I am very eager to find out what the price will be for these motors, this will have a huge impact in General Aviation. A banal 4 cylinder 100 HP petrol engine is ~$20,000 ("aviation price") and the weight is a bit over 60 kg, if my math is right a Magnax motor can be as light as 5 kg (even 10 kg is fabulous) but the cost needs to balance the huge price of batteries: the $20,000 petrol engine with 140 liter fuel tanks gives a flight time of almost 10 hours, batteries for that flight time would be insanely expensive and possibly quite heavy. But most people don't fly more than 5-6 hours, so a reduction to 6 hours would be acceptable for 95% of the people.
Another positive impact to GA is you don't need to adjust for mass and balance that much, batteries have a fixed center of gravity that does not change while discharging, while fuel tanks impact the plane's center of gravity as they go from full to empty. Less trimming, simpler flying.
And not the last, it is eliminating any problems with carburetors, mixture, air density or inverted flight: none of these affect an electrical motor, but it needs to be considered for the likes of Cessna where you need to adjust the (fuel/air) mixture depending on the altitude.
And it improves propeller efficiency, simplifying constant speed propeller operation. It can be easily fully automated.
All good news, but seeing it happen is a different story: it can take 3 to 5 years, more that a decade or never to reach mass availability and adoption in general aviation. It has the potential to make the market explode (in the positive way), but there is so much politics involved there are chances the status quo will be maintained. Let's see.
I’m absolutely ignorant on the topic of aircraft propulsion, but I’d always assumed that the diminishing mass of fuel that one was carrying around with oneself as the flight progresses is a key advantage that electric-propulsion aircraft can never hope to replicate (short of dropping battery packs with parachutes as they become exhausted of charge).
Am I absolutely wrong or is it not actually much of a factor?
You are right in the way you are thinking, but you don't have the full information: in a 600 kg plane the fuel is 100kg. The mass reduction does not make such a big impact, especially as you rarely top the tanks (you can carry more luggage or a heavier pilot & passenger) and you never empty it (30 minute reserve is usually raised to 1 hour reserve), so you have a 10% variation of the total mass of the plane on regular flights: no significant impact.
On the other side, large planes carry a lot more fuel as a percentage of the total mass, it really matters to them.
I hope to hear actual pilots chiming in, but from first principles:
It shouldn't be a large factor. Drag is independent of mass, and while lifting the fuel to cruising altitude takes energy, most of the flight should ideally be cruising.
The rocket equation doesn't apply; that's for an entirely different regime.
While drag is "independent" of mass, the lift required to maintain level flight is affected by weight, and drag is affected by lift. A heavier airplane will absolutely require more power to cruise.
If as you say most people fly for 5-6 hours wouldn’t we need the 10 hour range just to be safe? A 6 hour range when most people fly 5-6 hours is dangerously cutting it close.
They might need to reduce their flying time slightly, but you don't need hours and hours of reserve power unless you're flying long distances over the ocean (which requires specially certified equipment anyway). The FAA only requires 30 minutes of reserve fuel, or 45 minutes if flying at night. That is almost certainly enough to get you to the nearest usable airfield.
Also, bear in mind that it's much easier to accurately and reliably measure a battery's state of charge than it is to measure how many gallons of fuel are in an airplane's wing.
I agree that electric airplanes is a highly desirable goal.
I don't, however, get the point about propeller efficiency, as is it not about matching the pitch to the airspeed? Fixed-pitch propellers have a maximum efficiency at one particular airspeed (and maximum thrust at, in general, a different particular airspeed), regardless of what sort of motor is turning them.
Constant speed propellers are more efficient than fixed pitch; in order to keep the propeller rpm in the optimal point you have to adjust the engine gas control and the propeller pitch, not extremely complicated but not simple enough to be allowed for light sport planes - it is considered too complex for that.
If you play with the propeller pitch, the force on the engine will make it change the rpm; if you change the engine rpm to the optimal of your propeller, you don't always have the best pitch, so you adjust it and this will impact the rpm. With an electrical motor the power delivery is much more robust, so you can adjust the pitch and then set the motor to the desired rpm and that's it.
> you can adjust the pitch and then set the motor to the desired rpm and that's it.
Normal operation of a constant-speed propeller involves setting the desired rpm via the pitch control, and then adjusting the power, via the throttle, according to your purpose (such as level cruise at a specific IAS, or climb at maximum sustainable power), with the propeller govenor maintaining the chosen rpm via pitch changes, and I do not see how electric power changes this relationship. I understand that electric power might simplify making a sort of FADEC for electric airplanes (so that there is only one power control), and that constant-speed propellers could eke out more duration from the batteries, but now you are adding the cost and complexity of a constant-speed prop. I am not sure that it would be justified in a light airplane having a cruise speed not much higher than its best climb speed.
Yes, for some light airplanes a constant speed propeller is not required, but if it is simple enough and you get sizable benefits (even 10% more range), then why not?
There are many planes in Europe that have the cruise speed much higher than the best climb speed. The best climb speed is around 100-120 km/h for light planes, while several plane models have the cruise speed over 200 km/h, up to 250 km/h. I am not aware of any plane with cruise speed below 200 km/h to use constant speed propellers, they have fixed pitch propellers, but the faster ones have in-flight adjustable pitch. I personally flew 7-8 different models of planes, only one with adjustable pitch, but they were all in the LSA class and const-speed is not used there.
There's a French startup that makes some pretty cool turbine range extenders for the general aviation market. Great power to weight ratios, and they come with the maintenance benefits of microturbines, which only have a single moving part. I can't remember exactly, and they don't have it in their specs, but I think they even use gasfoil bearings which means there is no need for oil lubrication.
100 kg of fuel and 50 kg less on the engine weight allows for a lot of batteries. Not sure what is the flight time, but if someone can help with energy density we can calculate the exact number. I wildly guess it is more than 1 hours, but definitely less than 6 hours.
Later edit: I did some calculations, the result is less than 30 minutes.
Another positive impact to GA is you don't need to adjust for mass and balance that much, batteries have a fixed center of gravity that does not change while discharging, while fuel tanks impact the plane's center of gravity as they go from full to empty. Less trimming, simpler flying.
And not the last, it is eliminating any problems with carburetors, mixture, air density or inverted flight: none of these affect an electrical motor, but it needs to be considered for the likes of Cessna where you need to adjust the (fuel/air) mixture depending on the altitude.
And it improves propeller efficiency, simplifying constant speed propeller operation. It can be easily fully automated.
All good news, but seeing it happen is a different story: it can take 3 to 5 years, more that a decade or never to reach mass availability and adoption in general aviation. It has the potential to make the market explode (in the positive way), but there is so much politics involved there are chances the status quo will be maintained. Let's see.