Structural failure due to harmonic vibration

Jay Honeck wrote in news:1194537883.203290.75060
@e9g2000prf.googlegroups.com:

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.

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


Two completely different airplanes. You've obviously been drinking the tidy
bowl as well as sniffing the furntiure polish.


Bertie

Jay Honeck wrote in
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...

Oven cleaner is my bet


Bertie

"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...

Would you count KSEA to KJFK as Trans-continental?


Yes.

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.]

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

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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

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Jay

After the two crashes they found the problem and fixed it but then
they didn't sell good to airlines due to crash history.

Navy bought a large number (with MAD gear) after fix, that are now
configured to the P-3C Orion (ASW) configuration and many P-3's were
sold around the world in ASW confguration. Navy is still using them
while waiting for a new bird. There is a request out to industry for a
new bird???

Big John

****************************************


On Thu, 08 Nov 2007 06:09:52 -0800, 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?

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

Jay Honeck wrote:

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...?

Lockheed reused the Electra name. The 1930s Electra (think Amelia Earhart)
was a piston twin. The 1950s Electra was a 4 engine turboprop airliner.

http://www.constable.ca/sd076a.jpg

http://www.spain4uk.co.uk/images/wil...tra_G-LOFE.jpg

John Galban=====N4BQ (PA28-180)

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Jay Honeck wrote:

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...?

Lockheed reused the Electra name. The 1930s Electra (think Amelia Earhart)
was a piston twin. The 1950s Electra was a 4 engine turboprop airliner.

http://www.constable.ca/sd076a.jpg

http://www.spain4uk.co.uk/images/wil...tra_G-LOFE.jpg

John Galban=====N4BQ (PA28-180)

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Message posted via http://www.aviationkb.com