Why don't aircraft fly even higher, for even greater efficiency?

Clash Royale CLAN TAG#URR8PPP

up vote
2
down vote

favorite

After reading various superb QA on here I now see that (basically) aircraft are more efficient per passenger-mile, at higher altitudes.

Why don't we go even higher, than current typical airliner cruising altitudes?

What's the deal?

If there's an efficiency transition, have we reached it?

aerodynamics airliner engine efficiency

share|improve this question

edited 2 hours ago

Federico♦

24.9k14100151

asked 2 hours ago

Fattie

187821

add a comment | 

up vote
2
down vote

favorite

After reading various superb QA on here I now see that (basically) aircraft are more efficient per passenger-mile, at higher altitudes.

Why don't we go even higher, than current typical airliner cruising altitudes?

What's the deal?

If there's an efficiency transition, have we reached it?

aerodynamics airliner engine efficiency

share|improve this question

edited 2 hours ago

Federico♦

24.9k14100151

asked 2 hours ago

Fattie

187821

add a comment | 

up vote
2
down vote

favorite

up vote
2
down vote

favorite

After reading various superb QA on here I now see that (basically) aircraft are more efficient per passenger-mile, at higher altitudes.

Why don't we go even higher, than current typical airliner cruising altitudes?

What's the deal?

If there's an efficiency transition, have we reached it?

aerodynamics airliner engine efficiency

share|improve this question

edited 2 hours ago

Federico♦

24.9k14100151

asked 2 hours ago

Fattie

187821

After reading various superb QA on here I now see that (basically) aircraft are more efficient per passenger-mile, at higher altitudes.

Why don't we go even higher, than current typical airliner cruising altitudes?

What's the deal?

If there's an efficiency transition, have we reached it?

aerodynamics airliner engine efficiency

aerodynamics airliner engine efficiency

share|improve this question

edited 2 hours ago

Federico♦

24.9k14100151

asked 2 hours ago

Fattie

187821

share|improve this question

edited 2 hours ago

Federico♦

24.9k14100151

asked 2 hours ago

Fattie

187821

share|improve this question

share|improve this question

edited 2 hours ago

Federico♦

24.9k14100151

edited 2 hours ago

Federico♦

24.9k14100151

edited 2 hours ago

Federico♦

24.9k14100151

24.9k14100151

asked 2 hours ago

Fattie

187821

asked 2 hours ago

Fattie

187821

asked 2 hours ago

Fattie

187821

187821

add a comment | 

add a comment | 

3 Answers
3

active

oldest

votes

up vote
2
down vote

Some do (or have in the past) but very high altitudes present there own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and decent at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the airframe saw much greater wear and tear per cycle than its lower altitude friends.

At some point you get near the coffin corner a point at which, even if you have enough thrust your stall speed exceeds your critical mach number (effectively your wing cant work right). The U2 spy plane is capable of flying right on this edge.

One of the big practical limiting factors is also the rapid decent requirement for airframe certification. The FAA requires that in the event of a depressurization the aircraft can get down to 10,000 ft. (no oxygen required altitude) in 10 minutes as discussed here. The higher you go the faster the emergency decent needs to be, eventually this becomes an engineering issue and the airframe becomes the limiting factor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

Dave

58.1k4104212

• 
  
  
  

  
  

  
  
  
  
  
  

  
  fascinating about the emergency descent issue..
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
  – Dave
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
1
down vote

Please meet the ceiling altitude.

Above this altitude the aircraft cannot fly fast enough to generate enough lift to stay aloft.

This is affected by:

• weight (more weight needs more lift)


• engine power (more lift means more drag, that is overcome by engine power)


• L/D ratio (if you can have less drag for the same lift, you can fly a bit higher, all the rest being equal)

So, overall, engines are getting better, but you gain more flying a bit lower, at your ideal cruise speed, and thus consuming less.

share|improve this answer

answered 2 hours ago

Federico♦

24.9k14100151

• 
  
  
  

  
  

  
  
  
  
  
  

  
  ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
  – Federico♦
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Keyword "Coffin Corner"
  – Noah Krasser
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
  – Federico♦
  31 mins ago
  

  
  
  
  

add a comment | 

up vote
0
down vote

You are correct in understanding that airlines primarily fly higher in order to have a more efficient flight, as there is significantly less drag due to the thinning of the atmosphere.

