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propilot83
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Engine Fan Blade Rub

Fri May 04, 2018 3:41 am

Can any pilot tell me if engine fan blades can rub against the inside nacelle of the engine??? I know fan blades have a very minimal clearance from the engine cowling, but can it ever rub against the cowling interior during turbulence or anything? And if it could rub against the cowling, what would happen? I always wanted to know this, thanks.
 
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jetmech
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Re: Engine Fan Blade Rub

Fri May 04, 2018 4:08 am

propilot83 wrote:
I know fan blades have a very minimal clearance from the engine cowling, but can it ever rub against the cowling interior during turbulence or anything? And if it could rub against the cowling, what would happen?

Yes they can.

The fan casing is made with an abradable liner such that the tips of the fan blades can rub against and even remove material if need be.

Regards, JetMech
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propilot83
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Re: Engine Fan Blade Rub

Fri May 04, 2018 7:54 am

jetmech wrote:
propilot83 wrote:
I know fan blades have a very minimal clearance from the engine cowling, but can it ever rub against the cowling interior during turbulence or anything? And if it could rub against the cowling, what would happen?

Yes they can.

The fan casing is made with an abradable liner such that the tips of the fan blades can rub against and even remove material if need be.

Regards, JetMech


Is there a video on youtube or somewhere else where they demonstrate this in the testing phase during manufacturing. I'm just very curious as to what happens exactly when the fan blade tips rub against the fan casing. And what do you mean "remove material if need be." Thanks for answering my question.
 
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jetmechanicdave
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Re: Engine Fan Blade Rub

Fri May 04, 2018 8:08 am

Just like jetmech said the Abraidable Shroud. It’s a hard clay consistency.
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zeke
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Re: Engine Fan Blade Rub

Fri May 04, 2018 10:53 am

propilot83 wrote:
Can any pilot tell me if engine fan blades can rub against the inside nacelle of the engine??? I know fan blades have a very minimal clearance from the engine cowling, but can it ever rub against the cowling interior during turbulence or anything? And if it could rub against the cowling, what would happen? I always wanted to know this, thanks.


Not much happens, the engine and nacelle is designed that way, the material the fan makes contact with erodes a little, if they deem necessary at a later maintenance event the liner can be replaced.
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TurboJet707
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Re: Engine Fan Blade Rub

Fri May 04, 2018 2:33 pm

This was actually a big problem with the early PW JT9D engines on the 747-100 and it caused many delays in delivery of the 747. At some point, resulted in thirty aircraft being parked outside the Everett factory with concrete blocks hanging from the pylons, awaiting redesigned engines:

Image

The problem was also described as 'ovalling' in the case of the JT9D. It took quite some time to sort out and this wasn't good for the relation that Boeing had with Pratt & Whitney, to put it mildly. I read that a Boeing test pilot deliberately blew two engines, one after the other, on a test flight when the P&W CEO was with him in the cockpit. The P&W guy was frightened and the message was clear and taken seriously from that moment. Joe Sutter's book '747' contains some fascinating stories about this period.

A bit more detail about this rubbing problem can be found in this article from a 1969 Flight International issue

http://www.flightglobal.com/pdfarchive/ ... 03200.html
http://www.flightglobal.com/pdfarchive/ ... 03201.html

Also see viewtopic.php?t=762715
 
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Balerit
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Re: Engine Fan Blade Rub

Fri May 04, 2018 3:09 pm

The strip they are talking about especially on the JT9's, is the fan blade rub strip. When the fan rotates at high rpm, the blades stretch and rub or bed into this abradable strip, allowing a tight seal that stops air flowing over the tip of the blade thus preventing loss of power. At night you can see the tips glowing on new engines during the first run.
Licensed Aircraft Maintenance Engineer (retired).
 
lowbank
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Re: Engine Fan Blade Rub

Fri May 04, 2018 5:35 pm

On Trent engines some liners are machined and some cassette type liners are pre-machined before assembly.
The blades then cut the liners on first run up so you get the minimum clearance you can have.

Many years ago I had to do a quality investigation as we delivered an 800 blade 2 mm to long. That cut a nice oversized path which meant the liners had to be replaced, the tip was slightly blue on that one.
Every days a school day.
 
