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Thread: Super Cub Structural Failure

  1. #81

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    Thread drift happens. Last “relevant” post was 11 days ago. I‘m sure it will come back soon........
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  2. #82
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    Sorry for the drift but I wanted to set the record straight!
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  3. #83
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    Kind like a real life conversation.

    After reading all the links I am curious what else was wrong with the Maule besides bending the struts.
    Steve Pierce

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  4. #84

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    Pilot said the turbulence was so severe that seat frame had broken loose and his head jammed the roof.
    Quote Originally Posted by Steve Pierce View Post
    Kind like a real life conversation.

    After reading all the links I am curious what else was wrong with the Maule besides bending the struts.
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  5. #85

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    I believe we were talking about structural failures so I posted this story about this poor pilot that survived severe turbulence ,,I'd like to thank Mr. Matlock for his additional input ,,,
    Quote Originally Posted by Eddie Foy View Post
    Sorry for the drift but I wanted to set the record straight!
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  6. #86
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    Quote Originally Posted by kirkangus View Post
    Pilot said the turbulence was so severe that seat frame had broken loose and his head jammed the roof.

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    Thanks, I missed that part. Scanned through it all to fast.
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  7. #87
    Eddie Foy's Avatar
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    It isn't in there. That was probably from Scruggs. He is a little loose with the truth. About like the Maule that the Air Force bought him.

    Quote Originally Posted by Steve Pierce View Post
    Thanks, I missed that part. Scanned through it all to fast.
    Last edited by Eddie Foy; 07-30-2020 at 04:03 PM.
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  8. #88
    Eddie Foy's Avatar
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    You are welcome.

    Quote Originally Posted by kirkangus View Post
    I believe we were talking about structural failures so I posted this story about this poor pilot that survived severe turbulence ,,I'd like to thank Mr. Matlock for his additional input ,,,

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  9. #89
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    Getting upset by an F16 opposing pass would have scared the crap out of me in any light aircraft. Good reason to be aware, vigilant and check notams. The airspace is big right up until it’s not.

    Many pilots have come out of uncontrolled flight and bent the airframe during recovery. Which is way better than the alternative.

    I expect it may be hard to not overreact as up until that point the entire situation was going the other way. Loss of control, panic, disorientation. But the first thing you do is land, before any bends before breaks.

    In the report it notes that the Maule pilot had a ASEL PPL issued in 1989. Would this indicate the first issuance or a renewal of some sort.? The pilot reported having 6000 hrs 3 years later in 1992.


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  10. #90
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    Quote Originally Posted by Farmboy View Post
    In the report it notes that the Maule pilot had a ASEL PPL issued in 1989. Would this indicate the first issuance or a renewal of some sort.? The pilot reported having 6000 hrs 3 years later in 1992.
    In the old days this was called P-51 time. (Parker 51) For you youngsters, Parker made pens.
    N1PA
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  11. #91
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    If you've ever gotten a replacement for a change of address, the date on your license will be that date, not the original issue date.

  12. #92

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    If I recall this thread started with concern of rear spar failures.
    A number of years back when I was looking at the Javron cub at his display at Osh I was curious about the box structure aft of the rear spar, In this image look at the top center forward of the aileron and flap juncture.
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    I now recognize the sheet structure mid span is there to reduce the chance of the spar buckling. This structure is added to greatly resists any fore-aft movement of the spar caps reducing the chance of the spar bending from high loads.
    Regards, Charlie
    Super Coupe E-AB build in process

  13. #93
    Eddie Foy's Avatar
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    Mine says 2018 because I got a new rating.

    Quote Originally Posted by skywagon8a View Post
    In the old days this was called P-51 time. (Parker 51) For you youngsters, Parker made pens.
    "Put out my hand and touched the face of God!"

  14. #94

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    With regards to Chutes in Cirrus’s: are there any Cirrus owners on here, that have done the Cirrus recurrent (or initial) training, that can tell us what Cirrus teaches?

    I had a Cirrus owner tell me Cirrus standard Ops was to pull the BRS in the event of an engine failure?

    Is there anyone who has gone through the Cirrus Simulator program that can elaborate?

  15. #95
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    I’m not a owner nor have I had citrus training, but my understanding from those that have is you are correct. ANY power issue and they say pull the handle.


