Structural failure due to harmonic vibration

Out of physics curiousity, can anyone point to any references on induced
vibrations in aircraft (or any other mechanical) structures associated
with or caused by parametrically induced induced *subharmonic* or
*parametric* oscillations?

["Parametric oscillation" = a phenomena well known in electronics and
optics, in which if a structure has natural resonances with resonant
frequencies f1 and f2, and the structure is then excited or "pumped"
with a periodic force at a "pump" frequency fp = f1 + f2, this can cause
coupled oscillations to occur and grow at the "signal" and "idler"
frequencies f1 and f2.]

Wikipedia says, "Later, an investigation revealed that the tail structure had
failed on the new design from what is known as "natural resonance, or period of
vibration." Sounds like the natural frequency was too low....

Ron Wanttaja

Is this the same kind of flutter that affects the Bonanza V-tail?

On Nov 8, 7:46 am, Dudley Henriques wrote:
Does anyone have any more information on this phenomenon, and this
crash specifically? Also, are there any Super Electras still flying
and, if so, how did they solve this problem?
--

Do a search for Lockheed Electra, Tell City Crash, 1960 I believe.
Reference that with propeller whirl mode, and you should come up with
all you'll ever need to know about resonant frequency as relates to
destructive force.
DH

Dud,
Isnt Harmonics and Whirl Mode Flutter two diferent things ? I used to
fly a turboprop that had Whirl Mode issues (And a crash resulting from
this), but not any resonance restrictions. On the other hand, I flew
Scouts that when equiped with a certain propeller (For banner towing)
had restrictions on certain RPM ranges because of resonance issues.
They were traeted as two entirely different restrictions.
KFB

F. Baum wrote:
On Nov 8, 7:46 am, Dudley Henriques wrote:
Does anyone have any more information on this phenomenon, and this
crash specifically? Also, are there any Super Electras still flying
and, if so, how did they solve this problem?
--
Do a search for Lockheed Electra, Tell City Crash, 1960 I believe.
Reference that with propeller whirl mode, and you should come up with
all you'll ever need to know about resonant frequency as relates to
destructive force.
DH

Dud,
Isnt Harmonics and Whirl Mode Flutter two diferent things ? I used to
fly a turboprop that had Whirl Mode issues (And a crash resulting from
this), but not any resonance restrictions. On the other hand, I flew
Scouts that when equiped with a certain propeller (For banner towing)
had restrictions on certain RPM ranges because of resonance issues.
They were traeted as two entirely different restrictions.
KFB

Yes, in the true sense of definition. I haven't done any research on the
Electra crashes and the cause. It was my understanding that whirl mode
was a direct cause link. Any Harmonics interface would probably have
been considered as a peripheral result of how the whirl mode transmitted
through the resonant frequency of the structure.
Understanding the entire sequence is fairly complicated.
See Bertie's post above this one. I believe he has explained it fairly well.
DH

--
Dudley Henriques

On Nov 8, 9:29 am, Dudley Henriques wrote:

Dud,
Isnt Harmonics and Whirl Mode Flutter two diferent things ? I used to
fly a turboprop that had Whirl Mode issues (And a crash resulting from
this), but not any resonance restrictions. On the other hand, I flew
Scouts that when equiped with a certain propeller (For banner towing)
had restrictions on certain RPM ranges because of resonance issues.

KFB

Yes, in the true sense of definition. I haven't done any research on the
Electra crashes and the cause. It was my understanding that whirl mode
was a direct cause link.
Exactimundo. In the later Electra it was, but I doubt they had much
knowledge of this in 1938. In fact, Whirl mode wasnt much of an issue
until the 1950s when they started using small (By comparison)
lightwieght engine/gearboxes with massive props mounted on long moment
arms. I would argue that the harmonics/ resonance issue that brought
down the 1938 Electra is a completely different kettle of fish.

Any Harmonics interface would probably have
been considered as a peripheral result of how the whirl mode transmitted
through the resonant frequency of the structure.

Whoa! Slow down, your making my head hurt .

Understanding the entire sequence is fairly complicated.
See Bertie's post above this one. I believe he has explained it fairly well.
DH

Once again, Bertie saves the day

--
Dudley Henriques- Hide quoted text -

- Show quoted text -

F. Baum wrote:

Exactimundo. In the later Electra it was, but I doubt they had much
knowledge of this in 1938. In fact, Whirl mode wasnt much of an issue
until the 1950s when they started using small (By comparison)
lightwieght engine/gearboxes with massive props mounted on long moment
arms. I would argue that the harmonics/ resonance issue that brought
down the 1938 Electra is a completely different kettle of fish.


I haven't done any research at all on any of this; especially the 1938
crash.


--
Dudley Henriques

"F. Baum" wrote in
oups.com:

On Nov 8, 9:29 am, Dudley Henriques wrote:

Dud,
Isnt Harmonics and Whirl Mode Flutter two diferent things ? I used
to fly a turboprop that had Whirl Mode issues (And a crash
resulting from this), but not any resonance restrictions. On the
other hand, I flew Scouts that when equiped with a certain
propeller (For banner towing) had restrictions on certain RPM
ranges because of resonance issues.

KFB

Yes, in the true sense of definition. I haven't done any research on
the Electra crashes and the cause. It was my understanding that whirl
mode was a direct cause link.
Exactimundo. In the later Electra it was, but I doubt they had much
knowledge of this in 1938. In fact, Whirl mode wasnt much of an issue
until the 1950s when they started using small (By comparison)
lightwieght engine/gearboxes with massive props mounted on long moment
arms. I would argue that the harmonics/ resonance issue that brought
down the 1938 Electra is a completely different kettle of fish.

Any Harmonics interface would probably have
been considered as a peripheral result of how the whirl mode
transmitted through the resonant frequency of the structure.

