Electric planes

[lolachampcar]

until the economics for hydrocarbon transport get much much worse..............................

 

[daniel]

until the economics for hydrocarbon transport get much much worse..............................

When that happens, synthetic fuels will still be more economical then heavy batteries. There's just no getting around the fact that a plane has to climb up out of the gravity well, and heavy batteries cost a LOT of energy to lift.

 

[ThomasD]

How large of a power plant would you need to charge multiple aircraft at once? Range loss in winter

 

[Etna]

How large of a power plant would you need to charge multiple aircraft at once? Range loss in winter

For eVTOLs it's on a similar scale as a semi truck, at the low end of the Megawatt Charging System specifications, so definitely not an issue.

For larger regional airplanes operating short routes, which would represent the top end of battery powered propulsion feasibility, count about three to five Semi trucks. Again, not a showstopper but it does take some infrastructure planning. If you have several airplanes charging at once at a small airport, this can be addressed with battery buffers the same way this is already done today with electric ferries in small towns (Cavotec among others does this in Norway for example). In terms of power generation, an example I like to use is Lihue in Kauai. It has a 17 MW peak/52MWh storage Tesla solar farm a few miles away from the airport that is delivering electricity today at a competitive price, and you would need only twice that solar farm area, incidentally fitting inside Lihue airport perimeter, to power electric regional transportation for 2500 passengers per day on a 90 nautical miles range. About what Hawaiian Airlines does between Honolulu and Lihue.

So there is generally no power plant required even at remote airports like these. This can be economically addressed already today with solar (or other renewables) and battery buffers. A larger airports near urban centers, the charging infrastructure would be similar to an industrial park. It does require some planning but the business case for the charging infrastructure is there, particularly when leveraging local ground transportation charging requirements (semi trucks and robotaxis operating to-from the airport).

Range loss in winter is an issue for cars, not so much for electric airplanes. They are operating at much higher mean power levels per pound, where excess heat dissipation from batteries, inverters, motors and cables can be a challenge even in the winter (think drastically reduced heat exchange capacity at low atmospheric pressure). So there is generally no range loss in the winter, in some cases (fast airplanes) it's actually the opposite thanks to reduced cooling drag requirements. It may be different for low and slow electric trainer aircraft already flying today, I haven't looked at those.

 

[lolachampcar]

One of my most enjoyable threads to follow.... Thanks to all for the neat posts!

 

[ThomasD]

Would the aircraft be able to carry the same weight load as a AV gas or jet fuel A/C?

 

[Etna]

Would the aircraft be able to carry the same weight load as a AV gas or jet fuel A/C?

Of course, as long as it is a clean sheet design rather than a retrofit or incorrectly sized aircraft.

It's actually super simple. Say you want to carry a payload of 2500 lb, you set aside 30% of the takeoff weight for batteries and 57% for the aircraft empty weight (no small or medium sized aircraft ever gets below that number), that leaves 13% for the payload. So you get 2500 lb / 13% and this gives a required takeoff weight of approximately 19000 lb, right at the edge of Part 23 certification.

For an AV gas or jet fuel A/C you can still get pretty decent range with 15% fuel mass fraction at maximum payload, rather than the 30% required for battery powered aircraft or very long range airliners. So the math works out like 15% fuel, 60% empty weight (not 57% because aircraft is lighter and some weights are fixed), leaving 25% for payload which means takeoff weight equal 2500 lb / 25% = 10000 lb.

Thus for the same job (not the same range but just something barely viable for electric), the AV gas or jet fuel A/C weighs 10000 lb and the electric aircraft weighs 19000 lb. Weight penalty sensitivity of airplanes is far worse than cars.

That's why stories about retrofitting existing airplanes with electric propulsion have to be taken with a semi truck of salt. Best case you end up with zero payload.

A few electric aviation startups also had no idea about this pretty basic aircraft sizing concept, and are now in serious trouble.

 

[daniel]

In other words, you could build an electric airplane with the same load weight as a given jet airplane, but the electric plane would be significantly heavier, and probably physically larger, and being heavier, would consume more energy.

 

[swaltner]

I wouldn't call them turbines, but rather ducted fans, but yes, that's the setup of the Lilium. Ducted Fan refers to the layout of the propeller, while turbine refers to how it converts stored energy into useful work.

Similar to something like a Harrier Jump Jet, the Lilium directs all airflow from the motors straight down to hover. As it increases airspeed, the wings start generating lift, so the airflow from the motors can be directed to the rear to provide more thrust and less direct lift. As it slows down past the normal stall speed for the wing's airfoil, the "exhaust" again needs to be directed down to keep the aircraft from falling. Edit: in the video, you can see the motors start out pointing almost vertical and then at 45 kts, they are angled at maybe about 45 degrees. As they expand the flight envelope in their flight testing into even higher airspeeds, you'll likely see the motors angle back to almost straight horizontal.

