The bolts that hold our wings on.

StevieTimes said:
Did you see this?


The pilot was quoted as saying "We barely tapped that wing when poof! The bolt that holds the spar sheered off, and the wing pulled itself out. They should make that area more beefy, like bolts all over, not just two. That design, Piper got from Grumman, and I think they should revisit it."
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If the pilot in question was the Piper pilot he doesn't know his airplane very well. From the video, it doesn't look like the collision from the helicopter did much except to slam the wing into the runway which broke the wing. I'd like to know the background on that video.
 
Mtns2Skies said:
Shear force vs. Tensile force.
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Not really. A Lycoming's engine shockmount bolts are in tension, like the firewall bolts. There's a difference in the torque requirements, though, and that is reflected in the bolt sizes. The shockmounts are thick rubber things that have a tubular spacer between them that absolutely must be clamped really tight so it doesn't fret against the thick steel washers molded into the outer end of the shockmounts. The two shockmount halves and the spacer must form a unitized assembly. It takes a heavy bolt to take that clamping force without stretching, stripping or breaking. The smaller bolts that hold the engine mount structure to the firewall pass through aluminum structure that cannot be clamped too tightly or it will deform, extruding and cracking it. Cessna typically uses a 3/8" bolt there.

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StevieTimes said:
The pilot was quoted as saying "We barely tapped that wing when poof! The bolt that holds the spar sheered off, and the wing pulled itself out. They should make that area more beefy, like bolts all over, not just two. That design, Piper got from Grumman, and I think they should revisit it."
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I've always been partial to low wings for their looks and I always preferred how they flew. I have a lot of time in Archers, but I was never that confident in their wing attachment. Especially for a trainer.. it just seems too insubstantial.. and the in the majority of crashes and breakups you see the wing tends to break clean off at the root.. vs some other point at midspan. Other planes you'll see the failure somewhere at midspan.. and the commercial jets fail at midspan too in the ultimately load test. I would thing the weak spot of the wing should NOT be the root attachment point

Timbeck2 said:
From the video, it doesn't look like the collision from the helicopter did much except to slam the wing into the runway which broke the wing
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I watched it several times to try and get the sequence right, and if you slow the video to 0.25 and watch it frame by frame you can see that the collision from the helicopter does indeed break about 1/3 of the left wing clean off.. while the Robinson appears virtually undamaged. The loss of 1/3 of the left wing looks like is was caused that side to lose lift, hit the ground, and then snap off entirely. Not much he could have done at that point, once he lost that left portion of the wing he likely also lost control continuity and was just along for the ride at that point. Lot of energy there for sure, but the fact that the Robinson doesn't appear to have sustained any damage while the Piper loses 1/3 of its wing is telling. I would have expected the wing to slice clean through the chopper, or at least take a piece of the chopper with it

**you can get an idea for the energy as well by noticing that there's very little yaw on the Piper post collision and the chopper also doesn't seem to get knocked about too much either... which is further proof that the wing barely transferred any energy at all before just snapping off

Too bad, I like Pipers.. but I want what I'm flying to feel more rugged than that
 
Didn't the wing hit right where the engine is on the Robinson? I would expect aluminum to shear like that when hitting an engine case.
 
EdFred said:
Didn't the wing hit right where the engine is on the Robinson? I would expect aluminum to shear like that when hitting an engine case.
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Right, I mean it hit the most husky part of the Robinson.. but you would expect some damage, and for the Robinson to be a little more thrown off balance, at the minimum. You would expect some plastic shrouds and other components to come off.. even if the actual block puts up a bigger fight than sheet aluminum. You have at least a 2,000 lb object going 60-70 mph hitting another object that is much less than half the weight of the Piper. That wing barley scratched it, the chopper hardly moved, and the Piper barely yaw.. it just clipped the wing right off

Not really confidence inspiring
 
Yeah, but at the same time look at how cars look utterly destroyed except for the cage. You want that energy dissipation to happen.
 
Tantalum said:
Right, I mean it hit the most husky part of the Robinson.. but you would expect some damage, and for the Robinson to be a little more thrown off balance, at the minimum. You would expect some plastic shrouds and other components to come off.. even if the actual block puts up a bigger fight than sheet aluminum. You have at least a 2,000 lb object going 60-70 mph hitting another object that is much less than half the weight of the Piper. That wing barley scratched it, the chopper hardly moved, and the Piper barely yaw.. it just clipped the wing right off

Not really confidence inspiring
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So what would it have taken to be "confidence inspiring"? A mid-air collision with no damage to either aircraft? Quite frankly if the impact had been almost anywhere else other than near the center of mass of the helicopter, the outcome for the Robinson would have been a great deal worse.

