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#91
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Spinner strobing as a "Bird Strike Countermeasure"
cavelamb himself writes:
Or else I won't Like You any nore. I'm not looking for friends. I'm only here to discuss aviation. |
#92
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Spinner strobing as a "Bird Strike Countermeasure"
Mxsmanic wrote:
cavelamb himself writes: Or else I won't Like You any nore. I'm not looking for friends. I'm only here to discuss aviation. No. I don't think so. I think you are here to taunt people and be a nusance. |
#93
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Spinner strobing as a "Bird Strike Countermeasure"
[Note: nonstandard attribution layout.]
Beryl wrote: Entertaining thread this turned into. Anyway, here's a nice illusion. http://img408.imageshack.us/img408/8067/imagegm1.gif Concentrate on the + in the middle. An illusory green dot soon appears. Moments later, pink dots seem to disappear. Very interesting and neat. cavelamb himself wrote: I'll repost this one here - so it's easier to find? HEHEHE! http://www.sonnyradio.com/spinninglady.html It took some doing, but by glancing to one side (and sometimes briefly closing my eyes and trying to imagine the reverse spin) I was able to switch the perceived rotation direction. However, I have it on good authority that I do not have an IQ of anywhere near 160. :-) A couple times I had a shift in perceived rotation direction without looking away. cavelamb himself wrote: I think this one is awesome. Can these really be the same color??? http://www.home.earthlink.net/~cavel....htm#samecolor Hard to believe indeed. I decided to do an image copy from the browser and pasted the copy into the MS Windows Paint program. Copied two square chunks of each of the two labeled board squares and pasted them side-by-side. Sure enough they are the same color. |
#94
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Spinner strobing as a "Bird Strike Countermeasure"
On Dec 4, 9:48 pm, Airbus wrote:
And the front fan on a turbofan is turning at around 40-50 revolutions per second, not thousands. Guess again. Well, I think he made a pretty good "guess" - the GE90-115B tha powers the 777 turns (front fan) at 2550RPM, or 42.5 RPS. He probably didn't ahve to guess much, as these facts are easily and irrefutably verified. I "guess" you haven't learned that. . . Not too many folks bother to do a little research. It gets easier all the time, what with Google and all that. Things like fan speeds are easily available, and with a tiny bit of arithmetic the rotational speed per second is easily calculated. Some posters just diss anything someone else says, mostly because they didn't know it first or perhaps becuase of who is saying it. There's a well-known phenomenon that can incapacitate pilots. A propeller spinning so that it cuts through the sun's glare and causes a stroboscopic effect on the pilot's eyes can result in confusion. A frequency of less than between 25 and 55 Hz, depending on the individual, can cause dizziness or nausea. It's called "flicker vertigo" and the fact that it happens tells me that the human eyeball (or at least the visual cortex) does have a frequency function of some sort. 25 Hz on a two-blade prop would be 750 RPM and 55 would be 1650. Some tests have found that frequencies as low as four to 20 Hz will induce it rapidly. See this: http://www.flightsafety.org/hf/hf_mar-apr04.pdf When I get the prop between the sun and my eyeballs I have to increase the RPM to get rid of it. It's painful. Dan |
#95
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Spinner strobing as a "Bird Strike Countermeasure"
Here's an illusion I can't expain at all.
http://amiedotcom.blogspot.com/2005/...hat-i-see.html been told it has to do with resolving frequencies in space, not time, but it's way past my number crunchiing skills. On Dec 4, 8:47 pm, Jim Logajan wrote: [Note: nonstandard attribution layout.] Beryl wrote: Entertaining thread this turned into. Anyway, here's a nice illusion. http://img408.imageshack.us/img408/8067/imagegm1.gif Concentrate on the + in the middle. An illusory green dot soon appears. Moments later, pink dots seem to disappear. Very interesting and neat. cavelamb himself wrote: I'll repost this one here - so it's easier to find? HEHEHE! http://www.sonnyradio.com/spinninglady.html It took some doing, but by glancing to one side (and sometimes briefly closing my eyes and trying to imagine the reverse spin) I was able to switch the perceived rotation direction. However, I have it on good authority that I do not have an IQ of anywhere near 160. :-) A couple times I had a shift in perceived rotation direction without looking away. cavelamb himself wrote: I think this one is awesome. Can these really be the same color??? http://www.home.earthlink.net/~cavel....htm#samecolor Hard to believe indeed. I decided to do an image copy from the browser and pasted the copy into the MS Windows Paint program. Copied two square chunks of each of the two labeled board squares and pasted them side-by-side. Sure enough they are the same color. |
#96
