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  #11  
Old 09-24-2010, 08:20 PM
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mike newall mike newall is offline
 
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Pierre,

Interesting - normally our 320/321/330's are rock solid in the cruise, however the mini busses do have a tendency to have a strange tail end roll movement when you are descending fast - 340kts.

Stops when you level to decelerate and configure to land

340kts to 15 miles is quite achievable......
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  #12  
Old 09-24-2010, 09:01 PM
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Ironflight Ironflight is offline
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I was playing with it a little more on the long cruise from California today - still there, but let me not overemphasise it. Many people wouldn't notice it at all. Definitely not a case of sensor quantization - we don't even see a tick in altitude or picth - it is simpply something I can feel. The interestign thing is that once you have it trimmed properly, it goes away - much "finer" trim indictaor than even the display can give you.

Paul
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  #13  
Old 09-29-2010, 09:41 AM
elippse elippse is offline
 
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[quote=Alex;470069]It sounds like you have a classic example of a limit cycle going back and forth over a deadband boundary.
QUOTE]

As well as servo deadband, it might also be control-surface deadband due to boundary-layer buildup. There are a number of ways to alleviate this. One of these is to thicken the upper and lower leading-edge surface of the elevator by 10% of the thickness of the trailing edge of the horizontal stab. This thickening would have the appearance of a curved surface tangent to the edge of the gap and the following surface, more-or-less a quarter-round. In connection with this thickening, by blended it so as to produce a slighlty concave surface on the upper and lower elevator surfaces, this is even better. By doing this, three results will occur; the dead-band will be decreased, the horizontal surface drag will be reduced about 10%, and the flutter tendency will be reduced. Hooray for Bondo!
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  #14  
Old 12-06-2010, 04:21 AM
chrish chrish is offline
 
Join Date: Nov 2010
Location: Australia
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Quote:
Originally Posted by pierre smith View Post
Last December, my wife and I flew in an Airbus mailing tube, out to California, and the darn thing had the most annoying slight Dutch roll the whole way....very annoying but it would roll a couple degrees right, hesitate, then roll a couple degrees left...for thousands of miles!

The proud front crew were standing, thanking everyone as they de-planed and I hesitated and told the Captain, "Sir, don't be offended but I'm a CFI and your airplane did Dutch rolls all the way out here. The autopilot needs adjusting, I think." To which he replied, "I didn't think anyone would notice."
Best,
I noticed this in the cruise on my first jump seat familiarisation ride while converting to the 330. I think the 330-200 does it more noticeably than the 330-300 (the 200 is shorter). After 5 years I am used to it, but anyone down the back gets a rock and roll ride, especially in turbulence. Not uncommon to have people throwing up in the last couple of rows ;-)
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