Airfoil Lifting Force, miscellaneous discussion from the archive of the Physics Teaching list server PHYS-L, phys-l@atlantis.cc.uwf.edu >>> Item number 386, dated 95/04/14 10:40:14 -- ALL Date: Fri, 14 Apr 1995 10:40:14 CST Sender: Forum for Physics Teachers From: "James M. Espinosa" Subject: BERNOULLI'S EQUATION THIS NOTE IS ABOUT THE RECENT DISCUSSION ON BERNOULLI'S EQUATION. IT IS NOT TRUE THAT BERNOULLI'S EQUATION APPLIES ONLY TO INCOMPRESSIBLE FLUIDS, SUCH AS WATER BUT NOT TO AIR. ANYBODY WHO HAS DERIVED THAT EQUATION WOULD KNOW THAT INCOMPRESSIBILITY IS A SUFFICIENT CONDITION. BUT A NECESSARY CONDITION IS THAT THE DENSITY REMAIN CONSTANT. SO, IF A FLOW OF AIR OCCURS WITH CONSTANT DENSITY, SO THAT EVEN THOUGH AIR IS COMPRESSIBLE IT WOULD NOT GET COMPRESSED, THEN BERNOULLI'S EQUATION APPLIES TO THAT FLOW. IT MAY APPEAR THAT THE NEARNESS OF THE STREAMLINES IMPLIES COMPRESSION BUT IT MAY ONLY MEAN THAT THE AIR IS FLOWING THROUGH A SMALLER CROSS SECTION AT A HIGHER SPEED. JAMES M. ESPINOSA >>> Item number 606, dated 95/04/22 20:09:16 -- ALL Date: Sat, 22 Apr 1995 20:09:16 CST Sender: Forum for Physics Teachers From: "James M. Espinosa" Subject: Magnus effect and explanation Several weeks ago there appears to have been some disagreement on whether the Magnus effect and Bernoulli's equation could refer to the same phenomena, such as in the context of airplane lift. Later there was a discussion on description versus explanation. I think these two themes can be connected. The Magnus effect is the description of a phenomenon; the motion of a projectile, like a tennis ball, out of a vertical plane when the projectile is spinning. The explanation of the Magnus effect comes from Bernoulli's equation where the spin produces a difference in flow speeds and a difference in pressure. The description is about "what" happens or "how" it happens, while the explanation is "why" it happens. James M. Espinosa >>> Item number 889, dated 95/05/04 20:12:44 -- ALL Date: Thu, 4 May 1995 20:12:44 CST Reply-To: Forum for Physics Teachers Sender: Forum for Physics Teachers From: "James M. Espinosa" Subject: Airplane lift and Bernoulli's equation Several weeks ago there was a discussion on what it was that produced lift on the wing of an airplane and whether Bernoulli's equation was relevant in this case. It seems to me that most notes stated that Bernoulli's principle was not applicable in the case of airplane lift. I have for many years given my students of first year physics the explanation of lift precisely as an application of that principle. Because of the controversy I looked up some sources on flight. I highly recommend the following elementary book: "Aerodynamics" written by the famous aerodynamic physicist Theodore von Karman. In there he writes: In earlier times the instinctive impression was that the air hits the inclined wing surface and that the airplane is there- fore carried by the air below. We now see that the airplane wing is at least partially hung up or sucked up by the air passing along the upper surface. As a matter of fact, the contribution to the total lift from the negative pressure or suction developed at the upper surface is larger than the contribution from the positive pressure at the lower surface. James M. Espinosa >>> Item number 914, dated 95/05/05 07:47:59 -- ALL Date: Fri, 5 May 1995 07:47:59 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: Airplane lift and Bernoulli's equation On Thu, 4 May 1995, James M. Espinosa wrote: > Several weeks ago there was a discussion on what it was that produced > lift on the wing of an airplane and whether Bernoulli's equation was > relevant in this case. It seems to me that most notes stated that > Bernoulli's principle was not applicable in the case of airplane lift. > I have for many years given my students of first year physics the > explanation of lift precisely as an application of that principle. > Because of the controversy I looked up some sources on flight. I > highly recommend the following elementary book: "Aerodynamics" written > by the famous aerodynamic physicist Theodore von Karman. In there he > writes: > In earlier times the instinctive impression was that the air > hits the inclined wing surface and that the airplane is there- > fore carried by the air below. We now see that the airplane > wing is at least partially hung up or sucked up by the air > passing along the upper surface. As a matter of fact, the > contribution to the total lift from the negative pressure or > suction developed at the upper surface is larger than the > contribution from the positive pressure at the lower surface. As a member of the venemously anti-bernoulli camp I must say: sounds good to me! My beef was with the explanations which assume that the ENTIRE explanation of lift must be centered ONLY on the low pressure on the upper wing surface, while totally ignoring the fact that all the forces involved are reaction forces which act to direct a jet of air downwards after the trailing edge of the wing. Also ignored is the fact that a positive angle of attack is required. Now defining "angle of attack" for various wing sections is another story... Someone recently asked me this: how can anyone say that the lower pressure above a wing explains lift properly, since we should never say that vacuums create "suction forces." Does not ALL the lifting force come from below the wing? .....................uuuu /oo\uuuu........,......................... William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 922, dated 95/05/05 13:25:03 -- ALL Date: Fri, 5 May 1995 13:25:03 -0500 Sender: Forum for Physics Teachers From: "Jack Uretsky, Internet:, HEP Division, Argonne National Lab, Argonne, IL 60439" Subject: Re: Airplane lift and Bernoulli's equation Hi all- William Beaty writes *********************************************************************** As a member of the venemously anti-bernoulli camp I must say: sounds good to me! My beef was with the explanations which assume that the ENTIRE explanation of lift must be centered ONLY on the low pressure on the upper wing surface, while totally ignoring the fact that all the forces involved are reaction forces which act to direct a jet of air downwards after the trailing edge of the wing. *********************************************************************** This argument misuses Newton's third law. If I want the force of the air on the wing, I look at the pressure difference at the wing surface. This comes directly from Bernoulli. If I want to look at the effect of the wing on the air, then I look at the downward directed jet of air. Regards, Jack >>> Item number 943, dated 95/05/06 17:08:36 -- ALL Date: Sat, 6 May 1995 17:08:36 -0700 Sender: Forum for Physics Teachers From: Rob Knapp Subject: Re: Airplane lift and Bernoulli's equation On Fri, 5 May 1995, William Beaty wrote: > > Someone recently asked me this: how can anyone say that the lower > pressure above a wing explains lift properly, since we should never say > that vacuums create "suction forces." Does not ALL the lifting force > come from below the wing? > Sounds as though we're getting into Aristotle on causes: is the low pressure above the wing a proximate cause, an efficient cause, or no kind of cause? Seems to me that the whole pattern of pressure is what you have to look at. After all, does the Earth cause the ball in my hand to fall when I let it go? or does the ball cause its own fall? Answer: yes to both. Rob Knapp >>> Item number 1304, dated 95/05/27 11:26:31 -- ALL Date: Sat, 27 May 1995 11:26:31 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: Airplane lift and Bernoulli's equation In cleaning out old email, I found this. It got me thinking... On Fri, 5 May 1995, Jack Uretsky wrote: > Hi all- > William Beaty writes > *********************************************************************** > As a member of the venemously anti-bernoulli camp I must say: sounds good > to me! My beef was with the explanations which assume that the ENTIRE > explanation of lift must be centered ONLY on the low pressure on the upper > wing surface, while totally ignoring the fact that all the forces > involved are reaction forces which act to direct a jet of air downwards > after the trailing edge of the wing. > *********************************************************************** > > This argument misuses Newton's third law. If I want the force of > the air on the wing, I look at the pressure difference at the wing surface. > This comes directly from Bernoulli. If I want to look at the effect of the > wing on the air, then I look at the downward directed jet of air. Regards, Jack You're right. I'm slipping slightly into the misconception which describes Newton's third as "actions" rather than FORCES. However, there's still another viewpoint that one can take about airfoils where the downward- directed jet of air is important: reaction engines. To All: A major characteristic of reaction engines is that mass is accelerated in order to accelerate the craft. It is true that the term "reaction" in Newton's third law is easily mistaken as referring to motions, and is true that students can acquire misconceptions about Newton's third law *only* applying to reaction engine situations. However, I don't believe that anything is accomplished by focusing only on the airfoil surface pressure while ignoring the relation between airfoils and rockets, jet engines, helicopters, cannons on carts, etc. I attained a major "aha" experience when I realized that airfoils were not a separate case, and that airfoils are a subset of reaction engines. I believe that I acquired a *much* firmer grasp upon airfoil operation because of this. And I've come to realize that the "Bernoulli" explanation is the barrier that prevented me from realizing this sooner, and it is still making airfoil operation mysterious to many. The "Bernoulli" explanation is not wrong. But it is very misleading. Here are some analogies. Wouldn't it be misleading to explain a jet engine *only* in terms of lift generated by the tiny airfoils formed by the turbine blades? Would it not be misleading to analyze a rocket engine *only* in terms of the pressure and velocity of the gasses at various points on the surface within the combustion chamber, while totally ignoring the exhaust jet and the acceleration of its mass? Would it be wrong to promote this explation to such a widespread extent that people are unfamiliar with the "reaction engine" concept, that textbooks and reference books NEVER mention or depict exhaust jets, and that most instructors adhere mightly to this view, see no use for alternative views, and don't consider alternatives as being correct? Such is the situation with explanations of aircraft wings. "Bernoulli" has taken over. So, I should not be attacking "Bernoulli" explanations as being incorrect. The situation is not so simple. Instead, "Bernoulli" explanations are subtly twisted and tend to create misconceptions. They communicate assumptions that the wings of aircraft are somehow different than rockets and jets (and even helicopters!) They vastly amplify one feature of a complete explanation of flight at the expense of a clear understanding of the whole picture. They lead to genuine mistakes: most diagrams used in "Bernoulli" explanations incorrectly show that the air flow is not redirected by the wing. They crush creative understanding because they cause a "worship" of a single "correct" viewpoint, rather than exploration of numerous alternative ways of looking at a phenomena. And "Bernoulli" explanations ignore the useful concepts involving conservation of momentum, calculation of acceleration of the craft in terms of acceleration of gas masses, and the "aha" experience gained through realization of the unity in explanation between apparently unrelated phenomena. .