Quick Electric Machines

[Enthalpy]

Hi Frank, thanks for your interest!

Thermal engines tend to be less efficient than the fuel cells' 60%, but they improved quickly in the past two decades, and the difference is small now. As thermal engines are much lighter than fuel cells, the alternative must be considered, sure. 600kg less would sell 6 seats more, big difference.

Hydrogen is difficult to bring to a combustion chamber.

• Injected liquid in a piston engine prior to compression, it freezes air's water vapour and possibly the carbon dioxide, and as hydrogen vaporizes, the extra volume to be compressed spoils the engine's efficiency.
• Injected gaseous and lukewarm in a piston engine prior to compression, the extra volume to be compressed spoils the engine's efficiency. Still bad.
• Injected gaseous after compression is as bad as before compression.
• Injected liquid after compression is the least bad option at a piston engine. Hot air components won't freeze, and this squanders the least power. However, it demands a damn strong injection pump, much worse than the difficult pump of a common Diesel engine, and the whole pump and circuit must work at 20K. Design is badly difficult AND operations get complicated, as the whole circuit must be cooled before start.
• In a turbomachine, hydrogen should be injected after air compression for the same reasons, but this demands a pump much more powerful than now, and again pre-cooling before starting the engine. I put there
  http://www.chemicalforums.com/index.php?topic=91121.msg325955#msg325955 (log in to see the drawings)
  and especially this message for hydrogen alone
  http://www.chemicalforums.com/index.php?topic=91121.msg333549#msg333549
  some pumping cycles with the necessary power, and they inject the hydrogen already hot in the chamber, which helps stabilize the flame. Meant for ramjets and scramjets but fit turbomachines too. It's more rocket than aeroplane technology, and hasn't been developed for airliners up to now. Understand: long and costly. Simpler cycles are possible with turbomachines.

Hot output from fuel cells: the 40% wasted energy must go somewhere, yes. My doubt is: how heavy is a heat exchanger to make use of this? Each time I tried, heat exchangers were too heavy to outperform alternative solutions. And if you can operate the fuel cell at a pressure higher than the chamber of the thermal engine that uses the waste heat, to inject the fuel cell outlet in the chamber without a heat exchanger, then you must first pump the air and the hydrogen to that pressure, which is nearly as bad and pretty complicated too.

The rest is less of a problem, for instance hydrogen combustion is already known from the more difficult scramjets.

[Frank]

Thanks!  For short hops flights, maybe consider compressed hydrogen instead, still higher volumetric energy density than Li-ion batteries and much lighter.  Then there's Skylon for LH2 powered spaceflight - Skylon (spacecraft) - Wikipedia:  https://en.wikipedia.org/wiki/Skylon_(spacecraft)  Hydrogen Turbojet engines are being developed.

[Enthalpy]

I put thoughts in the liquid hydrogen tank because compressed hydrogen needs a tank too heavy.

Also, liquid hydrogen is less dangerous than compressed one.

[Frank]

Hydrogen powered, fuel cell electric aircraft company: Electric Air Taxi – HY4:  http://hy4.org/sample-page

 

[Enthalpy]

Here's an example of gearless ring motor for the described Dornier 328: 1400kW at 20Hz.

10mm thick Neorec53b magnets (Nd-Fe-B from Tdk) at the D=0.84m rotor move with 52.8m/s and provide 1.16T at +60°C in 2mm gap, of which prestressed graphite composite wound filaments occupy 1mm to hold the magnets.

The L=0.16m rotor and 3-phase stator have 24 pole pairs (though differing numbers would cog less). The conductors pass once per pole through an own slot, so the peak voltage is 468V. The magnets are 80% as wide as the poles, so the waveform provides a fundamental amplitude of 1.21*468V_pk. No fractional pitch here, but the slot skew is +-1/7 the pole width, multiplying by 0.967 the fundamental si H₁=548V_pk=388V_eff and 1400kW take 1203A_eff=1701A_pk per phase.

The inverter needs inconvenient 1100V_DC (if no H₃). Multi-turn coils in parallel are more usual and may enable <500V_DC, but then only a very symmetric machine avoids stray currents. Fractional pitch would bring known advantages and stay <3000V_DC.

