bigphilnyc
Topic Author
Posts: 3874
Joined: Sat Jan 19, 2002 10:43 pm

### How Do Planes Fly?

Like, I see them up, like, in the air.....and stuff.

But how?
Phil Derner Jr.

saintsman
Posts: 2037
Joined: Fri Mar 15, 2002 12:34 am

### RE: How Do Planes Fly?

Without getting too technical its mainly down to the air around us. Firstly you don't need an engine to fly an aeroplane (gliders etc the obvious examples) but you do need something to provide the means of staying in the air and that is an aerofoil. The aerofoil is either the wing of an aeroplane or the rotorblades of a helicopter and is designed to be a special shape. This shape, when moved through the air (and an engine helps here) causes the air to have a higher pressure under the surface of the wing and if you can get a sufficient pressure difference you will generate enough force, which we call lift, to overcome the weight of the aircraft and allow it to fly.

If there is a difference of several pounds per square inch (PSI) between top and bottom of the wing and you add up all those pounds that would be produced over the whole surface it then becomes apparent as to why an aircraft weighing hundreds or tonnes can fly.

There are a couple of examples of how lift is produced. If you get hold of a piece of paper, hold it on the top two edges placed next to you mouth and gently blow down over the top surface you will see that the paper will start to move up. Another example is when you get an open door slam in your face when another door is opened and the wind blows through the house. That rush of air blowing past the door has a lower pressure than the air behind the door. This difference in pressure forces the door to move and enough force exists for the door to move fast and slam. if there is that much force generated on a door you can imagine how much force can be generated by a highly designed wing.

I hope that this gives you an idea and if you still want more info there are loads of guys on this site will be able to supply info in as great a detail that you could possibly need.

bigphilnyc
Topic Author
Posts: 3874
Joined: Sat Jan 19, 2002 10:43 pm

### RE: How Do Planes Fly?

So then, like, why do birds flap?

And also, you spelled it wrong, it's "airplane", not "aeroplane".

Phil Derner Jr.

ben88
Posts: 1037
Joined: Fri Dec 31, 1999 4:49 pm

### RE: How Do Planes Fly?

btw time to find a new career, you're not very funny.

bigphilnyc
Topic Author
Posts: 3874
Joined: Sat Jan 19, 2002 10:43 pm

### RE: How Do Planes Fly?

I as goofing a bit, but I really did want an in=dpt answer, like Saintsman gave.

Thank you Saintsman.

Phil Derner Jr.

PPGMD
Posts: 2398
Joined: Sun Sep 30, 2001 5:39 am

### RE: How Do Planes Fly?

Airspeed and money, that is how airplanes fly.

Filler Filler Filler
At worst, you screw up and die.

Ralgha
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

### RE: How Do Planes Fly?

Airplane and aeroplane are both correct spellings depending on what type of English you are writing.

How a bird flies is quite complicated, but a bird's wing is much the same as an airplane's wing. The same principles of pressure apply. The difference is that a bird can flap it's wings to produce lift when standing still and an airplane must rely on airspeed to generate lift.

When a bird flaps its wings, it doesn't just move them straight up and down. In addition to moving the whole wing up or down, the bird will also twist the wing, and "fold" the wing. Folding means decreasing the wingspan.

When a bird flaps down, it also twists the leading edge of the wing down. This has the effect of generating airflow over the wing from the leading edge to the trailing edge. The twisted wing also orients the lift vector forward, providing thrust for the bird.

When a bird flaps up, it twists the leading edge of the wing up, again generating airflow from the leading to trailing edge. However, because the wing is twisted up, the lift vector is now pointing behind the bird, adding drag and slowing the bird down. If the bird is not landing, this is undesirable, so the bird will "fold" it's wings at the same time, making the wingspan less and the generated drag less. Conversly, when landing or slowing down, the wings would be folded on the down stroke, generating less thrust.

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

erj-145mech
Posts: 305
Joined: Tue Oct 02, 2001 4:21 am

### RE: How Do Planes Fly?

Then on the other hand
(a) a helicopter meerly beats the air into submission.
(b) Airbus's are so ugly, the earth repells them

Bizjets
Posts: 135
Joined: Sat Jun 25, 2005 5:11 pm

### RE: How Do Planes Fly?

Here... read this book... it explains everything.

It's available from barnesandnoble.com here. Its pricy, but well worth it.

bizjets

Notar520AC
Posts: 1517
Joined: Sat Jul 21, 2001 6:53 am

### RE: How Do Planes Fly?

Basically, to make a long story short, airflow passes over the curved surface of the wing, faster on the top, and slower under the bottom. This faster movement creates a low pressure zone on the top of the wing and the fast movement a high pressure zone on the underside of the wing. It's easier to float upwards into low pressure than down into high pressure, so the airplane goes up. This process is called lift. Thrust allows the airplane to start going, and once it's going the wing will take care of the rest, until the airflow over the wing is no longer sufficient to sustain lift, and then the airplane falls out of the sky, which is known as a stall.

I suggest you do some research on the four fources, (Lift, Weight, Drag, and Thrust) which will give you a better idea.

