OD-BWH From , joined Dec 1969, posts, RR: Posted (10 years 12 months 4 days 4 hours ago) and read 11984 times:
I've recently flown onboard the A330-200 and A321, and in both aircraft, a loud knocking noise was heard everytime the landing gears are deployed before landing. I've heard that many times. What is this noise from?
I've flown the 777 also, and i'm sure there's no such noise...
LimaFoxTango From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 12 months 4 days 2 hours ago) and read 11916 times:
im guessing that noise you hear is when they locked into place when fully extended. you will tend to hear this knock on any aircraft that has retractable gears. you will also hear that knock as the retact as well. i guess some are louder than others. i guessing someone here will elaborate on the technical side of it.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 7, posted (10 years 12 months 3 days 3 hours ago) and read 11719 times:
The oleos are already at full extension when the enter the gear well. Thus, when the gear is extended there should be no noise from shock strut (oleo) extension. There is a small variety of things you may be hearing. I'm no Airbus expert (worked Boeings and Douglas most of my career), but I suspect you're hearing the doors closing after the gear extension cycle is complete. You may also be hearing the gear locking mechanism going over-center, but I doubt it.
Wirelock From , joined Dec 1969, posts, RR:
Reply 8, posted (7 years 9 months 3 weeks 3 days 17 hours ago) and read 11331 times:
Oleos are pressurized so the are always at full extend unless with aircraft weight on them. done a few functional tests of the A320 LDG in my time. from looking at this from the outside the things that make noise are the sound of the over centre locks engaging, doors closing. sometimes the PTU will kick in so maybe you are hearing this
JetMech From , joined Dec 1969, posts, RR:
Reply 11, posted (7 years 9 months 3 weeks 2 days 16 hours ago) and read 11161 times:
Quoting Air2gxs (Reply 7): The oleos are already at full extension when the enter the gear well. Thus, when the gear is extended there should be no noise from shock strut (oleo) extension.
Quoting Tdscanuck (Reply 10): There are a (very) few airliners that can retract the oleos prior to stowage for space reasons
The A330 / A340 has a gear shortening mechanism on the wing gears. The external crank mechanism for this can be seen just ahead of the rear wing landing gear trunnion point in this photo.
What you both say is true however. The pressurised nitrogen and landing gear fluid are housed in a "shock cartridge" that is free to slide up and down inside the main landing gear casting. Thus, when the A330 / A340 wing landing gear retracts, the crank pulls the sliding shock cartridge into the main landing gear casting via a mechanical linkage internal to the landing gear casting. The sliding shock catridge in turn pulls the inner cylinder, bogie beam and hence wheel and brake assemblies towards the main gear casting as well. The end effect is a physical shortening of the wing landing gear.
The internal mechanism is so arranged that upon extension of the wing gear, an overcentre lock is formed inside and against the wing gear main casting upon full lengthening of the gear. This overcentre mechanism locks the sliding shock cartridge inside the main gear casting, and allows it to take the landing shock as well as the weight of the aircraft.
You are corrrect. As you know, but I will explain for those who don't, the wing gear for both A330/340 shorten because it is the same gear for both aircraft. It has to shorten due to the lost space where the ctr gear stows on a A340 but be long enough for ground clearance for A330 larger engines. Jean Dixon predicts: But the A330 has no center gear? Again, correct, but the big empty space is still there.