The bars superimpose 48 flat enamelled e=0.5mm W=6mm conductors that may be lasercut or etched from much bigger sheets for easier turns. I hope to introduce them sequentially in the slots. Estimated with optimism at 0.25m per bar, they show 1.35mohm per phase and lose 5.9kW in total.

The 480Hz azimuthal induction in the slots is 0.31T_pk near the teeth, so the eddy currents in the conductors lose 1.4kW in total. I didn't evaluate the radial induction component.

The stamped 4mil lamination are of Supermendur (Fe-Co from MKMagnetics) used at 1.87T_pk. This enables three 7mm wide slots per 55mm pole. They lose 40W/kg at 480Hz, or 2.7kW between the slots and 2.2kW outside.

All these losses, 12.2kW=0.87%*1400kW, can be conducted away by the bars within 22K if some grease makes the contact with the laminations. Outside the slots, the conductors are spread to cool by ventilation, and they rotate one position in the slot between two slots, as a simpler form or "Litz" (=braided) wire.

The stator currents superimpose 94mT at the gap, needing additional 45V_pk in quadrature per phase. The laminations don't saturate. The induction through the slots need additional 71V_pk in quadrature per phase. The machine could be shorter, thicker, lighter. Fractional pitch would ease here.

Here are masses in radius order:

 54kg Fe-Co external
 34kg Cu
 68kg Fe-Co between slots
  1kg Graphite
 25kg Magnets
 42kg Steel
------
224kg Sum

The shaft, rings, bearings, casing, fans are not included. More poles would enlighten the motor.

Marc Schaefer, aka Enthalpy

[Enthalpy]

I described here on Apr 08, 2013 an APU that tells how smaller a motor is if it rotates fast
http://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=737931
1270kW machine too, but estimated 16kg for 813Hz instead of 224kg for 20Hz. The two-stage gear needs maintenance and weighs a bit too.

An intermediate solution, with a single-stage gear and a medium diameter motor, may be considered too.

Planetary (epicyclic) gears are compact and powerful at small electric motors. Would they be good for electric aeroplanes?
wikipedia

[Frank]

1 hour ago, Enthalpy said:

Planetary (epicyclic) gears are compact and powerful at small electric motors. Would they be good for electric aeroplanes?

Since planetary gears are used in turboprop engines and/or turbofan engines, I think yes.

Also, I've noticed a sort of upper limit to existing permanent magnet motors of ~400 Hz or so, is there an induction resonance or high power electronic switching limit, or in other words, what limits the top frequency of electric motors?

[Enthalpy]

No hard limit. It's a matter of diameter, of an angular speed convenient for the other items on the shaft, and of optimization rather than clear barriers.

Magnetic materials can operate at kHz, MHz, even GHz (though less useful at many GHz). But over few kHz, the good materials use to be brittle, which I'd dislike at an aeroplane. One can misuse iron laminations at higher frequencies, but at some point the higher frequency becomes a drawback then, not an advantage.

Power electronics can still switch efficiently at 100kHz for instance, but in the MW or GW domain, lower frequencies are better. Then you want to switch must faster than the produced waveform that powers the machine, which puts a strong limit. My waveforms are a new solution to this
https://www.scienceforums.net/topic/110665-quasi-sine-generator/?do=findComment&comment=1041409

Electric machines improve with the peripheral speed, which is limited by feasibility (in a dam), centrifugal force, and possibly the speed of sound and aerodynamic losses. Presently, a sleeve of hardened steel circles the fastest rotors. I proposed to wind graphite+matrix filaments instead. 50-100m/s is common in 1GW turbogenerators, 200m/s is reasonable with permanent magnets, while variable reluctance can be much faster. A small centrifuge can rotate much faster than 400Hz, but a D=1.3m turbogenerator rotor at 100m/s only achieves 25Hz.

[Enthalpy]

A battery-powered aeroplane can tow airgliders. Towing is the major cost of a glider flight, as the aircraft used presently are too big, designed for a higher speed, and consume lots of expensive special gasoline. Batteries power the very short flight easily and use cheap electricity. The market isn't huge, but an electric tugplane is simple to design and build, its use saves much money, so it could be a first commercial success for electric planes.

