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A330 Yaw And Roll Stability Vs 777  
User currently offlineQantasHeavy From Australia, joined Jan 2005, 379 posts, RR: 1
Posted (8 years 11 months 1 day 22 hours ago) and read 5956 times:

I ride the A330, 737-800 and 767 almost weekly and the 777/747-400 at least monthly.

Have noticed that the A330, while quiet and smooth in the cruise phase, seems to be particularly unstable in the descent phase of the flight. It seems to "float" with considerable yaw and roll. The Boeing aircraft seem to hold their angle of attack with and experience upward or sideways movement from winds, etc., where the 330 feels as though it moves about its axis considerably in any unstable air. Not to say turbulence does not effect all of the types, but the 330 seems to consistently feel loose on descent.

Not trying to start an A vs. B argument, but I fly often and the difference in the sensation of movement is quite noticable. Was sitting next to an Emirates exec recently on an 330 who, during some very rough aircraft movements while descending, who commented that the Airbus wing makes it feel much more unstable in turbulence and that the effect on the flight deck is even worse.

If there a fundamental design difference that makes one appear more stable than the other... a 777 seems to plow through much more smoothly.

19 replies: All unread, jump to last
 
User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 11 months 1 day 22 hours ago) and read 5915 times:

I think crosswind corrections with Airbus sidesticks are a bit tricky relative to corrections using traditional yokes.

User currently offlineJush From Germany, joined Apr 2005, 1636 posts, RR: 3
Reply 2, posted (8 years 11 months 1 day 22 hours ago) and read 5864 times:

Quoting N79969 (Reply 1):
I think crosswind corrections with Airbus sidesticks are a bit tricky relative to corrections using traditional yokes.

How should that explain the effect mentioned as the descent is usually done under autopilot.
I can't help you out with information though.

rEgds
jush



There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
User currently offlineA319XFW From , joined Dec 1969, posts, RR:
Reply 3, posted (8 years 11 months 1 day 21 hours ago) and read 5807 times:

You might get more/better answers in Tech/Ops

User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 4, posted (8 years 11 months 1 day 21 hours ago) and read 5750 times:

Quoting Jush (Reply 2):
How should that explain the effect mentioned as the descent is usually done under autopilot.
I can't help you out with information though.

I do not know. Perhaps the human or computer input are very similar in terms of correction...That is just my own guess.

I had a chance to speak to a few A320 pilots and also to fly a full-motion A320 simulator. The cross wind correction felt weird to me. (But then again I am a low hour private pilot) The A320 pilots said it took some getting used to...


User currently offlineIkramerica From United States of America, joined May 2005, 21562 posts, RR: 59
Reply 5, posted (8 years 11 months 1 day 20 hours ago) and read 5642 times:

there's a 777 pilot (capt. Lim) who has a blog who talks about this issue re: stability and turbulence and how the design of the 777 wings especially helps out in various situations that will disturb a 330/340 more. This is not an issue of safety by any means, nor does he imply that, only a matter of wing and stabilizer design philosophy.

but again, ask in tech ops. someone will have more details on the answer.



Of all the things to worry about... the Wookie has no pants.
User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6517 posts, RR: 54
Reply 6, posted (8 years 11 months 1 day 15 hours ago) and read 5510 times:

Any wing just produces lift to counter gravity. When there is turbulence, then there really isn't much a wing designer can do about that.

QantasHeavy, you seem to have a rather routine flight schedule. Could it be so that you mostly land with the 777 in the morning, evening or at nighttime? And often land on a bus at midday or in the afternoon?

Most severe turbulence is created by the sun producing different heating on different landscape types. Therefore it will be most prominent from noon until late afternoon.

Quoting N79969 (Reply 1):
I think crosswind corrections with Airbus sidesticks are a bit tricky relative to corrections using traditional yokes.

You don't fight crosswind with a sidestick or yoke. You fly down the final approach straight and level with a track which fits the glideslope, but a heading slightly into the wind. Then just before touch down you adjust your heading to fit the track, not with sidestick/yoke, but with the rudder pedals. Game over.

On smaller airliners you sometimes sideslip a little to keep track and heading equal down the glideslope, and then land on one wheel only.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineDon81603 From Canada, joined Jul 2005, 1185 posts, RR: 0
Reply 7, posted (8 years 11 months 1 day 15 hours ago) and read 5500 times:

Quoting A319XFW (Reply 3):
You might get more/better answers in Tech/Ops

Uh, this IS Tech/Ops...



Eagles may soar, but weasels don't get sucked into jet engines.
User currently offlineGreasespot From Canada, joined Apr 2004, 3085 posts, RR: 20
Reply 8, posted (8 years 11 months 1 day 14 hours ago) and read 5497 times:

Quoting N79969 (Reply 1):
I think crosswind corrections with Airbus sidesticks are a bit tricky relative to corrections using traditional yokes.

 no 

Both the 330 and 777 are fly by wire.....A computer is doing the actual flying....NOT the control sticks....The computer just reacts to inputs...



Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17118 posts, RR: 66
Reply 9, posted (8 years 11 months 1 day 14 hours ago) and read 5493 times:

Quoting Greasespot (Reply 8):

Both the 330 and 777 are fly by wire.....A computer is doing the actual flying....NOT the control sticks....The computer just reacts to inputs...

Hey, Ms Spot is back! Missed ya!

I agree that the physical input controller should matter little. The Airbus stick is a roll rate selector, while the Boeing yoke is a proportional flight surface deflection controller. However, as has been stated, the autopilot is flying in the phases of flight described so what's the diff?

