Structural failure due to harmonic vibration

I've just finished reading the tale of the first round trip coast-to-
coast flight (which was accomplished by mid-air refueling,
occasionally from milk cans) from Spokane, WA to the east coast and
back, way back in 1929. They flew a distance of 10,000 miles (they
circled over airports whilst refueling) without landing. A
fascinating story, printed in a terrific magazine, "Aviation History".

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.

This is something I've never heard much about. I understand harmonic
vibration can destroy any structure, given enough time and amplitude
-- but wouldn't a pilot be aware of such an event occurring in
flight? I picture something similar to flying a twin without synching
the props -- the noise and vibration will just about drive you crazy.

I don't have any further information on this crash, so I suppose the
vibration could have destroyed the engine mounts, causing the engines
to depart the airframe. This would probably be impossible to detect
from the cockpit before disaster struck.

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?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
I've just finished reading the tale of the first round trip coast-to-
coast flight (which was accomplished by mid-air refueling,
occasionally from milk cans) from Spokane, WA to the east coast and
back, way back in 1929. They flew a distance of 10,000 miles (they
circled over airports whilst refueling) without landing. A
fascinating story, printed in a terrific magazine, "Aviation History".

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.

This is something I've never heard much about. I understand harmonic
vibration can destroy any structure, given enough time and amplitude
-- but wouldn't a pilot be aware of such an event occurring in
flight? I picture something similar to flying a twin without synching
the props -- the noise and vibration will just about drive you crazy.

I don't have any further information on this crash, so I suppose the
vibration could have destroyed the engine mounts, causing the engines
to depart the airframe. This would probably be impossible to detect
from the cockpit before disaster struck.

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?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

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

--
Dudley Henriques

On Thu, 08 Nov 2007 09:46:52 -0500, Dudley Henriques wrote:

Jay Honeck wrote:
I've just finished reading the tale of the first round trip coast-to-
coast flight (which was accomplished by mid-air refueling,
occasionally from milk cans) from Spokane, WA to the east coast and
back, way back in 1929.

Hmmmm....interesting definition of "coast to coast." Spokane is "on the coast"
the say way Pittsburgh is (e.g., hundreds of miles inland).

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....

Ron Wanttaja

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.

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

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

Tina wrote:
Jay, somewhere I had seen a film of a flight test of a glider whose
wings started a distructive vibration.

http://www.youtube.com/watch?v=mxFOHoy-UNQ

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...ation/200711/1

Tina wrote:
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.

http://www.youtube.com/watch?v=8D7YCCLGu5Y

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...ation/200711/1

Ron Wanttaja wrote:
On Thu, 08 Nov 2007 09:46:52 -0500, Dudley Henriques wrote:

Jay Honeck wrote:
I've just finished reading the tale of the first round trip coast-to-
coast flight (which was accomplished by mid-air refueling,
occasionally from milk cans) from Spokane, WA to the east coast and
back, way back in 1929.

Hmmmm....interesting definition of "coast to coast." Spokane is "on the coast"
the say way Pittsburgh is (e.g., hundreds of miles inland).

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....

Ron Wanttaja

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

--
Dudley Henriques

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.

Ron Wanttaja wrote in
:

On Thu, 08 Nov 2007 09:46:52 -0500, Dudley Henriques
wrote:

Jay Honeck wrote:
I've just finished reading the tale of the first round trip
coast-to- coast flight (which was accomplished by mid-air
refueling, occasionally from milk cans) from Spokane, WA to the
east coast and back, way back in 1929.

Hmmmm....interesting definition of "coast to coast." Spokane is "on
the coast" the say way Pittsburgh is (e.g., hundreds of miles inland).

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....



Yes, but the Later Electra was a classic lesson in resonant freq
failure, though quite a different thing to the failure that the earlier
Electra had. IIRC two L188s were lost when a precession induced whirl
set up a torsional action in the nacelles which in turn overstresed the
wing. in short, a bit of turbulence would get one prop wobbling whihc
would start the wing wobbling which would get the second prop on the
same side wobbling and the whole thing would increase in amplitude until
the wing failed.
A redisgend engine mount and reskinning the wings with the next gauge
aluminum cured the problem.


Bertie