johnny1488 1 #1 March 8, 2003 I've been reading a lot on aerodynamics and read up on both theories. Bernoulli says that air flows faster over the top skin creating lower pressure and lift. The other theory (summed up) has an updraft in front of the nose and a down draft over the top of the canopy. Newtons law states that if the air pushes down on the canopy the canopy pushes back up on the air. This is not to be confused with the idea that the air deflects down under the wing. In this theory Bernoulli is an after effect. Johnny --"This ain't no book club, we're all gonna die!" Mike Rome Quote Share this post Link to post Share on other sites
relyon 0 #2 March 8, 2003 IIRC, circulation theory essentially combines the two. See Theory of Wing Sections for more detail than you'll ever care to know. Bob (edited to fix link) Quote Share this post Link to post Share on other sites
Jib 0 #3 March 8, 2003 For anyone who's interested, here's some basic aerodynamic stuff from NASA, including a lift calculator. http://www.lerc.nasa.gov/WWW/K-12/airplane/short.html -------------------------------------------------- the depth of his depravity sickens me. -- Jerry Falwell, People v. Larry Flynt Quote Share this post Link to post Share on other sites
quade 3 #4 March 8, 2003 AAAHHHGGGRRRGGGHHH . . . Run away!!!quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
pilotdave 0 #5 March 8, 2003 Lift is due to the pressure distribution around the airfoil. Where the air is moving faster, it has lower pressure, just as Bernoulli says. What causes the pressure distribution is more complicated than just the curved upper surface and flat bottom, but the fact is that when the forces caused by the pressure distribution are integrated around the airfoil, a net upward force is produced. Upwash and downwash are really results of this. Circulation and lifting line theory are more mathematical ways of estimating lift. Newton's laws apply too, but they, at least his second law, really deals with the change in momentum the wing causes in the air. The change in momentum of the air will equal the lift. No single theory EXPLAINS lift. It's really complicated. But each individual theory applies in it's own way. Dave Quote Share this post Link to post Share on other sites
USPA 0 #6 March 8, 2003 Whahahahahaha... Ok, I'll bite... Bottom flat???? Look again! The trouble with skydiving; If you stink at it and continue to jump, you'll die. If you're good at it and continue to jump, you'll see a lot of friends die... Quote Share this post Link to post Share on other sites
kallend 1,672 #7 March 8, 2003 QuoteI've been reading a lot on aerodynamics and read up on both theories. Bernoulli says that air flows faster over the top skin creating lower pressure and lift. The other theory (summed up) has an updraft in front of the nose and a down draft over the top of the canopy. Newtons law states that if the air pushes down on the canopy the canopy pushes back up on the air. This is not to be confused with the idea that the air deflects down under the wing. In this theory Bernoulli is an after effect. Bernoulli said absolutely nothing about air going around airfoils. Bernoulli's theorem is derived from Newton's Laws. They are not independent explanations of fluid dynamics. It is experimentally verified that a lifting airfoil has (a) an updraft ahead of it, (b) a downdraft behind it, (c) airflow over the upper surface that is faster than airflow over the lower surface, (d) a pressure difference between top and bottom surfaces that is consistent with Bernoulli's theorem and with the amount of lift produced, and (e) the total momentum of the downwash is consistent with the lift, in accordance with Newton's 3rd law. What difference does a poll make? Unless you are polling aerodynamics experts, the result is just silly.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
billvon 2,464 #8 March 8, 2003 > Newtons law states that if the air pushes down on the canopy the canopy > pushes back up on the air. This is not to be confused with the idea that > the air deflects down under the wing. Newton's laws adequately account for lift. There are many simplifications of the complex process of lift, but any analysis will find a higher pressure beneath the wing due to air being deflected downwards. Quote Share this post Link to post Share on other sites
AndyMan 7 #9 March 9, 2003 QuoteWhat difference does a poll make? Unless you are polling aerodynamics experts, the result is just silly. Not at all. The poll results are that most people don't give a rats ass about the physics of lift. After reading this debate countless times, I too, don't give a rats ass... _Am__ You put the fun in "funnel" - craichead. Quote Share this post Link to post Share on other sites
