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The "modest" construction quality of modern, mid-line DSLR's



 
 
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  #1  
Old May 8th 13, 04:07 AM posted to rec.photo.digital.slr-systems
J. Clarke[_2_]
external usenet poster
 
Posts: 1,273
Default The "modest" construction quality of modern, mid-line DSLR's

In article ,
says...

On Sat, 16 Mar 2013 02:27:15 +0100, Wolfgang Weisselberg
wrote:
: RichA wrote:
:
: Weakness, focus problems (very likely due to plastic's inherent
: incapability to be machined as accurately as metal,
:
: Please provide proof
:
: it's tendency to
: change shape/size radically with temperature changes.
:
: Quite unlike metal, which *never* expands or contracts.
:
: Please look up the de Havilland DH 106 Comet 1.
: Fun when the planes disintegrate in the air after 20k hours
: due to *metal* fatigue.

Likewise the Lockheed Electra. So much vibration was transmitted into the body
of the plane that at least one airline provided soft cushions for the
passengers' feet. IIRC, they still used them, even after they were required to
reduce the plane's maximum speed by about 100 knots. But after the speed
reduction the planes at least stopped falling apart in the air.


The speed reduction was temporary until the cause of the problem could
be determined. It was determined, it was fixed, and the Electra
airframe continued in production for another 50 years. The vibration
problem was also fixed--the two were not related.

The new plastic planes are quite an improvement. They only got grounded when
their batteries started catching on fire. :^)

Bob



  #2  
Old May 8th 13, 03:36 PM posted to rec.photo.digital.slr-systems
PeterN[_3_]
external usenet poster
 
Posts: 703
Default The "modest" construction quality of modern, mid-line DSLR's

On 5/7/2013 11:07 PM, J. Clarke wrote:
In article ,
says...

On Sat, 16 Mar 2013 02:27:15 +0100, Wolfgang Weisselberg
wrote:
: RichA wrote:
:
: Weakness, focus problems (very likely due to plastic's inherent
: incapability to be machined as accurately as metal,
:
: Please provide proof
:
: it's tendency to
: change shape/size radically with temperature changes.
:
: Quite unlike metal, which *never* expands or contracts.
:
: Please look up the de Havilland DH 106 Comet 1.
: Fun when the planes disintegrate in the air after 20k hours
: due to *metal* fatigue.

Likewise the Lockheed Electra. So much vibration was transmitted into the body
of the plane that at least one airline provided soft cushions for the
passengers' feet. IIRC, they still used them, even after they were required to
reduce the plane's maximum speed by about 100 knots. But after the speed
reduction the planes at least stopped falling apart in the air.


The speed reduction was temporary until the cause of the problem could
be determined. It was determined, it was fixed, and the Electra
airframe continued in production for another 50 years. The vibration
problem was also fixed--the two were not related.


I believe that Lockheed was well aware of the risk, some safety
engineers had warned management, but the warnings were ignored in the
interest of timely delivery.


--
PeterN
  #4  
Old May 9th 13, 02:12 AM posted to rec.photo.digital.slr-systems
J. Clarke[_2_]
external usenet poster
 
Posts: 1,273
Default The "modest" construction quality of modern, mid-line DSLR's

In article ,
says...

On 5/7/2013 11:07 PM, J. Clarke wrote:
In article ,

says...

On Sat, 16 Mar 2013 02:27:15 +0100, Wolfgang Weisselberg
wrote:
: RichA wrote:
:
: Weakness, focus problems (very likely due to plastic's inherent
: incapability to be machined as accurately as metal,
:
: Please provide proof
:
: it's tendency to
: change shape/size radically with temperature changes.
:
: Quite unlike metal, which *never* expands or contracts.
:
: Please look up the de Havilland DH 106 Comet 1.
: Fun when the planes disintegrate in the air after 20k hours
: due to *metal* fatigue.

Likewise the Lockheed Electra. So much vibration was transmitted into the body
of the plane that at least one airline provided soft cushions for the
passengers' feet. IIRC, they still used them, even after they were required to
reduce the plane's maximum speed by about 100 knots. But after the speed
reduction the planes at least stopped falling apart in the air.


The speed reduction was temporary until the cause of the problem could
be determined. It was determined, it was fixed, and the Electra
airframe continued in production for another 50 years. The vibration
problem was also fixed--the two were not related.


I believe that Lockheed was well aware of the risk, some safety
engineers had warned management, but the warnings were ignored in the
interest of timely delivery.


You can believe anything you want to. I was an engineer at Hamilton
Standard and I worked on that propeller. These events happened before
my time but I had access to everything that was known about that
propeller and there was a lot in the files about figuring out the
vibration modes in support of Lockheed's effort to resolve the problem.
The people who worked the problem were still there and this is one of
the projects that they liked to talk about--from an engineering
viewpoint it was "interesting".

