Boeing and Airbus fly new planes for first time Airbus and Boeing have both debuted new commercial jets. Boeing's 787-10 took to the skies over South Carolina last Friday and spent four hours and fifty eight minutes strutting its stuff. The 787-10 is the biggest variant of the 787, also known as the “Dreamliner”. The plane boasts the same 60m wingspan and 574cm cross- …
but then again they look just the same than nearly all commercial jets that came out before.
OK, they use new materials, engines and electronics, but basically all these passenger jets are direct descendants of the 707 and DC8 models of the late 50s.
Sure, jet design is expensive and no one wants to go for a disruptive design that might fail, but somehow this evolutionary approach is a bit boring.
The one that looks exactly like my last few coats, please ------------------>
Exactly what sort of 'disruptive design' are you wishing for, a flying wing?
Flying wings are not so practical for passenger jets. What I am wishing for is something that shortens the time I have to spend in a cramped space with bad air and smelly fellow passengers that share the same armrest. Cruise speed of the 707 was 977km/h. Cruise speed of the 787 is, well, erm, 903 km/h.
60 years of progress and we are moving slower than our grandfathers.
Edit: @AC, I agree with you. yes, there has been a lot of progress. Certainly in commercial point of view. affordable tickets are nothing to sneer at. On the other hand I feel optimisation was too one sided. No one is really pushing the limits. Certainly not the airline companies.
>Cruise speed of the 707 was 977km/h. Cruise speed of the 787 is, well, erm, 903 km/h.60 years of progress and we are moving slower than our grandfathers.
And how much fuel did the 707 burn per hour per passenger ? There was something that got you there faster but Concorde was extremely expensive and thirsty. There was also the Convair subsonic jet the CV 880 with a cruise speed of 990kph but that flunked because of the 707's slower but more efficient cruise speed.
Ye cannae change the laws of physics, an inescapable equation - K.E. = 1/2 m v2
There's a reason that the speeds havent increased much from what they are now - it's called the Transition Zone, the area between subsonic and supersonic (0,8-1,0 Mach, so about 960km/h and up) is highly unstable and really bad for your cruising efficiency. By staying out of this area you save a bunch of fuel. Going into the Supersonic regime unfortunately causes lots of problems with heat, even just going slightly above mach 1.0, means your unlikely to be able to use Alumnium for your Skins anymore (at least not leading edge). Not to mention the problems with sonic boom, and similar issues.
Supersonic solutions have been looked at in the time since Concorde - most famously Boeing did the study of the Sonic Crusier. But theyre investigations found that economically, the Airlines werent interested because passengers were not willing to pay the premium to save a couple of hours of flight.
On the topic of Composites, it will be the next generation of aircraft that benefit from the weight savings of using Composite structures. Aerospace certification authorities are extremely conservative. Because there was no long term data on Composite structures under flight loads (i.e. for the entire flight life of an aircraft), Designers had to use huge safety factors on the Composites meaning they weighed the same as the old metallic structures. Now that the data is there, the next Generation of aircraft will be able to use reduced design factors and so weight saving will start. You actually already see that to a degree on the A350, as Airbus was able to use the A400M as its Composite test bed. Maintenance of Composites has also been a problem which is another reason for building them extra strong and heavy, but now that Solutions are getting real world experience the additinal safety factors for this will be reduced.
Finally, the reason all aircraft look pretty much the same is that they are actually pretty much the optimum design for Subsonic flight. Delta's and flying wings might be more efficient at supersonic, but for subsonic its hard to achieve any real saving comapred to whats already in the air. So sorry, but dont expect any major design changes until someone works out how to make a supersonic aircraft thats as efficient as a subsonic aircraft and does something about the sonic boom problem...
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>That equation is irrelevant to the discussion at hand:
Oh yes it is, the faster you go you need to square your input energy even before you start to account for drag and gravity. Basic thermodynamics.
Where do you think that equation (D = CdρV2A/2) is derived from ?
Note the squared velocity term.
>as there is plenty of energy stored in the fuel tanks.
The more energy (i.e. mass) you have in the fuel tanks only makes matters worse as you have both an increased gravitational down force and energy required to reach your cruising speed.
Please don't throw equations around until you fully understand them.
Oh yes it is, the faster you go you need to square your input energy even before you start to account for drag and gravity. Basic thermodynamics.
Not a pilot, are you? Drag is everything.
Where do you think that equation (D = CdρV2A/2) is derived from ?
It's the drag equation - which you'd know if you understood aerodynamics in any meaningful fashion. And it doesn't come from anything to do with kinetic energy, as you'd know if you'd read the very first link Google gives for the aerodynamic drag equation.
