5 ms·

I wonder if with electric we can fly higher like much higher maybe 80k to 90k since we don’t have to worry about the engine stalling. Could this also make the f

by taf2 7y ago

I wonder if with electric we can fly higher like much higher maybe 80k to 90k since we don’t have to worry about the engine stalling. Could this also make the flight times comparable or faster? For sure less turbulence. As someone who lives on a flight path I’m eager for the change in noise pollution too- though I’m worried the transition will take decades...

CraftThatBlock 7y ago
Higher means lower air density, meaning less lift, meaning higher power usage, which is even more critical with electric
- smileysteve 7y ago
  Lower air density also means both lower drag and more slippage; would definitely need adjustable pitch.
- gnode 7y ago
  Although electric motors are capable of very high power density. If the flight is substantially shorter than the full range, flying at a faster speed, or higher altitude may be practical.
rootusrootus 7y ago
I imagine planes could fly a bit higher, but aeroydynamics are still going to be a big factor. See also coffin corner.
base698 7y ago
Engines don't stall, planes do. Plane stalls are about aerodynamics, and nothing to do with the engine. Current engine designs operate poorly at higher altitudes for a number of reasons: less air density meaning less oxygen to burn and less air to push against. Turbine engines can flame out, which maybe that's what you were referring: https://en.m.wikipedia.org/wiki/Flameout https://en.m.wikipedia.org/wiki/Flameout
- whamlastxmas 7y ago
  Stalling is a term also used with engines, and it's pretty clear he's talking about engines not working at altitude so "stall" is probably the correct term
  - base698 7y ago
    Only with layman and in the media when incorrectly describing an aerodynamic stall and conflating two.
    - roghummal 7y ago
      https://en.wikipedia.org/wiki/Stall_(engine) https://en.wikipedia.org/wiki/Stall_(engine)
      - base698 7y ago
        That's about manual transmission automobiles. I've never heard it referenced in aviation other than non-pilots or people who know airplanes.
- taf2 7y ago
  Yeah I’d imagine most of the reasons sited from this hat wiki article don’t apply to an electric plane. But yeah air density would definitely be an issue but I thought the nasa Helios flight showed 90k to be the upper limit? So figured pushing to bear that altitude could be achieved and possibly beneficial since it would avoid bad weather and reduce drag... I guess was imagining the bulk of the engine power would be consumed at the start of the flight to reach altitude and then from there mostly glide until descending to land... but I’m not an aviation engineer at all just dreaming of quieter sky’s and less pollution
  - sokoloff 7y ago
    In my estimation, the shortest practical path to less pollution (at least less net carbon emission) is to use electricity to synthesize jet-fuel. Take yesterday's carbon dioxide, turn it into tomorrow's jet fuel, making the fuel carbon-neutral.
semi-extrinsic 7y ago
You can't really go above the Armstrong limit (~60k feet) in a passenger airplane without adding huge complexity in handling the event of cabin pressure loss. https://en.wikipedia.org/wiki/Armstrong_limit https://en.wikipedia.org/wiki/Armstrong_limit
- taf2 7y ago
  I see that does making exceeding 60k pretty scary. I was from London to Denmark and we had cabin pressure loss I think we were maybe at 30k and dropped pretty fast to 20 if I recall correctly. The sensation that I remember was slow motion and shock from the flight attendant as the masks did not deploy. Later after landing the captain told us during preflight they set the cabin pressure incorrectly such that as we went too high an emergency system kicked in the prevent the cabin from exploding... I was maybe 12 so the details are fuzzy but definitely the take away is cabin pressure loss is no joke
  - sokoloff 7y ago
    Hard to puzzle the details there without knowing the aircraft type, but in the pressurized piston plane I fly, there is a main outflow valve used to regulate pressure that's under my (indirect) control and a safety outflow valve that's set just over the rigged max pressure differential (such that it partly dumps the cabin if that pressure is exceeded). Given that your flight didn't get the "rubber jungle" of deployed masks, the cabin pressure probably never dropped precipitously low, but rather started to oscillate as the safety valve dumped and closed, but never dumped enough to deploy the masks and the crew declared and descended in order to sort things out. A small number aircraft (non-airliners) are lost each year due to pressurization issues. It's a serious business, even in the high 20s and 30s (of 1000' MSL). Single pilots are required to continuously wear O2 mask at/above FL350 (35000') and one pilot of a two pilot crew must continuously wear O2 over FL410. Between FL350 and FL410, two pilot crews may rely on quick-donning masks. This is believed to be a commonly violated regulation (in that air crews regularly do not wear the required mask when things are operating smoothly).
    - 7y ago
dTal 7y ago
"Engines stalling" is not really the factor that limits altitude. The problem is that the thinner the air, the faster you have to go to stay up. Eventually the required speed enters the transsonic region, and you start needing way more power. There comes a point where your engines just don't have the oomph to push you fast enough to stay up. If you want to go higher, there are basically two ways - more oomph, and better wing loading (i.e. less weight or bigger wings.) Electric aviation has many merits, but being a lightweight source of plentiful oomph is not currently among them.
tim333 7y ago
I'm doubtful about passenger aircraft but the Facebook solar plane was supposed to go to 90k feet https://en.wikipedia.org/wiki/Facebook_Aquila https://en.wikipedia.org/wiki/Facebook_Aquila

by taf2 7y ago

CraftThatBlock 7y ago

Higher means lower air density, meaning less lift, meaning higher power usage, which is even more critical with electric

smileysteve 7y ago
Lower air density also means both lower drag and more slippage; would definitely need adjustable pitch.
gnode 7y ago
Although electric motors are capable of very high power density. If the flight is substantially shorter than the full range, flying at a faster speed, or higher altitude may be practical.

