Surviving with a broken pitch link

[Oliver Kunze]

Hi,

I am wondering what the consequences of a broken rotating pitch link of a >=
4-bladed rotor will be. From my understanding, the free-to-pitch blade will
eventually come to a high angle of attack that the airloads will crush its
structure and if not the debris will destroy the other rotor blades, the
centrifugal forces of the out-of-balance rotor with the remaining blades
will destroy the rotor head and/or the gearbox.
On the other hand I've seen some FMEAs that say that a broken pitch link
will "only" cause "severe vibration" with "land ASAP" consequences for the
ship.

Any opinions on that (I hope not, made by own experience) ?


Oliver

[Bob]

Lay off the mushrooms

[poncej]

I think a well blade design will not increase the angle of attack in a
free pitch condition. will be unstable not just in broken pitch-link
condition.
jorge

Oliver Kunze wrote:
>
> Hi,
>
> I am wondering what the consequences of a broken rotating pitch link of a >=
> 4-bladed rotor will be. From my understanding, the free-to-pitch blade will
> eventually come to a high angle of attack that the airloads will crush its
> structure and if not the debris will destroy the other rotor blades, the
> centrifugal forces of the out-of-balance rotor with the remaining blades
> will destroy the rotor head and/or the gearbox.
> On the other hand I've seen some FMEAs that say that a broken pitch link
> will "only" cause "severe vibration" with "land ASAP" consequences for the
> ship.
>
> Any opinions on that (I hope not, made by own experience) ?
>
> Oliver

[Beav]

"Oliver Kunze" > wrote in message
...
> Hi,
>
> I am wondering what the consequences of a broken rotating pitch link of a
> >=
> 4-bladed rotor will be. From my understanding, the free-to-pitch blade
> will
> eventually come to a high angle of attack that the airloads will crush its
> structure and if not the debris will destroy the other rotor blades, the
> centrifugal forces of the out-of-balance rotor with the remaining blades
> will destroy the rotor head and/or the gearbox.
> On the other hand I've seen some FMEAs that say that a broken pitch link
> will "only" cause "severe vibration" with "land ASAP" consequences for the
> ship.
>
> Any opinions on that (I hope not, made by own experience) ?

A blade with the correct C/G should immediately go to flat pitch and stay
there, and it's my guess that most blades are designed and built to have
that C/G in the correct place. 30% back from the leading edge or less would
do that, but get beyond 33% back and the blade would be seriously unstable.


Beav

[Steve R.]

"Beav" > wrote in message
...
>
> "Oliver Kunze" > wrote in message
> ...
>> Hi,
>>
>> I am wondering what the consequences of a broken rotating pitch link of a
>> >=
>> 4-bladed rotor will be. From my understanding, the free-to-pitch blade
>> will
>> eventually come to a high angle of attack that the airloads will crush
>> its
>> structure and if not the debris will destroy the other rotor blades, the
>> centrifugal forces of the out-of-balance rotor with the remaining blades
>> will destroy the rotor head and/or the gearbox.
>> On the other hand I've seen some FMEAs that say that a broken pitch link
>> will "only" cause "severe vibration" with "land ASAP" consequences for
>> the
>> ship.
>>
>> Any opinions on that (I hope not, made by own experience) ?
>
> A blade with the correct C/G should immediately go to flat pitch and stay
> there, and it's my guess that most blades are designed and built to have
> that C/G in the correct place. 30% back from the leading edge or less
> would do that, but get beyond 33% back and the blade would be seriously
> unstable.
>
>
> Beav

Agreed! Also, I've seen models loose a pitch link with the old style wood
blades that had CG's too far aft as Beav mentions. The blade itself was not
destroyed as Oliver implied. Instead, it either went to full pitch or went
into an overwhelming flutter that made it impossible for the engine to
maintain proper rotor rpm and/or the pilot to maintain control of the
helicopter. Either way, it was "rekit" time. :-(

Fly Safe,
Steve R.