Originally Posted by Dan Winterland
PBL. Thanks for the diagram. I had to stare at it for a long time before I could work out what it was trying to tell me. I thinks it's what I always understood - that lift decreases with compressability.
What I was hoping it would tell you is that C_L_Max occurs at different angles of attack depending on Mach number. Which shows (if you take C_L_Max to represent the point of stall) that the point of stall is dependent on Mach number, contrary to your suggestion that the "notion[.] ... that stall is speed dependent .... ha[s] been eradicated years ago"
BOAC seems to want to maintain the view that this stuff is "theory" (whatever that may mean; we are talking about the physical characteristics of the airfoils you chaps fly, as demonstrated by wind tunnel data). I find that a bit odd, since Boeing Aero is a magazine which is designed to address practical issues for pilots, so one may take it that Boeing thinks this "theory" is relevant to flying their airplanes.
BOAC says
Originally Posted by BOAC
from a piloting point of view- compressibility etc has no relevance on stalling
I can't see that. The diagrams tell me a different story. Not to you?
Originally Posted by BOAC
the driver nowadays has guidelines of 'normal' pitch attitudes at different altitudes and does not need to know or care about shock separation,
Shock separation occurs with overspeed. We were talking about stall.
Originally Posted by BOAC
.....As long as he/she can differentiate between high-speed and low-speed buffet and carry out the appropriate recovery action, that is enough.
With respect, no it's not enough. There are two different kinds of high-speed buffet: that caused by approach to stall and that caused by overspeed. The "appropriate recovery actions" are different in those two cases and the pilot needs to distinguish them. Anecdotal simulator evidence, from a reliable source, suggests to me that not all line pilots can.
BTW, I am curious as to what the new Airbus procedures are for stall warning at cruise altitudes. It used to be to reduce back-pressure on the stick.
Also BTW, I am surprised that some people are suggesting you can't stall an Airbus (say, an A330) in Normal Law. You can, obviously, if you encounter a strong-enough gust. You can also stall it in Alternate Law, for the same reason. And in Alternate Law, in case of an ADR DISAGREE, high-AoA protection is lost in any case, so you can stall it without a gust in that situation.
PBL