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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
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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.

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