quade 3 #10 March 9, 2003 quade's theory of lift . . . the easy equation. This equation accounts for all froms lift and applied to all aircraft from the lowly Cessna 150 to the Space Shuttle.Lift = M -- that's it.M is Money.The more money you have, the more lift you can have generated.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
johnny1488 1 #11 March 9, 2003 Its just that I see many explanations of lift only use the pressure differences as how lift is achieved. It doesnt explain symetrical wings or inverted flight. Also according to the bernoulli only theory, for a cessna wing to lift a plane of 4000lbs with just the acceleration of air over the wing, the wing would have to be as tall as the wingspan (according to the equal transit times theory) Equal transit times doesnt exist, (according to what i've read) but im just looking to see why that theory still holds water. Johnny --"This ain't no book club, we're all gonna die!" Mike Rome Quote Share this post Link to post Share on other sites
cgross 1 #12 March 9, 2003 Well I have a degree in Atmospheric physics, and have been studying both for years. Bernuli(sp) is closer to being right than Newton. Newton was good, but the physics of fluids was not his bag!!!! Chris Quote Share this post Link to post Share on other sites
ernokaikkonen 0 #13 March 10, 2003 >The more money you have, the more lift you can have generated. Ok, this one I can understand.... Quote Share this post Link to post Share on other sites
Samurai136 0 #14 March 10, 2003 It pulls the toggles and it flares.... My preciousssss.....Ken "Buttons aren't toys." - Trillian Ken Quote Share this post Link to post Share on other sites
kallend 1,672 #15 March 10, 2003 QuoteIts just that I see many explanations of lift only use the pressure differences as how lift is achieved. It doesnt explain symetrical wings or inverted flight. Also according to the bernoulli only theory, for a cessna wing to lift a plane of 4000lbs with just the acceleration of air over the wing, the wing would have to be as tall as the wingspan (according to the equal transit times theory) Equal transit times doesnt exist, (according to what i've read) but im just looking to see why that theory still holds water. Do not attribute to Bernoulli, who was a first class mathematician, the half-baked explanations you see in junior high level science books and, unfortunately, some FAA publications for pilots. There is no rule that says the air going over the top of the wing has to arrive at the trailing edge in the same time it take the air going underneath. It is application of this "rule" by morons that leads to claims that Bernoulli's theorem doesn't explain lift of symmetrical wings, etc. etc. And Newton's laws must apply, unless we are considering relativistic speeds or galaxy sized or atom-sized wings. To repeat, there is NO inconsistency between Newton's Laws and the pressure differences predicted by Bernoulli's equation, provided you do the physics correctly.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
kallend 1,672 #16 March 10, 2003 Quote Well I have a degree in Atmospheric physics, and have been studying both for years. Bernuli(sp) is closer to being right than Newton. Newton was good, but the physics of fluids was not his bag!!!! Chris Ask for your tuition money back, they robbed you!... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
nacmacfeegle 0 #17 March 10, 2003 I would have thought that someone with a degree in Atmospheric Physics would have known how to spell Bernoulli. -------------------- He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me. Thomas Jefferson Quote Share this post Link to post Share on other sites
winsor 189 #18 March 10, 2003 QuoteI've been reading a lot on aerodynamics and read up on both theories. Bernoulli says that air flows faster over the top skin creating lower pressure and lift. The other theory (summed up) has an updraft in front of the nose and a down draft over the top of the canopy. Newtons law states that if the air pushes down on the canopy the canopy pushes back up on the air. This is not to be confused with the idea that the air deflects down under the wing. In this theory Bernoulli is an after effect. Bernoulli's equation is one of conservation of energy along a streamline. It states that the amount of energy in a fluid - pressureXvolume potential, kinetic, and massXheight potential - stays constant, end of story. Most of the popular treatments of the subject ("Fizix Made Easy!") are classic cases of the blind leading the blind. The scientist did not prove that a bumblebee can't fly - a bumblebee proved that the scientist's model needed further development. Belief has no place in scientific investigation, and physics is not amenable to solution by quorum. The questions you asked were fundamentally flawed. Oh, and knowledge may not set you free, but ignorance can kill you deader than hell. Blue skies, Winsor Quote Share this post Link to post Share on other sites
