Simviation Forum - Engine Mount

Dec 28^th, 2005 at 8:47pm

Bubblehead Offline
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Is it true that wing mounted jet engines are held by shear pin/s so that in the event of a serious rotor imbalance the affected engine is designed to fall off to prevent damage to the wing.

Bubblehead

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Reply #1 - Dec 29^th, 2005 at 7:04am

beaky Offline
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I doubt it- it'd be less hazardous to shut it down before things got to that point. I can't see having a manually-operated release to drop an engine to prevent the worst-case vibration scenario, which would mean... dropping an engine. Doesn't make sense. And if you're talking about a passive release system, similar logic applies: you'd want that engine to stay put as long as possible.
Airliners have landed successfully after losing an entire engine, but not every time it's happened... sometimes the unit will still be generating enough thrust to take it up over the leading edge of the wing- this could be a problem, obviously.

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Reply #2 - Dec 29^th, 2005 at 9:40am

Jakemaster Ex Member

I seriously doubt it. A sheer pin would be a lot easier to break or fall out if you were flying in rough conditions. Also, dropping an engine would be a bad idea. Heres why: Engines are very heavy, dropping one would cause an extreme imbalance, and the plane would become impossible to control. Ever flown with one engine? Even the lack of power makes it very defficult to control, throw in a weight change and you're screwed. Also, do you have any Idea how much damage a Jet engine dropped from altitude would cause? Some impact craters are made by items smaller than jet engines (grant it they are fallin faster).

So the answer to your question is no. Now, Jet engines are held in place by a few pins, they basically just hang there

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Reply #3 - Dec 29^th, 2005 at 11:20am

Bubblehead Offline
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What you guys said make a lot of sense. A couple more questions however.

1. How long before an engine running at full speed come to a complete stop after being shut down.

2. Have you ever seen a rotating element such as the jet rotor suffer an imbalance while running at full speed?

The reason I have asked these questions was because I had substantial training in noise and vibration analysis while in the Navy and I've seen what it would do to a gas turbine engine if it suffers an imbalance condition. It literally self distructs.

Thanks.

Bubblehead

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Reply #4 - Dec 29^th, 2005 at 12:40pm

elite marksman Offline
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#1, it depends. If I took an old rust jet thats been in storage for 50 years it will stop pretty quick(assuming I can even get her going), but if I took a brand new turbine out of Pratt & Whitney's factory it would take a couple of minutes. It all depends on how well and often the mechanics lubed the engine.

#2 In person, no, but while my brother was training to be a mechanic somebody gave him a video of an engine that had not been maintained correctly in a while and had serious metal fatiuge, It was running up on the ground when a blade came off. He showed it to me, wasn't pretty, certaintly not what you want to happen in flight.

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Reply #5 - Dec 29^th, 2005 at 12:45pm

Craig. Offline
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Engines falling off inflight have caused some serious accidents, I believe the DC10 crash in Chicago was caused by an engine which fell off. However they are designed to rip off in the event of a crash landing in water and on the ground.

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Reply #6 - Dec 29^th, 2005 at 2:30pm

Fly2e Offline
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New technology from BAE Systems....

Quote:

Health Check for Jet Engines

Catastrophic engine failure in jet aircraft can be prevented using a new form of radar. The radar keeps constant watch over the engine intake and automatically warns if foreign objects have been sucked in, creating havoc. The same technology can be used to ‘listen’ for subtle changes in the engine’s vibrations and give early warning of trouble.

Maintenance engineers can then take action to repair any damage before it reaches dangerous levels.

The ATC has developed a unique system called Engine Health Diagnosis Using Radar (EHDUR) which can monitor the condition of the jet engine’s air intake and compressor fans. It is able to tell the difference between damaging and non-damaging objects which enter the engine accidentally. “The front stages of a jet engine are highly strung. If something is accidentally ingested it may cause damage to the fan blades which may not be visible by inspection” said David Shephard, project manager at the ATC. “Presently, this type of damage can only be picked up by visual inspection by ground maintenance crews”. he says.