Aircraft structures are by necessity built to be as light as practical while meeting the design requirements for their intended purpose. To my knowledge ramming the outboard section of the wing into a helicopter while both are in flight is NOT part of Piper's design criteria. To emphasize the point about light weight here's a couple of shots of the tailcone structure in a Cessna 172. Those bulkheads are formed aluminum. The skins that are riveted on to them, and carry the shear loads, are even thinner aluminum. This is what connects the horizontal stabilizer, the elevator, the vertical stabilizer, the rudder and all the forces those impart to the rest of the airplane. Think about that the next time you go up and spin one of these babies. :cool:

Skyhawk Tailcone1.JPG Skyhawk Tailcone2.JPG

If any mechanical or structural contraption invented by man is not maintained properly there is always the potential for wear and corrosion to result in a failure. That's why bridges and highway overpasses sometimes collapse. And they are built a hell of a lot more robustly than airplanes. Does that stop you from driving over them? Your fears about the wing attachment on Pipers is irrational. But then being a pilot (and even worse for some of us, an airplane owner) is also irrational... :D
 
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SixPapaCharlie said:
I've determined I'm an aviation hypochondriac...

I get that it it is engineered and even over engineered but maybe a cotter pin or another couple bolts... Even a bit of safety wire...

...I'm fully convinced if I ever designed a plane it would be too heavy to get off the ground.
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Apparently you are not alone. A few days ago a Cessna Skyhawk showed up in the maintenance hangar next door. The owner must have felt the vertical stabilizer was seriously under-designed as he took it upon himself to "improve" it by sandwiching it between two reinforcing plates. I'm not sure how he sized the bolts, but there's three of them, which is 50% more than your wing. ;)

I wasn't quick enough to get a picture of it on the plane unfortunately. The guys in the shop are just too quick and efficient, but they tell me the owner (a crop duster) actually flew the thing twice with this "design modification" installed.

172 Tail Patch1.JPG 172 Tail Patch2.JPG
 
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GRG55 said:
So what would it have taken to be "confidence inspiring"? A mid-air collision with no damage to either aircraft? Quite frankly if the impact had been almost anywhere else other than near the center of mass of the helicopter, the outcome for the Robinson would have been a great deal worse.
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Gotta build them light. But Pipers, when they have any kind of damage for whatever reason, appears like they tend to lose their wings entirely, and at the root, while others will lose sections of their wings or just see local crumpling and bending, or a failure somewhere at midspan. Mooney, Cirrus, Tobago, Trinidad etc., all have either no record of inflight breakups (loss of wing) or extremely few.. the Mooney solid spar, the Cirrus solid carbon fiber spar, and the Tobago and Trinidad's design seem to be more prudently built structures than Piper's tiny metal nob that comes out the bottom with the screws in it

Many highwings experience different loads with the strut, with the strong being in tension and the center wing box mostly in compression and straight sheer, no real bending moments there.. so the 172 / 182 wings always seemed remarkably tough. Granted, without the strut, didn't we see some 210s lose their wings? Just seems like an area where I'll gladly sacrifice 50 lbs of useful to have a more solid setup there

Maybe I'm just another aerohypochondriac though!
 
Timbeck2 said:
If the pilot in question was the Piper pilot he doesn't know his airplane very well. From the video, it doesn't look like the collision from the helicopter did much except to slam the wing into the runway which broke the wing. I'd like to know the background on that video.
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Just to be clear, my quote of the pilot was satire. I need to learn to put smileys on my posts.
 
A couple shots during construction of my RV-9A's wings. Very beefy aluminum bar stock on spar at wing root, that plugs into an equally beefy spar carrier in the fuselage. 10 bolts per side (four of them 7/16") with most of the force in shear. I thought Rustoleum Blue was a nice color for the aileron pushrods.

Can't see it in the photo, but where the tanks attach to the fuselage, the bracket has an open-ended slot to allow the tanks to pull free in a crash with less chance of rupturing. You tighten the bolt to a torque that lets it slip apart with enough force.

Also, shot of rear spar attachment to fuselage. Castle nut/cotter pin here because there's a small bit of rotation when the wings flex. I spent a long time measuring and drilling that hole, as it sets wing incidence and you have to make sure there's pleeeeeenty of edge distance. Measure 10 times, drill once! :)


IMG_3717.JPG

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I read someone bragged to Burt Rutan about beefing up a Long EZ wing, and he said
"Congratulations - you just turned a six G airplane into a two G airplane"

Or words to that effect. . .
 
