Crashes in the News - Thread

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wktaylor

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Guys...

Be cautious about over-'beefing' specific parts within an assembly. A stronger spar fitting doesn't always make a stronger spar assembly... especially when stiffness/load concentration or centroidal [load] axis miss-matches occur. An effective design pays attention to the fit/flow of structural details as an entire assembly.

The V-tail Bonanzas ['V' stabs are no longer in production] failures did not tend to occur on all models... just those that Beech made small incremental design-on... with minimal aero and stress analysis, such as for a small gross weight and/or CG range increase. The sum of small changes + small changes + small changes + etc... back-to-back-to-back... with minimal critical thinking and flight testing... led to a false sense of safety and superiority. When Beech was forced to test specific models at limits, they were astonished that design structural-load exceedances occurred that could/did fail V-stabs. As I understood it, when Beech engineers and managers finally understood the enormous gravity of their profoundly catastrophic 'miss-judgements'... some never recovered emotionally and quit.

This was similar to counterpart engineers/managers directly responsible for Space Shuttle disasters.


'War story'. As a Young engineer for the USAF, I had a engineer-then-manager who had used 'conventional repair design thinking' to patch a cracked T-38A wing-skin close to the wing-root... without completely eliminating the crack. The repair failed catastrophically during a sharp turning maneuver as the crack... which had still been seeing load cycles and continued to slowly grow without leaking fuel... expanded instantaneously across the skin panel... outside of the repair patch boundaries... to the point the wing failed. Yes: both pilots [IP, SP] died. This repair WAS approved by others... but HE personally carried that burden of responsibility... and it weighed heavy.
 

Daleandee

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Guys...

Be cautious about over-'beefing' specific parts within an assembly. A stronger spar fitting doesn't always make a stronger spar assembly...
You speak truth! Even on the simple ultralights we have at our field I've advised the owners against always wanting to "make it mo' betta" by beefing up certain parts. Some can't grasp the concept of a load path or the fact that some parts that are easy to inspect and replace are designed to wear so that the parts that are more difficult to inspect and repair/replace don't wear as quickly.

This seems to happen a lot with landing gear where pilots keep beefing it up to prevent it from bending or breaking and the result is damage to the fuse where the gear is connected. As Paul B. says in his video, "learn to land the airplane!"
 

mcrae0104

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A stronger spar fitting doesn't always make a stronger spar assembly... especially when stiffness/load concentration or centroidal [load] axis miss-matches occur.
I completely agree that a structural system must be analyzed as a system, and not individual parts which may be changed without consequence to the overall system, but I must admit I don't know what you mean by a "centroidal axis mismatch." Can you explain what you mean please?
 

Vigilant1

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The repair failed catastrophically during a sharp turning maneuver as the crack... which had still been seeing load cycles and continued to slowly grow without leaking fuel...
FWIW, A T-38 wing could crack a LOT without leaking fuel, since there's no fuel in those wings. Just structural aluminum, honeycomb, and aluminum skins.
Most of the fuel in the T-38 is in cells located in the dorsal spine.
The planes did have a problem with corrosion within the honeycomb. If water gets in there, trouble isn't far behind. The F-5s sold to tropical countries frequently developed big problems.
 

speedracer

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Guys...

Be cautious about over-'beefing' specific parts within an assembly. A stronger spar fitting doesn't always make a stronger spar assembly... especially when stiffness/load concentration or centroidal [load] axis miss-matches occur. An effective design pays attention to the fit/flow of structural details as an entire assembly.

The V-tail Bonanzas ['V' stabs are no longer in production] failures did not tend to occur on all models... just those that Beech made small incremental design-on... with minimal aero and stress analysis, such as for a small gross weight and/or CG range increase. The sum of small changes + small changes + small changes + etc... back-to-back-to-back... with minimal critical thinking and flight testing... led to a false sense of safety and superiority. When Beech was forced to test specific models at limits, they were astonished that design structural-load exceedances occurred that could/did fail V-stabs. As I understood it, when Beech engineers and managers finally understood the enormous gravity of their profoundly catastrophic 'miss-judgements'... some never recovered emotionally and quit.

This was similar to counterpart engineers/managers directly responsible for Space Shuttle disasters.


'War story'. As a Young engineer for the USAF, I had a engineer-then-manager who had used 'conventional repair design thinking' to patch a cracked T-38A wing-skin close to the wing-root... without completely eliminating the crack. The repair failed catastrophically during a sharp turning maneuver as the crack... which had still been seeing load cycles and continued to slowly grow without leaking fuel... expanded instantaneously across the skin panel... outside of the repair patch boundaries... to the point the wing failed. Yes: both pilots [IP, SP] died. This repair WAS approved by others... but HE personally carried that burden of responsibility... and it weighed heavy.
Klaus Savier told me about looking at a Long EZ project. He asked the builder why he had installed 5/16" canard bolts (two) instead of the plans call out for 1/4" ones. The guy said "more strength." Klaus said "The 1/4" bolts are good for 30 G. Did you plan on pulling more G's than that?"
 

Flivverflyer

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As a now retired Boeing structural design engineer, I can say a few words about load axis transfer with components in bending. We struggled with it constantly, as my team did a lot of our work in the wing-to-fuselage integration area.

Think of two joints: Joint A is a plate bolted up against another plate, and Joint B is a plate joined between two outer plates. "A" puts all of the fasteners in single-shear load condition, where bolt bending must be considered. There is also a "jog" in the load path from one plate centroid to the next. "B" imposes a double-shear load to the fasteners, so that they are not subject to bolt bending, only shear. The load path from the single plate to two plates is on one common axial plane, so no "jog". Shimming is usually part of the game with a double-shear joint, so you don't put any bolt-up stresses on the two outer plates.
 

mcrae0104

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Thanks, @Flivverflyer . I'm familiar with that concept in bolted joint design but had never heard "centriodal axis mismatch" applied. Nice to learn something new.
 

wktaylor

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Air Safety Institute releases early analysis of fatal accident — General Aviation News

The Aircraft Owners and Pilots Association Air Safety Institute (ASI) has released a new video providing an initial analysis of a tragic accident that took place earlier this month.

<<embedded Video>>

On Oct. 11, 2021, a Cessna 340 crashed into a neighborhood in Santee, California, killing the pilot and one person on the ground and seriously injuring two others.

The pilot, who was experienced in the airplane, had flown this exact route several times before the accident. As he was vectored for the approach into Montgomery Field (KMYF), weather conditions were turbulent with ragged ceilings from 1,700 to 2,000 above ground level (agl).

“In our Early Analysis: N7022G, the AOPA Air Safety Institute wants to help pilots understand what is known about the accident and some issues the National Transportation Safety Board (NTSB) is expected to look at during their investigation,” said AOPA’s ASI Senior Vice President Richard McSpadden. “It’s important to remember this video was made based solely on information that is currently available to help provide an understanding of the accident at this time. The NTSB could conclude further information during their investigation that was previously unknown, which could alter our understanding of this accident.”

Early Analysis videos provide an initial assessment of prominent mishaps that generate large public interest and may indicate important safety lessons for the general aviation community, he added.
 

N804RV

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Air Safety Institute releases early analysis of fatal accident — General Aviation News

The Aircraft Owners and Pilots Association Air Safety Institute (ASI) has released a new video providing an initial analysis of a tragic accident that took place earlier this month.
Some so-called "expert" , that I've never heard of, also posted a youtube video that went viral, and somewhat "muddied the waters" over what was known and what was assumed. I'd like to think the AOPA video was an attempt to reign in some of the skuttle-butt.
 
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