Mixing
How can flying high minimize drag and increase fuel efficiency?
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As a plane goes higher, the engines have to work harder to compensate for the air density, therefore it will require more fuel in order provide the same power at lower altitudes.
But I always hear that flying high means less fuel burnt.
How can that be the case?
engine fuel
edited 16 mins ago
Steve V.
14.1k464129
asked 15 hours ago
Abdull
838
 |Â
show 3 more comments
up vote
5
down vote
favorite
As a plane goes higher, the engines have to work harder to compensate for the air density, therefore it will require more fuel in order provide the same power at lower altitudes.
But I always hear that flying high means less fuel burnt.
How can that be the case?
engine fuel
edited 16 mins ago
Steve V.
14.1k464129
asked 15 hours ago
Abdull
838
5
Less air molecules means less drag...
– Ron Beyer
15 hours ago
5
On what basis do the engines have to "work harder"?
– Greg Hewgill
15 hours ago
4
Flying at high altitude produces the same amount of drag, because you must fly faster in order to get enough lift power. BUT, it allows you to cover more ground miles with the same power setting in given amount of time, compared to what would you cover flying at low levels. Why? Because the air density is lower at altitude. There's also a significant temperature benefit for the engines. They run more efficient in low temperatures.
– Electric Pilot
14 hours ago
1
Related, maybe even a dupe?
– Pondlife
14 hours ago
Greg, I flew multi engine airplane and I've noticed that for every thousand feet my RPM indicators slightly decrease. I have to add more power to maintain the same airspeed. some times it get to the point where I'm at full power and I'm barely getting the normal cruise speed.
– Abdull
14 hours ago
 |Â
show 3 more comments
up vote
5
down vote
favorite
up vote
5
down vote
favorite
As a plane goes higher, the engines have to work harder to compensate for the air density, therefore it will require more fuel in order provide the same power at lower altitudes.
But I always hear that flying high means less fuel burnt.
How can that be the case?
engine fuel
edited 16 mins ago
Steve V.
14.1k464129
asked 15 hours ago
Abdull
838
As a plane goes higher, the engines have to work harder to compensate for the air density, therefore it will require more fuel in order provide the same power at lower altitudes.
But I always hear that flying high means less fuel burnt.
How can that be the case?
engine fuel
engine fuel
edited 16 mins ago
Steve V.
14.1k464129
asked 15 hours ago
Abdull
838
edited 16 mins ago
Steve V.
14.1k464129
asked 15 hours ago
Abdull
838
edited 16 mins ago
Steve V.
14.1k464129
edited 16 mins ago
Steve V.
14.1k464129
edited 16 mins ago
Steve V.
14.1k464129
14.1k464129
asked 15 hours ago
Abdull
838
asked 15 hours ago
Abdull
838
asked 15 hours ago
Abdull
838
838
5
Less air molecules means less drag...
– Ron Beyer
15 hours ago
5
On what basis do the engines have to "work harder"?
– Greg Hewgill
15 hours ago
4
Flying at high altitude produces the same amount of drag, because you must fly faster in order to get enough lift power. BUT, it allows you to cover more ground miles with the same power setting in given amount of time, compared to what would you cover flying at low levels. Why? Because the air density is lower at altitude. There's also a significant temperature benefit for the engines. They run more efficient in low temperatures.
– Electric Pilot
14 hours ago
1
Related, maybe even a dupe?
– Pondlife
14 hours ago
Greg, I flew multi engine airplane and I've noticed that for every thousand feet my RPM indicators slightly decrease. I have to add more power to maintain the same airspeed. some times it get to the point where I'm at full power and I'm barely getting the normal cruise speed.
– Abdull
14 hours ago
 |Â
show 3 more comments
5
Less air molecules means less drag...
– Ron Beyer
15 hours ago
5
On what basis do the engines have to "work harder"?
– Greg Hewgill
15 hours ago
4
Flying at high altitude produces the same amount of drag, because you must fly faster in order to get enough lift power. BUT, it allows you to cover more ground miles with the same power setting in given amount of time, compared to what would you cover flying at low levels. Why? Because the air density is lower at altitude. There's also a significant temperature benefit for the engines. They run more efficient in low temperatures.
– Electric Pilot
14 hours ago
1
Related, maybe even a dupe?
– Pondlife
14 hours ago
Greg, I flew multi engine airplane and I've noticed that for every thousand feet my RPM indicators slightly decrease. I have to add more power to maintain the same airspeed. some times it get to the point where I'm at full power and I'm barely getting the normal cruise speed.
