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Super Cub Structural Failure

If I am correct the rear spar buckled at or near the strut attach point.
As you had mentioned the spar web was Swiss cheese with lightening holes, The Swiss cheese being my term.
 
CharlieN said:
That video of the Cirrus ditching has always bothered me since I first viewed it. The wind in the cute was dragging the plane down under faster than he could collect his gear. Appears the Cirrus is able to float quite well and might remain on the surface for some time after a ditching but being dragged by the chute did not do him any favors.

I agree about the perceived value of a chute when one commonly flies low altitudes.
Click to expand...

I personally know several pilots that have ditched aircraft like the RV8, Cessnas, Piper twins etc. and were able to deal with it without a chute.

250 NM NorthEast of Maui is where the Trades are incredibly strong (I known from sailing to the islands first hand). The pilot was lucky that he didn’t “Kite surf” too far. Very convenient to be rescued by a luxury cruise ship.

Note: Pilot deployed chute about 6000’ AGL. Cirrus recommendation is minimum 400’ but I wouldn’t test it.

https://cirrusaircraft.com/wp-content/uploads/2014/12/CAPS_Guide.pdf

immediate deployment of the CAPS is required. The minimum demonstrated altitude loss for a CAPS deployment from a one-turn spin is 920 feet. Activation at higher altitudes provides enhanced safety margins for.
Click to expand...
 
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We had a Cirrus pop the chute (for some unknown reason, wasn't structural, I think a bad running engine). It got the couple down safely, they egressed, then the plane got dragged 1/4 mile until it got caught up on a power pole, then it snapped the wood pole! It was a windy day in the Pocatello area.....for days I got asked if it was me and my plane, right! Then I was asked if had a chute. Flying low, for better or for worse, is an excellent reason not to have one. Patey has made his decision, more power to him, the guy is amazing.
 
Tony (TXPacer) and I were camped at Oshkosh last year when the mass arrival of Cirrus's came in. hey were stacked up as far as the eye could see. Tony said " dam, we missed a perfect photo shop opportunity." Took me a minute as usual to get it but still laugh when I think about it.
 
Re: Cirrus in ocean,
I think he handled his situation quite well, he was directed to be close to a ship that has a rescue craft aboard. There was time to get a helicopter there. It just surprised me how the plane was dragged under in a short time.
Personally he might have been better off with a conventional ditching.

And with what you found in your research, having a chute when much of ones flying is not much over 500' makes it a questionable value to trust the investment in weight and money. I would rather wear a chute. Probably equal value/risk.

Just what is the probability of breaking a properly built plane?
We all fly with the unknown risk of a possible system failure. Being that would commonly be a power related issue. I would prefer to fly the plane down.
Granted a read of reports be they compiled by Kathryn or sourced elsewhere makes it clear many people do not do things well under pressure.
 
I don’t think that the video from Boulder should be the reason to disregard this technology. That particular incident was a midair and the chute deployment was believed to be a result of the impact.


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silflexer said:
I don’t think that the video from Boulder should be the reason to disregard this technology. That particular incident was a midair and the chute deployment was believed to be a result of the impact.
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My comments were based on reading NTSB accident reports. This Boulder accident was just one occasion.
 
Very sad. My bet is that the fellow was dead or knocked out during the ride down under canopy. Some mid air impacts can be as violent as a bad car wreck. If the impact was violent enough to deploy the chute it must have been pretty bad. I hope he didn't suffer.

Kurt
 
Correct me if I am wrong but those chutes are manual deployment only.
 