A turbine, particularly in the aviation industry, refers to a gas turbine engine that typically burns Jet A fuel. The turbine is the core of the engine that burns fuel and produces thrust and/or rotation. You can have a gas turbine engine built in several different styles: turboshaft (common on all but the smallest helicopters), turbojet, turbofan, turboprop.

As stated, Lilium continues to expand the flight envelope for their aircraft. They posted a video yesterday with it flying at 130 kph (70 kts compared to 45 kts in the previous video). At 1:35 in this latest video, the ducted fans are simply providing horizontal thrust with the wing being the sole source of vertical lift. As it slows down, the fans/motors transition back from providing horizontal thrust to only providing vertical thrust.

They definitely seem to have their flight control systems figured out. This looks very stable in flight.

 

[replicant]

Has this been debunked already?

 

[Etna]

Has this been debunked already?

It's actually a pretty good overview with nicely presented charts, I did not find anything in there that needs debunking.

Conventional airplanes burn less fuel per typical passenger load than a car, so it's no surprise that electric airplanes can do the same. One could argue what those typical loads really are and whether that is a fair comparison.

 

[petit_bateau]

Lilium piece

Bjorn’s Corner: Sustainable Air Transport. Part 30. Lilium Jet VTOL. - Leeham News and Analysis

July 28, 2022, ©. Leeham News: This week, we analyze the Lilium Jet VTOL. It’s a vectored thrust design, but it’s different enough in its characteristics from the vectored thrust VTOLs we looked at in Part 28 (Joby... Read More

leehamnews.com

following on from

and

 

[MontyFloyd]

It is good to see a workable EA, and 100% of thrust equipment is used for VTOL as well as flight.
My only concern is using so many ducted fans, making it small also makes it less efficient.

I would look at larger (thus fewer) larger diameter fans.

And a STOL design, 500ft take off.

 

[cybertrucker]

The main problem with batteries is, landing weight is the same as take-off weight.

Which means EV planes should weigh close to the weight of an ICE plane with empty tanks. I am not even sure today we are anywhere close to that in terms of gravimetric density for even the highest energy density LiOn battery with Co & Ni.

What are you talking about? All the airplanes I have flown are designed to land with a full tank.

Or look up any regional turboprop specifications, maximum landing weight is generally very close to maximum takeoff weight. As in 95% full tank.

That is correct, as an Aerospace Engineer that has certified multiple platforms and systems that are directly applicable to this, we always end up certifying max landing weight very close to max TO weight except with special conditions. It's not as efficient really because the lighter an aircraft gets through it's flight plan the lower AOA needed to maintain lift and therefor the CoD reduced make for more efficient flying, but it can be accounted for just fine.

The best selling Jet Airliner of all time is the 737. Currently, the most common example is the Next Generation 737-800.

Max Takeoff weight 174,000 pounds.

Max Landing weight 146,000 pounds.

That is a SIGNIFICANT difference

 

[Electroman]

Isn’t that one of the reasons they do a fuel dump if an aircraft for unforeseen reason has to land right after take off? (besides the risk of fire if it crashes)

 

[petit_bateau]

Isn’t that one of the reasons they do a fuel dump if an aircraft for unforeseen reason has to land right after take off? (besides the risk of fire if it crashes)

No, the 737 series does not have a fuel dump. It has to burn off excess fuel by flying circles, ditto for the A320 series. The max TO weight exceeding max landing weight is indeed an issue for quite a few commonly used civil aircraft. Electric aircraft can't avoid this issue, which in turn means structure need to be designed at-birth for the max anticipated future stretched version.

(A380 suffered from overdesign in that respect re structure etc, for similar reasons. The 380s that were built were never the fully stretched versions that were the ultimate intent.)

 

[daniel]

I disagree with the statement that "The main problem with batteries is, landing weight is the same as take-off weight." I think the main problem is overall weight.

 

[HVM]

Maybe when we don't need all that ethanol for pet.. gasoline (coz BEVs), we can (instead of drinking it) run our planes with it.

 

[MontyFloyd]

I disagree with the statement that "The main problem with batteries is, landing weight is the same as take-off weight." I think the main problem is overall weight.

Above is corollary to fundamental issue: energy density of a battery is a tiny fraction to the energy a pound of Jet A has.

It is the Law of God (aka, Physics)

 

[evp]

Above is corollary to fundamental issue: energy density of a battery is a tiny fraction to the energy a pound of Jet A has.

It is the Law of God (aka, Physics)

"I believe that the laws of physics are here for our guidance, and should be followed whenever possible." - Garrison Keillor