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How Does A Wing Generate Lift?  
User currently offlinePanAm747 From United States of America, joined Feb 2004, 4242 posts, RR: 8
Posted (12 years 9 months 2 weeks 3 days 10 hours ago) and read 4188 times:

Wow, I'm a little confused on this.

Every groundschool and every pilot book I have taught me that this was the CORRECT theory:

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

So is Jeppesen wrong?


Pan Am:The World's Most Experienced Airline - P(oor) S(ailor's) A(irline): San Diego's Hometown Airline-Catch Our Smile!
14 replies: All unread, jump to last
 
User currently offlinePPGMD From United States of America, joined Sep 2001, 2453 posts, RR: 0
Reply 1, posted (12 years 9 months 2 weeks 3 days 9 hours ago) and read 4101 times:

Yes, its is wrong. Its a little too complicated to explain in text with out some sort of drawings. Maybe someone will dig up a page to describe it more in depth for you.


At worst, you screw up and die.
User currently offlineIMissPiedmont From United States of America, joined May 2001, 6346 posts, RR: 33
Reply 2, posted (12 years 9 months 2 weeks 3 days 9 hours ago) and read 4093 times:

It's half wrong. The molecules do not travel faster in order to "meet" the molecules they were with at the leading edge.

Think of the top of the wing as one half of a constricted pipe, the top half being formed by the air pressure from above. The air must travel faster to get an equal amount through a smaller area. This is the heart of the Bernoulli effect. An equal amount of air passing through a smaller space must travel faster, hence lower pressure. Nothing magical, just elementary physics.



Damn, this website is getting worse daily.
User currently offlineSkyguy11 From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 9 months 2 weeks 3 days 8 hours ago) and read 4078 times:

^^ Is there such a thing as 'elementary' physics!?

That is a good website BTW! Yeah, the reason most private pilot textbooks explain lift in the incorrect mannar is that it is simpler and easier to understand. The real theory of lift involves physics and difficult to explain theories that takes a lot of study to really understand. But it makes complete sense when you think about it. Think of an inverted wing. There is less distance on top of the inverted wing than there is on the bottom. Does this mean that the wing is creating lift in the 'wrong' direction? Absolutely not! Lift is a product of the downforce created by the wing forcing the air down, which is directly related to angle of attack and airspeed.


User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1662 posts, RR: 1
Reply 4, posted (12 years 9 months 2 weeks 3 days 8 hours ago) and read 4073 times:

Leave us not forget the Coanda Effect, which describes why the airflow above the surface of the wing doesn't just keep going in a straight line away from the wing's curvature but, instead, conforms to it.
Its the same reason that, if you pour coffee out of a cup at a 45-degree angle, the coffee runs down the side of the cup instead of falling straight down. If you increase the angle of the coffee cup, its "angle of attack," the coffee "separates" from the cup and falls straight down. The Coanda Effect is why angle of attack, and not speed, defines the stall break.


User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 5, posted (12 years 9 months 2 weeks 3 days 6 hours ago) and read 4061 times:

Just for the record, some commercial pilot texts describe it incorrectly, as well as private pilot texts. But as a pilot, I think I'll let the engineers and physicists worry about the exact mechanics. When I'm shooting a partial panel approach to minimums, I'm not wondering, "Is this newtonian lift or Bernoulian?" Although it is good for a pilot to grasp the general concept.

User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 6, posted (12 years 9 months 2 weeks 3 days 3 hours ago) and read 4045 times:

IMissPiedmont,
that's another incorrect theory. Bernoullis principle is valid but not really relevant. The pressure decrease comes from the air accelerating downward as it follows the curvature of the wings upper surface. There is no pressure gradient in a fluid without acceleration and vice versa. SkyGuy and ThirtyEcho are spot on.




I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineSailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6
Reply 7, posted (12 years 9 months 2 weeks 3 days 2 hours ago) and read 4035 times:

Kutta-Joukowski theorum óf Fluid Mechanics. the lift, L, of an airfoil is given by L = pTVl, where p is the density, T is the circulation, V is the velocity, and l is the length of the airfoil. Basically, the wing adds a circulation to the airflow. (use simple vector analysis on the flow to compute it)

SailorOrion


User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 8, posted (12 years 9 months 2 weeks 2 days 15 hours ago) and read 4010 times:

Dang guys...
Now you've all got me really confused. I thought all along it was the "Lifties" that pushed up on the wing when you were flying.
Jetguy


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 9, posted (12 years 9 months 2 weeks 2 days 3 hours ago) and read 3995 times:

Jetguy,
these are the official reasons, of course. The real reason aircraft fly is of course....

...PFIL, or Passenger Fear Induced Lift. The lift comes from all the pax grabbing onto their armrests and pulling. It is easy to see. The engines and take off roll are simply there to put enough fear into the pax. On takeoff, as the noise and vibration picks up, they all grab hold of their armrests and off you go.

On approach, since they're all relaxed after inflight meals and a drink or two, you need flaps and perhaps even spoilers to make sure you get enough lift. If you find yourself below the glideslope, you might even have to add a burst of power to frighten them enough!

Yes, cargo ops is dangerous. It really takes quite a pilot to scare a cabin full of mail!

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineKlaus From Germany, joined Jul 2001, 21522 posts, RR: 53
Reply 10, posted (12 years 9 months 2 weeks 1 day 9 hours ago) and read 3968 times:

Wow! Now I´ve got it!!!  Big thumbs up  Big thumbs up  Big thumbs up

(Next time I´ll remember not to let my fellow passengers do all the work for me!  Wink/being sarcastic)


User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1662 posts, RR: 1
Reply 11, posted (12 years 9 months 2 weeks 1 day 8 hours ago) and read 3965 times:

FredT, you forgot the effect of flaps and slats. Both devices are primarily noisemakers; as the aircraft slows for landing, flaps are deployed and they make a lot of noise, causing the pax to pull up on the armrests again. Slats serve the same function except that they make a kind of groaning noise that causes the pax to say "What's that?" and pull harder. During a go-around, the engines are set for max noise and the flaps are retracted at the same time to cause max terror; this is accompanied by a recording played through the PA system of people screaming, crying and saying "Oh my God!" that causes the greatest amount of armrest pulling.

User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 12, posted (12 years 9 months 2 weeks 1 day 8 hours ago) and read 3961 times:

There are many instances in our lives when scientific concepts are just too complex to expect everyone (including pilots) to understand the principles responsible for certain phenomena as intimately as someone who has devoted a great deal of time studying.

In the effort to effectively teach a lay-person the basics, we sometimes take liberties with the accepted theories in order to simplify them to a level that gets the point across well enough for the context it's presented. It may not be exactly correct, but it's easy to accept.

The theory of lift with respect to aircraft is one such subject and this debate can go on ad-nauseum as everyone adds their 2 cents....


 Smile





User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 13, posted (12 years 9 months 2 weeks 21 hours ago) and read 3940 times:

Now, now. We all know that it's money that makes airplanes fly.

User currently offlinePPGMD From United States of America, joined Sep 2001, 2453 posts, RR: 0
Reply 14, posted (12 years 9 months 2 weeks 20 hours ago) and read 3945 times:

Yep money it is, espically after that last check I wrote.


At worst, you screw up and die.
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