long wire antenna
in [Repair]
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From: Arfa Daily on 10 Mar 2010 13:10 "Phil Hobbs" <pcdhSpamMeSenseless(a)electrooptical.net> wrote in message news:4B96EEFD.5010406(a)electrooptical.net... > On 3/8/2010 8:53 PM, Arfa Daily wrote: >> "Phil Allison"<phil_a(a)tpg.com.au> wrote in message >> news:7vj3h1F7nuU1(a)mid.individual.net... >>> >>> "Arfa Daily" >>> >>>>> It's not unlike a wing. Almost any surface flat on the bottom and >>>>> curved >>>>> on the top can produce lift. >>>>> >>>> >>>> So how come a symmetrical wing, such as might be found on a stunt >>>> plane, >>>> still flies, and most asymmetric wings fly quite happily upside down ? >>>> :-) >>>> >>> >>> >>> ** I ask people who *think* they know how a plane flys that same Q. >>> >>> Stumps them all the time. >>> >>> Goes to show how simple explanations are often highly flawed. >>> >>> >>> >>> ..... Phil >>> >>> >> >> I saw an interesting dissertation on this some time back, which put >> forward >> a much more complex but better believable theory as to how a wing flies. >> I >> don't really remember the details, but it relied heavily on the wing's >> angle >> of attack into the air, to produce the pressure differential, and hence >> lift. I seem to recall that it was the opposite way round from the >> 'conventional' teaching of increased speed of the air over the top of the >> wing reducing the pressure, and that this theory had the attack angle >> causing compression under the wing, thereby increasing the pressure to >> produce lift. I do, however, remember it saying that air has no >> 'intelligence', and just because two previously adjacent molecules became >> divided above and below the wing, there was nothing to say that they had >> to >> form back up in the same way as they left the back edge of the wing, >> which >> would require the air to move faster over the longer upper surface. I >> believe it did say that the air actually does travel faster over the >> curved >> face of the wing, and that the fact that it does, does produce a >> reduction >> in pressure. However, this reduction is small, and only contributes a >> very >> limited amount of lift, compared to the main mechanism that's at work. >> >> Arfa >> >> > > The Bernoulli principle (the one about the faster air flow corresponding > to lower pressure) is sort of like the second law of thermodynamics (the > one about heat never spontaneously flowing from cold to hot). It's a > shortcut way to get the right answer, but doesn't have the satisfying feel > of a real physical derivation. > > BTW by symmetry, symmetric wings require an angle of attack to generate > lift. Otherwise how do they know which way to push? > > Cheers > > Phil Hobbs > Agreed, and that's the way I understood it. In fact as far as I understand it, any wing, irrespective of its sectional shape, requires an 'angle of attack' to fly, and how well a wing flies on any particular aircraft, is a function of balancing angle of attack against drag so caused, and the power input required to overcome that drag. I also understood that this was partly the reason that jet aircraft tend to land and take off with a very 'nose up' attitude, to increase the angle of attack and hence the amount of lift whilst the airspeed is relatively low. Accepting that angle of attack, and the necessary power to drive the wing through the air being available, is the primary mechanism of lift generation, then I am having difficulty understanding why some here have contended that holding your hand out of a moving car window with an attack angle, is not a valid example of lift generation. Your arm certainly gets lighter when you do this, so is that not lift ? Way, waaaay off topic, but a bit of a fun discussion ... Arfa