You know what a resonance is? Where you keep feeding energy into
something at the same frequency at which it vibrates when struck? Well
this was the problem. It wasn't that Lockheed was careless--they had
designed to cope with every vibration frequency that the engine and
propeller were known to produce--this wasn't horribly difficult as the
propeller and engine turned at a constant speed. The trouble is that
the propeller in this case started vibrating in a way that had not been
anticipated (by anybody, not just Lockheed) that was hitting a resonant
frequency of the engine mount.

This is not something that a "safety engineer" could predict. This is
not something that the propeller manufacturer could predict. This is
not something that, in 1959, the entire scientific community working
together could have predicted because the computing power to predict it
simply did not exist in the world. It had to be determined by extensive
testing, which was a significant engineering project in itself, and by
analysis of the wreckage, which showed unexpected damage to the bearings
on the blade shanks. Hamilton ultimately did figure it out and at that
point, knowing the nature of the problem, Lockheed was able to work up a
reliable fix.

Note that the whirl mode vibration that was breaking the airplane was
different from the vibration that causing the comfort problems and the
two fixes were unrelated--the comfort problem was fixed by changing the
angle of incidence of the nacelles, the structural problem required very
extensive modifications to the engine mount and the outer wing
structure.



  #5  
Old May 9th 13, 06:04 AM posted to rec.photo.digital.slr-systems
PeterN[_3_]
external usenet poster
 
Posts: 703
Default The "modest" construction quality of modern, mid-line DSLR's

On 5/8/2013 9:12 PM, J. Clarke wrote:
In article ,
says...

On 5/7/2013 11:07 PM, J. Clarke wrote:
In article ,

says...

On Sat, 16 Mar 2013 02:27:15 +0100, Wolfgang Weisselberg
wrote:
: RichA wrote:
:
: Weakness, focus problems (very likely due to plastic's inherent
: incapability to be machined as accurately as metal,
:
: Please provide proof
:
: it's tendency to
: change shape/size radically with temperature changes.
:
: Quite unlike metal, which *never* expands or contracts.
:
: Please look up the de Havilland DH 106 Comet 1.
: Fun when the planes disintegrate in the air after 20k hours
: due to *metal* fatigue.

Likewise the Lockheed Electra. So much vibration was transmitted into the body
of the plane that at least one airline provided soft cushions for the
passengers' feet. IIRC, they still used them, even after they were required to
reduce the plane's maximum speed by about 100 knots. But after the speed
reduction the planes at least stopped falling apart in the air.

The speed reduction was temporary until the cause of the problem could
be determined. It was determined, it was fixed, and the Electra
airframe continued in production for another 50 years. The vibration
problem was also fixed--the two were not related.


I believe that Lockheed was well aware of the risk, some safety
engineers had warned management, but the warnings were ignored in the
interest of timely delivery.


You can believe anything you want to. I was an engineer at Hamilton
Standard and I worked on that propeller. These events happened before
my time but I had access to everything that was known about that
propeller and there was a lot in the files about figuring out the
vibration modes in support of Lockheed's effort to resolve the problem.
The people who worked the problem were still there and this is one of
the projects that they liked to talk about--from an engineering
viewpoint it was "interesting".

You know what a resonance is? Where you keep feeding energy into
something at the same frequency at which it vibrates when struck? Well
this was the problem. It wasn't that Lockheed was careless--they had
designed to cope with every vibration frequency that the engine and
propeller were known to produce--this wasn't horribly difficult as the
propeller and engine turned at a constant speed. The trouble is that
the propeller in this case started vibrating in a way that had not been
anticipated (by anybody, not just Lockheed) that was hitting a resonant
frequency of the engine mount.

This is not something that a "safety engineer" could predict. This is
not something that the propeller manufacturer could predict. This is
not something that, in 1959, the entire scientific community working
together could have predicted because the computing power to predict it
simply did not exist in the world. It had to be determined by extensive
testing, which was a significant engineering project in itself, and by
analysis of the wreckage, which showed unexpected damage to the bearings
on the blade shanks. Hamilton ultimately did figure it out and at that
point, knowing the nature of the problem, Lockheed was able to work up a
reliable fix.


All I can and will say, is that my belief is not based upon mere
speculation. Andthere are times when memos disappear from files.

Note that the whirl mode vibration that was breaking the airplane was
different from the vibration that causing the comfort problems and the
two fixes were unrelated--the comfort problem was fixed by changing the
angle of incidence of the nacelles, the structural problem required very
extensive modifications to the engine mount and the outer wing
structure.


True.



