XFSUgimpLB41X From United States of America, joined Aug 2000, 3695 posts, RR: 36 Reply 1, posted (10 years 10 months 2 days 5 hours ago) and read 5911 times:
DBOBA From Germany, joined Aug 2001, 21 posts, RR: 0 Reply 2, posted (10 years 10 months 1 day 14 hours ago) and read 5874 times:
That is probably the Power Transfer Unit (PTU), a product produced by a very well knon German company. That device is very efficient, but they forgot to think about the sound. So if you hear the sound - everything is allright.
Gordon
Klaus From Germany, joined Jul 2001, 20145 posts, RR: 57 Reply 3, posted (10 years 10 months 1 day 12 hours ago) and read 5867 times:
DBOBA: That is probably the Power Transfer Unit (PTU), a product produced by a very well knon German company. That device is very efficient, but they forgot to think about the sound. So if you hear the sound - everything is allright.
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 9 Reply 5, posted (10 years 10 months 20 hours ago) and read 5842 times:
The Power Transfer Unit is used to transfer hydraulic power between the 2 main systems without transferring any fluid. This is accomplished by having a hydraulic motor in one circuit, connected to a hydraulic pump in the second circuit. I think Airbus calls them the red and green circuits. Say the pump is in the red, the motor in the geen. When red pressure drops, the motor on the green side starts to turn, thereby turning the pump on the red side, increasing the flow of hydraulic fluid on the red side. This raises the pressure back to normal, and the unit stops.
The reason for the noise is that the PTU accelerates up very fast, then stops just as suddenly. Each burst of speed takes a couple of seconds -- maybe as much as 5. The it stops for a while, and as pressure drops in red to a certain level, it picks back up.
The PTU is a safety measure, used when one engine is out and there is insufficient hydraulic power in that system to drive a selected function (say flap, or landing gear). The PTU is bi-directional, so it can supply either side when as needed.
Gordon - There are 2 PTU manufacturers on the A320 family - the 321's and 319's have a different design which is quieter than the original A320 PTU's. Also, as far as I know both PTU's are US designs, but the earlier model may be made in a German plant - I don't know for sure. I know one of the guys who designed the original A320 PTU and I was on the team that designed the newer one.
Regardless of which PTU is installed, the self-test described above is noisy. Stay away from Row 13!
SUDDEN From Sweden, joined Jul 2001, 3956 posts, RR: 7 Reply 6, posted (10 years 10 months 17 hours ago) and read 5811 times:
I work at an airport and I must agree that the A-320 engines have a sound of it's own. I was on a flight ones, and this sound You could also hear from inside. It comes as soon as the trottle up for T/O. Sat beside a woman that tought something was wrong with the plane, but I calmed her down and told her that the sound from the engines is correct. But have also wonderd why they have this sound.
Boeing-Lover From , joined Dec 1969, posts, RR: Reply 7, posted (10 years 10 months 13 hours ago) and read 5797 times:
Hi,
having talked with somebody who worked long years for airbus (marketing), he told me that at the beginning of the A320 era (meaning the A320-100) there were several problems with passengers complaining about the noise being to loud while flying. With this passenger input a new cabin isolation were installed (A320-200 and A320-100 being refitted) to reduce the noise and I must admit that Airbus did a goog job here, because toay the A320 is quiet in the cabin, although he´s it´s own special sound.
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 9 Reply 8, posted (10 years 10 months 12 hours ago) and read 5794 times:
From the above posts, it appears that the noise in question is not the PTU, since it only runs for a minute or so during engine startup, and then in during an in-flight engine shutdown.
F-WWAI From Andorra, joined Dec 1999, 131 posts, RR: 0 Reply 9, posted (10 years 10 months 9 hours ago) and read 5804 times:
depends on when the specific sound was heard:
a) PTU (hydraulic Power Transfer Unit),
a swash-plate multiple piston two-way motor/pump,
is tested briefly during second engine start, will only give few cycles of noise (kind of grinding rough) IF PARKING BRAKE IS ON.
If Parking brake is off, and one engine is running, the PTU stays ON until the second EDP delivers correct pressure. That may last a while and is a bit annoying to the pax in the seating area concerned. It happens at departures at Air France due to special push-back equipment.
The PTU may, under certain condition also come ON for a few cycles during Landing Gear retraction after lift-off.
b) airborne single tone fan noise
is present on high by-pass turbofans during and after take-off. It's the consequence of fan blades running supersonic and depends on power setting and airspeed. Disappears at higher airspeed.
