I used to fly my dads Piper Aztec got my twin complex in that plane, I really miss it oh well maybe someday.
> Date: Wed, 19 Mar 2008 21:11:41 -0400> From: [EMAIL PROTECTED]> To: > [email protected]> Subject: Re: catalina27-talk: Keel Fairing> > > Since we are over to airplanes, does anyone know where a Beech GB-2 may > > be found.> My father-in-law owned one the the past and is wondering where it > might > have gotten off to.> Did not if Dave S. was familiar with this > model.> > David Shugarts wrote:> > Hi, Dave--> >> > Now it's getting > interesting. I just wish we had a boat designer to chime in> > here, as we > are way over on the aviation side of this thing, I think.> >> > As an > aviation editor for about 15 years, I got to hop into a lot of> > aircraft, > including the 177RG, which I liked a lot. Our company plane was an> > M20J > and I also did aerobatic training in an 8KCAB, which has the> > > "semi-symmetric" wing airfoil because they figured you'd want to be inverted> > > a lot. (There's one of those still missing, with Steve Fossett in it.)> >> > > Regards,> >> > Dave S. (II)> >> >> > On 3/17/08 2:32 PM, "David Shaddock" > <[EMAIL PROTECTED]> wrote:> >> > > >> Hi, other Dave S.--> >> Your hunch is > correct; laminar flow in water disappears at a pretty low for> >> the > waterline lengths and foil lengths we're discussing. After I wrote my> >> > comments earlier, I went back through the thread and found the link to Bryon> > >> Anderson's excellent article, which explained everything I was trying to> > >> cover in a better fashion, with diagrams too. He mentions 5 knots as the> > >> approximate speed at which we lose laminar flow. That's oversimplifying,> > >> but it gives you an idea. But laminar flow has a lot to do with the NACA> > >> profile--some profiles intentionally move the maximum depth aft in order > to> >> maximize laminar flow; the idea is to keep the lift working for you as > long> >> as possible. My last plane was a Cessna 177RG, which had a laminar > flow> >> wing designed to keep the flow 'attached' for 70% of its surface or > better> >> at speeds of about 170 mph. It took a long time getting off the > ground, but> >> was incredibly efficient in the air. It was very different > from my friend's> >> 175 (we traded for a while so he could get his > commercial license), which> >> had a fat high-lift wing that got you off the > runway in a third of the> >> distance but only provided 2/3 the top speed for > the same power and fuel> >> burn.> >>> >> Just because a flow goes turbulent, > we're still interested in it and it can> >> still perform some useful work. > Besides, it's kind of a necessary evil; you> >> can't just provide the part > of the foil that gives you laminar flow and then> >> remove the rest <grin>. > The whole profile works together.> >>> >> Now, you mentioned vortex > generators... They sell dimpled surface material> >> for airplanes to put on > the surfaces where the flow starts to detach, under> >> the theory that the > dimples (like the ones on golf balls, except standing> >> proud of the > surface) generate mini-vortices that help keep the flow (albeit> >> > turbulent) attached. Makes me wonder what this would do on the aft faces of> > >> a keel. I notice my BMW has raised bumps all over the edges and strut for> > >> the side-view mirrors, to cut wind noise by keeping the flow attached so > it> >> can't escape and whistle.> >>> >> But let's talk for a minute about > porpoises. Capable of 25 knots> >> underwater, and without a turbulent > boundary layer... I guess they don't> >> understand Reynolds numbers. > Apparently they have a paper-thin outer skin> >> with a thin spongy layer > below that covering their real skin. One theory> >> says they can detect > turbulence and adjust their body shape to reduce it by> >> controlling this > soft layer. Dr. Kenneth Davidson studied them heavily and> >> figured their > speed was more due to their streamlined shape and the smooth,> >> oily skin, > but later research does suggest that the softness is apparently> >> as > important as the skin. But I wonder why my inflatable isn't quicker...> >> > Anyway, since I don't see a mechanism for the porpoises to control this fat> > >> layer, maybe it's a passive thing. I don't think I'm ready to plaster my> > >> keel with neoprene to try it out, but it makes me wonder if the flexible> > >> layer couldn't react to impending turbulence and change shape just enough > to> >> keep the flow attached.> >>> >> Dave Shaddock> >>> >> -----Original > Message-----> >> From: [email protected]> >> [mailto:[EMAIL > PROTECTED] On Behalf Of David Shugarts> >> Sent: Monday, March 17, 2008 12:14 > PM> >> To: [email protected]> >> Subject: Re: catalina27-talk: > Keel Fairing> >>> >>> >>> >>> >>> >> Hi, Dave--> >>> >> That's all true, more > or less, but what I have a strong hunch you will find> >> is that these foils > do not give us laminar flow at our speeds and angles of> >> attack.