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  16. #96
    Farmboy's Avatar
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    Demonstrated Deployment Parameters

    400’ (561’ G5*) - Demonstrated loss of altitude from a straight and level CAPS deployment

    920’ (1081’ G5*) - Demonstrated loss of altitude from a 1 turn spin

    135 KIAS - VPD (SR20 G1/G2) - Maximum demonstrated deployment speed for CAPS

    133 KIAS - VPD (SR20 G3/SR22/SR22T) - Maximum demonstrated deployment speed for CAPS 140 KIAS - VPD (SR22/SR22TG5) - Maximum demonstrated deployment speed for CAPS

    *Demonstrated parameters for the G5 were calculated from G5 parachute drop tests simulating a 3,600 lbs airplane

    Possible CAPS Deployment Situations

    CAPS should be activated in the event of a life-threatening emergency where CAPS deployment is determined to be safer than continued flight and landing.

    • Loss of Control - A loss of control is when the airplane does not respond as the pilot expects and may result from flight control or system failure, turbulence, disorientation, icing or pilot loss of situational awareness. If a loss of control occurs, CAPS should be activated immediately.

    • Engine Failure Not Over a Runway – If a forced landing is required onto any surface other than a runway, CAPS activation is strongly recommended. If a forced landing over rough or mountainous terrain, over water, in fog, at night, or in low IMC conditions is required, CAPS activation is strongly recommended.

    • Engine Failure Over a Runway - During engine failures within gliding distance of a runway, the pilot must continually evaluate the situation.

    - At 2,000 ft AGL, if the landing is assured the pilot may continue to the runway. If not assured then activate CAPS.

    - At 1,000 ft AGL, if the landing is still assured, the pilot may continue, recognizing that the risks associated with landing short, runway overrun or low altitude loss of control likely exceed those of a timely CAPS deployment. If the landing is not assured by at least 400 ft (561 ft G5) AGL the pilot should immediately activate CAPS.

    • Pilot Incapacitation - Pilot incapacitation may occur from a wide variety of causes, ranging from a pilot’s medical condition to a bird strike that injures the pilot. If incapacitation occurs and the passengers are not trained to land the aircraft, CAPS activation is strongly recommended.

    • Mid-Air Collision - A mid-air collision will likely render the airplane uncontrollable by damaging the control system or primary structure. Unless it is apparent that structural and control system damage has not occurred, CAPS activation is strongly recommended.

    • Structural Failure - A structural failure has never occurred in a Cirrus aircraft. However, if a structural failure were to occur, CAPS activation is strongly recommended.


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  17. #97

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    Another approach at this structural failure, A question for Mike Patey if you are in audience.
    You stated the investigators cut out all the structure as they determined they need.

    How about the other wing?

    Could the fabric be opened up to photograph the structure for all to see?
    My curiosity is if any additional bracing had been added around the lift strut attachment.
    I expect there is no additional structure there. We have many guys and gals here who would love to get a good look at the lightening holes in these spars.
    I was going to add more comment but will refrain until we all can get a chance to see both front and rear spars in this plane.
    Regards, Charlie
    Super Coupe E-AB build in process
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  18. #98
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    Charlie, that's what I was thinking, too. Thanks for bringing it up.

    I keep looking at that Javron box structure too, doing my best to imagine the forces.

  19. #99

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    Quote Originally Posted by RVBottomly View Post
    Charlie, that's what I was thinking, too. Thanks for bringing it up.

    I keep looking at that Javron box structure too, doing my best to imagine the forces.
    In the Pipers, the metal spars get most all their strength in the web. The spar caps offer very little strength in the overall picture. The spars in reality rely on the ribs to prevent twisting which long ago it had been determined to not have much in reserve. Therefore the additional structure is used to box the spar to prevent twisting which is the act of buckling.
    Regards, Charlie
    Super Coupe E-AB build in process
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  20. #100
    skywagon8a's Avatar
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    Actually it is the compression ribs which control the twist. The ribs only hold the fabric shape.
    N1PA

  21. #101
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    Quote Originally Posted by skywagon8a View Post
    Actually it is the compression ribs which control the twist. The ribs only hold the fabric shape.
    I've often wondered why the compression struts did not have some vertical triangulation. The only compression member with anti-twist between spars is the N-Strut.

    I did a test on wood ribs and found that each had a measurable amount of resistance to spar twist. I'll have to go back to my notes, but I think it was around 12-15 pound-feet twist before failure at the rear spar point. Add those ribs up and there is something there.
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  22. #102

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    Quote Originally Posted by skywagon8a View Post
    Actually it is the compression ribs which control the twist. The ribs only hold the fabric shape.
    Hate to be the critic but you should go over the math some more. The struts are way to few and far between to offer much of any resisting to twist / buckling of the spars.