The more energy (i.e. mass) you have in the fuel tanks only makes matters worse as you have both an increased gravitational down force and more energy required to reach your cruising speed.
That's important for a rocket. Not nearly so much for an aircraft
Please don't throw equations around until you fully understand them.
Far be it from me to accuse anyone here of hypocrisy, but seriously - you clearly don't fly, so you might want to give some credit to those that do...
Vic.
>Far be it from me to accuse anyone here of hypocrisy, but seriously - you clearly don't fly, so you might want to give some credit to those that do...
Vic.
No I'm a Chemist, thermodynamics is par for the course.
Ok Einstein, why does fuel consumption increase with payload ?
No I'm a Chemist, thermodynamics is par for the course.
But you're still going to argue subjects over which you have no knowledge. Is that also par for the course?
why does fuel consumption increase with payload ?
There are a number of factors, none of which are similar to the crap you've been touting so far.
The KE of a 787 at MTOW and at max cruising speed - a situation you'll never actually achieve - is less than 5.7GJ. With Jet A-1 quoted at a minimum of 42.8MJ/Kg, that's the energy of less than 133Kg of fuel - or less than 450Kg if you assume a 30% engine efficiency. The same 787 has a fuel capacity of over 101,000Kg - almost 3 orders of magnitude higher than the amount required to propel the aircraft to the KE that you claimed was the dominant factor in fuel use. So either Boeing are massively over-specifying their fuel needs, or - just perhaps, just putting this out there - you might be completely wrong when discussing topics you clearly know nothing about.
Vic.
> you might be completely wrong when discussing topics you clearly know nothing about.
Do you not understand simple physics ?
Double the 787-8's velocity assuming it doesn't fall apart.
Firstly normal cruising speed
Operating weight empty = 119,950kg, velocity (cruising speed of 903km/h) = 251m/s
KE = ((119,950)/2) * (250*250) = 3.78GJ
Double it
KE = ((119,950)/2) * (502*502) = 15.11GJ
for MTOW of 227,930 kg
KE = ((227,930)/2) * (251*251) = 7.18GJ
KE = ((227,930)/2) * (502*502) = 28.72GJ
I don't know where you get:
"The KE of a 787 at MTOW and at max cruising speed - a situation you'll never actually achieve - is less than 5.7GJ. "
Clearly bollocks.
Do you not understand simple physics ?
One of us doesn't.
Double itKE = ((119,950)/2) * (502*502) = 15.11GJ
Even if you could do that - which you can't - that's still a very, v ery long way short of the energy required for a flight. 101,000Kg of Jet A-1 at 42.8MJ/Kg is over 4.3TJ. Your maths is still three orders of magnitude out.
I don't know where you get:"The KE of a 787 at MTOW and at max cruising speed - a situation you'll never actually achieve - is less than 5.7GJ. "
Simple mathematics. MTOW of a 787 is between 228t and 254t, depending on variant. Max cruise speed is 511kt. Even you can work out the KE from those numbers.
Clearly bollocks.
And yet surprisingly close to your nominal figure of 3.78GJ. And both numbers are so very, very different from the 4.3TJ in the wings.
So now perhaps you'd like to address that discrepancy, rather than just throw around meaningless numbers? You've got three orders of magnitude to account for.
Vic.
>And yet surprisingly close to your nominal figure of 3.78GJ. And both numbers are so very, very different from the 4.3TJ in the wings.
Yes you are stupid, that's assuming no other opposing forces once you have attained said velocity but hey shall we throw in drag per second then add gravitational downforce per second. Note from the drag equation the squared velocity term, look familiar does it ? It's the opposing KE force applied to the equation.
You are quoting total available fuel energy, try realising all that energy at once, you'll have might big fucking bang. How many newtons thrust does your engines provide ?
By the way what is the difference between velocity and speed, a very important concept ?
>Simple mathematics. MTOW of a 787 is between 228t and 254t, depending on variant. Max cruise speed is 511kt. Even you can work out the KE from those numbers.
WTF ? I've already done it for you as proof.
Now stop bullshitting you know what you are talking about.
Yes you are stupid
Nice to see the standard of debate is so high.
that's assuming no other opposing forces once you have attained said velocity
And that's exactly the point. Drag is everything. All that energy in the tanks is there to overcome drag. Your KE figure is entirely irrelevant; it is somewhere around 0.1% of the energy required for the flight, which is why my initial post mentioned that it was irrelevant. Drag is everything - have I said that? Drag is everything. That's where al the energy goes, and that's why I mentioned the drag equation in my first post. You keep harping on about KE, and now even you seem to have realised that it is irrelevant.
hey shall we throw in drag per second then add gravitational downforce per second
Now you're just making stuff up. Look at the units of what you've just attempted to throw in the air, and it should be obvious even to you that that is nonsensical.
