Was a bit breezy in Alberta

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Posthumane
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Was a bit breezy in Alberta

#1 Post by Posthumane » Wed Oct 18, 2017 12:32 pm

Winds gusting well past 50 kts. Quite a bit of damage around the province. One casualty was my 172A, which broke free of its tiedowns and did a backflip. A sad end to a great aircraft.
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Re: Was a bit breezy in Alberta

#2 Post by '97 Tercel » Wed Oct 18, 2017 12:52 pm

Brutal!!
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looproll
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Re: Was a bit breezy in Alberta

#3 Post by looproll » Wed Oct 18, 2017 12:55 pm

Whoa! That's awful. Sorry you lost your airplane.

Not the first time I've seen that in Alberta (Lethbridge area - winds 50G70KT)
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pelmet
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Re: Was a bit breezy in Alberta

#4 Post by pelmet » Wed Oct 18, 2017 2:13 pm

What airport? And what sort of tiedown were you using?
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Re: Was a bit breezy in Alberta

#5 Post by dirtdr » Wed Oct 18, 2017 2:44 pm

Dam. That sucks. Shitty Deal.
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Re: Was a bit breezy in Alberta

#6 Post by pdw » Wed Oct 18, 2017 2:48 pm

It's very sad, looking at this picture ... and what is there to do ? I've called up owners a few times when a tiedown has worked loose on one side, and got them there just in time during a storm. Once was even without permission when I couldn't reach them, but called afterward to let them know (but when it's calm again who really can relate to the strong gusting at the time? ).

I say it should be OK to scout for iffy ropes ahead of any unusal/approaching storm or in progress (make the students do it ?) ... or just making the effort to alert the occasional flyer/ owner (rarely goes to the airport) to a potentially weak tiedown situation.

My favourite aircraft ...
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Re: Was a bit breezy in Alberta

#7 Post by Posthumane » Wed Oct 18, 2017 3:21 pm

Pelmet, the airport is CYXH (Medicine Hat). The tiedowns were ratchet straps, supposedly rated to 900 lbs. They were probably a year and a half old, so maybe weakened by the sun. They weren't loose, they just snapped right in the middle. Next time I'm buying some super heavy duty ones like you see on semis...

The aircraft was last flown about a week ago. Was planning on going on a longer flying trip this week down to the states, but I guess that's not happening now. When the mechanics from the local AME turned it right side up, the entire tail came off the rest of the fuselage at the point where it was weakened from the blow when the aircraft first flipped.
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Re: Was a bit breezy in Alberta

#8 Post by CpnCrunch » Wed Oct 18, 2017 5:04 pm

Sorry to hear that, really nice plane. When I owned it we had a few windstorms, but never any damage. However the year after I sold to you, another guy had his plane destroyed at Drumheller, so maybe I just got lucky. I used nylon rope to tie down...occasionally it worked a little bit loose during strong winds and the plane weathercocked a bit, but never had any problems.

Hopefully you were properly insured.
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Re: Was a bit breezy in Alberta

#9 Post by Aussiecat » Wed Oct 18, 2017 7:25 pm

:( :( :( Sorry for the loss of your plane, it was a wild and windy day in mid Ab ( dog didn't even want to go for a walk ). I heard the southern part of province was stronger
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Re: Was a bit breezy in Alberta

#10 Post by pelmet » Wed Oct 18, 2017 10:23 pm

Posthumane wrote:Pelmet, the airport is CYXH (Medicine Hat). The tiedowns were ratchet straps, supposedly rated to 900 lbs. They were probably a year and a half old, so maybe weakened by the sun. They weren't loose, they just snapped right in the middle. Next time I'm buying some super heavy duty ones like you see on semis...

