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AA7295
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Y1, 787, 777NG, 747-8 Engine Speed Increase

Fri Aug 03, 2007 10:29 pm

I was wondering if it would be possible to safely operate Y1, 787, 777NG and 747-8, however instead of having GEnx or RR Trents, they have a new form of engines that have a higher thrust which increase the speed to say Mach 1.1. Would this stress the fuselage? Would the aircraft need to have modifications to strengthen it so it could travel at these speeds?

I ask this because of all the marvels and technological breakthrough in the aviation world, the speed of commercial aircraft has really not exceeded 0.85 Mach.

Regards,
AA7295
 
JTR
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Fri Aug 03, 2007 10:36 pm

I know this is more of a technical question than a marketability question, but look at the examples of the Sonic Cruiser and Concorde. Sure, Boeing and Airbus have the engineering ability to design and build an SST, but who would buy it? The Sonic Cruiser didn't take off due in large part because airlines wanted a more efficient jet rather than a faster one.

I think the place we'll see supersonic civilian jets in the private jet market (isn't Suhkoi making one?) because when you have enough money to burn buying a jet, you can probably afford a lot of jet A.
 
katekebo
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Fri Aug 03, 2007 10:58 pm

Simple answer - no, it's not possible. Going through the sound barrier requires a huge increase in thrust/power, and imposes very significant stress on the airframe. It is technically not possible without a major redesign of the airframe and aerodynamic profile of the wing, and it would be hopelessly uneconomic.

A short physics briefing. When an object tries to go faster than speed of sound (Mach 1), the flow properties of air change dramatically. Below speed of sound, air is a compressible fluid. When you reach the speed of sound, air starts to behave like an incompressible fluid (more like a liquid, instead of a gas). Can you notice the difference between the resistance of moving your hand across air vs. moving it in the water? This gives you an idea of what it takes to move an object through a compressible and incompressible fluid. Although it's a great simplification, it kind of gives a rough idea of what it takes to "break the sound barrier".
 
BigAppleCoder
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Fri Aug 03, 2007 11:12 pm

Quoting Katekebo (Reply 2):
Simple answer - no, it's not possible

It's not safely possible. All aircraft have a maximum operating speed known as Vne. While you can exceed it (e.g. in a high-speed dive) it will lead to catastrophic structural failure resulting in loss of the airframe and all souls on board.
 
tdscanuck
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Fri Aug 03, 2007 11:32 pm

Quoting AA7295 (Thread starter):
I was wondering if it would be possible to safely operate Y1, 787, 777NG and 747-8, however instead of having GEnx or RR Trents, they have a new form of engines that have a higher thrust which increase the speed to say Mach 1.1.

Not possible. Katekebo is dead on with the increase in structural loads that come with going supersonic. In addition to that, supersonic aerodynamics are significantly different than subsonic. You'd have to change the wing, all of the control surfaces, and the FBW system.

For all intents and purposes, it would take a new airplane.

The engine is probably the least difficult part of that particular problem since almost all current supersonic jets operate the engines in subsonic airflow anyway.

Quoting AA7295 (Thread starter):
I ask this because of all the marvels and technological breakthrough in the aviation world, the speed of commercial aircraft has really not exceeded 0.85 Mach.

It's just not economical to go faster than that. Passengers are willing to pay a (small) premium for increased speed and you significantly improve utilization as you speed up but the cost takes off like a rocket as you go above about 0.85-0.87 Mach and the business case goes out the window.

Tom.
 
SailorOrion
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Fri Aug 03, 2007 11:41 pm

Quoting Katekebo (Reply 2):
A short physics briefing. When an object tries to go faster than speed of sound (Mach 1), the flow properties of air change dramatically. Below speed of sound, air is a compressible fluid. When you reach the speed of sound, air starts to behave like an incompressible fluid

 redflag 

Air (or any fluid for that matter) behaves like an incompressible fluid as Mach Numbers below around 0.3 or 0.2. At supersonic speeds, there's nothing even remotely incompressible about the flow. The difference you are describing is the difference is viscosity between air and water, which has nothing to do with incompressibility. Simply speaking, viscosity is a property of the fluid (depending on variables like temperature), while compressibility is a property of the flow configuration. Incompressibility basically means that the density is constant ALONG THE STREAMLINES, nothing more, nothing less.