It's the opposing KE force applied to the equation.
No, it isn't. There is a square term in there - as there are many square terms in mathematics. But if it were related to the KE of the aircraft, it would have the mass of the aircraft in there as well. You might notice that it does not.
You are quoting total available fuel energy, try realising all that energy at once, you'll have might big fucking bang
And now you are confusing energy with power. I thought you were a chemist and thermodynamicist?
By the way what is the difference between velocity and speed, a very important concept ?
How is it relevant in this context? You're just throwing irrelevancies around now in the hope of having something stick. Your earlier posts were indicative ofd someone who'd not properly thought through what he was posting. Now you're just into nonsense territory.
WTF ? I've already done it for you as proof.
And yet you still haven't addressed how that energy is so much less than the energy required for flight. Even if we take your worst-case figure for an aircraft doing over 1000mph, you're still a rounding error in the energy required for flight. Yet you cling to this attitude that even 28GJ is somehow of any significance whatsoever to the flight; it simply isn't.
Now stop bullshitting you know what you are talking about.
Yeah, pot, kettle, ....
Vic.
>Drag is everything. All that energy in the tanks is there to overcome drag. Your KE figure is entirely irrelevant; it is somewhere around 0.1% of the energy required for the flight, which is why my initial post mentioned that it was irrelevant. Drag is everything - have I said that? Drag is everything.
WTF !
Seriously, stop digging you are making yourself a laughing stock.
>Erm, Vic is correct throughout. Drag eats your fuel, kinetic energy is no concern. Yours, a physicist. OK, ex-physicist. ----- totally me ---->
So what's drag ?
Erm the kinetic energy of the fluid/gas hitting you and multiplying it by a constant (drag coefficient) and the area of your object and using your velocity (i.e the resultant velocity, you could have a tailwind). Hence drag reduces your kinetic energy and thus velocity so you must increase the kinetic energy of your system by using the kinetic thrust of the engines to keep the system in equilibrium. They are opposing forces of the same equation. Drag is a squared function due to KE this only serves to make matters worse the faster you go. Simple frictional force in opposition to applied force QED the more kinetic energy you have the more drag you have. It's all a function of KE.
Are people just thick or obtuse on this subject ?
> Are people just thick or obtuse on this subject ?
Let me word this differently: the main part of the energy used through the whole flight (assuming it's not super short) is spend on the friction (which scales with abs(v)^2). The kinetic energy part is finished as soon as you have gained full speed, and that part is _small_ in quantity as Vic has indicated).
The situation is similar to doing a couple of hundred miles by car: go 80 km/h to use something near enough to optimal gas consumption, go 250 km/h and see how much that costs you. That's almost exclusively caused by friction.
If you are actually still puzzled at this point: why does an object flying in vacuum (in the absence of forces) keep constant speed? Hint: no friction.
Classical mechanics, about week two.
>The kinetic energy part is finished as soon as you have gained full speed,
You possess kinetic energy which is being dissipated by the opposing force of drag, if you didn't replace your kinetic energy by thrust you would slow down and crash or land. You are constantly being slowed down so you are actually constantly accelerating to maintain speed, i.e constantly changing velocity. Scalars and vectors.
Basic GCSE physics.
Newton's third law, for every action there is an equal and opposite reaction.
No, no, no.
> constantly accelerating to maintain speed,
Accelerating means _gaining_ speed, or, in other words
> i.e constantly changing velocity.
which is not happening when you just keep the velocity.
Here is another hint: Suppose the mass is vanishingly small, what does that change in friction? Answer: nothing.
In yet other words: if you split the work into the "acceleration to top speed" and "friction" parts. You'll see (do the bloody calculations!) that the acceleration part is very small for all reasonable masses.
If Vic's computation above is correct (and it looks like that) then even with mass = 0 you'd save about 1 per cent of the work. And that is even neglecting that inertia tends to give you back much of that (small) part at the decelerating phase.
I'll stop, so beer shall end this discussion. ---- Prost! ---->
> You are constantly being slowed down so you are actually constantly accelerating to maintain speed, i.e constantly changing velocity.
If you are maintaining speed (and direction) then you are _not_ accelerating at all (see definition).
What you are missing is that the plane's movement through the air is accelerating parts of that air in various directions, mostly downwards. The energy required to do this is opposed by the thrust of the engines.
> That's almost exclusively caused by friction.