The aircraft was last flown about a week ago. Was planning on going on a longer flying trip this week down to the states, but I guess that's not happening now. When the mechanics from the local AME turned it right side up, the entire tail came off the rest of the fuselage at the point where it was weakened from the blow when the aircraft first flipped.
Thanks, Sorry about the loss. I can see one strap on the nose along with the ratchet and possibly the remnants of a strap on one of the wings. I have never seen that used on aircraft for tiedowns and would assume that you can ratchet them down really tight as compared to using rope.
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Re: Was a bit breezy in Alberta

#11 Post by anofly » Thu Oct 19, 2017 4:06 pm

I am very sorry for the loss of a good aircraft, love those fastbacks!!


there may be things i dont understand about straps vs rope, but nylon rope, one half inch, is about 4000 odd pounds to break, and if there are 3 of them on a plane...

https://www.engineeringtoolbox.com/nylo ... _1513.html
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Re: Was a bit breezy in Alberta

#12 Post by GyvAir » Thu Oct 19, 2017 4:41 pm

Straps are quick and easy to make the exact length required if you don't want to learn to tie a knot.
However, they look great until something shifts enough that the lower hook falls out of the ring on the tarmac. I've seen this many times. I've definitely seen more broken straps than ropes over the years, as well. The only broken ropes I've seen were obviously rotten to start with.
I suspect most ropes have more substantially more give than ratchet straps, allowing some cushioned movement, rather than a shock and snapping action with a non-stretchable strap.
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Re: Was a bit breezy in Alberta

#13 Post by Posthumane » Thu Oct 19, 2017 6:37 pm

I used nylon rope for a while (that I got with the plane from CpnCrunch) but retired them after a couple years since I thought they were getting a bit sun bleached. Switched to straps because I thought they were more convenient. One thing I didn't like about the nylon ropes is that I could never get them quite tight, so when the plane was rocking in gusts it was tugging on the ropes instead of a constant pull. Of course, that was before I knew how to tie a taughline hitch - now I would be able to get them very tight if I wanted to use them.

One trick for getting the ratchet straps to stay on in case the plane shifts is to use high strength locking carabiners on the ends instead of the supplied hooks. That way if some slack develops, they will still stay attached. Of course, I didn't have those on my straps and was just using the hooks in this case, but it would have made no difference.

Anofly - the breaking strength of 1" webbing strap is also around 3000 lbf. The 900 lb rating is the working load, which is generally less than 1/3 of the breaking strength, and sometimes is derated even more depending on the application. Keep in mind that a knot in the rope or strap will weaken it significantly - up to 50% reduction for a sheet bend or bowline.

I may switch back to ropes on the next plane... but I still like the convenience of straps so I'm not sure.
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Re: Was a bit breezy in Alberta

#14 Post by trampbike » Thu Oct 19, 2017 6:50 pm

Sorry for your airplane!

28.99'' was the altimeter setting when I took off that day. Quite the impressive low, steadily moving through at 35kts.
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Re: Was a bit breezy in Alberta

#15 Post by photofly » Thu Oct 19, 2017 9:35 pm

One thing I didn't like about the nylon ropes is that I could never get them quite tight, so when the plane was rocking in gusts it was tugging on the ropes instead of a constant pull.
I don’t think the pull is constant, with taut lines. I think it’s still subject to the same dynamic wind loads superimposed on a heavy static load. Higher dynamic loads even, because the plane can’t give. And invisible. Without the extra pre-load of the ratchet mechanisms your straps might even have held.

Personally I prefer the lines loose enough to let the plane rock around on the soft undercarriage which is designed to absorb the energy, than let the tie down rings and main spars fight against the rope tension.

Note: after extensive research on the interwebs thingy, I see opinions are split about taut vs not-taut.