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 1312, dated 95/05/28 15:47:17 -- ALL Date: Sun, 28 May 1995 15:47:17 EDT Sender: Forum for Physics Teachers From: Paul Camp Subject: Re: Airplane lift and Bernoulli's equation Boy, Bill, you're brave! Do you explore minefields with a pitchfork too? I agree wholeheartedly with you about the worship of the BP -- it is in the end a rather abstract idea that obscures some of the underlying physics. I had the same sort of "aha" experience as you but for me it came at the end of a party of epic proportions when we were vegging out on the TV. A commercial for some airline came on and I noticed that the airplane was pointed uphill though it seemed to be flying horizontally. The naive (and incorrect) presentation of BP that one usually finds in textbooks causes major conceptual problems when you try to understand such things as why stunt aircraft have symmetrical wings or how those experimental NASA aircraft with the upside down wings avoided flying into the dirt. In the end, it is probably a good idea to look at a problem from as many different points of view as you can. I believe Arnold Arons mentions this once or twice. Paul J. Camp "The Beauty of the Universe Assistant Professor of Physics consists not only of unity Coastal Carolina University in variety but also of Conway, SC 29526 variety in unity. pjcamp@coastal.edu --Umberto Eco (803)349-2227 The Name of the Rose fax: (803)349-2926 >>> Item number 1327, dated 95/05/28 17:03:27 -- ALL Date: Sun, 28 May 1995 17:03:27 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: Airplane lift and Bernoulli's equation On Sun, 28 May 1995, Paul Camp wrote: > Boy, Bill, you're brave! Do you explore minefields with a pitchfork > too? Heh! Actually, I think the "bernoulli" thing is more like an infected wound on the K-12 physical sciences. If you bump the wrong part of the doggie, you might get bit! But does this indicate a need to avoid the painful part, or a need to clean it out and treat it? > I had the same sort of "aha" experience as you > but for me it came at the end of a party of epic proportions when we > were vegging out on the TV. A commercial for some airline came on and > I noticed that the airplane was pointed uphill though it seemed to be > flying horizontally. Excellent one! Have you ever seen the cover from (??) Aviation Week where a private jet is flying over a fog-filled valley at sunrise, and below the plane is a trough blasted down into the "surface" of the fog, complete with scrolls of wingtip vortices? A neat one. I wish I could see a film like this. ANd the same thing, but with helicopter! .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 1329, dated 95/05/29 11:25:02 -- ALL Date: Mon, 29 May 1995 11:25:02 -0400 Sender: Forum for Physics Teachers From: Robert Curtis Subject: Re: Airplane lift and Bernoulli's equation I find it fun to explore this "half-truth" in my physics classes by going through the whole explanation of air-foils, with some demonstrations etc., and then ask "So, how is it possible for aeroplanes to fly up-side-down?" I have some video tapes from air shows which we then view..... It makes for a memorable class. (And then there is always the traditional explanation of color vision to deal with....) Bob Curtis Hackensack High School Hackensack NJ >>> Item number 1368, dated 95/05/30 19:21:29 -- ALL Date: Tue, 30 May 1995 19:21:29 -0500 Sender: Forum for Physics Teachers From: Marc Kossover Subject: Re: Airplane lift and Bernoulli's equation On Mon, 29 May 1995, Robert Curtis wrote: > (And then there is always the traditional explanation of > color vision to deal with....) Okay, I'll bite. I always seem to be the fish that gets caught in the troll. * What is traditional explanation of color vision? * How is this view wrong? * So, how does color vision work anyway? * How can I check to show that the traditional view is incorrect and that other proposed views are correct? Thank you. Marc Kossover kossover@tenet.edu 'Tis folly to expect people not to act according to their nature. >>> Item number 2856, dated 95/09/10 10:30:02 -- ALL Date: Sun, 10 Sep 1995 10:30:02 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Bill Nye's airplane wing (fwd) Yes, the "airfoil explanation controversy" continues. Can anyone see any factual errors in what I'm telling the guy below? ---------- Forwarded message ---------- Date: Sun, 10 Sep 1995 10:25:04 -0700 (PDT) From: William Beaty To: (delete) Subject: Bill Nye's airplane wing > As in most 'AHA's, the realization of a concept is a simple visual image. > Since my deteriorating memory won't allow me to reconstruct the exact > conversation, I will attempt to paraphrase, mainly to capture the visual image. > > Air particle A and air particle B start the race at the same point at the > leading edge of the airfoil. A goes above, B goes below. B has a shorter > path to the trailing edge than A does, so naturally, A has to go faster > because other laws of physics (that I had already bought off on) say that > they both have to meet at the other side at the same time. Oh dear. I was afraid of this. The above explanation has the misconception in it. The major problem is that symmetrical wings (with equal pathlengths above and below), thin membrane wings, and upside down wings all generate lift, so the above explanation using pathlength differences is not correct. Take a look at: http://amasci.com/miscon/miscon.html under the MISCONCEPTIONS LIST file. > (Or there would > be a rip in the temporal fabric of space?) So, A goes faster than B. Now, > is it the Boullian?, laws say that a particle moving at a given speed exerts > a pressure normal to its velocity vector that is greater than that pressure > exerted by a particle going faster. Here's part of the visual image: That > faster guy isn't around long enough to put pressure on the things it > touches. Since fast guy A puts less pressure on the upper side of the > airfoil than slower guy B, the result is a net sucking upward. Bernoulli's law, yep. It does play a part in any explanation of airfoil function. But there are two problems: in real aircraft, particles which separate at the leading edge DO NOT recombine at the trailing edge, and are left separated forever after, so there is no necessity for the upper one to go faster. The other problem is mentioned above, that symmetrical wings generate lift (and are used on acrobatic planes and I think on fighters) and that there are exotic wings with flat tops and curved bottoms, and THESE generate lift as well. Also, the path length above and below the wings of the Wright Brothers' flying machine was identical, and Nye's explanation would make you predict that their machine wouldn't fly, no? The misconception that Bill Nye is spreading doesn't originate with him. It is very old, and it continues to exist because it's in many textbooks and is being taught to more people even as we speak. I find this sort of thing fascinating, since it's a sort of information "virus," with a life of its own. The truth is that there are two ways to CALCULATE lift, and both methods can be made into explanations of lift. 1. Because of the shape and tilt of a wing, when it cuts through the air it leaves an "empty" space behind its top surface and a "filled" space in front of its lower surface. Air encountering its lower surface is slowed down, so by Bernoulli's law it exerts a greater pressure on the surface there. Air passing by the upper surface is drawn into the empty space behind the wing and is sped up. By Bernoulli's law the high-speed air exerts a lower pressure on the upper surface. So, wings create lift because of pressure differential. 2. As a wing cuts through the air, it applies a downward force upon the air. This comes about because of the tilt and shape of the wing. The underside of the wing deflects air downwards. Since the airflow adheres to the upper surface, the upper wing surface also deflects air downwards. There is a downward force on the air, and as a result, the wing is forced upwards. If you measure the total mass of air being accelerated downwards, you can calculate the force between the wing and the air, and this is simply the lifting force. So, wings create lift because of reaction forces. Which one is right? Both. Which one should be used? Well, the first one steers around the fact that wings push air downwards. Wings are identical in function to helicopter rotors, ship propellors, and jet engine turbine blades which all operate by throwing mass one way and moving the other way. Also, the first explanation usually (but not always) includes an incorrect description involving the necessity of particles A and B splitting and rejoining after the wing has past. And the first one implies that symmetrical wings won't work (they do,) and implies that a plane cannot fly upside down (it can.) So, now you know which one I prefer! By the way, you can contact Bill Nye directly at: The Office of Bill Nye the Science Guy Nye .