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:

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Harry K- Hide quoted text -

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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

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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

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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."