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jetmech
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Re: Engine Fan Blade Rub

Sun May 06, 2018 8:11 am

propilot83 wrote:
Is there a video on youtube

I couldn't find anything on Youtube unfortunately.

propilot83 wrote:
And what do you mean "remove material if need be."

As others have noted, the abradable liner is made of a material that is softer than the fan blades. Thus, if the blade tip should contact the abradable liner due to centrifugal growth or g forces, the blade tip can literally "carve" away the liner material to produce the necessary clearance.

I believe that most compressor and turbine rotor blades operate against abradable liners as well as labyrinth seals for the same reason, that is to allow these items to remove material if need be during operation. The wear of abradable liners and opening up of blade tip and labyrinth seal clearances is one of the major contributors to the degradation in engine performance and efficiency with age.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
Wacker1000
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Re: Engine Fan Blade Rub

Sun May 06, 2018 4:49 pm

propilot83 wrote:
Can any pilot tell me if engine fan blades can rub against the inside nacelle of the engine???


You have some serious issues if a blade is rubbing against the nacelle.
 
gregorygoodwin
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Re: Engine Fan Blade Rub

Mon May 07, 2018 7:27 pm

I'm not a pilot, I work as a structures tech. We do a lot of work on the abraded shroud. It is located under the fan path and is made to allow a close tolerance between the blade tips and the fan casing. On the GE engines,the fan path is above a large cell aluminum honeycomb that has a micro-balloon resin applied to it. The fan blades will abrade this honeycomb-resin as the blades stretch when spooled up. Interestingly enough, if you ever get to see a Apollo crew capsule, the heat shielding on the bottom of the capsule seems to be the very same material. The Rolls-Royce RB211s have a similar construct except they use a small core honeycomb and resin design. On our P&W engines, they use a grooved fiberboard type of material under the fan path. The GE's and Rolls engine seem to require repairs, the P&W design is rarely a problem. But, to answer your question, the fan blades should never contact the fan casing which is located under the abraded shroud which is about a half inch thick. In case you are wondering, the repairs we do are usually the result of the resin/micro-balloons detaching from the honeycomb cells. In this case, you can mix up more resin/micro-balloons and fill in the missing material. Rolls RB211's use a structural void filler that you press down into the honeycomb cells, both an easy fix. If the shroud becomes detached from the fan case you have to remove fan blades, cut out the detached area, and do a heat bonded repair to seat the new honeycomb and then fill it with the resin/micro-balloons and let everything cure before the plane can resume service.

Gregory
 
WPvsMW
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Re: Engine Fan Blade Rub

Mon May 07, 2018 11:11 pm

Great, detailed reply! The highlight of my a.net reading today.
 
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propilot83
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Re: Engine Fan Blade Rub

Wed May 09, 2018 4:26 am

gregorygoodwin wrote:
I'm not a pilot, I work as a structures tech. We do a lot of work on the abraded shroud. It is located under the fan path and is made to allow a close tolerance between the blade tips and the fan casing. On the GE engines,the fan path is above a large cell aluminum honeycomb that has a micro-balloon resin applied to it. The fan blades will abrade this honeycomb-resin as the blades stretch when spooled up. Interestingly enough, if you ever get to see a Apollo crew capsule, the heat shielding on the bottom of the capsule seems to be the very same material. The Rolls-Royce RB211s have a similar construct except they use a small core honeycomb and resin design. On our P&W engines, they use a grooved fiberboard type of material under the fan path. The GE's and Rolls engine seem to require repairs, the P&W design is rarely a problem. But, to answer your question, the fan blades should never contact the fan casing which is located under the abraded shroud which is about a half inch thick. In case you are wondering, the repairs we do are usually the result of the resin/micro-balloons detaching from the honeycomb cells. In this case, you can mix up more resin/micro-balloons and fill in the missing material. Rolls RB211's use a structural void filler that you press down into the honeycomb cells, both an easy fix. If the shroud becomes detached from the fan case you have to remove fan blades, cut out the detached area, and do a heat bonded repair to seat the new honeycomb and then fill it with the resin/micro-balloons and let everything cure before the plane can resume service.

Gregory


So basically can the tip of those flan blades basically hit against the abraded shroud, because you know how there is turbulence during flight or when an aircraft is taking off and you see the engines kind of wiggling around (the engine cowling), would or could this cause the fan blades to rub against the engine cowling?
 