Another point: a typical cessna is rated to -1.76g. At a max weight of 2300 lbs, a pair of straps tightened to 2000lbs each now takes the aircraft more or less to its load limit. Every amount of lift provided by the wind over the wings is opposed by increased tension in the straps, which now exceeds the design capabilities of the airframe.
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Re: Was a bit breezy in Alberta

#16 Post by Posthumane » Fri Oct 20, 2017 7:54 am

The taut vs slack thing - my thought was that although the dynamic loading from a gust may be the same between a taut and slack line, with the slack line there is also the momentum of the rocking airplane. A rope with some amount of stretch that could be preloaded slightly might be the best solution. Typically the preload on my straps is no more than 50-100 lbs, just enough so it's not loose and floppy. Another consideration is that when the wind is coming at the craft from the side (as it was that night), when the plane rocks the wing sticks up into the wind even more, which puts even more force on the tie downs.
photofly wrote:Another point: a typical cessna is rated to -1.76g. At a max weight of 2300 lbs, a pair of straps tightened to 2000lbs each now takes the aircraft more or less to its load limit. Every amount of lift provided by the wind over the wings is opposed by increased tension in the straps, which now exceeds the design capabilities of the airframe.
Well, yes and no. Tightening the straps to 2k lbs would definitely be bad as that puts the strut in compression to its design load limit (I assume the strut is the weak point in that configuration). However, additional lift in the wings causes additional tension in the straps, but that tension is not transferred to the struts or airframe. On a free body diagram you would simply see two additional opposing vertical forces (lift and strap tension), assuming the strap is vertical.
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Re: Was a bit breezy in Alberta

#17 Post by photofly » Fri Oct 20, 2017 8:05 am

Posthumane wrote:A rope with some amount of stretch
I agree - like climbing rope, for example.
additional lift in the wings causes additional tension in the straps, but that tension is not transferred to the struts or airframe. On a free body diagram you would simply see two additional opposing vertical forces (lift and strap tension), assuming the strap is vertical.
True, if the lift is distributed to act at the tie-down point. I guess it would be, because that's where the designer would put the strut.

I also have a concern about tight inelastic tie down ropes or straps that are close to vertical. Then the only thing stopping the aircraft starting to move laterally are the chocks. For a vertical, non-stretchy rope there's a mechanical advantage that means if the aircraft moves forwards, backwards or sideways even slightly the rise in tension is theoretically infinite. At that point you are hoping the real rope stretches before the wing and strut fail.
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Re: Was a bit breezy in Alberta

#18 Post by Tailwind W10 » Fri Oct 20, 2017 8:07 am

Posthumane, unfortunately you're not alone. I drove into Villenueve (ZVL) last night. Saw a plane on its back in the east parking area. Don't know what it was, just saw it from the road. I wonder if the owner has been to it in the last couple of days, he may not know.

Gerry
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Re: Was a bit breezy in Alberta

#19 Post by Posthumane » Fri Oct 20, 2017 8:18 am

That's sad to hear Tailwind. I would assume that with villeneuve being a staffed airport, someone would have notified the owner. I got a call from the FSS as soon as it happened because the ELT was going off, so I had to run out to the airport to shut it off, and re-secure the airplane to keep it from sliding towards another aircraft.
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Re: Was a bit breezy in Alberta

#20 Post by digits_ » Fri Oct 20, 2017 5:09 pm

photofly wrote: Another point: a typical cessna is rated to -1.76g. At a max weight of 2300 lbs, a pair of straps tightened to 2000lbs each now takes the aircraft more or less to its load limit. Every amount of lift provided by the wind over the wings is opposed by increased tension in the straps, which now exceeds the design capabilities of the airframe.
This is an interesting remark. I'm wondering if you can just conclude this without more information on how everything is designed.

Strictly legally speaking I don't think you can claim any limitations are exceeded, as limitations are -as far as I know- referenced to "in flight".

From an engineering/structural point of view, it is more interesting. How do you determine the load/stress, and which part of the airframe is more critical?
Without tiedowns, you already have the wings and fuel creating a force on the struts and wing attachement points. A rough estimate could be 300 LBS for a wing and another 180 LBS for full fuel, another 20 LBS for the wing strut so roughly 500 LBS per side.

