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 What Makes Airplanes Fly?
 Ziggy From United States of America, joined Jun 2001, 178 posts, RR: 0Posted Thu Aug 2 2001 05:00:23 UTC (13 years 8 months 1 day 12 hours ago) and read 1503 times:

 Since right now their seems to be a lack of interchanging opinions, I thought I would try to start a intriguing subject. This question was broght up in my advanced aerodynamics class. 1. Is it Bernolli's law that effects lift or 2. Is it Newton's 2nd law (for every action their is a opposite and equal reaction) i.e. The airfoil pushes air downward (downwash) pushing the aircraft into the air. I would just like to hear some of the other points of view out there.
 XFSUgimpLB41X From United States of America, joined Aug 2000, 4253 posts, RR: 36 Reply 1, posted Thu Aug 2 2001 05:27:20 UTC (13 years 8 months 1 day 12 hours ago) and read 1459 times:

 This was discussed quite in detail a few weeks ago. I believe it is a combination of the two at varying ratios depending on airspeed and such.
 Chicks dig winglets.
 Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6 Reply 2, posted Thu Aug 2 2001 05:33:49 UTC (13 years 8 months 1 day 12 hours ago) and read 1450 times:

 Super, challenging question! Both principles are correct, complementing one another. Bernouli effect causes higher pressure under foil, lower above -- differential acting on foil area pushes up on airfoil, creating lift. By Newton's 2nd law, the airfoil pushes down on the air around it with force equal to lift. If you map the air pressure below the foil, you will see a distribution of higher to lower pressure from the foil down to the ground. As you move away from the airfoil, the pressure decreases and spreads out in area. At ground level, there is a slight pressure rise above ambient (ie, ambient being any point far from the airfoil) covering a very large area. Integrating pressure x area over the ground yields the lift generated by the foil! (It's not really that surprising, is it?) That means that the ground is pushing up against the air, ie supporting the air, which is supporting the airfoil. So good-old Newton is vindicated again. I seem to remember solving this problem in aero engineering class in 1970 or so. Maybe one day I will try to find those notes. Pete
 DE727UPS From United States of America, joined Nov 2000, 814 posts, RR: 13 Reply 3, posted Thu Aug 2 2001 05:40:18 UTC (13 years 8 months 1 day 12 hours ago) and read 1434 times:

 You're all wrong....it's MONEY that makes an airplane fly.
 Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6 Reply 4, posted Thu Aug 2 2001 05:41:40 UTC (13 years 8 months 1 day 12 hours ago) and read 1433 times:

 hehe - you got me! Money can make anything fly!
 IMissPiedmont From United States of America, joined May 2001, 6382 posts, RR: 32 Reply 5, posted Thu Aug 2 2001 06:42:37 UTC (13 years 8 months 1 day 11 hours ago) and read 1428 times:

 Ever try to make a brick fly?
 it's getting harder not to tell people they are really odd if they think an airplan can be sexy.
 Aaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2 Reply 6, posted Thu Aug 2 2001 07:27:03 UTC (13 years 8 months 1 day 10 hours ago) and read 1430 times:

 if it flies, floats, or f**ks it's going to be expensive... >>>I thought I would try to start a intriguing subject <<< try...it doesn't take much start...nope intriguing...yes subject...try "argument" instead http://www.airliners.net/discussions/tech_ops/read.main/18810/ everyone has their own opinion, and I promise not to post on this thread again; so if this starts a wildfire, just remember that it's too complex for a simple answer. aaron
 Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6 Reply 7, posted Thu Aug 2 2001 13:59:46 UTC (13 years 8 months 1 day 3 hours ago) and read 1410 times:

 I said i my earlier post that Bernouli is the principle that generates lift from airflow around a foil. We definitely agree on that. But regardless of how a force s generated, Newton's 2nd Law ALWAYS holds whenever a force is present. I guess I did not quite get what was meant by the air hitting the foil, but that is irrelevant anyway. Here's a problem: A man is drivng a covered truck full of birds. The truck weighs 10,000 pounds empty, the birds weigh 5,000 pounds, for a total loaded weight of 15,000 pounds. He comes to a bridge that has a 10,000 pound weight limit. He scares the crap out of the birds to make them all fly (while still remaining inside) at once, and then attempts to cross the bridge. Will the truck just weigh 10,000 pounds while the birds are in flight, and be able to cross the bridge safely?
 Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6 Reply 8, posted Thu Aug 2 2001 14:05:26 UTC (13 years 8 months 1 day 3 hours ago) and read 1406 times:

 Oops, I was having a senior moment above -- I was referring to Newton's 3rd Law (action-reaction) not second law (force-mass-acceleration).
 Ikarus From United Kingdom, joined Jan 2001, 3524 posts, RR: 2 Reply 9, posted Thu Aug 2 2001 14:11:58 UTC (13 years 8 months 1 day 3 hours ago) and read 1406 times:

 That truck question is incredibly interesting..... If it is a closed truck, I say it still weighs 15000 pounds. It does not matter whether the birds are supported by the branches in their cages or the air in their cages. No loss of mass occurs, across the border between inside the truck and the outside world (unless it is a cage, and not a fully closed container), and so the mass of the system "truck" itself remains constant. Thr truck will fall into the river.... Regards Ikarus
 Western727 From United States of America, joined Jan 2007, 784 posts, RR: 4 Reply 10, posted Thu Aug 2 2001 14:54:15 UTC (13 years 8 months 1 day 2 hours ago) and read 1403 times:

 Awww, here we go again...
 Jack @ AUS
 XFSUgimpLB41X From United States of America, joined Aug 2000, 4253 posts, RR: 36 Reply 11, posted Thu Aug 2 2001 19:38:50 UTC (13 years 8 months 22 hours ago) and read 1385 times:

 Does Denny need to pull out his metaphysics book so we can properly and logically ponder of this?
 Chicks dig winglets.
 Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6 Reply 12, posted Fri Aug 3 2001 03:55:01 UTC (13 years 8 months 13 hours ago) and read 1364 times:

 Ikarus is right. Read my post near the top of this section. You can look at it two ways. Ikarus looked at it as a control volume with fixed mass; therefore, the weight of the truck remains the same whether the birds are airborne or not, as long as gravitational field remains unchanged. Another way is to look at how each bird affects the airflow inside the truck, determine the resulting pressure distribution over the floor of the truck, integrate it over the floor area, and thus obtain the force of the air acting downward on the floor. This will undoubtedly be 5000 lb, which is the weight of the airborne birds. Now extend this problem to the whole world. Assuming the earth's surface to be the "floor" of the world, does it matter whether planes are parked or flying when considering how much "weight" the "floor" must support? Pete
 Airplay From , joined Dec 1969, posts, RR: Reply 13, posted Sun Aug 5 2001 19:00:54 UTC (13 years 7 months 3 weeks 6 days 22 hours ago) and read 1332 times:

 Everyone knows that paperwork makes airplanes fly.
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