– Abdull
14 hours ago
5
5
Less air molecules means less drag...
– Ron Beyer
15 hours ago
Less air molecules means less drag...
– Ron Beyer
15 hours ago
5
5
On what basis do the engines have to "work harder"?
– Greg Hewgill
15 hours ago
On what basis do the engines have to "work harder"?
– Greg Hewgill
15 hours ago
4
4
Flying at high altitude produces the same amount of drag, because you must fly faster in order to get enough lift power. BUT, it allows you to cover more ground miles with the same power setting in given amount of time, compared to what would you cover flying at low levels. Why? Because the air density is lower at altitude. There's also a significant temperature benefit for the engines. They run more efficient in low temperatures.
– Electric Pilot
14 hours ago
Flying at high altitude produces the same amount of drag, because you must fly faster in order to get enough lift power. BUT, it allows you to cover more ground miles with the same power setting in given amount of time, compared to what would you cover flying at low levels. Why? Because the air density is lower at altitude. There's also a significant temperature benefit for the engines. They run more efficient in low temperatures.
– Electric Pilot
14 hours ago
1
1
Related, maybe even a dupe?
– Pondlife
14 hours ago
Related, maybe even a dupe?
– Pondlife
14 hours ago
Greg, I flew multi engine airplane and I've noticed that for every thousand feet my RPM indicators slightly decrease. I have to add more power to maintain the same airspeed. some times it get to the point where I'm at full power and I'm barely getting the normal cruise speed.
– Abdull
14 hours ago
Greg, I flew multi engine airplane and I've noticed that for every thousand feet my RPM indicators slightly decrease. I have to add more power to maintain the same airspeed. some times it get to the point where I'm at full power and I'm barely getting the normal cruise speed.
– Abdull
14 hours ago
 |Â
show 3 more comments
3 Answers
3
active
oldest
votes
up vote
17
down vote
accepted
Flying higher means less drag because the air is thinner; therefore, you can fly faster at altitude and hence travel farther on less fuel.
However, flying higher also means less oxygen available to burn your fuel, so available horsepower decreases with altitude.
There is a special altitude at which these two effects (drag reduction and available power reduction) achieve a crossover point. This is called the critical altitude and it is there where you achieve optimum cruise and best economy.
If you want to fly higher than critical altitude, you will fly slower because the power loss is greater than the drag reduction and you will spend more time in the air.
answered 14 hours ago
niels nielsen
1,4241313
9
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
3
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
add a comment |Â
up vote
0
down vote
This is a good question but first we must clarify something.
There is a major difference between propeller driven aircraft and pass through turbine propelled aircraft. Without getting to technical in this explanation, let’s leave propeller driven aircraft alone for the moment and keep our answer to the confines of high bypass ratio turbine driven engines.
The long definitive answer involves a great deal of physics, another subject we will not get to rhetorical about at this time. We will however consider Bernoulli’s principles concerning fluids and the airfoil or wing. This brings us to our first thought; consider the atmosphere, or air, around us as a fluid. Now that was simple enough.
When an airplane takes flight it must defeat its greatest foe, Newton’s contribution to this question, gravity. In its most simple terms, the ability to defeat gravity requires an opposing force that is greater than the weight of the mass being lifted. In aviation this comes from the lift created, of course, by the wings.
To help make this possible on airplanes the wings are shaped with a leading edge, that is the part that first hits the air, then a highly rounded upper surface, known as camber, and much flatter lower surface which come together at the trailing edge. (Just a moment more, I’m getting to your answer.) Now we apply Bernoulli’s principal.
Looking at air as a fluid, in principle Bernoulli’s theory is this. The air traveling over the top of the wing is moving at a faster speed than the air traveling under the wing. In theory, this would cause greater pressure under the wing (lift) and less pressure over the wing as the air is rushing from the leading edge to the trailing edge. The reasoning here is that when the air molecules are separated by the leading edge of the wing, the molecules passing over the top, which has a longer surface due to the added camber, must move faster in order to reach the trailing edge at the same moment as the air passing below the wing. Now we get to the part concerning thicker (heavier) air mass and thinner (lighter) air mass and the effects on “liftâ€Â.