Assuming a positive lift in tie down attitude:

If there is now a steady wind, the wing will start to lift, and thus initially reducing the stress on the wing strut and attachement points.

If the plane is tied down, we start with stress on the tie down ring, which means stress on the strut and wing attachement points. Wing loading will now decrease the tension in the wing strut and on the wing attachement points. Stress will increase on the point where the wing strut is attached to the wing, and possibly "inside" the wing. The extra tension in the wing would be similar to pulling positive G's, and not negative ones: the plane is pulling up by the wind, while being tied down, similar as pulling up from a dive while fighting inertia. This increases the allowed G's significantly and would explain why the rings are made so strong.

However, are wing tie down rings structural? You'd think you could fly without them, which would make them not-structural, which means they might have non certified/non-tested/unknown limits on what force you can put on them. If you strap the heck out of them: would the rings / struts or wings break first?

From a design point of view, why would the designers make the tie down rings stronger than the force that would overstress the airframe. Did they think about that, or decided any damage by a flipped over airplane would always be worse than a plane that might get overstressed at the tie down points.. ?
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Re: Was a bit breezy in Alberta

#21 Post by photofly » Fri Oct 20, 2017 6:22 pm

Posthumane correctly put me right by pointing out that lift generated by the wings isn’t reacted by the spar or strut while the aircraft is tied down. So there’s no danger of airframe over-stress due to lift.

I do wonder about the tie-down ring hinges though.
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Re: Was a bit breezy in Alberta

#22 Post by RatherBeFlying » Sun Oct 22, 2017 8:12 pm

Was it the strap or the ratchet that failed?

If the strap failed, was it at a stress concentration point?

Stop by a climbing store. You won't find ratchet straps or polypropylene ropes there. Get some dynamic rope and a book on knots.
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Re: Was a bit breezy in Alberta

#23 Post by co-joe » Thu Oct 26, 2017 11:32 pm

I wonder about the UV effect on those straps. I would imagine that lighter coloured straps might be less affected. Going full on Herc straps just seems like overkill and could lead to over tightening really easily. I have had darker coloured ratchet straps come appart after holding the canopy on an old beater pickup for a couple seasons. They literally disintegrated.
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Re: Was a bit breezy in Alberta

#24 Post by Beefitarian » Sat Oct 28, 2017 10:54 am

Hey guys. I'd like to share two crazy ideas I thought of here.

First you could lesson the uv effects on the straps (or ropes) if you made some nice cloth tubes out of a uv resistant cloth like they make fishing shirts out of. Think a really long shirt sleeve without the shirt. Not sure how to source the material.

Second, you could make or buy some lift spoilers that attatched to the top of the wings. They used to be somewhat common in the old days. If I made them I would integrate them into a cover to keep uv off the wings too. Easier to see and you could put them in the trunk of your car before flying, plus you don't have to sweep the snow and frost off the wings.

Sorry to see your plane upside down. Have they said it's for sure beyond repair?
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Re: Was a bit breezy in Alberta

#25 Post by Posthumane » Sun Oct 29, 2017 8:14 am

UV weakening of the straps is definitely a possibility. The straps broke in the middle, not at the attachment point to the hooks or anywhere near the ratchet mechanism.

Beef - I thought of the same ideas as you before, just never implemented them. My wife and I made a set of wing covers for the plane out of a rubberized rip stop nylon, and my thought was to add a little sleeve to the top surface where a rigid spoiler insert could be added. Trouble is, I didn't use the wing covers outside of the winter months as they were a bit of a pain to put on and take off.

The plane is definitely beyond repair. And if there was any doubt about its repair-ability, the local AMO that was hired to flip the aircraft back over sealed the deal by essentially crushing the the rear section of fuselage and ripping off the tail in the process.

I'm parting out what's left of the aircraft, so if anybody needs any interior bits, landing gear, or engine parts (O-300) let me know. In other news, I'm thinking of buying a Mustang 2 from Sask.
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