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6 hours ago, N201MKTurbo said:

My plane was tied down at KTUS once when a T storm came through. It broke the city chains. The plane traveled about 200 yards across the ramp and was stopped by a King Air’s propellor. 

Those tie down eyebolts are stupid strong.

Yes they are. I was at Sun n Fun when the tornadoes hit, there was neither damage to the tie down rings or my ropes, and my plane did not move. The plane beside me broke two of three tie downs and hit the plane on its other side.

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6 hours ago, N201MKTurbo said:

My plane was tied down at KTUS once when a T storm came through. It broke the city chains. The plane traveled about 200 yards across the ramp and was stopped by a King Air’s propellor. 

Those tie down eyebolts are stupid strong.

Yes they are. I was at Sun n Fun when the tornadoes hit, there was neither damage to the tie down rings or my ropes, and my plane did not move. The plane beside me broke two of three tie downs and hit the plane on its other side.

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17 hours ago, PT20J said:

All engineering is a trade off. There really isn't that much force on the eyes when the plane is tied down. They probably won't hold in a hurricane or tornado, but by reducing the break away force they can protect the spar against the more likely occurrence of taxiing away with the wing tied down.  Lot's of airplane structures are designed that way; for instance, the engine mounts on jets are designed to break away and let the engine fall if it goes out of balance enough to risk structural damage to the wing.

My point is that airplanes incorporate many non-obvious design decisions, and you need to be careful when making changes.

Skip

I don’t think it would damage the spar.  The angle piece that the tie down screws into is Huck bolted to the lower spar cap.

Clarence

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19 hours ago, PT20J said:

All engineering is a trade off. There really isn't that much force on the eyes when the plane is tied down. They probably won't hold in a hurricane or tornado, but by reducing the break away force they can protect the spar against the more likely occurrence of taxiing away with the wing tied down.  Lot's of airplane structures are designed that way; for instance, the engine mounts on jets are designed to break away and let the engine fall if it goes out of balance enough to risk structural damage to the wing.

My point is that airplanes incorporate many non-obvious design decisions, and you need to be careful when making changes.

Skip

Huh? Not on any of the jets I work on and maintain. That's what the throttles are for and the idle cutoff position if the engine develops severe problems. I'd like to see some documentation to your point on the engine mounts designed to break away.

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21 hours ago, PT20J said:

Careful about nuts and other mods - these are designed to be breakaway so you don't damage the spar if you forget to untie.

no these are not, there are very few items on a aircraft with a design shear point and none of those are designed to break away from the aircraft.

Brian

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20 hours ago, PT20J said:

the engine mounts on jets are designed to break away and let the engine fall if it goes out of balance enough to risk structural damage to the wing.

WHAT???? where are you getting this info?? first off the FAA would never let that happen, can you image the danger of having engines falling from the sky over a city because the engine had a catastrophic failure. 

Brian

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I would bet good money the tie downs are NOT designed to break away, when Hurricane Dolly came through here there was QueenAir tied down that got all kinds of twisted up, left main was off the ground the right was fully compressed, it was several days before someone got brave enough to cut the ropes

Edited by RLCarter
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1 hour ago, orionflt said:

WHAT???? where are you getting this info?? first off the FAA would never let that happen, can you image the danger of having engines falling from the sky over a city because the engine had a catastrophic failure. 

Brian

There is evidence of an engine falling off a DC10 out of Chicago...  broken bolts after a maintenance mishap...

That didn’t end well for anybody.

Rapid weight imbalance, rapid thrust imbalance, and probably a bunch of control loss...

 

Something must have gotten lost in the translation in this thread...

1) tie downs are needed to be as strong as possible for a reason.  Even if damaging the plane is required to keep it in place...

2) If you damage a wing spar because you forget to untie the plane, you have one very powerful engine... or you got a good running start...

3) I have seen the results of a broken tie down rope... new C150 owner at the tie-down doing a run-up, without feet on the brakes...

snapped one rope, and spun around the other... met nose to nose with the neighboring plane...

4) Loading up a springy line, snapping a bolt, releasing energy randomly... could be deadly to somebody on the ramp...

5) randomly releasing a QueenAir in hurricane would be a horrible idea...  most broken tie-downs, in that case lead to flipped and bent planes... planes that roll away, roll into others on the ramp...

Break-away bolts for this application are pretty unlikely to be a good idea.

Best regards,

-a-

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8 minutes ago, RLCarter said:

I would bet good money the tie downs are designed to break away, when Hurricane Dolly came through here there was QueenAir tied down that got all kinds of twisted up, left main was off the ground the right was fully compressed, it was several days before someone got brave enough to cut the ropes

your example just helps prove that there is not a designed breakaway point in tiedowns. what you have is a failure point when the material can no longer stand up to the forces being exerted on it. 

Brian

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2 minutes ago, orionflt said:

your example just helps prove that there is not a designed breakaway point in tiedowns. what you have is a failure point when the material can no longer stand up to the forces being exerted on it. 