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 2862, dated 95/09/11 10:28:26 -- ALL Date: Mon, 11 Sep 1995 10:28:26 -0500 Sender: Forum for Physics Teachers From: "JACK L. URETSKY (C) 1995; HEP DIVISION, ARGONNE NATIONAL LAB, ARGONNE, IL 60439" Subject: Re: Bill Nye's airplane wing (fwd) Hi all- William Beatty writes ****************************************************** Oh dear. I was afraid of this. The above explanation has the misconception in it. The major problem is that symmetrical wings (with equal pathlengths above and below), thin membrane wings, and upside down wings all generate lift, so the above explanation using pathlength differences is not correct. ************************************ That mis-states the case. Symmetrical wings only generate lift (as will a flat plate) when they are tilted with respect to the direction of travel. The net result is that the airpath above the wing is longer that the air path below the wing, thereby bringing Bernoulli into play. So Nye's explanation is essentially correct, or, as we used to say in the Navy, "It's close enough for government work." Beatty adds: ******************************************************** The truth is that there are two ways to CALCULATE lift, and both methods can be made into explanations of lift. 1. Because of the shape and tilt of a wing, when it cuts through the air it leaves an "empty" space behind its top surface and a "filled" space in front of its lower surface. Air encountering its lower surface is slowed down, so by Bernoulli's law it exerts a greater pressure on the surface there. Air passing by the upper surface is drawn into the empty space behind the wing and is sped up. By Bernoulli's law the high-speed air exerts a lower pressure on the upper surface. So, wings create lift because of pressure differential. 2. As a wing cuts through the air, it applies a downward force upon the air. This comes about because of the tilt and shape of the wing. The underside of the wing deflects air downwards. Since the airflow adheres to the upper surface, the upper wing surface also deflects air downwards. There is a downward force on the air, and as a result, the wing is forced upwards. If you measure the total mass of air being accelerated downwards, you can calculate the force between the wing and the air, and this is simply the lifting force. So, wings create lift because of reaction forces. Which one is right? Both. Which one should be used? Well, the first one steers around the fact that wings push air downwards. Wings are identical in function to helicopter rotors, ship propellors, and jet engine turbine blades which all operate by throwing mass one way and moving the other way. Also, the first explanation usually (but not always) includes an incorrect description involving the necessity of particles A and B splitting and rejoining after the wing has past. And the first one implies that symmetrical wings won't work (they do,) and implies that a plane cannot fly upside down (it can.) ************************************************* Not true. There is one way to CALCULATE lift. That is by calculating the airflow around the given wing shape, and determining the pressure differential from Bernoulli. The fact that there is a net flow downward in the wake of the wing is a consequence of Newton's 3d law, but that fact does not help you to do an a priori lift/drag calculation when you are designing a new wing profile. It is a misconception, also, that fighters are designed with symmetrical wings (so that they can fly inverted). Most such aircraft cannot do extended inverted flight because of lubrication difficulties with the power plant. The wing design is a compromise between high speed and critical low speed characteristics - one wants to be able to walk away from the aircraft after the flight. Regards, Jack "'Is it claimed that Dr. Cook's achievement is a Fact, or is it a miracle?' 'Why so?' 'Because if it is a Miracle, any sort of evidence will answer, but if it is a Fact, proof is necessary'" Mark Twain, "Official Report to the I.I.A.S. (1909) >>> Item number 2870, dated 95/09/11 22:45:10 -- ALL Date: Mon, 11 Sep 1995 22:45:10 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: Bill Nye's airplane wing (fwd) First a question: are others here interested in this stuff? If it's boring, I'd be happy to start replying privately. On Mon, 11 Sep 1995, JACK L. URETSKY (C) 1995; HEP DIVISION, ARGONNE NATIONAL LAB, ARGONNE, IL 60439 wrote: > > Hi all- > William Beaty writes > > ****************************************************** > > Oh dear. I was afraid of this. The above explanation has the > > misconception in it. The major problem is that symmetrical wings (with > > equal pathlengths above and below), thin membrane wings, and upside down > > wings all generate lift, so the above explanation using pathlength > > differences is not correct. > > ************************************ > > That mis-states the case. Symmetrical wings only generate lift > (as will a flat plate) when they are tilted with respect to the direction > of travel. The net result is that the airpath above the wing is longer > that the air path below the wing, thereby bringing Bernoulli into play. > So Nye's explanation is essentially correct, or, as we used to say in the > Navy, "It's close enough for government work." I agree that I'm trying to change the emphasis in the explanation, but I don't think this is a misstatement. I do agree that the Bernoulli Law plays a part in explaining lift. My beef is with the specifics of Nye's explanation: the assertion that the asymmetrical path length *of the wing surfaces* is the cause of lift, and the implication that lift is only generated by wings having asymmetrical crossections. I also find fault with the particle A/B split/rejoin explanation. If we always explain the lifting force by referring to an asymmetrical wing, and if we state that the force arises because the wing is more curved on top than below, won't students get the idea that asymmetry is *required*? Won't they then be confused by upside-down flight, and won't they reject the fact that planes with symmetrical wings can fly? Today I was discussing this subject with a friend, and I came up with yet another viewpoint on this subject (oh no! ;) ) I state that all wings, regardless of their shape, can only generate lift when they are tilted with respect to the airflow. Before you jump on me for this, let me elaborate. The definition of attack angle involves the drawing of a line between leading and trailing edge, right? Consider a bilaterally symmetric teardrop-shaped wing crossection at zero angle of attack. The air that streams from the trailing edge of this wing flows straight back with no deflection, and there is no lift generated. __------___ / ---___ | ---___ | ___--- \ ___--- --______--- NOT TILTED If I now modify the teardrop so it has a bump on its front, the bump becomes the new leading edge, right? Suppose the bump is below the centerline. Then we must say that the leading edge of this wing is now below the old center line, and the line that we draw from leading edge to trailing edge will now be at a significantly negative attack angle. Yet this little bump on the leading edge is so small that it does *not* generate significant lift, so the wing as a whole does not behave as if it is tilted. __------___ / ---___ | ---___ | ___--- \_ ___--- ---______--- SMALL LEADING-EDGE BUMP LEADS TO ASSIGNMENT OF NEGATIVE ATTACK ANGLE The air still streams undeflected from the trailing edge. The apparent negative tilt is an artifact of the way we define attack angle. Now here's the important part: if we now adjust our asymmetrical-bumped wing to remove the negative attack angle, we accomplish a REAL tilting of the wing. The air really starts flowing faster over the top, the wing really starts deflecting air downwards from its trailing edge, and a significant lifting force appears. The end result: the wing now has a zero attack angle, yet it acts as if it is significantly tilted. __------__ / --__ | --__ | --__ \_ ________ -------------- OBVIOUS TILT, YET ZERO ATTACK ANGLE See what I'm getting at? You argue that the "Bernoulli" explanation is correct because asymmetrical wings can give lift at zero angle of attack. I believe that this is flawed, because the purely geometrical definition of attack angle allows wings to be tilted when the attack angle is zero. If I were to judge the tilt of a wing by examining the geometry of the trailing edge or the stream of air behind it rather than by looking at the line drawn through the cross section, I will find that lifting force only appears when the air is deflected and the wing acts "tilted," regardless of whether the attack angle is zero or not. > Beaty adds: > ******************************************************** > > The truth is that there are two ways to CALCULATE lift, and both methods > > can be made into explanations of lift. > > Not true. There is one way to CALCULATE lift. That is by calculating > the airflow around the given wing shape, and determining the pressure > differential from Bernoulli. I disagree. This may be the traditional way of calculating lift, but I believe it is also possible to calculate the airflow around a given wing shape, determine the mass and the vertical acceleration of all parcels of air, and derive the lifting force. > The fact that there is a net flow downward in the wake of the wing > is a consequence of Newton's 3d law, but that fact does not help you to > do an a priori lift/drag calculation when you are designing a new wing > profile. Why not? Please correct me if I'm wrong, but it is my understanding that Newton's third law can be applied to the wake, and lift/drag can then be calculated. Engineers might avoid this technique because of extra work and less elegant results, but this doesn't mean the method doesn't work. The air mass/acceleration calculation leads directly to the explanation that lift is *caused* by reaction forces during the deflection of air. Understand that I'm not arguing that the exiseance of the reaction-forces- explanation implies that the pressure-differential explanation is wrong. The two explanations are not mutually exclusive. > It is a misconception, also, that fighters are designed with > symmetrical wings (so that they can fly inverted). Most such aircraft > cannot do extended inverted flight because of lubrication difficulties > with the power plant. The wing design is a compromise between high speed > and critical low speed characteristics - one wants to be able to walk away > from the aircraft after the flight. I'll bow to you on this one. I've been told that acrobatic single-prop planes have nearly symmetrical wing crossections, and this makes inverted flight easier (and landing presumably harder.) Is this wrong? My original point was that inverted flight is not so rare, and that symmetrical wings do function. .