--
PeterN
  #6  
Old May 10th 13, 05:43 AM posted to rec.photo.digital.slr-systems
J. Clarke[_2_]
external usenet poster
 
Posts: 1,273
Default The "modest" construction quality of modern, mid-line DSLR's

In article ,
says...

On 5/8/2013 9:12 PM, J. Clarke wrote:
In article ,
says...

On 5/7/2013 11:07 PM, J. Clarke wrote:
In article ,

says...

On Sat, 16 Mar 2013 02:27:15 +0100, Wolfgang Weisselberg
wrote:
: RichA wrote:
:
: Weakness, focus problems (very likely due to plastic's inherent
: incapability to be machined as accurately as metal,
:
: Please provide proof
:
: it's tendency to
: change shape/size radically with temperature changes.
:
: Quite unlike metal, which *never* expands or contracts.
:
: Please look up the de Havilland DH 106 Comet 1.
: Fun when the planes disintegrate in the air after 20k hours
: due to *metal* fatigue.

Likewise the Lockheed Electra. So much vibration was transmitted into the body
of the plane that at least one airline provided soft cushions for the
passengers' feet. IIRC, they still used them, even after they were required to
reduce the plane's maximum speed by about 100 knots. But after the speed
reduction the planes at least stopped falling apart in the air.

The speed reduction was temporary until the cause of the problem could
be determined. It was determined, it was fixed, and the Electra
airframe continued in production for another 50 years. The vibration
problem was also fixed--the two were not related.

I believe that Lockheed was well aware of the risk, some safety
engineers had warned management, but the warnings were ignored in the
interest of timely delivery.


You can believe anything you want to. I was an engineer at Hamilton
Standard and I worked on that propeller. These events happened before
my time but I had access to everything that was known about that
propeller and there was a lot in the files about figuring out the
vibration modes in support of Lockheed's effort to resolve the problem.
The people who worked the problem were still there and this is one of
the projects that they liked to talk about--from an engineering
viewpoint it was "interesting".

You know what a resonance is? Where you keep feeding energy into
something at the same frequency at which it vibrates when struck? Well
this was the problem. It wasn't that Lockheed was careless--they had
designed to cope with every vibration frequency that the engine and
propeller were known to produce--this wasn't horribly difficult as the
propeller and engine turned at a constant speed. The trouble is that
the propeller in this case started vibrating in a way that had not been
anticipated (by anybody, not just Lockheed) that was hitting a resonant
frequency of the engine mount.

This is not something that a "safety engineer" could predict. This is
not something that the propeller manufacturer could predict. This is
not something that, in 1959, the entire scientific community working
together could have predicted because the computing power to predict it
simply did not exist in the world. It had to be determined by extensive
testing, which was a significant engineering project in itself, and by
analysis of the wreckage, which showed unexpected damage to the bearings
on the blade shanks. Hamilton ultimately did figure it out and at that
point, knowing the nature of the problem, Lockheed was able to work up a
reliable fix.


All I can and will say, is that my belief is not based upon mere
speculation. Andthere are times when memos disappear from files.


OK, now you're going off into tinfoil hat territory.

Note that the whirl mode vibration that was breaking the airplane was
different from the vibration that causing the comfort problems and the
two fixes were unrelated--the comfort problem was fixed by changing the
angle of incidence of the nacelles, the structural problem required very
extensive modifications to the engine mount and the outer wing
structure.


True.



  #7  
Old May 10th 13, 05:25 PM posted to rec.photo.digital.slr-systems
Alan Browne
external usenet poster
 
Posts: 12,640
Default The "modest" construction quality of modern, mid-line DSLR's

On 2013.05.08 21:12 , J. Clarke wrote:

Note that the whirl mode vibration that was breaking the airplane was
different from the vibration that causing the comfort problems and the
two fixes were unrelated--the comfort problem was fixed by changing the
angle of incidence of the nacelles, the structural problem required very
extensive modifications to the engine mount and the outer wing
structure.


I recall flying the Grumman Tiger. The 180 hp Lycoming version of the
aircraft (AA-5B) tach had a yellow-band of about 100 RPM in the normal
operating (green band) range - you could not operate the airplane in
that RPM band. (Fixed pitch prop). During the check ride you operated
it there for about 10 or 20 seconds in order to recognize the vibration.

Nice little airplane. Fast - IIRC we could get a nice round 130 kts at
65% / 8000 ASL. Do not drink coffee before flight. (5 hour legs were
not unusual - flying eastbound, climb to just below oxygen required and
catch a good 25 - 30 kt. tailwind at 11,500 - lower throttle setting for
about 120 kts TAS. - that's economy cruise! Westbound, cruise at 70%
for 135 TAS - keep it lower and out of the higher alt. headwinds - 4
hour legs).

--
"A Canadian is someone who knows how to have sex in a canoe."
-Pierre Berton
 




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