Jutlander
Topic Author
Posts: 43
Joined: Sat Nov 24, 2018 11:04 am

Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 7:18 pm

Modern aircraft have an incredible gliding range. From cruise altitude they can glide for a few thousand kilometers before they touch the ground.

This got me thinking, couldn't that gliding range be used to save fuel? Let's say for a TATL flight, the aircraft climbs to it's maximum altitude. Then the engines are switched off and the plane starts gliding. It continues gliding until it has reached a low altitude, then the engines are switched back on and it climbs up again.

All the time the engines are switched off and the plane is gliding, there is forward movement but there is no fuel consumption. Only for the short stages in between when the aircraft climbs back up there is fuel consumption. In my opinion, this would save quite a bit of fuel compared to the current way of flying where the aircraft stays on altitude and the engines are constantly on. But how accurate is this? What are the other pros and cons?
 
paullam
Posts: 173
Joined: Sun Feb 15, 2015 12:08 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 7:21 pm

Interesting idea but what makes you think that a plane can glide for “a few thousand kilometres” as you state in your post? That’s far from true...
712 733 734 735 737 738 739 744 752 763 77E 77L 77W 788 789 | A20N 318 319 320 321 332 333 343 346 388 | ASK21 | AT75 AT76 | BCS3 | C152 C172 C182 C210 | CR2 CR7 | DH8C DH8D | E190 | F70 F100 | LJ24 | PA31 | RJ85 RJ1H | SF34 | SU9 | YK2
 
Jutlander
Topic Author
Posts: 43
Joined: Sat Nov 24, 2018 11:04 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 7:33 pm

Air Transat 236 did.
 
jetblueguy22
Posts: 3238
Joined: Thu Nov 29, 2007 12:26 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 7:44 pm

Jutlander wrote:
Air Transat 236 did.

Except it more more like 120km, not thousands
Look at sweatpants guy. This is a 90 million dollar aircraft, not a Tallahassee strip club
 
flipdewaf
Posts: 2893
Joined: Thu Jul 20, 2006 6:28 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 7:57 pm

Jutlander wrote:
Air Transat 236 did.

An aircraft will glide approximately the same distance as it’s lift to drag ratio as the aircraft trades gravitational potential energy to kinetic energy whilst kinetic energy is lost through drag. For any modern transport category aircraft this is reasonably around 20:1 ratio. This means that at cruise altitude (about 11km) will give you about 220km of glide.

Being up high gives certain benefits to comfort, distance specific fuel burn, sector time (affecting pay and capital utilisation).

Climbing and descending continuously will also cause additional cycling in certain components leading to additional maintenance and increased failure risk.

I have been thinking whist I write this about how I’d feel being at 1000ft over the North Atlantic at night with the pilots hoping it starts for the next go.

I like the question though, makes one think about the fundamentals.

Fred


Sent from my iPhone using Tapatalk
Image
 
Flow2706
Posts: 193
Joined: Sat Jan 28, 2017 7:20 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 8:14 pm

The technique described by you is often used when ferrying gliders with an auxiliary engine when there are no thermals but the aircraft needs to go somewhere. However this would be unpractical for airlines due to engine design (start cycles causes a lot of wear on the engine, also there is an element of thermal shock involved). Furthermore this procedure would not result in the safety level desired in commercial aviation as a failed start attempt could result in a ditching with little chance of survival for the occupants.
 
patrickjp93
Posts: 384
Joined: Thu Aug 22, 2019 12:00 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Fri Sep 27, 2019 9:20 pm

Flow2706 wrote:
The technique described by you is often used when ferrying gliders with an auxiliary engine when there are no thermals but the aircraft needs to go somewhere. However this would be unpractical for airlines due to engine design (start cycles causes a lot of wear on the engine, also there is an element of thermal shock involved). Furthermore this procedure would not result in the safety level desired in commercial aviation as a failed start attempt could result in a ditching with little chance of survival for the occupants.


flipdewaf wrote:

In the era of composite fuselages and wings, the cycling problem is largely mitigated on those components, but as for the engines, can we lower them to some minimal thrust to keep all components warm during the glide phase to minimize the thermal shock on them from a startup? Instead of a full startup it would be a steady thrust increase back to climb thrust on components that never completely cooled.