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propilot83
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Re: Engine Fan Blade Rub

Wed May 09, 2018 4:26 am

gregorygoodwin wrote:
I'm not a pilot, I work as a structures tech. We do a lot of work on the abraded shroud. It is located under the fan path and is made to allow a close tolerance between the blade tips and the fan casing. On the GE engines,the fan path is above a large cell aluminum honeycomb that has a micro-balloon resin applied to it. The fan blades will abrade this honeycomb-resin as the blades stretch when spooled up. Interestingly enough, if you ever get to see a Apollo crew capsule, the heat shielding on the bottom of the capsule seems to be the very same material. The Rolls-Royce RB211s have a similar construct except they use a small core honeycomb and resin design. On our P&W engines, they use a grooved fiberboard type of material under the fan path. The GE's and Rolls engine seem to require repairs, the P&W design is rarely a problem. But, to answer your question, the fan blades should never contact the fan casing which is located under the abraded shroud which is about a half inch thick. In case you are wondering, the repairs we do are usually the result of the resin/micro-balloons detaching from the honeycomb cells. In this case, you can mix up more resin/micro-balloons and fill in the missing material. Rolls RB211's use a structural void filler that you press down into the honeycomb cells, both an easy fix. If the shroud becomes detached from the fan case you have to remove fan blades, cut out the detached area, and do a heat bonded repair to seat the new honeycomb and then fill it with the resin/micro-balloons and let everything cure before the plane can resume service.

Gregory


So basically can the tip of those flan blades basically hit against the abraded shroud, because you know how there is turbulence during flight or when an aircraft is taking off and you see the engines kind of wiggling around (the engine cowling), would or could this cause the fan blades to rub against the engine cowling?
 
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Starlionblue
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Re: Engine Fan Blade Rub

Wed May 09, 2018 5:38 am

Yes, the fan blades can rub against the shroud. You want minimum clearance for airflow reasons, but larger clearance for structural reasons. The compromise is that the blades are allowed to rub on occasion. The engine structure is not rigid enough to prevent blade clearance changes during operation.

Turbulence and manoeuvring move the shaft, and thus the blades, in relation to the nacelle,

As I understand, and please correct me if I am wrong, it ovaling (mentioned above) is a somewhat different phenomenon. In a pitch maneuver, for example rotation, the nacelle flexes a little, extending along the vertical and contracting along the horizontal, thus the term OVALing. You can think of it as G forces trying to pull the nacelle away from the pylon. This naturally means that blade clearance changes along the tip path. It was a massive problem on early 747s.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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jetmech
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Re: Engine Fan Blade Rub

Wed May 09, 2018 6:30 am

gregorygoodwin wrote:
On our P&W engines, they use a grooved fiberboard type of material under the fan path.


Perhaps P&W were trying to provide a labyrinth seal type configuration to further minimise tip leakage?

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
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747classic
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Re: Engine Fan Blade Rub

Wed May 09, 2018 8:13 am

Starlionblue wrote:
Yes, the fan blades can rub against the shroud. You want minimum clearance for airflow reasons, but larger clearance for structural reasons. The compromise is that the blades are allowed to rub on occasion. The engine structure is not rigid enough to prevent blade clearance changes during operation.

Turbulence and manoeuvring move the shaft, and thus the blades, in relation to the nacelle,

As I understand, and please correct me if I am wrong, it ovaling (mentioned above) is a somewhat different phenomenon. In a pitch maneuver, for example rotation, the nacelle flexes a little, extending along the vertical and contracting along the horizontal, thus the term OVALing. You can think of it as G forces trying to pull the nacelle away from the pylon. This naturally means that blade clearance changes along the tip path. It was a massive problem on early 747s.


