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#41
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On Fri, 09 Sep 2005 10:47:52 -0400, T o d d P a t t i s t
wrote: A change in height is not an indication that the vertical component of the total aerodynamic force is less or more than weight. Only an accelerating change in height indicates an imbalance in forces. Constant climbs, constant descents, fully developed spins, etc. all have the vertical component equal to weight. Sorry, I wrote before I thought. I meant "no change in acceleration" and didn't catch that he had stated "Steady sinking" and "fully developed" He's right. I'll go crawl away now... Jim http://www.unconventional-wisdom.org |
#42
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"T o d d P a t t i s t" wrote in message ... "Dudley Henriques" dhenriques@noware .net wrote: both descriptions (often referred to as the Bernoulli and Newton descriptions) are 100% correct Not AGAIN!!!!!!!!! Dudley Now Dudley, you don't say that to every new student who tries to steer with the yoke while taxiing, do you? OMG, not another student who's got it wrong -when will it ever end! Similarly, there is an endless supply of people who haven't yet figured out what "lift" is. It will never ever stop. The best we can do is to do a better job of teaching it at the pilot level (the quality of instruction on this is abysmal), and a better job of answering the questions that arise. :-) Just an attempt at a small bit of "inside" humor here...obviously misguided. Dudley Henriques |
#43
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Peter Duniho wrote:
Hilton wrote: Todd's reply to this clearly shows why Roger's statement is wrong. No, it doesn't. See my reply to Todd and Stefan's reply here to understand what we are all talking about. You wrote "Had his definition of lift been correct, he would have been exactly correct." Ummm, OK. But lift is well-defined and it is not defined as the force that opposes weight. So, you can redefine whatever you want, doesn't make it right. Hilton |
#44
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"Hilton" wrote in message
ink.net... You wrote "Had his definition of lift been correct, he would have been exactly correct." Ummm, OK. But lift is well-defined Actually, part of the problem is that "lift" is poorly defined. It means different things in different contexts. and it is not defined as the force that opposes weight. Actually, most basic aviation texts written for pilots DO define lift as "the force that opposes weight". You should not be faulted for having never read one; after all, the texts certainly gloss over many important facts, and it's not necessary to have studied one to become a pilot. But many pilots DO use them as a reference, and they DO define lift in exactly the way you seem to think they do not. So, you can redefine whatever you want, doesn't make it right. I'm not the one doing the "redefinition". The word "lift" is simply not a technical term. You can get closer by using the phrase "aerodynamic lift", but ultimately you simply need to know in what context you're using the word. Pete |
#45
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Hilton wrote:
But lift is well-defined and it is not defined as the force that opposes weight. That's the way Jeppesen describes it. George Patterson Give a person a fish and you feed him for a day; teach a person to use the Internet and he won't bother you for weeks. |
#46
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Nothing about curvature, nothing about pressure. My point exactly. OK check this out... http://scienceworld.wolfram.com/phys...lliEffect.html I think this makes my point. G |
#47
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"Hilton" wrote in message ink.net... Peter Duniho wrote: Hilton wrote: Todd's reply to this clearly shows why Roger's statement is wrong. No, it doesn't. See my reply to Todd and Stefan's reply here to understand what we are all talking about. You wrote "Had his definition of lift been correct, he would have been exactly correct." Ummm, OK. But lift is well-defined and it is not defined as the force that opposes weight. So, you can redefine whatever you want, doesn't make it right. Hilton I would tend to agree with you on this point, but with a caveat. Unfortunately for many student pilots searching for information on lift, many of the data sources in use at the student pilot level present subjects like lift improperly in my opinion anyway. Rather than state a definition of lift, the "definition" actually passes that stage and presents what lift DOES! It's a fine point, but it is worthy of note for the more "scientific minds" among us :-) I've always STARTED an explanation of lift by presenting it initially as the aerodynamic force that opposes the relative wind, NOT the force that opposes gravity or weight. (That comes later :-))) Again, it's a fine point, and there are many ways to discuss definition, and if nothing else, what you are discussing here with others on the group helps demonstrate why the subject of lift is so misunderstood by the student pilot community. (Not your fault BTW :-) I think I've spent more time discussing lift with students through the years than any other single aspect of flight. Part of the reason for that is the confusion caused by the community's seeming insistence on presenting lift in a non standard written form. Dudley Henriques |
#48
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buttman opined
I have always been under the impression that lift is the product of airspeed and angle of attack, and that lift is the measure of upward force acting on the plane at a given time. For instance, if you are doing slow flight, your wings are producing the same amount of life that you would be if you were cruising, GIVEN that you did not lose or gain any altitude during the maneuver. My instructor, which is a very knowledgable guy tried telling me that lift has nothing to do with airspeed. He said that lift is directly and soley related to AOA and AOA only. So if you are doing slow flight, you are producing more life than you are when you're cruising. I overheard a ATP guy who flies King Air's say that this huge 20 ton military plane he used to fly would fly approaches at 110 knots, and I heard him say "It is able to do this because it producing so much lift", which I took as him defining lift as my instructor does. So whats the deal here? Are we just thinking of two diffrent concepts? Lift = Cl(AOA) * Area * V^2 -ash Cthulhu in 2005! Why wait for nature? |
#49
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The distinction is really a thought convenience to help us talk about
what is going on and not a real physical difference. Lift is really drag directed upwards. -- Roger Long |
#50
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Stall is not loss of lift but loss of stability in the airstream.
Stability is the ability to reach a steady state. A fully stalled wing will develop just as much lift as an unstalled one but will seek an angle of attack that will result in a steady state by sinking faster. This makes most aircraft head nose first for the ground which feels like loss of lift. For a more complete explanation: http://www.avweb.com/news/airman/184307-1.html -- Roger Long |
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