The typical flight profile is to manoeuvre on the runway, wait for operations on the cable and the glider, take off, climb in <5min to ~800m, release the glider, plunge to the airfield and land. Some Li batteries are designed for quick charge and discharge; I take data from Saft's VL25PFe, safer thanks to Li-phosphate and efficient enough here: 28Ah, 0.94kg, 360kJ/kg, 1700W/kg (yes, 200s). They show the feasibility but are not an optimized choice, nor did I check the availability and price.

300kg batteries provide 108MJ and up to 510kW. Electronics, a geared motor and the propeller convert just 120kW_e (163HP) to 90kW traction. Neighbours would appreciate a silent propeller.

Several features shall avoid messing with the towing cable. The bigger wing at the rear shall counter vertical forces by the glider better. An additional rudder can fit at the bottom.

The design has a fixed landing gear and no landing flaps for safety and cost. 35m/s operation and 25m/s stalling permit the 44kg/m². The D>1.9m propeller pulls 2.6kN at 35m/s frame speed.

350kg frame, 300kg battery and 100kg pilot total 750kg tugplane flight mass. Climbing at 5m/s with a 600kg glider takes 1.9kN, moving the L/D>35 glider 0.2kN more, leaving 0.5kN to move the tugplane, for which L/D>15 suffices - the aspect suggests L/D>25.

30s equivalent full-power of ground operations and take-off, then 160s climbing, use 23MJ or 21% discharge depth at 4*C pace, sparing the batteries meant for 17*C. They should last >15 000 cycles or about 10 years; that cost remains to check. Electricity costs only 2€ per cycle. Regenerative braking by the propeller would be useful. A 100kW cable must be brought to the runway.

85MJ_e left after towing can still fly the tugplane for 130km and 1h at L/D=15, or rather 220km and 1.7h at L/D=25. That's important for safety, and to convey the tugplane, and for secondary uses.

Marc Schaefer, aka Enthalpy

[swansont]

2 hours ago, Enthalpy said:

A battery-powered aeroplane can tow airgliders. Towing is the major cost of a glider flight, as the aircraft used presently are too big, designed for a higher speed, and consume lots of expensive special gasoline. Batteries power the very short flight easily and use cheap electricity. The market isn't huge, but an electric tugplane is simple to design and build, its use saves much money, so it could be a first commercial success for electric planes.

The typical flight profile is to manoeuvre on the runway, wait for operations on the cable and the glider, take off, climb in <5min to ~800m, release the glider, plunge to the airfield and land. Some Li batteries are designed for quick charge and discharge; I take data from Saft's VL25PFe, safer thanks to Li-phosphate and efficient enough here: 28Ah, 0.94kg, 360kJ/kg, 1700W/kg (yes, 200s). They show the feasibility but are not an optimized choice, nor did I check the availability and price.

 

Aviation fuel has an energy density > 40 MJ/kg, and the bonus of not having to fill the tank up all the way (i.e. the mass is variable) so you don't have to provide additional lift for a short flight — you just load less fuel.  Does the efficiency of a battery-powered engine make up for this?  

https://en.wikipedia.org/wiki/Aviation_fuel#Energy_content

Jet-A doesn't look to be that much more expensive than gasoline

https://slate.com/news-and-politics/2008/04/how-much-does-it-cost-to-fill-up-the-tank-on-a-corporate-jet.html

6.75 lbs/gal, so that's a little over 3 kg, or about 120-130 MJ. For electricity, it's around $0.12 per kWh, which is 3.6 MJ. So about $3 - $4 for 120 MJ. Perhaps half the cost, but not accounting for the extra weight you have to lug into the air because you've got all those batteries, which means you need additional fuel. (plus the amortized cost of the batteries over their useful life)

2 hours ago, Enthalpy said:

Neighbours would appreciate a silent propeller.

I'm sure they would , but what connection is there to this? I can appreciate that the electric engine would be silent, but the propeller?

[Enthalpy]

Thanks for your interest!