Now, it's also worth mentioning that only 1 (2?) aircraft flying today could do this: the 787 (A350?), because the pressurization systems are not driven by engine bleed air, but by secondary intake turbines.
 
johns624
Posts: 2223
Joined: Mon Jul 07, 2008 11:09 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sat Sep 28, 2019 6:39 pm

How would this work for ATC with planes constantly changing altitude?
 
mmo
Posts: 1791
Joined: Thu Apr 18, 2013 3:04 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sat Sep 28, 2019 8:29 pm

Jutlander wrote:
In my opinion, this would save quite a bit of fuel compared to the current way of flying where the aircraft stays on altitude and the engines are constantly on. But how accurate is this? What are the other pros and cons?


Just out of curiosity, how far do you think an average widebody could glide from a cruising altitude of FL 390? You mentioned "thousands of kilometers before they touch the ground", where did you get that information?

Also, what is the aircraft suppose to do regarding things such as electrics, pneumatics and hydraulics? The aircraft will have hydraulics, but it will be at a reduced rate, no electrics and no pneumatics.

What about the increase in engine maintenance due to the increase in climb power cycles?
Finally, could you provide the fuel savings and how you arrived at them?
If we weren't all crazy we'd all go insane!
 
LH707330
Posts: 2212
Joined: Fri Jun 15, 2012 11:27 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 2:21 am

I like the outside-the-box thinking, but there are two things I can think of that would make this less efficient than just cruising higher:

1. Temperature: engines are thermodynamically more efficient at higher altitudes because the temperature of the air is lower, so they get a better delta-T through the engines.
2. Density: the air is thinner up there, so the amount of air you need to push out of the way is smaller. Descending into thicker air would negate this and cause you to go slower.
 
Canuck600
Posts: 198
Joined: Tue Aug 01, 2017 5:24 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 3:47 am

All those climbs back up to cruise altitude would likely burn way more fuel then you would save by the intermittent gliding.
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 9:08 am

johns624 wrote:
How would this work for ATC with planes constantly changing altitude?


There is work being done to have a solution ( chaotic (direct p2p) routing, flexible "glidepath" height.
https://www.dlr.de/fl/en/desktopdefault ... abid-1149/
not sure which of these programmes are relevant.
( in recent meetup with a friend i got word of mouth transfer on what is planned for the future.)

IMU flights are fully planned in 4D space and will get morphed just in time to meet up with contingencies.
Murphy is an optimist
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 9:11 am

Canuck600 wrote:
All those climbs back up to cruise altitude would likely burn way more fuel then you would save by the intermittent gliding.


you won't do see saw glides with idle thrust periods.
The plan is to have "perfect" ( optimax time/fuel/..) descent to the target destination.

today you have higher sinkrates than what would be energy efficient.
Murphy is an optimist
 
johns624
Posts: 2223
Joined: Mon Jul 07, 2008 11:09 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 11:59 am

WIederling wrote:
Canuck600 wrote:
All those climbs back up to cruise altitude would likely burn way more fuel then you would save by the intermittent gliding.


you won't do see saw glides with idle thrust periods.
The plan is to have "perfect" ( optimax time/fuel/..) descent to the target destination.

today you have higher sinkrates than what would be energy efficient.
That's not what the OP is suggesting. Reread his post.
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 12:23 pm

johns624 wrote:
WIederling wrote:
Canuck600 wrote:
All those climbs back up to cruise altitude would likely burn way more fuel then you would save by the intermittent gliding.


you won't do see saw glides with idle thrust periods.
The plan is to have "perfect" ( optimax time/fuel/..) descent to the target destination.

