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Spinner strobing as a "Bird Strike Countermeasure"



 
 
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  #61  
Old December 4th 07, 06:33 PM posted to rec.aviation.piloting, rec.aviation.homebuilt
Tina
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Posts: 500
Default Spinner strobing as a "Bird Strike Countermeasure"

If any of you have tried to use a strobe light to determine rotational
speed, you'll remember harmonics are a serious problem.

If there's a single mark on a shaft, it will appear stationary if the
flash rate is equal to the time it takes the shaft to turn once. It
will also appear stationary if its rate is half of that time, (it will
blink on the spot every other time) a quarter of that time, and so on.
It gets worse. If the blink rate is twice that of the shaft speed, the
spot will appear stationary, but only half as intense, since one flash
will 'lock' the spot, and the next will illuminate the opposite side
of the shaft at an unmarked place.

To make this relevant to aviation, replace spot with prop blade.


On Dec 4, 11:17 am, 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.

Harry K- Hide quoted text -

- Show quoted text -


  #62  
Old December 4th 07, 06:55 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
[email protected]
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Posts: 2,892
Default Spinner strobing as a "Bird Strike Countermeasure"

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

Remove .spam.sux to reply.
  #63  
Old December 4th 07, 07:25 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Mxsmanic
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Posts: 9,169
Default Spinner strobing as a "Bird Strike Countermeasure"

Gig 601XL Builder writes:

Wrong, exactly backwards wrong. Rutger was correct.


The frame is a painted raster. The image is the complete set of visual data
for simultaneous assimilation.
  #64  
Old December 4th 07, 07:25 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Mxsmanic
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Posts: 9,169
Default Spinner strobing as a "Bird Strike Countermeasure"

writes:

You do know this stuff is archived ...


That's the best part.
  #65  
Old December 4th 07, 07:26 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Mxsmanic
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Posts: 9,169
Default Spinner strobing as a "Bird Strike Countermeasure"

Yes - I have a name writes:

I'm sure I've seen wheels on cars that appear to be moving backwards. Are my
eyes defective?


No, but your memory is imperfect. You've never seen that in real life, only
on TV and in films, or under stroboscopic lighting.
  #66  
Old December 4th 07, 07:28 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Mxsmanic
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Posts: 9,169
Default Spinner strobing as a "Bird Strike Countermeasure"

Maxwell writes:

This phenomenon is apparent to the naked eye under continuous
lighting conditions.


No, it is not.

You might need to wait for a three or four blade prop, but
it DOES happen in real life.


No, it does not. Continual assertions to the contrary will not change this.
  #67  
Old December 4th 07, 07:29 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Maxwell
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Posts: 1,116
Default Spinner strobing as a "Bird Strike Countermeasure"


"Mxsmanic" wrote in message
...
Yes - I have a name writes:

I'm sure I've seen wheels on cars that appear to be moving backwards. Are
my
eyes defective?


No, but your memory is imperfect. You've never seen that in real life,
only
on TV and in films, or under stroboscopic lighting.


No it's because YOU have never seen anything in REAL LIFE retard.

If it hasn't been on a tv or computer screen, you have so little experience
YOU don't realize it exists.



  #68  
Old December 4th 07, 07:33 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Yes - I have a name[_2_]
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Posts: 44
Default Spinner strobing as a "Bird Strike Countermeasure"

"Mxsmanic" wrote in message
...
Yes - I have a name writes:

I'm sure I've seen wheels on cars that appear to be moving backwards.

Are my
eyes defective?


No, but your memory is imperfect. You've never seen that in real life,

only
on TV and in films, or under stroboscopic lighting.


Translation: I don't understand it, so it can't happen.

Looks like I've been MXed (The absolute denial of common knowledge).


  #69  
Old December 4th 07, 07:46 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Paul Tomblin
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Posts: 690
Default Spinner strobing as a "Bird Strike Countermeasure"

In a previous article, Mxsmanic said:
Yes - I have a name writes:

I'm sure I've seen wheels on cars that appear to be moving backwards. Are my
eyes defective?


No, but your memory is imperfect. You've never seen that in real life, only
on TV and in films, or under stroboscopic lighting.


Wikipedia references some scientific papers that show three distinct cases
of people seeing it non-strobing (ie natural sunlight).

1. People see the effect on car wheels, mostly because hubcaps have
reflective surfaces that cause a strobing of the light in natural
sunlight, but also because of other things changing the light, like
shadows or the reflection off other objects.

2. People see the effect when their eyes are being vibrated. The article
addresses people seeing it when humming, but I suspect the same effect
could happen with the low frequency noise that permeates an airplane
cockpit.

3. There is some controversy about an effect that *some* people see when
they stare at a moving pattern of dots for periods of time greater than 30
seconds (some needing to stare as long as 10 minutes before they see it).
Some scientists are saying that it shows that our brain processes vision
in discrete frames. Others say it's a totally different effect.

I've never seen it in the air, and I'd never heard of it until I read the
wikipedia article, but it turns out that Maxwell and others are correct
and you're wrong. I guess I should have known.


--
Paul Tomblin http://blog.xcski.com/
"My band is called Imation CDR 74m 650 MB...have you seen our CDs?"
  #70  
Old December 4th 07, 07:49 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Yes - I have a name[_2_]
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Posts: 44
Default Spinner strobing as a "Bird Strike Countermeasure"

"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...


Shut the **** up, MX.

So Say We All!



 




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