I operated the JT9D-7 engine at the 747 for many years.
- After installation of the thrust yoke the ovalisation issue during T/O was almost eliminated.
- The abreadable seals were installed to optimise the fan blade tip clearance, for optimum fan performance.
- However, especially at the outboard engines of the 747 the movement of the nacelle structure was sometimes excessive (turbulence , landing, and reverse opearation.), so the abreadable seals were sometimes rubbed outside limits.
- This excessive rubbing could even cause a fan stall. The kind of stall happened at a certain pitch attitude, mosly during the initial climb out. Sudden thrust loss, auto thrust restore, loud frequent bangging and stopped after slight thrust reduction.. No visible abnormal engine indications. Because of the repeating large thrust variations a complete pylon check was required.
I encountered two of this events myself.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Tristarsteve
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Re: Engine Fan Blade Rub

Wed May 09, 2018 8:44 am

Many years ago I worked for Gulf Air with the RB211 on the Tristar. We had a shop that replaced engine modules, but no test bed. The 04 module (HP comp combustor and HP turbine) had a very limited life and we were always changing them. The HP turbine was limited to 1500 cycles, which it never achieved!
Anyway, after fitting the new engine to the aircraft, we had to do the test bed runs. There was a series of tests in the AMM, tests 1 to 17. We did them all, and with a lot of practice I could do the lot in about 40 minutes. One of these tests was test 04 which was called running in. We operated the brand new engine at different thrust settings and accelerated up and down to a schedule. It took about 20 minutes and the idea was to abrade these linings before service. After this we checked the performance, and hope that there was some EGT margin to enable us to release the engine. It was always minimal, about 20 degC, and sometimes negative! But we were running in an OAT of 35degC, which engines in those days were not really designed for.
 
gregorygoodwin
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Re: Engine Fan Blade Rub

Wed May 09, 2018 7:12 pm

To Propilot83,
Yes, the fan blades will rub the shroud, which is what it is designed for. I'm not sure how much movement the fan stage experiences when in flight, but these big fan engines are very stout and are incredibly balanced assemblies. You can easily spin one with your hand. Also, there may be some confusion in terminology. The fan blades are contained inside the engine fan case which is part of the engine itself. The cowlings are what surround the engine assembly. The cowlings must be latched at a certain tension which helps stabilize them to the engine pylon. This is a required inspection item on our aircraft. Also, if you open a cowling for any reason, it must be written up on a non-routine maintenance form or in the aircraft log book to ensure that it gets properly closed. While the cowlings come close to the engine when they are closed, they should not be touching it. This would lead to chafing that could be dangerous, like rubbing into a bleed air line.
While there is some movement of the engine in flight, the amount of chaffing by the fan blades isn't much. Most abradable shrouds I see have very little wear cut into them.

To Jetmech,
The P&W shrouds have several grooves milled into them going around the circumference of the fan blade path. They are in segments that are about eight to ten inches long and are bonded into place. To me, they look like caramel colored Masonite board. Not sure what they are made of. In all my years of repairs I've never had to work on the P&W shrouds. .Also, while you may feel wear grooves in the GE and Rolls Royce shrouds (kind of like running your hand across a disc brake) , the P&W shrouds seem to never have signs of wear.

Gregory
 
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jetmech
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Re: Engine Fan Blade Rub

Thu May 10, 2018 4:09 am

gregorygoodwin wrote:
The P&W shrouds have several grooves milled into them going around the circumference of the fan blade path. They are in segments that are about eight to ten inches long and are bonded into place. To me, they look like caramel colored Masonite board. Not sure what they are made of. In all my years of repairs I've never had to work on the P&W shrouds. .Also, while you may feel wear grooves in the GE and Rolls Royce shrouds (kind of like running your hand across a disc brake) , the P&W shrouds seem to never have signs of wear.


Indeed. I remember on the GE's that you could always see the aluminium honeycomb poking through the liner material.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
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747classic
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Re: Engine Fan Blade Rub

Thu May 10, 2018 10:29 am

Propilot83, you asked almost the same question several years ago (2009), see : viewtopic.php?t=762109 and got fairly equal answers from still present responders, incl. myself.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Apprentice
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Re: Engine Fan Blade Rub

Tue May 15, 2018 8:56 am

Hi: blade rubbing is the result of desire to restrict engines inneficiency.
Should clarence is large enough, air, from high pressure blade side will move foward, to low press side trhough blade tips in a similar way it happen in a wing. (That is one reason of why wing tips are for). On some engines, on some stages, blade tips are joint toghether, to avoid air circulation and or blade tip vibration, but again, this come at extra weight.