    The testing RV did is pretty darn close to the numbers that Piper's style of riveted ribs as well.
    If you refer back to the image that Steve P posted of a CC failed rear spar you will note the total buckling is between ribs. If the added support of what was designed in for the 2000# gross weight had been added that buckling might well have been much different if not even failed.
    Regards, Charlie
    Super Coupe E-AB build in process
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  23. #103
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    Quote Originally Posted by CharlieN View Post
    Hate to be the critic but you should go over the math some more. The struts are way to few and far between to offer much of any resisting to twist / buckling of the spars.

    The testing RV did is pretty darn close to the numbers that Piper's style of riveted ribs as well.
    If you refer back to the image that Steve P posted of a CC failed rear spar you will note the total buckling is between ribs. If the added support of what was designed in for the 2000# gross weight had been added that buckling might well have been much different if not even failed.
    This picture?

    The buckling was prevented at the compression rib. The buckling which did occur was caused by an outside impact force.
    N1PA
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  24. #104
    wireweinie's Avatar
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    Wow that's ugly! Glad I play with wires.

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  25. #105

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    Quote Originally Posted by skywagon8a View Post
    This picture?

    The buckling was prevented at the compression rib. The buckling which did occur was caused by an outside impact force.
    Air loads or impact, it is still a single point failure. Looks to me it is very clear nothing prevented or reduced any buckling. The failure was not spread out as should be if the engineering were closer to what is should be.
    Regards, Charlie
    Super Coupe E-AB build in process

  26. #106
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    Quote Originally Posted by CharlieN View Post
    Air loads or impact, it is still a single point failure. Looks to me it is very clear nothing prevented or reduced any buckling. The failure was not spread out as should be if the engineering were closer to what is should be.
    Charlie, You know that the engineering is done for the flight loads, not crash damaging loads. You are mixing apples and oranges.
    N1PA
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  27. #107
    RVBottomly's Avatar
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    What I reported on the wing ribs was conservative.

    I applied 10 pounds to the front spar location before deformation of the rib. At 31" spacing between spars that's 310 pound-inches or 25.8 pound feet of torque resistance on the rear spar.

    https://www.supercub.org/forum/showt...l=1#post756031

  28. #108

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    Quote Originally Posted by skywagon8a View Post
    Charlie, You know that the engineering is done for the flight loads, not crash damaging loads. You are mixing apples and oranges.
    No, no I am not. A simple ground loop should not destroy a major component of an aircraft. There have been in flight failures of Cub wings dating back many decades.
    A fuselage should not collapse around it's occupants with mild mishaps. There are to many that have done so.
    I have spent my life working on survivability of structures. The plane I am building is just one example showing the differences in structure to achieve the goal. It is not for everyone but I believe in walking away, even if one might be limping.
    Single point failures should have been designed out of these structures long ago. Some companies have addressed a number of the issues, but the severity of that spar failure from what is not even a crash makes it clear that some have not.
    The Cub fuselages have needed quite a few added braces which most people do, kudos to them since they care and understand. But no one has addressed failure of landing gear mount points, Why? Safety cables, Why? Fix the problem.
    The main reason I am building a look alike is I have no desire to even consider the lack of survivability in my original J4.
    Someone might want to continue with the restoration of my original plane but it is not me.
    On my current build some people feel my wings are a copy of the RV series of wings, they are not. Wings should not buckle in flight especially when the fix does not even add weight. End
    Regards, Charlie
    Super Coupe E-AB build in process

  29. #109
    Steve Pierce's Avatar
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    You can break an anvil if you try hard enough. Probably hard to make it fly.
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  30. #110

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    There have been in flight failures of Cub wings dating back many decades.

    okay, now you have me worried. What is the failure mode of that wing? Does it happen to J3s as well? I had not heard of an in-flight Cub wing failure, except after failure of a lift strut.

    I have cold- straightened spars. The amount of force that takes is stunning!

  31. #111
    www.SkupTech.com mike mcs repair's Avatar
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    Super Cub Structural Failure

    Quote Originally Posted by bob turner View Post
    There have been in flight failures of Cub wings dating back many decades.
    .

    I have cold- straightened spars. The amount of force that takes is stunning!
    That because you didn’t heat it first and reheat treat it before straitening it. Bringing it to it’s annealed (soft) condition temporarily. (I am not a fan of doing this either..) just replace spar



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  32. #112
    www.SkupTech.com mike mcs repair's Avatar
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    Super Cub Structural Failure

    Quote Originally Posted by mike mcs repair View Post
    That because you didn’t heat it first and reheat treat it before straitening it. Bringing it to it’s annealed (soft) condition temporarily. (I am not a fan of doing this either..) just replace spar