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 2882, dated 95/09/12 10:39:38 -- ALL Date: Tue, 12 Sep 1995 10:39:38 -0500 Sender: Forum for Physics Teachers From: Rick Tarara Subject: airplane wings The BERNOULLI OR NOT BERNOULLI debate seems to have continued (on and off) for most of the two years I've been on the list. I've stayed out of this one (even more ignorance on this topic than most), but it does seem to me that THE BEST example of semi-pure bernoulli lift would be the various man-powered airplanes which incorporate very large wing surfaces but fly at very low speeds. [AND I'm sure are totally incapable of inverted flight.] ***************************************************************************** Richard W. Tarara "Now we sit through Shakespeare in Deptartment of Chemistry & Physics order to recognize the quotations." Saint Mary's College --Orson Welles Notre Dame, IN 46556 219-284-4664 PHYSICS SOFTWARE AVAILABLE AT rtarara@saintmarys.edu http://estel.uindy.edu:70/1/aapt/rickt/software ****************************************************************************** >>> Item number 2883, dated 95/09/12 12:11:57 -- ALL Date: Tue, 12 Sep 1995 12:11:57 EDT Sender: Forum for Physics Teachers From: Paul Camp Subject: Re: airplane wings > but it does seem > to me that THE BEST example of semi-pure bernoulli lift would be the various > man-powered airplanes which incorporate very large wing surfaces but fly > at very low speeds. [AND I'm sure are totally incapable of inverted flight.] > > ***************************************************************************** > Richard W. Tarara I don't understand how this differs from what Bill is proposing. A large wing surface directs a large volume of air downward at low acceleration as opposed to a smaller, faster wing directing a smaller volume at a higher acceleration. Paul J. Camp "The Beauty of the Universe Assistant Professor of Physics consists not only of unity Coastal Carolina University in variety but also of Conway, SC 29526 variety in unity. pjcamp@coastal.edu --Umberto Eco (803)349-2227 The Name of the Rose fax: (803)349-2926 >>> Item number 2886, dated 95/09/12 12:20:26 -- ALL Date: Tue, 12 Sep 1995 12:20:26 -0500 Sender: Forum for Physics Teachers From: Rick Tarara Subject: Re: airplane wings On Tue, 12 Sep 1995, Paul Camp wrote: > > to me that THE BEST example of semi-pure bernoulli lift would be the various > > man-powered airplanes which incorporate very large wing surfaces but fly > > at very low speeds. [AND I'm sure are totally incapable of inverted flight.] > > I don't understand how this differs from what Bill is proposing. A > large wing surface directs a large volume of air downward at low > acceleration as opposed to a smaller, faster wing directing a smaller > volume at a higher acceleration. > Because, (as I view the films I've seen on man-powered flight), staying aloft does not seem to demand keeping the nose constantly up. The wings seem to provide sufficient lift in LEVEL flight as long as the air flow is above a minimal value. >>> Item number 2900, dated 95/09/13 00:40:41 -- ALL Date: Wed, 13 Sep 1995 00:40:41 -0500 Sender: Forum for Physics Teachers From: "JACK L. URETSKY (C) 1995; HEP DIVISION, ARGONNE NATIONAL LAB, ARGONNE, IL 60439" Subject: Re: airplane wings Hi all- Here's the way that I see aerodynamics, as applied to wings'n things that go fly-fly. I'm not much interested in the verbal descriptions, I'll leave it to others to sort those out. I want to solve the equations of fluid dynamics for the adiabatic, irrotational flow of an inviscid, incompressible fluid. The full equations are incredibly complicated and still not completely understood, but in the limit we are discussing, things are quite simple. Irrotationality means that the velocity has no curl. It is therefore the gradient of a potential function. Incompressibility means that the divergence of the velocity vanishes (after insisting upon conservation of mass) in the absence of sources or sinks. Adiabaticity, and Newton's 2d law lead me to Bernoulli's equation. The result? The velocity field satisfies Gauss' law (the same as for the electric field), and is the gradient of a potential function which turns out to be proportional to the pressure. So now we just do the theory of static electric fields (in a different context). An airfoil is a surface of constant potential (the flow normal to the surface must vanish). The surfaces of constant potential are perpendicular to the surfaces of constant velocity (the latter are the streamlines). Conserva- tion of matter tells us that the net flow bounded by two streamlines must be the same at every surface of constant potential. In the latter sense, the particles that separate at the leading edge of a wing must "meet" at the trailing edge. The presence of a constant potential surface in an asymptotically uniform flow distorts the flow everywhere in space in precisely the same manner that a constant potential surface in an asymptoticall uniform electric field distorts the electric field everywhere in space. The mathematics is identical for the two cases. The job of the physicist or engineer, as I see it, is to predict the results of experiments. Mathematical descriptions, such as the one that I have just given, enable one to make those predictions. The verbalizations that have occupied this thread are mere mnemonics that we can use to remind ourselves of the appropriate mathematical descriptions - once we are familiar with those descriptions. Regards, Jack "'Is it claimed that Dr. Cook's achievement is a Fact, or is it a miracle?' 'Why so?' 'Because if it is a Miracle, any sort of evidence will answer, but if it is a Fact, proof is necessary'" Mark Twain, "Official Report to the I.I.A.S. (1909) >>> Item number 2902, dated 95/09/13 08:13:28 -- ALL Date: Wed, 13 Sep 1995 08:13:28 -0400 Sender: Forum for Physics Teachers From: Kip Subject: Re: airplane wings You wrote: > On Tue, 12 Sep 1995, Paul Camp wrote: > > > to me that THE BEST example of semi-pure bernoulli lift would be the various > > > man-powered airplanes which incorporate very large wing surfaces but fly > > > at very low speeds. [AND I'm sure are totally incapable of inverted flight.] > > > > I don't understand how this differs from what Bill is proposing. A > > large wing surface directs a large volume of air downward at low > > acceleration as opposed to a smaller, faster wing directing a smaller > > volume at a higher acceleration. > > > Because, (as I view the films I've seen on man-powered flight), staying > aloft does not seem to demand keeping the nose constantly up. The wings > seem to provide sufficient lift in LEVEL flight as long as the air flow > is above a minimal value. The position of the nose has no bearing on the angle of attack of the wings when comparing different aircraft: The wings are attached at the angle appropriate to the airspeed that the plane will fly. I fly single engine Cessnas, and at cruising airspeeds in level flight, the nose of the plane is level. -Kip Shaffer >>> Item number 2907, dated 95/09/13 07:58:38 -- ALL Date: Wed, 13 Sep 1995 07:58:38 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: airplane wings On Tue, 12 Sep 1995, Rick Tarara wrote: > The BERNOULLI OR NOT BERNOULLI debate seems to have continued (on and > off) for most of the two years I've been on the list. I've stayed out of > this one (even more ignorance on this topic than most), but it does seem > to me that THE BEST example of semi-pure bernoulli lift would be the various > man-powered airplanes which incorporate very large wing surfaces but fly > at very low speeds. [AND I'm sure are totally incapable of inverted flight.] But, at least for those using the classic "Bernoulli" explanation, thin wings like the large, slow ones used in early aircraft present a serious problem because of the equal pathlengths above and below. If the particle-A particle-B explanation is used, it wouldn't lead to predictions of lift being created. And as for ignorance, my own ignorance doesn't keep me from blathering on about this topic! My blatant errors will be corrected and subtle ones exposed. I highly recommend jumping into the arguement. Often the "stupid questions" start the most informative threads. The only thing I worry about is my explaining something to someone like the original Bill Nye poster BEFORE I've had a chance to pass my arguements through the phys-L annealing oven! ;) .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 2910, dated 95/09/13 11:03:00 -- ALL Date: Wed, 13 Sep 1995 11:03:00 -0500 Sender: Forum for Physics Teachers From: Rick Tarara Subject: Re: airplane wings On Wed, 13 Sep 1995, William Beaty wrote: > But, at least for those using the classic "Bernoulli" explanation, thin > wings like the large, slow ones used in early aircraft present a serious > problem because of the equal pathlengths above and below. If the > particle-A particle-B explanation is used, wouldn't lead to predictions of > lift being created. > > And as for ignorance, my own ignorance doesn't keep me from blathering on > about this topic! My blatant errors will be corrected and subtle ones > exposed. I highly recommend jumping into the arguement. Often the > "stupid questions" start the most informative threads. ........ > OK, here's a 'stupid question'. In the 'Bernoulli' explanation of lift the air must move faster across the top of the wing than across the bottom--the path being longer across the top. HOW does the wing shape produce a force on the air in the correct direction to accellerate it at the front (and presumably) decellerate it at the rear? Seems to me at a quick glance that both contact forces (bouncing off) or viscous drag forces would slow the air across the top?? The question about 'current' man-powered planes IS--CAN the flight of these planes be attributed PRIMARILY to Bernoulli lift--or not? If not, then the anti-Bernoulli forces would seem to win; if so, then most other planes are probably a combination of Bernoulli, vortex, redirected air, etc. forces. Without a classic 'airfoil' shape, there would be no 'Bernoulli' lift, and therefore ALL the lift would be attributable to other forces. With the right shape (if Bernoulli works at all) then SOME of the lift would come from Bernoulli. Another question to ask (of someone who knows about planes) is if the 'stall' speed is different between upright and inverted flight. If some appreciable part of a plane's lift IS due to Bernoulli, then (at a given 'attack' angle), the stall speed should be greater in inverted flight. ***************************************************************************** Richard W. Tarara "Now we sit through Shakespeare in Deptartment of Chemistry & Physics order to recognize the quotations." Saint Mary's College --Orson Welles Notre Dame, IN 46556 219-284-4664 PHYSICS SOFTWARE AVAILABLE AT rtarara@saintmarys.edu http://estel.uindy.edu:70/1/aapt/rickt/software ****************************************************************************** >>> Item number 2919, dated 95/09/13 17:23:37 -- ALL Date: Wed, 13 Sep 1995 17:23:37 -0400 Sender: Forum for Physics Teachers From: Malcolm Davis Subject: Re: airplane wings In-Reply-To: Paul Camp's message of Tue, 12 Sep 1995 12:11:57 -0400 (EDT) I'm sure I've said this before, but I think the Bernoulli vs. Downward airflow argument is a non-argument. It is identical to a wonderful discussion question Van Nie uses: What force stops a car whose wheels do not skid? The force exerted