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Electric Planes. Why Not?
3

Electric Planes. Why Not?

Electric Planes. Why Not?

(OP)
Article on Engineering.com

The article claims that electric powered aircraft will be much quieter than heat engine powered aircraft. Is this true? I was under the impression that what I hear from an aircraft flying overhead is the propeller or the rotor(s). Modern airliners are not muffled. They use high bypass turbo-fans, one of whose benefits is that they are quieter. Am I correct?

--
JHG

RE: Electric Planes. Why Not?

I'm sure you get some noise from the hot section of the engine, what with the continual fuel explosion.

another day in paradise, or is paradise one day closer ?

RE: Electric Planes. Why Not?

I would think that engine noise is going to be pretty loud without muffling. I once lost my muffler on the I-5, and the clue was sudden onset of VERY loud engine noise. And this is without a propeller, being a car and all that.

A 747 take off from LAX can be heard from at least 4 miles away, and there are airports where it's mandatory to do a full-power takeoff, which is particularly noisy.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Electric Planes. Why Not?

(OP)
IRstuff,

I anticipate that electric aircraft will be propeller driven. An alternate approach is a ducted fan, but either way, you are disturbing air.

--
JHG

RE: Electric Planes. Why Not?

@IR ... applicable to small GA planes with IC engines. I assumed the OP was talking more about transport jets (talking about high by-pass engines)?

I see the turbine hot section being replaced with an electric generator, the cold by-pass air going around the hot section with the compressor blades shrouded by the nacelle (sort of ducted).

I think most noise is coming from the hot section, that the by-pass compressor is shrouded by the nacelle.

I think that an electric generator replacing the hot section would be quieter.

another day in paradise, or is paradise one day closer ?

RE: Electric Planes. Why Not?

For little airplanes it is my understanding that it is mostly propeller noise although in the case of the rotax 91X series most of what one hears appears to be the reduction gear box.

I note the article didn't talk about how current electric aircraft have the same propulsion reliability as piston engine aircraft.

I think electric may allow multi engine configurations (once the reliability issues have been solved) running much smaller propellers and those propellers running with a lower tip speed which will have a large impact on noise. Something like the NASA X57.

RE: Electric Planes. Why Not?

...need a really long extension cord...

Dik

RE: Electric Planes. Why Not?

@IR, ok, but you did lead with a discussion about your car losing it's muffler which is more like an IC in a GA plane (rather than a jet).

and yes, if it's an open rotor (like a GA plane) probably most noise from the propeller, but not so for a jet with a high by-pass compressor shrouded by the nacelle.

another day in paradise, or is paradise one day closer ?

RE: Electric Planes. Why Not?

(OP)
rb1957,

I was thinking more about general aviation craft. One advantage of turbofans is they move more air at a lower velocity, which is what makes them quieter. If you were building an electric powered 747, would you use propellers or ducted fans? How much air would you have to disturb to get 350tonnes of aircraft off the ground? The process does not sound quiet.

--
JHG

RE: Electric Planes. Why Not?

There are a number of other reasons for why you would not use propellers on a 747:

> SAFETY -- turbo fans are fairly well shielded for catastrophic failures of the fans
> size -- to the first order, thrust is thrust, which requires a certain amount of air to be moved
> efficiency -- turbofans are more efficient than propellers or ducted fans at jet speeds

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Electric Planes. Why Not?

I'd "simply" replace the hot turbine with an electric motor. Boeing tried ultra high by-pass (or open rotor) back in the 90s and it didn't work well (possibly due to aft mounted engines, in disturbed airflow behind the wings); and that was a much smaller plane than a '47 (something like a 150 seater).

I think the basic lay-out of the airliner engine is close to optimal, so I think the electrical question is can you make an electric motor that'll output the same power as a current hot section and still be as small as the hot section (to fit within current engine profiles ? ... not to say that we have to use today's engines, but as a measure of proven efficiency ... if the generator is bigger, then the overall size will probably get bigger which will probably negatively impact efficiency.

The next electrical question is where is this power coming from ?

another day in paradise, or is paradise one day closer ?

RE: Electric Planes. Why Not?

We have auxiliary powered sailplanes with electric motors, when they take off at full power, they at not quiet, you still have the propeller noise.
B.E.

You are judged not by what you know, but by what you can do.

RE: Electric Planes. Why Not?

that tail mounted engine looks funny/odd ... most engines go to lengths to avoid ingesting boundary layer, now we've got one designed to to exactly that ?

another day in paradise, or is paradise one day closer ?

RE: Electric Planes. Why Not?

