| Doug McLaren wrote: | >
| > No, I haven't. What I have clearly stated is right up there, and I | > didn't trim it out so you can refer to it if desired. | | Well I have refered to it and do not have a real clue as to what you | think other then downwash behind the wing causes lift. So I am going | to try finding out what you think by simply asking yes/no questions.
Allow me to restate my position on the matter (though I did change it a bit to add in the word `wing', so it's more clear) --
I don't believe that a wing can create aerodynamic lift without also creating downwash. (At least without creative definitions of the terms lift or downash.)
You'll notice that I'm saying nothing about vortexes, Bernoulli, the Coanda effect, specific airfoils or anything else in that statement. I'm keeping it simple.
I'm still not quite certain ... do you agree or disagree with my premise? | 1.Do you believe tip vortexes are created somehow by wings? Please | answer yes or no.
I've not really said anything about tip vortexes. But it does look like wings create them, or are at least involved in their creation. Is that your point?
| 2. If tip vortexes are created by wings do you think they cause lift? | Yes means they cause lift. No means they do not cause lift. Please | answer yes or no.
I've never really said anything about what causes lift in this thread, at least not since I made my `I don't believe that aerodynamic lift can exist without downwash' statement.
| 3. Does a model airplane wing compress the air somehow someplace? | Please answer yes or no.
If the model airplane wing is creating lift, it's also creating downwash. Anything else is not something I was discussing.
Aerodynamics of far-subsonic flight is generally based on the the assumption that air isn't compressible (and that therefore the air is not compressed.) This is just an approximation and isn't completely true, but it generally works and gives us reasonably accurate results.
| 4. Is the Conanda effect a direct and demanded result of Newton's | laws? Please answer yes or no.
I've said nothing about the Conanda effect, or the Coanda effect for that matter.
Do I believe that the Coanda effect is real? It seems to be. Do I believe that the Coanda effect obeys Newton's laws? Yes.
Do I believe that Newton's laws require the Coanda effect? I don't think so, but I really haven't given it a lot of thought. Ultimately, the `laws' of aerodynamics are the end result of applying Newton's laws and other similar `fundamental' laws to large numbers of particles, so it wouldn't surprise me if the Coanda effect could be seen as ultimately the result of some application of Newton's laws. I don't see how it's relevant, however.
| 5. If I define efficiency of lift production as follows:
{ `lift divided by drag' was the general definition, which I have no problem with. }
... I don't feel like looking up airfoil data. If you have a point, provide the figures yourself, and use it to come to your point.
| 6. Do you think that the incidence meter you buy at the hobby shop | measures the correct angle of incidence for all airfoils? Please | answer yes or no.
I've never bought an incidence meter. Your question is based on an incorrect premise, and is therefore moot. That, and my fundamental premise doesn't really discuss how a wing creates lift and downwash -- instead, it just says that if you have one, you have the other.
Model airplanes are often grossly overpowered, so eyeballing this stuff often gives very acceptable results. And while I've been flying gliders a lot lately, they're ARFs or kits and so I let the designers worry about the incidence of the wing. They seem to fly well, so I'm happy with them. Perhaps I could tweak out 1.2% better performance by adjusting some things, but I don't care enough to do it.
| 7. If the answer to question 6 is no do you think the meter measures | angle of attack for all airfoils? Please answer yes or no.
Moot. My premise says nothing about angle of attack.
| > If it's 5000 feet up, the weight of the plane is spread out over many | > millions of square feet, and so only a very tiny part of that would be | > pushing on you -- and the atmosphere is pushing up on you too, so you | > won't feel it. | | I think I said I was standing 500 - thats hundred - not 5000 feet below | the plane. If I mistyped I am sorry. I intended to say 500. No | downwash. No movement of leaves.
Right, you did say 500 feet. But even so, the weight of the plane is spread out over what probably amounts to millions of square feet.
Also note that the plane is probably flying 300+ mph -- that's 440 feet per second. It's only approximately 500 feet away for a tiny fraction of a second. One second later, it's 666 feet away (assuming it's flying level, and it was directly overhead.)