by the brake shoes on the brake drums? or the force exerted by the wheels on the road? The answer is ... both. The force of the wheels on the road provides the net force which decelerates the car, but since this is a static frictional force it can dissipate no energy. The force on the brake drums is kinetic friction which dissipates the energy, but produces no net force on the car. Malcolm -- Malcolm E. Davis Macromolecular Modeling Email : davis@nod.bms.com Bristol-Myers Squibb Phone : 609-252-4324 P.O.Box 4000 FAX : 609-252-6030 Princeton, NJ 08543-4000 Office : LV H.3812 Disclaimer: I speak for myself only. (Of course, you're free to listen. :-) >>> Item number 2923, dated 95/09/13 18:41:13 -- ALL Date: Wed, 13 Sep 1995 18:41:13 -0500 Sender: Forum for Physics Teachers From: "JACK L. URETSKY (C) 1995; HEP DIVISION, ARGONNE NATIONAL LAB, ARGONNE, IL 60439" Subject: Re: airplane wings Hi all- Inertia is accounted for in the Bernoulli equation, which relates pressure differential (F, in F=ma) to change in velocity. The inertia term is the density. In considering jets, one has to consider the boundaries through which the jets flow. See Vol. II of Sommerfeld's lectures, Ch 6, where it is found that (in 2-dimensions, in this case) jets do indeed contract. Incidentally, the sketch that I suggest that you consider is essentially shown in Sec. VI.29 (it shows the streamlines, which are like the E-field lines). The mathematics tells us, with considerable precision, that one must consider the flow pattern in all of space, and that it is nonsense to talk about the behavior of the "stream of air". The electrostatic analogy flows from the fact that the two situations are described by PRECISELY the same equations. That fact becomes the starting point for discussion. The language that you choose to use depends upon the "spin" that you want to put upon the conclusions. Regards, Jack ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > ********************************************************* > On another topic: a flat plate is moved through the air at a small angle > of attack. Do you know a good verbal explanation for *why* the relative > speed of air near the plate is faster above and slower below? If > particles divide at the leading edge, follow the wing surface, and meet at > the trailing edge, it certainly appears that they must take equal path > lengths and should have equal speeds. > **************************** > Like a good physics teacher, I'll answer with a question. > Can you use the electrostatic analogy to sketch the equipotential > lines around a conducting plate that is held at an angle to a > uniform electic field? > Regards, > Jack *************************************************** Sender: Forum for Physics Teachers From: William Beaty Subject: Re: airplane wings Yes, but doesn't this ignore inertia? Doesn't this electrostatics analogy predict that gasses exiting a jet engine would spread in aall directions, when they actually form a narrow jet (and create large reaction forces?) Won't similar problems arise with an airfoil, where a stream of air behaves as if "launched" at a downward angle from the trailing edge? >>> Item number 2930, dated 95/09/13 19:17:35 -- ALL Date: Wed, 13 Sep 1995 19:17:35 -0800 Sender: Forum for Physics Teachers From: "David J. Hamilton" Subject: Glider Design! All this talk of airplane wings reminds me of a marvelous little program called Glider Design! written by Michael Kamprath. It is a computer assisted design program for simple balsa wood gliders, complete with teacher and student materials (in MicroSoft Word) suitable for 9-12 grades (possibly lower grades as well). I happened by this accidentally one day last year and used it in a general science class after our unit on fluid dynamics. My classes ended up building gliders, making several modifications, etc. It fit my needs quite well and I would like to recommend it. The best news is it's free (most accessible download is from Kamprath's home page - http://www.earthlink.net/~kamprath/home.html). I know he has a Mac version, those of you who are still stuck using DOS/Windows or whatever may be out of luck. I hope I'm not proclaiming old news, but since I found it by accident, I thought others may not have heard of it. BTW - If any of you Bernoulli experts have seen the instructional materials I'd appreciate a critique of Kamprath's brief mention of how the angle of attack of the flat wings creates lift (he mentions the Bernoulli effect but does not go into detail). Regards, Dave ********************************************************************** * * * David J. Hamilton, Ed.D. "And gladly wolde he lerne, * * Franklin HS and gladly teche." * * Portland, Oregon * * djhamil@teleport.com Geoffrey Chaucer * * * ********************************************************************** >>> Item number 2931, dated 95/09/14 09:42:33 -- ALL Date: Thu, 14 Sep 1995 09:42:33 EDT Sender: Forum for Physics Teachers From: Paul Camp Subject: Re: airplane wings > I'm sure I've said this before, but I think the Bernoulli vs. Downward > airflow argument is a non-argument. > Malcolm E. Davis This, I believe, was Bill's original point. Paul J. Camp "The Beauty of the Universe Assistant Professor of Physics consists not only of unity Coastal Carolina University in variety but also of Conway, SC 29526 variety in unity. pjcamp@coastal.edu --Umberto Eco (803)349-2227 The Name of the Rose fax: (803)349-2926 >>> Item number 2932, dated 95/09/14 07:33:22 -- ALL Date: Thu, 14 Sep 1995 07:33:22 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: airplane wings On Wed, 13 Sep 1995, Malcolm Davis wrote: > I'm sure I've said this before, but I think the Bernoulli vs. Downward > airflow argument is a non-argument. It is identical to a wonderful > discussion question Van Nie uses: What force stops a car whose wheels > do not skid? The force exerted by the brake shoes on the brake drums? > or the force exerted by the wheels on the road? Yes, I'm aware of this. If you'll read this whole thread, you'll see that this is NOT what I'm complaing about (at least this time!) The Bernoulli explanation is not wrong. The problem is that the usual explanation in K-6 textbooks and children's science books has several serious mistakes, most of the books have the SAME mistakes, and most of the books do not contain the easily-grasped 3rd-law explanation but concentrate entirely on Bernoulli. If these books had done Bernoulli explanations correctly, I never would have had cause for complaint. > The answer is ... both. The force of the wheels on the road > provides the net force which decelerates the car, but since this is a > static frictional force it can dissipate no energy. The force on the > brake drums is kinetic friction which dissipates the energy, but > produces no net force on the car. Yes, and does a rocket create thrust by creating a force-pair and ejecting matter out the back, or by creating a higher pressure at the front of its combustion chamber than the rear? Both! But it would be quite misleading if books always ignored the 3rd-law view, ignored the ejected matter, and concentrated entirely on the pressure-difference within the engine. This would make rocket-thrust effects very difficult to understand. This is why I take exception to the way K-6 texts explain airfoil lift. .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 2940, dated 95/09/14 12:55:02 -- ALL Date: Thu, 14 Sep 1995 12:55:02 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: airplane wings On Wed, 13 Sep 1995, Rick Tarara wrote: > The question about 'current' man-powered planes IS--CAN the flight of > these planes be attributed PRIMARILY to Bernoulli lift--or not? If not, > then the anti-Bernoulli forces would seem to win; if so, then most other > planes are probably a combination of Bernoulli, vortex, redirected air, > etc. forces. Without a classic 'airfoil' shape, there would be no > 'Bernoulli' lift, and therefore ALL the lift would be attributable to > other forces. With the right shape (if Bernoulli works at all) then SOME > of the lift would come from Bernoulli. I, the raving anti-bernoulli flamer, ;) would say that neither side wins, and this is not the issue. A tilted flat wing does not *work* by 3rd-law effects. In fact, it can be *explained by* 3rd-law effects, or it can be *explained by* appeals to Bernoulli equation. The same is true of non-tilted wings with flat bottoms and curved tops. It's not an issue of part of the lift coming from Bernoulli effects and part from 3rd-law. Instead, it is possible to *totally* explain lift with either method. So, how does the airfoil really work? Both ways, and depending on the application, situation, grade level of the audience, etc., one may be a much better explanation than the other. My complaint is with books which do the Bernoulli explanation wrong, which have erroneous and misleading diagrams, and whose authors seem to think that the Bernoulli explanation is correct and the Newton's 3rd-law explanation is wrong. Those with WWW capability can take a look at pictures I drew of good/bad wing diagrams at http://www.eskimo.com/miscon/miscon4.html. Also see http://amasci.com/miscon/miscon.html for some interesting other stuff. .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 2941, dated 95/09/14 13:25:28 -- ALL Date: Thu, 14 Sep 1995 13:25:28 -0700 Sender: Forum for Physics Teachers From: William Beaty Subject: Re: airplane wings On Wed, 13 Sep 1995, JACK L. URETSKY (C) 1995; HEP DIVISION, ARGONNE NATIONAL LAB, ARGONNE, IL 60439 wrote: > Hi all- > Inertia is accounted for in the Bernoulli equation, which relates > pressure differential (F, in F=ma) to change in velocity. The inertia > term is the density. Hmmm, I still can't visualize this. If the electrostatic analogy is applied to a 2-D flow around a circular rod, won't the upstream and downstream flow patterns be mirror images of each other? Yet inertia effects should make the upstream and downstream flows not be simply mirror images. If I swap polarities in the electrostatic analogy, the pattern of field lines should be unaltered, yet if I swap flow direction for the flow around the cylinder, I would expect the asymmetric upstream/downstream pattern to change orientation. In other words, can the electrostatic analogy explain the fact that I can blow a paper across my desk with my lungs and lips, but sucking doesn't accomplish the same thing? (Ignore turbulence, imagine this done below the turbulent regime.) > In considering jets, one has to consider the boundaries through > which the jets flow. See Vol. II of Sommerfeld's lectures, Ch 6, where > it is found that (in 2-dimensions, in this case) jets do indeed contract. > Incidentally, the sketch that I suggest that you consider is > essentially shown in Sec. VI.29 (it shows the streamlines, which are > like the E-field lines). > The mathematics tells us, with considerable precision, that > one must consider the flow pattern in all of space, and that it is > nonsense to talk about the behavior of the "stream of air". This is very true. I'm guilty of trying to simplify the wing airflow by only examining the part that's quite near the wing. > The electrostatic analogy flows from the fact that the two > situations are described by PRECISELY the same equations. That fact > becomes the starting point for discussion. The language that you > choose to use depends upon the "spin" that you want to put upon the > conclusions. But I still have the mental image of the flow through an orifice giving two different patterns depending on the direction of the air at the orifice, but an e-field giving a single pattern regardless of polarity. This suggests to me that the electrostatic analogy is overly simplified and cannot be used on the wing unless the fluid is extremely viscous. What am I missing here? .