Explanation:

However, there are a couple issues that grow as you raise your altitude. Your wings and engines are more efficient in providing lift and thrust respectively at lower altitudes. The wings create lift via the difference in air pressure going over and underneath the wings. When you increase your altitude, your wings become less efficient because while there is less drag, you now need to increase the speed of air passing your wings in order to retain the same pressures, which then produce the same lift.

Supersonic flight (flight over Mach 1) is significantly different than subsonic flight. The air will separate from the wing when it breaks the sound barrier, and will thus cause you to lose lift. As stated in the previous paragraph, as you increase your altitude you need to increase your speed. Then, as you approach Mach 1, drag increases exponentially. The average jetliner cruises at 0.75 mach, so you can see that we are already close enough for comfort to this barrier.

The engines themselves are also reliant on air passing through them to provide thrust, and will become less efficient at higher altitudes.

In short:

In short, it really becomes a balancing act, where you have to determine if the extra altitude, and speed, is worth the drastic increase in fuel needed to power the engines to get you to an appropriate speed for your altitude. With today's technology, it is not considered cost-effective.

For comparison, the supersonic "Concorde" jet topped out at roughly 60,000 feet, while the subsonic "747" jet tops out at roughly 45,000 feet.

share|improve this answer

answered 1 hour ago

Matt

42614

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function ()
return StackExchange.using("mathjaxEditing", function ()
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix)
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
);
);
, "mathjax-editing");

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "528"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
convertImagesToLinks: false,
noModals: false,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

 

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name Email

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2faviation.stackexchange.com%2fquestions%2f56541%2fwhy-dont-aircraft-fly-even-higher-for-even-greater-efficiency%23new-answer', 'question_page');

);

Post as a guest

Name Email

3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

active

oldest

votes

active

oldest

votes

up vote
2
down vote

Some do (or have in the past) but very high altitudes present there own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and decent at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the airframe saw much greater wear and tear per cycle than its lower altitude friends.

At some point you get near the coffin corner a point at which, even if you have enough thrust your stall speed exceeds your critical mach number (effectively your wing cant work right). The U2 spy plane is capable of flying right on this edge.

One of the big practical limiting factors is also the rapid decent requirement for airframe certification. The FAA requires that in the event of a depressurization the aircraft can get down to 10,000 ft. (no oxygen required altitude) in 10 minutes as discussed here. The higher you go the faster the emergency decent needs to be, eventually this becomes an engineering issue and the airframe becomes the limiting factor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

Dave

58.1k4104212

• 
  
  
  

  
  

  
  
  
  
  
  

  
  fascinating about the emergency descent issue..
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
  – Dave
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
2
down vote

Some do (or have in the past) but very high altitudes present there own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and decent at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the airframe saw much greater wear and tear per cycle than its lower altitude friends.

At some point you get near the coffin corner a point at which, even if you have enough thrust your stall speed exceeds your critical mach number (effectively your wing cant work right). The U2 spy plane is capable of flying right on this edge.

One of the big practical limiting factors is also the rapid decent requirement for airframe certification. The FAA requires that in the event of a depressurization the aircraft can get down to 10,000 ft. (no oxygen required altitude) in 10 minutes as discussed here. The higher you go the faster the emergency decent needs to be, eventually this becomes an engineering issue and the airframe becomes the limiting factor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

Dave

58.1k4104212

• 
  
  
  

  
  

  
  
  
  
  
  

  
  fascinating about the emergency descent issue..
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
  – Dave
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
2
down vote

up vote
2
down vote

Some do (or have in the past) but very high altitudes present there own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and decent at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the airframe saw much greater wear and tear per cycle than its lower altitude friends.

At some point you get near the coffin corner a point at which, even if you have enough thrust your stall speed exceeds your critical mach number (effectively your wing cant work right). The U2 spy plane is capable of flying right on this edge.

