Spinner strobing as a "Bird Strike Countermeasure"

In article ,
cavelamb himself 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.



Hey, I was about to post that.


I'll repost this one here - so it's easier to find?
HEHEHE!

http://www.sonnyradio.com/spinninglady.html


I think this one is awesome.
Can these really be the same color???

http://www.home.earthlink.net/~cavel....htm#samecolor

Yes, they really can and really are the same colour..

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling four 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."

In rec.aviation.piloting Harry K wrote:
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.

Yes, but how many virtual blades will you see?

Simple example: You are illuminating a 2 bladed prop running at 1000 RPM
with a strobe light pulsing at 4000 pulses per minute.

In the time between pulses, the prop makes 1/4 of a turn.

The prop is therefor lite up every 1/4 turn and it appears as though
the prop has 4 blades.


--
Jim Pennino

Remove .spam.sux to reply.

In article , says...



"Airbus" wrote in message
...
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.
. .


Do you really think you see and visualize motion constantly. Perhaps you
should spend a little more time around and airport yourself. Many
propellers, especially the large diameter props found on radial engines,
will appear at times to be rotating slower, or backwards. It's a fainter
image than recorded on film, but the partnership of the human eye and brain
does not realize fluid motion.


Well, I must admit I don't have much experience with large radial engines.
Moreover, I accept the argument that some AC ramp lighting at night can produce
stroboscopic effects with props - I have not seen it myself, even though I
frequently fly at night, but I do accept the principle - if you get your plane
in the right position with respect to line-frequency, AC lighting at night you
should see stroboscopic effects, which will include "backwards turning"
illusdion, depending on your prop speed. So I stand corrected on this.

In article , says...



"Mxsmanic" wrote in message
.. .
Roger (K8RI) writes:

At cruise RPM that effect would be completely lost. There's not a
bird or human alive that can discern stroboscopic effects of more than
a couple hundred cycles let alone over a 1000. Most of us can't even
discern 60 cps.

Birds have much better vision than human beings,


Demonstrably true.



and I don't believe
anyone
has tested their ability to discern stroboscopic effects.


You're out on a limb there. There has been A LOT of testing on birds' vision,
and they don't necessarily ask your opinion. . .



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. . .

"Peter Clark" wrote in message
...
On Tue, 4 Dec 2007 12:29:29 -0600, "Maxwell"

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

Wait, I did a KF a while back - did I read this right that now it is
trying to tell people they don't really know what they see?

Yep, that's just about the size of it.

"Mxsmanic" wrote in message
...
Paul Tomblin writes:

It tells me that the people who wrote the Wikipedia article are smarter
than you or me.

Because they agree with what you wish to believe?

I've written a lot of Wikipedia articles myself. Do you believe what I've
written because I put it in Wikipedia?

Wikipedia quotes multiple scientific papers. So far all you've quoted is
yourself.

Wikipedia usually quotes, at best, a number of sources, which may or may
not
be reliable, be they scientific papers or not.

But you are still a much more unreliable source than Wiki.

On 2007-12-05, Airbus wrote:
Well, I must admit I don't have much experience with large radial engines.
Moreover, I accept the argument that some AC ramp lighting at night can produce
stroboscopic effects with props - I have not seen it myself, even though I
frequently fly at night, but I do accept the principle - if you get your plane
in the right position with respect to line-frequency, AC lighting at night you
should see stroboscopic effects, which will include "backwards turning"
illusdion, depending on your prop speed. So I stand corrected on this.

I've seen it plenty of times.

Not caused by lighting, but you can see the strobing effect in this
video I shot, caused by the frame rate of the video camera (note, the
strobing is at 50Hz since the source video is PAL):

http://www.youtube.com/watch?v=Nf5unfWZLDA

--
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.

In article ,
says...


Yes - I have a name wrote:
"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...


Shut the **** up, MX.




So Say We All!




So, which way is the naked lady spinning?

http://www.sonnyradio.com/spinninglady.html


Some kind of joke?
I easily see it spinning either way - I'll bet a lot of people do.
Sort of like reversing an isometric cube with your eyes.
Can't be as hard as they say. . .

In article ,
says...


Airbus writes:

You're out on a limb there. There has been A LOT of testing on birds'
vision,
and they don't necessarily ask your opinion. . .

Which tests have been done?

Forget it dude - I'm not like you - will not make categorical statements
about subjects I know nothing about. I do not pretend, like you, to know what
studies may have been done. You seem to feel that somùething you do not know
(which you must admit encompasses the near totality of subjects) cannot exist.




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 obtained the facts from the engine specifications, so no guessing was
required.


I'm so impressed.
It's not the mathematical genius (dividing an RPM number by 60) that impresses
me so much - the real genius is that this guy understood WHY he had to divide
by 60 (to convert minutes to seconds). Subtle - I'm sure few will have the
intellectual presence to grasp it!

cavelamb himself wrote:



So, which way is the naked lady spinning?

http://www.sonnyradio.com/spinninglady.html


I called it up and saw her rotating CCW for about a minute even after
bleinking and looking around the room and then back at the pic she was still
CCW.

Then I looked up and book marked the page and and then sent a link to my
wife and when I looked back she was CW. And just now I popped back over and
she is still CW.