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Spinner strobing as a "Bird Strike Countermeasure"



 
 
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  #181  
Old December 6th 07, 06:04 AM posted to rec.aviation.piloting,rec.aviation.homebuilt
Alan Baker
external usenet poster
 
Posts: 244
Default Spinner strobing as a "Bird Strike Countermeasure"

In article
,
Harry K wrote:

On Dec 5, 2:05 pm, wrote:
In rec.aviation.piloting Harry K wrote:





On Dec 4, 8:25 pm, wrote:
In rec.aviation.piloting Harry K wrote:


snip
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.- Hide quoted text -


- Show quoted text -
Nope. The prop appears stationary and you see only the two.
What you see is the complete image (frame), not a composite of 4
'frames'.


I'm talking about eyeballs and strobed light here, there are no "images"
or "frames" involved.

What you see is a prop blade in whatever position it is in when
the light goes off.

If the light is going off every quarter turn, you see a particular
blade end in four different places each a quarter turn apart.

If the light is going off every sixth of a turn, you see a particular
blade end in six different places each a sixth of a turn apart.

--
Jim Pennino

Remove .spam.sux to reply.- Hide quoted text -

- Show quoted text -


Yes, but you will see them (along with all the others) one at a time.
Not the entire sequence at once or even a composite. It is the same
as taking a snap shot with shutter speed fast enough to stop the
motion, it will show all blades, in this case it will show two blades
and no 'virtual' blades. You can prove it with a fan and a variable
strobe light but I suspect that will not be a common kitchen
appliance .

Harry K


You are apparently unacquainted with the phenomenon known as
"persistence of vision".

Look it up.

--
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."
  #182  
Old December 6th 07, 06:55 AM posted to rec.aviation.piloting,rec.aviation.homebuilt
[email protected]
external usenet poster
 
Posts: 2,892
Default Spinner strobing as a "Bird Strike Countermeasure"

In rec.aviation.piloting Harry K wrote:
On Dec 5, 2:05 pm, wrote:



What you see is a prop blade in whatever position it is in when
the light goes off.

If the light is going off every quarter turn, you see a particular
blade end in four different places each a quarter turn apart.

If the light is going off every sixth of a turn, you see a particular
blade end in six different places each a sixth of a turn apart.

--
Jim Pennino

Remove .spam.sux to reply.- Hide quoted text -

- Show quoted text -


Yes, but you will see them (along with all the others) one at a time.
Not the entire sequence at once or even a composite. It is the same
as taking a snap shot with shutter speed fast enough to stop the
motion, it will show all blades, in this case it will show two blades
and no 'virtual' blades. You can prove it with a fan and a variable
strobe light but I suspect that will not be a common kitchen
appliance .


Um, no.

Assuming everything is synchronous, you will see what appears to be
multiple blades because of eye persistence, the same reason movies
appear to smoothly move.

It is the same as taking snap shots with shutter speed fast enough
to stop the motion, and taking an integral number of snap shots
during the rotation.

Take one snap shot when the blade tip is straight up, take the
next when the blade has moved 90 degrees, the next when the blade
has moved another 90 degees, take the last when the blade has moved
another 90 degrees.

Make slides of the pictures and put them on top of each other to
simulate eye persistence.

Replace "take the snap shot" with "flash the strobe".

You can prove it with a fan and a variable strobe light.

--
Jim Pennino

Remove .spam.sux to reply.
  #183  
Old December 6th 07, 07:19 AM posted to rec.aviation.piloting,rec.aviation.homebuilt
d.g.s.
external usenet poster
 
Posts: 60
Default Spinner strobing as a "Bird Strike Countermeasure"

On 12/3/2007 8:32 PM Mxsmanic ignored two million years of human
evolution to write:

At any given moment there are thousands of aircraft powered by turbofans in
flight.


At any given moment, you're a total dip****. You also lie a lot.
--
dgs
  #184  
Old December 6th 07, 02:46 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Airbus
external usenet poster
 
Posts: 119
Default Spinner strobing as a "Bird Strike Countermeasure"

In article ,
says...


On Dec 5, 2:05 pm, wrote:
In rec.aviation.piloting Harry K wrote:





On Dec 4, 8:25 pm, wrote:
In rec.aviation.piloting Harry K wrote:


snip
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.- Hide quoted text -


- Show quoted text -
Nope. The prop appears stationary and you see only the two.
What you see is the complete image (frame), not a composite of 4
'frames'.


I'm talking about eyeballs and strobed light here, there are no "images"
or "frames" involved.

What you see is a prop blade in whatever position it is in when
the light goes off.

If the light is going off every quarter turn, you see a particular
blade end in four different places each a quarter turn apart.