Rgds
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"A NO" is a positive answer., "DON'T KNOW" is not. My Tutor (a wise man)
 
Egerton
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Re: Engine Fan Blade Rub

Tue May 15, 2018 11:09 am

TurboJet707 wrote:
This was actually a big problem with the early PW JT9D engines on the 747-100 and it caused many delays in delivery of the 747. At some point, resulted in thirty aircraft being parked outside the Everett factory with concrete blocks hanging from the pylons, awaiting redesigned engines:

Image

The problem was also described as 'ovalling' in the case of the JT9D. It took quite some time to sort out and this wasn't good for the relation that Boeing had with Pratt & Whitney, to put it mildly. I read that a Boeing test pilot deliberately blew two engines, one after the other, on a test flight when the P&W CEO was with him in the cockpit. The P&W guy was frightened and the message was clear and taken seriously from that moment. Joe Sutter's book '747' contains some fascinating stories about this period.

A bit more detail about this rubbing problem can be found in this article from a 1969 Flight International issue

http://www.flightglobal.com/pdfarchive/ ... 03200.html
http://www.flightglobal.com/pdfarchive/ ... 03201.html

Also see viewtopic.php?t=762715


The Flight drawings of those days were superb. They illustrate the sort of issues which currently effect the P&W GTF installation for the A320 NEOs. The particular installation was different to all others GTFs, was never flight tested during the development stage, and only came to light during the airworthiness testing of aeroplane. No true solution has been applied to the installation, just fixes to the engine.
 
Apprentice
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Re: Engine Fan Blade Rub

Tue May 15, 2018 11:30 am

Hi:

TurboJet707 wrote:
This was actually a big problem with the early PW JT9D engines on the 747-100 and it caused many delays in delivery of the 747. At some point, resulted in thirty aircraft being parked outside the Everett factory with concrete blocks hanging from the pylons, awaiting redesigned engines:

Image

The problem was also described as 'ovalling' in the case of the JT9D. It took quite some time to sort out and this wasn't good for the relation that Boeing had with Pratt & Whitney, to put it mildly. I read that a Boeing test pilot deliberately blew two engines, one after the other, on a test flight when the P&W CEO was with him in the cockpit. The P&W guy was frightened and the message was clear and taken seriously from that moment. Joe Sutter's book '747' contains some fascinating stories about this period.

A bit more detail about this rubbing problem can be found in this article from a 1969 Flight International issue

http://www.flightglobal.com/pdfarchive/ ... 03200.html
http://www.flightglobal.com/pdfarchive/ ... 03201.html

Unable to open pdf archives, any help?

Rgds
“An AME, with just a Mechanic Role”, as per one of our pilots
"A NO" is a positive answer., "DON'T KNOW" is not. My Tutor (a wise man)
 
Apprentice
Posts: 490
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Re: Engine Fan Blade Rub

Tue May 15, 2018 11:31 am

Hi:
Unable to open FlightGlobal pdf archives. Any hel0?

Rgd
“An AME, with just a Mechanic Role”, as per one of our pilots
"A NO" is a positive answer., "DON'T KNOW" is not. My Tutor (a wise man)
 
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TurboJet707
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Re: Engine Fan Blade Rub

Tue May 15, 2018 2:33 pm

Hmmm, strange, still works fine here. I assume you have Acrobat Reader running on your PC?
 
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propilot83
Topic Author
Posts: 625
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Re: Engine Fan Blade Rub

Thu May 17, 2018 4:02 am

Starlionblue wrote:
Yes, the fan blades can rub against the shroud. You want minimum clearance for airflow reasons, but larger clearance for structural reasons. The compromise is that the blades are allowed to rub on occasion. The engine structure is not rigid enough to prevent blade clearance changes during operation.

Turbulence and manoeuvring move the shaft, and thus the blades, in relation to the nacelle,

As I understand, and please correct me if I am wrong, it ovaling (mentioned above) is a somewhat different phenomenon. In a pitch maneuver, for example rotation, the nacelle flexes a little, extending along the vertical and contracting along the horizontal, thus the term OVALing. You can think of it as G forces trying to pull the nacelle away from the pylon. This naturally means that blade clearance changes along the tip path. It was a massive problem on early 747s.


Thank you very much for answering properly, appreciate it, now I know and understand.

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