Whoa! Slow down, your making my head hurt .

Understanding the entire sequence is fairly complicated.
See Bertie's post above this one. I believe he has explained it
fairly well. DH

Once again, Bertie saves the day


Ta da.

But I'm only repeaing what little i know about it.
Best check with an expert before you go out and design your own
airliner.


Bertie

"F. Baum" wrote in news:1194534592.304042.93710
@v23g2000prn.googlegroups.com:

On Nov 8, 7:46 am, Dudley Henriques wrote:
Does anyone have any more information on this phenomenon, and this
crash specifically? Also, are there any Super Electras still
flying
and, if so, how did they solve this problem?
--

Do a search for Lockheed Electra, Tell City Crash, 1960 I believe.
Reference that with propeller whirl mode, and you should come up with
all you'll ever need to know about resonant frequency as relates to
destructive force.
DH

Dud,
Isnt Harmonics and Whirl Mode Flutter two diferent things ? I used to
fly a turboprop that had Whirl Mode issues (And a crash resulting from
this), but not any resonance restrictions. On the other hand, I flew
Scouts that when equiped with a certain propeller (For banner towing)
had restrictions on certain RPM ranges because of resonance issues.
They were traeted as two entirely different restrictions.
KFB



That's right. The whirl mode thing is a bit different, but there's a
common thread in that they both rely on frequency. I've flown quite a
few airplanes that had veboten RPM bands for various reasons. Lots of
old Radials with steel props had rather large bands because of the
probablity of turning the prop into a rather large piano string and
thereby putting too much stress on either the blade or the crank.
AFAIK prop inspection/replacement was the only AD ever put on a Stearman
75 on account of this problem. Generally it isn't an issue with wood
props, BTW, since their resonancy is intricate and wide rather than
narrow and focused.
Which is why you don't see a lot of stainless steel violins.
I'm not familiar with the tail problem on the Lockheed 10/12 so don;'t
even know if was related to harmonics from the prop. It's probable that
buffeting from the props could cause a resonant flutter in tail
surfaces, though. That airplane was rght at th eleading edge of
technology in it;s day, when cantilever aluminum structures were all the
rage. Beech had problems with their similar model 18 in that they
fjukked up the design of the center section leading, eventauly, to a few
shed wings and a nasty and seriously ugly AD to strap the outer panel
spars to each other to relieve it.

Bertie



Bertie

The T-28A had a bad problem. At normal cruise RPM the vibrations of
the big wide paddle bladed prop would cause the crank to fail at a
square cut corner on it.

They restricted constant operation in a wide band of RPM ( and
undercut the square corner (where prop shaft met the crank throw) and
bird still lost props and became a glider.

Navy in their T-28B put a new engine and prop on it and no problems.
Some times it pays to go sloppy seconds )

Big John

On Thu, 8 Nov 2007 17:25:08 +0000 (UTC), Bertie the Bunyip
wrote:

"F. Baum" wrote in news:1194534592.304042.93710
:

On Nov 8, 7:46 am, Dudley Henriques wrote:
Does anyone have any more information on this phenomenon, and this
crash specifically? Also, are there any Super Electras still
flying
and, if so, how did they solve this problem?
--

Do a search for Lockheed Electra, Tell City Crash, 1960 I believe.
Reference that with propeller whirl mode, and you should come up with
all you'll ever need to know about resonant frequency as relates to
destructive force.
DH

Dud,
Isnt Harmonics and Whirl Mode Flutter two diferent things ? I used to
fly a turboprop that had Whirl Mode issues (And a crash resulting from
this), but not any resonance restrictions. On the other hand, I flew
Scouts that when equiped with a certain propeller (For banner towing)
had restrictions on certain RPM ranges because of resonance issues.
They were traeted as two entirely different restrictions.
KFB



That's right. The whirl mode thing is a bit different, but there's a
common thread in that they both rely on frequency. I've flown quite a
few airplanes that had veboten RPM bands for various reasons. Lots of
old Radials with steel props had rather large bands because of the
probablity of turning the prop into a rather large piano string and
thereby putting too much stress on either the blade or the crank.
AFAIK prop inspection/replacement was the only AD ever put on a Stearman
75 on account of this problem. Generally it isn't an issue with wood
props, BTW, since their resonancy is intricate and wide rather than
narrow and focused.
Which is why you don't see a lot of stainless steel violins.
I'm not familiar with the tail problem on the Lockheed 10/12 so don;'t
even know if was related to harmonics from the prop. It's probable that
buffeting from the props could cause a resonant flutter in tail
surfaces, though. That airplane was rght at th eleading edge of
technology in it;s day, when cantilever aluminum structures were all the
rage. Beech had problems with their similar model 18 in that they
fjukked up the design of the center section leading, eventauly, to a few
shed wings and a nasty and seriously ugly AD to strap the outer panel
spars to each other to relieve it.

Bertie



Bertie

Big John wrote in
:

The T-28A had a bad problem. At normal cruise RPM the vibrations of
the big wide paddle bladed prop would cause the crank to fail at a
square cut corner on it.

They restricted constant operation in a wide band of RPM ( and
undercut the square corner (where prop shaft met the crank throw) and
bird still lost props and became a glider.

Navy in their T-28B put a new engine and prop on it and no problems.
Some times it pays to go sloppy seconds )


He he.
Kind of surprising that the engine still had that weakness at that stage
of it's career. Variants had been around for over a decade and those hadn't
exactly been treated with kid gloves.
A friend of mine learned to fly in one of those.. I have to say I was
mightely impressed at the time. IIRC it was during a brief period in time
when the T-34 was being replaced with the initially troublesome T-34C, so
they were just going straight into the T-28b.
I remember seeing the books for the damned thing all over his apartment.
Unreal.


Bertie