New electric aircraft propulsion unit

[Groucho]

This looks interesting - an impressive power pack. The article says

"The combination of an electric motor with a combustion engine allows the use of a turbine that is not only much smaller than the current ones, but can be used with maximum efficiency during flight."

Anyone know how this works? How much electrical power is required and where could it be generated?

Siemens develops world-record electric motor for aircraft (http://interestingengineering.com/siemens-develops-world-record-electric-motor-for-aircraft/)

[Goldenrivett]

Hi Groucho,

I guess it works by having a combustion engine that only needs to develop the power equivalent of MCT. The electric motor + battery + combustion engine would only need produce take off thrust for up to say 10 mins.

How much electrical power is required 260 kW.
where could it be generated? by the combustion engine.

See Rolls-Royce Marine Olympus - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Rolls-Royce_Marine_Olympus)
RR Gas turbine Olympus and Tyne engines are commonly used to generate electricity on ships.

[Groucho]

Yes, but it is the reference to the 'turbine' that puzzles me.

[ZeBedie]

I guess you could have just one turbine, on the basis that if it fails, you use the batteries to get the aircraft safely back on the ground.

[EEngr]

This could also replace the gearbox needed for a turboprop. Turbine/generator runs to produce the average power requirements at whatever speed is most efficient. A variable frequency drive takes this power, together with battery power and spins this motor at the prop's design speed. No gears needed.

Designers are also not constrained by the mechanical layouts of shaft/gearbox driven propellers. The turbine/generator(s) could be located in the wing box area with these motors out in the nacelles on the wings. There would be some aerodynamic improvements as well.

For a single turbine/generator failure, the remaining sources could still drive all the propellers (at reduced power) resulting in no yaw (and resulting correction).

[DaveReidUK]

Yes, but it is the reference to the 'turbine' that puzzles me.

It wouldn't surprise me if something had been lost in translation from the original German press release.

[Chu Chu]

Doesn't it just mean a smaller turbine (jet) engine?

I am a little curious about how an aircraft with a takeoff weight of two tons could carry 100 passengers, though. Maybe a blimp with wings?:)

[DaveReidUK]

I am a little curious about how an aircraft with a takeoff weight of two tons could carry 100 passengers, though.Try this version of the article, written by someone who at least appears to know what they are talking about:

https://www.eaa.org/en/eaa/eaa-news-and-aviation-news/2015-news/04-29-2015-siemens-aviation-motor-achieves-new-electric-motor-powerweight-benchmark

It makes it clear that a 2-tonne MTOW aircraft is what the current engine is capable of powering, whereas 100 seats (actually "50-100") is a design goal for the longer term.

No mention of turbines, either. :O

[Goldenrivett]

Hi Dave,
No mention of turbines, either. :O
But the article does say "“This innovation will make it possible to build series hybrid-electric aircraft with four or more seats,”
Wikipedia says "http://en.wikipedia.org/wiki/Hybrid_electric_vehicle" that the electric motor part is powered by batteries (short term) and conventional internal combustion engine (longer term).

So unless the aircraft carries a very long extension cable (at least equal to its published range), then there has to be a conventional gas turbine / electricity generator.

[Ditched]

My take on it is that it is closer to a Diesel-Electric setup than a hybrid. The breakthrough here being the weight reduction of the electric motor itself. Diesel-Electric has it advantages in high-power installations more commonly found on ships or trains, the downside being the weight of the whole installation, you have to add a generator and an electric motor instead of a gearbox. In big land/sea based power installation having the combustion engine run at a constant speed at its optimum design rpm saves a lot of fuel and will outweigh the weight savings of a gearbox. If Siemens managed to reduce the weight of the generator and electric motor to a point where it becomes a viable installation on aircraft the potential benefits are plentyful. A more redundent power installation, if one generator would fail, all propellors could be powered from the remaining generator(s). Plus the aerodynamic advantages of a much a more flexible system layout.

[TURIN]

Many advantages.
Power system (engine) can be placed where it is most effective aerodynamically and also with regard to C of G.

Imagine. The engines aft of the C of G away from passengers and fuel tanks.
However the propulsion can go anywhere the designer seems most effective.

Or vice versa. Engines up front, props at the back.

The powertrain redundancy for the V22 Osprey would certainly be a lot simpler.

[alexd10]

A more redundent power installation, if one generator would fail, all propellors could be powered from the remaining generator(s). Plus the aerodynamic advantages of a much a more flexible system layout

Plus a lot of possible prime energy sources (besides the extension cable mentioned in a post above and the obvious gas turbine generators APU-like ), like fuel cells - with no rotating parts, and many electricity storage solutions -yet in the developing stages, plus...plus.... but all of them after 5 -10 years

[Intruder]

The powertrain redundancy for the V22 Osprey would certainly be a lot simpler.
Not necessarily...

