5 ms·

The web page claims that the electric motor can output 2000 kW at 10 kW/kg. For comparison, Europrop TP400, a modern turboprop engine, has 8200 kW 1938 kg (=

by quanto 5y ago

The web page claims that the electric motor can output 2000 kW at 10 kW/kg. For comparison, Europrop TP400, a modern turboprop engine, has 8200 kW 1938 kg (= 4.1 kW/kg) So, although the electric motor is smaller by a factor of 4, its power density is about 2.5 times higher. The web page claims that the motor design is scalable up to 4000 kW, which is great. The fastest turboprop airplane was TU-114, a Soviet airliner in the 50's that flew almost as fast as modern jet airliners. TU-114 uses four engines (Kuznetsov NK-12) that are the most powerful turboprop engines ever in production (11000 kW at 2900 kg). We need more powerful electric motors to emulate this performance..

JumpCrisscross 5y ago
> although the electric motor is smaller by a factor of 4, its power density is about 2.5 times higher Is there any standard way of calculating this with the battery / full tank?
- sokoloff 5y ago
  I think it’s most appropriate to compare vs “tanked for a given/defined range (including reserves)” rather than fully tanked. Airliners are rarely flown with full tanks, because that’s rarely needed. (Tanks are often sized for maximum ferry missions rather than maximum cabin load missions.)
- mojomark 5y ago
  See my comment to answer this question. Volumetric power density impacts are neglected in the OP's 'back of the napkin' estimate comparison. As you suspect, you need to account for the motor size and the specific application to see if this motor is a benefit to you. Complicating matters is the fact that the OEM does a poor job of presenting these metrics up front on the landing page.
scoopertrooper 5y ago
Big claims for sure, but it looks like they're tied in with ARPA-E and a major airline. So, it's not some backwoods mechanics making bold claims about their infinite energy machine that runs on their special brew of moonshine. https://mediacentre.easyjet.com/story/14628/easyjet-partner-wright-electric-selected-for-u-s-department-of-energy-electric-aircraft-programme https://mediacentre.easyjet.com/story/14628/easyjet-partner-...
antattack 5y ago
Do longer/larger prop blades translate to better efficacy? I wonder if we would be better off with array of smaller electric motors rather than pursuing 1:1 replacement of ICE engines.
- bdavis__ 5y ago
  all of those options have been studied for years; how many motors, what they weigh, where they are mounted, blades on the prop, rpm on the prop, any gear reduction. there is a room of aircraft designers that will show you why the current design is the "sweet spot", and the technical reasons that drove them there. my point being this was all analyzed ahead of time, in modeling. no-one just said, "lets go with 4 foot props"..
  - antattack 5y ago
    Electric motors are more compact, need less cooling, work well at all altitudes, have likely more mounting options, can spin fast, offer different power curve, probably easier to service and diagnose. I think there's enough of differentiating factors that could move the "sweet spot" when compared to ICE motors.
- matthewfcarlson 5y ago
  I think lots of little motors are the approach lilium is taking. https://lilium.com/ https://lilium.com/ I’m a firmware engineer not an aviation engineer so I have no idea what the efficiency would be.
- richk449 5y ago
  This NASA project seems to be pursuing that line if thinking https://www.nasa.gov/specials/X57/ https://www.nasa.gov/specials/X57/
- dexen 5y ago
  Depends on flight speeds and prop rotation (tip speed specifically), but the propellers have for a long time had a 90+% efficiency already. Ideally, a long and narrow one-bladed propeller would have best performance, somewhat similar to sailplane's wing. For practical reasons (ease of balancing and limited diameter) we use two or more shorter blades, even if it causes minor efficiency loss. A compounding concern is that of a propeller tip speed - when it approaches speed of sound, the physics of airflow become complex and it's very hard to maintain efficiency - and near impossible to maintain reasonable noise levels. This necessitates keeping blades of high speed propellers rather short. The Tu-114 was exceptionally loud for a plane, both due to propeller speed concerns, and also due to contra-rotating propellers inherently causing increased turbulence. There is a good four-part series on propeller theory and practice: https://www.youtube.com/watch?v=SgoPPg8oVt8&list=PLD2EcpzcvT-vGulRAAkOS6P73CfTo2dME https://www.youtube.com/watch?v=SgoPPg8oVt8&list=PLD2EcpzcvT...
mrfusion 5y ago
Why not make a ducted engine? Just replace the fuel burning part of a jet engine with this motor?
- baybal2 5y ago
  Why do you need a duct?
  - eloff 5y ago
    Jet engines achieve higher speeds and efficiencies.
    - baybal2 5y ago
      No, not efficiencies. Jet engines have lower efficiencies than propellers up to near 0.8 speeds of sound, and terrible ones at low speeds, and low altitudes. Last generation airliners have designed cruise speeds below 0.8 speeds of sound. So, a propeller can still be a viable option at that speed, it will just have to be enormous.
      - eloff 5y ago
        If propellers are more efficient, then why do airlines use jet engines? Noise? Reliability? There's a reason jet engines completely dominate the market for commercial airliners. Would making the propellers electric change that?
        yetihehe 5y ago
        Because jet engines have better power to weight ratio than cylinder engines.
        xyzzyz 5y ago
        The comparison talked about here is not between jet and piston engines, it’s about turbofans and turboprops.
baybal2 5y ago
A question to ask... is it the engine weight only, or engine + its gearbox? It's very easy to make very high power to ratio electric engine, if RPMs, and voltages can be arbitrarily high.
Symmetry 5y ago
Not surprising, the electric motor has some fairly high quality energy flowing in but the gas motor has to act as a heat engine as well, converting localized heat into higher quality energy as it goes. That means a comparison of power densities between electric and internal combustion motors aren't entirely fair. But it also means that electrical motors have a big advantage in that it's a lot easier to add more of them. It looks like aircraft with many propellers along the length of the wing might have real advantages over single propellor aircraft and that's only something that's practical with electric motors.
mojomark 5y ago
> The web page claims that the electric motor can output 2000 kW at 10 kW/kg. > For comparison, Europrop TP400... > 8200 kW 1938 kg (= 4.1 kW/kg) FROM SITE: >2 MW - 2x improvement in []size[] over megawatt scale motors being demonstrated in the aerospace industry >10kW/kg specific power - a 2x improvement compared to available aircraft propulsion motors. To make a fare comparison, you need to also compare the volumetric power densities (i.e. power delivered within a volume envelope vice just under a given mass threshold). This is true for both energy and power densities - and it drives me bananas that these metrics aren't clearly specified for every single energy storage and conversion device. Why does this matter? Because increasing a vehicle engine volume demands more supporting structure (frame), which generally drives up overall vehicle mass (hence cost of construction) and if the vehicle is operating in some fluid (air or water) the resistance to motion increases which drives up your installed energy and power for the same speed. Imagine if you increase your car's mass pwr density by 2X, but doing so grows your engine compartment volume by 2X. Was that a wash? You can't tell until you eveluate the construction cost, energy storage and mpg impacts of having a larger car frame. Same is true with any vehicle. Mass (specific) density is important, but volumetric density is too. Both need to be compared for a more thorough apples:apples comparison.
dgudkov 5y ago
>TU-114 uses four engines (Kuznetsov NK-12) that are the most powerful turboprop engines ever in production (11000 kW at 2900 kg). Interesting detail about the NK-12 (according to Wikipedia): The design that eventually became the NK-12 turboprop was developed after World War II by a team of Soviet scientists and deported German engineers under Ferdinand Brandner, who had worked for Junkers previously; ... Thus, the NK-12 design evolved from late-war German turboprop studies.