From: Phil Hobbs on 10 Mar 2010 13:49 On 3/10/2010 1:10 PM, Arfa Daily wrote: > "Phil Hobbs"<pcdhSpamMeSenseless(a)electrooptical.net> wrote in message > news:4B96EEFD.5010406(a)electrooptical.net... >> On 3/8/2010 8:53 PM, Arfa Daily wrote: >>> "Phil Allison"<phil_a(a)tpg.com.au> wrote in message >>> news:7vj3h1F7nuU1(a)mid.individual.net... >>>> >>>> "Arfa Daily" >>>> >>>>>> It's not unlike a wing. Almost any surface flat on the bottom and >>>>>> curved >>>>>> on the top can produce lift. >>>>>> >>>>> >>>>> So how come a symmetrical wing, such as might be found on a stunt >>>>> plane, >>>>> still flies, and most asymmetric wings fly quite happily upside down ? >>>>> :-) >>>>> >>>> >>>> >>>> ** I ask people who *think* they know how a plane flys that same Q. >>>> >>>> Stumps them all the time. >>>> >>>> Goes to show how simple explanations are often highly flawed. >>>> >>>> >>>> >>>> ..... Phil >>>> >>>> >>> >>> I saw an interesting dissertation on this some time back, which put >>> forward >>> a much more complex but better believable theory as to how a wing flies. >>> I >>> don't really remember the details, but it relied heavily on the wing's >>> angle >>> of attack into the air, to produce the pressure differential, and hence >>> lift. I seem to recall that it was the opposite way round from the >>> 'conventional' teaching of increased speed of the air over the top of the >>> wing reducing the pressure, and that this theory had the attack angle >>> causing compression under the wing, thereby increasing the pressure to >>> produce lift. I do, however, remember it saying that air has no >>> 'intelligence', and just because two previously adjacent molecules became >>> divided above and below the wing, there was nothing to say that they had >>> to >>> form back up in the same way as they left the back edge of the wing, >>> which >>> would require the air to move faster over the longer upper surface. I >>> believe it did say that the air actually does travel faster over the >>> curved >>> face of the wing, and that the fact that it does, does produce a >>> reduction >>> in pressure. However, this reduction is small, and only contributes a >>> very >>> limited amount of lift, compared to the main mechanism that's at work. >>> >>> Arfa >>> >>> >> >> The Bernoulli principle (the one about the faster air flow corresponding >> to lower pressure) is sort of like the second law of thermodynamics (the >> one about heat never spontaneously flowing from cold to hot). It's a >> shortcut way to get the right answer, but doesn't have the satisfying feel >> of a real physical derivation. >> >> BTW by symmetry, symmetric wings require an angle of attack to generate >> lift. Otherwise how do they know which way to push? >> >> Cheers >> >> Phil Hobbs >> > > Agreed, and that's the way I understood it. In fact as far as I understand > it, any wing, irrespective of its sectional shape, requires an 'angle of > attack' to fly, and how well a wing flies on any particular aircraft, is a > function of balancing angle of attack against drag so caused, and the power > input required to overcome that drag. I also understood that this was partly > the reason that jet aircraft tend to land and take off with a very 'nose up' > attitude, to increase the angle of attack and hence the amount of lift > whilst the airspeed is relatively low. > > Accepting that angle of attack, and the necessary power to drive the wing > through the air being available, is the primary mechanism of lift > generation, then I am having difficulty understanding why some here have > contended that holding your hand out of a moving car window with an attack > angle, is not a valid example of lift generation. Your arm certainly gets > lighter when you do this, so is that not lift ? > > Way, waaaay off topic, but a bit of a fun discussion ... > > Arfa > > Because it's Usenet, and half the fun is the idiotic nitpicking. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Michael A. Terrell on 10 Mar 2010 18:24 Leonard Caillouet wrote: > > AZ Nonad wrote: > > > > I wasn't the idiot who suggested that waving your hand around from > > a car window was an example of lift. > > Actually, it is. It might even be an example of a wing, depending on how > you shape your hand. You appear to be looking for an argument and enjoy > insulting people rather than fostering understanding. Oh, but that is > supposed to be OK on Usenet? Sorry, intelligent discourse can take place > even here. > > Leonard Too many people are ignoring him on the design newsgroup, so he's trolling here. -- Greed is the root of all eBay.