Is it the wing or the stability programming built into the flight control systems?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 10, posted (8 years 11 months 1 day 14 hours ago) and read 5483 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting Starlionblue (Reply 9):
Is it the wing or the stability programming built into the flight control systems?



His description of the feel sounds as if it's a mild form of dutch yaw stability. If that's the case, it could be related to any number of things....wing dihedral, wing sweep, yaw damper performance, etc.

The tail on the 777 could be a little more effective than the 330 at damping the oscillations, as well.




2H4





Intentionally Left Blank
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 11, posted (8 years 11 months 1 day 14 hours ago) and read 5479 times:

Quoting Don81603 (Reply 7):
Quoting A319XFW (Reply 3):
You might get more/better answers in Tech/Ops

Uh, this IS Tech/Ops...

Often, technical threads will get moved over here from GA. That was probably posted before it was in Tech/Ops.



Position and hold
User currently offlineStratofortress From United States of America, joined Dec 2005, 178 posts, RR: 1
Reply 12, posted (8 years 11 months 1 day 11 hours ago) and read 5445 times:

777 is bigger than 330 and therefore will experience less impact from turbulence. More mass (777) needs more force to be moved, hence identical turbulence/crosswind will have greater effect on 330 than 777... A little Cessna will get tossed around in winds that have no significant impact on a 747.

Additionally, the difference in damper performance and actual airfoil design (as already mentioned in other posts) may enhance the effect of physics described above.



Forever New Frontiers
User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 13, posted (8 years 11 months 1 day 11 hours ago) and read 5444 times:
AIRLINERS.NET CREW
DATABASE EDITOR



How does the wing loading compare? All else being equal, how much of a difference would that make?




2H4





Intentionally Left Blank
User currently offlineAA777 From United States of America, joined May 1999, 2544 posts, RR: 28
Reply 14, posted (8 years 11 months 1 day 9 hours ago) and read 5425 times:

I flew IAD-AMS last week on a KL 332, and we took off in a crosswind, and as soon as the nose lifted off I felt oscillations and rolling that seemed rather uncontrolled. It was actually a very uncomfortable feeling, that I have never felt to such an extent on any plane, and certainly never on a 777. The rest of the flight was great though, very smooth and VERY quiet. I would also say that the 332 seemed to float or feel like it was flying lighter through the air... hard to describe. But it feels like the 777 has more presence in the air, is less easily tossed about.

-AA777


User currently offlineStratofortress From United States of America, joined Dec 2005, 178 posts, RR: 1
Reply 15, posted (8 years 11 months 1 day 9 hours ago) and read 5416 times:

The higher the wing load, the more "turbulence resistant" the aircraft.

A highly loaded wing has higher inertia, hence it will take higher force to affect its state i.e. move it in a different direction. A wing with 50 lbs/sqft load will be harder to move than a 40 lbs/sqft loaded wing. A heavy box is easier to move than a light box.... you get the idea.

Based on the quick calculation, an empty 330-300 has a wing loading of 69 lbs/sqft, while an empty 777-300 is around 77 lbs/sqft, which means that 777 will be less affected by the gusts.


Since we are on the topic of turbulence: Do two heavis take off closer to each other, than a heavy followed by an empty 737?... I should probably start another tread to answer this question.



Forever New Frontiers
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 16, posted (8 years 11 months 1 day 4 hours ago) and read 5382 times:

Quoting Stratofortress (Reply 15):
A heavy box is easier to move than a light box

A good analogy, but I think you wrote it backwards. The light box will be more easily tossed around by turbulent winds than the heavy one  Smile

Quoting Stratofortress (Reply 15):
Do two heavis take off closer to each other, than a heavy followed by an empty 737?

Wake turbulence is an entirely different animal. Again, wing loading plays a large part, not just overall weight; this is why 757s will often be treated as "heavies" even though they're not widebody. A plane in a lighter wake turbulence category departing after a heavier one should plan to lift off the runway before and climb slightly above the heavier jet to avoid its wake. Similarly, on descent, the lighter jet should descend slightly above and touch down slightly after the heavy. There are also time seperation requirements; ATC, being responsible for issuing takeoff and landing clearances, is very well-versed in them. The wake can be moved around by winds though, and that's part of the reason ATC will instruct the lighter jet "caution wake turbulence." Like all clear-air turbulence, it's impossible to see, but more dangerous than "normal" turbulence caused by wind shear aloft because of its spinning nature. It has the potential to invert a plane very quickly.



Position and hold
User currently offlineStratofortress From United States of America, joined Dec 2005, 178 posts, RR: 1
Reply 17, posted (8 years 11 months 23 hours ago) and read 5311 times:

Ooops! Sure did get it backward. Should have stated "A light box is easier to move than a heavy box.... you get the idea."

Thanks.



Forever New Frontiers
User currently offlineMandala499 From Indonesia, joined Aug 2001, 6957 posts, RR: 76
Reply 18, posted (8 years 11 months 23 hours ago) and read 5292 times:

How about one doing a VSI/SPD descent off the VNAV profile while the other's doing an open descent/LVL CHG descent in light turbulence?

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineEKDriver From United Arab Emirates, joined Jan 2006, 16 posts, RR: 3
Reply 19, posted (8 years 10 months 2 weeks 3 days ago) and read 4976 times:

I've flown many Airbus types, and have felt the ride is MUCH better and more controlled than most Boeings i've ever flown. The Soft altitude the Autopilot uses when at the cruise altitude, makes small altitude excursions +/- 100' hardly noticeable.

As for unstable in the descent, have many hours on the 330, its a BIG wing, very efficient especially the -200. I've never had any problems. The RR engined version is a bugger to slow down, but its a great ship.

I've been on the 777 in fairly bumpy conditions and like the ride it also provides.

EKDriver


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