Who says helicopter blades have to turn?

Joseph Nebus

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Aug 26, 2012, 2:35:46 AM8/26/12

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Short video of a helicopter as taken by a camera with shutter
speed matching the blade frequency:

http://www.youtube.com/watch?v=cxddi8m_mzk&feature=player_embedded

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Xho Jingleheimerschmidt

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Aug 26, 2012, 6:04:35 PM8/26/12

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On 08/25/2012 11:35 PM, Joseph Nebus wrote:
> Short video of a helicopter as taken by a camera with shutter
> speed matching the blade frequency:
>
> http://www.youtube.com/watch?v=cxddi8m_mzk&feature=player_embedded

Was that an accident, or did they do it on purpose?

And before you laugh at the question, consider how many videos/films of
helicopters there are that don't warrant posting on youtube, or mention
on AFCA.

Xho

K_S_ONeill

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Aug 26, 2012, 6:34:42 PM8/26/12

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I was wondering the same thing. Can modern digital cameras change the
image rate on demand?

Pastime

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Aug 27, 2012, 4:15:44 PM8/27/12

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K_S_ONeill wrote:

> On Aug 26, 5:04 pm, Xho Jingleheimerschmidt <xhos...@gmail.com> wrote:
> > On 08/25/2012 11:35 PM, Joseph Nebus wrote:
> >
> > > Short video of a helicopter as taken by a camera with shutter
> > > speed matching the blade frequency:
> >
> > >http://www.youtube.com/watch?v=cxddi8m_mzk&feature=player_embedded
> >
> > Was that an accident, or did they do it on purpose?
> >
> > And before you laugh at the question, consider how many videos/films of
> > helicopters there are that don't warrant posting on youtube, or mention
> > on AFCA.
>

> I was wondering the same thing. Can modern digital cameras change the
> image rate on demand?

I wondered the same too as well also, and then thought that maybe the
helicopter's on-board engine management computer thingy was running
the engine at a round number of RPM that happened to sync with the
video, purely because (say) 200rpm was a setting on the controls.

In other words, two pieces of machinery (helicopter and camera) both
running at human-friendly (round-numbered) rates, more likely to
coincide, etc.

(That is probably the most poorly-worded post I've come up with since
I quit drinking, but I'm not sure I can word it any better in a
rewrite.)
--
John

Kevin

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Aug 27, 2012, 6:07:44 PM8/27/12

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On Mon, 27 Aug 2012 21:15:44 +0100, Pastime <wsub...@tznvy.pbz>
wrote:

Sadly, helicopter main rotor systems don't have an rpm control in the
cockpit. They have a constant rpm, the pitch of the blades is what
the controls vary, and the rpm is not usually a nice round number.
That's why I thought the camera must have an adjustment, since it's
apparently shooting at some oddball number of frames per second.

art...@yahoo.com

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Aug 27, 2012, 7:54:01 PM8/27/12

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Not Vic Morrow.

Sanford Manley

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Aug 28, 2012, 12:12:18 AM8/28/12

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On 8/27/2012 7:54 PM, art...@yahoo.com wrote:
> Not Vic Morrow.
>

Some people go all to pieces when the least little thing happens.

--
Sanford

art...@yahoo.com

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Aug 28, 2012, 10:42:49 AM8/28/12

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And then they lose their heads.

Pastime

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Aug 28, 2012, 12:49:13 PM8/28/12

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Wow, thanks for a great answer. So, it really is puzzling, then.
--
John

David Lesher

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Aug 28, 2012, 2:32:37 PM8/28/12

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Kevin <K_S_O...@yh.com> writes:

>Sadly, helicopter main rotor systems don't have an rpm control in the
>cockpit. They have a constant rpm, the pitch of the blades is what
>the controls vary, and the rpm is not usually a nice round number.
>That's why I thought the camera must have an adjustment, since it's
>apparently shooting at some oddball number of frames per second.

I thought it was a function of engine RPM, and that was what made life
....interesting...

Add collective, engine slows so add power but wait tail rotor
slowed too so you need more rudder but then.....

{Maybe turbine-powered ones are different....}

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Xho Jingleheimerschmidt

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Aug 28, 2012, 8:14:05 PM8/28/12

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On 08/27/2012 03:07 PM, Kevin wrote:
>
> Sadly, helicopter main rotor systems don't have an rpm control in the
> cockpit. They have a constant rpm, the pitch of the blades is what
> the controls vary, and the rpm is not usually a nice round number.

But as the pitch changes, the drag would change, which would change the
load on the motor. That would tend to change the RPM, unless there was
a governor designed to keep the RPM constant. Why would someone go to
the effort to keep the RPM constant, rather than just keeping it within
some broad safety range?

Xho

Kevin

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Aug 28, 2012, 10:19:07 PM8/28/12

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Well, that certainly sounds reasonable. I wasn't an engineer, I just
worked on them. What I remember is that a Huey, for example, had an
rpm of about 301 and could vary something like +- 5% safely. Why it
had to be in such a narrow range is beyond my pay grade.

It may be, now that I think of it, that I'm wrong and that the engine
throttle acts as an rpm control, but that as you put more demands on
it you have to throttle up. That actually sounds reasonable, now that
I think about it. I wasn't a pilot either.

You could go well over 100% main rotor rpm in an auto rotation, when
the main rotor was decoupled from the engines. I remember doing an
autorotation in a Blackhawk were we went over some limit and had to
file a report; I think the limit was 125% of the rpm limit, something
like that.

--
Kevin

Hactar

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Sep 11, 2012, 10:37:15 PM9/11/12

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In article <503d5ed2$0$26565$ed36...@nr5-q3a.newsreader.com>,

Do modern (L) helicopters have an RPM regulator?

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Xho Jingleheimerschmidt

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Sep 13, 2012, 10:41:45 AM9/13/12

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On 09/11/2012 07:37 PM, Hactar wrote:
> In article <503d5ed2$0$26565$ed36...@nr5-q3a.newsreader.com>,
> Xho Jingleheimerschmidt <xho...@gmail.com> wrote:
>> On 08/27/2012 03:07 PM, Kevin wrote:
>>>
>>> Sadly, helicopter main rotor systems don't have an rpm control in the
>>> cockpit. They have a constant rpm, the pitch of the blades is what
>>> the controls vary, and the rpm is not usually a nice round number.
>>
>> But as the pitch changes, the drag would change, which would change the
>> load on the motor. That would tend to change the RPM, unless there was
>> a governor designed to keep the RPM constant. Why would someone go to
>> the effort to keep the RPM constant, rather than just keeping it within
>> some broad safety range?
>
> Do modern (L) helicopters have an RPM regulator?
>

I don't believe helicopters belong to political parties, Binny.

Xho