One of the big practical limiting factors is also the rapid decent requirement for airframe certification. The FAA requires that in the event of a depressurization the aircraft can get down to 10,000 ft. (no oxygen required altitude) in 10 minutes as discussed here. The higher you go the faster the emergency decent needs to be, eventually this becomes an engineering issue and the airframe becomes the limiting factor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

Dave

58.1k4104212

Some do (or have in the past) but very high altitudes present there own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and decent at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the airframe saw much greater wear and tear per cycle than its lower altitude friends.

At some point you get near the coffin corner a point at which, even if you have enough thrust your stall speed exceeds your critical mach number (effectively your wing cant work right). The U2 spy plane is capable of flying right on this edge.

One of the big practical limiting factors is also the rapid decent requirement for airframe certification. The FAA requires that in the event of a depressurization the aircraft can get down to 10,000 ft. (no oxygen required altitude) in 10 minutes as discussed here. The higher you go the faster the emergency decent needs to be, eventually this becomes an engineering issue and the airframe becomes the limiting factor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

Dave

58.1k4104212

share|improve this answer

share|improve this answer

edited 1 hour ago

edited 1 hour ago

edited 1 hour ago

answered 1 hour ago

Dave

58.1k4104212

answered 1 hour ago

Dave

58.1k4104212

answered 1 hour ago

Dave

58.1k4104212

58.1k4104212

• 
  
  
  

  
  

  
  
  
  
  
  

  
  fascinating about the emergency descent issue..
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
  – Dave
  1 hour ago
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  fascinating about the emergency descent issue..
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
  – Dave
  1 hour ago
  

  
  
  
  

fascinating about the emergency descent issue..
– Fattie
1 hour ago

fascinating about the emergency descent issue..
– Fattie
1 hour ago

@Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
– Dave
1 hour ago

@Fattie there is a hard number for that time as well, I dont remember it off hand but im trying to find it now.
– Dave
1 hour ago

add a comment | 

up vote
1
down vote

Please meet the ceiling altitude.

Above this altitude the aircraft cannot fly fast enough to generate enough lift to stay aloft.

This is affected by:

• weight (more weight needs more lift)


• engine power (more lift means more drag, that is overcome by engine power)


• L/D ratio (if you can have less drag for the same lift, you can fly a bit higher, all the rest being equal)

So, overall, engines are getting better, but you gain more flying a bit lower, at your ideal cruise speed, and thus consuming less.

share|improve this answer

answered 2 hours ago

Federico♦

24.9k14100151

• 
  
  
  

  
  

  
  
  
  
  
  

  
  ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
  – Federico♦
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Keyword "Coffin Corner"
  – Noah Krasser
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
  – Federico♦
  31 mins ago
  

  
  
  
  

add a comment | 

up vote
1
down vote

Please meet the ceiling altitude.

Above this altitude the aircraft cannot fly fast enough to generate enough lift to stay aloft.

This is affected by:

• weight (more weight needs more lift)


• engine power (more lift means more drag, that is overcome by engine power)


• L/D ratio (if you can have less drag for the same lift, you can fly a bit higher, all the rest being equal)

So, overall, engines are getting better, but you gain more flying a bit lower, at your ideal cruise speed, and thus consuming less.

share|improve this answer

answered 2 hours ago

Federico♦

24.9k14100151

• 
  
  
  

  
  

  
  
  
  
  
  

  
  ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
  – Federico♦
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Keyword "Coffin Corner"
  – Noah Krasser
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
  – Federico♦
  31 mins ago
  

  
  
  
  

add a comment | 

up vote
1
down vote

up vote
1
down vote

Please meet the ceiling altitude.

Above this altitude the aircraft cannot fly fast enough to generate enough lift to stay aloft.

This is affected by:

• weight (more weight needs more lift)


• engine power (more lift means more drag, that is overcome by engine power)


• L/D ratio (if you can have less drag for the same lift, you can fly a bit higher, all the rest being equal)

So, overall, engines are getting better, but you gain more flying a bit lower, at your ideal cruise speed, and thus consuming less.

share|improve this answer

answered 2 hours ago

Federico♦

24.9k14100151

Please meet the ceiling altitude.