Brian

Too early....lol, my post has been corrected to NOT designed to breakaway 

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Just now, RLCarter said:

I don't think the OP eye bolts will ever break with a 3/4" shank.

depends on the material they are made of and the load they are designed to hold. on our aircraft there are many different types of fasteners, the structural hardware is designed to handle different loads and forces then the nonstructural hardware.  one of the key factors is the shear strength, the 3/4 in non structural bolt shanks sheer strength may not be able to handle the type of load being exerted when used as a tiedown.

Brian    

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5 hours ago, M20Doc said:

I don’t think it would damage the spar.  The angle piece that the tie down screws into is Huck bolted to the lower spar cap.

Clarence has a really good point here. I realize that I don't really know that the eyebolts are designed to break away. I just noticed how easy it was to pop one and assumed that, so my apologies for stating something I didn't know to be fact. BTW on my '78 J, we repaired my goof with a helicoil and noticed that the other side had been previously helicoiled, so that one had probably been popped, too. I was just trying to make the point that we should be circumspect when selecting parts and making modifications to airplanes.

Someone mentioned static thrust, and I'll throw in that Rob McDonnell, who was Mooney chief engineer at the time, sent me some data way back in 1991 and it includes an estimated static thrust for the M20M of 1000 lbs.

The example of the jet engine attachment is absolutely true. The engines are mounted with fuse pins designed to fail in shear under excessive load. I first learned about this from a friend who is a powerplant flight test engineer for Boeing, but you can easily find references to this with Google. Here's a quote from https://reports.aviation-safety.net/1992/19921004-2_B742_4X-AXG.pdf

"1 .6.3 .1 Pylon to Wing Attachment Design. The design of the engine nacelle and pylon incorporates provisions that preclude a wing fuel cell rupture in case of engine separation, by means of structural fuses . A clean breakaway of the nacelle and/or pylon from the wing is ensured when the shear loading of the fuse pins exceeds the design load conditions. The structural fuse concept utilizes hollow shear pins at the four wing attachment fittings between pylon and wing. The wing support structure and fittings have been designed sufficiently stronger than the fuse pins thus safeguarding the wing from structural damage in case of an overload condition . The nacelle and engine are attached to the pylon bulkheads through forward and aft engine mount fittings . The pylon is essentially a two cell torque box containing three bulkheads: a forward engine mount bulkhead, an aft engine mount bulkhead and a rear closure bulkhead . Pylon to wing attachments are made at the aft end of the upper link, the aft end of the diagonal brace and at the two pylon midspar fittings . The fuse pin at the forward end of the upper link, the aft end of the diagonal brace and at both midspar fittings are the primary fuse pins. The fuse pins at the forward end of the upper link and the aft end of the diagonal brace are designed to fail at a slightly lower load than the fuse pins at the other ends in order to assure a controlled separation of the pylon from the wing."

Skip

 

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26 minutes ago, PT20J said:

The engines are mounted with fuse pins designed to fail in shear under excessive load. I first learned about this from a friend who is a powerplant flight test engineer for Boeing, but you can easily find references to this with Google. Here's a quote from https://reports.aviation-safety.net/1992/19921004-2_B742_4X-AXG.pdf

that makes more sense, it is not designed to separate the engine from the wing due to a catastrophic failure but to protect the fuel cell from being breached in an incident where the engine is torn off the wing IE crash or impact with another object.

Brian  

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51 minutes ago, orionflt said:

that makes more sense, it is not designed to separate the engine from the wing due to a catastrophic failure but to protect the fuel cell from being breached in an incident where the engine is torn off the wing IE crash or impact with another object.

Correct. As I now understand it, the fuse pins are designed to shear under excessive load most likely during impact. My original discussion (long ago) with my Boeing friend related to the DC-10 that lost an engine in flight due to maintenance damage to the attachments during engine installation. I may have confused the two issues. The engines are designed to separate but not under the conditions I originally stated.

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I can't find an answer to a simple question.  I understand the POH says to remove the tiedown rings before flight.  Were they really expecting a pilot to clamber under to remove the rings and then crawl (in the rain or snow) to reinstall them every time they tied down again.  What is the reason to remove?  weight? aerodynamics?  rings falling on a person on the ground? structural integrity? aesthetics? mandatory exercise/stretching after a long flight?

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20 minutes ago, Cyril Gibb said:

I can't find an answer to a simple question.  I understand the POH says to remove the tiedown rings before flight.  Were they really expecting a pilot to clamber under to remove the rings and then crawl (in the rain or snow) to reinstall them every time they tied down again.  What is the reason to remove?  weight? aerodynamics?  rings falling on a person on the ground? structural integrity? aesthetics? mandatory exercise/stretching after a long flight?

I think it’s like some high performance cars that insist on using high grade fuel. They will work just fine on regular, but they won’t make the power that they barg about. Most people would never notice. The Mooney will go 1 knot slower or so and who wants to go slow.

BTW mine come off when I jack the plane.

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