today you have higher sinkrates than what would be energy efficient.
That's not what the OP is suggesting. Reread his post.


and that was my answer:

you won't do see saw glides with idle thrust periods. or engines "dead" either. :-)
Murphy is an optimist
 
frmrCapCadet
Posts: 3136
Joined: Thu May 29, 2008 8:24 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 2:30 pm

I think the OP has inadvertently proposed a perpetual motion fallacy.
Buffet: the airline business...has eaten up capital...like..no other (business)
 
OldAeroGuy
Posts: 3886
Joined: Sun Dec 05, 2004 6:50 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 5:40 pm

The most economical flight profile is a constantly climbing cruise to stay at optimum airframe M*(L/D).

If the engine is well matched to the airframe, the engines will always be operating in the TSFC "bucket".

The proposed saw tooth descent/climb proposal will always have the airframe operating at suboptimal M*(L/D), except perhaps at the point you decide to reduce engine power.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Canuck600
Posts: 198
Joined: Tue Aug 01, 2017 5:24 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 11:21 pm

"This got me thinking, couldn't that gliding range be used to save fuel? Let's say for a TATL flight, the aircraft climbs to it's maximum altitude. Then the engines are switched off and the plane starts gliding. It continues gliding until it has reached a low altitude, then the engines are switched back on and it climbs up again"

That's what the op posted so there would be repetitive climbs involved.
 
timh4000
Posts: 196
Joined: Fri Dec 07, 2018 1:14 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Sun Sep 29, 2019 11:41 pm

It would burn more fuel by having intermittent climbing. Even if the problems of hydraulics and electrical is solved, all too often course adjustments need to be made. And in the event of a tcas warning your options have been cut in half. Also, the glide phase has the plane not only losing altitude but speed as well. Traveling east ground speeds easily go well into 600mph range, and sometimes even 700mph. Losing all that speed while in the glide phase the trips will take considerably longer.
 
spacecadet
Posts: 3462
Joined: Thu Sep 20, 2001 3:36 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Mon Sep 30, 2019 2:02 am

frmrCapCadet wrote:
I think the OP has inadvertently proposed a perpetual motion fallacy.


That was my immediate thought, and I'm surprised that it took until your post to bring it up. This is kind of like asking if a car in stop and go traffic can save fuel compared to one going the same route at constant speed. No matter how you try to conserve energy, the answer will always be no. It will always take more energy to change states than to remain in a constant state. (Note that "energy" is independent of the type of fuel involved; I'm not talking about a hybrid or electric car getting better gas mileage in stop and go traffic than an all-gas powered car at constant speed. I'm talking about the energy required to get from one place to another, which is also the issue here.) On top of that you have the fact that aircraft are designed to operate most efficiently while cruising at high altitudes and the fact that the thinner air at high altitudes creates less drag, but more fundamentally the standard laws of physics apply. All else being equal (ie. identical aircraft), you can't use less energy constantly going up and down than you would just staying level.

There are equations that can easily prove this, but it's been a long time since I took high school physics so I don't remember exactly what they are. Maybe someone else remembers them.
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
 
rbretas
Posts: 51
Joined: Mon Aug 22, 2016 10:21 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Mon Sep 30, 2019 5:39 am

spacecadet wrote:
No matter how you try to conserve energy, the answer will always be no. It will always take more energy to change states than to remain in a constant state.


In theory, you are correct. But in practice you have to consider that an engine requires energy just to keep it working (besides the energy used to generate power). That is specially important considering that thermal engines are not efficient at low loads (specially gas turbines). So if you reduce the time an engine is operating, you also reduce the fuel consumption.

That is why those hypermiling car records are made by repeating cycles of acceleration then cruising in idle, instead of just keeping a constant speed as we usually learn as the most fuel efficient way. Of course this only works if the engine is OFF, not idling, which would never work on a turbine (thermal stress, risks in restarting, and the drag it produces when it is off). If you could store the engine in the frame and completely turn it off (as some sailplanes do), this method would probably be more efficient than just cruising at high altitudes.
 
