I have been sitting in Vienna airport watching planes land and take off for the last few hours, and I can't help wondering about wing size.
I broadly understand the idea of air flow and the differences in pressure on the top and bottom sides of the wings, but I still would have thought that the surface area needed to be larger for many of these planes than it actually is - either in terms of span or depth.
Is it just pure force that makes it possible for such relatively small wings to lift such huge vessels into the air? Or is size of wing not that important? Is there some optimal ratio of size to weight?
They're all fitted with improbability drives obviously
the runway at Vienna airport is a giant conveyor belt 😉
Not sure I understand the question but yes, various forces have to be considered when designing a wing. Largely governed by the mass you want to lift and the thrust you have to play with.
...and just because some wise ass will say it, whether it's sat on a conveyor belt or not.
see. in before my half serious post even... 🙄
My best friend is a senior lecturer in aeronautical engineering at Glasgow University.
I've asked him broadly the same question and , according to him.....
"It's magic. We just throw in loads of long, complicated words and bullshit numbers and calculations to make it look all difficult and scientific so that we don't get burned as witches."
They would work if there were no wings at all. Because magic.
Straight from the horses mouth.
They're all going bloody fast too, until they land when they are merely going fast. Them the flaps are deployed to increase the area and chord angle, (if I remember the right term from basic aerodynamics lots of years ago).
edit - I much prefer Perchy's explanation though.
What about if the treadmill is going uphill?
Just re-reading; notice the flaps and slats that extend for landing and take off. They generate more lift at lower speed. Effectively making the wing bigger. Does that help?
I vaguely remember something about aerodynamic lift largely being rubbish, at least for things like fighter planes, as they are not designed to be stable and lifty and just use their wings as things that cut air at angle to make them go up.
Not really sure about big planes. I still think that they should not really be able to fly and, one day, people will realise that and they'll stop working.
flaps and slats
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[i]They would work if there were no wings at all. Because magic.
Straight from the horses mouth. [/I]
but is the horse running?
the flappy things help till they get to altitude then its all about drag reduction to save fuel.
Did some work for the guys at Thurleigh wind tunnel, and they were working on aerofoils for Airbus. They had some statistics on fuel saving and cost and investment that I can't remember but it was all very impressive.
but is the horse running?
Yep.
Backwards.
On a conveyor belt.
but is the horse running?
Patience...
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but is the horse running?
He is. But he's on a treadmill. So actually he isn't. Or is he?
[quote=willard ]I vaguely remember something about aerodynamic lift largely being rubbish, at least for things like fighter planes, as they are not designed to be stable and lifty and just use their wings as things that cut air at angle to make them go up.
Kind of. What you're referring to there is still aerodynamic lift, it's just not due to the shape of the wings and Bernoulli's principle, which is the usual lie we are told about how planes generate lift. Fundamentally all planes generate lift through Newton 3 - they deflect air downwards and this results in an upward force on the wings. Mostly this is due to angle of attack - ie having the front edge of the wing higher than the rear edge. Put your hand under a tap and deflect the water sideways and you're demonstrating exactly the same principle.
Fundamentally all planes generate lift through Newton 3 - they deflect air downwards and this results in an upward force on the wings
That's only half of it: air moves faster over the top part of the wing (it has to go further in the same time) which lowers the pressure compared to the lower part of the wing. This basically sucks the plane up.
So it's magic sucking that keeps the plane in the air.
Nope - the old schoolboy thing about planes being sucked up by the bernouilli principle is simplistic and incomplete/inaccurate I understand.
Otherwise
1) why do so many high performance planes [i]not [/i]have classic foil shaped wings?
2) How do planes fly upside down?
3) Why should packets of air going over the longer upper surface travel faster to keep up with those going under the wing in order to justify that explanation? (And they don't...)
see here https://en.wikipedia.org/wiki/Lift_(force)#Simplified_physical_explanations_of_lift_on_an_airfoil
ie what [b]aracer [/b] said plus a bit more
Yup, Bernoulli doesn't have much directly to do with aircraft lift - it's not a closed system for a start*. What aircraft wings are, basically, are a shape that has a positive angle of attack for the least amount of drag.
If it was all about Bernoulli, aircraft wouldn't be able to fly upside down.
(*the point of Bernoulli is, in a closed system like a pipe, the same number of atoms have to pass the same point in the same time. So they have to go faster and have fewer of them in a smaller pipe, so lower pressure)
Stick your hand out the window of a moving car. If you hit the right angle of attack (leading edge higher than trailing edge) you will feel a lifting sensation. If you're not going fast enough you won't generate any lift. When you do go faster the angle you need to hold will vary.
That basically demonstrates why airspeed is important and why you'd never take off on a treadmill (no airspeed).
Any plane could fly upside-down irrespective of wing shape if the pilot got the angle of attack right and kept up the speed. The passengers might get a bit nervous though. In normal flight it's the air being stretched over the top of the aerofoil shape that creates the suction that keeps the plane aloft. The lighter the plane, the shallower the angle of attack and the less fuel is used in pushing the plane along. A very fast plane doesn't need much aerofoil shape.
[quote=mogrim ]That's only half of it
Nope - it's the whole of it. Newton 3 would still apply even if Bernoulli's effect was important (it isn't, though it does contribute). Bernoulli's principle still results in air being deflected downwards.