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page >>> Item number 2966, dated 95/09/15 13:18:59 -- ALL Date: Fri, 15 Sep 1995 13:18:59 EDT Sender: Forum for Physics Teachers From: James McLean Subject: Re: airplane wings > > In fact, it can be *explained by* 3rd-law effects, or it can be > *explained by* appeals to Bernoulli equation. > > Instead, it is possible to totally explain lift with either method. > > > Those with WWW capability can take a look at pictures I drew of good/bad > wing diagrams at http://www.eskimo.com/miscon/miscon4.html. > > William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 Your WWW page says 'Aircraft wings do not get their lift from the "Bernoulli effect"', but it's clear from the first paragraph above that that is one possible explanation. Perhaps closer to the mark would be 'Aircraft wings do not get their lift from having a rounded upper surface'. --James McLean grad student Cornell University ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ RECENT ADDITIONS ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ From billbeskimo.com Fri Sep 26 07:48:57 1997 Date: Sun, 21 Sep 1997 07:20:50 -0700 (PDT) From: William Beaty To: Jack Lambie Subject: Re: LIFT Hi Jack! Is your below message part of PHYS-L archive? Shall I add it to my "Lift misconceptions" webpage as part of the PHYS-L text file on lift? On Sun, 21 Sep 1997, Jack Lambie wrote: > 3298PHYS-L@UWF.BITNET > > > The Mystery of Lift Solved > As the airplane moves the wings deflect air. The air molecules are > forced to go down and forward and above the wing up, backwards and > down, below the wing. The air reacts in an equal and opposite direction > to the way it was moved and pushes back by way of pressure changes. > There can be no pressure change without moving air. > Does this mean all those books about airplanes are wrong? Does > everything have to be rewritten? > Yes. Of course! continuing to spread the Bernoulli Virus must end. > However I can see a tremendous learning lesson. By using to the > old books with the poor explanations and asking questions about the > Bernoulli description the student can see the anomalies. The learner > develops the realization that to understand anything it should be > explained from more than one point of view. Also those accustomed to > the weight of authority in numbers will find that just because every > book uses the Bernoulli effect as the total explanation of lift does > not make it correct. A better understanding of science, the meaning of > explanations is gained through the history of describing lift. > > Aerodynamics is a most intriguing field. I like it because it is so > stimulating to think about what is really going on. Just about > anything said in that field can be true and false depending on size of > the object, the speed and the purpose of the design. For example: > > The teardrop shape has lowest drag at higher speeds but a sphere has > lowest drag at very slow speed. > > A raindrop is not tear-shaped but is a wiggling flattened blob. > > A rough surface has lower drag at slow speed but higher drag at high > speed. > A flat airfoil has better lift going very slow but a thicker curved > airfoil wing has better lift a bit faster. > > A airfoil curved on the bottom and almost flat on top is better for > lift just below the speed of sound to delay shock waves and lower drag. > > Highest lift is with an airfoil more deeply arched on both top and b > bottom. > Flying near speed of sound things are different. Sharp edges or > swept wings are used to delay drag used that give very poor lift at > slower speeds, unless you really fly slowly, like bugs and model planes. > > Then they too need sharp leading edges and almost flat airfoils. > Flies have little hits sticking out on their wing edges to make the air > turbulent which, in a fly-sized creature, is very viscous, sticky. > > Most interesting is the confusion and misinformation in describing > lift and drag. > > This article explains this most contentious aspect, lift, correctly so > we can all enjoy this most subtle of technical subjects. But why is > something that has successfully allowed us to fly for almost a hundred > years still argued about? > > Here is the ^Óstandard^Ô explanation of lift, then why this > approach has gradually created a chorus of detractors pointing out the > many anomalies. I^Òll discuss why is not ^Ótrue^Ô and give examples of > confusion wrought by the Bernoulli Suction idea. The reaction > explanation will be shown to be more simple, descriptive what is > actually happening more accurately and with power and goodness > Most of us have been exposed to this explanation of lift because it > is included in many science books, encyclopedias and even the Federal > Administration ^ÓHandbook on flight^Ô. > ^ÓAn airplane flies because the wing is shaped with a greater > curve on the top of the surface than the bottom. The air flowing over > the wing must travel farther over the top than the bottom so it must > speed up to meet the air that went past from which it was divided. As > Bernoulli pointed out in 1796 ^ÓWhen air speeds up the pressure drops.^Ô > Thus the reduced air pressure over the top of provides most of the > lift^Ô. > That idea has become pretty much the most common text book and > encyclopedia explanations of lift. Other descriptions of lift, the > circulation explanation. The Action-reaction, air is pushed down by a > wing and the air pushing back holds it up. > The action-reaction explanation is simpler, describes more Most > of us have been exposed to this explanation of lift because it is > included in many science books, encyclopedias and even the Federal > Administration ^ÓHandbook on flight^Ô. > Describing lift by the faster-air-suction-idea results in such > mistaken ideas they have caused a waste of time and money for > aerodynamic experimenters. > The standard ^ÓAn airplane flies^Ô says the wing is shaped with a > greater curve on the top of the surface than the bottom. The air > flowing over the wing must travel farther over the top than the bottom > so it must speed up to meet the air that went past from which it was > divided. As Bernoulli pointed out in 1796 ^ÓWhen air speeds up the > pressure drops.^Ô Thus the reduced air pressure over the top of > provides most of the lift. > > > Air does not rush over and airplane wing and does not rush over the top > of an air foil faster than under the bottom. In real life the wing moves > through still air. > > The slight downwash behind the wing is not caused by the pressures > around the wing. > > An airplane flies through the air. The air is not going over or under > the wings but is being deflected from its stationary position by the > planes passage. The plane is the thing doing the rushing. As its body > and wings go through the air subsonic of course, the air ahead of the > the plane begins to move out of the way, Some goes up as the wing > approaches and some is pushed down. The air has mass and inertia. It > wants to stay where it is and when moved it makes a reaction exactly > equal and opposite on the object that is moving it by... how else? > Pressure changes. The pressure change is in response to deflecting air. > > Since deflection, reaction, and the pressure changes happen instantly > and simultaneously what is the first cause? In the Smithsonian Exhibit > on Lift it says the pressure causes the down wash. Does pressure cause > the air to deflect or does the deflected air cause pressure changes? It > can be described either way but only one is true in the scientific > sense. > Now we have to do a bit of Philosophy. There are many absolutely > true statements that are not true in the scientific sense. Ask any > ;pilot what makes a plane fly and he will say ^ÓMoney^Ô. > Having owned airplanes all my life I must agree that is crucial. One of > my students in response to that said, ^ÓThe key to the magneto.^Ô A glider > student pilot said, ^ÓThe tow^Ô. And so on. You can think of a lot of > completely true statements like that that really don^Òt go the the > deepest understanding of lift. So in the scientific sense.. > What is ^ÓTrue^Ô? > In science ^ÓTrue^Ô, is > 1: The simplest description, > 2:Is not a ^Óas if^Ôstory^Ô but adheres to the physically happening. > 2: Fits the most cases and > 3: is closest to our experience. > The description of reaction to acceleration describes everything > moving: In rockets, a mass of fuel is accelerated in one direction the > rocket goes the other way. > A helicopter accelerates a mass of air down and in reaction it > goes up. We put our hand out of the car window and feel the push, the > reaction, resulting from the air being deflected but we don^Òt feel the > absolute change in air pressure. We do feel the reaction carried to our > hand by air pressure. > Putting your hand over a wing while in flight would not give the > sensation there is a lower pressure but we do feel the reaction when the > plane lifts off or pulls up. > We can't tell air pressure, unless we are on a fast elevator or > airplane climbing or descending and our ears pop. > A car goes around a corner and the acceleration, change in > direction, we feel by our bodies reaction to a sideways force. > We can feel action and reaction easily so it is more in our experience > than air pressure. > > Any deflection of the air both the reaction and the pressure > differences on the object doing it , such as a wing, are instant and > simultaneous. Because they happen at the same time would that make > them equal as cause? There is a compelling case to pick reaction of > pressure as the ^Ócause^Ô. > We define ^Ócaused by^Ô with action. The wing is moving the air so it > doing something that ^Ócauses^Ô lift. > The reaction to this cause results in pressure > differences. Just because the reaction and pressure change is > simultaneous doesn^Òt make them equal when we talk about cause. > More important using reaction describes how any object that > deflects air sets up an equal and opposite reaction. Reaction also > explains a wider range of situations, not just those in fluids. The > simplicity of action=reaction, plus its ability to be sensed easily by > us humans gives the ^Ótrue^Ô cause, not changes in fluid pressure. > Reaction as the cause of pressure change. Reaction to deflecting > (accelerating) the air is the PRIMARY cause and the changes in pressure > is the SECONDARY EFFECT that transfers the reaction to the body. > In the NASM section ^ÓWhat makes a Wing Work^Ô the explanation is > confused by using the secondary effect to explain lift. > ^ÓA wing is shaped and tilted so the air moving over it moves faster > than the air under it. As the air speeds up, the pressure goes down. So > the faster moving air above exerts less pressure on the wing with the > slower moving air below. The result is an upward push on the wing-lift. > It then talks about the amount of lift being affected by the size shape > and angle it meets the oncoming air. > What's wrong with that? First the air is not oncoming. The plane is > flying through it. Why the confusing, to students, change in reference? > It might be fine for aerodynamicists working with wind tunnels but for > the public tell it like its really happening. Well you say ,^ÔIts > easier to explain with the air moving over the wing, its all relative > anyway. There is no difference if the wing moves or if the air moves. ^Ó > Ok. If you want to do it that way, but you better explain to > the student or beginning pilot that this explanation is not the the true > state of affairs but aerodynamicists jargon and an ^Óas if^Ô one that you > are using because you think its easier to explain that way, probably > because that's the way you learned. > For a student in school or ab-initio pilot it makes no sense > because they think of the airplane as going through the air. > Again is the confusion of primary and secondary effects to > explain lift. A wing airfoil is designed to deflect air efficiently > so the most lift reaction is gotten with the least energy used. > Usually it is curved more on the top than the bottom but not > always. A training type hang glider has equal curves on the top and > bottom of the wing, small flyers like insects and model throw gliders > have flat airfoils and jetliners are more curved on the bottom than the > top because they need less lift at there fast cruising speeds. > The exhibit was surely not written with any input from knowledgeable > people. > Using Bernoulli is entirely passe. He died long before anyone > thought of an airplane wing lifted by his theory of pressure change with > speed. > Of course there are pressure differences over a wing or body as it > moves through a fluid or a fluid moves over it. That is correct. But Dan > Bernoulli^Òs theorem is really no explanation of anything. It is just a > statement of the relationship between speed and pressure. > Pressure can be measured with gauges connected to taps, little > holes in the surface and offer great possibilities for mathematical > description and computer prediction and analysis but they are not the > primary cause. Think about it. There can be no pressure change without > deflecting air. The first cause is the air being > deflected. > The New Smithsonian Air and Space Museum is a classic example of the > confusion wrought by the ^Óvirus infection^Ô of the Bernoulli > explanation. > The Smithsonian^Òs ^ÓBernoulli Brain Teasers^Ô can better be > described by action-reaction. It should be called ^ÓNewtonian Brain > Teasers.^Ô > ^ÓAn airfoil seen from the side is curved on top and nearly flat on > the bottom. As a wing moves through the air, the air divides to pass > above and below the wing. Since the wing^Òs upper surface is curved, the > air rushing over the top speeds up and stretches out. This decreases the > air pressure above the wing. The air flowing below the wing in a fairly > straight line so its speed and air pressure remain the same.^Ô > The wing is moving through the air, and, below the speed of > sound, the air senses the coming wing. Air above moves forward, then > up and back and below it is pushed forward and down. The air is pulled > along by friction. As the wing moves by The more quickly the air that > has been moved slows and stops the lower the drag. If it is pulled along > with the wing it uses a lot more energy and has higher drag. > Training hang gliders have a single surface airfoil. Its the same > distance over the bottom as over the top. How can it fly? > How does a plane fly upside down? > How come model planes and insects with flat airfoils fly so well? > Since the airfoil shape has not changed why does lift increase as > the angle of attack increases? > The answer to these questions are clear when lift is described as > the result of deflecting air downwards. Any shape can create lift at a > positive angle of attack. > ^ÓHold piece of paper between your fingers and blow over > it. It pulls up. Why?^Ô Air above and below the breath of wind is pulled > from its position into the high speed flow. If air is moved down the > equal and opposite action is an up force. This force is transferred to > the paper by pressure which pulls it up. > ^ÓTake two balloons put a little water in them for steadiness then > tie each with a foot of string and hang them a few inches apart Blow > between them. Newton would say they move toward each other because the > air is deflected in a curve over the balloon^Òs surface. Its > acceleration from its straight path and the resulting reaction is a pull > on the balloon. > When you go around the curve in a car. You are pulled to the > outside. So also the air going around the balloons sets up a force > opposite to the accelerations of the air that force makes the balloons > move toward each other. > ^ÓA ping pong ball is put on a flexible straw tube and you blow in > it with the ball balanced on top. The ball does not blow away but stays > in place. Why?^Ô > The Newtonian or reaction explanation is simply that the air going > around the curve has the equal and opposite reaction to its change in > direction, which creates an instantaneous force pulling on the ball from > all sides. If it starts to move to one side it is quickly self > correcting because if the air is cut off from one side and increased on > the other with its attendant increase in force pulling it back over the > center of the tube. The more air being moved the greater reactive force. > ^ÓTake a thimble, put a piece of light cardboard over it with tack > through it extending into the hole . Blow into the thimble and the card > stays in place instead of blowing away.^Ô My Reaction explanation is that > the air coming out of the hole goes around the corner at the edge of > the hole in the thimble and the cardboard. Its direction is changed. > When it goes around the corner that deflection makes a pull on the edge > of the object making the air turn . That pull holds the cardboard in > place. > The ^ÓDid You Know^Ô section shows an obstacle, it looks like a > streamlined shape like a fairing over the NDB antenna on an airplane. > It says, ^ÓWhen moving air encounters an obstacle ---its path narrows as > it flows around the object-------Freely flowing air ---speeds up where > its path narrows and slows back down where it widens.^Ô > Any grade school student would look at that as say, ^ÓBut Mr. > Lambie the air flow widens as it goes around the object. It has to or it > would have to go right through the object. I would have to say,^ÔAn > obvious observation. ^ÓGood for you. You are a intelligent student to > question an explanation that doesn^Òt make sense.^Ô > Here^Òs how I would explain this example with the True description. > The air must widen, not narrow, to go around any object. The > object deflects the air, that is, causes it to moved. This > instantaneously sets up a reaction opposite to its deflection. This, > over the curve, would be a pull . The counter reaction, of course, > is transferred to the object by a minus pressure. How else? > The primary cause of the pressure change is reaction due to the > air being ^Ówidened^Ô out as it moved around the object. > The ^ÓDid You Know?^Ô Has a most confusing example. It shows a > truck and a car passing and says that the sideward tug you feel on your > car when you pass a large truck going in the opposite direction is > caused by air pressure. The passing vehicles form a constriction that > speeds up the flow of air, reducing the pressure between them (it makes > no difference which is moving the air or vehicles. The result is the > same. The higher pressure on the other side of the car pushes it toward > the truck during the split second they pass.^Ô > But my observant student would say. ^ÓI looks to me that if only > the air were moving the truck would have a tailwind and the car headwind > so there would be no deflection on air by the truck at all.^Ô True my > good student, but as poor as this example is, it would work somewhat > because the car pushing the strong headwind out of the way would be > deflecting the air causing an equal and opposite reaction which would > give a pull. The pull reaction is transferred to the front corners of > the car as a lower pressure which the truck would also feel as a pull. > I have done two education TV shows on this and written about it in > all 7 of my books. It seems radical. It would negate every aviation and > bird book dealing with movement in air and water and require rethinking > for teachers. No more blind copying of the encyclopedia by magazines and > newspapers. > Yet, I have discussed this for years with aerodynamicists Dr. Bob > LIebeck, Dr. Peter Lissaman, Dr. Paul Mac Cready, Barnaby Wainfain. > Bruce Carmichael and my friend Balan Menen. The are unanimous in > agreement with this interpretation and description being correct. > How come the ^ÓCurved airfoil^Ô fallacy and why is it so often > repeated? Why the Bernoulli description has become the most used is a > good question for research. One teacher likened it to a computer virus > that spreads and spreads. Bernoulli^Òs simple faster lower pressure > relationship ideas were picked up when people first began to fly. His > faster flow low pressure idea was presented to explain how lift is > created and , while not a true explanation, somehow appealed to the > pilots and aerodynamicists. Why? > Most people then would not to think that a special shape, curved > more on the top would be the secret of lift. Perhaps it gave a certain > mystique and power to those involved with airplanes. We all like to > think we have special knowledge and this was a perfect and subtle > explanation of lift. > The general feeling I get is, perhaps excepting Paul MacCready, is > that it doesn^Òt rate the time involved in changing a way of looking at > something they already know and understand. > I suppose it is like when I talk about legal language to lawyers. > They largely agree that legal verbiage is redundant, ambiguous, archaic > that its almost illiterate. But they are accustomed to it and know what > is being said so who cares. Its their job. Why make plain language law. > Then people wouldn^Òt hire lawyers. > > > As the first director of Education at LA^Òs Museum of Science qnd > Industry I developed a correct and superb description of lift using a > water ^Ówind^Ô tunnel. > (Author of ^ÓComposite Construction for Homebuilt Aircraft^Ô $20 signed > and mailed. > ^ÓUltralight Airmanship^Ô $10 from the author signed and PP. > Others in the library > ^ÓBuilding and Flying Gliders and Sailplanes^Ô > ^ÓComposite Construction for Radio Controlled Models^Ô > ^ÓHomebuilt Rotorcraft^Ô > ^ÓUltralight Kit Book^Ô > ^ÑAlso lots of Aviation and Aerodynamic articles and ^ÓCondor Flight^Ô in > Air and Space 1987. > POB 1231 Morongo Valley, CA 92256 > Phone and FAX 760 363 6806 > jlambie@mail.idt.net > .