There are a few biasses in my comparison. Tugplanes used presently were designed >50 years ago while I compare with a more up-to-date design and modern materials. They are too big: most accommodate 4 people while only the pilot is needed there to tow a glider. They are too fast: meant for >200km/h or more while towing is done at 110km/h. So my comparison is unfair in that the reference is unfit for the job. Or said differently, I compare with the existing stuff, not with what a new, specialized combustion engine tugplane could achieve.

Other comparison elements are more fair. Conversion from electricity to shaft power is >95% efficient, but from fuel it's rather 40% (or less with the old engines), giving an other 2.5* advantage to batteries, over the 2* you mentioned. Then, piston engines that power the existing tugplanes use aviation gasoline, not jet fuel. With high octane rating, low water, formulated with lead for old engines, Avgas 100LL costs typically 2.5€/L here in ol' Europe, ouch.

The tugplane's descent contains almost 1/2 the energy put in the ascent, so maybe 1/3 or 1/4 can be gotten back to the battery.

A turbine sized for small aircraft would use cheap jet fuel, but presently small turbines are rare and demand a special license. A Diesel engine could burn jet fuel and be less inefficient than the present Volkswagen and Lycoming that are 0.5 century old designs - several aviation Diesel were under development 25 years ago.

Maintenance is costly with a piston engine and nearly unnecessary for an electric motor. The battery must be kept under surveillance, but electronics does it for free.

Fill less the tank: in my estimate, I wanted a battery 5* bigger than the minimum, because the pilot wants the capability to wait in the air or join an other airfield if something goes wrong. That would be the same with a fuel.

So while I didn't check how good a new design with a combustion engine would be, the usual comparison is that electricity (at the present taxes...) is easily 3* cheaper than gasoline for the same flight and design epoch.

----------

Battery cost: I had feared a replacement every season, due to the very frequent charges and discharges. The estimated 10 years lifespan that result from shallow discharge are a relief to me.

----------

Silent propeller: this is a recommendation, not a consequence from the electric motor. I should have made it clearer. Once the motor is silent, most noise comes from the propeller, which shall bear the emphasis.

The first standard means for that is a more solid propeller, with more blades, wider. This goes in the good direction for regenerative braking. The other means is to bend the blade tips backwards.

[swansont]

So you're comparing a new design with an electric motor vs an old design with combustion, instead of comparing electric vs combustion in a new design. That kinda skews the analysis, don't you think? 

[Enthalpy]

Yes.

On the other hand, I just compare what can be done with the existing stuff. Tugplanes presently in activity were designed 50 years ago and built 40 years ago. No newer design with a combustion engine replaced them, despite fuel to operate these antiques costs a lot.

So to imagine if an electric tugplane has a chance on the market, I compare it with with the present fleet, rather with an alternative inexistent option.

Pessimism would let say that if newer thermal designs didn't get through, the electric one won't neither. But an electric tugplane has some advantages.

If willing to compare a new electric design with a new combustion engine design, we might forecast that power is 3* cheaper with electricity, maintenance is much faster, and construction looks cheaper (far from obvious, because combustion engines are often modified car engines). But this is only extrapolation and gut feeling, as neither one nor the other exists.

[Enthalpy]

More and more aeroplanes go electric, as the Beeb reports from Le Bourget
bbc.com
some claiming far better performance from battery-powered craft than my estimates here despite their wing isn't as wide.

Hydrogen is missing in the report. Because of that, "electric" aeroplanes are said not to fly far, but the limit results from batteries. Hydrogen tanks and fuel cells give aeroplanes much more range than kerosene does.

[Enthalpy]

The German federal government wants to help hydrogen aeroplanes and other uses of hydrogen
n-tv.de
which I feel absolutely reasonable, since hydrogen gives them the range that batteries presently don't.

I hope they include helicopters! Kerosene doesn't suffice for them, batteries even less, hydrogen is the solution to flight duration and range.
scienceforums
Helicopters could adopt hydrogen before fixed-wing aircraft do.

I believe my vacuum-insulated tanks for liquid hydrogen are lighter than other storage methods
This thread on Apr 14, 2013
maybe safer too
scienceforums

[Enthalpy]

A potential target for quick electric motors are vacuum cleaner.