:) Hi, I have been on this site but this is my first time spending the moment to register and post. I love all the comments on this thread. Great discussion :) I wish I had a lot more information on my friends crash but I can share what I know for sure. This was a custom built cub and the spars were drilled out in hopes to save weight. Something I would never do but we can’t be sure yet if that was the cause but it certainly is a contender. What we do know is that it was the rear spar or bracket at the strut attachment area broke ur buckled. The reason we don’t know exactly is because the Investigation team when they went out there cut out the entire section of the rear spar including All the attachments at the wing strut attachment area. That certainly indicates that it was likely one of those. My friend said he wish he had looked but he had compound fractures and that was the last thing on his mind. The next time he saw and looked at the plane that entire section was cut out for inspection. I would lean towards the circles cut out but That would be speculation and I have heard of (second hand) of rear spars buckled before. Mother Nature can swing a big bat at times. I personally think the cub is a tank and can handle about all you toss at it. There is spar reinforcing inserts that I strongly recommend that have been around for years. I’m anxious to learn more and will openly share everything as soon as I know. We all benefit with the facts. To answer a couple other questions, scrappy wings are a complete redesign and built specific to its size weight and power. I’m not sure how much cub will be left in them but they are cub “Ish”. Parachutes aren’t much help at 100 feet where we often like to get on the deck now and then. They have often had great success at below 500 at times but they don’t want people thinking that and waiting to long to make the decision to pull the handle. Hopefully most of the time we are above that. Usually if we are to low for a chute we have ground right at our feet safe enough to just land on. My plan for any emergency will certainly be just land it. I live in the high Rockies so even when flying low from one second to the next we go from 500 feet agl to 7,000 feet agl in 3 seconds. 95 percent of my flying is high enough that I may want my parachute option and I’m more than high enough for that choice. Also I’m certainly trying a few new things with scrappy so 70 lbs is ok by me. I’ll match the wings to account for that weight, speeds and all other mods. I hope this put a little light on the Brocken spar. I’m so sorry I don’t have the final results but I will share it, for sure. Fly safe, have fun. Cheers everyone
 
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You are an inspiration Mike! Thanks for sharing your endeavors. Looking forward seeing more, and sharing your passion of aviation. Stay safe and healthy, and hope to meet you one day. Cheers


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Mike patey said:
...What we do know is that it was the rear spar or spar attachment point or bracket. ... I would lean towards the circles cut out but we have had cubs over the decades snap the rear spar in turbulence multiple times without any modifications.... There is spar reinforcing inserts that I strongly recommend that have been around for years.
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Welcome aboard Mike, I admire your ability to think outside the box and to place those thoughts to active use.

When you say "rear spar or spar attachment point or bracket" are you referring to the wing root attachment to the fuselage or the strut attachment location? Or at some point in between?
Also "snap the rear spar in turbulence multiple times" is a very strong statement. Do you mean broke or just buckled? And can you be specific in which location of the spar this took place? There are spar web reinforcements which beef up the area of the web at the lift strut attachment locations. Did your referenced spars fail inboard between the strut and root?
This type of in flight failure in a Cub is not known to me. After having struck something, yes. But, not in flight without having struck something.
 
Welcome to the SC site Mike,
Knocks me down from being one of the only designer- builders to be posting here.
 
Thanks for your post Mike. I to am curious about these buckled spars in turbulence. I have seen this in ground loops but never in flight. Wipair makes an STC'd gross weight kit which includes a doubler on top of the spar cap over the rear spar and Dakota Cubs 2300 lb wings have doublers on the spar web at the strut attach. Always interested in how things are built, why and how they fail.
 
Mike, great comments.

Years ago, and I can’t remember the reference so this may all be hogwash, so take it with a grain of salt. In any case folks with TriPacers we’re trying to get more speed out of them and someone came up with the idea of negative flap setting. Kind of like what Maule did with the MX-7 series. A couple folks tried it with a modest increase in speed due to decrease in drag. Not to long after doing the negative flap thing, one of the airplanes had a rear spar failure(I think it was found on inspection and didn’t result in a crash, and I don’t know what part or portion of the rear spar allegedly failed). Evidently the moment arm for the lift distribution with the negative flap exceeded the rear spar design forces. If the above is true, perhaps the Piper rear spar design just barely meets the normal conditions explored during certification. If you combine that with gust loads in excess of the design loads, that could well be the cause of the failure.