Above this altitude the aircraft cannot fly fast enough to generate enough lift to stay aloft.

This is affected by:

• weight (more weight needs more lift)


• engine power (more lift means more drag, that is overcome by engine power)


• L/D ratio (if you can have less drag for the same lift, you can fly a bit higher, all the rest being equal)

So, overall, engines are getting better, but you gain more flying a bit lower, at your ideal cruise speed, and thus consuming less.

share|improve this answer

answered 2 hours ago

Federico♦

24.9k14100151

share|improve this answer

share|improve this answer

answered 2 hours ago

Federico♦

24.9k14100151

answered 2 hours ago

Federico♦

24.9k14100151

answered 2 hours ago

Federico♦

24.9k14100151

24.9k14100151

• 
  
  
  

  
  

  
  
  
  
  
  

  
  ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
  – Federico♦
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Keyword "Coffin Corner"
  – Noah Krasser
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
  – Federico♦
  31 mins ago
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
  – Fattie
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
  – Federico♦
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Keyword "Coffin Corner"
  – Noah Krasser
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
  – Federico♦
  31 mins ago
  

  
  
  
  

ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
– Fattie
1 hour ago

ahh! cannot fly fast enough to generate enough lift! lame query, but could they just make the wings bigger, no ?? awesome info...
– Fattie
1 hour ago

@Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
– Federico♦
1 hour ago

@Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems
– Federico♦
1 hour ago

Keyword "Coffin Corner"
– Noah Krasser
1 hour ago

Keyword "Coffin Corner"
– Noah Krasser
1 hour ago

@NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
– Federico♦
31 mins ago

@NoahKrasser coffin corner is different. that's where structural integrity comes into play instead of engine power
– Federico♦
31 mins ago

add a comment | 

up vote
0
down vote

You are correct in understanding that airlines primarily fly higher in order to have a more efficient flight, as there is significantly less drag due to the thinning of the atmosphere.

Explanation:

However, there are a couple issues that grow as you raise your altitude. Your wings and engines are more efficient in providing lift and thrust respectively at lower altitudes. The wings create lift via the difference in air pressure going over and underneath the wings. When you increase your altitude, your wings become less efficient because while there is less drag, you now need to increase the speed of air passing your wings in order to retain the same pressures, which then produce the same lift.

Supersonic flight (flight over Mach 1) is significantly different than subsonic flight. The air will separate from the wing when it breaks the sound barrier, and will thus cause you to lose lift. As stated in the previous paragraph, as you increase your altitude you need to increase your speed. Then, as you approach Mach 1, drag increases exponentially. The average jetliner cruises at 0.75 mach, so you can see that we are already close enough for comfort to this barrier.

The engines themselves are also reliant on air passing through them to provide thrust, and will become less efficient at higher altitudes.

In short:

In short, it really becomes a balancing act, where you have to determine if the extra altitude, and speed, is worth the drastic increase in fuel needed to power the engines to get you to an appropriate speed for your altitude. With today's technology, it is not considered cost-effective.

For comparison, the supersonic "Concorde" jet topped out at roughly 60,000 feet, while the subsonic "747" jet tops out at roughly 45,000 feet.

share|improve this answer

answered 1 hour ago

Matt

42614

add a comment | 

up vote
0
down vote

You are correct in understanding that airlines primarily fly higher in order to have a more efficient flight, as there is significantly less drag due to the thinning of the atmosphere.

Explanation:

However, there are a couple issues that grow as you raise your altitude. Your wings and engines are more efficient in providing lift and thrust respectively at lower altitudes. The wings create lift via the difference in air pressure going over and underneath the wings. When you increase your altitude, your wings become less efficient because while there is less drag, you now need to increase the speed of air passing your wings in order to retain the same pressures, which then produce the same lift.

Supersonic flight (flight over Mach 1) is significantly different than subsonic flight. The air will separate from the wing when it breaks the sound barrier, and will thus cause you to lose lift. As stated in the previous paragraph, as you increase your altitude you need to increase your speed. Then, as you approach Mach 1, drag increases exponentially. The average jetliner cruises at 0.75 mach, so you can see that we are already close enough for comfort to this barrier.

