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How Do Planes Fly?  
User currently offlineBigPhilNYC From United States of America, joined Jan 2002, 4077 posts, RR: 54
Posted (12 years 3 months 3 weeks 5 days 20 hours ago) and read 2503 times:

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

But how?


Phil Derner Jr.
18 replies: All unread, jump to last
 
User currently offlineSaintsman From United Kingdom, joined Mar 2002, 2065 posts, RR: 2
Reply 1, posted (12 years 3 months 3 weeks 5 days 20 hours ago) and read 2483 times:

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.


User currently offlineBigPhilNYC From United States of America, joined Jan 2002, 4077 posts, RR: 54
Reply 2, posted (12 years 3 months 3 weeks 5 days 19 hours ago) and read 2466 times:

So then, like, why do birds flap?

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




Phil Derner Jr.
User currently offlineBen88 From United States of America, joined Dec 1999, 1093 posts, RR: 3
Reply 3, posted (12 years 3 months 3 weeks 5 days 19 hours ago) and read 2464 times:

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

User currently offlineBigPhilNYC From United States of America, joined Jan 2002, 4077 posts, RR: 54
Reply 4, posted (12 years 3 months 3 weeks 5 days 19 hours ago) and read 2463 times:

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

Thank you Saintsman.  Smile

Ben, your shoes are untied.




Phil Derner Jr.
User currently offlinePPGMD From United States of America, joined Sep 2001, 2453 posts, RR: 0
Reply 5, posted (12 years 3 months 3 weeks 5 days 13 hours ago) and read 2413 times:

Airspeed and money, that is how airplanes fly.


Filler Filler Filler



At worst, you screw up and die.
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 6, posted (12 years 3 months 3 weeks 5 days 13 hours ago) and read 2413 times:

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.

 Big thumbs up



09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineErj-145mech From United States of America, joined Oct 2001, 306 posts, RR: 1
Reply 7, posted (12 years 3 months 3 weeks 5 days 10 hours ago) and read 2394 times:

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


User currently offlineBizjets From France, joined Jun 2005, 0 posts, RR: 0
Reply 8, posted (12 years 3 months 3 weeks 5 days 1 hour ago) and read 2334 times:

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



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


bizjets


User currently offlineNotar520AC From United States of America, joined Jul 2001, 1606 posts, RR: 4
Reply 9, posted (12 years 3 months 3 weeks 2 days ago) and read 2215 times:

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
User currently offlinePerthGloryFan From Australia, joined Oct 2000, 751 posts, RR: 0
Reply 10, posted (12 years 3 months 3 weeks 1 day 17 hours ago) and read 2200 times:

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:
http://www.airliners.net/discussions/tech_ops/read.main/36074/6/
http://www.airliners.net/discussions/tech_ops/read.main/18126/
http://www.airliners.net/discussions/tech_ops/read.main/39822/6/
http://www.airliners.net/discussions/tech_ops/read.main/32715/6/
http://www.airliners.net/discussions/tech_ops/read.main/3360/6/

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!

 Smile/happy/getting dizzy

PGF


User currently offlineWestjet_737 From Japan, joined Nov 1999, 869 posts, RR: 6
Reply 11, posted (12 years 3 months 3 weeks 1 day 2 hours ago) and read 2147 times:

How does time fly?

 Smile


User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 12, posted (12 years 3 months 3 weeks 1 day ago) and read 2138 times:

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


User currently offlineRydawg82 From United States of America, joined Sep 2001, 868 posts, RR: 8
Reply 13, posted (12 years 3 months 3 weeks 17 hours ago) and read 2125 times:

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



You can take the pup out of Alaska, but you can't take the Alaska out of the pup.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 14, posted (12 years 3 months 3 weeks 14 hours ago) and read 2112 times:

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.
User currently offlinePPGMD From United States of America, joined Sep 2001, 2453 posts, RR: 0
Reply 15, posted (12 years 3 months 3 weeks 14 hours ago) and read 2111 times:

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.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 16, posted (12 years 3 months 3 weeks 13 hours ago) and read 2107 times:

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.  Big grin

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineIkarus From United Kingdom, joined Jan 2001, 3524 posts, RR: 2
Reply 17, posted (12 years 3 months 2 weeks 5 days 11 hours ago) and read 2047 times:

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


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 18, posted (12 years 3 months 2 weeks 4 days 10 hours ago) and read 2013 times:

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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