In order to for the wings to produce the lift needed to defeat gravity you must have thrust and lots of it! Now we enter into the power (engines) production that is required to create flight. As we all know, an airplane must be moving into the air mass in order to obtain the effects required to produce flight also known as the lighter than air effect. So in principle, the shortened version, the air passing over and under the wings must produce a lift equivalency greater than the weight of the aircraft. There is a formula but we’ll skip that here and just state this, the airmass flowing around the wings must be equal to or greater than the mass of the airplane. There, we have flight... well sort of.
You see the weight of air at sea level is much greater than the air at say 30,000 feet. Here again, in principle, the amount of air flowing across the wing on takeoff, by mass, is more at mean sea level than it would be at 5,000 feet. Since this is a principle of mass verses mass (in this case in order to defeat the effects of gravity), the fluid principles of Bernoulli’s would apply well here. So what are the effects on engine performance?
Modern power plants today are engineered to direct less airflow through the engine or turbine section of the power plant. The ratios have changed dramatically in the last decade with most engines diverting 80% or more of the air flow around the core and exiting as additional thrust at the tail. These engines, as one could imagine, consume extreme amounts of air as it flows through and around the core, or power unit, and exits the tail as super heated energy and thrust. To maintain this thrust the amount of air mass must remain fairly constant. So, how is this accomplished at 38,000 feet? And what about the thinner air passing over the airfoils?
Well, here is where physics and the dynamics of air mass come into play but in a much simpler way than you might expect. Remember the role that the wing plays in all of this? Air pressures above and below the wings can still be easily maintained at higher altitudes. Why? Because of the much greater amount of air passing over the wing surfaces at speeds often over 500 mph. You see, it’s the air molecules that hold the secret to air mass and density. At speeds like this the air density is super compressed to allow far more lift than needed to maintain flight. Then there is the engine question.
Since air is composed of gasses (mainly nitrogen with about 20% oxygen and other gasses mixed in) at the molecular level, they too can be “squeezed†under tremendous pressure and therefore compressed to create an even mixture through a jet engine. This ability to compress huge amounts of air while flying at high altitudes again makes up for loss of mass and density. Since the engine is moving between 500 and 600 mph, the intake or ingesting of plenty of air through the core and surround is no problem.
The added bonus is this; thin air creates less friction on the aircraft and much cooler air temperatures (normally around -60 degrees) as the air flows through the engine. There is also a slight reduction in fuel cost flying at these higher altitudes as we normally reduce our throttles 10 to 20 percent while at cruising altitude. This of course is dependent on the aircraft type and any head or tail wind!
answered 8 mins ago
Joe
1
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up vote
-2
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Adding to the answer by Niels Nielsen, the special altitude changes (increases) during the flight as the power required reduces as the weight of the aircraft decreases due to fuel consumption. But these effects also depend on the type of propulsion (jet vs propeller). If you want to find out more about this. Search about power required and power available plots for aircraft.
answered 6 hours ago
Johann
1
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1
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
17
down vote
accepted
Flying higher means less drag because the air is thinner; therefore, you can fly faster at altitude and hence travel farther on less fuel.
However, flying higher also means less oxygen available to burn your fuel, so available horsepower decreases with altitude.
There is a special altitude at which these two effects (drag reduction and available power reduction) achieve a crossover point. This is called the critical altitude and it is there where you achieve optimum cruise and best economy.
If you want to fly higher than critical altitude, you will fly slower because the power loss is greater than the drag reduction and you will spend more time in the air.
answered 14 hours ago
niels nielsen
1,4241313
9
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
3
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
add a comment |Â
up vote
17
down vote
accepted
Flying higher means less drag because the air is thinner; therefore, you can fly faster at altitude and hence travel farther on less fuel.
However, flying higher also means less oxygen available to burn your fuel, so available horsepower decreases with altitude.
There is a special altitude at which these two effects (drag reduction and available power reduction) achieve a crossover point. This is called the critical altitude and it is there where you achieve optimum cruise and best economy.
If you want to fly higher than critical altitude, you will fly slower because the power loss is greater than the drag reduction and you will spend more time in the air.
answered 14 hours ago
niels nielsen
1,4241313
9
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
3
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
add a comment |Â
up vote
17
down vote
accepted
up vote
17
down vote
accepted
Flying higher means less drag because the air is thinner; therefore, you can fly faster at altitude and hence travel farther on less fuel.
However, flying higher also means less oxygen available to burn your fuel, so available horsepower decreases with altitude.
There is a special altitude at which these two effects (drag reduction and available power reduction) achieve a crossover point. This is called the critical altitude and it is there where you achieve optimum cruise and best economy.
