EasyJet Airbus turbofan blades rattling

[Tec7]

All, not sure if this is something to be concerned about, probably not, but would like to know the answer.

I fly EasyJet Airbus A320[I think] around 3-4 times a month, on domestic routes. In the past few weeks, I have noticed when boarding, as the fan blades inside the engine cowlings slowly rotate, on some of the planes there is a noticeable "rattle", like the blades are catching something as they turn. Sometimes it is one, or both engines. Last night, on a flight home from Newcastle, it seemed a much newer Airbus, and there was no rattle at all as the blades rotated.

I also noticed, on one flight where the rattle was evident during boarding, as the engines powered up during and after take-off, the rattle seemed to become more of a vibration, varying with the speed of the engines. Is this varying behaviour on different planes normal?

Regards
John

[Double Hydco]

Hello John (and welcome),

No, it's nothing to be concerned about. The fan baldes move slightly in their mount, and make the clank you can hear as you board the aircraft. Also, there is an abrasive rub strip between the fan tip and the rest of the engine and sometimes the blade will rub on this, making quite a noise!

It's quite normal for different airframes to make different (or no) vibration. It can vary with speed or altitude, and be traced to a variety of things like engines, flight control position or the airframe itself.

Hope this puts your mind at rest....

DH

[jpoth06]

Perfectly normal :)

[Fareastdriver]

All goes back to the WW II. During the development of jet engines there were massive problems with the turbines in the hot end of the combustion chamber. A solid turbine wheel with the blades all machined from the solid was unpredictable as to how or where it expanded or warped when it got hot. Machining the blades seperately with fir-tree shaped roots with similar shaped mountings in the boss enabled the blades to heat up and expand independently. Initially they would be loose and held in by centrifical force until they heated up and fitted themselves into the mounting. Now having small lumps of metal to deal with drilling holes internally in the boss and blades to allow air to cool the blades followed.
I have been told it was a British idea and the Germans never cracked it. That is why the Meteors of the RAF were not allowed to fly over German territory in case one went down and the Germans found out.
The technique is used on fan blades on modern engines so when it is cool before take-off the blades are loose so they rattle but on landing they are warm and tight.

[TurningFinals]

Hi there.

I work on the A319 as dispatch/ramp and when i first started i was wandering the same thing.

However, one day the blades were spinning but not very fast. I discovered that if you look at the 12 o'clock of the engine, you can see that as the blade moves through the 12 o'clock position, it moves horizontally in it fixing. (appologies if that does not sound very clear, kinda hard to describe)

But basically, there is just a little bit of play in the blades and it is them moving as they spin round.

Next time you board and the fans are moving slowly, try to have a look.

TF.

[boardingpass]

It's just the engineers sticking the equivalent of baseball cards in the spokes of your bicycle wheel.

[spannersatcx]

The noise you can hear are the mid span shrouds (or clappers) banging together, these are on the CFM-56, don't know about the V2500, with the engines turning slowly when the blade at TDC moves slightly past this point it basically flops over and the midspan shrouds contact and this is the noise you can hear, it is perfectly normal. Some engines have the mid span shrouds some don't. The other engine fitted to the 320 the V2500 I don't believe has this.

You should be outside on a windy day on an old 747 classic with RRR or JT9 engines fitted, it is deafening.

[Tec7]

Thanks to everyone, appreciate you taking the time, mind now at rest!

Regards
John

[dubh12000]

.................
The technique is used on fan blades on modern engines so when it is cool before take-off the blades are loose so they rattle but on landing they are warm and tight.

Not quite. No heat up that end. It's purely the centrifical force on the fan blades.

[simonchowder]

Dont worry about it friend, sit back and enjoy the flight i fly all the time with my job, i know very little about the techy bits but i do know the aircraft are flown by highly qualified pilots, and their maintained by highly qualified licensed engineers, both groups id trust with my life in fact i do every time i fly and i never ever think is this aircraft safe, i know it is.

[singpilot]

The blades are designed to be able to move in their mounts to a lead/lag position to seek a 'balance'. Theoretically, they all seek and find the same lead/lag spot and the entire disk stays balanced.

I'll sometimes see a vibration reading increase after a long leg up at altitude, and it will change with power settings. Usually, a pass thru a cloud or some type of precip will solve the vibes reading (undetectable by feel 'usually'), but a sit on the tarmac with them windmilling and clanging will solve it too. What has happened is that the dirt up at altitude (yes, it is there) will 'clog' the slots that the blades swing in, and some will 'hang'.

So the long and short of it is that the noisy clang while windmilling on the ground is a good thing.

[smudgethecat]

Dirt at altitude clogging the slots... are you for real ?

[nacluv]

I was near a C17 recently which had all 4 windmilling merrily away. The clanking noise was deafening!

[TURIN]

What has happened is that the dirt up at altitude (yes, it is there) will 'clog' the slots that the blades swing in, and some will 'hang'.

Nearly 30 years in the business and I learn something new everyday. :hmm:

Occasionally fan blades will jam together. The mid span snubbers overlap slightly causing a group or all of the blades to be fixed. IE unable to move in their mounts to adopt a balanced position. Some call this effect shingling. Not seen it for a while as modern engines do not have mid span snubbers. The giveaway was the fan blades rotating silently instead of the familier clacking noise. A tap with a huge leather mallet usually did the trick. :ok:

Modern engines such as the GE90, RR Trent, IAE V2500 etc have composite/carbon fibre wide chord fan blades that are stiff enough to not require support along their span. (No clacking).

[singpilot]

SMUDGETHECAT wrote

Dirt at altitude clogging the slots... are you for real ?

Absolutely. One of the F/O's duties on the Gulfstreams (Speys and Tays) was to wipe the fan blades so they looked 'clean' to the pax as they boarded.

I may even have pics of the before and after.

If you'd ever been above FL410, it is actually worse up there.

EDIT: Headlines today..... Dust cloud from deserts of China circles the world in 13 days. Tracked by a sattelite, dust travelled in the relatively stable upper atmosphere above 36000 feet.....

We found the longer the leg, the dirtier the fans. The fan blades in the Speys were painted off-white, and every nick or bug smack had a wake trail of dust.

Guess you'd have to have been up there to not ask if I was for real....

[Fargoo]

To be fair this is a thread about the CFM's fitted to Easyjet Airbus' , to which I concur with Turin. Interesting story about the Gulfstreams above 41000 ft though, must be very close to their operating ceiling?

[Swedish Steve]

Dirt at altitude clogging the slots... are you for real ?

Well I don't know where it comes from, but in the V2500 engines on the Qatar A319s there is always sand. After shutdown at ARN I can scoop a couple of teaspoonsfull out of the exhaust every time, and it is stuck on all the fan blades.

[Skyfan]

A good size storm can suck up untold amounts of crud from the boundary layer. This is an extreme example :eek: YouTube - sandstorm hits Riyadh city (http://www.youtube.com/watch?v=FoLumQPf0r0)

The finer particles can reach 40k feet no problem and can hang around for days. They aren't always visible but I'm betting if you're clocking along at 250kts+ you'll pick up more than a handful. :)

[smudgethecat]

i ve removed and refitted more cfm 56 fan blades than i care to remember and ive never ever found the "slots" cloggged with dirt ,what all this has to do with cfm56 fan blades making a racket on the ground when windmilling is beyond me

[TURIN]

Have to agree, however on the JT8 (B737) we used to do regular compressor washes during the summer months. Apparently it improved SFC by a considerable margin. Can't see that it helped clean the root but I could be wrong-again. :O