Armadillo1
Posts: 518
Joined: Thu Apr 20, 2017 5:14 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Mon Sep 30, 2019 7:11 am

stop about gliding and talk about longer descent (may be with separated route for this near each airport)

the issue i see is a longer flight hours for crew.
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Mon Sep 30, 2019 9:29 pm

Armadillo1 wrote:
stop about gliding and talk about longer descent (may be with separated route for this near each airport)

the issue i see is a longer flight hours for crew.


see my post #12 ( if no deletions happen )
Murphy is an optimist
 
User avatar
DocLightning
Posts: 21553
Joined: Wed Nov 16, 2005 8:51 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Tue Oct 01, 2019 2:02 am

I would think of this in terms of averages. Drag decreases with altitude. So if you start at FL400, drift down to FL200 and then climb back up, you are at an average of FL300 when you could just stay up at FL400 and take advantage of lower drag. Airliners are very efficient in cruise and get more efficient as fuel is burned off. It's climb that burns a lot of fuel.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
Sasha
Posts: 862
Joined: Tue May 18, 1999 3:26 am

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Tue Oct 01, 2019 10:35 am

Is anyone considering the comfort of those on board? Not everybody is a professional pilot or a NASA X-15 test pilot :). Constant changes of altitude with the accompanying pressure effects are inevitably going to affect at least some of the passengers, esp. due to health conditions, post-surgery etc.
An2/24/28,Yak42,Tu154/134,IL18/62/96,B737/757/767,A310/320/319,F100,BAe146,EMB-145,CRJ,A340-600,B747-400,A-330-300,A-340
 
Armadillo1
Posts: 518
Joined: Thu Apr 20, 2017 5:14 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Tue Oct 01, 2019 10:36 am

Sasha wrote:
Is anyone considering the comfort of those on board? Not everybody is a professional pilot or a NASA X-15 test pilot :). Constant changes of altitude with the accompanying pressure effects are inevitably going to affect at least some of the passengers, esp. due to health conditions, post-surgery etc.

can be less effect than today's fast descent with spoilers
 
User avatar
Starlionblue
Posts: 19390
Joined: Fri Feb 27, 2004 9:54 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Wed Oct 02, 2019 4:42 am

patrickjp93 wrote:
Flow2706 wrote:
The technique described by you is often used when ferrying gliders with an auxiliary engine when there are no thermals but the aircraft needs to go somewhere. However this would be unpractical for airlines due to engine design (start cycles causes a lot of wear on the engine, also there is an element of thermal shock involved). Furthermore this procedure would not result in the safety level desired in commercial aviation as a failed start attempt could result in a ditching with little chance of survival for the occupants.


flipdewaf wrote:

In the era of composite fuselages and wings, the cycling problem is largely mitigated on those components, but as for the engines, can we lower them to some minimal thrust to keep all components warm during the glide phase to minimize the thermal shock on them from a startup? Instead of a full startup it would be a steady thrust increase back to climb thrust on components that never completely cooled.

Now, it's also worth mentioning that only 1 (2?) aircraft flying today could do this: the 787 (A350?), because the pressurization systems are not driven by engine bleed air, but by secondary intake turbines.


Side note but the A350 has a bleed system run by the engines, in the "traditional" manner.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
patrickjp93
Posts: 384
Joined: Thu Aug 22, 2019 12:00 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Wed Oct 02, 2019 1:55 pm

Starlionblue wrote:
patrickjp93 wrote:
Flow2706 wrote:
The technique described by you is often used when ferrying gliders with an auxiliary engine when there are no thermals but the aircraft needs to go somewhere. However this would be unpractical for airlines due to engine design (start cycles causes a lot of wear on the engine, also there is an element of thermal shock involved). Furthermore this procedure would not result in the safety level desired in commercial aviation as a failed start attempt could result in a ditching with little chance of survival for the occupants.


flipdewaf wrote:

In the era of composite fuselages and wings, the cycling problem is largely mitigated on those components, but as for the engines, can we lower them to some minimal thrust to keep all components warm during the glide phase to minimize the thermal shock on them from a startup? Instead of a full startup it would be a steady thrust increase back to climb thrust on components that never completely cooled.