The whole thing is way, way more complex even that in that wiki article (it is entitled "simplified"!) - I was simplifying before. I've done a bit of fluid dynamics and I know people who've done PhDs in it and it is a horrendously complex subject - I don't think even the people designing the wings completely understand it.
[quote=globalti ]In normal flight it's the air being stretched over the top of the aerofoil shape that creates the suction that keeps the plane aloft.
That's still a fallacy - even on "slow" planes with heavily shaped wings it's still effectively the angle of attack generating most of the lift.
Anyway, back to the OP - most people don't appreciate just how big the wings are on a typical plane. Not only the area, but also the volume. I did some work with tanker conversions of VC10s many years ago, and the batch I was involved with they didn't bother putting any extra tanks in the fuselage, that was largely empty space. The whole functional point of those aircraft was to lift the wings into the air - that being where all the fuel was stored. With the wings full of fuel there wasn't much margin to lift extra fuel in the fuselage so they decided it wasn't worth the extra trouble. I also remember people working inside the wing tanks.
That basically demonstrates why airspeed is important and why you'd never take off on a treadmill (no airspeed).
Except aircraft work by pushing against the air, ground speed doesn't matter, so an aircraft on a treadmill will take off completely normally, assuming the treadmill is as long as a runway.
What happens to the horse? If you put a treadmill on top of horse,will the treadmill take off?
That basically demonstrates why airspeed is important and why you'd never take off on a treadmill (no airspeed).Except aircraft work by pushing against the air, ground speed doesn't matter, so an aircraft on a treadmill will take off completely normally, assuming the treadmill is as long as a runway.
That's so wrong it's almost convincing.
Here we go...
..before this ends up being several dozen pages of why a plane will and won't take off on the treadmill, can someone define the actual question we're asking? It's critical to the answer:
A plane sat on a treadmill will take off in some circumstances.
Anything sat on a treadmill which miraculously can match the rotational speed of the wheels exactly, will not move by definition of the question. It's irrelevant what is attached to the wheel.
That's the trick 😀 Hat BenC
Except aircraft work by pushing against the air, ground speed doesn't matter, so an aircraft on a treadmill will take off completely normally, assuming the treadmill is as long as a runway.
That's so wrong it's almost convincing.
I read that as 'it's what the aircraft is doing relative to the air that matters, not what the ground is doing', which is correct.
Anything sat on a treadmill which miraculously can match the rotational speed of the wheels exactly, will not move by definition of the question. It's irrelevant what is attached to the wheel.
A treadmill which can do that will pretty quickly reach the speed of light.
Still no one cares about the horse 🙁
A treadmill which can do that will pretty quickly reach the speed of light.
I doubt it would be the speed of light as the thrust of all engines is finite. I agree, it would be ridiculously fast, ridiculously quickly but it's a hypothetical question with a hypothetical answer.
I read that as 'it's what the aircraft is doing relative to the air that matters, not what the ground is doing', which is correct.
Yup. If it has a magic treadmill which, basically, detects when the aircraft moves forwards and increases speed, then the treadmill will very rapidly speed up to the point where the wheel drag (usually naff all) matches the aircraft thrust - i.e. very fast indeed, shortly followed by the tyres exploding / bearings catching fire etc.
This horse?
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Still no one cares about the horse
WTLF?
(What's The Lifting Force?)
I doubt it would be the speed of light as the thrust of all engines is finite.
As long as the wheel friction is less than the thrust for any speed, then it'll reach the speed of light. So yes, it's a daft example in the real world - this is one of those puzzles where the answer depends exactly on how the question is phrased.
Yup. If it has a magic treadmill which, basically, detects when the aircraft moves forwards and increases speed, then the treadmill will very rapidly speed up to the point where the wheel drag (usually naff all) matches the aircraft thrust - i.e. very fast indeed, shortly followed by the tyres exploding / bearings catching fire etc.
Yep, I agree but that's bringing aspects of reality into a hypothetical, arguably silly question. Like I said, unless someone quotes the original version of the question that everyone misquotes, it's a pretty futile discussion. Pretty sure it contained all the usual hypothetical, university exam type assumptions, like; assume the earth is flat...etc.
As long as the wheel friction is less than the thrust for any speed, then it'll reach the speed of light.
hmmm, ok, I'll think about that a bit more...
damn it, I really need to finish this report. ...must ...close....browser...
And if you swap air for water, you end up with the tiny wings used on America's cup yachts which lift a few tonnes out of the water.
That's still a fallacy - even on "slow" planes with heavily shaped wings it's still effectively the angle of attack generating most of the lift.
Explain this then.
Anyway, back to the OP - most people don't appreciate just how big the wings are on a typical plane.
Similarly, it's difficult to really comprehend just how big runways are, so when you see planes out of the airport windows they don't look very big. Runways are massive; walking from one side to the other of a commercial runway takes a surprisingly long time.
Explain this then.
Seems it creates a similar air flow to that of a flat wing with a positive angle of attack?
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Explain this then.
That's the Magnus Effect, like with golf balls, the spinning ball or cylinder effectively creates a positive angle of attack by pushing air up at the front and down at the back.