In the ones I know, a series-connected motor provides the 50m/s to the centrifugal compressor. Well proven, but the commutator and brushes wear out and cost something to produce. It adds also noise to the compressor's one.

A brushless or a squirrel-cage motor would improve the reliability and noise, with proper design for the brushless. The drive electronics costs little (processor fans have some) and saves the commutator.

The present series-connected motor may rotate at 20-30m/s as the compressor is wider than the rotor. A squirrel-cage or brushless motor rotates easily at 100-150m/s, which saves motor mass.

Does my graphite fibre winding around the rotor bring more? Not sure. Quietness speaks against supersonic rotors. The engine's shape, short and wider than the compressor, would also be less convenient. But to improve the pressure, yes.

==========

Quick electric motors would improve turbomolecular pumps for deep vacuum.

They must rotate as fast as possible as compared with the molecules' speed, which is about Mach 1, or quite a lot for the residual hydrogen. An impeller of good aluminium can move its tips at >400m/s, expensive steel faster.

Fast brushless or squirrel cage motors achieve ~200m/s at the gap. My graphite fibre winding doubles that, for a much shorter motor easily built.

==========

Hydraulic pumps must achieve 210, 350, rarely 700 or 1500 bar. They are piston pumps typically. For 350 bar, a single staged centrifugal pump needs 350m/s tip speed, reasonable for good steel. 700 bar needs excellent steel, 1500 bar two stages.

The centrifugal pump would be much smaller and silent than the piston pump, potentially more reliable and cheaper too. It needs a quick motor. Here too, a 400m/s rotor outperforms a 200m/s one.

==========

High-pressure water jets clean façades, hard grounds and more. 500 bar or more result usually from a piston pump. A smaller, more silent and potentially cheaper centrifugal pump would achieve 500 bar from 370m/s impeller tip speed, reasonable for good steel, and 1000 bar from 526m/s, still accessible.

Again, it needs a quick motor, and a 400m/s rotor outperforms a 200m/s one.

==========

High-pressure water jets cut metal sheets. 2000+bar result usually from a piston pump. A smaller, more silent and potentially cheaper centrifugal pump would achieve 1000 bar from 526m/s impeller tip speed, accessible to excellent steel. The higher pressure would need few stages.

A 400m/s rotor outperforms a 200m/s one at the quick motor.

==========

Every German hobbyist has a "Minischleifer", a hand-held 130W+ 30,000rpm electric motor that spins grinding, polishing, milling, drilling bits. No idea how common these tools are elsewhere.

I've seen only motors with a commutator and brushes. They are noisy, sensitive to the abundant dust, clumsy, and they get hot.

A fast squirrel cage would improve that, a brushless motor of silent design even more. The casing would enclose completely the stator and have surrounding blown fins as usual for squirrel cages, gaining much reliability at once. The more efficient motor would run cooler.

Without commutator, the motor could run on a safe voltage like three-phase 48V instead of 240V. The present alternative is 12Vdc, where the commutator limits to meagre 20W.

Present rotors move at 50m/s, an awful lot for a commutator, easy for a squirrel cage. Shall this increase? The diameter can't. Maybe some tools accept more speed, nothing obvious for polishing or grinding wheels. Tools with a smaller diameter may be interesting. But a shorter, lighter and cooler motor would be welcome.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Airbus' Press officer said few years ago that an "electric" A320 would have very limited transport capacity and range "because batteries are too heavy". So here are figures about a Boeing 737-800 NG with hydrogen and fuel cells.

The B737-800 can take 26.0m³ = 21.1t kerosene.
wikipedia
42% efficient engines transform that to 0.39TJ at the shafts. 60% efficient fuel cells and 95% electronics and motors make this energy from 5.7t liquid hydrogen in 5.7t tanks as described on
Apr 14, 2013 here

What's the peak power of one CFM56-7B26 kerosene engine?
wikipedia
Its D=1.54m fan pulls up to 118kN while the Trent 800's D=2.8m fan pulls up to 415kN. The Trent 800 can produce 36MW at the shaft, which scales to 9.9MW for the CFM56-7B26. Fuel cells for the Toyota Mirai weigh 0.5kg/kW
wikipedia
so 2*9.9MW need 9.9t fuel cells.