I can't see how presently available battery technology will allow for a practical electric plane. The energy density is not there with available battery chemistries.

Seems like greedy financial sharks are looking to dupe nontechnical VC investors.

RE: Electric Planes. Why Not?

Hello! To my mind there will be only 2 types of engines in aviation in the future: electric and gas turbine.Electric motors will be used for airplanes with weight untill about 1000 kg in another cases - gas turbines as the most effective heat engines.

RE: Electric Planes. Why Not?

Pipistrel has just sold a fleet of 2 seat basic http://www.pipistrel.si/plane/alpha-electro/overvi... trainers that are electric powered to a flight school in central California. The aircraft have a duration of just over an hour before needing re charging. Since the average flying lesson is one hour ,that works out.
Pipistrel and the flight school are now trying to sort out the paperwork with the FAA , this actually may need a re write of a couple of regulations , since the FAA were not big on electric powered aircraft.
B.E.

You are judged not by what you know, but by what you can do.

RE: Electric Planes. Why Not?

Yes, Pipistrel is very good and innovative company... I know about their plane. It's very cool for fly training centres because people fly by laps at most... You can replace battery very fast and have a new flight. It's very comfortable

RE: Electric Planes. Why Not?

I just came back from the APEC show this week (Applied Power Electronics Conference). One of the technical sessions I sat in covered battery topics. John Goodenough of Li-Ion development fame was the first speaker. https://en.wikipedia.org/wiki/John_B._Goodenough

One of the speakers in this technical session covered the use of batteries for vehicle mobility - Cars, Marine, and Aerospace. Of course Cars are the big electric mobility player at the moment. In marine, he could only point to a tourist boat in Norway that was a diesel-electric hybrid as an example. In Aircraft - - - !!!! Nothing!. He briefly covered the possible combinations of battery-propulsion or hybrid engine-generator-battery-electric propulsion, but quickly pointed out that due to weight, and the energy density/weight of fuel over the energy density/weight of batteries the only possible practical combination was the Hybrid engine-generator-battery-electric propulsion with the battery deleted due to weight, and default to just a engine-generator-electric propulsion system! No one in the session made any statement challenging this, and the room was full of industry and academic power and battery experts!

I actually work in Wichita, the aircraft capital of the world, and Cessna did a one-off single propeller electric demonstrator about 9 years ago just to show the concept. The local aviation museum has a steam-engine that was used a 100 years ago to power a plane on a single flight. Frankly, at the moment, a battery power plane makes about as much sense as a steam-engine powered plane. Yes, you can make either technology power a plane, but there is no economic sense to it.

RE: Electric Planes. Why Not?

Let's do the math. Best battery around at the moment is probably Tesla. Their 85 kWh battery weighs 540 kg. A Cessna has a 212 litre tank, so we could replace that with a 30 kWh battery. 30 kWh is of course 108 MJ. 212 litres of fuel is about 7300 MJ. The efficiency of whatever ancient technology they use on the Cessna is perhaps 10% or a little better. So on a /like for like/ basis the electric Cessna has 15% of the 'fuel' available to it. Would it even be allowed to take off?

Obviously you can devote more payload to fuel, and I'd agree that an electric motor is lighter than that big lump of oily metal, but a factor of 6 is an enormous hurdle to overcome.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Electric Planes. Why Not?


With the electric trainer ,
the 17 kWh battery pack was dual-redundant and designed to be either quickly replaceable within minutes or charged in less than one hour,
The cost of the recharge at this time is about $ 4.00
The Avgas for a similar sized trainer would be about $30.0 Depending where you live, it could be as high as $100.
B.E.

You are judged not by what you know, but by what you can do.

RE: Electric Planes. Why Not?

Fine. if you design a special purpose machine with a particular usage profile, yes, batteries will work. What I was arguing with was "To my mind there will be only 2 types of engines in aviation in the future: electric and gas turbine".

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Electric Planes. Why Not?

In my opinion inertia of thinking and untrusting to new technologies are only things that restrain using electric
motors in aviation. I suppose in light aviation it will be like in the world of rc models: in the begining most modelists didn't trust to electric motors and batteries but nowadayas most of them use it. It's much more practical.
Of course this process will take much more time in real aviation. This video about big airplane with rc model components: https://www.youtube.com/watch?v=eNSN6qet1kE.
As for gas turbine it's really effective engines for aviation but large price restrain wide usage of them.The only hope is on modern technologies of manufactoring, for instance metal alloy 3D printing. It'll be able to decrease manufactoring expenses.

RE: Electric Planes. Why Not?

