Whining flaps

[ZAZOO]

Recently I flew on a Boeing 767-300 and sat with a great view of the wings and flight controls.

As we started the taxi to the runway the pilots dropped the flaps and this whining sound was heard Continuously as they came down it was so loud it made passengers and even I look at each other with faces suggesting the that's not normal look.

It was the same thing when flaps up were selected. And then for the approach into LGW it was horrendous even louder and kind of eerie if I might add for passengers as the weather was not interesting with winds gusting the aircraft was slow and low in a bank when full flaps was selected down in stages.

What causes this loud whining sound and is it normal I have never experienced this so loud before.

Thanks for any help.

Zazoo.

[Lu Zuckerman]

My terminology may not be correct but the noise you heard was the power control unit which is most likely a gearbox driven by a hydraulic motor. The gearbox is mechanically linked to the flap screw jacks which drive the flaps in and out. The noise is sometimes amplified through the airframe

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The Cat

[This message has been edited by Lu Zuckerman (edited 28 February 2001).]

[QAVION]

The sound may have been unfamiliar to you because you perhaps have not sat in that area of the cabin before(?). I recall a while back, sitting in First Class on a 747 for the very first time and heard a noise which sounded like a bandsaw just after takeoff. I realised, shortly after my initial shock, what it was (the tire rubbing against the brake pad), but it did take me by surprise.

I'd say that smaller aircraft tend to put you closer to the "action", so to speak.... So, generally, the noises will appear louder.

Not that I'm saying there _wasn't_ anything wrong with the flaps... :)

Rgds.
Q.

[Jim lovell]

I noticed the loud whining sound on a 767 trip. I was on a 767-200 and it did sound quite loud- but i was sitting right next to the wing at the time so that may explain it. I noticed the noise on the 747-400 but not as loud. I think it all depends where you're sitting. I had an awesome seat next to the left wing on the 767-300 on a trip to Sydney. The view was just fantastic as we crossed low over Botany Bay to land. As the flaps were being selected down i could see through the gap striaght down the water below. Sitting next to a wing is cool because that's where all of the action is happening and on a big jet like a 767 it's awesome seeing it all happen so neatly!

[GJB]

BAe-146 is even worse. Flaps retraction after T/O produces a horrendous whinning and groaning noise.

[RRAAMJET]

On the 767/757 the flaps and slats are driven ( normally ) by hydraulic Power Drive Units , 3 on the 767 and 2 on the 757. These in turn drive torque tubes to the canoe fairings you see on the wings, where screwjacks actually move the flaps. You probably heard the PDU's.

GJB: the racket on the 146 is completely different - it's caused by a high-energy escape of airflow between the flaps and the fuselage wall.

[ZAZOO]

I can understand your point Lu and RRAAMJET but I have flown in quite a few aircrafts with a seat allocation next to the wings and do realize that a whining noise is heard when flaps and slats are being selected. But in this case I felt the sound was extremely loud and could be heard in all areas of the cabin.

Is it possible that after a lot of cycles (resulting to age and then wear) during flaps and slats selection the drive units or screw jacks make a louder noise when in operation.

Thanks guys
Zazoo

[Speedbird48]

On the Boeing products the flaps are driven by a hydraulic motor below the cabin floor. The motor drives the flaps through a screw jack system and is quite noisy.
On the 146 it is a different problem as the noise is caused by aerodynamics, namely the airflow between the flap and the side of the fuselage. We always made an announcement to warn the pax of the impending howl prior to operating the flaps.

[Blacksheep]

Zazoo,

You don't say where you were actually sitting in the B767-300, but just aft of the wing on the left side you would be above the Air Driven Hydraulic Pump (ADP). This is only supposed to operate in certain conditions such as when very high demand on the centre hydraulic system (such as Flap Operation simultaneously with Landing Gear operation) causes centre system pressure to fall below 1900 PSI. In certain fault conditions, especially a defective pressure switch, the pump may operate when it is not really needed. If it WAS running you would certainly notice the unusually loud noise as would other passengers. This is not a serious fault and there is no risk involved, it just wears out the ADP faster!

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Through difficulties to the cinema

[Jim lovell]

The whining noise mentioned on the 146- can this be heard from the ground when a 146 flies overhead i wonder? I have on many occasions heard a loud whining noise whenever watching a 146 fly overhead(i live near a flightpath), but this noise is only heard when the a/c is 2-3 miles away from me but is nonetheless quite noticeable and distinct to this type of a/c. Is this due to the flaps or perhaps just the engines spooling up/down???