The engines themselves are also reliant on air passing through them to provide thrust, and will become less efficient at higher altitudes.

In short:

In short, it really becomes a balancing act, where you have to determine if the extra altitude, and speed, is worth the drastic increase in fuel needed to power the engines to get you to an appropriate speed for your altitude. With today's technology, it is not considered cost-effective.

For comparison, the supersonic "Concorde" jet topped out at roughly 60,000 feet, while the subsonic "747" jet tops out at roughly 45,000 feet.

share|improve this answer

answered 1 hour ago

Matt

42614

add a comment | 

up vote
0
down vote

up vote
0
down vote

You are correct in understanding that airlines primarily fly higher in order to have a more efficient flight, as there is significantly less drag due to the thinning of the atmosphere.

Explanation:

However, there are a couple issues that grow as you raise your altitude. Your wings and engines are more efficient in providing lift and thrust respectively at lower altitudes. The wings create lift via the difference in air pressure going over and underneath the wings. When you increase your altitude, your wings become less efficient because while there is less drag, you now need to increase the speed of air passing your wings in order to retain the same pressures, which then produce the same lift.

Supersonic flight (flight over Mach 1) is significantly different than subsonic flight. The air will separate from the wing when it breaks the sound barrier, and will thus cause you to lose lift. As stated in the previous paragraph, as you increase your altitude you need to increase your speed. Then, as you approach Mach 1, drag increases exponentially. The average jetliner cruises at 0.75 mach, so you can see that we are already close enough for comfort to this barrier.

The engines themselves are also reliant on air passing through them to provide thrust, and will become less efficient at higher altitudes.

In short:

In short, it really becomes a balancing act, where you have to determine if the extra altitude, and speed, is worth the drastic increase in fuel needed to power the engines to get you to an appropriate speed for your altitude. With today's technology, it is not considered cost-effective.

For comparison, the supersonic "Concorde" jet topped out at roughly 60,000 feet, while the subsonic "747" jet tops out at roughly 45,000 feet.

share|improve this answer

answered 1 hour ago

Matt

42614

You are correct in understanding that airlines primarily fly higher in order to have a more efficient flight, as there is significantly less drag due to the thinning of the atmosphere.

Explanation:

However, there are a couple issues that grow as you raise your altitude. Your wings and engines are more efficient in providing lift and thrust respectively at lower altitudes. The wings create lift via the difference in air pressure going over and underneath the wings. When you increase your altitude, your wings become less efficient because while there is less drag, you now need to increase the speed of air passing your wings in order to retain the same pressures, which then produce the same lift.

Supersonic flight (flight over Mach 1) is significantly different than subsonic flight. The air will separate from the wing when it breaks the sound barrier, and will thus cause you to lose lift. As stated in the previous paragraph, as you increase your altitude you need to increase your speed. Then, as you approach Mach 1, drag increases exponentially. The average jetliner cruises at 0.75 mach, so you can see that we are already close enough for comfort to this barrier.

The engines themselves are also reliant on air passing through them to provide thrust, and will become less efficient at higher altitudes.

In short:

In short, it really becomes a balancing act, where you have to determine if the extra altitude, and speed, is worth the drastic increase in fuel needed to power the engines to get you to an appropriate speed for your altitude. With today's technology, it is not considered cost-effective.

For comparison, the supersonic "Concorde" jet topped out at roughly 60,000 feet, while the subsonic "747" jet tops out at roughly 45,000 feet.

share|improve this answer

answered 1 hour ago

Matt

42614

share|improve this answer

share|improve this answer

answered 1 hour ago

Matt

42614

answered 1 hour ago

Matt

42614

answered 1 hour ago

Matt

42614

42614

add a comment | 

add a comment | 

 

draft saved

draft discarded

 

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name Email

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2faviation.stackexchange.com%2fquestions%2f56541%2fwhy-dont-aircraft-fly-even-higher-for-even-greater-efficiency%23new-answer', 'question_page');

);

Post as a guest

Name Email

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name Email

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name Email

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name Email

Name Email

Name

Email

Name Email

Name

Email