Path: utzoo!utgpu!watserv1!watmath!att!cbnews!military
From: willner%cfa183@harvard.harvard.edu (Steve Willner)
Newsgroups: sci.military
Subject: Re: Soviet F/B
Message-ID: <15569@cbnews.ATT.COM>
Date: 14 Apr 90 04:10:52 GMT
References: <15435@cbnews.ATT.COM>
Sender: military@cbnews.ATT.COM
Lines: 41
Approved: military@att.att.com



From: willner%cfa183@harvard.harvard.edu (Steve Willner)
In article <15435@cbnews.ATT.COM>, referring to the "Cobra maneuver"
performed by the Su-27, I asked:
> Does 110 or 120 degrees refer to _angle of attack_ or to _pitch angle_?  
> The two are not synonymous; I can easily believe the latter, but the 
> former seems almost impossible.  
 
Here's what Aviation Week had to say in their March 5 issue:
"[Two Soviet pilots] flew several "Cobra" profiles, a rapid deceleration
maneuver during which the throttles are cut on the Su-27's two
30,000-lb. thrust Lyulka AL31F engines and the aircraft is pitched
rapidly up past the vertical position, sometimes as far as 110-120 deg. 
As the aircraft decelerates, the nose is pitched down and the aircraft
is recovered with power and accelerated in horizontal flight."
 
The article also states that the speed goes from 200 to 65 knots and
the altitude loss is only 100 feet.
 
The AWST information refers to pitch angle, but what about angle of
attack?  Mary Shafer has kindly explained to me that the whole pitch-up
maneuver takes place so rapidly that the airplane flight path continues
forward.  This means that the angle of attack is essentially equal to
the pitch angle and really does exceed 90 degrees.  This means that the
Su-27 was (briefly) flying (slightly) backwards!  
 
I'm impressed!   
 
[Mary also makes the point that aeronautical types use many different
coordinate systems.  Here I'm using "pitch angle" to mean the
instantaneous angle between horizontal and the aircraft fuselage
reference and "angle of attack" to mean the angle between fuselage
reference (or airfoil reference) and the relative wind.  I think these
are the usual definitions in semi-technical discussions.  In a steady
vertical climb, for example, the pitch angle would be 90 degrees and
the angle of attack would be 0 degrees by these definitions.]  
 
Mary also points out that the Cobra maneuver actually takes very little
time, though some slow-motion videos don't make that obvious.
~