The hydrogen, its tanks and the fuel cells sum 21.3t, as much as the kerosene. Motors replace the 2*2.4t engines, this should save mass, with a gear definitely.

80m³ hydrogen fit uneasily in the present design. I dislike the old proposals of a long tank above the passengers. Six long tanks could hang under the wing together with six motors and fans. Ellipsoids would be D=1.3m L=15.2m plus some insulation and shock-proof fairings.

The long-range B777 Dreamliner would draw the same conclusion: hydrogen + tanks + fuel cells 20t lighter than kerosene, but the volume fits uneasily.

So while the short-range Dornier 328 can just upgrade its nacelles to hydrogen
September 16, 2018 here
medium and long-range airliners need stronger adaptations, or better a new design.

Drawings may come, later hence maybe.
Marc Schaefer, aka Enthalpy

[Enthalpy]

Here's a Boeing 737-800 NG with hydrogen nacelles. Six D=1.6m L=13.1m ellipsoids carry the hydrogen. Their construction is already described.

They cumulate as much cross-section as the cabin but can be sleeker. Six tanks improve that over two, and they take less height. They are away from the cabin's doors.

Motors being cheap, I prefer one per tank. More fan area improves the efficiency. The rear fans interact favourably with the drag. Exchanging electricity suffices for redundancy, while the hydrogen doesn't leave the nacelles.

The nacelles' pylons can carry the fuel cells and also the flap actuators.

The tanks are exposed below the wing. I used to consider it a drawback, but at least a controlled belly landing separates the hydrogen from the travellers.

This design adapts to other plane sizes and ranges.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Here's a Burt Rutan's Voyager-style B737-class airliner with two hulls for hydrogen and one for the passenger and crew.

The cabin and the D=2.2m L=19.2m ellipsoid tanks are to scale. The centre of mass and the wing area are not significant.

These longer tanks cumulate 2/3 of the cabin cross area and are sleek, plus the rear fan interacts favourably with their drag. This design might improve the drag.

A tandem, where the front wing extends beyond the tanks, is possible too.

Marc Schaefer, aka Enthalpy

[Enthalpy]

The French government too wants to fly in 15 years airliners with hydrogen, fuel cells and electric motors
ouest-france - bfmtv (both in French)
Safran, a manufacturer of gas turbines, answers "burn the hydrogen instead". The others big actors answer "ambitious" despite the motors are obvious, the fuel cells exist already in Japan, and the tanks are a low-tech I described already.

Start-up companies fly their demonstrators presently, with designs meant for the market. They would achieve airliners ahead of the big companies, if they were allowed to.

[Enthalpy]

The Atecopol collective spreads doubt about the hydrogen amount needed by airliners
blogs.mediapart.fr (in French)
"10 000 wind turbines just to feed the planes starting from Roissy" (France's biggest airport), so here are my figures.

Some 240 000 airliners a year start from Roissy, needing about 10Mt kerosene that produce 0.4EJ heat.

The better efficiency of fuel cells needs 0.2EJ/year from hydrogen. Engines that burn the hydrogen, as Safran would like, are nonsense.

A 5MW terrestrial wind turbine produces mean 1.3GW or 40TJ/year. 50% yield to hydrogen takes 10 000 wind turbines, OK. Germany has already 30 000.

These wind turbines cost 14G€ and save yearly 80 000 000 barrels kerosene. Crude oil at 40usd costs yearly 3G€, kerosene 7G€.

The production pays the investment in 2 years, after that it's all profit. Very few investments bring money that quickly.

This single operation would reduce France's trade deficit by 1/20^th.

[Enthalpy]

As electric aeroplanes develop, efficiency wants them to use the propellers as turbines to charge some accumulator during the descent. Most electric motors double as efficient generators, but good asymmetric profiles for propeller blades make bad turbine profiles as on the right part of the sketch, because their curvature has the wrong orientation.

A symmetric blade profile would improve a lot the turbine operation, but is less efficient during the more important propeller operation.