On the topic, going supersonic is not only a question of engines. First of all, the airframe needs to be totally different in shape. While in subsonic flows it is advantageous to have rounded leading edges (see the nose of commercial airlines and the profile of wings), supersonic profiles and fuselages should have sharp leading edges.

Secondly, when approaching the sound barrier, drag increases dramatically (starting at a given Mach Number that depends mostly on the sweep, forward or backward, of the wing). After the sound barrier, drag will reduce gradually to Mach Number of something like 1.4 to 1.6 until it increases again.

Thirdly, jet engines become inherently less efficient with increased airspeed (measured in change of momentum vs. mass of propellant) as opposed to rocket engines which maintain their propulse efficiency. Simply speaking, the specific impulse (read: http://en.wikipedia.org/wiki/Specific_impulse , it's a decent page) drops with velocity.

Technologically speaking, the greatest challenge of going supersonic is the sonic boom. You'll need to design an aircraft whose sonic boom in cruise does not reach the ground, otherwise you'll be restricted to supersonic flight over open water. This is one of the points (besides the extraordinary maintenance cost) which basically killed the Concorde: It could basically only be used for a very very limited choice of routes.

SailorOrion
 
futurecaptain
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sat Aug 04, 2007 1:26 am

Quoting AA7295 (Thread starter):
new form of engines that have a higher thrust which increase the speed to say Mach 1.1.



Quoting AA7295 (Thread starter):
the speed of commercial aircraft has really not exceeded 0.85 Mach.

It's not just a matter of bumping up the cruise speed a few tenths of a mach. As you reach Mach 1 and for awhile after that drag increases dramatically. To really have an efficient plane you need to nearly double the cruise speed to around mach 1.5-1.7. Such an increase requires alot of re-working of the aircraft.
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sat Aug 04, 2007 2:15 am

Quote:
A large loss in propulsive energy due to the formation of shocks causes wave drag. Up to a free-stream Mach number of about 0.7 to 0.8, compressibility effects have only minor effects on the flow pattern and drag. The flow is subsonic everywhere.

As the flow must speed up as it proceeds about the airfoil, the local Mach number at the airfoil surface will be higher than the free-stream Mach number. There eventually occurs a freestream Mach number called the critical Mach number at which a sonic point appears somewhere on the airfoil surface, usually near the point of maximum thickness and indicates that the flow at that point has reached Mach 1.

As the free-stream Mach number is increased beyond the critical Mach number and closer to Mach 1, larger and larger regions of supersonic flow appear on the airfoil surface. In order for this supersonic flow to return to subsonic flow, it must pass through a shock or what is considered to be pressure discontinuity.

This loss of velocity is accompanied by an increase in temperature, that is, a production of heat. This heat represents an expenditure of propulsive energy which may be presented as wave drag. These shocks appear anywhere on the airplane including wings, fuselage, engine, etc. where, due to curvature and thickness, the localized Mach number exceeds 1.0 and the airflow must decelerate below the speed of sound.

For transonic flow the wave drag increase is greater than would be estimated from a loss of energy through the shock. In fact, the shock wave interacts with the boundary layer so that a separation of the boundary layer occurs immediately behind the shock. This condition accounts for a large increase in drag which is known as shock-induced (boundary-layer) separation.

The free-stream Mach number at which the drag coefficient of the airplane increases markedly is called the drag-divergence Mach number. Large increases in thrust are required to produce any further increases in airplane speed. If an airplane has an engine of insufficient thrust, its speed will be limited by the drag-divergence Mach number.

From: http://www.suite101.com/lesson.cfm/17507/821/3

There are a couple of high subsonic A/C - The Citation X (M.92) and the Convair 990 (M.89) are two civilian examples.
 
dl767captain
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sat Aug 04, 2007 2:17 am

i could see the return of sonic cruisers when we have an alternative fuel that is very cheap and all the airlines are paying for are the companies that supply the hydrogen to the plane (hydrogen works great for cars and that is where i believe it is going, for planes i have no idea but this is just and idea that might or might not work) hydrogen is so simple and cheap to make and therefore cheap to buy. if airlines had a cheap fuel that didn't damage the environment and basically gave off water as the byproduct (the thing that hydrogen is made of) then we would see the return of the sonic cruiser because airlines would have money again and the plane would be economically and environmentally friendly
 
SailorOrion
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sat Aug 04, 2007 2:20 am

I don't see how a fuel that needs to be stored at 20.28K (-253°C or -423F) is "simple". It also has a much lower volumetric energy content than kerosene (about one third).