Now, it's also worth mentioning that only 1 (2?) aircraft flying today could do this: the 787 (A350?), because the pressurization systems are not driven by engine bleed air, but by secondary intake turbines.


Side note but the A350 has a bleed system run by the engines, in the "traditional" manner.


Thought I remembered that correctly :)

So only 1 aircraft could feasibly even try such a thing right now, though I think what other people are saying wrt burning more fuel on climb and thus negating the gains is probably also correct.
 
User avatar
Starlionblue
Posts: 19390
Joined: Fri Feb 27, 2004 9:54 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Wed Oct 02, 2019 2:47 pm

patrickjp93 wrote:
Starlionblue wrote:
patrickjp93 wrote:


In the era of composite fuselages and wings, the cycling problem is largely mitigated on those components, but as for the engines, can we lower them to some minimal thrust to keep all components warm during the glide phase to minimize the thermal shock on them from a startup? Instead of a full startup it would be a steady thrust increase back to climb thrust on components that never completely cooled.

Now, it's also worth mentioning that only 1 (2?) aircraft flying today could do this: the 787 (A350?), because the pressurization systems are not driven by engine bleed air, but by secondary intake turbines.


Side note but the A350 has a bleed system run by the engines, in the "traditional" manner.


Thought I remembered that correctly :)

So only 1 aircraft could feasibly even try such a thing right now, though I think what other people are saying wrt burning more fuel on climb and thus negating the gains is probably also correct.


The energy to pressurise the cabin has to come from somewhere. It does not make a material difference to the (in)feasibility of the proposed climb-glide profile.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
patrickjp93
Posts: 384
Joined: Thu Aug 22, 2019 12:00 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Wed Oct 02, 2019 3:30 pm

Starlionblue wrote:
patrickjp93 wrote:
Starlionblue wrote:

Side note but the A350 has a bleed system run by the engines, in the "traditional" manner.


Thought I remembered that correctly :)

So only 1 aircraft could feasibly even try such a thing right now, though I think what other people are saying wrt burning more fuel on climb and thus negating the gains is probably also correct.


The energy to pressurise the cabin has to come from somewhere. It does not make a material difference to the (in)feasibility of the proposed climb-glide profile.


The 787's battery system can probably sustain it on glide as long as you put restrictions on amperage to the charge ports throughout the passenger cabin, use ultra-low-wattage IFEs, limit WiFi bandwidth on glide, etc.. And those batteries will then be recharged on climb. There again we may need a couple generations newer supercapacitor tech based on graphene so the charging and discharging can be faster without negatively impacting the lifetime of the temporary storage. High-current battery charging greatly reduces the number of sustainable cycles.
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Thu Oct 03, 2019 9:32 am

Starlionblue wrote:
Side note but the A350 has a bleed system run by the engines, in the "traditional" manner.


That is afaics not relevant.
You need power in both solutions ( electric or pneumatic cabin pressurization.)

If you cut out the engines there is neither enough electric power ( 787 ) or
enough ( if any ) pneumatic (A350) power available.
In both cases you have to run the APU. No idea if the APU in either craft
is capable of keeping up all required for regular flight systems running.
Murphy is an optimist
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Thu Oct 03, 2019 12:57 pm

patrickjp93 wrote:
The 787's battery system can probably sustain it on glide as long as you put restrictions on amperage to the charge ports throughout the passenger cabin, use ultra-low-wattage IFEs, limit WiFi bandwidth on glide, etc..


787 batteries have three core tasks:
start APU ( only the rear one afaik.)
operate electric brake on engine out landing below RAT cut out speed.
back up/buffer instrumentation supply.

