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05-26-2005, 08:02 PM   #781
choirboy
Yankee Racers - Founder

Joined: Jun 2003
Location: Honolulu, Hawaii
Oddometer: 17,466
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?

05-26-2005, 08:06 PM   #782
Kaumajet
H.I.D. Positive

Joined: Jun 2003
Location: Ottawa
Oddometer: 10,137
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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05-26-2005, 08:11 PM   #783
choirboy
Yankee Racers - Founder

Joined: Jun 2003
Location: Honolulu, Hawaii
Oddometer: 17,466
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.

So what happens when the disc drives the turbine? BOOM!? Or does it go out? Or does the gearbox take the brunt?

05-26-2005, 08:15 PM   #784
Photog
Charismatic Megafauna

Joined: Oct 2003
Location: Cackalacky
Oddometer: 46,308
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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05-26-2005, 08:16 PM   #785
Kaumajet
H.I.D. Positive

Joined: Jun 2003
Location: Ottawa
Oddometer: 10,137
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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"I understand the dilemma. Correct spelling takes time that could be spent licking the windows on the short bus." mac62

"There is just something special about a stripper with a tail" ilmostro

05-26-2005, 08:22 PM   #786
choirboy
Yankee Racers - Founder

Joined: Jun 2003
Location: Honolulu, Hawaii
Oddometer: 17,466
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.

05-26-2005, 08:48 PM   #787
ian408
Oh?

Joined: Apr 2003
Location: Santa Clara, CA
Oddometer: 14,615
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!

Ian

 05-26-2005, 08:58 PM #788 Max Power Secret Agent     Joined: Oct 2003 Location: Whistler, U.S.A. Oddometer: 4,526 Some specs on the B3. Everest shmeverest.........How high is the moon? __________________ Hi Ho Silver... Away!
 05-26-2005, 10:36 PM #789 TREE Interloper     Joined: Jan 2002 Location: Nova Scotia Oddometer: 3,303 Speaking of heavy loads...... 220 TONS towed 50 miles on the Hover Barge by Columbia Helicopters, 1982 Link HERE
 05-26-2005, 10:43 PM #790 Oly Deadlines whooshing by     Joined: Jan 2004 Location: Underground Gardens Oddometer: 8,099 We saw this bad boy take off from Yosemite Valley yesterday afternoon.
05-26-2005, 10:47 PM   #791
Max Power
Secret Agent

Joined: Oct 2003
Location: Whistler, U.S.A.
Oddometer: 4,526
Quote:
 Originally Posted by Oly We saw this bad boy take off from Yosemite Valley yesterday afternoon.

MBB BK 117.

Cool.

A little info HERE
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05-26-2005, 10:50 PM   #792
Weirdo OP
Welcome to you're "DOOM"

Joined: Oct 2003
Location: Prince Rupert BC
Oddometer: 4,460
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.

05-26-2005, 10:52 PM   #793
Weirdo OP
Welcome to you're "DOOM"

Joined: Oct 2003
Location: Prince Rupert BC
Oddometer: 4,460
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.

 05-26-2005, 10:53 PM #794 ian408 Oh?     Joined: Apr 2003 Location: Santa Clara, CA Oddometer: 14,615 I think that's the medivac flight. If it is, do you know what happened? Ian
05-26-2005, 10:57 PM   #795
ian408
Oh?

Joined: Apr 2003
Location: Santa Clara, CA
Oddometer: 14,615
Quote:
 Originally Posted by WeirD 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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