If you want to fly higher than critical altitude, you will fly slower because the power loss is greater than the drag reduction and you will spend more time in the air.
answered 14 hours ago
niels nielsen
1,4241313
Flying higher means less drag because the air is thinner; therefore, you can fly faster at altitude and hence travel farther on less fuel.
However, flying higher also means less oxygen available to burn your fuel, so available horsepower decreases with altitude.
There is a special altitude at which these two effects (drag reduction and available power reduction) achieve a crossover point. This is called the critical altitude and it is there where you achieve optimum cruise and best economy.
If you want to fly higher than critical altitude, you will fly slower because the power loss is greater than the drag reduction and you will spend more time in the air.
answered 14 hours ago
niels nielsen
1,4241313
answered 14 hours ago
niels nielsen
1,4241313
answered 14 hours ago
niels nielsen
1,4241313
answered 14 hours ago
niels nielsen
1,4241313
1,4241313
9
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
3
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
add a comment |Â
9
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
3
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
9
9
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
You don't necessarily fly slower above that altitude, you just fly more inefficiently. The issue is that the stall speed increases at the same point you start approaching critical mach, so the "window" between these two speeds gets smaller, which is known as the coffin corner.
– Ron Beyer
13 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
Got it, thanks. Is it true that above critical altitude, to maintain altitude constant requires progressively larger amounts of pitch-up trim? if so, is the inefficiency issue related to increased induced drag?
– niels nielsen
10 hours ago
3
3
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
In fact the aircraft is designed to fly at that sweet spot and ideally it would only fly at that altitude and speed. The design problem is to get the aircraft to fly for takeoff and landing speeds. Hence flaps.
– mckenzm
9 hours ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
"so available horsepower decreases with altitude" I would stress this part - because if you want <some power> and can obtain that up to <some height> ... then you will save fuel all the way up to that height with limited tradeoffs to power. Above that - you start trading power for drag.
– UKMonkey
33 mins ago
add a comment |Â
up vote
0
down vote
This is a good question but first we must clarify something.
There is a major difference between propeller driven aircraft and pass through turbine propelled aircraft. Without getting to technical in this explanation, let’s leave propeller driven aircraft alone for the moment and keep our answer to the confines of high bypass ratio turbine driven engines.
The long definitive answer involves a great deal of physics, another subject we will not get to rhetorical about at this time. We will however consider Bernoulli’s principles concerning fluids and the airfoil or wing. This brings us to our first thought; consider the atmosphere, or air, around us as a fluid. Now that was simple enough.
When an airplane takes flight it must defeat its greatest foe, Newton’s contribution to this question, gravity. In its most simple terms, the ability to defeat gravity requires an opposing force that is greater than the weight of the mass being lifted. In aviation this comes from the lift created, of course, by the wings.
To help make this possible on airplanes the wings are shaped with a leading edge, that is the part that first hits the air, then a highly rounded upper surface, known as camber, and much flatter lower surface which come together at the trailing edge. (Just a moment more, I’m getting to your answer.) Now we apply Bernoulli’s principal.
Looking at air as a fluid, in principle Bernoulli’s theory is this. The air traveling over the top of the wing is moving at a faster speed than the air traveling under the wing. In theory, this would cause greater pressure under the wing (lift) and less pressure over the wing as the air is rushing from the leading edge to the trailing edge. The reasoning here is that when the air molecules are separated by the leading edge of the wing, the molecules passing over the top, which has a longer surface due to the added camber, must move faster in order to reach the trailing edge at the same moment as the air passing below the wing. Now we get to the part concerning thicker (heavier) air mass and thinner (lighter) air mass and the effects on “liftâ€Â.
In order to for the wings to produce the lift needed to defeat gravity you must have thrust and lots of it! Now we enter into the power (engines) production that is required to create flight. As we all know, an airplane must be moving into the air mass in order to obtain the effects required to produce flight also known as the lighter than air effect. So in principle, the shortened version, the air passing over and under the wings must produce a lift equivalency greater than the weight of the aircraft. There is a formula but we’ll skip that here and just state this, the airmass flowing around the wings must be equal to or greater than the mass of the airplane. There, we have flight... well sort of.
You see the weight of air at sea level is much greater than the air at say 30,000 feet. Here again, in principle, the amount of air flowing across the wing on takeoff, by mass, is more at mean sea level than it would be at 5,000 feet. Since this is a principle of mass verses mass (in this case in order to defeat the effects of gravity), the fluid principles of Bernoulli’s would apply well here. So what are the effects on engine performance?