In the case of a car, then yes, there is friction in the bearings, in the tires. But the main drag in a car moving fast is the result of pushing the air aside, accelerating it from stationary to some velocity, compressing it slightly at some points, and not being able to recover the energy expended in doing so.
> If you are actually still puzzled at this point: why does an object flying in vacuum (in the absence of forces) keep constant speed? Hint: no friction.
'Flying' in a vacuum is an oxymoron.
> Classical mechanics, about week two.
Classical, as in Aristotelian.
> Classical, as in Aristotelian.
Yes, everything you say is correct, thanks. I did my posts while tired.
Oh look, beer o'clock again!
----
Ok let me ask you three questions.
1) Switching engines off at T=0 will kinetic energy of the aircraft be equal to the force of gravity, drag and friction ?
2 ) What is the direction of your energy gradient as per the second law of thermodynamics ?
3 ) What will be the kinetic energy of an aircraft if it doubles it's speed ?
> Simple frictional force
Aerodynamic 'Drag' is not 'friction' (though there may be a small amount of actual friction*). Drag is the result of accelerating the air in various directions, mainly downwards (otherwise the plane would fall out of the sky). The force required to do this imparts an 'equal and opposite' force on the structure (see Newton).
* aerodynamic heating, especially in supersonic flight, is mainly not caused by 'friction', it is because compressing a gas, as happens at the leading edge, raises it temperature (see Gay-Lussac).
"Drag is the result of accelerating the air in various directions, mainly downwards (otherwise the plane would fall out of the sky)"
That's rubbish, it's the Venturi effect that keeps a plane up, whereby air moving quickly over the top of the wing exhibits less pressure than the slower air moving under the wing, thus sucking the plane upwards. Nothing to do with pushing air downwards (like a rocket)
0/10.
> That's rubbish, it's the Venturi effect that keeps a plane up, whereby air moving quickly over the top of the wing exhibits less pressure than the slower air moving under the wing, thus sucking the plane upwards. Nothing to do with pushing air downwards (like a rocket)
I can tell that you have never stood, or lay down, at the end of a runway.
> 0/10.
I am not sure whether that is a score you are giving to your post or a prediction of the up/down votes that you will get. Perhaps it is dual purpose.
> That's rubbish, it's the Venturi effect that keeps a plane up, whereby air moving quickly over the top of the wing exhibits less pressure than the slower air moving under the wing, thus sucking the plane upwards. Nothing to do with pushing air downwards (like a rocket)
Actually it has _everything_ to do with pushing air downwards. A plane's wing is an air pump that pushes air downwards. Without doing that it would fall from the sky (and sometimes that happens). It is just that the plane is flying along faster than the air is going down so it streams in a down wash behind the aircraft.
A helicopter rotor blade is exactly like a wing, except it moves through the air, pumping it downwards, without the fuselage needing to move forward. This can easily be seen in any photograph of a helicopter flying low over the sea, or over long grass or crops. An agricultural aircraft, flying low, causes the same effect on crops.
The amount and downward speed of the air that is required can be directly calculated from the mass of the aircraft and gravitational acceleration (ie the weight), just as it is calculated for a rocket exhaust, or the efflux from a VTOL aircraft.
Think of it this way. Normal air pressure over a particular area of land has a certain value (average is 14.7 lb per sq in or so at sea level). This is caused by the weight of all the air over that area. ie the column of air over 1 sq inch of ground from the ground up to space weighs around 14.7 lb (depending on weather, altitude of ground, etc). If a plane flies into the volume of air over a particular area (much more than 1 sq in) then the weight of that plane adds to the weight of all that air. This would increase the pressure at ground level over that area (granted by a small amount). The only way to increase the pressure between the aircraft and the ground over that area is for the plane to pump air from above it to below it.
A hovering helicopter close to the ground does this very well over quite a small area and the air pressure increase is easily measured (and is equal to the weight of the helicopter divided by the area covered by its downwash). A 747 does exactly the same except the area covered is very large and often well behind the current position of the plane, but at the end of a runway when it is landing it is _very_ noticeable.
The pressure distribution above, below and around the wing is part of the means of pumping the air downwards. Air at some distance above the wing 'falls' into the lower pressure caused by the alleged 'venturi effect' while the higher pressure created under the wing pushes air below that downwards.
Gravity applies a force of mass x 32 ft/sec/sec. The plane opposes that by accelerating air downwards, taking a particular mass of air in each second that is, in effect, stationary and accelerating it in a downwards direction (and also in unwanted lateral and rotational directions) until the mass of air in each second x acceleration applied matches the force of gravity pulling at the aircraft (more if it is climbing).
why does fuel consumption increase with payload ?