The cross-shaft between the props will still be necessary, since it is imperative that they both provide near-equal thrust. OTOH, you MIGHT be able to get an electric motor on the wingtip that is powerful enough, but smaller/lighter than the turbine. Putting those high-current electric wires to the end of the wings will be a problem itself...

[Vinnie Boombatz]

From 4 years ago, at an earlier stage of development:

Siemens - Electricity in the air (http://www.siemens.com/innovation/apps/pof_microsite/_pof-fall-2011/_html_en/aviation.html)

"A Siemens electric motor with an output of 70 kilowatts powers the propeller, drawing its energy from batteries mounted in the wings. Once the motor glider reaches its cruising altitude, the pilot switches on a small 30-kilowatt combustion engine. The sole purpose of this rotary engine is to provide energy for the electric motor through a generator, which simultaneously recharges the batteries."


Two years ago at the Paris Air Show, including video:

Siemens Hybrid Electric Aircraft Debuts in Paris [VIDEO] | Electric Vehicle News (http://www.electric-vehiclenews.com/2013/06/siemens-hybrid-electric-aircraft-debuts.html)

"The plane's propeller is powered by a 70kW electric motor from Siemens. Electricity is supplied by a small Wankel engine from Austro Engine with a generator that functions solely as a power source. A Siemens converter supplies the electric motor with power from the battery and the generator. Fuel consumption is very low since the combustion engine always runs with a constant low output of 30kW. A battery system from EADS provides the increased power required during takeoff and climb."

"The next development step will be to further optimize the entire drive train. Siemens scientists are currently working on a new electric motor that is expected to be five times lighter than conventional drives. In two years, another aircraft is expected to be equipped with an ultra-light electric drive."

Press release and photos for the 2015 version:

World-record electric motor for aircraft - Siemens Global Website (http://www.siemens.com/press/en/feature/2015/corporate/2015-03-electromotor.php)

World-record electric motor for aircraft (http://phys.org/news/2015-04-world-record-electric-motor-aircraft.html)

A bit more technical detail on this page:

https://www.siemens.com/innovation/en/home/pictures-of-the-future/mobility-and-motors/electromobility-electrically-powered-flight.html

"This is because an intelligent hybrid drive combining an electric motor and a combustion engine can use turbines that not only are significantly smaller than those of today but can also be continuously operated at peak efficiency during flight. Today’s turbines, by contrast, are designed to deliver a maximum level of power that is only required during takeoff and ascent. Aside from that, they only require 60 percent of their maximum output. 'With a kerosene-electric hybrid drive system, the turbine would run continuously at optimum power and provide energy, via a generator, for the electric motor powering the propeller,' Anton explains. 'During takeoff, extra energy would be provided by a battery.' "

[DaveReidUK]

Thanks for that last link, from which it's clear that the reference to a turbine was in the context of the upscaled, airliner-class version of the concept, as opposed to the current GA hybrid drive that has a conventional internal combustion engine to generate the electrical power.

Mystery solved!

[Uplinker]

As an aside, I am surprised that HGV trucks don't utilise the diesel-electric method. One whould have thought such a system would save shedloads of fuel, and make the trucks far easier to drive, by doing away with heavy clutches, gearboxes and two speed axles etc.

[onetrack]

Trucks that utilise hybrid diesel-electric drive have been on the market for around 7 yrs at least. There are no really large size units yet, but they will probably appear sometime in the future.
The hybrid diesel truck concept is still effectively in the commercial-proving stage, but the ones in service are providing satisfactory service at lower daily operating cost and with reduced emissions, which are important in urban environments.

However, the diesel hybrid design is complex and comes with more electrical problems and "gremlins" than a regular diesel truck.
Then there is the higher maintenance levels as the hybrid ages. Batteries need to be replaced every few years, and there are more components overall, leading to higher maintenance costs. The diesel-hybrid resale value is also poor.

Then there is the higher potential for fires and electrical short circuits with hybrid designs, due to the substantial increase in the amount of wiring and electrical circuits and components.

The major setback for diesel hydrid market penetration is increased efficiency and cleaner emissions from the newer diesel engines. Regular diesel trucks are a well-proven concept with modest repair costs as compared to hybrids.
Thus, the diesel-hybrid truck (and bus) designs still have a way to go with efficiency gains and lowered "whole of life" owning and operating costs, before they can be proven to be a much more attractive option to purchasers.

Hino Hybrid Light Duty (http://www.hino.com.au/300/hybrid/)

Hino Trucks / Hino COE - Diesel and Diesel-Electric Hybrid (http://www.hino.com/coe/story_922.php)

Volvo FE Hybrid - Volvo FE Hybrid : Volvo Trucks - United Kingdom & Ireland (http://www.volvotrucks.com/trucks/uk-market/en-gb/trucks/volvo-fe-hybrid/Pages/volvo-fe-hybrid.aspx)

[Adaze]

Won't it be interesting in future...electric props, aerodynamic improvements. Downsizing combustion engines to fit power load. You could bury them inside sound-absorbing intake/exhaust ducting...Heck, you're going to need to tie bells on to let you know when ones sneaking up on you.