Was it Burt Rutan that said, when considering adding something to an airplane, to throw that item up into the air. If it falls back to earth, its too heavy?

Or words to that effect...
 
GRG55 said:
Apparently you are not alone. A few days ago a Cessna Skyhawk showed up in the maintenance hangar next door. The owner must have felt the vertical stabilizer was seriously under-designed as he took it upon himself to "improve" it by sandwiching it between two reinforcing plates. I'm not sure how he sized the bolts, but there's three of them, which is 50% more than your wing. ;)

I wasn't quick enough to get a picture of it on the plane unfortunately. The guys in the shop are just too quick and efficient, but they tell me the owner (a crop duster) actually flew the thing twice with this "design modification" installed.
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Look at the kink in the aft fin spar. That's why he stuck those doublers on there; he'd damaged the fin somehow. Has a death wish, though...
 
Dan Thomas said:
Look at the kink in the aft fin spar. That's why he stuck those doublers on there; he'd damaged the fin somehow. Has a death wish, though...
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Yes, a grain bin got tipped over by the wind and fell on it.
But I gotta admit, crop dusters are a crazy bunch...
 
FastEddieB said:
...the horizontal stabilizer of the Sky Arrow is held on by a wingnut - albeit a safety-wired wing nut.
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It's a butterfly nut...which no doubt adds extra lift!

Sundancer said:
I read someone bragged to Burt Rutan about beefing up a Long EZ wing, and he said
"Congratulations - you just turned a six G airplane into a two G airplane"

Or words to that effect. . .
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Certainly, reinforcements can just distribute the loads to other parts of the airframe that weren't designed to take them. :eek:

I like the story about Colin Chapman designing his race cars...keep taking tubes out of the space frame until something breaks, then put one back in. :)
 
GRG55 said:
This is what connects the horizontal stabilizer, the elevator, the vertical stabilizer, the rudder and all the forces those impart to the rest of the airplane. Think about that the next time you go up and spin one of these babies. :cool:
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Think about that the next time you see someone pushing down on the stabilizer to pick up the nosewheel to swing the airplane around. Do that a few times and the forward stab spar cracks at the center lightening hole. The nose ribs bend and crack. Cessna has an SB on the spar damage and advise the installation of a doubler kit, and tell folks that pushing on that stab is verboten. That part of the stabilizer was never designed to handle that sort of loading.

It's too bad that the old service manuals told you to do this. Someone didn't consult the engineers.
http://www.tennesseeaircraft.net/cessna-approved-bad-training/
 
GRG55 said:
Yes, a grain bin got tipped over by the wind and fell on it.
But I gotta admit, crop dusters are a crazy bunch...
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I found a cropsprayer with skins patched with galvanized steel sheet. I read about another cropspray outfit that had some irate famer take a shot at one of their airplanes. The bullet went right through a propeller blade, so they filed the edges of the bullet hole nice and smooth and went back to flying. I saw, at a prop overhaul shop, a prop blade off a cropsprayer that had about ten inches of the tip missing. Busted right off. The pilot flew back to base like that. The vibration must have loosened every rivet in the airplane and probably trashed every instrument and radio.
 
Thoughts about bolt strength are interesting. I too look at the bolts holding my 61 year old 182's wing on & think how small they appear.

Since we take our L-23 glider's wings off several times a year to store it in it's trailer I see the wing attachments quite often. The two wing pins look very beefy & maybe a little overkill considering the glider weighs only 780 pounds empty. So now that I cognitively know that the pins are hell for stout you're think I wouldn't think about the wing's integrity but that's not the case. Since I'm usually in the rear seat at the leading edge of the wing & there is no engine noise, I hear every creak & groan of the aluminum wing.

So then I start wondering how strong the main spars is that the pins are attached to.

We humans have to worry about something.
 
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My experience has been that on high airframe hour airplanes the structure surrounding the wing bolts are more likely to have fatigue issues than the bolts. The lugs on the carrythru and carrythru s themselves are more important to inspect than the bolts on Cessnas.
 
saddletramp said:
Thoughts about bolt strength are interesting. I too look at the bolts holding my 61 year old 182's wing on & think how small they appear.

Since we take our L-23 glider's wings off several times a year to store it in it's trailer I see the wing attachments quite often. The two wing pins look very beefy & maybe a little overkill considering the glider weighs only 780 pounds empty. So now that I cognitively know that the pins are hell for stout you're think I wouldn't think about the wing's integrity but that's not the case. Since I'm usually in the rear seat at the leading edge of the wing & there is no engine noise, I hear every creak & groan of the aluminum wing.