I propose (but didn't check if this is already done, as usual) to reverse the rotor's rotation as a turbine, as on the left part of the sketch. Then, the accordingly oriented blades have the curvature in the adequate direction, hence can be asymmetric and efficient for both operations. Most electric machines are good in both directions.

Marc Schaefer, aka Enthalpy

[Enthalpy]

My proposal has imperfections too. As the circumferential speed decreases at a blade near the propeller's axis, the blade is built twisted to maintain everywhere a good angle of attack in the upstream air speed. Alas, this twist has the wrong orientation in my turbine operation.

This increases the drag near the turbine's centre, where the blade moves flat in the wind. Mitigations must exist: reduce the twist, increase the blade-to-air speed ratio, reduce the blades' lift near the centre with a narrow round profile or a wider nose. If gearless, the electric machine favours a wider nose too.

Whether this propeller-turbine is better than a nearly-symmetric profile? No qualitative answer.

Maybe a vane stage can deflect the air before the turbine, by an angle that depends on the distance to the centre, and be retracted in the nacelle during propeller operation. This looks easier if the propeller sits behind the motor.

Edited December 20, 2020 by Enthalpy

[Enthalpy]

Turbofans use presently to equip planes faster than propellers do, and have a rectifying stator stage behind the fan rotor. The stator blades hold also a casing than reduces blade noise.

With electric motors, which depend less on fast air intake, the fan would rather sit behind the motor, and the stator be a permanent vane stage before the rotor.

Orienting the vane blades would give more control over the fan operation, as at fighter jets. Different orientations depending on the distance to the axis, using blades in several parts or deformable blades, would bring efficient operation as a regenerative turbine, as suggested in my previous message. This needs orientable rotor blades, not trivial.

==========

If both the vane stage and the fan stage can rotate around the axis, the plant could rotate mainly the fan for propulsion, and let mainly the vane stage rotate for regenerative braking. Then possibly, the blades can have fixed orientations and shapes. This may need duct sections varied in flight. The vane and fan can sit far apart from an other, for instance upstream and downstream the electric machine(s).

Marc Schaefer, aka Enthalpy

[Enthalpy]

A superconducting motor for aircraft was developed in Russia
Russia Today (in French)
and these search keywords produce 1 million hits:
superconductor aircraft motor
with many companies and agencies involved
Rolls-Royce - Moscow Aviation Institute - and more

Many target electric power transmission from few gas turbines to distributed thrust. This lacks ambition. Distribution saves power but still emits CO₂, despite we have no time to waste. The future is hydrogen tanks and fuel cells, as I described in this thread, and it needs little development. Car fuel cells can fly right now, aircraft should lighten them more radically than cars needed to. By the way, a hydrogen-fed gas turbine consumes inherently twice as much hydrogen for being a thermal engine and is nonsense.

I suggested aluminum wires in aircraft. They make reliably all terrestrial power lines, so aircraft manufacturers could wake up
scienceforums - scienceforums
Reliable connectors may need some R&D, but thereafter I'll trust aluminum better than superconducting lines.

Helicopters and quadcopters should adopt hydrogen tanks and fuel cells even before fixed-wing aircraft do, as they need them for flight duration and range
scienceforums

I described an APU generator with permanent magnets and copper wires, without gears:
scienceforums
and see no need there for superconductors that add failure modes. Electric machines improve directly with azimuthal speed. They also improve with size, so generators bigger than an APU work even better.

I described waveforms for high-frequency inverters in an other thread, that's low-tech development
scienceforums especially scienceforums

In this thread, the motors I propose for propellers and fans have either a (reasonably) big diameter or a gear. A superconducting motor brings both together with efficiency, but I would not accept the added failure modes. A geared quick electric machine with copper windings is extremely lightweight, small, efficient, reliable. Humans know to build gears now, whose wear can be checked. This avoids the random risks added by superconductivity.

My electrostatic machines too are efficient at low azimuthal speed. They aren't on the clear web any more, as Saposjoint and Physforums closed, but are on my CD
saposjoint - physforum - lofi.physforum (dead links)
I didn't check what they bring to aircraft motors. They add failure modes linked with airtightness, as superconductors do, and they add high voltages, but need no cold.

Edited March 30, 2021 by Enthalpy