If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#101
|
|||
|
|||
Backwash Causes Lift?
"Morgans" wrote in news:XaYMi.122$uc1.57
@newsfe12.lga: "Bertie the Bunyip" wrote It´s the main reason I´m here. Remind me again. What is the main reason you're here? I think I just told you. Why do you feel the need to answer his posts? Sport Bertie |
#102
|
|||
|
|||
Backwash Causes Lift?
Dudley Henriques wrote in
: TheSmokingGnu wrote: Dudley Henriques wrote: Crash Lander wrote: I'd like to see what his thoughts are on String Theory. LOL. I'm sure he'd most likely say that twine was better :-)) What, and discount the obvious implications that Duct Tape has on modern thinking? TheSmokingGnu Ah, duct tape!! Where would aviation be without it ? Absolutely. Or speed tape if you go a bit faster. Bertie |
#103
|
|||
|
|||
Backwash Causes Lift?
On Oct 3, 10:48 pm, wrote:
On Oct 3, 9:26 pm, TheSmokingGnu wrote: Le Chaud Lapin wrote: Yes, I am. It's a combination of many things taking place at once. Vacuum generation by the forward motion of the wing is one of them. And the other is the displacement of air downward. By the bottom part of the wing, right? Remember, when Newton was talking about the whole action/reaction thing, he did not say you could arbitrarily define the sources of forces. He was talking specifically about two objects, A and B, A generating a force on B, and B generating a reciprocal force on A. If you have compression under a wing do to extended flaps and laminar friction of airflow, for example, then the lower surface of the wing forces air downward, and the air beneath the lower surface forces wing upward. If you have have downwash above the wing, the downwash has to be due to a force acting to move the air downward. I've argued that it is effectively normal atmospheric pressure, acting against what effectively becomes a partial vacuum generated by the forward displacement of the wing, above the wing. Newton did not say that you could arbitarily say, "Oh, there is some air moving downward, I'll just pick a convenient reason arbitrarily." Another way to look at this is to imagine a "level" wing with heavy flap extension. Have an "air gorilla" move the entire wing forward, in an abrupt motion, not given air anytime to redistributed. If this is done, there will be compression beneath the wing, strong at the boundary of compression, or in the flap pocket. Behind the win (above it, but behind flaps), there will be .... a huge void! Now, if air is suddenly allowed to flow, yes indeed, there would be downwash above the wing into the void, but the wing itself will not be causing this downwash. It will be the pressure surrounding the void causing the downwash. Since the source of movement of this air is not the wing but the air above it, Newton's law cannot be used will-nilly to say thay that there was some kind of action, so this must be the reaction. You have to attribute the forces to their sources. In this case, someone said Newtons law had to be use under penalty of death, it would be simple: Take a thin layer or air right at the boundary between the void and ambient air. If another thin layer of ambient air pushes against this thin layer, the thin layer will will push back against the ambient thin layer. This is reciprocity of forces. The reason that the first thin layer "loses" the pushing battle is because there nothing to oppose the first thin layer as it moves into the void. The molecules of the second thin layer has its friends to contend with. After the first thin layer has moved into the void, those molecules can no longer participate in pushing at the ambient air (because they have assumed new position in space - neither air nor people are telekinetic) and thus we get air flow. Of course, there are not layers, but a distribution of momentum of the particles, but this is close enough. So in summary, downwash cause by high ambient pressure confronting a void must not be used to contribute to lifting force of the wing. One _can_ say that the pressure under the wing see no opposing force in the relative void above the wing does result in net upward force. -Le Chaud Lapin- |
#104
|
|||
|
|||
Backwash Causes Lift?
Bertie the Bunyip wrote:
Dudley Henriques wrote in : TheSmokingGnu wrote: Dudley Henriques wrote: Crash Lander wrote: I'd like to see what his thoughts are on String Theory. LOL. I'm sure he'd most likely say that twine was better :-)) What, and discount the obvious implications that Duct Tape has on modern thinking? TheSmokingGnu Ah, duct tape!! Where would aviation be without it ? Absolutely. Or speed tape if you go a bit faster. Bertie NASCAR!!!! Great folks! D -- Dudley Henriques |
#105
|
|||
|
|||
Backwash Causes Lift?
TheSmokingGnu wrote:
Then why do wings generate lift at negative AOA? Surely the immense vacuum pressures generated would immediately pull any flying craft desperately into the Earth the moment the wing crossed that threshold (say, in a descent). Think "Relative Wind". Then rethink negative AOA. |
#106
|
|||
|
|||
Backwash Causes Lift?
Still waiting for the conservation of momentum derivation. My husband,
also trained as an engineer, casually remarked he didn't think you could get from Newton's First Law to the that confirms my memory, but we are both willing to have that belief rebutted. He also pointed out that how a CFI might explain how a VOR works would not satisfy an engineer. For that matter, the physics of flight as explained to a student pilot would not satisfy someone who might be interested in designing, as opposed to flying, an airplane, but I don't think the manuals you are looking at are in error. I would point out that each field has its own language, and you denying the conventions used in aviation -- drag, lift and so on -- demonstrates an unbecoming trait for a student, and even a worse one for an employee. You may want to rething that attitude if you use it in real life. On Oct 3, 11:14 pm, Le Chaud Lapin wrote: On Oct 3, 8:38 pm, Tina wrote: "We" are not in need of getting to the bottom of this. Most of us have been there and done that.This particular writer, if she chooses to analyse physics problems, tends to use the Newtonion approximations as first principles. The good news is my profession doesn't demand those skills often. I would, however, be interested, as I mentioned earlier, how you derive conservation of mV from Newton's force/acceleration relationship. I think you made that claim earlier in this thread. Hmm...I was afraid you would say that. A non-hand-waving explanation would too close to the quantum, and so...it's a bit much to discuss, at least right now. I've posted more messages in this thread in small period of time than I have ever for any other topic, in the history of using USENET, or...as one might say, dN/dt 0, where N is number of messages. -Le Chaud Lapin- |
#107
|
|||
|
|||
Backwash Causes Lift?
Crash Lander writes:
I'd like to see what his thoughts are on String Theory. String theory is a theory based on math rather than physical reality. |
#108
|
|||
|
|||
Backwash Causes Lift?
Le Chaud Lapin writes:
I am not an expert either, but I know enough to know that the explanations I am reading in books are, at best, misleading. That's an open secret in aviation. The mechanism of lift has been widely explained incorrectly for years. |
#109
|
|||
|
|||
Backwash Causes Lift?
Le Chaud Lapin writes:
Yes, I am. It's a combination of many things taking place at once. Vacuum generation by the forward motion of the wing is one of them. Gravity does that, not the forward motion of the wing. Without gravity, the wing would simply move upwards until the effective angle of attack were no longer positive. |
#110
|
|||
|
|||
Backwash Causes Lift?
TheSmokingGnu writes:
Then why do wings generate lift at negative AOA? They don't. That's a very common misconception, even among pilots. The effective AOA is always positive when the wing is generating lift. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
How much lift do you need? | Dan Luke | Piloting | 3 | April 16th 07 02:46 PM |
Theories of lift | Avril Poisson | General Aviation | 3 | April 28th 06 07:20 AM |
what the heck is lift? | buttman | Piloting | 72 | September 16th 05 11:50 PM |
Lift Query | Avril Poisson | General Aviation | 8 | April 21st 05 07:50 PM |
thermal lift | ekantian | Soaring | 0 | October 5th 04 02:55 PM |