From julian@avbrief.com Fri Oct 25 16:55:38 2002 Path: news.redhat.com!news-reader.ntrnet.net!news.onramp.ca!xcski.com!nntp1.roc.gblx.net!nntp.gblx.net!nntp.gblx.net!newsfeed.cwix.com!newsfeed.icl.net!newsfeed.fjserv.net!proxad.net!proxad.net!news-hub.cableinet.net!blueyonder!newspeer1-gui.server.ntli.net!ntli.net!newsfep1-win.server.ntli.net.POSTED!53ab2750!not-for-mail From: "Julian Scarfe" Newsgroups: rec.aviation.student References: <3dae8e0d_1@news.iprimus.com.au> <3fa7bd49.0210171009.7e9eaec@posting.google.com> <9b435a74.0210240851.529d1662@posting.google.com> Subject: Re: explanation of lift Lines: 63 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Message-ID: Date: Fri, 25 Oct 2002 11:54:30 +0100 NNTP-Posting-Host: 80.2.246.217 X-Complaints-To: abuse@ntlworld.com X-Trace: newsfep1-win.server.ntli.net 1035543261 80.2.246.217 (Fri, 25 Oct 2002 11:54:21 BST) NNTP-Posting-Date: Fri, 25 Oct 2002 11:54:21 BST Organization: ntl Cablemodem News Service Xref: news.redhat.com rec.aviation.student:41717 Hello Jan-Olov, I was wondering when you'd drop in... "Jan-Olov Newborg" wrote in message news:9b435a74.0210240851.529d1662@posting.google.com... > The bad thing about John S. Denkers website above is that try to > explain Lift physically by help of mathematical modelled > Potential/Circulation theory! > > Thatīs not possible. It's a model that has been at the heart of the calculation of aerodynamic coefficients for 80 years. If it's "not possible", then aircraft designers must have got real lucky with the shapes they picked. :-) > Circulation Theory is not the cause of Wings Lift! > > The mathematically superpositioned Circulation velocity field is just > a correction of the physical unreal velocity field created by LaPlace > equations! So are you saying that all these correct aerodynamic coefficients have been calculated using a model that is so far away from reality that it's "physically unreal"? A conspiracy, perhaps? ;-) > Lift is physically explained better here: > http://www.rz.uni-frankfurt.de/~weltner/Flight/PHYSIC4.htm Weltner > Lift Good old Weltner. He's confident that there's only one proper way to explain lift. He plays around with some equations, which are essentially F = m*a (or should that be m*a = F), and suddenly comes to the conclusion: "The faster flow at the upper side of the wing is the consequence of low pressure and not its cause." An equation is an equation, not a statement of cause and effect. Why (and how) does the wing "deflect the air"?... Because of the pressure differences set up by the presence of the wing... Why are there pressure differences set up around the wing?... Because it deflects the air... chicken...egg...chicken...egg... > http://www.aa.washington.edu/faculty/eberhardt/lift.htm Don't read this without Denker's critique. In particular, Eberhardt makes a mistake in the section on Ground Effect -- a sign error -- which displays a significant misunderstanding of fluid mechanics. http://www.monmouth.com/~jsd/fly/lift.htm > http://www.aa.washington.edu/courses/aa101/aa101_09.pdf Take a look at slide 7. "Classical Theory Predicts: Cl = 2*pi*a (for a symmetric airfoil)" followed in slide 8 by a graph of this in practice. This is your "Potential/Circulation theory". If it's so wrong, why are they presenting it? Julian Scarfe