If somebody blows a fan on you from across the room for one second, you're not likely to even feel it. If they left it on for many seconds, you might eventually feel it.
A helicopter involves a wing moving through the air, and yet not leaving the scene of the crime if it's hovering. Allow me to give you two yes/no questions --
1) do you believe that a hovering helicopter's blades are are fundamentally just wings/airfoils? (If you think that they somehow follow different aerodynamic rules, please be explicit about how you think they differ.)
2) do you believe that a hovering helicopter creates downwash?
| > Either way, the Earth is ultimately supporting (on the average) the | > entire weight of the plane, both when it's landing and when it's | > flying. | | Yes, I understand the conservation of mass.
It's not so much a matter of conservation of mass, but that the plane is pushing down with certain amount of weight and it has to be supported somehow, or it'll fall down. If the air is supporting it, then something has to be supporting the air, and that would have to be the Earth.
In large amounts, air is very heavy. The weight of a plane, even a
747 or so, is pretty insignificant compared to the air around it to
500 feet or so. The mass that the plane adds to a square of air 1000 feet on each side is a very small percentage of the total mass, so it's not likely to be detected by a human, but I imagine that the right equipment could detect it easily enough.
| > This stuff really isn't on-topic at all. Would you like to move it to | > sci.physics? (I suspect that the regulars there would rip you to | > pieces, but you might enjoy that.) | | You know how to copy the thread to a new news group just as well as I | do. But thinking that physicists are the sole authoritys on fluid | mechanics is a bit of a push.
I'm not saying that at all. I'm saying that it's the most appropriate Usenet group I can find for a discussion of this sort. There aren't any aerodynamics groups that I can find, and there's no rec.aviation.technology group that I can see.
I'll crosspost this post to sci.physics, and I'll set followups to go only there. If you wish to continue this discussion with me on Usenet, let's do it there rather than here.
| 10. In a link provided very kindly by another poster: | |
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| | Please refer to figure 3.2. Do you believe this diagram reasonably | accurately displays the actual air flow patterns around an airfoil.
I'm not so sure about the upwash part, but the downwash part looks good. It's hard to tell from the picture, but I'm assuming that the air well in front of the wing was horizontal.
| I will specify that this diagram is for an airfoil which has an | infinite aspect ratio (which is a detail the author of the web site | probably felt was unneeded detail which would confuse the casual | reader).
If infinite bothers you, just pick a wing that's a mile long. Or ten miles long. Or whatever. As the aspect ratio gets larger and larger, the relative effects of the ends of the wing will have to get smaller and smaller.
| I will also specify that this diagram is for one specific reynolds | number and is not intended to be accurate in every detail for every | single reynolds number(which is also detail the author did not feel | was needed).
He is obviously simplifying things ... probably because he wanted to just write a few pages on it, rather than a book. Seems a reasonable compromise.
| Further I will specify that the airflow past the foil is well under | the speed of sound which I honestly do not recall if the author | addressed in any way.
His overall web site is about general aviation, so assuming speeds well below that of the speed of sound seems appropriate. Usually if somebody is talking about supersonic aerodynamics, or even aerodynamics near the speed of sound, it's usually clear.
| By the way, I have seen the pic of the plane coming out of the clouds | before as I am sure most people on this group have also. All I see is | a very striking picture of tip vortexes.
Yes, it does show the tip vortexes very well. But you'll notice that there's also a `hole' in the cloud where the plane just flew through ... but I can see where it would be convenient to blame that hole on the vortexes rather than on downwash. It seems reasonable that one wouldn't even be able to visually separate the two phenomena on any normal sized wing, at least not in a carefully controlled environment like a wind tunnel. I guess it wasn't a very convincing example -- I can see that.
| Sorry but I see no evidence | of downwash in this picture at all. But it still is a really neat | picture. The pic I am referring to is Figure 5 at the web site: | |
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| | It is going to take me a while to learn what you actually think by | asking yes no questions. But it seems the only way forward.
I've already made my position (at least the one I'm defending in this thread) clear. It seems to me that you're just trying to confuse it with many of your questions, but so be it.