The system can give an automatic warning if ‘Foreign Object Damage’ (FOD) to a fan blade is imminent. This speed of warning can be vital as minor damage can rapidly grow in the fast moving environment of a jet engine. “A blade can fall off an engine within minutes of a fault occurring. Cracks can develop quite rapidly following damage especially as performance of jet engines becomes higher and higher” says David.

The breakthrough in radar technology needed to create EHDUR is the use of miniature antennas which are fitted into existing engine inspection ports or the engine’s air intake. These antennas are designed not to interfere significantly with the airflow into the jet. As well as monitoring FOD, the system is also capable of giving the engine a constant ‘health check’. The radar can be used to monitor mechanical vibration of the moving parts at the compressor stage and then sense if any changes to the normal patterns have occurred. By detecting changes to the vibration, early diagnosis of specific faults should be possible. An engine’s operating characteristics change over time as a result of FOD, vibration and general wear and EHDUR could provide the ability to measure and analyse this wear.

This capability is of increasing importance since new aircraft designs are required to include integrated ‘vehicle health management’ technology that monitors not just engines but also on-board systems and structures. EHDUR is currently being evaluated with the help of Rolls-Royce and the UK MoD and successful blind trials have been performed in ground test facilities using the Harrier’s famous Pegasus engine. The technology is not restricted to any particular type of jet engine so there are excellent prospects for EHDUR as a standardised system for any jet engine.

“We hope to get this flown soon using the Advanced Technology Demonstrator Centre at BAE Systems Warton site in the UK. If successful, the system could be equally useful for both military and civil jet engines and could be in service during the next five years.” says David.

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Reply #7 - Dec 29^th, 2005 at 2:38pm

Fly2e Offline
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or you could replace an engine and use the wrong rivets!!!

Quote:

AIRCRAFT taking off from Manchester Airport could have crashed into part of a jumbo jet engine which had fallen on to the runway.

A disturbing report by aviation inspectors published today blamed the incident on the standard of maintenance on the Pakistan International Airlines Boeing 747, which was carrying 303 passengers.

Another report on a separate incident revealed bosses at Manchester had adopted new docking procedures after a jet which was trying to park beside a terminal building crashed into an air bridge which was left in the wrong position.

No one was hurt in either incident, but government inspectors made a series of recommendations.

The standard of maintenance on the PIA jumbo was severely criticised after a large part of one of its four engines sheared off shortly after it landed after flying in from New York.

The pilot of another jet who saw it fall off alerted air traffic controllers who stopped other aircraft from landing while the debris was cleared.

Debris

A report by the Air Accident Investigation Branch said: ". . . in less favourable circumstances, an aircraft taking off on the same runway, shortly afterwards, could have been at risk of colliding with the debris on the runway at a critical time."

The report slammed the standard of maintenance after inspectors found the wrong rivets had been used and work was not recorded.

The report said: "It would appear that the rivets . . . were replaced without any reference to a manual or understanding of their purpose. It also seems that the installer . . . considered them so unimportant that their installation was not recorded or mentioned."

Inspectors also recommended more rigorous maintenance routines after the incident in 2002.

Manchester has adopted new docking procedures after a jet which was trying to park beside a terminal building crashed into an air bridge.

The left-hand engine of an Air Transat Airbus A310 which had just landed from Toronto, with 255 passengers on board, was severely damaged, according to the report.

A technical problem had left the air-bridge - used by passengers to get on and off the plane - in the wrong position.

An airport spokesman said: "We have worked closely with the AAIB throughout their investigations and as reported in their recommendations, we are changing our procedures accordingly."

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Reply #8 - Dec 29^th, 2005 at 4:44pm

<Ramos> Ex Member

Quote:

Engines falling off inflight have caused some serious accidents, I believe the DC10 crash in Chicago was caused by an engine which fell off. However they are designed to rip off in the event of a crash landing in water and on the ground.

a cessna c172 crashed into the DC-10's left engine.

i wouldn't think that the shear pin thing would be a good idea.with terrorists, all is made easier for the plane to crash with something like this. all you need is the smallest device to disable the manual pin operation or on the pin itself, and bam (and literally BAM!) engine's away and aircraft out of control.

Ramos

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Reply #9 - Dec 29^th, 2005 at 4:48pm

Craig. Offline
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Just remember that was before the flight and weakend the joints.

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Reply #10 - Dec 29^th, 2005 at 4:50pm

gryshnak Offline
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Quote:

Engines falling off inflight have caused some serious accidents, I believe the DC10 crash in Chicago was caused by an engine which fell off. However they are designed to rip off in the event of a crash landing in water and on the ground.

Some years ago on another forum I asked Don Stackhouse (a man with a great deal of aerodynamic experience) about fowler flaps, and part of his reply was this:

There was a rather graphic example at Chicago O'Hare airport a number of years ago of what happens when flaps become unrestrained. The DC-10 uses two shear pins to attach each wing engine, designed to fail and let the engine fall safely free of the aircraft if it locks up. Without this, the tremendous rotational inertia of the engine rotors could rip the engine out of the airplane, perhaps taking the pylon and parts of the wing spar with it. These forward pins, which normally carry most of the weight of the engine, have required inspections. There is a special (and somewhat time-consuming to install) fixture used to support the engine while the forward pin is pulled for inspection. Some of the mechanics were taking a shortcut, using a forklift and a strap instead of the fixture to support the engine. They didn't realize that in the process they were overstressing the rear pin, setting it up for a premature failure.

Just as the subject aircraft (with a full load of passengers) rotated on takeoff, the rear pin failed. Still producing takeoff thrust, the engine pivoted forward and upward around the forward shear pin, going up and over the top of the wing and taking all of the hydraulic lines that ran inside the leading edge of the wing with it. These lines supplied the flap actuators. Suddenly without hydraulic pressure to keep them open, all the flaps on that side of the airplane immediately RETRACTED.

With takeoff flaps still deployed on one wing, and zero flaps on the other, the ailerons were hopelessly overwhelmed by the massive difference in lift between the two wings. The airplane immediately and inexorably rolled toward the flapless wing, carving a long, deep furrow in the ground with its wingtip before finally impacting nose-down and nearly inverted. There were no survivors. The missing engine, with its failed shear pins and some fragments of hydraulic lines, was found lying on the runway not far from the point of liftoff.

Gryshnak

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Reply #11 - Dec 29^th, 2005 at 5:41pm

<Ramos> Ex Member

man i swear it was a plane collision....

[looks up on planecrashinfo.com]

http://www.planecrashinfo.com/w790525.htm

my apologies...

[looks for what i was talking about]

i have no idea what i was thinking... i thought i knew something about a cessna striking an aircraft...

whatever...

ramos

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Reply #12 - Dec 29^th, 2005 at 5:47pm

Craig. Offline
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This case actually I believe was caused by a forklift collidiing with the engine when it was being fitted. Or something like that.

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Reply #13 - Dec 29^th, 2005 at 6:12pm

Hagar Offline
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Quote:

Engines falling off inflight have caused some serious accidents, I believe the DC10 crash in Chicago was caused by an engine which fell off. However they are designed to rip off in the event of a crash landing in water and on the ground.

Here's an interesting report into that accident. This is also the one that Gryshnak referred to. Click Next to continue. http://lessons.air.mmac.faa.gov/l2/Am191/sum1a/

I could be wrong but seem to recall that the engines on some early transatlantic jet airliners could be jettisoned in an emergency. I thought this involved explosive bolts & it would usually only be contemplated over water. It would obviously only be practical on aircraft with the engines mounted in pods like the 707 & maybe even the 747.

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Reply #14 - Dec 29^th, 2005 at 7:33pm

elite marksman Offline
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I could have sworn that that was a MD-11 involved in that incident. Guess not.

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