Modern power plants today are engineered to direct less airflow through the engine or turbine section of the power plant. The ratios have changed dramatically in the last decade with most engines diverting 80% or more of the air flow around the core and exiting as additional thrust at the tail. These engines, as one could imagine, consume extreme amounts of air as it flows through and around the core, or power unit, and exits the tail as super heated energy and thrust. To maintain this thrust the amount of air mass must remain fairly constant. So, how is this accomplished at 38,000 feet? And what about the thinner air passing over the airfoils?
Well, here is where physics and the dynamics of air mass come into play but in a much simpler way than you might expect. Remember the role that the wing plays in all of this? Air pressures above and below the wings can still be easily maintained at higher altitudes. Why? Because of the much greater amount of air passing over the wing surfaces at speeds often over 500 mph. You see, it’s the air molecules that hold the secret to air mass and density. At speeds like this the air density is super compressed to allow far more lift than needed to maintain flight. Then there is the engine question.
Since air is composed of gasses (mainly nitrogen with about 20% oxygen and other gasses mixed in) at the molecular level, they too can be “squeezed†under tremendous pressure and therefore compressed to create an even mixture through a jet engine. This ability to compress huge amounts of air while flying at high altitudes again makes up for loss of mass and density. Since the engine is moving between 500 and 600 mph, the intake or ingesting of plenty of air through the core and surround is no problem.
The added bonus is this; thin air creates less friction on the aircraft and much cooler air temperatures (normally around -60 degrees) as the air flows through the engine. There is also a slight reduction in fuel cost flying at these higher altitudes as we normally reduce our throttles 10 to 20 percent while at cruising altitude. This of course is dependent on the aircraft type and any head or tail wind!
answered 8 mins ago
Joe
1
New contributor
Joe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
up vote
0
down vote
This is a good question but first we must clarify something.
There is a major difference between propeller driven aircraft and pass through turbine propelled aircraft. Without getting to technical in this explanation, let’s leave propeller driven aircraft alone for the moment and keep our answer to the confines of high bypass ratio turbine driven engines.
The long definitive answer involves a great deal of physics, another subject we will not get to rhetorical about at this time. We will however consider Bernoulli’s principles concerning fluids and the airfoil or wing. This brings us to our first thought; consider the atmosphere, or air, around us as a fluid. Now that was simple enough.
When an airplane takes flight it must defeat its greatest foe, Newton’s contribution to this question, gravity. In its most simple terms, the ability to defeat gravity requires an opposing force that is greater than the weight of the mass being lifted. In aviation this comes from the lift created, of course, by the wings.
To help make this possible on airplanes the wings are shaped with a leading edge, that is the part that first hits the air, then a highly rounded upper surface, known as camber, and much flatter lower surface which come together at the trailing edge. (Just a moment more, I’m getting to your answer.) Now we apply Bernoulli’s principal.
Looking at air as a fluid, in principle Bernoulli’s theory is this. The air traveling over the top of the wing is moving at a faster speed than the air traveling under the wing. In theory, this would cause greater pressure under the wing (lift) and less pressure over the wing as the air is rushing from the leading edge to the trailing edge. The reasoning here is that when the air molecules are separated by the leading edge of the wing, the molecules passing over the top, which has a longer surface due to the added camber, must move faster in order to reach the trailing edge at the same moment as the air passing below the wing. Now we get to the part concerning thicker (heavier) air mass and thinner (lighter) air mass and the effects on “liftâ€Â.
In order to for the wings to produce the lift needed to defeat gravity you must have thrust and lots of it! Now we enter into the power (engines) production that is required to create flight. As we all know, an airplane must be moving into the air mass in order to obtain the effects required to produce flight also known as the lighter than air effect. So in principle, the shortened version, the air passing over and under the wings must produce a lift equivalency greater than the weight of the aircraft. There is a formula but we’ll skip that here and just state this, the airmass flowing around the wings must be equal to or greater than the mass of the airplane. There, we have flight... well sort of.
You see the weight of air at sea level is much greater than the air at say 30,000 feet. Here again, in principle, the amount of air flowing across the wing on takeoff, by mass, is more at mean sea level than it would be at 5,000 feet. Since this is a principle of mass verses mass (in this case in order to defeat the effects of gravity), the fluid principles of Bernoulli’s would apply well here. So what are the effects on engine performance?