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skywagon8a said:
Welcome aboard Mike, I admire your ability to think outside the box and to place those thoughts to active use. When you say "rear spar or spar attachment point or bracket" are you referring to the wing root attachment to the fuselage or the strut attachment location? Or at some point in between? Also "snap the rear spar in turbulence multiple times" is a very strong statement. Do you mean broke or just buckled? And can you be specific in which location of the spar this took place? There are spar web reinforcements which beef up the area of the web at the lift strut attachment locations. Did your referenced spars fail inboard between the strut and root? This type of in flight failure in a Cub is not known to me. After having struck something, yes. But, not in flight without having struck something.
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thanks for the clarification question. I’m not great at writing 🤷*♂️ To be more specific and my words certainly weren’t when I go back a read it. The part that the investigation team took was the entire section of the rear spar directly at the strut attachment. I wish I could answer what of all those components or component that failed first or was the spar broke or buckled. We don’t know because they took the entire section and cut it from the plane and every part around it. Also you are correct my statement was to broad on “broken rear spars in the past”. The better clarification word is yours “buckled” I would say it broke right there but that would better imply a crack so my apologies. Buckled is a better description 👍🤠. My question I have always wanted answered but seem to hear from a guy who knows a guy that had a buckled spar in flight, (not saying fatal) but noticed a bend when landed after severe turbulence. Here’s my question? If those truly exists, was that plane ground looped and started a problem unseen weeks or years before. Sadly the logs may not always reflect an oops that someone didn’t see anything damaged and never wanted to log the impact of the wing. I personally think the cub is absolutely a structural tank that can handle about all you can toss at it. The bottom line is I just haven’t had my hands on these story buckled spars myself but two, my hangar Neighbors that parts are hauled away waiting for answer and another that was ground looped. aside from those it’s been stories from builders and repair centers, were they looped and damaged before we may never know.
 
Just as a footnote, I remember in "Wager with the Wind" that Sheldon folded a wing on a PA-14 in turbulence. There's a brief reference to it in the old SI article about him:
"...Farther along the same track Sheldon passes over the tall cottonwoods that once caught his spinning plane and broke the fall after clear air turbulence had folded a wing back at 2,500 feet. (He sold the bent remains of that plane for $50.)"
https://vault.si.com/vault/1972/02/14/off-into-the-wild-white-yonder
 
Cubus Maximus said:
Just as a footnote, I remember in "Wager with the Wind" that Sheldon folded a wing on a PA-14 in turbulence. There's a brief reference to it in the old SI article about him:
"...Farther along the same track Sheldon passes over the tall cottonwoods that once caught his spinning plane and broke the fall after clear air turbulence had folded a wing back at 2,500 feet. (He sold the bent remains of that plane for $50.)"
https://vault.si.com/vault/1972/02/14/off-into-the-wild-white-yonder
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I remember reading that as well but have never heard or seen anything else about it.
 
Unfortunately many cubs get abused and the incident never gets logged or inspected. Pilots/mechanics look the other way due to inexperience or may be even neglect.

Notable examples: Ground loops, over speeding (IAS Vfe ) the with flaps in the pattern, hard landings, improper repairs/mods, shady logbooks, snow damage, tie down gusts

A well built ship flown/maintained correctly is not dangerous!
 
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Excessive snow loads or wind gusts (front but mainly rear from what I've seen) while parked can damage.

The note in #49 about a change in expected span load distribution is interesting. Might be worthwhile to remove weight inboard (via the inferred reflexed flap issue) during a standard +G static load test.

Gary
 
Used and abused for 70 plus years and they are still flying. I have seen loose false spars from overspending flaps and my 13,000 hour Super Cub had worn through the leading edges at the screw holes holding them to the spar.
Found this on a pre-buy for my brother. Rear spar had a slight tweak from a groundloop somewhere in its life.
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More recent Carbon Cub FX3 groundloop.
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You guys are awesome. I love the comments on all these threads. The time all of you spend here to educated openly will lead to safer repairs, more aware pilots and ultimately it will save lives! What a great forum.
 
I meant to include one of my favorite quotes, "You can tear up an anvil if you try hard enough." Can't remember who told me that but it has stuck with me over the years.
 
I worked on a cub in early 90’s that had both rear spars Bent in flight... guy liked to do loops... till he bent it. Then sold the project. Certified cub... still flying in homer I would assume.


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