[ZeBedie]

As an aside, I am surprised that HGV trucks don't utilise the diesel-electric method. One whould have thought such a system would save shedloads of fuel,

Apologies for the thread drift, but the easiest way to get better fuel economy from trucks is to modify the drivers habits, such that they don't go rushing up to junctions and then slam on their brakes, as if fuel was free (well, it is, to them).

[Linktrained]

"Batteries need to be replaced every few years..."

Our domestic batteries. 18 miles from London, were installed in 1914 and replaced when "The Mains" came available in 1944. They were charged weekly in the Summer, twice weekly in the Winter to provide lighting, only, at 50 volts D.C. The dilute sulphuric was a bit smelly !
Perhaps something better may have been found, now, after a century.

[rh200]

Trucks that utilise hybrid diesel-electric drive have been on the market for around 7 yrs at least. There are no really large size units yet, but they will probably appear sometime in the future.

Like all systems it cost versus benifits. The "dynamic range" of the usage patterns can make it difficult. This is no different to small hybrids. The fact you have two different drive trains available, means if your usage pattern is such that the hybrid won't work, you go for the standard model.

Apologies for the thread drift, but the easiest way to get better fuel economy from trucks is to modify the drivers habits, such that they don't go rushing up to junctions and then slam on their brakes, as if fuel was free (well, it is, to them).

Generally correct and has been for decades.

Its the same issue with all technologies, trains drive system, versus road transport etc. Its the usage pattern varience that dictates if a technology will be useful over a product population.

Whats good about some of these "cute" technologys, is that they can be used in a specific market for a decade or so to get data. As material science etc. develops, then the engineering jump into other markets isn't so great.

[alexd10]

OK, it seems that electrical drive of propellers is on the road ...

But are anybody knowing of an attempt to develop electrical/hybrid "regenerative braking" ?
I mean propellers capable to change pitch to run as RATs along with reversible electric motors switched to generating regime ? I think that on a long descent there are a lot of energy which could be "harvested"

[DaveReidUK]

I mean propellers capable to change pitch to run as RATs along with reversible electric motors switched to generating regime ? I think that on a long descent there are a lot of energy which could be "harvested"Windmilling props, in other words.

I don't think that's a great idea, in any phase of flight.

[Intruder]

Why not? A speedbrake function should be feasible, once the electric prop idea is good enough for deployment. It's little different in concept than flat pitch in a turboprop.

[Julija Iljenk]

I mean propellers capable to change pitch to run as RATs along with reversible electric motors switched to generating regime ? I think that on a long descent there are a lot of energy which could be "harvested"

agree!

you are quite right for the propellers, but current electric propulsion is only limited to small jets.

All-electric aircraft ? are we far from an environmental utopia? (http://www.aerotime.aero/en/people/people-news/editorial/17518-all-electric-aircraft-%E2%80%93-are-we-far-from-an-environmental-utopia)

Check this out

[EMIT]

AlexD10

Technically it is probably possible to "harvest" electrical energy with reverse generation, but what is the use?

Coming in from high altitude, the aircraft basically glides in at idle power. If the propellers would be used as windmills, then the aircraft would have much higher drag, so the path would be steeper.

In order to have that steeper path available, the aircraft would have to stay at higher cruise level for a longer time, which would require cruise thrust in stead of idle.

Furthermore, in order to store all the harvested energy, the aircraft would have to haul along, all the time, a massive pack of batteries, which would also cost extra energy.

Elecric cars are a "succes" only because of all the government subsidies given on them, keep that bull manure out of aviation please!

[Dont Hang Up]

But are anybody knowing of an attempt to develop electrical/hybrid "regenerative braking" ?
I mean propellers capable to change pitch to run as RATs along with reversible electric motors switched to generating regime ? I think that on a long descent there are a lot of energy which could be "harvested"

I suspect the most efficient way to recoup the energy used to get to cruising altitude is a power-off descent in the lowest drag configuration possible (i.e exactly as now).

Regenerative props will, by definition, create much drag and therefore only be effective as speed brakes. However, as such they will recover at least some energy from an otherwise non-optimum managed descent profile.

[TURIN]

Quote:
The powertrain redundancy for the V22 Osprey would certainly be a lot simpler.


Not necessarily...

The cross-shaft between the props will still be necessary, since it is imperative that they both provide near-equal thrust. OTOH, you MIGHT be able to get an electric motor on the wingtip that is powerful enough, but smaller/lighter than the turbine. Putting those high-current electric wires to the end of the wings will be a problem itself...


Wouldn't two motors on each wingtip provide better redundancy than the cross shaft.

Low current wiring to the wing tips. Step down transformers...etc.

Where there's a will..