Hi, Tim--
I think your summation of it as "like a Chevy" is a pretty good analogy. To
go back to the source, I have now heard Frank Butler answer a number of
sophisticated questions with what sure sounded like naivete to me, so I have
a hunch that our factory keel section was a "oh, whatever" decision at the
time. Then these better keel sections would naturally be an improvement, but
only because the bar was set so low.
It would be interesting to hear from an expert here, because I just feel as
though the designers of the cool toys are way beyond NACA foils. Or perhaps
they really are more about the bulb than the keel section itself. For
instance, if we could hang a heavy lead bulb on a carbon fiber keel, we
would probably do it, and we might find that ANY keel foil would be fine for
the purpose.
BTW, this link: http://www.hanleyinnovations.com/glossary.html, shows a few
cases where the NACA 0012 was used in aircraft, but it also shows that some
venerable aircraft (e.g., the Cessna 150/152) had one foil at the wing root
and another at the tip (in other words, more sophisticated). Notably, the
B-17 Flying Fortress had it as the root foil (love that airplane!).
Regards,
Dave S.
On 3/17/08 12:03 AM, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
> I don't profess to have any knowledge whatsoever when it comes to fluid
> dynamics, I have just been going on threads on SA and bits and pieces of
> knowledge that I've read from different designers.
>
> I think that as far as high performance (e.g., sport boats, hulls that
> will plane
> off the wind) sailboats are concerned, a bulb on a keel foil is pretty
> much the
> name of the game. Certainly heavy displacement and cruising boats will
> look toward other keel configurations. But the NACA foils offsets have pretty
> much been determined to be the go-to configurations for fast keel struts
> in the sportboat world. There are a few arguments over whether a 0011 section
> might be faster than a 0012 seciton (with a resulting decrease in
> strength/robustness
> to loads, etc) for example, but the 0012 shape seems to be the chevy
> pickup when
> it comes to most foil sections below the waterline.
>
> These are fairly simple shapes. Pretty easy for an amateur to cut with a
> hot wire,
> or for a CNC machine to do it. (http://www.youtube.com/watch?v=q7uvq4RlhHM)
> I can certainly imagine that areonautical designers would have the need to
> come up
> with more complex shapes for specialized, shape-specific demands, executed
> at high speed with enormous G-force loads in the atmosphere, and new
> materials and production techniques would allow for a huge amount of
> variability when it comes to foil offsets these days.
>
> But these are just simple symmetrical foils shapes that you can order up
> and get made pretty cheaply on-line...I just ordered a 54" piece of
> spyderfoam cut to NACA0012 sections,
> for about a hundred bux incl. delivery. It's a dream-world out there now
> for home boat (or aircraft) builders!
>
> tf
>
>
>
>
>> My ears perk up here. First, I confess ignorance. Are boat keels based on
>> NACA foils, and do they apply to water, as opposed to air? Perhaps there
>> was
>> a series of NACA foils intended for water? I just never paid attention to
>> that part of things, although I studied NACA airfoils for my own purposes
>> many years ago. I vaguely recall a factor called Reynolds Number that
>> would
>> govern foils in various media, such as air and water. Can you elaborate?
>>
>> Regards,
>>
>> Dave S.
>>
>> PS--I was just a layman studying the foils at the time, but I went through
>> them all pretty carefully. It seemed to me that they were kind of empircal
>> in nature. I got the impression that the great virtue of a NACA foil, for
>> an
>> aircraft designer of the 1930s or 1940s, was that it was thoroughly tested
>> and predictable. However, it seemed as though a lot of developments of
>> later
>> decades, such as the Clark-Y, not to mention variable sweeps and tapers,
>> variable chords and foils in a given wing, etc., began to favor departures
>> from the NACA foils (except when mere predictability was the goal, as in
>> vertical stabilizer foils). So, although I later got into aviation writing
>> and was constantly looking for NACA foils, I didn't find many in the wings
>> of light aircraft. In my time, we saw NASA come out with the GAW-1, and I
>> have always assumed that later, composite aircraft designers were free to
>> work with an infinitely variable foil in mind.
>>
>>
>>
>>
>> On 3/16/08 8:40 PM, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
>>
>>>>>> but they also value every advantage they can get.
>>>
>>> key words^, huh?
>>>
>>> nice explanation, Chris.
>>>
>>> So I guess Compu-Keel is still around?
>>>
>>> http://www.compukeel.com/
>>>
>>> odd because you get NACA foil specs on-line for free...but I guess all
>>> class
>>> legal keels cant be derived from NACA sections.
>>>
>>> tf
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