( capacity is rather limited. it is sized to allow supplying the brakes for one landing at rather high currents apparently.)

extra: operate the aircraft in "sleep mode": door actuation, tanking, emergency lighting. initial issue: batteries "played" empty.
Murphy is an optimist
 
patrickjp93
Posts: 384
Joined: Thu Aug 22, 2019 12:00 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Thu Oct 03, 2019 1:10 pm

WIederling wrote:
patrickjp93 wrote:
The 787's battery system can probably sustain it on glide as long as you put restrictions on amperage to the charge ports throughout the passenger cabin, use ultra-low-wattage IFEs, limit WiFi bandwidth on glide, etc..


787 batteries have three core tasks:
start APU ( only the rear one afaik.)
operate electric brake on engine out landing below RAT cut out speed.
back up/buffer instrumentation supply.

( capacity is rather limited. it is sized to allow supplying the brakes for one landing at rather high currents apparently.)

extra: operate the aircraft in "sleep mode": door actuation, tanking, emergency lighting. initial issue: batteries "played" empty.


Modification is a given; don't get me wrong, but I think the batteries (they are very high-capacity Lithium-Cobalt beasts) can sustain the instruments and necessary functions as long as restrictions are put on power to the passenger cabin during glide phases.
 
WIederling
Posts: 8888
Joined: Sun Sep 13, 2015 2:15 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Thu Oct 03, 2019 2:30 pm

patrickjp93 wrote:
Modification is a given; don't get me wrong, but I think the batteries (they are very high-capacity Lithium-Cobalt beasts) can sustain the instruments and necessary functions as long as restrictions are put on power to the passenger cabin during glide phases.


<1.5kWh available. 2.2kWh nominal.

Instrumentation is relatively low power. ( but as long as you are flying it will
be powered by the RAT.)

But do you have an idea what IFE consumes per seat?
and what power the pressurization sucks up?

there is a good reason that the battery is not involved in that domain.
Lets assume that one starter generator ( rated @225kW ) can just about supply all regular consumers.
( there are 2 per engine and 2 on the APU. )

a comparable battery @2kWh capacity would in theory hold 53 seconds
( for real it would be well beyond rated loads ( 1000A) and break its fuse as current demand is 7500A. )
Murphy is an optimist
 
patrickjp93
Posts: 384
Joined: Thu Aug 22, 2019 12:00 pm

Re: Would a climb/glide schedule save fuel compared to a constant cruise altitude flight?

Thu Oct 03, 2019 2:44 pm

WIederling wrote:
patrickjp93 wrote:
Modification is a given; don't get me wrong, but I think the batteries (they are very high-capacity Lithium-Cobalt beasts) can sustain the instruments and necessary functions as long as restrictions are put on power to the passenger cabin during glide phases.


<1.5kWh available. 2.2kWh nominal.

Instrumentation is relatively low power. ( but as long as you are flying it will
be powered by the RAT.)

But do you have an idea what IFE consumes per seat?
and what power the pressurization sucks up?

there is a good reason that the battery is not involved in that domain.
Lets assume that one starter generator ( rated @225kW ) can just about supply all regular consumers.
( there are 2 per engine and 2 on the APU. )

a comparable battery @2kWh capacity would in theory hold 53 seconds
( for real it would be well beyond rated loads ( 1000A) and break its fuse as current demand is 7500A. )


Given IFEs are made with the same sub 1 watt ARM processors you can find in tablets and smart phones, you can easily make one that only consumes 2 watts while performing just as well as what leads the industry. OLED panels, minimal DRAM, cache-less flash storage, and make them rebootable with a button press at the seat rather than by a station in the cabin. With the networking gone, there's half your power budget for IFEs removed.

So for 300 seats on a 789 (AC runs 298), that's 600 watts. Hardly a problem for a half ton LiCo battery. The real issue is charging phones and laptops. That would have to be either severely limited or just disabled on glide phases.

Who is online

Users browsing this forum: Bing [Bot], thaigold, tommy1808 and 27 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos