bunyip I don't know what you on about, or what you're confusing in Kermode's book, but please please stop saying
<font face="Verdana, Arial, Helvetica" size="2">...if you have an infinite A you would not have wingtip vortices and so you would not have any lift. And that's using Kermode again.</font>
My head hurts
and I'm sorry I can't help you out...