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

Mcrit over wings or not?

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

Mcrit over wings or not?

Old 4th Feb 2008, 16:16
  #1 (permalink)  
Thread Starter
 
Join Date: Nov 2003
Location: Northern CND
Posts: 15
Likes: 0
Received 0 Likes on 0 Posts
Mcrit over wings or not?

In my books they talk of Mcrit as point on the WINGS where airflow reaches M1.0. However on an aircraft like the 747 airflow will reach M1.0 over the hump before the wings.

So is:

Mcrit the speed when airflow over a point on the WINGS reach M1
OR
Mcrit is the speed when airflow over a ANY point on the aircraft reaches M1.

Thanks
themulleye is offline  
Old 4th Feb 2008, 19:34
  #2 (permalink)  
 
Join Date: May 2007
Location: Manchester, UK
Age: 38
Posts: 128
Likes: 0
Received 0 Likes on 0 Posts
My understanding is that Mcrit is the highest speed at which no parts of the aircraft are supersonic. So in the context of this definition it wouldn't really matter whether the first part to go supersonic is the wing, or in the case of the 747, the hump.
David Horn is offline  
Old 4th Feb 2008, 22:04
  #3 (permalink)  
 
Join Date: Aug 2003
Location: Sale, Australia
Age: 80
Posts: 3,832
Likes: 0
Received 0 Likes on 0 Posts
Extensive discussion here by people who have some grip on the subject http://www.pprune.org/forums/showthread.php?t=83506

Post #29 by Flamgat in the above thread includes Boeings definition

"Critical Mach number is a term aerodynamicists use to quickly compare the "drag rise" or "compressibility drag" of several wing design alternatives. At Boeing, we define critical Mach number as the Mach number, at a constant lift coefficient, where the drag coefficient is 20 counts greater than the drag coefficient at the incompressible Mach number."

Last edited by Brian Abraham; 4th Feb 2008 at 22:14.
Brian Abraham is offline  
Old 5th Feb 2008, 00:19
  #4 (permalink)  
 
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,179
Likes: 0
Received 0 Likes on 0 Posts
I suspect it could legitimately be used to mean anything, depending on how it was phrased.

"Mcrit" of the aircraft
"Mcrit" of the wing (3d)
"Mcrit" of the section (2d)

And so on...

It doesn't really have much importance as a practical concern, once the design has started, anyway....
Mad (Flt) Scientist 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.