A320 Engine Air Intakes have been improved for better noise suppression after the initial level was judged a bit "challenging" for passengers. The old air intakes on the very first serial numbers are, however, still around and you might fly on them in Europe. It's not a big issue anyway.
is the sound you were adressing in the the initial query one of the above?
cheers,
FW
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 9 Reply 11, posted (10 years 10 months 6 hours ago) and read 5779 times:
Further to what I said earlier about the PTU, I used the example of red and green systems. Now I am in the office and I checked on my data and discovered that Airbus calls them Yellow, Green. The PTU is between Yellow and Green.
Goldenshield From United States of America, joined Jan 2001, 5040 posts, RR: 14 Reply 12, posted (10 years 9 months 4 weeks 1 day 16 hours ago) and read 5755 times:
could "before takeoff" also be confused with, say, "before pushback"?. I know alot of people dont know the correct term.
and if that is the case, the ground hydraulic system is on for the operation of the cargo doors, and brakes.
the MD-80 has a really bad habit of being noisy with its aux pump as well.
Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
Sebolino From France, joined May 2001, 3611 posts, RR: 6 Reply 13, posted (10 years 9 months 4 weeks 1 day 11 hours ago) and read 5753 times:
The sound is heard while the plane is pushed back or rolling to the track for take off. it's a short sound which occurs many times, say 20 to 40 times.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 14, posted (10 years 9 months 4 weeks 1 day 11 hours ago) and read 5751 times:
I just figured it out. The Clunking that you hear are the brakes. 20 to 40 times though.... hmmm must be a long or hilly taxi to the runway. And yes, I guess that would sound like luggage moving.
XFSUgimpLB41X From United States of America, joined Aug 2000, 3695 posts, RR: 36 Reply 15, posted (10 years 9 months 4 weeks 1 day 6 hours ago) and read 5740 times:
Its definitely the hydraulic transfer units... Ive been around A320's for many years.. Youll sometimes hear them at the gate, but it is mostly during taxi before departure. It is really the only noises youll hear during taxi...and they are quite loud especially if you have the wing seats. I cant really type house it sounds.. but it is kinda of a woooooo.. wooooooo. some times it is in short bursts, and other times longer ones. People always have some really wild guesses as to what it is...but i can assure you everyone always comes off the A320 asking what the heck that was...and that is it.
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 9 Reply 16, posted (10 years 9 months 4 weeks 22 hours ago) and read 5731 times:
Definitely sounds like the PTU. It runs between the first and second engine starts. The second engine may not be started until the a/c is near the runway -- ie taxi on one engine to save fuel.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1 Reply 17, posted (10 years 9 months 4 weeks 18 hours ago) and read 5726 times:
You guys seem to be fixated on this PTU. The poster added additional information and said 20 to 40 times on the way to the runway. My company prohibits single engine taxi and yet we still experience the noises that Sebolino describes. The PTU is definitely not operating with both engines running. I am sticking with my previous post for now.
XFSUgimpLB41X From United States of America, joined Aug 2000, 3695 posts, RR: 36 Reply 18, posted (10 years 9 months 4 weeks 16 hours ago) and read 5725 times:
My dad flew the thing for 8 years. Everytime we ride someone always asks him what that noise is during taxi (with both engines running), and every time it is the same answer- the hydraulic transfers.
Cricri From France, joined Oct 1999, 581 posts, RR: 9 Reply 19, posted (10 years 9 months 4 weeks 13 hours ago) and read 5724 times:
During the years i worked as flight attendant, i didn't count all the times when pax called me to tell that it's a shame to put a dog in the cargo area because it was barking all the time. In fact and depending on everyone's perception of course, the PTU sound can be compared to a barking dog for persons hearing it for the 1st time..
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 9 Reply 20, posted (10 years 9 months 3 weeks 6 days 23 hours ago) and read 5703 times:
Assuming that a plane taxis to the runway on a single engine, the PTU noise is very likely. As one of the engineers designing the newer PTU, I was advised that scenario was possible -- despite JG's airline prohibiting that practice.
NoUFO From Germany, joined Apr 2001, 7479 posts, RR: 15 Reply 22, posted (7 years 1 month 4 weeks 1 day 17 hours ago) and read 5598 times:
Quoting DBOBA (Reply 2): That is probably the Power Transfer Unit (PTU), a product produced by a very well knon German company
Produced by a very well known American company. One of our American friends here worked on its development. The same company produced its successor which is a bit slower but less noisy.
Beautiful things can be built even from stones placed in your way. - Goethe
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