Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

buffet margins

Tech Log The very best in practical technical discussion on the web

buffet margins

Old 15th Nov 2010, 03:23
  #1 (permalink)  
Thread Starter
 
Join Date: Jun 1999
Location: over there
Posts: 117
Likes: 0
Received 0 Likes on 0 Posts
buffet margins

Can anybody give me the answer to the following;

1)What is the minimum acceptable margin against the stall buffet at cruise?

My answer is .3g but not sure.

2)What is the normal margin against buffet at optimum cruise?

My answer would be 1.3g but then again not 100% sure

Thanks

Mango
Mango is offline  
Old 15th Nov 2010, 03:56
  #2 (permalink)  
 
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,179
Likes: 0
Received 0 Likes on 0 Posts
From the Airbus publication "Getting to Grips with Aircraft Performance", page 145:

In order to maintain a minimum margin against buffeting and ensure good aircraft maneuverability, it is necessary to determine an acceptable load factor limit below which buffeting shall never occur. This load factor limit is generally fixed to 1.3. This value is an operating limitation, but not a regulatory one. The corresponding altitude is called the “1.3g buffet limited altitude” or “buffet ceiling”.
So 1.3 is a "normal minimum" but I'm sure someone has a counterexample out there somewhere.

The example that follows indicates a case where the selected cruise Mach could be in a range where the buffet margin is 1.3 or greater. There will be cases where the optimum lies in the middle of that range, and so the margin would be higher than 1.3.
Mad (Flt) Scientist is offline  
Old 15th Nov 2010, 19:13
  #3 (permalink)  
 
Join Date: Jul 2007
Location: The Netherlands
Age: 40
Posts: 81
Likes: 0
Received 0 Likes on 0 Posts
Airbus excepts the cruise altitude (ALT CRZ) that provides a margin of .2. Higher it will not except.
zonnair is offline  
Old 15th Nov 2010, 20:00
  #4 (permalink)  
 
Join Date: May 2001
Location: A few degrees South
Posts: 809
Likes: 0
Received 0 Likes on 0 Posts
.3 is a luxury. In the old non-FMC planes you (and the flight engineer) decide for yourself. .2 and .25 were common.
latetonite is offline  
Old 16th Nov 2010, 10:01
  #5 (permalink)  
Thread Starter
 
Join Date: Jun 1999
Location: over there
Posts: 117
Likes: 0
Received 0 Likes on 0 Posts
Airbus excepts the cruise altitude (ALT CRZ) that provides a margin of .2. Higher it will not except.
The .2g buffet is a airbus FMGC limitation but as "Mad (Flt) Scientist" stated the 1.3g is an operating limitation. So I'm still not sure what the answer is.

If anybody could clarify this for me that would be great.

mango
Mango is offline  
Old 18th Nov 2010, 07:48
  #6 (permalink)  
 
Join Date: Oct 2010
Location: Below Radar
Age: 54
Posts: 16
Likes: 0
Received 0 Likes on 0 Posts
G margins and their representation on the PFD

I am not aware that 0.3 is a limitation, but think of it like this:

0.2g you need to bank the aircraft at least 33 degrees to get the low of high speed buffets, and as you know that the airbus A320 family VLS represent 0.2g.

0.3 you need at least 39.7 almost 40 degrees of bank and the airbus long range VLS is representing 0.3g.

VLS is corrected for Mach effect to maintain either 0.2g or 0.3g buffet margin (aircraft specific), I think it happens at or above 25000ft but not positive about the altitude.

From an operation point of view you might want to have 0.3g margin in turbulence conditions.

TruthHurts
TruthHurts is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.