pilotdave 0 #19 March 11, 2003 QuoteIts just that I see many explanations of lift only use the pressure differences as how lift is achieved. It doesnt explain symetrical wings or inverted flight. Also according to the bernoulli only theory, for a cessna wing to lift a plane of 4000lbs with just the acceleration of air over the wing, the wing would have to be as tall as the wingspan (according to the equal transit times theory) Equal transit times doesnt exist, (according to what i've read) but im just looking to see why that theory still holds water. The classic airfoil shape with a curved upper surface and flat bottom surface (yes, i realize thats not what canopies look like) is not the main factor in achieving the faster, lower pressure airflow over the top. Symmetric airfoils work due to the angle of attack. The leading edge needs to be curved to be able to move the stagnation point (the very very front edge) down when the wing is at a positive angle of attack. That effectively moves the chord line down at the leading edge giving the wing an effective camber. The more aerodynamics I study, the more I realize this stuff is much more complicated than it seems. There are no exact solutions for solving for the lift a wing will produce. Boeing and PD use computational fluid dynamics to figure this stuff out. But the lift IS caused by the pressure distribution around the wing, which is caused by variations in the speed of the flow around the wing. Dave Quote Share this post Link to post Share on other sites
dreamsville 0 #20 March 11, 2003 Thank you for distilling all of this. I haven't had physics since my second year at the Cornell University School of Engineering. Since I have forgotten a bunch of what I knew and haven't the patience to re-learn all of whatever-it-was, I rely upon inquiry and the time-tested reliability of the Performance Designs wing to keep me alive another day to write this drivel. |I don't drink during the day, so I don't know what it is about this airline. I keep falling out the door of the plane. Harry, FB #4143 Quote Share this post Link to post Share on other sites
skydivejersey 0 #21 March 12, 2003 Can someone explain this one to me as it still beats the hell out of me... An airfoil generates lift by the lower pressure on the top of the wing. How the f*ck can a plane fly upside down. The lift should be pulling it into the ground. Quote Share this post Link to post Share on other sites
quade 3 #22 March 12, 2003 QuoteAn airfoil generates lift by the lower pressure on the top of the wing. How the f*ck can a plane fly upside down. The lift should be pulling it into the ground. Actually, it does it the exact same way only much less efficiently. You can make a barn door fly, but it's very inefficient. Shaping the wing makes it work better.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
billvon 2,464 #23 March 12, 2003 >How the f*ck can a plane fly upside down. By going from a positive to a negative angle of attack. (It's really still positive, because it's negative but the plane has rotated 180 degrees . . .) A simple way to see this is to push on a yoke when you're flying. The plane will nose down as you change the wing's angle of attack, and lift decreases. Push it hard enough and you'll get plastered to the ceiling as the wing generates _negative_ lift. On normal wings you have to go pretty far past neutral to generate negative lift, but on aerobatic wings (which are often symmetrical) it's just as easy to fly upside down as right side up - as long as you maintain the right angle of attack. Quote Share this post Link to post Share on other sites
dreamsville 0 #24 March 12, 2003 Sorry for going a bit off the thread. Do you know of situations where skydivers have exited the aircraft when it was upside down? |I don't drink during the day, so I don't know what it is about this airline. I keep falling out the door of the plane. Harry, FB #4143 Quote Share this post Link to post Share on other sites
pilotdave 0 #25 March 12, 2003 QuoteSorry for going a bit off the thread. Do you know of situations where skydivers have exited the aircraft when it was upside down? | There is at least one video of this on skydivingmovies.com. That Pink skyvan in germany has done it. Really weird to see... the video looks like a perfectly normal exit until you notice the sky is brown and the ground is blue....then the planes goes down, not up. /misc/episode22.mov Dave Quote Share this post Link to post Share on other sites