But in helicopters it's much different, although not entirely, but I'm not going to go into that right now.

Fly Mickey D Helicopters!
-Notar520AC
BMW - The Ultimate Driving Machine

PerthGloryFan
Posts: 725
Joined: Fri Oct 27, 2000 9:48 pm

### RE: How Do Planes Fly?

airflow passes over the curved surface of the wing, faster on the top, and slower under the bottom.

??? Really???

Get the real story here with a neat interactive demo:
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
and here:
http://www.avweb.com/articles/liftsuck/

This topic has been covered a number of times before, a quick search gives:

But of course this is an aviation forum so no doubt this "discussion" will always be with us.

Comedian eh ... try this one (which I use to explain to first year college students) - electronic components, such as transistors, diodes, capacitors, etc, work because they're fill of smoke. Don't believe me? Well, for example, connect an electrolytic capacitor the wrong way around across a DC power supply and wind it up. Poof! The capacitor bursts open releasing all the smoke and it then no longer works. So it must be the smoke that makes it work!

PGF

Westjet_737
Posts: 845
Joined: Wed Nov 03, 1999 8:42 am

### RE: How Do Planes Fly?

How does time fly?

Guest

### RE: How Do Planes Fly?

Dear BigPhilNYC -
They definitely fly good, they fly nice, and pretty high, some at 13,000 meters.
Be careful, some are a little "tricky" to handle...
As I would agree we have "knowledgeable amateurs (and experts)" here...
(s) Skipper

RyDawg82
Posts: 835
Joined: Fri Sep 14, 2001 8:30 am

### RE: How Do Planes Fly?

Wassup Phil?

Check these two sites out...

http://www.howstuffworks.com/category.htm?cat=Aviat

and

http://www.monmouth.com/~jsd/how/

Lemme know if these work for you....

Take Care,
Ry

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: How Do Planes Fly?

PFIL. Passenger Fear Induced Lift. As the aircraft accelerates down the runway, it starts making noise and shaking. Passengers grab hold of the armrests of their seat, their knuckles going white. That is what lifts an aircraft.

When you need extra lift, you can extend the flaps. They make more noise.

Cargo aircraft don't fly. That's just something They want us to believe. In reality, they're not full of cargo. They're carrying men in black suits, trained to be especially nervous when flying.

Either that, or they fly by pushing air down in whatever way they can.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

PPGMD
Posts: 2398
Joined: Sun Sep 30, 2001 5:39 am

### RE: How Do Planes Fly?

FredT,

You have to respect frieght dogs, it is pretty hard to scare cargo to get the lift that you need.
At worst, you screw up and die.

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: How Do Planes Fly?

PPGMD,
yeah, that is why they are careful to maintain their reputation as being a bit on the reckless side... while pretending to dislike it.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

Ikarus
Posts: 3399
Joined: Mon Jan 08, 2001 10:18 pm

### RE: How Do Planes Fly?

Bizjets: Noooooo! Not Andersen's "Fundamentals of Aerodynamics"!!!! I HATE that book. It's just useless to learn anything from in self study. You need a professor or tutor or something to lecture the stuff to you more slowly and easier to understand than that...

Fundamentally, it is because the airfoil generates vorticity - i.e. a rotation of the air. The rotation is not the only movement - it is merely added to the normal movement of the air. The rotation acts such that it accelerates the airflow above the airfoil and decelerates the airflow below it. Behind the airfoil, there is downwash, and in front of it, there is upwash.

Faster air equals lower static pressure. Often, Bernoulli's formula is quoted here (total pressure = static pressure + dynamic pressure = constant), but it is valid for incompressible flow only, and only in the regions unaffected by viscosity. So basically, it is useful as tool for explanation and demonstration, and for very simple calculations, but in most useful cases more complex calculations are necessary.

How does the vorticity get into the air? That was, for me, for a long while the question I did not understand. Then I came across a (simplified) explanation that made sense to me. Ideal (inviscid, irrotational, incompressible, adiabatic) airflow behaves such that there is no lift, no drag, no force on the airfoil. So, using a symmetric airfoil at a positive angle of attack for example, it leaves the airfoil at a point on the upper surface, and hits it at a point on the lower surface (I am talking about the 2 stagnation points). There is no problem for the air to follow the mathematical prediction in the latter case: it can flow around the round leading edge without much of a problem. But at the trailing edge, the air would have to flow around a sharp edge, and then flow backwards. This would mean a near-zero radius of rotation, and an infinite central force pulling the air around the corner. That is physically impossible. So instead, the air separates at the trailing edge (Kutta condition), which causes repercussions in the entire airflow: A distortion: The rotation.

Anyway, without sketches, these explanations are a bit useless, I suppose...

Regards

Ikarus

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: How Do Planes Fly?

Yeah, avoid "Fundamentals of Aerodynamics". It is for those with an aero background who want to learn the intricasies. For the basics, get Andersen's "Introduction to Flight" or, even better, the classic "Aerodynamics for Naval Aviators". Sorry, no time to look up the ISBNs right now.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

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