Spinner strobing as a "Bird Strike Countermeasure"

In article ,
Maxwell wrote:

"Roger (K8RI)" wrote in message
...
On Sun, 02 Dec 2007 22:09:30 -0000, Jim Logajan
wrote:

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.



"Mike Noel" wrote in message
...
True, but aren't we talking about 40 cps when the prop RPM is 2400?


Seems I have heard the 16 cps is all that is required for movies to appear
continuous. I think the human eye loosed it around 12 or 13. However, we
don't seen consciously either. Hence the reason an aircraft propeller will
appear to be revolving slowly backwards at times.

Visual perception is funny and complex.

black & white films were 16 frames/second.
Color films are 24 frames/second

U.S. TV is 60 fields/second, European is 50/second.
This is driven more by the need for phospors that 'decay' rapidly enough
to not produce 'blurred' motion than perception issues.

OTOH, A significant number of people can perceive 'flicker' in conventional-
tube fluorescent lamps. which is at 120 flickers/second.

Also, the eye -- and brain -- 'notices' things that are too fleeting for
conscious identification. Google 'subliminal' advertizing -- IIRC, lab
tests showed that injected imagery with a duration of only a few milliseconds
had 'measurable' effects.

In article ,
says...


Visual perception is funny and complex.

black & white films were 16 frames/second.
Color films are 24 frames/second


The frame-rate was increased from 16 to 24 at the introduction of sound (not
color). The increased linear speed was desirable to improve fidelity of the
analog optical soundtrack on the film. In either case, 24 or 16 FPS, each image
is projected three or two times (respectively) to produce an effective rate of
48 - this was done to avoid perception of flicker.



Also, the eye -- and brain -- 'notices' things that are too fleeting for
conscious identification. Google 'subliminal' advertizing -- IIRC, lab
tests showed that injected imagery with a duration of only a few milliseconds
had 'measurable' effects.



Oh NO! Not Vance Packard and the "Hidden Persuaders"!!

U.S. TV is 60 fields/second, European is 50/second.

And it takes two interlaced fields to make a frame, therefore US
broadcast TV standard (NTSC) is actually only 30 frames per second.
Europe's PAL and SECAM standards are both 50 interlaced fields per
second, yielding 25 actual frames per second.

On Mon, 03 Dec 2007 02:52:14 -0000,
(Robert Bonomi) wrote:

In article ,
Maxwell wrote:

"Roger (K8RI)" wrote in message
...
On Sun, 02 Dec 2007 22:09:30 -0000, Jim Logajan
wrote:

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.



"Mike Noel" wrote in message
...
True, but aren't we talking about 40 cps when the prop RPM is 2400?


Seems I have heard the 16 cps is all that is required for movies to appear
continuous. I think the human eye loosed it around 12 or 13. However, we
don't seen consciously either. Hence the reason an aircraft propeller will
appear to be revolving slowly backwards at times.

Visual perception is funny and complex.

black & white films were 16 frames/second.
Color films are 24 frames/second

U.S. TV is 60 fields/second, European is 50/second.
This is driven more by the need for phospors that 'decay' rapidly enough
to not produce 'blurred' motion than perception issues.

OTOH, A significant number of people can perceive 'flicker' in conventional-
tube fluorescent lamps. which is at 120 flickers/second.

I seriously doubt they can. I can discern the flicker in *some*
fluorescent lights, but I can not discern 120 cps on a strobe. I
think what they are seeing is the "sputter" of a cold lamp or a light
that isn't starting correctly. The flicker I see in those lamps is
considerably slower than 120 or even 60 cps.

First, for any flicker the phosphor has to be defective which means
the lamp is already defective so we can't expect it to be behaving
normally.

it would be interesting to see if those same people can discern even
60 cps in a strobe.

Also, the eye -- and brain -- 'notices' things that are too fleeting for
conscious identification. Google 'subliminal' advertizing -- IIRC, lab
tests showed that injected imagery with a duration of only a few milliseconds
had 'measurable' effects.

It's controversial, but has been called one of the greatest myths of
all time. It's generally accepted they are ineffective.
http://www.sciam.com/article.cfm?art...E19&sc=I100322
According to the Scientific American article they at best distract the
viewer.

Roger (K8RI)

Maxwell writes:

Seems I have heard the 16 cps is all that is required for movies to appear
continuous.

Motion pictures use 24 ips, repeated once, giving 48 fps (24 images shown
twice each). The motion is smooth as long as the image isn't too bright,
large, or fast-moving. Sometimes a stroboscopic effect can be seen in the
latter cases. It can be hidden by allowing image elements to blur.

You can see this effect very clearly on TV (30 ips in the U.S.) when sporting
events are showing that have been recorded with high shutter rates in the
cameras. Each image is sharp and it's easy to see that a succession of
individual images is being shown on the screen, even at 30 ips.

I think the human eye loosed it around 12 or 13.

Higher than that. Twelve images per second tends to look noticeably jerky.

Hence the reason an aircraft propeller will
appear to be revolving slowly backwards at times.

Not when being observed directly. That only happens in movies and video due
to the interaction between the imaging rate and the rotation rate of the
propeller.

"Mxsmanic" wrote in message
...
Maxwell writes:

Seems I have heard the 16 cps is all that is required for movies to
appear
continuous.

Motion pictures use 24 ips, repeated once, giving 48 fps (24 images shown
twice each). The motion is smooth as long as the image isn't too bright,
large, or fast-moving. Sometimes a stroboscopic effect can be seen in the
latter cases. It can be hidden by allowing image elements to blur.

You can see this effect very clearly on TV (30 ips in the U.S.) when
sporting
events are showing that have been recorded with high shutter rates in the
cameras. Each image is sharp and it's easy to see that a succession of
individual images is being shown on the screen, even at 30 ips.

I think the human eye loosed it around 12 or 13.

Higher than that. Twelve images per second tends to look noticeably
jerky.

Hence the reason an aircraft propeller will
appear to be revolving slowly backwards at times.

Not when being observed directly. That only happens in movies and video
due
to the interaction between the imaging rate and the rotation rate of the
propeller.

Wrong again you clueless twit.

Wolfgang Schwanke schrieb:

Hz flicker CRT televisions, and most people don't notice it. Americans
who've grown up with 60 Hz NTSC report noticing bad flicker with
European PAL televisions.

But they see at last twice the same colour... :-)

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, and I don't believe anyone
has tested their ability to discern stroboscopic effects. And the front fan
on a turbofan is turning at around 40-50 revolutions per second, not
thousands.

"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, and I don't believe
anyone
has tested their ability to discern stroboscopic effects. And the front
fan
on a turbofan is turning at around 40-50 revolutions per second, not
thousands.

Guess again.

Maxwell writes:

Guess again.

It wasn't a guess.