Yes, I'm. And you Greg hint that I've written a nonsense:)? I don't argue that nowadays the weight of fuel and pistion engine less than battery and electric motor for the same durability of flight. But it's more comfortable, cheaper and ecological for short time flights (I mean light aviation). Anyway we should decrease greenhouse gas emission in the nearest several years... I apologize for my English:)

RE: Electric Planes. Why Not?

The electric motor has now been established in the self launching sailplane community for some 5 years now, where the flight profile requires a full power climb for 10 to 15 min's then shut down and stow until the glider needs power for a save when low, or the thermals die at the end of the day and the aircraft needs to get home. This involves saw tooth flying because the propeller's are optimized for climb not cruise, so you climb, stow the motor, then glide, then repeat as needed.
The advantages of electric, are lighter weight for the power unit , better control and no loss of power with altitude. Dis advantages limited power supply. However with a self launching sailplane this is a not a factor since it does not need much duration anyway. The newer lithium ion batteries are so much lighter these days, I recently received a 20 amp hour Li battery to replace a gel cell of the same size, when I got it, the battery was so light, I thought the shipper had forgotten to put the battery in the box, I rapidly opened the box and was relieved to find that in fact it was in there. As the battery science advances, the dis-advantages will become less and less. Remember there are crude solar powered aircraft out there now.
B.E.

You are judged not by what you know, but by what you can do.

RE: Electric Planes. Why Not?

Yes Greg ,
That was done by Eric Raymond an acquaintance of mine, in a home built motor glider to prove the concept.
He also was responsible for some of the design work on Piccard's aircraft before they agreed to dis agree.
He is now making solar powered light aircraft.
B.E.

You are judged not by what you know, but by what you can do.

RE: Electric Planes. Why Not?

I've watched video of Eric Raymond's flight and was really amazed. We didn't have progress without such pioneers. And this is another confirmation that the future of light aviation is electricity.

RE: Electric Planes. Why Not?

Quote (EvanS)

In my opinion, inertia of thinking and untrusting to new technologies are only things that restrain using electric motors in aviation.

Well sure..., plus the pesky limitations of known Physics and present-day Chemistry.

Irrational extrapolation is much worse in all respects than essential skepticism. Such beliefs and opinions accomplish nothing except to distract and impede effective progress.

Such eco-campaigning can negatively impact sensible decision-making, and thus delay deployment of timely, cost-effective, and good-enough interim solutions. Thus such wishful thinking may actually increase the CO2 total Area Under The Curve.

Although a (solar-powered) electric airplane has circled the planet (taking about the same time as running), and a human-powered helicopter has lifted off (in a gym), campaigning for these sorts of things to be widely fielded now is a distraction and a diversion.

To be clear, little electric airplanes for basic flight training are already here. They do circuits for an hour, on $3 worth of power. Nice.

If battery technology ever reaches the point where it can power an airliner across the Pacific, then it'll have benefits far beyond merely powering an airliner across the Pacific.

Research into battery technology should be encouraged. Lobbying for its applications too early is not beneficial.

RE: Electric Planes. Why Not?

Like mentioned above an electric air plane would need to be propeller driven or ducted fan. And even now going to 50% efficient diesel engines with compounding and propellers or ducted prop would save millions of gallons of jet fuel. In the old days there were some prop planes that didn't do too bad as far as speed, I think with the aerodynamics now a proper design prop or ducted prop plane could do as good as a jet speed wise. Jet engines are very very expensive, and very fuel hungry, and is the reason for large capacity aircraft.
Never will there be a lithium battery powered plane, they are now restricted for transport on many airlines.

RE: Electric Planes. Why Not?

(OP)
enginesrus,

There is an interesting engineering principal at work here. During WWII, Republic did some awful things to a poor defenseless Pratt and Whitney Double Wasp and they got a P47J up to an airspeed of 504mph. The airspeed record for piston aircraft is presently held by a souped up Grumman Bearcat at around 528mph. The technology of piston engines and propellers has plateaued. I doubt these aircraft are fuel efficient at these speeds.

Most of us did not notice this because turbo-jets were coming in and making aircraft faster. A common factoid about Canada's Avro Arrow is that it did over Mach 2, faster than most current military jets. In fact, turbo-jet technology plateaued in the late fifties with the Lockheed SR71 Blackbird. The Vietnam war revealed the importance of manoeuvrablity and view out of cockpits. If you look up the Boeing 707, you will find that its turbo-jets enable it to out-run current airliners. Modern turbo-fans are quieter, more fuel efficient and less polluting, but they are not quite as fast. Three out of four ain't bad!

