, but if you open the intakes and let in just enough air mass to cool the batteries this is probably the lowest total energy solution. Because you minimize extra weight added and the drag induced…ok, high velocity air, I see your point.