Linked Questions

23
votes
6answers
9k views

Why then don't aircraft fly even higher, for even greater efficiency? [duplicate]

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 ...
6
votes
3answers
4k views

How can flying high minimize drag and increase fuel efficiency? [duplicate]

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 to provide the same power at lower altitudes. But I always hear ...
6
votes
2answers
18k views

Why has the maximum service ceiling of Boeing and Airbus products remained about the same for 30 years? [duplicate]

When Boeing introduced the 747-100 in 1969, its maximum ceiling was 45,100 feet; half a century later, when Boeing introduced the 777x, its maximum ceiling was 43,100 feet. Similarly, the maximum ...
4
votes
0answers
6k views

Why do (jet) airplanes fly at tropopause (and not higher) [duplicate]

I've got a question which is nearly answered by the following thread however not fully to my satisfaction. Why do jet engines get better fuel efficiency at high altitudes? The question ultimately ...
1
vote
2answers
3k views

What is the typical cruising altitude for a civil airplane? [duplicate]

I'd like to know the interval of altitudes airliners usually cruise at (and its reasons)? And if there are international restrictions about this? Also I read somewhere that recently about a ...
0
votes
1answer
895 views

Why do planes fly so high? [duplicate]

It so occurs to me that commercial airliners cruise at altitudes of over 30,000 feet. But why do they fly so high if there are many dangers such as cabin de-pressurization when they can simply fly ...
1
vote
2answers
672 views

Would cone shapes grills in front of jet engines prevent damage in case of a bird strike? [duplicate]

If cone shaped grills pointing forward were in front of jet engines would they make bird parts slide outside towards the back of the engine and away?
2
votes
2answers
567 views

Could an airliner get better fuel efficiency at higher altitude? [duplicate]

By higher I mean like 60k feet instead of 30k. Seems like the rate limiting step is engine performance at 60k feet. Are people working engines that can operate at higher altitudes? How close are we ...
1
vote
0answers
225 views

Why airliners fly so high even when winds are more suitable at a lower altitude? [duplicate]

While playing a flight sim, I noticed West winds were very strong at levels >FL350 and weaker around FL270 above the US. I took a look at Flight Radar 24 to see at which level actual airliners were ...
1
vote
0answers
47 views

How is a design cruise altitude picked? [duplicate]

Different planes have different design cruise altitudes, given by the manufacturer. You can find these in their Airport Planning Manuals or in Jane's All the World's Aircraft. I know that the first ...
67
votes
10answers
85k views

Why do jet engines get better fuel efficiency at high altitudes?

I'm told that this is true, but I can't imagine why. It seems like the fact that there is less air would make the engines less efficient... But that probably just shows how little I know about jet ...
67
votes
5answers
37k views

What determines the maximum altitude a plane can reach?

What factors determine the maximum altitude for a plane? Is it limited by wing design, engine thrust, and so on? Is there a formula by which one can calculate the maximum altitude a plane can reach?
37
votes
4answers
17k views

Why do private jets such as Gulfstream fly higher than other civilian jets?

I heard in a TV show that private jets such as Gulfstream can fly at about 50,000 ft, higher than other civil jets. Is it an aerodynamic reason (lighter aircraft to be sustained in a less dense air) ...
67
votes
3answers
14k views

Are we at peak speed efficiency for jet airliners at Mach 0.85?

The cruising speed of large jet airliners has not increased in the past four decades. The 747 cruised at Mach 0.85 and the new Dreamliner 787 also cruises at Mach 0.85 even though it was designed 40 ...
24
votes
4answers
5k views

Why are heavy flaps better than just a bigger wing?

Flaps increase lift during landing and T/O. But when retracted, they do nothing. The space needed to stow the common fowler flaps can't be used for anything else - fuel or structure. Extended flaps ...
34
votes
7answers
8k views

Why are jet aircraft never designed with a slower cruise speed?

All jet airliners have a cruise speed between Mach 0.82 and Mach 0.85. At those speeds the aircraft are flying at their maximum subsonic speed. Any greater cruise speed would only be ...
31
votes
4answers
19k views

How does wind affect the airspeed that I should fly for maximum range in an airplane?

I have heard that wind affects the actual airspeed that I should fly for maximum range in an aircraft. I understand that wind will not affect the airspeed that I should fly if I am looking for ...
17
votes
3answers
5k views

Can high-bypass turbofans cruise at high altitude?

They have talked for years about re-engining the B-52 with something more modern than its TF33-P-3/JT3D turbofans, which are fairly low-bypass (1.42:1 for the JT3D). Modern engines are much higher ...
15
votes
3answers
6k views

What are the limiting factors for high altitude planes (e.g: U2 or SR71) preventing them from going higher?

I'm curious as to why planes like the U2 Dragon Lady and the SR71 Blackbird couldn't fly higher. What physical constraint set their operational ceiling? Pilots wore spacesuits, so that wasn't the ...
10
votes
2answers
7k views

What is Tropopause height, and how is it determined?

I have seen the term "Tropopause height" used in a flight navigation plan. What is it and how is it determined?
3
votes
2answers
4k views

why are regional cruising altitudes higher than those of international much longer flights?

How come, for example, the average cruising altitude of let's say the Westjet Boeing 737-600 from CYWG to CYVR flies at an altitude of 38,000 feet-40,000 feet, yet the Air Transat Airbus 330-200 ...
14
votes
3answers
3k views

Why were the windows on the Concorde about the size of a hand?

I just saw a comparison between the 787 and Concorde windows. I could be wrong but it almost seems like a hand could cover the majority of the window.
9
votes
2answers
2k views

What is the one-engine-inoperative maximum range flight configuration?

I was talking with a friend about what things would happen if you experienced engine problems in cruise. We were wondering the following: What things would need to be changed to arrive in the optimal ...
9
votes
1answer
4k views

What engine power setting is used during cruise?

I am trying to work out what engine power setting is used during the cruise phase of commercial flights but I can't find anything about it in the usual spots. Anyone have any idea what percent of ...
7
votes
1answer
1k views

Based on this fuel flow chart, why isn't it more optimum to remain at an intermediate altitude rather than climbing?

I am having a bit of confusing as to why people say planes gets more efficient as they fly higher. Because on a typical long haul flight the Fuel Flow of the aircraft will obviously be much more that ...
7
votes
2answers
796 views

What should be the minimum time spent in cruise (for e.g. a B737)?

Having a short sector to fly, it would not be convenient to climb all the way up to the best cruise altitude, since the time in climb would burn more fuel than that necessary for a flight at lower ...
3
votes
2answers
165 views

Optimizing the airplane for best cruising altitude and velocity

In the conceptual phase of the design, I am optimizing various entities of an airplane for the best cruising altitude and speed to reduce the cost, which also includes MTOW and fuel weight. Consider a ...
0
votes
0answers
157 views

How turbofan engine efficiency increases over altitude or speed? [duplicate]

I am confused a lot about the efficiency and thrust relation with altitude and velocity of an aircraft. If thrust is related to air mass flow and velocity diffrence of bypassed air - exhaust gases ...
1
vote
1answer
92 views

Reduction in Service Ceiling / Change in RVSM

I did some research and minimum vertical separation used to be 2000ft but it changed to 1000ft in 2002 and they want to change it to 500ft on american territory. Is this correct? Why they wouldn't ...
0
votes
0answers
80 views

How do turbofan engines work efficiently at cruising altitude, when the air is thinner? [duplicate]

At FL350, for example, the air is considerably thinner than at ground level. How do jet engines efficiently provide thrust when considering fuel consumption for a certain throttle setting?