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number of rotor blades



 
 
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  #11  
Old November 26th 03, 06:39 PM
Sla#s
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"Rob Fonhof" wrote in message
...
Just a theoretical question that someone may be able to help with.
Alot of helicopters have only two rotor blades, ie:Robinsons, Bells, etc.
Others have multiples, ie:dauphins with 4, Hughes etc.
If a blade is thrown on a two blade, bend over and kiss your rear bye bye.
What would happen if you had a 4, 5, or even 6 blade?Would you still be

able
to autorotate? I know the airframe would probably vibrate violently, but
would it be survivable in an autorotate, or even low power to at least get
to the ground.
Have there been instances in the past where this has happened with a 2
blade.


Brantly B2s had a problem in the early '70s. I personally saw a blade come
off one. The other blades pulled the gearbox off the airframe. Two on board
but only one was killed as the machine was only at 20 ft.

Slatts



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  #12  
Old November 26th 03, 07:36 PM
Stan Gosnell
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"Helimech" wrote in
:

About 2 years ago Herman Hospital in Houston, TX lost a BK117 due to a
M/R blade loss. They were on approach, I seem to recall about 100 ft
AGL, and broke a TT strap (badly corroded). The M/R gearbox left the
aircraft and all 3 souls were lost. This was the first time a blade
had slung in the BO105 (same head) or BK117 history. Then I remember
years ago Donald Trumps Agusta A109 lost a blade up in NY with several
of his VP's aboard. All were killed. Then there were the M/R spindle
problems with the S76 when it first came out. Your right though, a M/R
separation is very, very rare. JC


I had forgotten about the Hermann ship. The BH206 also had TT strap
problems when it was new, and shucked a few blades, IIRC.

--
Regards,

Stan

  #14  
Old November 27th 03, 04:26 AM
Helimech
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I guess that's why Bell still has the 2 year calendar life on their straps.
Bit of a overkill but I guess they never want to see those days again. JC

"Stan Gosnell" wrote in message
...
"Helimech" wrote in
:

About 2 years ago Herman Hospital in Houston, TX lost a BK117 due to a
M/R blade loss. They were on approach, I seem to recall about 100 ft
AGL, and broke a TT strap (badly corroded). The M/R gearbox left the
aircraft and all 3 souls were lost. This was the first time a blade
had slung in the BO105 (same head) or BK117 history. Then I remember
years ago Donald Trumps Agusta A109 lost a blade up in NY with several
of his VP's aboard. All were killed. Then there were the M/R spindle
problems with the S76 when it first came out. Your right though, a M/R
separation is very, very rare. JC


I had forgotten about the Hermann ship. The BH206 also had TT strap
problems when it was new, and shucked a few blades, IIRC.

--
Regards,

Stan



  #15  
Old November 28th 03, 03:19 AM
Micbloo
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About 2 years ago Herman Hospital in Houston, TX lost a BK117 due to a
M/R blade loss. They were on approach, I seem to recall about 100 ft
AGL, and broke a TT strap (badly corroded). The M/R gearbox left the
aircraft and all 3 souls were lost.


And caused the subsequent grounding
of many BK117s in the EMS community
as they had to do an inspection. But I think most ships were quickly back in
service.
  #16  
Old November 28th 03, 11:45 PM
[email protected]
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Losing a MR blade in flight results in certain death, but what about
having a blade delaminate? That is, part of the skin comes off but
the main chord is still attached?

Dennis.


Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm

  #17  
Old November 29th 03, 04:02 AM
Helimech
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Well its a rough ride down but definitely controllable. The BK117 has had
this happen numerous times (I would guess about 15 times, all landed
safely). The engine cowling is being left unlatched (this is not the
mechanics or pilots story) and is coming open in flight striking the M/R
blades. The M/R blades tear the cowling off the airframe and upward into
the rotor system. The result is almost always large sections of M/R
skin/foam being ripped off a blade or two. I've seen several BK blades that
had 3 foot sections missing, from the spar back. The worst one I ever saw
was an Omniflight BK that lost the last 6-8 feet of the Skin/foam off 1
blade. All that was left on the outer 6-8 feet of one blade was the spar.
Like swinging a stick around. The pilot did a great run on landing in some
frozen field but he said everything was just a blur all the way down from
the imbalance. I've heard many stories of aircraft loosing large parts of
blades (shot off) in Vietnam. It livable if you just loose the light stuff.
Most of the weight is spar and metal eroision strip, thats the stuff you
want to keep onboard. I've been looking thru my stuff since this tread
started looking for a weight figure I read one time on what the centrifical
load was on a 206 M/R blade but can't find it. I remember it was a whole
lot more force than I ever would have guessed. Made me respect for the
strength of those TT straps.JC

wrote in message
...

Losing a MR blade in flight results in certain death, but what about
having a blade delaminate? That is, part of the skin comes off but
the main chord is still attached?

Dennis.


Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm



  #18  
Old November 30th 03, 06:56 PM
John Roncallo
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Rob Fonhof wrote:

Just a theoretical question that someone may be able to help with.
Alot of helicopters have only two rotor blades, ie:Robinsons, Bells, etc.
Others have multiples, ie:dauphins with 4, Hughes etc.
If a blade is thrown on a two blade, bend over and kiss your rear bye bye.
What would happen if you had a 4, 5, or even 6 blade?Would you still be able
to autorotate? I know the airframe would probably vibrate violently, but
would it be survivable in an autorotate, or even low power to at least get
to the ground.
Have there been instances in the past where this has happened with a 2
blade.
Thanks in advance.
Rob Fonhof




I did see some article (I don t know where) stating the Sikorsky S-61
could survive a thrown blade. I find this hard to believe, since
throwing a blade would create an enormous out of balance on the order of
60,000 lb at about 5 Hz. If the ship remained in one piece and weighed
20,000 Lb. The pilot would feel the equivalent of someone shaking them
back and forth 5 time per second at 3 g's or more if it were empty. I
see a persons neck breaking in a short time. And in fact this is usually
the scenario I've been told. If you throw a blade the ocupants will be
dead before the aircraft hits the ground.

Opinions posted here are my own and do not represent the company I work for.

John Roncallo

  #19  
Old November 30th 03, 08:00 PM
Dave Jackson
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Sikorsky has a couple of patents for 'Rotor system having alternating length
rotor blades'. [U.S. patent #5,620,303]

This is not to suggest that the removal of a portion of the blade on the
ground is the same as the removal of a portion of the blade in the air.


"Shaber CJ" wrote in message
...
Subject: number of rotor blades
From: Stan Gosnell


It isn't survivable, just as losing a wing on an airplane isn't
survivable, except in the most unusual of circumstances.

--
Regards,

Stan


I do know a an accident with a glider where the pilot lost a wing, spin

down
into a marsh with big fluffy trees and survied. It happened in Florida a

few
years ago and the glider was a 1-26.

Craig



  #20  
Old November 30th 03, 11:10 PM
[email protected]
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I had heard that the centrifugal load on the hub from the blade is
something like 25,000 lbs for a small helicopter. I'm sure that there
is a formula somewhere that takes the total weight of the blade, the
RPM and the length. I don't have it though. I'd have to brush up on
my calculus to figure out the formula. I'm sure that someone here
probably has it already figured out.

Dennis.

"Helimech" wrote:

blades (shot off) in Vietnam. It livable if you just loose the light stuff.
Most of the weight is spar and metal eroision strip, thats the stuff you
want to keep onboard. I've been looking thru my stuff since this tread
started looking for a weight figure I read one time on what the centrifical
load was on a 206 M/R blade but can't find it. I remember it was a whole
lot more force than I ever would have guessed. Made me respect for the
strength of those TT straps.JC



Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm

 




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