From: mm on 22 Mar 2010 01:00 On Tue, 9 Mar 2010 01:53:39 -0000, "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote: > >"Phil Allison" <phil_a(a)tpg.com.au> wrote in message >news:7vj3h1F7nuU1(a)mid.individual.net... >> >> "Arfa Daily" >> >>>> It's not unlike a wing. Almost any surface flat on the bottom and curved >>>> on the top can produce lift. >>>> >>> >>> So how come a symmetrical wing, such as might be found on a stunt plane, >>> still flies, and most asymmetric wings fly quite happily upside down ? >>> :-) >>> >> >> >> ** I ask people who *think* they know how a plane flys that same Q. >> >> Stumps them all the time. >> >> Goes to show how simple explanations are often highly flawed. >> >> >> >> ..... Phil >> >> > >I saw an interesting dissertation on this some time back, which put forward >a much more complex but better believable theory as to how a wing flies. I >don't really remember the details, but it relied heavily on the wing's angle >of attack into the air, to produce the pressure differential, and hence >lift. I seem to recall that it was the opposite way round from the >'conventional' teaching of increased speed of the air over the top of the >wing reducing the pressure, and that this theory had the attack angle >causing compression under the wing, thereby increasing the pressure to >produce lift. I do, however, remember it saying that air has no >'intelligence', and just because two previously adjacent molecules became >divided above and below the wing, there was nothing to say that they had to >form back up in the same way as they left the back edge of the wing, which >would require the air to move faster over the longer upper surface. I Wait a second. The air isn't really moving. It's the plane that is moving and the air is pretty much standing still, except where the propeller blows it around but I don't think that's the whole wing. So the molecules that were together before the plane got there are still almost together after the wing slices through the air. >believe it did say that the air actually does travel faster over the curved >face of the wing, and that the fact that it does, does produce a reduction >in pressure. However, this reduction is small, and only contributes a very >limited amount of lift, compared to the main mechanism that's at work. And what's the main mechanism? >Arfa >
From: mm on 22 Mar 2010 01:08
On Mon, 08 Mar 2010 22:26:11 -0500, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: >On Mon, 08 Mar 2010 21:00:51 -0600, AZ Nomad ><aznomad.3(a)PremoveOBthisOX.COM> wrote: > >>On Mon, 08 Mar 2010 21:47:35 -0500, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: >>>On Mon, 08 Mar 2010 20:29:02 -0600, AZ Nomad >>><aznomad.3(a)PremoveOBthisOX.COM> wrote: >> >>>>On Mon, 08 Mar 2010 21:12:26 -0500, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: >>>>>On Tue, 9 Mar 2010 01:53:39 -0000, "Arfa Daily" >>>>><arfa.daily(a)ntlworld.com> wrote: >>>> >>>>>>I saw an interesting dissertation on this some time back, which put forward >>>>>>a much more complex but better believable theory as to how a wing flies. >>>> >>>>>It's not really that complex. Didn't you ever, as a kid, hold your arm >>>>>out the car window with your hand flat and "fly" it up and down as you >>>>>changed the angle of attack? That's really all that's necessary. An >>>>>airplane could fly (if not very efficiently) with wings made from flat >>>>>sheets of plywood. >>>> >>>>All you've got there is an inclined plane. You aren't creating lift. >>>> >>>>Try it without the car. >> >>>The saying goes something like: with enough power, you could fly a >>>brick. The lift comes from the angle of attack. >> >>Nope. You're just describing a fin. >> >>Lift comes from turbulance on the upper edge causing a vacuum. >>Without the airfoil, what you have is pre wright brothers technology >>which didn't fly. > >The Wright's were pretty smart and used a good airfoil design, otherwise They were smart. They built a wind tunnel to see which wing shape had the most lift. >they'd have had to wait for another generation of efficient (power vs >weight) internal combustion engines to make the first flight. Good >designs have less drag and do produce more lift. Poor designs need more >thrust. > >Ever fly one of those balsa wood gliders? (Do they even still make >those?) I think so but maybe not out of wood anymore. Actually funniest home videos last Sunday had a section on people being hit by their own planes. All were bigger than what we had, 18" wing span seemed typical (although maybe people with planes like we had can't afford video cameras, or aren't so caught up in themselves that they video little stuff like this.) >?Body & rudder, wings, and elevators all punched out of a flat >sheet. It's punched out of a flat sheet, but the slot in the fuselage is curved with the center higher. They at least believe she airfoil shape is neceessary for somethin to fly well. >Stick on a prop and a rubber band engine and it does fly. > >Rack time ... |