rootusrootus 7y ago

I imagine planes could fly a bit higher, but aeroydynamics are still going to be a big factor. See also coffin corner.

base698 7y ago

Engines don't stall, planes do. Plane stalls are about aerodynamics, and nothing to do with the engine. Current engine designs operate poorly at higher altitudes for a number of reasons: less air density meaning less oxygen to burn and less air to push against. Turbine engines can flame out, which maybe that's what you were referring: https://en.m.wikipedia.org/wiki/Flameout https://en.m.wikipedia.org/wiki/Flameout

whamlastxmas 7y ago
Stalling is a term also used with engines, and it's pretty clear he's talking about engines not working at altitude so "stall" is probably the correct term
- base698 7y ago
  Only with layman and in the media when incorrectly describing an aerodynamic stall and conflating two.
  - roghummal 7y ago
    https://en.wikipedia.org/wiki/Stall_(engine) https://en.wikipedia.org/wiki/Stall_(engine)
    - base698 7y ago
      That's about manual transmission automobiles. I've never heard it referenced in aviation other than non-pilots or people who know airplanes.
taf2 7y ago
Yeah I’d imagine most of the reasons sited from this hat wiki article don’t apply to an electric plane. But yeah air density would definitely be an issue but I thought the nasa Helios flight showed 90k to be the upper limit? So figured pushing to bear that altitude could be achieved and possibly beneficial since it would avoid bad weather and reduce drag... I guess was imagining the bulk of the engine power would be consumed at the start of the flight to reach altitude and then from there mostly glide until descending to land... but I’m not an aviation engineer at all just dreaming of quieter sky’s and less pollution
- sokoloff 7y ago
  In my estimation, the shortest practical path to less pollution (at least less net carbon emission) is to use electricity to synthesize jet-fuel. Take yesterday's carbon dioxide, turn it into tomorrow's jet fuel, making the fuel carbon-neutral.

semi-extrinsic 7y ago

You can't really go above the Armstrong limit (~60k feet) in a passenger airplane without adding huge complexity in handling the event of cabin pressure loss. https://en.wikipedia.org/wiki/Armstrong_limit https://en.wikipedia.org/wiki/Armstrong_limit

taf2 7y ago
I see that does making exceeding 60k pretty scary. I was from London to Denmark and we had cabin pressure loss I think we were maybe at 30k and dropped pretty fast to 20 if I recall correctly. The sensation that I remember was slow motion and shock from the flight attendant as the masks did not deploy. Later after landing the captain told us during preflight they set the cabin pressure incorrectly such that as we went too high an emergency system kicked in the prevent the cabin from exploding... I was maybe 12 so the details are fuzzy but definitely the take away is cabin pressure loss is no joke
- sokoloff 7y ago
  Hard to puzzle the details there without knowing the aircraft type, but in the pressurized piston plane I fly, there is a main outflow valve used to regulate pressure that's under my (indirect) control and a safety outflow valve that's set just over the rigged max pressure differential (such that it partly dumps the cabin if that pressure is exceeded). Given that your flight didn't get the "rubber jungle" of deployed masks, the cabin pressure probably never dropped precipitously low, but rather started to oscillate as the safety valve dumped and closed, but never dumped enough to deploy the masks and the crew declared and descended in order to sort things out. A small number aircraft (non-airliners) are lost each year due to pressurization issues. It's a serious business, even in the high 20s and 30s (of 1000' MSL). Single pilots are required to continuously wear O2 mask at/above FL350 (35000') and one pilot of a two pilot crew must continuously wear O2 over FL410. Between FL350 and FL410, two pilot crews may rely on quick-donning masks. This is believed to be a commonly violated regulation (in that air crews regularly do not wear the required mask when things are operating smoothly).
  - 7y ago

dTal 7y ago

"Engines stalling" is not really the factor that limits altitude. The problem is that the thinner the air, the faster you have to go to stay up. Eventually the required speed enters the transsonic region, and you start needing way more power. There comes a point where your engines just don't have the oomph to push you fast enough to stay up. If you want to go higher, there are basically two ways - more oomph, and better wing loading (i.e. less weight or bigger wings.) Electric aviation has many merits, but being a lightweight source of plentiful oomph is not currently among them.

tim333 7y ago

I'm doubtful about passenger aircraft but the Facebook solar plane was supposed to go to 90k feet https://en.wikipedia.org/wiki/Facebook_Aquila https://en.wikipedia.org/wiki/Facebook_Aquila