It has to do with the lift-to-draft ratio, doesn't it? The function of the wing is to generate lift from the air flow over it. The amount of lift you need is related to the weight of the airplane. Ultimately, that effort comes from the engines and fuel they consume.
(Not a rhetorical question, I'm curious if my understanding is even vaguely correct.)
The function of the wing is to generate lift from the air flow over it. The amount of lift you need is related to the weight of the airplane.
Yeah, mostly.
To achieve more lift for the same airspeed, you need to raise the nose slightly to increase the Angle of Attack. This gives you more lift at the cost of an increased drag coefficient Cd.
Vic.
What I am wishing for is something that shortens the time I have to spend in a cramped space with bad air and smelly fellow passengers that share the same armrest
Many people have said the same - but when the airlines tested that market, what they found is that people actually choose the cramped and smelly flight over the more expensive one that is both faster and more comfortable.
TL;DR: people choose the cheap flights, and that means cramped.
Vic.
"Flying wings are not so practical for passenger jets."
Apart from the lack of windows: From a comfort and space point of view they'd be pretty good.
The big problem with all flying wing designs is evacuation capabilities.
The A380's ~880 passenger loading is significantly smaller than its all-economy seating capabilities because of this. (But on the other side, carrying fewer people than that allows more revenue cargo in the belly which is also important for airlines)
Exactly what sort of 'disruptive design' are you wishing for, a flying wing?
Although that's not so much disruptive as an evolution of Concorde, but a delta wing will make a pleasingly distinct silhouette in the sky compared to other airliners.
Sure, jet design is expensive and no one wants to go for a disruptive design that might fail, but somehow this evolutionary approach is a bit boring.
The 787 family was intended to be disruptive, but hasn't been really. Carbon fibre, electric ancillary systems instead of air bleed, superior comfort; it all sounds disruptive, but it hasn't turned out that way. It's heavier than intended, the electrics have been problematic, and the comfort ain't that great (the airlines generally squeeze in an extra seat per row, and omit the optional sound deadening to save weight).
Don't get me wrong - 787 is now a pretty good aircraft, but it's not lived up to the initial billing. That's partly the fault of the airlines which jam in the extra seat and skip the optional sound deadening, and it's not the featherweight suggested by the chosen construction material.
It is more efficient, and a large part of that is the engines from RR and GE. It wouldn't be worth it otherwise. Putting those same engines on old airframes, one of the things Airbus is doing, is pretty efficient too and a lot cheaper.
Airbus is a good demonstration of 'disruptive'. By incorporating some very minor design differences they've gone from nothing to we'll over half the global market. The most important example is the A320 family vs 737. The only real difference is that the A320 is a bit wider, and has longer under carriage. From Airbus's point of view this is as disruptive as they've had to be to pinch most of the narrow body market from Boeing.
Anyway, if disruptive airliner design gets no more ambitious than that, it kinda suggests that the basic layout is already fairly optimal. It leads to cheaper maintenance (easy access to the engines), good fuel consumption (long/thin tubes are the easiest shape to push through the air), and it's cheap to make them different lengths to be able to sell an aircraft to suit the customer's needs.
Blended wings and other such ambitious designs are probably better technology from an aerodynamic point of view, but commercially they're very doubtful. A big part of the 'cost' of the A380 has been updating the airport facilities to deal with it; and that was simply adding another air bridge. A blended wing design sounds really difficult to get an air bridge up alongside it, so all that would have to change. Very expensive.
@AC:
Airbus certainly didn't go from "nothing", since it was formed as a consortium of assorted European manufacturers.
Other than A320 being a bit wider (not that much, mind you!) and having higher undercarriage, there is one vastly more important change: A320 allow automatic baggage handling (with load containers) as opposed to manual baggage handling on 737. In fact, what Boeing should do is revive the 757 and offer it at 737 cost level.
Yes, I am omitting what gets them from "revive the 757" and "offert it at 737 cost level", but ultimately, if Boeing offered a modern in A319-A321 variety of sizes (or slightly larger for the same capacity), they would have a winner. As Airbus gains foothold, servicing A320 family becomes as inexpensive as servicing 737, which makes Boeing's position untenable in the long run.
@lglethal: At cruise altitude (FL350, 35,000 ft. and up), speed of sound is ca. 1062-1063 km/h (compared to ca. 1225 km/h at sea level). 787's speed at cruise altitude is Mach 0.85 -- precisely in the transonic zone, which actually gives the most efficiency.
Going higher than the speed of sound creates a problem with heating up (air pressure can displace air particles only up to the speed of sound, so compression heating does not occur up to the speed of sound).
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