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a320fan
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 1:10 pm

DocLightning wrote:
767333ER wrote:
I have heard the PTU run during gear retraction on takeoff on every A320 I have been on that I have sat over the wing and it has usually pulsates quite quickly. It is certainly harder to hear compared to when it runs on the ground, but it is there.


I have never once heard the PTU run after both engines start. I can hear gear retraction, but I do not hear the PTU. Gear retraction is a dull rumble and then some dull thumps.


One time flying JQ from MCY to MEL the PTU was barking from pushback/engine start, taxi out and backtrack, approach, and after landing taxi in. I can't specifically recall hearing it at all on any other A320 flight I've taken before or since. My mother, who is a nervous flyer was quite concerned about the sound on taxi out, and I doubt it was a single engine taxi out as the gate would probably only be 200 metres from the runway at MCY.
A319, A320, A321, A330-200, A350-900, A380, 737-700, 737-800, 777-200ER, 777-300, 777-300ER, 787-8, Q300, Q400
 
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aerorobnz
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 2:33 pm

I have heard all sorts of other sounds on aircraft, even a Sumatran tiger in the hold and I have flown just on 100 flights in the A32x series aircraft and I have never heard anything I would identify as a "barking dog" sound. (thanks Bose) so I turned to youtube for assistance. I guess it is less obvious from the front of the aircraft

For those of you like me who had not identified this sound
http://www.youtube.com/watch?v=bqyO5NBsWUM
Flown to 147 Airports in 62 Countries on 83 Operators and counting. Wanderlust is like Syphilis, once you have the itch it's too late for treatment.
 
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NearMiss
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 2:52 pm

I always thought it was a DJ scratching a vinyl record :mrgreen:
"There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
 
MIAspotter
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 3:13 pm

Awww man!

I love the PTU noise, it´s like a trademark, just leave it!

I love hearing it on shutdown when it goes mental, most passengers are like :?: :?: :?:

Just think of it as another subtle reminder that you are onboard a ¨live¨ machine.
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767333ER
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 3:49 pm

DocLightning wrote:

I have never once heard the PTU run after both engines start. I can hear gear retraction, but I do not hear the PTU. Gear retraction is a dull rumble and then some dull thumps.


Here's some examples of what I'm talking about:

https://m.youtube.com/watch?v=88S4AprJSfk
Heard at 8:27

https://m.youtube.com/watch?v=0HotElnN6aY
Heard at 6:39

I believe it runs because the landing gear is only powered by the Green system which one under demand probably makes the PTU draw power from the Yellow system that is under less demand. I hope this makes sense.
Been on: 732 733 734 73G 738 752 763 A319 A320 A321 CRJ CR7 CRA/CR9 E145 E175 E190 F28 MD-82 MD-83 C172R C172S P2006T PA-28-180

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alyusuph
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 4:06 pm

They should not touch the /kapa/ braking noise on the A330, nobody should touch it!
I am not an Airbus or Boeing fan, just an aircraft fan
 
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hOMSaR
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 4:29 pm

MIAspotter wrote:
Awww man!

I love the PTU noise, it´s like a trademark, just leave it!

I love hearing it on shutdown when it goes mental, most passengers are like :?: :?: :?:

Just think of it as another subtle reminder that you are onboard a ¨live¨ machine.


Maybe they can digitize the sound and play it through the speakers on future Airbuses, sorta like how some digital cameras make the stupid electronic shutter and film-winding sound when you take a photo.
I was raised by a cup of coffee.
 
masi1157
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 6:29 pm

767333ER wrote:
It does seem rather odd that they would put a silencing device near the EDP in hope of silencing the PTU which is essentially mounted to part of the aft wall of the main gear well which is clearly far from the engines. I wasn't aware though that the EDPs made any audible noise. I know the ACMPs make noise and I am convinced that one of the two types of these offered on the A320 is especially loud, but don't think they could make those any quieter.


The EMPs are even easier to reduce because they run at constant speed. The EDPs are driven by the engines' N2 that varies quite a bit. During cruise their noise can become rather nasty in the cabin above the MLG bay. That is what the extra silencers are for. The PTU noise is not changed at all.

Gruß, masi1157
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wingscrubber
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 7:09 pm

Looks like the original flightglobal article got deleted, the link no longer works... Too late, the internet has it now, original text;

-----

Airbus has modified its A320neo to eliminate the characteristic ‘barking dog’ noise generated by the A320’s power transfer system during ground manoeuvring.