Modern power plants today are engineered to direct less airflow through the engine or turbine section of the power plant. The ratios have changed dramatically in the last decade with most engines diverting 80% or more of the air flow around the core and exiting as additional thrust at the tail. These engines, as one could imagine, consume extreme amounts of air as it flows through and around the core, or power unit, and exits the tail as super heated energy and thrust. To maintain this thrust the amount of air mass must remain fairly constant. So, how is this accomplished at 38,000 feet? And what about the thinner air passing over the airfoils?
Well, here is where physics and the dynamics of air mass come into play but in a much simpler way than you might expect. Remember the role that the wing plays in all of this? Air pressures above and below the wings can still be easily maintained at higher altitudes. Why? Because of the much greater amount of air passing over the wing surfaces at speeds often over 500 mph. You see, it’s the air molecules that hold the secret to air mass and density. At speeds like this the air density is super compressed to allow far more lift than needed to maintain flight. Then there is the engine question.
Since air is composed of gasses (mainly nitrogen with about 20% oxygen and other gasses mixed in) at the molecular level, they too can be “squeezed†under tremendous pressure and therefore compressed to create an even mixture through a jet engine. This ability to compress huge amounts of air while flying at high altitudes again makes up for loss of mass and density. Since the engine is moving between 500 and 600 mph, the intake or ingesting of plenty of air through the core and surround is no problem.
The added bonus is this; thin air creates less friction on the aircraft and much cooler air temperatures (normally around -60 degrees) as the air flows through the engine. There is also a slight reduction in fuel cost flying at these higher altitudes as we normally reduce our throttles 10 to 20 percent while at cruising altitude. This of course is dependent on the aircraft type and any head or tail wind!
answered 8 mins ago
Joe
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This is a good question but first we must clarify something.
There is a major difference between propeller driven aircraft and pass through turbine propelled aircraft. Without getting to technical in this explanation, let’s leave propeller driven aircraft alone for the moment and keep our answer to the confines of high bypass ratio turbine driven engines.
The long definitive answer involves a great deal of physics, another subject we will not get to rhetorical about at this time. We will however consider Bernoulli’s principles concerning fluids and the airfoil or wing. This brings us to our first thought; consider the atmosphere, or air, around us as a fluid. Now that was simple enough.
When an airplane takes flight it must defeat its greatest foe, Newton’s contribution to this question, gravity. In its most simple terms, the ability to defeat gravity requires an opposing force that is greater than the weight of the mass being lifted. In aviation this comes from the lift created, of course, by the wings.
To help make this possible on airplanes the wings are shaped with a leading edge, that is the part that first hits the air, then a highly rounded upper surface, known as camber, and much flatter lower surface which come together at the trailing edge. (Just a moment more, I’m getting to your answer.) Now we apply Bernoulli’s principal.
Looking at air as a fluid, in principle Bernoulli’s theory is this. The air traveling over the top of the wing is moving at a faster speed than the air traveling under the wing. In theory, this would cause greater pressure under the wing (lift) and less pressure over the wing as the air is rushing from the leading edge to the trailing edge. The reasoning here is that when the air molecules are separated by the leading edge of the wing, the molecules passing over the top, which has a longer surface due to the added camber, must move faster in order to reach the trailing edge at the same moment as the air passing below the wing. Now we get to the part concerning thicker (heavier) air mass and thinner (lighter) air mass and the effects on “liftâ€Â.
In order to for the wings to produce the lift needed to defeat gravity you must have thrust and lots of it! Now we enter into the power (engines) production that is required to create flight. As we all know, an airplane must be moving into the air mass in order to obtain the effects required to produce flight also known as the lighter than air effect. So in principle, the shortened version, the air passing over and under the wings must produce a lift equivalency greater than the weight of the aircraft. There is a formula but we’ll skip that here and just state this, the airmass flowing around the wings must be equal to or greater than the mass of the airplane. There, we have flight... well sort of.
You see the weight of air at sea level is much greater than the air at say 30,000 feet. Here again, in principle, the amount of air flowing across the wing on takeoff, by mass, is more at mean sea level than it would be at 5,000 feet. Since this is a principle of mass verses mass (in this case in order to defeat the effects of gravity), the fluid principles of Bernoulli’s would apply well here. So what are the effects on engine performance?
Modern power plants today are engineered to direct less airflow through the engine or turbine section of the power plant. The ratios have changed dramatically in the last decade with most engines diverting 80% or more of the air flow around the core and exiting as additional thrust at the tail. These engines, as one could imagine, consume extreme amounts of air as it flows through and around the core, or power unit, and exits the tail as super heated energy and thrust. To maintain this thrust the amount of air mass must remain fairly constant. So, how is this accomplished at 38,000 feet? And what about the thinner air passing over the airfoils?
