Well frankly I am stunned at the wealth of info in reply to my brief question. Thanks, guys!. .. . </font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica"> I dont know if small em is taking an exam or looking at the practical side.</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">It was partly just wanting to know How Things Work, and partly practical - but not even aviation related. I was musing over an engineering problem that involves a fan in a tube (no clues - patent pending!), and it struck me that it was similar to what I understood compressor stall to be. Turns out I was on more-or-less the right lines.. .. .em