The noise has been a familiar feature of the A320 family and originates in the power-transfer unit, a bi-directional device enabling the green and yellow hydraulic systems to pressurise one another.

It typically activates when the differential pressure between the two systems exceeds 500psi.

This activation is usually heard in the cabin as a distinctive repetitive sound from beneath the cabin floor, reminiscent of a high-speed drill, a buzz-saw or even a dog’s barking.

But Airbus A320 programme manager Klaus Roewe says that the airframer has developed a modification which “eliminates” this noise.

The noise is generated by vibrations within the pumps and the modification involves installing two additional dampers – one near the engines and the other near the wing root.

Airbus says the amendment means the issue has been “solved”.

But it stresses that, while the noise is a well-known aspect of the A320, it has never been a source of concern to customers.

---

Unfortunately the article is incorrect, how embarassing for Airbus. I assume the journalist made a gross misunderstanding, otherwise I am fearful of the single aisle ATA29 team's competency!

What is described, are probably the addition of attenuators / helmholtz resonators(which they are calling 'dampers'), which do help to reduce fluid borne pulsation and might help to reduce the in flight 'whine', but will do diddly squat to silence the PTU.

To stop the dog barking at the gate is very simple, simply turn the green system EMP off before shutting down the engines. Alternatively, press the PTU button on the hydraulics panel and it closes the PTU shut-off valve, if taxiing on the LH engine this would stop it operating un-necessarily during single engine taxi as well.

Personally I have seen passengers truly alarmed by it, and it annoys me because the purpose of the PTU is purely to help retract landing gear following a single engine failure, and can in fact be uni-directional - but because A320 is FBW, this drives you to a bi-directional one - and for some silly reason, the EMP is in the yellow system instead of the green where it's needed.
A bi-directional PTU with the EMP in the wrong system=dog bark.

This is fine except because the thirtiest landing gear consumers you're trying to support with the EMP are in the wrong system you have big efficiency losses trying to power them - the EMP is approx 76% efficient taking into account AC motor losses, volumetric and mechanical efficiency losses, but you're then turning two pumps connected by a shaft, losing a further 20% - in all, only half the delivered power becomes useable pressure. The rest becomes heat, and noise.

Heat in hydraulics is very bad. I personally spent a week in a lab watching a PTU slowly destroy itself from overheating (not A320, but easily could have been), as the elevated temperature breaks down the skydrol into corrosive microgel which then attacks the internals of the system, but this only occurs with low-demand prolonged 'chugging' that you all know as the barking dog. A single 'bark' by the way is the sudden spool-up of the PTU to 1500rpm or so before it crashes to a stop again. This creates a surge of flow until pressure balances, and is a saw-tooth stop-start profile.

As a result, I later sketched up a new design for a PTU that would greatly improve the redundancy and efficiency of a 3-system FBW aircraft by placing a back-driveable motor-generator between the two pumps driven through a differential gearbox and patented it, but at the time I was frustratingly not allowed to build it.

Rumour is, my patent is now being used on the Cessna longitude, and I'd love to see it implemented on A320, precisely because you would never hear it bark.
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767333ER
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Re: Airbus Muzzles The Barking Dog

Wed Jun 15, 2016 10:06 pm

masi1157 wrote:

The EMPs are even easier to reduce because they run at constant speed. The EDPs are driven by the engines' N2 that varies quite a bit. During cruise their noise can become rather nasty in the cabin above the MLG bay. That is what the extra silencers are for. The PTU noise is not changed at all.

Gruß, masi1157


On the A320 and most other planes that planes that have a motor pump constantly running throughout the flight the pump is barely audible or not audible at all because they are drowned out by the far louder engines. The only plane I can think of where the motor pumps are terribly loud is the 787, but they only run on demand. On the A320 the, the blue system pump is the one that always runs and it seems much quieter than the yellow system pump even though they are the same part. I know on the 737 for example they have mufflers attached to the motor pumps, but I'm not sure how much of an effect they have.
Been on: 732 733 734 73G 738 752 763 A319 A320 A321 CRJ CR7 CRA/CR9 E145 E175 E190 F28 MD-82 MD-83 C172R C172S P2006T PA-28-180

2 ears for spatial hearing, 2 eyes for depth perception, 2 ears for balance... How did Boeing think 1 sensor was good enough?!

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