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#311
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lift, wings, and Bernuolli
On Fri, 3 Mar 2006 at 15:21:11 in message
, "00:00:00Hg" wrote: On Fri, 03 Mar 2006 01:27:46 +0000, David CL Francis wrote: Above Mach one the air does not detect the approaching aircraft! :-) If it did, what would happen? The whole point is that disturbances in the air are propagated at or near the velocity of sound. It follows that at supersonic speeds nothing happens to the air until it reaches the supersonic aircraft, or vice versa. -- David CL Francis |
#312
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lift, wings, and Bernuolli
On Fri, 3 Mar 2006 at 02:27:02 in message
. net, Richard Lamb wrote: I hate to be a spoil sport (or dullard?), but... the (stationary) air does WHAT (as the wing passes by)??? The nature of things is such that the situation does not change if you change the frame of reference. It is normal in doing calculations to start with a frame of reference based on the aircraft. If you follow the aircraft then the air is going past it. The presence of the wing changes the air flowing past the aircraft in the same way as if you consider the aircraft passing through the air. The 'stationary' air as you call it has its local velocity and direction changed by the aircraft. -- David CL Francis |
#313
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lift, wings, and Bernuolli
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#314
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lift, wings, and Bernuolli
Alan Baker wrote: In article .com, wrote: .... Well then if the downflow is NOT balanced by upflow why doesn't the upper atmosphere run out of air? Because the air contacts the earth and *stops* moving downward. Could you define downflow? -- FF |
#315
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lift, wings, and Bernuolli
David CL Francis wrote:
On Fri, 3 Mar 2006 at 02:27:02 in message . net, Richard Lamb wrote: I hate to be a spoil sport (or dullard?), but... the (stationary) air does WHAT (as the wing passes by)??? The nature of things is such that the situation does not change if you change the frame of reference. It is normal in doing calculations to start with a frame of reference based on the aircraft. If you follow the aircraft then the air is going past it. The presence of the wing changes the air flowing past the aircraft in the same way as if you consider the aircraft passing through the air. The 'stationary' air as you call it has its local velocity and direction changed by the aircraft. Yeahbut... A handy frame of reference is - handy. But it can be very misleading..... |
#316
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lift, wings, and Bernuolli
Richard Lamb wrote:
David CL Francis wrote: On Fri, 3 Mar 2006 at 02:27:02 in message . net, Richard Lamb wrote: I hate to be a spoil sport (or dullard?), but... the (stationary) air does WHAT (as the wing passes by)??? The nature of things is such that the situation does not change if you change the frame of reference. It is normal in doing calculations to start with a frame of reference based on the aircraft. If you follow the aircraft then the air is going past it. The presence of the wing changes the air flowing past the aircraft in the same way as if you consider the aircraft passing through the air. The 'stationary' air as you call it has its local velocity and direction changed by the aircraft. Yeahbut... A handy frame of reference is - handy. But it can be very misleading..... For instance? If the air is moving, we expect a lower pressure. Nod to Bernoulli. But the air would also be moving along the bottom side of the wing also? And what would that do to the pressure under the wing? And if the pressure under the wing is below ambient.... |
#317
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lift, wings, and Bernuolli
Momentum is not conserved because energy has been added. Are you saying that a land vehicle with a horizontal fan to drive it along rails will not accelerate and move? Will the vehicle not build up momentum because of this?
Momentum is always conserved. If you see momentum disappearing, you are not looking at the whole system. In the case of the land vehicle propelled by a fan, the air blown back acquires momentum in one direction, exactly balanced by the momentum that the vehicle acquires, plus the (rotational) momentum (due to wheel friction) that the earth acquires. Jose -- Money: what you need when you run out of brains. for Email, make the obvious change in the address. |
#319
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lift, wings, and Bernuolli
Alan Baker wrote: In article .com, wrote: Alan Baker wrote: In article .com, wrote: ... Well then if the downflow is NOT balanced by upflow why doesn't the upper atmosphere run out of air? Because the air contacts the earth and *stops* moving downward. Could you define downflow? Sure. The aircraft passes through and air moves downward. As it moves its motion is dissipated into more and more air moving less and less, but eventually the momentum that was transferred to it is transferred back to the earth. -- Alan Baker Vancouver, British Columbia "If you raise the ceiling 4 feet, move the fireplace from that wall to that wall, you'll still only get the full stereophonic effect if you sit in the bottom of that cupboard." |
#320
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lift, wings, and Bernuolli
Jose wrote: Well I'm really hoping that Jose tries the card thumbtack soda straw thing. Actually, I did try it and it didn't "work" (that is, the card didn't float, which is what I think you expect to happen). I'm probably doing it wrong so I'll keep at it. When I get it to work, I'll report what happened and why (in newtonian terms) I think it did. Well after reading that I went and tried it myself and blew the card off the end of the straw so I must be doing it wrong too! I've known of this trick from childhood, (yes, I realize that some of you are thinking that could mean I first learned of it a few days ago) so by now I can't remember exactly how or even if I did it myself. Memory is like that. Could we reduce the crossposting? I think one newsgroup is more than sufficient. You chose, and I'll follow. -- FF |
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