[ZAZOO]

Good morning Blacksheep how did you guess!!! I was sitting on the left side just one row of seats aft of the wings and from my window I could actually look directly at the flaps e.t.c.

I think your answer to my question most have been the case thanks and much appreciated.

Regards
Zazoo

[foghorn]

Having flown as PAX on many types, there is nothing quite like the 146/AvroRJ for flap whine.

It has a rising tone like a gigantic bath emptying - really quite charismatic.

I guess I'm gonna get like one of those saddo who tapes train noises... help :) :)

[GJB]

SPEEDBIRD48 & RAMJET:

I stand corrected - thanks for that bit of info. It's a shame you weren't the crew when I had my 1st flight on a 146 as we weren't warned about the noise that would follow......

Needless to say there were many concerned faces looking around the cabin

[Lu Zuckerman]

To: Blacksheep and Zazoo

I feel like an absolute idiot. I performed the Reliability, Maintainability and Safety analysis on the Air Driven Hydraulic Pump used on the 767-400-ER while on contract to Fairchild Controls. I knew that this same type of unit was used on the 747 but I did not know it was used on other 767s, as Fairchild did not make it. At least, I never saw one in their repair shops. But being the idiot that I am, I didn’t even consider it when answering Zazoos’ question about the noise. It was my understanding that the unit was turned on during takeoff and landing and at all other times it operated on demand or, if the system malfunctioned.

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The Cat

[SevenFiftySeven]

Re: BAE 146 and flap noise.

Would agree wholeheartedly about the noise on flap retraction on the 146.
The first time I flew on one, I almost sh*t myself! I definately wasn't expecting that kind of noise on an aircraft so small, especially after being on a reasonably quite 777 for the last 8 hours.

I have to say that once you get used to it, it's quite nice - almost relaxing in a bizarre sort of way.

I fly on 146's now every month and think they are superb aircraft, especially when a little empty.
The landings are great, with the ATW pilots almost doing handbrake turns into the first taxiway possible :)

[spoilers yellow]

On the subject of 146/RJ flap noise.

It occurs with both the up and down selection of flap 18, No one has given me the definitive answer as to what actually causes the noise, but the best I have heard is simply that the change of airflow through and around the flaps causes it.

There is no such noise when other stages of flap are selected and it is exactly the same systems that are in use.
Still I agree it makes one hell of a noise and I believe that you CAN here it on the ground!

[RRAAMJET]

At a certain vip unit, in another life, in a land far away, we put considerable thought into how to get rid of the 146 whine. It CAN be reduced by the clever use of MoD half-broom heads (! don't ask how that ever came up ). Yes, you can hear it on the ground when below the a/c. Gives you an idea how effective those big flaps are - how intense that vortex must be.

767: the ADP should only work on anticipation of demand (gear, flaps, gnd spoilers)or system low pressure. Don't usually hear it on the ground. The control valve must have been stuck for it to run at other times, I would guess....

[ZAZOO]

Hi Lu not to worry my friend to tell you the truth I have learned so much from all you guys on this topic and its systems.

And if I might add its just great to see that we can find guys like you on pprune in the engineering field ready to respond to technical question from the rest of us.

And now I know where to log on to when I have technical problems back in the dark continent.

Much Respect
Zazoo

[SFly]

Ever been sitting in the front cabin of a 747 downstairs when he puts the gear down? Now that is noise!!! It was like the Seattle earthquake all over again!!

[fly4fud]

Come on guys!
This noise thing on the 146/ARJs is only when transitioning from sub to supersonic or the other way round. Really nothing to with flaps or whatever :)

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... cut my wings and I'll die ...

[ZK-NSJ]

SFLY:
yeah thats one hell of a noise,
when i was younger and travelled frequently
as an unaccompanied minor we always used to
get moved up to either the first or business
class cabins (depending on room) for landing
anyway this day we were approaching sydney
in a qf 744 i was sitting in the first class
cabin and boy did that nose gear coming down
make a noise,

[near enuf is good enuf]

Lu,

Afraid not. ADP not selectable on the 76.

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So that you may not be the martyred slaves of Time,
get drunk, get drunk,
and never pause for rest!
With wine, poetry, or virtue,
as you choose!"

[747FOCAL]

YOu wanna hear flap noise take a ride in an Airbus. Right at the gate when they power the hydraulics that bangin noise will scare the crap outa most people.

[PanicButton]

I flew in an Icelandair 757 seated front of the wing (row 9) from KEF-MSP. Didn't hear a thing. From MSP I flew with a Northwest 757 to LAX. Sat behind the wing on the right side and heard this loud whining sound each time the flaps were extended or retracted. the sound was so loud I would have thought everybody on the a/c heard it.