by quanto 5y ago

JumpCrisscross 5y ago

> although the electric motor is smaller by a factor of 4, its power density is about 2.5 times higher Is there any standard way of calculating this with the battery / full tank?

sokoloff 5y ago
I think it’s most appropriate to compare vs “tanked for a given/defined range (including reserves)” rather than fully tanked. Airliners are rarely flown with full tanks, because that’s rarely needed. (Tanks are often sized for maximum ferry missions rather than maximum cabin load missions.)
mojomark 5y ago
See my comment to answer this question. Volumetric power density impacts are neglected in the OP's 'back of the napkin' estimate comparison. As you suspect, you need to account for the motor size and the specific application to see if this motor is a benefit to you. Complicating matters is the fact that the OEM does a poor job of presenting these metrics up front on the landing page.

scoopertrooper 5y ago

Big claims for sure, but it looks like they're tied in with ARPA-E and a major airline. So, it's not some backwoods mechanics making bold claims about their infinite energy machine that runs on their special brew of moonshine. https://mediacentre.easyjet.com/story/14628/easyjet-partner-wright-electric-selected-for-u-s-department-of-energy-electric-aircraft-programme https://mediacentre.easyjet.com/story/14628/easyjet-partner-...

antattack 5y ago

Do longer/larger prop blades translate to better efficacy? I wonder if we would be better off with array of smaller electric motors rather than pursuing 1:1 replacement of ICE engines.