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Spinner strobing as a "Bird Strike Countermeasure"
On Dec 4, 8:14 pm, Tina wrote:
Here's an illusion I can't expain at all. http://amiedotcom.blogspot.com/2005/...hat-i-see.html been told it has to do with resolving frequencies in space, not time, but it's way past my number crunchiing skills. Looks to me more like a detail issue, with the resolution that diminishes with distance causing the illusion. Dan |
#97
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Spinner strobing as a "Bird Strike Countermeasure"
On Dec 4, 9:55 am, wrote:
In rec.aviation.piloting Harry K wrote: On Dec 3, 7:21 pm, Harry K wrote: On Dec 3, 2:45 pm, Just go look it up! wrote: On Mon, 03 Dec 2007 21:52:04 -0800, Airbus wrote: In article , says... When observed directly under artifical light that "flickers", the most obvious being a strobe light, but there are other types of artificial lights that have flicker. -- Fine - but which ones cause you to see the propellers turning in apparent reverse? Do you frequently operate your airplane indoors? Propellers are usually observed in natural light, which does not flicker. At night, on the rare occasions where you actually see the props clearly, it is from the aircraft's own lighting, which is DC. I have nbever seen the props turning backwards on a real plane - see it frequently in movies though. . . Night, near one of those big off-amber ramp lights, run the RPM up and down, there's a range where it will look like it's going backwards. I thought it was kind of interesting. It's something similar to the poor-man's "is my RPM somewhat right" test, it'll appear stopped at (I forget what RPM now) RPM and if your tach is somewhat near, viola.- Hide quoted text - - Show quoted text - Been a long, long time but my rusty math skills says it would be about 3600 unless I am wrong (per wife that is my normal state). That is the 1/2 harmonic of the rpm/flicker rate. 60 X 120 = 7200. The phenomenon should appear at 1/2, 1/4, double rate etc intervals. Harry K- Hide quoted text - - Show quoted text - After thinking that over... It gets worse. There will be multiple rpm that will show the effect under strobe conditions. With a 2 blade prop it can be sychronizing every 1/2 rev. 3-blade prop every 1/3 or 2/3 rev, etc. in addition to synching on the harmonics. It isn't that bad. Synchronization only occurs on integral fractions and engine RPM is usually 1000 and about 2700 RPM so the possibilities are limited. For a 2 bladed prop: 7200/2= 3600 - 1800 RPM 7200/3= 2400 - 2400 RPM and 1200 RPM 7200/4= 1800 - 1800 RPM and 900 RPM etc. I leave it to someone else to show how many blades you see at each RPM. -- Jim Pennino Since the prop appears stationary, you would see all the blades. Harry K |
#99
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Spinner strobing as a "Bird Strike Countermeasure"
Nice call, I can understand that now.
Thanks On Dec 4, 10:20 pm, wrote: On Dec 4, 8:14 pm, Tina wrote: Here's an illusion I can't expain at all. http://amiedotcom.blogspot.com/2005/...hat-i-see.html been told it has to do with resolving frequencies in space, not time, but it's way past my number crunchiing skills. Looks to me more like a detail issue, with the resolution that diminishes with distance causing the illusion. Dan |
#100
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Spinner strobing as a "Bird Strike Countermeasure"
On Dec 4, 5:47 pm, Jim Logajan wrote:
[Note: nonstandard attribution layout.] Beryl wrote: Entertaining thread this turned into. Anyway, here's a nice illusion. http://img408.imageshack.us/img408/8067/imagegm1.gif Concentrate on the + in the middle. An illusory green dot soon appears. Moments later, pink dots seem to disappear. Very interesting and neat. cavelamb himself wrote: I'll repost this one here - so it's easier to find? HEHEHE! http://www.sonnyradio.com/spinninglady.html It took some doing, but by glancing to one side (and sometimes briefly closing my eyes and trying to imagine the reverse spin) I was able to switch the perceived rotation direction. However, I have it on good authority that I do not have an IQ of anywhere near 160. :-) A couple times I had a shift in perceived rotation direction without looking away. cavelamb himself wrote: I think this one is awesome. Can these really be the same color??? http://www.home.earthlink.net/~cavel....htm#samecolor Hard to believe indeed. I decided to do an image copy from the browser and pasted the copy into the MS Windows Paint program. Copied two square chunks of each of the two labeled board squares and pasted them side-by-side. Sure enough they are the same color. I was curious if one-eyed people see the spin. Yep. My wife is, and I am 1/2 vision in one. Of course a simple experiment by closing one eye (either of mine) and it still rotates. I can see it either direction, blinking usually changes it. Back in the 60s I was at a remote site co-located with a radar site. It had one big antenna formed from open meshwork. I could not tell which direction it was rotating even though I _knew_ it was clockwise. Harry K |
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