Structural failure due to harmonic vibration

"Jay Honeck" wrote in message
ps.com...

Hmmm. If it happened to another Electra in 1960, that says a lot.
The crash I'm talking about happened in 1938.

I guess maybe they DIDN'T address the problem...?


Different aircraft.

"Jay Honeck" wrote in message
oups.com...

A coast-to-coast flight originating from Spokane? Spokane is in eastern
Washington, not far from the Idaho border. Must be nearly 400 miles from
the Pacific coast.


My mistake. The author called the flight "trans-continental" and
"across America" -- which my brain translated into "coast-to-coast"
for some reason...


I think most people would agree with you. I'd say a "trans-continental"
flight that started in Spokane and proceeded east failed to transit about
400 miles worth of continent.

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 -

Steven P. McNicoll wrote:
"Jay Honeck" wrote in message
oups.com...

A coast-to-coast flight originating from Spokane? Spokane is in
eastern Washington, not far from the Idaho border. Must be nearly
400 miles from the Pacific coast.


My mistake. The author called the flight "trans-continental" and
"across America" -- which my brain translated into "coast-to-coast"
for some reason...


I think most people would agree with you. I'd say a "trans-
continental" flight that started in Spokane and proceeded east failed
to transit about 400 miles worth of continent.

Would you count KSEA to KJFK as Trans-continental? If so the difference in
the distance of a great circle route flight would only be 193 miles.

Dudley Henriques wrote:

Ron Wanttaja wrote:

Dudley Henriques

wrote:

Jay Honeck wrote:

One of the pilots, Nick Mamer, went on to a career with Northwest
Air Lines. The author of the article states that he was killed in
1938 flying a Lockheed 14 Super Electra over Montana when the plane
crashed after suffering structural failure due to harmonic
vibration. All passengers and crew were killed.

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.

Wrong Electra, Dudley. Namer died in 1938 in the twin recip, twenty
years before the four-engine turboprop.

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....

Don't know anything at all about the earlier crash. Reading his post I
assumed he wanted information on the CAUSE of the crash. Since the
cause seemed to be harmonic vibration, I naturally steered him to the
1960 Electra crashes involving resonant frequency and whirl mode.
It is interesting that the earlier crash was the earlier Electra.
As an added note, I would think that anyone wishing data on this
phenomenon would want to reference the Lockheed Electra crashes in the
60's. DH

The Super Electra crash in Montana resulted from flutter. The aircraft
likely encountered turbulence, which set off the flutter, which in turn
tore the rudders and the tops of the vertical stabs off. The aircraft
was seen in a flat spin.

Flutter can be very destructive, with failure occurring within
seconds of onset.

It turned out that the test equipment Lockheed was using to determine
the natural frequency of the empennage gave inaccurate readings, so
the design was inadequate.

Here's a link to the accident report.

http://dotlibrary1.specialcollection...h%5C011038.pdf

Note that it was finalized less than three weeks after the accident.
I guess they worked more quickly in those days.

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 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

"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

Tina wrote in news:1194534978.130955.37540
@q5g2000prf.googlegroups.com:

Jay, somewhere I had seen a film of a flight test of a glider whose
wings started a distructive vibration. It was not pretty, the
amplitude of the vibration went from non existant to so great the wing
failed in what looked like 2 seconds. It happened so quickly it looked
doubtful the pilot could have reduced speed enough to stop it before
failure happened. I don't remember the details but the frequency might
have been the order of a couple of hertz -- so the wingtip went up a
little, down a little more, up even more, and after a few such cycles
as I remember it left the airplane.


Yeah, gliders are notorious for this sort of behaviour. It's not helped by
pilots lopping off or adding on large sections of wing for performance or
to fit the airplane into a class.


My memory is not clear, but the suddeness of onset to failure was
something that remains vivid (wonder if it's an accurate memory?).

Sounds like flutter, but it could be that the wings wer just at their
design limits. Plastic gliders are pretty flexible and this, combined with
control surfaces that have little or no mass or aerodynamic balance area
and a natural tendency to acclerate like you can't believe lead to a
relatively high incidence of flutter induced structural failures.

I've read of many and talked to one guy who had one. He shattered the
fuselage in a fraction of a second when his stab started rattling. It's one
of the reasons they wear 'chutes routinely.


Bertie