Hydrogen is not made of water. A water molecule is made up from two hydrogen atoms and one oxygen atom.

SailorOrion
 
prebennorholm
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sat Aug 04, 2007 6:54 am

Quoting DL767captain (Reply 8):
...hydrogen is so simple and cheap to make and therefore cheap to buy. if airlines had a cheap fuel that didn't damage the environment and basically gave off water as the byproduct (the thing that hydrogen is made of) then we would see the return of the sonic cruiser because airlines would have money again and the plane would be economically and environmentally friendly

Hydrogen is not an energy source. It is an energy accumulator. It is like a rechargeable battery. You spend energy on producing hydrogen, then get some of that energy back when you burn the hydrogen. Just like charging and discharging an electric battery, only not nearly as heavy.

If we produce hydrogen from a coal fired powerplant, then I wouldn't call it "environmentally friendly" at all. We can of course use a natural gas fired powerplant instead, or hydro powerplant, nuclear powerplant. Hydro powerplants spoil the nature, and some people don't fancy nuke plants very much either. Natural gas is already in short supply.

Therefore telling that the byproduct from burning hydrogen is water, that's simply false. The byproducts are CO2, spoiled nature, nuke waste etc. It doesn't even PRODUCE water as byproduct, it just gives back the same quantity of water as was spent to produce it. Or in fact a little less, because storing liquid hydrogen at 20 deg. K we will always need a boil off pressure valve (like on the top of the Shuttle tank) which will release hydrogen to the atmosphere. Where it will rise to the outer regions of the atmosphere and be blown away from planet Earth by the solar wind.

Hydrogen cheap? We could ask NASA next time they fill the Shuttle.
Always keep your number of landings equal to your number of take-offs
 
SailorOrion
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sat Aug 04, 2007 3:14 pm

Quoting Prebennorholm (Reply 10):
Hydrogen cheap? We could ask NASA next time they fill the Shuttle.

Sorry, but the fuel and the oxidizer only make a microscopic fraction of the Shuttle's operating cost  Smile

SailorOrion
 
brons2
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Sun Aug 05, 2007 12:26 am

I often tell people that Hydrogen is the Big Lie. It will never be a commercially sustainable fuel source for cars or airplanes.
Firings, if well done, are good for employee morale.
 
CoolGuy
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 2:11 am

I wonder what the maximum possible speed is for any of the airplanes mentioned in the title. For instance, what would happen if, at cruising altitude, an aircraft increased N1 to the maximum. I remember hearing that a commercial airliner excluding the SST aircraft once went faster than mach 1 for a very brief period (and I'm pretty sure it was a non-rev flight!). Anyone know?

Also, I keep hearing Airbus brag about it's flight envelope system, but would that also keep the aircraft below Vne?

[Edited 2007-08-08 19:12:44]
 
tdscanuck
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 3:02 am

Quoting CoolGuy (Reply 13):
For instance, what would happen if, at cruising altitude, an aircraft increased N1 to the maximum. I remember hearing that a commercial airliner excluding the SST aircraft once went faster than mach 1 for a very brief period (and I'm pretty sure it was a non-rev flight!). Anyone know?

There's another thread on this right now (it was a DC-8): Largest Narrow Body (by Ssflyboy25 Jul 23 2007 in Civil Aviation)

If you just firewalled the throttles, eventually something would break (probably the wing) and the rest of the aircraft would come apart shortly thereafter.

Quoting CoolGuy (Reply 13):
Also, I keep hearing Airbus brag about it's flight envelope system, but would that also keep the aircraft below Vne?

Yes. If you're at cruise in an Airbus you can push the throttle to the firewall (or pull it to idle) and nothing will happen to the engines. If you got going too fast it would throttle back the engines and pitch up (not sure in what order) to keep the speed down.

Tom.
 