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page From billbeskimo.com Sat Mar 29 16:15:40 1997 Date: Sat, 29 Mar 1997 15:19:01 -0800 (PST) From: William Beaty To: phys-l@atlantis.cc.uwf.edu Subject: Re: "How Things Work" Website On Sat, 29 Mar 1997, John Mallinckrodt wrote: > I do not happen to be a particular fan of the Bernoulli-based explanation > for lift and much prefer transfer of momentum arguments. On the other > hand, I thought the explanation provided at the "How Things Work" website > was rather good. I thought that most of the other material in the website is very good. It could be improved by adding a webpage index, since the file was up near 300K. I'd have liked to browse the file, rather than having to page down through the whole thing. > I'm curious about why you call the "airstreams must join at the trailing > edge" argument "false." In the steady state, laminar flow regime in which > the Bernoulli principle holds (and which is, admittedly, questionable for > airplane wings) mustn't this be the case? Nope. I'm not sure, but I suspect that in some simplifications to a 2-dimensional case, the parcels of air may indeed be required to rejoin at the trailing edge. If so, then this is an artifact of the simplifying assumptions, not a feature of real airfoils. In real, 3D wings there is a sort of singularity trailing behind the wing, called a "vortex sheet" in aerodynamics textbooks. When generating lift, the parcel underneath the airfoil is slowed and the parcel above speeds up. The parcels which were once adjacent are permanently separated from each other. As a consequence, an overall vortex motion appears, with the vortex core centered near the tip of the wing. The vortex core acts as a boundary for the edge of the vortex sheet. These are all 3D effects, and might not be possible in a "2D universe." While this does screw up the elementary-school aerodynamics explanation, it does clear up confusion about thin airfoils. In a thin airfoil the path lengths are equal, so how can the "Bernoulli Effect" apply? When an uncambered thin airfoil (e.g. sheet of plywood) generates lift, the air above is sped up and the air below slows down, and the parcels do not recombine at the trailing edge, nor do they need to. There is a relative difference in velocity, and so a differential pressure pointing upwards. "Bernoulli" therefor applies to tilted sheets of plywood, not just to cambered thick wings having unequal path lengths, and those who defend the "Bernoulli" explanation can breath a big sigh of relief. ...and then search for a better explanation for why the air above the airfoil *really* moves faster. Jan-Olov Newborg in Sweden, an associate of Dr. K. Weltner of the infamous "anti-bernoulli" papers in AJP and TPT, sent me a couple of GIFs which I should strip down and install on my webpage. They depict the path of a sheet of smoke, a "smoke pulse", as a wing flys perpendiculary through it in a wind tunnel. The GIF is pretty small, I've attached it to this message as a MIME file. It's also at: http://amasci.com/wing/airgif2.html http://amasci.com/wing/airfoil.html He mentions that this "phase shift" effect is proportional to lift. If any airfoil attack angle is adjusted in order to eliminate this phase shift, lift is eliminated as well. So, since the parcels of air do not rejoin, and in fact it seems that this "phase shift" is a necessary component of the lift-generating mechanism, it becomes very wrong to base the "Bernoulli" airfoil explanation on a requirement that the parcels rejoin at the trailing edge. I doubt that this fact will do much to counter the spread of this misconception. After all, it's in all the textbooks, and how can that many textbooks be wrong? ;) .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://amasci.com/ Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page Date: Tue, 28 Jul 1998 14:41:17 +1200 From: Marlyn Jakub To: phys-l@atlantis.uwf.edu Subject: RE: Raskin's Coanda effect article Bill Beaty wrote: >From: William Beaty >To: list physics teaching >Subject: Raskin COANDA EFFECT article >X-Authentication-Warning: eskimo.com: billb owned process doing -bs >X-Listprocessor-Version: 7.2 -- ListProcessor by CREN > > >The Airfoil-Lifting-Force article from QUANTUM magazine is now online on >Jeff Raskin's website: > > http://freebie.cfcl.com/jef/ > >Lots of good material regarding the incorrect "Bernoulli effect" >explanation of lifting force. It includes some A. Einstein history which I >have never before enountered. Apparently Einstein designed an airfoil >during WWI, but his thinking was based upon the usual incorrect >explanation of aerodynamic lift, and his design didn't work Einstein >found: > > "Although it is probably true that the principle of flight can be most > simply explained in this [Bernoullian] way it by no means is wise to > construct a wing in such a manner!" > >Not only does the "longer path gives faster flow" misconception suck in >students, educators, and textbook authors, it sucked in Albert too! > Bill, On 13DEC95, I wrote a criticism of this article for Phys-L readers. Again, I would strongly urge readers of Raskin's logic to add lots of salt before believing any of Raskin's claims. In short, Raskin uses air jets which are smaller than the wing object. This can be totally misleading. E.g. blow through in inverted small (5mm) funnel and you can hold a ping-pong ball inside the funnel...but with a downward blast of ping pong ball diameter, there's no lift for the ball to stay in the larger funnel. Raskin never mentions circulation because he cannot have much with flow only over the top of the wing. With circulation, flows over the wing are much larger than those under the wing, so the 2% figure only shows that he needed circulation in his model to get the better velocity estimates. Raskin claims that the back of the airfoil is most important, but the primary pressure lift profile is at the front third of the typical wing, where Raskin's arguments would seem to lead to the opposite conclusions. The semi-stall condition for wings is when the lift-off point moves forward from the rear edge of the airfoil, but there is still some lift...and a lot more drag. I have no conformation on the claim about Einstein's wing design or on Raskin's role in developing the Mac computer...perhaps Jobs or Wosniak can help on the latter. From airboy@PHYSICS.UCSB.EDU Tue Feb 2 18:27:09 1999 Date: Sun, 17 Jan 1999 10:22:28 -0800 From: Roger Freedman Reply-To: "phys-l@lists.nau.edu: Forum for Physics Educators" To: PHYS-L@LISTS.NAU.EDU Subject: Flight references I would like to suggest that the recent discussion of the origin of lift (which seems to be rehashed over and over and over again on this list, as well as elsewhere) could benefit from a consultation of the literature. (Yes, even in the age of the Internet, it serves us well to make careful study of published, peer-reviewed materials.) I recommend the following sources: * Alexander, R. McNeill. Exploring Biomechanics: Animals in Motion. Scientific American Library, 1992. Chapters 4 and 5 of this excellent semi-quantitative introduction to biomechanics describe the gliding, soaring, and flapping flight of birds and insects. There are some nice three-dimensional depictions of the airflow around aircraft and birds in flight. The author is a professor of zoology at the University of Leeds. * Anderson, John D., Jr. A History of Aerodynamics and Its Impact on Flying Machines. Cambridge University Press, 1997. A very extensive technical history (fully half the book covers the centuries before the Wright Brothers). The author is a professor of aerospace engineering at the University of Maryland. * Ashley, Holt. Engineering Analysis of Flight Vehicles. Addison-Wesley, 1974. Reprinted by Dover Publications, 1992. A superb graduate-level textbook that should be accessible to anyone with a physics degree. The book has clear, quantitative discussions of two- and three-dimensional wings. The author was a professor in the Department of Aeronautics and Astronautics at Stanford University (and an excellent teacher, as I can attest from personal experience). * Hubin. W. N. The Science of Flight: Pilot-Oriented Aerodynamics. Iowa State University Press, 1992. Written by a physicist (on the faculty at Kent State) who is also a pilot. The book has a wealth of real-life examples based on data from light airplanes. The extent of quantitative detail should be satisying to anyone reading this list. * Hurt, H. H, Jr.. Aerodynamics for Naval Aviators. U. S. Navy Publication NAVAIR 00-80T-80, 1960. (Reprinted by Aviation Supplies and Academics, Inc., and available from Aviation Book Co., 7201 Perimeter Road S., Suite C, Seattle WA 98108) Very clear textbook with excellent discussions of the three-dimensional aspects of airflow around aircraft. The author was on the faculty of the University of Southern California. As an aside, from my experience as a pilot I can attest that what *really* makes airplanes fly is MONEY! (There is a wonderful T-shirt for pilots that carries the slogan "If God had meant man to fly, he would have given him more money.") +++++++++++++++++++++++++++++++++++++++++++++++++++++++ Roger A. Freedman Department of Physics and College of Creative Studies University of California, Santa Barbara Mailing address: Department of Physics UCSB Santa Barbara CA 93106-9530 E-mail: airboy@physics.ucsb.edu WWW: http://www.physics.ucsb.edu/~airboy/ Voice: (805) 893-2345 FAX: (805) 893-3307 Voicemail: (800) 344-3147 x4322