Oh, ya shouldn't ha mentioned the 0014!
(You can call me Ray, you can call me Jay, but ya doesn't hafta call me
Johnson!)
--Demitri
On 3/17/08 7:27 PM, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
> thanks, man. I understand what you are saying and appreciate the time that
> you and everyone else, Dave Shu (one of you guys should consider changing
> your name to Demitri), Keith, Mark, and everyone else who has contributed to
> this thread (that started out as a simple keel-fairing question that Art
> started,
> thanks Art) has put into this discussion.
>
> For someone w/o an engineering background, it really helps to have this
> stuff explained clearly by people who have sailing backgrounds.
>
> Just dont no one tell me the foil should've been spec'ed 0014....
>
> --tf
>
>
>
>> 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
>>
>>
>>
>>
>>
>
>
>
