Spinner strobing as a "Bird Strike Countermeasure"

wrote in news:5fc94b93-52e4-4ee4-8c59-d46cd92a6702
@s19g2000prg.googlegroups.com:

On Dec 2, 5:59 pm, "Roger (K8RI)" wrote:
On Sun, 2 Dec 2007 17:02:07 -0600, "Maxwell"
wrote:

That's used to let people on the ground know if the engine is still
turning. An engine coasting to a stop is nearly silent and is silent
if you are out on the ramp wearing hearing protection.

Roger (K8RI)


Incorrect. The spiral on the fan hub is a bird deterrent measure. It
has nothing to do with ground personnel.

We use them to hypnotise ground staff into loading the chemicals we spray
out at altitude...


Bertie

"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.

I can say I worked in the engine shop at American for 15 years, and we were
always told it was a very cost effective bird strike tool. But that is no
guarantee. We always did say if you hadn't heard a good rumor my 10:00 am,
then start one.

But then again, it shouldn't be needed by ground personnel. If someone can
look at a high bypass engine and tell if it's turning fast enough to be
dangerous, the need to be teaching English in France or something.

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.

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.

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.

"Bertie the Bunyip" wrote

We use them to hypnotise ground staff into loading the chemicals we spray
out at altitude...
Have you been making spray clouds of dihydrogen oxide, again.

I thought there was finally a ban on loading that stuff onto airplanes,
except for small amounts that are directly used by the passengers.
--
Jim in NC

"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.

"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.

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... :-)

"Morgans" wrote in
news

"Bertie the Bunyip" wrote

We use them to hypnotise ground staff into loading the chemicals we
spray out at altitude...
Have you been making spray clouds of dihydrogen oxide, again.

I thought there was finally a ban on loading that stuff onto
airplanes, except for small amounts that are directly used by the
passengers.

Absolutely. As indicated in another thread, we'r eonly allowed ethanol
dotchaknow?


Bertie