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#1
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Engine-out procedures and eccentric forces on engine pylons
Long ago it occurred to me that a twin-engine jet running with one engine out
might be putting tremendous eccentric stress on the plyon and mounting of the running engine (meaning stress not aligned with the normal thrust vector of the engine). Today it occurred to me that this might not be true if the pilots adjust the attitude of the aircraft so that it is flying straight forward. The adjustments would create opposing forces that not only keep the aircraft in level flight but also realign the stress on the running engine, as if there were still two engines and symmetric forces on the pylons. Does this make sense? If so, are there limits to how far an aircraft can fly out of trim in such a way as to put unusual stress on engine pylons (even with all engines running). For example, does yawing sharply in a large jet put unacceptable stress on the pylons? -- Transpose mxsmanic and gmail to reach me by e-mail. |
#2
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Engine-out procedures and eccentric forces on engine pylons
Mxsmanic wrote
For example, does yawing sharply in a large jet put unacceptable stress on the pylons? You should see what those pylons do in heavy turbulence! The only stress is on the pilot who looks at them. :-) Bob Moore |
#3
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Engine-out procedures and eccentric forces on engine pylons
"Bob Moore" wrote... You should see what those pylons do in heavy turbulence! The only stress is on the pilot who looks at them. :-) My wife and I were on a flight a few years back in an A300 IIRC and we were in seats that gave us a clear view of the engine on the left wing. I was casually looking out at it when I noticed that it was oscillating back and forth quite noticeably and considerably, and we were only in light chop at the time. My first impression was HOLY #$%&! quickly followed by the realization that since it hadn't come off yet it must be normal. Judging by how much it was moving around you would have thought it was held on with bungee cords. BDS |
#4
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Engine-out procedures and eccentric forces on engine pylons
BDS wrote
Judging by how much it was moving around you would have thought it was held on with bungee cords. Nope! Back in my B-707 days, the engine was attached to the pylon with just three bolts about the size of your forefinger, and each of these bolts was designed to break-away and release the engine before it could do damage to the wing. Bob Moore |
#5
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Engine-out procedures and eccentric forces on engine pylons
Bob Moore writes:
You should see what those pylons do in heavy turbulence! The only stress is on the pilot who looks at them. :-) I've seen engine nacelles swaying merrily to and fro (along the wing axis) in turbulence but I didn't know if twisting forces applied to the pylons would be so easily tolerated. As it is, modern pylons, so seemingly frail and so apparently inviting of very concentrated stresses as they hold the engines way out in front of the wing, always look like an invitation for trouble to me. But I suppose if they are engineered properly they can hold, rather like that glass walkway that the Havasupai recently built out over the Grand Canyon. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#6
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Engine-out procedures and eccentric forces on engine pylons
Bob Moore writes:
Nope! Back in my B-707 days, the engine was attached to the pylon with just three bolts about the size of your forefinger, and each of these bolts was designed to break-away and release the engine before it could do damage to the wing. Well, that's certainly reassuring. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#7
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Engine-out procedures and eccentric forces on engine pylons
BDS wrote:
"Bob Moore" wrote... You should see what those pylons do in heavy turbulence! The only stress is on the pilot who looks at them. :-) My wife and I were on a flight a few years back in an A300 IIRC and we were in seats that gave us a clear view of the engine on the left wing. I was casually looking out at it when I noticed that it was oscillating back and forth quite noticeably and considerably, and we were only in light chop at the time. My first impression was HOLY #$%&! quickly followed by the realization that since it hadn't come off yet it must be normal. Judging by how much it was moving around you would have thought it was held on with bungee cords. BDS I love the window seat, but dammit, I cannot look at the wing ever. "Ok, if it didn't flex like that, it would be brittle and snap. It's supposed to bounce, it's not supposed to break" But nothing reassures me. |
#8
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Engine-out procedures and eccentric forces on engine pylons
Erik wrote:
I love the window seat, but dammit, I cannot look at the wing ever. "Ok, if it didn't flex like that, it would be brittle and snap. It's supposed to bounce, it's not supposed to break" But nothing reassures me. I find it helps in cases like these to watch a few videos of wing loading tests, so you can see really just *how* far those wings can go before breaking. http://www.youtube.com/watch?v=6Uo0C01Fwb8 TheSmokingGnu |
#9
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Engine-out procedures and eccentric forces on engine pylons
"Erik" wrote in message ... I love the window seat, but dammit, I cannot look at the wing ever. "Ok, if it didn't flex like that, it would be brittle and snap. It's supposed to bounce, it's not supposed to break" But nothing reassures me. I find counting missing rivets and watching spinning rivets takes my mind off the wing flex. |
#10
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Engine-out procedures and eccentric forces on engine pylons
I love the window seat, but dammit, I cannot look at the wing ever...... 1971 - My very first airline ride -- Delta DC-9 Tampa to Atlanta The wing looked very solid and very much "one with the airplane" --o-- 30 minutes later - My second airline ride -- PanAm 747 Atlanta to LA I coulda swore that the wings were flapping ~~o~~ I missed a lot of scenery :-) TP |
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