So then I start wondering how strong the main spars is that the pins are attached to.

We humans have to worry about something.
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The cantilever wing on the glider needs a much heavier structure than the strutted wing on your 182. Think about this: dig a hole a couple of feet deep and stick an eight-foot 1 x 4 in it, and fill the hole. Tie a piece of rope to the stick, about halfway up, and anchor the other end firmly to a stake about three feet away from the wide, flat side of the 1 x 4. This affair represents a strut-braced wing. Pull on the top of the 1 x 4, against the rope's tension. Pull hard. Now take the rope off, and we have a cantilever sructure like the sailplane. Pull hard again and see what happens to the stick.

It's all about leverage. A cantilevered spar needs to be way heavier and have much larger hardware because the forces are concentrated in a tiny area compared to the strut-braced wing. Either of the designs is built to 3.8G with a 150% safety factor beyond that. If you are a wise pilot and don't go aerobatting an airplane not designed for it, don't go flying VFR into IMC and end up spiralling, and stay out of thunderstorms, it isn't likely you'll break the structure.
 
saddletramp said:
Thoughts about bolt strength are interesting. I too look at the bolts holding my 61 year old 182's wing on & think how small they appear.
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The bolt you are looking at does not hold the wing on, All 150,172,182 have eccentric bushings to adjust the wing angle of incident the bolt simply holds the bushings, they carry the load.
 
I actually have my wing bolt AD due in about 20 hours from my tiger
 
Tom-D said:
The bolt you are looking at does not hold the wing on, All 150,172,182 have eccentric bushings to adjust the wing angle of incident the bolt simply holds the bushings, they carry the load.
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No, the front spar bolt goes though the carrythrough and spar root with no bushings. The aft spar carrythrough has large holes for the eccentrics and the aft spar root has a small hole to fit the bolt. The eccentrics clamp against the sides of the spar root; they don't go through it. They only bear weight against hole in the carrythrough, not the spar. the I have assembled enough of these, and adjusted them, to be quite familiar with them.
 
Dan, tell me something about my Cherokee 140 so I can repeat it to assure my passengers that the wing isn't going to fall off. So far I've got nuttin.
 
Dan Thomas said:
The Cherokee's bolts are only maybe eight inches apart, putting far more force on the spar roots and the hardware.
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Timbeck2 said:
Dan, tell me something about my Cherokee 140 so I can repeat it to assure my passengers that the wing isn't going to fall off. So far I've got nuttin.
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The Beech wing spar is built like a Brick Sh*t house. Wing attach bolts are there just to keeps folks happy..:rolleyes:
 
And there's this gap between the body and wing root.

I can shine a light through it.

Something to think about. This particular plane has a 1-foot section between the body and the actual Wing that's just a fiberglass fairing so that means the wing is actually attached a foot away from the body of the plane.

Grumman are weird

20180629_230612.jpg
 
GRG55 said:
Apparently you are not alone. A few days ago a Cessna Skyhawk showed up in the maintenance hangar next door. The owner must have felt the vertical stabilizer was seriously under-designed as he took it upon himself to "improve" it by sandwiching it between two reinforcing plates. I'm not sure how he sized the bolts, but there's three of them, which is 50% more than your wing. ;)

I wasn't quick enough to get a picture of it on the plane unfortunately. The guys in the shop are just too quick and efficient, but they tell me the owner (a crop duster) actually flew the thing twice with this "design modification" installed.

View attachment 64494 View attachment 64495
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Wow. I wonder how that entry in the maintenance logs would read?
 
Grumman wings are plenty strong.

https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20001212X20121&key=1

A Tiger on downwind for 16L at VNY ran into the wake turbulence of an airliner that had just crossed overhead on the ILS to runway 8 at BUR. The Tiger landed safely.

"The outboard 1/3 of the aircraft's left wing was deformed upward about 5 degrees with respect to the inboard section during an encounter with wake turbulence while on downwind leg for landing. The upper wing skins of both wings exhibited compression buckling, and the mass balance weights on both ailerons were separated and fell from the aircraft. The pilot reported that the flight was unremarkable until, while downwind for landing, there was an instantaneous jolt of sudden severe turbulence that ended before he could take any action. Data obtained from the airport noise abatement office showed that 2 minutes 23 seconds prior to the encounter, a heavy transport aircraft passed over the location on an ILS approach to another airport 6 miles away; the transport airplane was about 500 feet higher than the accident airplane as it crossed the location." ​
 
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