If the light is going off every sixth of a turn, you see a particular
blade end in six different places each a sixth of a turn apart.

--
Jim Pennino

Remove .spam.sux to reply.- Hide quoted text -

- Show quoted text -


Yes, but you will see them (along with all the others) one at a time.
Not the entire sequence at once or even a composite. It is the same
as taking a snap shot with shutter speed fast enough to stop the
motion, it will show all blades, in this case it will show two blades
and no 'virtual' blades. You can prove it with a fan and a variable
strobe light but I suspect that will not be a common kitchen
appliance .



Don't agree - I agree with Jim, and I do frequently use scientific strobe
analysers for decomposing motion. With such a tool, one must be very careful to
avoid harmonic illusions. Obvjects may appear to be moving in reverse, and
indeed phantom members may appear - a fan or prop or spoke for example may
easily appear to have more blades than it really has. Our eyes do not
immobilize instantaneous images beyond a certain speed - this makes it
possible for us to watch movies - or to be fooled by stroboscopic images.

  #185  
Old December 6th 07, 05:10 PM posted to rec.aviation.piloting, rec.aviation.homebuilt
Harry K
external usenet poster
 
Posts: 153
Default Spinner strobing as a "Bird Strike Countermeasure"

On Dec 5, 9:55 pm, wrote:
In rec.aviation.piloting Harry K wrote:





On Dec 5, 2:05 pm, wrote:
What you see is a prop blade in whatever position it is in when
the light goes off.


If the light is going off every quarter turn, you see a particular
blade end in four different places each a quarter turn apart.


If the light is going off every sixth of a turn, you see a particular
blade end in six different places each a sixth of a turn apart.


--
Jim Pennino


Remove .spam.sux to reply.- Hide quoted text -


- Show quoted text -

Yes, but you will see them (along with all the others) one at a time.
Not the entire sequence at once or even a composite. It is the same
as taking a snap shot with shutter speed fast enough to stop the
motion, it will show all blades, in this case it will show two blades
and no 'virtual' blades. You can prove it with a fan and a variable
strobe light but I suspect that will not be a common kitchen
appliance .


Um, no.

Assuming everything is synchronous, you will see what appears to be
multiple blades because of eye persistence, the same reason movies
appear to smoothly move.

It is the same as taking snap shots with shutter speed fast enough
to stop the motion, and taking an integral number of snap shots
during the rotation.

Take one snap shot when the blade tip is straight up, take the
next when the blade has moved 90 degrees, the next when the blade
has moved another 90 degees, take the last when the blade has moved
another 90 degrees.

Make slides of the pictures and put them on top of each other to
simulate eye persistence.

Replace "take the snap shot" with "flash the strobe".

You can prove it with a fan and a variable strobe light.

--
Jim Pennino

Remove .spam.sux to reply.- Hide quoted text -

- Show quoted text -


Hmmm...It looks like I will have to locate a strobe and try it. I
don't recall anything like that illusion back in my physics classes in
HS but that was near 60 years ago. Just one of those things where I
have to see it myself to believe it.

Harry K
  #186  
Old December 6th 07, 07:50 PM posted to rec.aviation.piloting,rec.aviation.homebuilt
Mxsmanic
external usenet poster
 
Posts: 9,169
Default Spinner strobing as a "Bird Strike Countermeasure"

dgs writes:

You aren't only here to discuss aviation.


I try to discuss aviation, if I can find anyone else who wants to.
  #187  
Old December 7th 07, 04:12 AM posted to rec.aviation.piloting, rec.aviation.homebuilt
george
external usenet poster
 
Posts: 803
Default Spinner strobing as a "Bird Strike Countermeasure"

On Dec 5, 2:01 pm, Mxsmanic wrote:


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


So that's where the inaccuracies about aviation came from...
Don't do it again
  #188  
Old December 7th 07, 07:45 AM posted to rec.aviation.piloting,rec.aviation.homebuilt
Mxsmanic
external usenet poster
 
Posts: 9,169
Default Spinner strobing as a "Bird Strike Countermeasure"

george writes:

So that's where the inaccuracies about aviation came from...


Who said anything about aviation?

Don't do it again


Or else what?
  #189  
Old December 7th 07, 03:21 PM posted to rec.aviation.piloting
Bertie the Bunyip[_19_]
external usenet poster
 
Posts: 3,851
Default Spinner strobing as a "Bird Strike Countermeasure"

Mxsmanic wrote in
:

george writes:

So that's where the inaccuracies about aviation came from...


Who said anything about aviation?

Don't do it again


Or else what?


Or you'll prove yourself to be an ever bigger dickhead than anyone thought,
I would imagine.

I disagree,of course, I have complete faith in you.


Bertie
 




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