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  33. #113
    cubdriver2's Avatar
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    Quote Originally Posted by CharlieN View Post
    No, no I am not. A simple ground loop should not destroy a major component of an aircraft. There have been in flight failures of Cub wings dating back many decades.
    A fuselage should not collapse around it's occupants with mild mishaps. There are to many that have done so.
    I have spent my life working on survivability of structures. The plane I am building is just one example showing the differences in structure to achieve the goal. It is not for everyone but I believe in walking away, even if one might be limping.
    Single point failures should have been designed out of these structures long ago. Some companies have addressed a number of the issues, but the severity of that spar failure from what is not even a crash makes it clear that some have not.
    The Cub fuselages have needed quite a few added braces which most people do, kudos to them since they care and understand. But no one has addressed failure of landing gear mount points, Why? Safety cables, Why? Fix the problem.
    The main reason I am building a look alike is I have no desire to even consider the lack of survivability in my original J4.
    Someone might want to continue with the restoration of my original plane but it is not me.
    On my current build some people feel my wings are a copy of the RV series of wings, they are not. Wings should not buckle in flight especially when the fix does not even add weight. End
    Thats the dog chasing his tail theory. Stronger heavier is more survivable but in fact it will crash at a faster speed. A lighter craft designed for the job + 10% added for stupidity will crash at a lower speed. Speed kills.

    Glenn
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  34. #114
    Steve Pierce's Avatar
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    Piper spars can only be legally straightened cold. There is a service bulletin, memo or instruction with the criteria. They don't cost that much, buy a new one and get on with life.
    Steve Pierce

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  35. #115

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    Both of those are true. I replaced the spars, then tried my hand at the service bulletin straightening. I was successful. It was a lot of work - you do not do it without some pretty robust tools.

    Again, I want to know what the failure mode is - if it fails in flight, it would be fatal. It only took a couple of lift strut fatalities to cause an AD of some fame. I think there were four lift strut failures, not counting the ones caught at inspection. You would think that if the rear spar had a history of buckling under aileron load, there would be an AD against it. Does it have such a history?
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  36. #116
    skywagon8a's Avatar
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    Quote Originally Posted by CharlieN View Post
    No, no I am not. A simple ground loop should not destroy a major component of an aircraft. There have been in flight failures of Cub wings dating back many decades.
    A fuselage should not collapse around it's occupants with mild mishaps. There are to many that have done so.
    I have spent my life working on survivability of structures. The plane I am building is just one example showing the differences in structure to achieve the goal. It is not for everyone but I believe in walking away, even if one might be limping.
    Single point failures should have been designed out of these structures long ago. Some companies have addressed a number of the issues, but the severity of that spar failure from what is not even a crash makes it clear that some have not.
    The Cub fuselages have needed quite a few added braces which most people do, kudos to them since they care and understand. But no one has addressed failure of landing gear mount points, Why? Safety cables, Why? Fix the problem.
    The main reason I am building a look alike is I have no desire to even consider the lack of survivability in my original J4.
    Someone might want to continue with the restoration of my original plane but it is not me.
    On my current build some people feel my wings are a copy of the RV series of wings, they are not. Wings should not buckle in flight especially when the fix does not even add weight. End
    Charlie, I agree with you that should not destroy, should not collapse, should have been designed, should not buckle in flight ought to be designed into an airplane. However show me in CAR 3 and CAR 4 where it says should not. There are specific parameters spelled out, should not is not among them. FAR 23 was an attempt to correct the deficiencies of those earlier regulations. That is just one reason why the costs of certifying a new design have risen as it has.

    I wasn't there, but that wing in Steve Pierce's picture was not the result of a simple ground loop. Landing gears do have side load requirements, there are no requirements that a wing not be permitted to buckle when it strikes the ground.

    You are to be commended for your attention to detail and safety in the building of your plane. You will also have to admit no manufacturer would design and build a plane such as yours, expecting to turn a profit. The manufacturers follow the regulations to a minimum, and sometimes exceeding the regulations, but to the extent you are doing.... not so. If the CAA now the FAA required it, that would be a different story.
    N1PA
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  37. #117
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    I have never heard of an in flight failure of a Piper wing exceept in the book "Wager With the Wind" on a PA14.
    Steve Pierce

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  38. #118
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    Yes, and in that case consider the source. if I’m not mistaken, all the strut issues I’m aware of, were a result of corrosion or other factors which weakened the structures. If you want a scary picture, look at a photo of the Taylorcraft “strut failure” that brought about the latest AD. That airplane was not even close to airworthy. If I recall, the original Piper strut AD was precipitated by similar conditions.

    MTV

  39. #119
    Cubus Maximus's Avatar
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    Just re-read that section Steve (page 68-70) - yikes!
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  40. #120

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    Thanks, Steve.

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