> >>> >> > In other words, going to windward, I believe you would find that we are> >> > nearly always in some form of turbulent flow, at some point in the keel> >> > section, unlike aircraft, where we do get laminar flow most of the time,> >> > over most of the wing.> >>> >> (BTW, the ratio of Reynolds numbers is 13:1, > water versus air. Don't hold me> >> to it, but I believe this is the > practical consideration when modeling> >> foils.)> >>> >> These days, there > are inexpensive underwater cameras that could perhaps show> >> us what our > keels are doing. It isn't a fair comparison, but I get a good> >> look at my > rudder and it always looks like it's in some degree of turbulent> >> flow > going to windward. (I have the old rudder, which is an anachronism.)> >>> >> > Regards,> >>> >> Dave S.> >>> >> PS-I am very familiar with the root versus > tip design concept for beneficial> >> stall behavior in aircraft, and we > could throw in wing twist if we wanted to> >> complete the picture. And let's > not even get started with Whitcomb winglets,> >> stall fences and stall > strips, not to mention vortex generators.> >>> >>> >> On 3/17/08 12:31 PM, > "David Shaddock" <[EMAIL PROTECTED]> wrote:> >>> >> > >>> The Cessnas and > other aircraft sometimes use different foil shapes at the> >>> root and tip > in order to make sure the inner part of the wing (closer to> >>> > >> the> >> > > >>> fuselage) stalls first, making the aircraft dive and regain speed > while> >>> still providing some control out at the wingtips to avoid a spin. > This> >>> isn't an issue with sailboats.> >>>> >>> But our keels can still > stall--the keel provides windward lift if it> >>> > >> doesn't> >> > >>> > stall, at the expense of some leeward slip. If the keel stalls, you lose> >>> > the lift and you see a lot more leeward slip/skidding.> >>>> >>> There are so > many NACA profiles that it's hard to imagine anyone using> >>> something > that's NOT a NACA profile--they have tested and published> >>> > >> results> > >> > >>> for hundreds of them, with some having only a tiny variation from > others.> >>> But those tiny variations can make measurable differences, > especially> >>> > >> since> >> > >>> we're operating our profile in a medium > 800 times denser than air. I have> >>> > >> a> >> > >>> book I used for > aircraft design purposes that's got everything they had> >>> published > through about 1990. At any rate, selection of the ideal profile> >>> for a > sailboat involves knowing the aspect ratio as well as the target> >>> speeds. > For example, there is a concept called the lift/drag bucket--a> >>> high-lift > keel profile provides a lot of drag, but might be a worthwhile> >>> price to > pay if you're trying to achieve the best VMG in light air,> >>> > >> because> > >> > >>> at low speeds the drag doesn't hurt as much and adding lift while> > >>> > >> minimizing> >> > >>> leeward slippage pays off. For higher speeds, a > lower-lift profile works> >>> better because when the boat is moving faster > through the water, you'll> >>> > >> get> >> > >>> a resultant increase in the > actual lift windward and have less drag to> >>> > >> worry> >> > >>> > about--but overall you'll see more leeward slippage.> >>>> >>> A bulb at the > bottom of the keel offers two things--for one thing, it> >>> minimizes the > tip vortex (which adds a great deal to drag), but mainly it> >>> helps > provide a lot of mass at the extreme draft, which provides more> >>> righting > moment. If the rules allow, you can carry more sail because of> >>> > >> the> > >> > >>> extra righting, and you'll heel less which means more sail upright > and> >>> working for you (although heeling may increase your waterline length > on> >>> > >> some> >> > >>> hulls and raise your speed). If the rules don't > allow added sail, you can> >>> take advantage of the increased righting > moment by cutting weight out in> >>> other areas and you'll accelerate > faster.> >>>> >>> The profile Tim has picked out for his sportboat is a good > one; at the> >>> speeds he might be getting on a planning boat, he could > probably have done> >>> well with a narrower profile, too, but this way he's > covered for a wide> >>> range of conditions.> >>>> >>> A lot of this > information is in Steve Killing's book on Yacht Design and> >>> also in > Skene's Elements of Yacht Design--but the later publications of> >>> > >> > that> >> > >>> are much more informed than the early ones).> >>>> >>> Dave > Shaddock> >>>> >>> -----Original Message-----> >>> From: > [email protected]> >>> [mailto:[EMAIL PROTECTED] On Behalf Of > David Shugarts> >>> Sent: Monday, March 17, 2008 10:52 AM> >>> To: > [email protected]> >>> Subject: Re: catalina27-talk: Keel > Fairing> >>>> >>>> >>>> >>>> >>> 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> >>>>>>> >>>>>>> >>>>>>> > >>>>>> > >>>>>> >>>>>> >>>>> > >>>>> >>>> > >> >> >> >> >> > _________________________________________________________________ Connect and share in new ways with Windows Live. http://www.windowslive.com/share.html?ocid=TXT_TAGHM_Wave2_sharelife_012008