Well, here is where physics and the dynamics of air mass come into play but in a much simpler way than you might expect. Remember the role that the wing plays in all of this? Air pressures above and below the wings can still be easily maintained at higher altitudes. Why? Because of the much greater amount of air passing over the wing surfaces at speeds often over 500 mph. You see, it’s the air molecules that hold the secret to air mass and density. At speeds like this the air density is super compressed to allow far more lift than needed to maintain flight. Then there is the engine question.
Since air is composed of gasses (mainly nitrogen with about 20% oxygen and other gasses mixed in) at the molecular level, they too can be “squeezed†under tremendous pressure and therefore compressed to create an even mixture through a jet engine. This ability to compress huge amounts of air while flying at high altitudes again makes up for loss of mass and density. Since the engine is moving between 500 and 600 mph, the intake or ingesting of plenty of air through the core and surround is no problem.
The added bonus is this; thin air creates less friction on the aircraft and much cooler air temperatures (normally around -60 degrees) as the air flows through the engine. There is also a slight reduction in fuel cost flying at these higher altitudes as we normally reduce our throttles 10 to 20 percent while at cruising altitude. This of course is dependent on the aircraft type and any head or tail wind!
answered 8 mins ago
Joe
1
New contributor
Joe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
This is a good question but first we must clarify something.
There is a major difference between propeller driven aircraft and pass through turbine propelled aircraft. Without getting to technical in this explanation, let’s leave propeller driven aircraft alone for the moment and keep our answer to the confines of high bypass ratio turbine driven engines.
The long definitive answer involves a great deal of physics, another subject we will not get to rhetorical about at this time. We will however consider Bernoulli’s principles concerning fluids and the airfoil or wing. This brings us to our first thought; consider the atmosphere, or air, around us as a fluid. Now that was simple enough.
When an airplane takes flight it must defeat its greatest foe, Newton’s contribution to this question, gravity. In its most simple terms, the ability to defeat gravity requires an opposing force that is greater than the weight of the mass being lifted. In aviation this comes from the lift created, of course, by the wings.
To help make this possible on airplanes the wings are shaped with a leading edge, that is the part that first hits the air, then a highly rounded upper surface, known as camber, and much flatter lower surface which come together at the trailing edge. (Just a moment more, I’m getting to your answer.) Now we apply Bernoulli’s principal.
Looking at air as a fluid, in principle Bernoulli’s theory is this. The air traveling over the top of the wing is moving at a faster speed than the air traveling under the wing. In theory, this would cause greater pressure under the wing (lift) and less pressure over the wing as the air is rushing from the leading edge to the trailing edge. The reasoning here is that when the air molecules are separated by the leading edge of the wing, the molecules passing over the top, which has a longer surface due to the added camber, must move faster in order to reach the trailing edge at the same moment as the air passing below the wing. Now we get to the part concerning thicker (heavier) air mass and thinner (lighter) air mass and the effects on “liftâ€Â.
In order to for the wings to produce the lift needed to defeat gravity you must have thrust and lots of it! Now we enter into the power (engines) production that is required to create flight. As we all know, an airplane must be moving into the air mass in order to obtain the effects required to produce flight also known as the lighter than air effect. So in principle, the shortened version, the air passing over and under the wings must produce a lift equivalency greater than the weight of the aircraft. There is a formula but we’ll skip that here and just state this, the airmass flowing around the wings must be equal to or greater than the mass of the airplane. There, we have flight... well sort of.
You see the weight of air at sea level is much greater than the air at say 30,000 feet. Here again, in principle, the amount of air flowing across the wing on takeoff, by mass, is more at mean sea level than it would be at 5,000 feet. Since this is a principle of mass verses mass (in this case in order to defeat the effects of gravity), the fluid principles of Bernoulli’s would apply well here. So what are the effects on engine performance?
Modern power plants today are engineered to direct less airflow through the engine or turbine section of the power plant. The ratios have changed dramatically in the last decade with most engines diverting 80% or more of the air flow around the core and exiting as additional thrust at the tail. These engines, as one could imagine, consume extreme amounts of air as it flows through and around the core, or power unit, and exits the tail as super heated energy and thrust. To maintain this thrust the amount of air mass must remain fairly constant. So, how is this accomplished at 38,000 feet? And what about the thinner air passing over the airfoils?
