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Old 05-26-2005, 09:02 PM   #781
choirboy
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Quote:
Originally Posted by BradVardy
No, the higher the density altitude, the higher the autorotation RPM for a give rotor system. Sometimes, when the auto RPM is set for lower altitudes, the rotor can overspeed in a fast descent, causing serious problems in the short and long term.
Yah, I wasn't sure if that was related to an autorotation or not. Disc speed is governed by the turbine, right? If you bottom pitch you still control disc speed by engine RPMs?
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Old 05-26-2005, 09:06 PM   #782
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Quote:
Originally Posted by choirboy
If you bottom pitch you still control disc speed by engine RPMs?
Disc speed is controlled by turbine speed (N2, Np or Nf) if the natural aerodynamic rotor speed is less that the power turbine, i.e., if the turbine is driving the rotor (normal ops). If the natural speed of the rotor is higher than the power turbine, that's freewheeling, and it's controlled by collective pitch.
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Old 05-26-2005, 09:11 PM   #783
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Quote:
Originally Posted by BradVardy
Disc speed is controlled by turbine speed (N2, Np or Nf) if the natural aerodynamic rotor speed is less that the power turbine, i.e., if the turbine is driving the rotor (normal ops). If the natural speed of the rotor is higher than the power turbine, that's freewheeling, and it's controlled by collective pitch.
I had to read that three times.

So what happens when the disc drives the turbine? BOOM!? Or does it go out? Or does the gearbox take the brunt?
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Old 05-26-2005, 09:15 PM   #784
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Quote:
Originally Posted by BradVardy
No, the higher the density altitude, the higher the autorotation RPM for a give rotor system. Sometimes, when the auto RPM is set for lower altitudes, the rotor can overspeed in a fast descent, causing serious problems in the short and long term.
Gotcha.

I'm guessing that the problems would be the rotor itself failing, or stresses on the rest of the mechanicals as a result of the overspeed?

My only fling-wing experience is with Gyros so I'm a bit clueless on this stuff.
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Old 05-26-2005, 09:16 PM   #785
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Quote:
Originally Posted by choirboy
I had to read that three times.

So what happens when the disc drives the turbine? BOOM!? Or does it go out? Or does the gearbox take the brunt?
No, it freewheels, or overspeeds. It can be controlled for the most part, but can get out of control in extreme conditions, or the re-engagement can be hell on the gearbox or sprag clutch(es). Repetative or hard re-engagement have caused problems in the past.
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Old 05-26-2005, 09:22 PM   #786
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Quote:
Originally Posted by BradVardy
No, it freewheels, or overspeeds. It can be controlled for the most part, but can get out of control in extreme conditions, or the re-engagement can be hell on the gearbox or sprag clutch(es). Repetative or hard re-engagement have caused problems in the past.
Oh. So the rotor can be disengaged from the drivetrain? I didn't know that - that was why I was having a hard time understanding what freewheeling was.
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Old 05-26-2005, 09:48 PM   #787
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Quote:
Originally Posted by BradVardy
No, it freewheels, or overspeeds. It can be controlled for the most part, but can get out of control in extreme conditions, or the re-engagement can be hell on the gearbox or sprag clutch(es). Repetative or hard re-engagement have caused problems in the past.
All this rotor head stuff is making my head spin. I gotta get off the sauce...

Thanks for splaining to us Blad!

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Old 05-26-2005, 09:58 PM   #788
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Some specs on the B3.







Everest shmeverest.........How high is the moon?
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Old 05-26-2005, 11:36 PM   #789
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Speaking of heavy loads......


220 TONS towed 50 miles on the Hover Barge by Columbia Helicopters, 1982

Link HERE
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Old 05-26-2005, 11:43 PM   #790
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We saw this bad boy take off from Yosemite Valley yesterday afternoon.

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Old 05-26-2005, 11:47 PM   #791
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We saw this bad boy take off from Yosemite Valley yesterday afternoon.


MBB BK 117.


Cool.

A little info HERE
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Old 05-26-2005, 11:50 PM   #792
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Quote:
Originally Posted by choirboy
Oh. So the rotor can be disengaged from the drivetrain? I didn't know that - that was why I was having a hard time understanding what freewheeling was.
It's just like a bicycle. You can apply power down a hill, but once the bike starts to go faster than you're peddling, you're legs are driving noting, or freewheeling. Just like a rotor system desynchronized from an engine.

The idea is that if the stove quites, the rotor system doesn't have to drive the engine during the autorotation.
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Old 05-26-2005, 11:52 PM   #793
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Quote:
Originally Posted by TREE

220 TONS towed 50 miles on the Hover Barge by Columbia Helicopters, 1982

Link HERE
I love that shot.




Lots.
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Old 05-26-2005, 11:53 PM   #794
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I think that's the medivac flight. If it is, do you know what happened?

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Old 05-26-2005, 11:57 PM   #795
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I love that shot.




Lots.
Pretty cool shot. But I have question, nope. Not a Loaded question (that would
be what clan does the cotton twill kilt belong to?). But how do you fly the
helicopter like that? I assume they're pulling the load for some distance. Right?
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