The primary advantage of turbo-fans and turbo-props is that they are mechanically simpler, so they are more reliable and they require less maintenance. This is why commuter STOL aircraft like Bombardier Dash 8s are powered by them.

I understand that modern laptop computers actually are slower than laptops from a few years ago. They have more efficient processors, allowing the batteries to run seven or eight hours between recharges, a good deal for most of us. Moore's Law is dead, at least until quantum computing comes in.

--
JHG

RE: Electric Planes. Why Not?

Turbines at first sight appear simpler than a recip. Things are not always how they appear though. Turbines are far more complex than most think. There is a reason they cost millions of dollars to manufacture and millions to rebuild.
The required materials, machining, fabrication and assembly is far more daunting than any old recip was. Also even rebuild time is many times more hours than the recips were. And yes in most cases the reliability factors of turbines are much higher as well as power density. But we are comparing apples to oranges so to say, as there are recip engines that meet and beat the reliability of turbines in now more modern times. Recips have the potential to exceed the economy of turbines now and into the future. Its funny though, what would prevent a regression of commercial aircraft power plants back to recip is not technical, but attitudes. I think that is true with a lot of different areas of engineering. Then there is the in the box thinking that is very difficult to break out of.

RE: Electric Planes. Why Not?

So, how could recips compete in commercial aviation?

First, to avoid building a parallel infrastructure, they'd have to run on Jet A.
... which suggests Diesels.
... which typically need turbochargers at high power levels.
... so there is still a need for some high temperature metal parts.
... even without the turbos, can they be air cooled, or is the weight and complexity
of liquid cooling justifiable?

Second, they need some speed. How to get that?
Ducted fans?
Unducted fans?
... either of which adds some complexity.
... could they ever be fast enough?

Mike Halloran
Pembroke Pines, FL, USA

RE: Electric Planes. Why Not?

Quote (MikeHalloran )

First, to avoid building a parallel infrastructure, they'd have to run on Jet A.
... which suggests Diesels.
... which typically need turbochargers at high power levels.
... so there is still a need for some high temperature metal parts.
... even without the turbos, can they be air cooled, or is the weight and complexity
of liquid cooling justifiable?

I have a 1920s nautical text somewhere, that talks about how great Diesels will be shortly when they mature the design. Hopefully not a strong parallel with wide spread use of electric powered.

RE: Electric Planes. Why Not?

(OP)
MikeHalloran,

Any piston engine that operates over 20,000ft needs to be supercharged somehow. For commercial aviation, there is the cost of maintaining the engines, then there is the cost of a $60M aircraft sitting in the hanger not earning income.

--
JHG

RE: Electric Planes. Why Not?

Just for fun, I'm trying to explore the assertion by enginesrus that recips could be competitive/ economical/ justifiable today.

Not at high altitudes. Supercharging the airframe has to add considerably to its cost, and part of the cost of idle time. Expensive airframes do not make much sense with economical engines.

Not on the same schedule as fanjets. Airscrews of any sort don't go that fast.
I had hopes for the unducted fans, but the optics of those scimitar blades have to be a tough marketing and PR problem.

Maybe they could carve out part of the market for turboprops, so no pressurization/ low altitudes, short legs, small airports, more leisurely schedules, that sort of thing.
Also subject to weather like turboprops, so a bumpy ride on many days.


Quote (enginesrus)

there are recip engines that meet and beat the reliability of turbines in now more modern times.

I'm very curious about that. I'm not in a related business. I thought state of the art in recips was a Lycoming flat four or six of fairly ancent design, nowadays with turbochargers, with a short time between rebuilds.

What did I miss?


Mike Halloran
Pembroke Pines, FL, USA

RE: Electric Planes. Why Not?

(OP)
MikeHalloran,

I don't select aircraft engines either.

We assume that for an aircraft, we look for high power to weight ratios and efficiency. You have a single engined aircraft. You are flying over the countryside and the engine conks out. What are the chances of you and the airframe surviving?

I suspect that those antique horizontally opposed engines are still on the market because they are reliable as all hell. All the breakability has been engineered out of them. Newer, more sophisticated engines are not to be trusted until they have been in production and use for twenty or more years.

Are you talking about supercharging the airframe, or pressurizing the airframe? DC3s are not pressurized, and I understand this is the reason they are still flying.

--
JHG

RE: Electric Planes. Why Not?

Comokid,
The FAA was supposed to come up with an alternative fuel for Avgas by 2018, it is now 2018 and that fuel is not here .
the closest thing on the horizon is a 91 octane unleaded by swift fuels, but even that is not avalable for widespread distribution yet.
B.E.

You are judged not by what you know, but by what you can do.

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