Well, here is where physics and the dynamics of air mass come into play but in a much simpler way than you might expect. Remember the role that the wing plays in all of this? Air pressures above and below the wings can still be easily maintained at higher altitudes. Why? Because of the much greater amount of air passing over the wing surfaces at speeds often over 500 mph. You see, it’s the air molecules that hold the secret to air mass and density. At speeds like this the air density is super compressed to allow far more lift than needed to maintain flight. Then there is the engine question.
Since air is composed of gasses (mainly nitrogen with about 20% oxygen and other gasses mixed in) at the molecular level, they too can be “squeezed†under tremendous pressure and therefore compressed to create an even mixture through a jet engine. This ability to compress huge amounts of air while flying at high altitudes again makes up for loss of mass and density. Since the engine is moving between 500 and 600 mph, the intake or ingesting of plenty of air through the core and surround is no problem.
The added bonus is this; thin air creates less friction on the aircraft and much cooler air temperatures (normally around -60 degrees) as the air flows through the engine. There is also a slight reduction in fuel cost flying at these higher altitudes as we normally reduce our throttles 10 to 20 percent while at cruising altitude. This of course is dependent on the aircraft type and any head or tail wind!
answered 8 mins ago
Joe
1
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answered 8 mins ago
Joe
1
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answered 8 mins ago
Joe
1
answered 8 mins ago
Joe
1
1
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New contributor
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Check out our Code of Conduct.
add a comment |Â
add a comment |Â
up vote
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Adding to the answer by Niels Nielsen, the special altitude changes (increases) during the flight as the power required reduces as the weight of the aircraft decreases due to fuel consumption. But these effects also depend on the type of propulsion (jet vs propeller). If you want to find out more about this. Search about power required and power available plots for aircraft.
answered 6 hours ago
Johann
1
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1
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
add a comment |Â
up vote
-2
down vote
Adding to the answer by Niels Nielsen, the special altitude changes (increases) during the flight as the power required reduces as the weight of the aircraft decreases due to fuel consumption. But these effects also depend on the type of propulsion (jet vs propeller). If you want to find out more about this. Search about power required and power available plots for aircraft.
answered 6 hours ago
Johann
1
New contributor
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
add a comment |Â
up vote
-2
down vote
up vote
-2
down vote
Adding to the answer by Niels Nielsen, the special altitude changes (increases) during the flight as the power required reduces as the weight of the aircraft decreases due to fuel consumption. But these effects also depend on the type of propulsion (jet vs propeller). If you want to find out more about this. Search about power required and power available plots for aircraft.
answered 6 hours ago
Johann
1
New contributor
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Adding to the answer by Niels Nielsen, the special altitude changes (increases) during the flight as the power required reduces as the weight of the aircraft decreases due to fuel consumption. But these effects also depend on the type of propulsion (jet vs propeller). If you want to find out more about this. Search about power required and power available plots for aircraft.
answered 6 hours ago
Johann
1
New contributor
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 6 hours ago
Johann
1
New contributor
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 6 hours ago
Johann
1
answered 6 hours ago
Johann
1
1
New contributor
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Johann is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
add a comment |Â
1
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
1
1
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
I see you cannot comment but if you improve your answer to show how maximize efficience for each type of engine I'm sure you wiull get enough upvotes to allow you to comment in the future
– jean
4 hours ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
– Ralph J
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
Adding on Ralph's comment: answers here should be self-contained. Adding and explaining one of these power required/available plots to your answer could achieve this.
– Sanchises
1 hour ago
add a comment |Â
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5
Less air molecules means less drag...
– Ron Beyer
15 hours ago
5
On what basis do the engines have to "work harder"?
– Greg Hewgill
15 hours ago
4
Flying at high altitude produces the same amount of drag, because you must fly faster in order to get enough lift power. BUT, it allows you to cover more ground miles with the same power setting in given amount of time, compared to what would you cover flying at low levels. Why? Because the air density is lower at altitude. There's also a significant temperature benefit for the engines. They run more efficient in low temperatures.
– Electric Pilot
14 hours ago
1
Related, maybe even a dupe?
– Pondlife
14 hours ago
Greg, I flew multi engine airplane and I've noticed that for every thousand feet my RPM indicators slightly decrease. I have to add more power to maintain the same airspeed. some times it get to the point where I'm at full power and I'm barely getting the normal cruise speed.
– Abdull
14 hours ago