CoolGuy
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 4:56 am

Quoting Tdscanuck (Reply 14):
Yes. If you're at cruise in an Airbus you can push the throttle to the firewall (or pull it to idle) and nothing will happen to the engines. If you got going too fast it would throttle back the engines and pitch up (not sure in what order) to keep the speed down.

Well that's convenient. It seems like you can't make any mistakes on an Airbus at cruising altitude. (Sounds like an old college class, where you had to really try hard in order to fail.) Airbus says that the reason it shows off its aircraft at airshows is because of the aircraft's controlled limits, but I have a feeling that it's still risky at airshows with or without the aid of a computer.

Quoting Tdscanuck (Reply 14):
If you just firewalled the throttles, eventually something would break (probably the wing) and the rest of the aircraft would come apart shortly thereafter.

Would it really do so? I wonder if it could really exceed Vne by that much, maybe just by 0.02M.
 
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Starlionblue
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 5:31 am

Quoting CoolGuy (Reply 13):
I wonder what the maximum possible speed is for any of the airplanes mentioned in the title. For instance, what would happen if, at cruising altitude, an aircraft increased N1 to the maximum. I remember hearing that a commercial airliner excluding the SST aircraft once went faster than mach 1 for a very brief period (and I'm pretty sure it was a non-rev flight!). Anyone know?

As mentioned, it was a DC-8.

Quoting CoolGuy (Reply 13):
Also, I keep hearing Airbus brag about it's flight envelope system, but would that also keep the aircraft below Vne?

Yes.

Quoting CoolGuy (Reply 15):

Well that's convenient. It seems like you can't make any mistakes on an Airbus at cruising altitude. (Sounds like an old college class, where you had to really try hard in order to fail.) Airbus says that the reason it shows off its aircraft at airshows is because of the aircraft's controlled limits, but I have a feeling that it's still risky at airshows with or without the aid of a computer.

Of course you can make mistakes. Even the safest aircraft can be crashed by a determined pilot.

flying at airshows is by and large only risky if you do it wrong. Case in point being the Mulhouse crash, where a determined pilot managed to crash a 320 despite all that fancy envelope protection.

Quoting CoolGuy (Reply 15):
Quoting Tdscanuck (Reply 14):
If you just firewalled the throttles, eventually something would break (probably the wing) and the rest of the aircraft would come apart shortly thereafter.

Would it really do so? I wonder if it could really exceed Vne by that much, maybe just by 0.02M.

0.02M is probably way within limits. But as mentioned something would break eventually. I think flaps, slats and other surfaces would start ripping off first.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 6:05 am

Quoting CoolGuy (Reply 15):
Airbus says that the reason it shows off its aircraft at airshows is because of the aircraft's controlled limits, but I have a feeling that it's still risky at airshows with or without the aid of a computer.

It's a little more nuanced than that. Airbus can fly right to the edge of the envelope (max angle banks, etc.) without fear of losing control, which looks really impressive at an airshow. All of Boeing's planes are physically capable of the same thing but there isn't much protection against a pilot error. Boeing decided as a matter of policy that the risk of something going wrong, small though it might be, is too large compared to the publicity gain from flying demonstrations. Airbus's envelope protection provides some risk mitigation and they've decided it's worth the risk.

So yes, it's risky to fly at an airshow. The only way to have zero risk is not fly (the Boeing solution). Airbus has less risk of a pilot error during a flying demo leading to a catastrophe than Boeing does.

Tom.
 
SailorOrion
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 8:48 pm

Quoting Starlionblue (Reply 16):
flying at airshows is by and large only risky if you do it wrong. Case in point being the Mulhouse crash, where a determined pilot managed to crash a 320 despite all that fancy envelope protection.

Was that A320 in normal law at the time of the crash at all?

SailorOrion
 
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Starlionblue
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RE: Y1, 787, 777NG, 747-8 Engine Speed Increase

Thu Aug 09, 2007 11:05 pm

Quoting SailorOrion (Reply 18):
Quoting Starlionblue (Reply 16):
flying at airshows is by and large only risky if you do it wrong. Case in point being the Mulhouse crash, where a determined pilot managed to crash a 320 despite all that fancy envelope protection.

Was that A320 in normal law at the time of the crash at all?

I think so. However the point being that even envelope protection is limited by the laws of physics. Engines only spool up so fast and if the aircraft is slowing and descending reversing the trend takes a bit of time.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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