From rabbit272@attbi.com Fri Oct 18 14:33:06 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!prodigy.com!wn13feed!worldnet.att.net!204.127.198.204!attbi_feed4!attbi.com!sccrnsc03.POSTED!not-for-mail From: "Harvey Louzon" Newsgroups: rec.aviation.student References: <3dae8e0d_1@news.iprimus.com.au> <3fa7bd49.0210171009.7e9eaec@posting.google.com> <3DAF7DE4.26EECEF3@cox.net> Subject: Re: explanation of lift Lines: 68 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: NNTP-Posting-Host: 12.212.219.200 X-Complaints-To: abuse@attbi.com X-Trace: sccrnsc03 1034958479 12.212.219.200 (Fri, 18 Oct 2002 16:27:59 GMT) NNTP-Posting-Date: Fri, 18 Oct 2002 16:27:59 GMT Organization: AT&T Broadband Date: Fri, 18 Oct 2002 16:27:59 GMT Xref: news.redhat.com rec.aviation.student:41185 "Hilton" wrote in message news:aooaok$ct7$1@nntp9.atl.mindspring.net... > Here are a couple. Let's see. Take a look at 7.6. Denker says: "We know > that VY depends on a balance between induced drag and parasite drag.." What > the heck does that mean? > It means that VY occurs at the point on the power curve at which there is the greatest excess horsepower. This is going to be close (but not precisely at) the point at which the sum of the induced and parasite drag is at a minmum. > Ok, another... In 13.3 he says "rotate at or near Vx." Is this consistent > with your POH? > Yes. For the C172 rotate is 55 kts and Vx is 60 kts. That meets my definition of "at or near". > In 7.3: He says: "The only option is to choose a less-draggy speed (closer > to VY)" Vy has nothing to do with having less drag. > Yes it does. The point is that at cruise speed you are well on the front side of the power curve. VY being lower than this and close to the point of minimum power required is, indeed, a point of much lower drag. > Denker equates Vy as the speed between the front-side and back-side of the > power-curve. This is inconsistent with pretty much every definition of the > power curve I've seen. > This is technically true. The point of max L/D and VY do not precisely cooincide. The reason is that at speeds just above L/D max the power available rises a little faster than the power required. Thus VY is typically a little faster than max L/D but not by much. > He defines AOA as "zero angle of attack corresponds to zero coefficient of > lift" - not consistent with your books - right? > This is matter of definition. Some people use the angle between the zero lift line (and not the chord line) and the relative wind as the AOA. This is convienent for certain applications. When coefficient of lift is plotted as a function of AOA this allows the curve to pass through the origin of the graph (0,0). This is just a convention. > About P-Factor: "The effect is never very large..." and "...small compared > to the helical propwash effect." Well it is true that p-factor is mostly a consideration when the wing is at a high AOA. h