bdavis__ 5y ago
all of those options have been studied for years; how many motors, what they weigh, where they are mounted, blades on the prop, rpm on the prop, any gear reduction. there is a room of aircraft designers that will show you why the current design is the "sweet spot", and the technical reasons that drove them there. my point being this was all analyzed ahead of time, in modeling. no-one just said, "lets go with 4 foot props"..
- antattack 5y ago
  Electric motors are more compact, need less cooling, work well at all altitudes, have likely more mounting options, can spin fast, offer different power curve, probably easier to service and diagnose. I think there's enough of differentiating factors that could move the "sweet spot" when compared to ICE motors.
matthewfcarlson 5y ago
I think lots of little motors are the approach lilium is taking. https://lilium.com/ https://lilium.com/ I’m a firmware engineer not an aviation engineer so I have no idea what the efficiency would be.
richk449 5y ago
This NASA project seems to be pursuing that line if thinking https://www.nasa.gov/specials/X57/ https://www.nasa.gov/specials/X57/
dexen 5y ago
Depends on flight speeds and prop rotation (tip speed specifically), but the propellers have for a long time had a 90+% efficiency already. Ideally, a long and narrow one-bladed propeller would have best performance, somewhat similar to sailplane's wing. For practical reasons (ease of balancing and limited diameter) we use two or more shorter blades, even if it causes minor efficiency loss. A compounding concern is that of a propeller tip speed - when it approaches speed of sound, the physics of airflow become complex and it's very hard to maintain efficiency - and near impossible to maintain reasonable noise levels. This necessitates keeping blades of high speed propellers rather short. The Tu-114 was exceptionally loud for a plane, both due to propeller speed concerns, and also due to contra-rotating propellers inherently causing increased turbulence. There is a good four-part series on propeller theory and practice: https://www.youtube.com/watch?v=SgoPPg8oVt8&list=PLD2EcpzcvT-vGulRAAkOS6P73CfTo2dME https://www.youtube.com/watch?v=SgoPPg8oVt8&list=PLD2EcpzcvT...

mrfusion 5y ago

Why not make a ducted engine? Just replace the fuel burning part of a jet engine with this motor?

baybal2 5y ago
Why do you need a duct?
- eloff 5y ago
  Jet engines achieve higher speeds and efficiencies.
  - baybal2 5y ago
    No, not efficiencies. Jet engines have lower efficiencies than propellers up to near 0.8 speeds of sound, and terrible ones at low speeds, and low altitudes. Last generation airliners have designed cruise speeds below 0.8 speeds of sound. So, a propeller can still be a viable option at that speed, it will just have to be enormous.
    - eloff 5y ago
      If propellers are more efficient, then why do airlines use jet engines? Noise? Reliability? There's a reason jet engines completely dominate the market for commercial airliners. Would making the propellers electric change that?
      - yetihehe 5y ago
        Because jet engines have better power to weight ratio than cylinder engines.
        xyzzyz 5y ago
        The comparison talked about here is not between jet and piston engines, it’s about turbofans and turboprops.

baybal2 5y ago

A question to ask... is it the engine weight only, or engine + its gearbox? It's very easy to make very high power to ratio electric engine, if RPMs, and voltages can be arbitrarily high.

Symmetry 5y ago

Not surprising, the electric motor has some fairly high quality energy flowing in but the gas motor has to act as a heat engine as well, converting localized heat into higher quality energy as it goes. That means a comparison of power densities between electric and internal combustion motors aren't entirely fair. But it also means that electrical motors have a big advantage in that it's a lot easier to add more of them. It looks like aircraft with many propellers along the length of the wing might have real advantages over single propellor aircraft and that's only something that's practical with electric motors.

mojomark 5y ago

> The web page claims that the electric motor can output 2000 kW at 10 kW/kg. > For comparison, Europrop TP400... > 8200 kW 1938 kg (= 4.1 kW/kg) FROM SITE: >2 MW - 2x improvement in []size[] over megawatt scale motors being demonstrated in the aerospace industry >10kW/kg specific power - a 2x improvement compared to available aircraft propulsion motors. To make a fare comparison, you need to also compare the volumetric power densities (i.e. power delivered within a volume envelope vice just under a given mass threshold). This is true for both energy and power densities - and it drives me bananas that these metrics aren't clearly specified for every single energy storage and conversion device. Why does this matter? Because increasing a vehicle engine volume demands more supporting structure (frame), which generally drives up overall vehicle mass (hence cost of construction) and if the vehicle is operating in some fluid (air or water) the resistance to motion increases which drives up your installed energy and power for the same speed. Imagine if you increase your car's mass pwr density by 2X, but doing so grows your engine compartment volume by 2X. Was that a wash? You can't tell until you eveluate the construction cost, energy storage and mpg impacts of having a larger car frame. Same is true with any vehicle. Mass (specific) density is important, but volumetric density is too. Both need to be compared for a more thorough apples:apples comparison.

dgudkov 5y ago

>TU-114 uses four engines (Kuznetsov NK-12) that are the most powerful turboprop engines ever in production (11000 kW at 2900 kg). Interesting detail about the NK-12 (according to Wikipedia): The design that eventually became the NK-12 turboprop was developed after World War II by a team of Soviet scientists and deported German engineers under Ferdinand Brandner, who had worked for Junkers previously; ... Thus, the NK-12 design evolved from late-war German turboprop studies.