What scares me is I understand what you are saying. so what is your thought on wings? not like a production wing keel but as in 12 meter wing keels as in and I hope I spell this right Kukabera or Austraila II.
> From: [EMAIL PROTECTED]> To: [email protected]> Subject: RE: > catalina27-talk: Keel Fairing> Date: Mon, 17 Mar 2008 14:49:41 -0500> > > Depends, Tim. I know that sounds like a copout answer--but generally, your> > question relates to how thickness of the section relates to stall--and the> > stall is affected by angle of attack more so than any other factor, but also> > relates to the curvature and profile of the section. How thick it is,> truly, > is only a small part of the situation. That's why I said MAY stall> earlier > and WILL create more drag. > > Consider, for example, using a very narrow, > high-aspect ratio keel. It's> going to be very efficient and provide a lot of > lift at higher speeds, but> it really has to count on a certain angle of > attack in order to generate> lift. The 12-meter yachts, for example, when > using a short keel section> that afforded a high aspect ratio, couldn't be > pinched and had to be sailed> full and by. Because they lacked some of the > lateral resistance, they slid> to leeward more, but because they were built > with fuller ends (higher> prismatic coefficient--kinda like your i550) they > held enough speed through> the water to make a better velocity made good and > got to the weather mark> faster after all. They just weren't very forgiving > of pinching. > > Your boat is going to be really light, and you've probably > got a good keel> section that's going to let you pinch a bit more without > killing you on> efficiency if you're a little above or below ideal speed. I > went down to my> library to try to find my NACA book so I could relate > exactly what it said> about the section you chose, but couldn't lay my hands > on it quickly. I> believe I recall, however, that I used it in the vertical > fin of the plane I> built because it was pretty forgiving and less inclined > to stall during> aerobatics (which provide a wide variety of angles of attack > for a vertical> fin because of aggressive yaw during slips and so forth), but > still slippery> enough that I could make time across country. I think offhand > you've made a> good choice.> > Dave Shaddock> > > -----Original Message-----> > From: [email protected]> [mailto:[EMAIL PROTECTED] On Behalf > Of [EMAIL PROTECTED]> Sent: Monday, March 17, 2008 1:45 PM> To: > [email protected]> Subject: RE: catalina27-talk: Keel Fairing> > > >>>A fatter profile, all other things> >>being equal, will generate more > lift at a given angle of attack, but may> >>also stall earlier and will > create more drag-partly due to increased> wetted> >>area, frontal profile, > and the induced drag that comes with lift.<<<> > > whoa whoa whoa.> > I > THOUGHT the fatter sections would:> - generate more lift thru a wider range > of angles of attack - GOOD> - create more drag- BAD> - STALL LATER- GOOD> > > whereas, thinner sections would:> - generate less lift thru the same range of > angles of attack - BAD> - create less drag - GOOD> - stall earlier - BAD> > > as defined above, you are saying fatter sections:> - generate more lift - > GOOD> - create more drag - BAD> - stall earlier - BAD> > and thinner > sections:> - generate less lift - BAD> - create less drag - GOOD> - stall > later - GOOD> > so it seems like, the way you have delineated the trade-offs, > there is> much less incentive to go with a thicker foil.> > Please > understand, I'm not trying to argue here, I'm just trying to grasp> the > concepts!> > I also understand that if the boat is planing downhill at 15 kn > the> thicker section is> going to be more forgiving!> > So I guess my > question is, once again, dont thicker sections stall LATER?> > thanks,> tf> > > > _________________________________________________________________ Climb to the top of the charts! Play the word scramble challenge with star power. http://club.live.com/star_shuffle.aspx?icid=starshuffle_wlmailtextlink_jan
