The Subject is LIFT

[Rick9619]

Touche CalebD

I am actually trying my best to learn how to fly a kite! Only have minimal experience with an asym. Trying to get better. Gonna do the Newport to Ensanada in April. Cant waitRick

 

[mortyd]

lift

moody is substantially correct, but all i was trying to say, from the beginning, is i find an advanced knowledge of aerodynamics has not helped my sailing, save a much more efficient use of my traveler. just like when i'm flying, i'm way to busy to think of theory, the same thing applies to a constantly changing wind and drunken power boaters.

 

[Ross]

Wow!!!! everything I ever wanted to know

about why my boat goes where I point her and soooo much more. D)

 

[Moody Buccaneer]

Geeks R Us ...

Yup, I'm a geek ... Sorry to bore you all, I have no life. Randy

 

[Ross]

Hey Randy, Here's a practical question

for this discussion. I sail an old Islander 30 with a rather full keel and attached rudder. The flat vertical surface of the keel is about 3 feet tall to the curve of a slack bilge and about 10 feet long. The boat draws about4.5 feet. By my figures I have about 30 square feet of keel to provide lateral resistance. I can't recall ever seeing a fin keeler with that much surface area. Now, I understand that one of the reasons for development of the fin keel was to reduce wetted area and therefore drag. In my post concerning the wind and the plywood I supposed that a fin keel would "sail" around her anchor more than a full keel boat would because of zero boat speed. So my question becomes "at what speed does the fin keel start to gain advantage over the long keel?"

 

[Rick9619]

Randy that was excellent

You finally said with math what us others have been trying to say for days."You don't need any formal education to understand low Reynolds number aerodynamics." Well that may be true, BUT what if some here are just looking for an explanation or even an analogy(I still like the hand out the window of the car) that one can grasp in the mind's eye rather than with a slide rule? Or even the ones that WISH they could understand just some low Reynolds number aerodynamics. I found your post fascinating though. Where you mentioned detached airflow at 15-18 degrees, is that why most helicopters with conventional rotor systems(articulating, rigid) cant do a loop? I remember a paper on that about 25 years ago. But you a geek... nah.. well maybe. Looking forward to your response to Ross's question. Hey could you do me a favor and put your formula for predicting the primes in your next post? I could use that.Cheers Rick

 

[Moody Buccaneer]

Um ... Ross ...

"at what speed does the fin keel start to gain advantage over the long keel?" As far a sailing performance, the fin keel should always have an advantage. They may require more accurate steering and sail trim to realize this advantage in some conditions.As far as boat handling, full keels should be easier to sail. Less prone to low speed stall and have high directional stability, but lower performance potential, particularly up wind. There may be a slight advantage to the full keel at very low boat speeds but it would be hard to prove.Full keels heave to better, and may "sail" at anchor less (but sailing at anchor is more a function of freeboard area).Rick - I've never tried to design a rotary wing craft. All my experience is in fixed wing, high performance R/C sailplanes and sailboats ... hence the background in low Re flight. I had to figure out why my planes were crashing ... I can't even guess why one helicopter can loop and another one cannot ... they fly by black magic as far as I know.

 

[Rick Webb]

Looping a Helicopter

It was my understanding (as a helicopter driver not an engineer) that any helicopter could loop so long as it maintained positive G. We were very limited on negative g capability it is good way to chop off the boom. The problem with doing a loop was maintaining enough air speed to go over the top and avoiding a stall same thing that keeps a 747 from doing a loop. I am trying to remember why it was a bad idea to do a roll something to do with the lead and lag on the rotor blades I was not brave, fearless, or stupid enough (pick one) to want to try. I know the Comanche would and perhaps the Apache will do a roll. Not much of any reason to do one unless helicopters start dog fighting.

 

[Rick9619]

Lift

Yeah I agree with black magic. I just remember in aero 101 reading a paper which was discussing that. Something about retreating blade stall and critical angle of attack on rotary craft. The retreating blade cant maintain more than 18 degrees AOA so the helicopter rolls, or stalls when you try to loop it. Besides when you pull back on the stick, the houses should get smaller.. you shouldnt go backwards Gotta go to work, gonna move about the country to Nashville today, theh San Jose tomorrow night. Hope we can keep this thread alive a bit longer. As I said I have a winged keel and a 4'6 draft. With all the new stuff coming out on the performance cruisers these days, how do we compare. Once again thanks for the discussion. I guess you kind of remind me of the guy in "Flight of the Phoenix". He saved all their a$$es.CheersRick

 

[Rick Webb]

Must Have Been A Different Movie

I remember James Stewart as the one who saved their butts.

 

[mortyd]

lift

rick, we must have gone to very different schools since all through my masters i never encountered one word about rotary wings. the closest i got to anything spinning was conmpressors and turbine in propulsion which stood me in good stead in two years of flight test at pratt and whitney or recovering from the spins induced in juarez while stationed at biggs in el paso. yes, i spent a year in hartford one sunday. w.c. fields.

 

[Ross]

Speaking of winged keels has anyone seen the

similarity between a winged keel and a bruce anchor? How do you heel the boat when she hit the bottom?

 

[r.w.landau]

Moody, thanks, that was impressive!

I know my boat goes forward and how to do it but the numbers are impressive.Ross, I have had some experience flying plywood and drywall myself.r.w.landau

 

[Rick9619]

lift... well we dig in

Ross... ouch im hurting from that one. I have talked with you often... I can do hull speed on a good day. You have said what you sail... I forget? Shot taken across the bow. Im still here. Rick W. I didnt say who saved there butts. You made an assumption there. Jimmy Steward rocks! But the model airplane guy... come on, give him some accolades. I was trying to get along with the engineers, im a pilot myself too. Mortyd, maybe I went to Slippery Rock... I just tried to expand and was fascinated by rotary wing flight way back then. Retreating blade stall, critical angle of attack, out of ground effect hover.. that sort of thing. Not maybe so good at that but I am a quick study. And based on your posts I really do respect you, I have a masters too. And since I just say "the weather is 55 degrees and we should have you at the gate about 10 minutes early" I really dont use it. Im just into everything about sailing. And I consider myself in about the seventh grade. Just the way it is.Cheers Rick

 

[Bob7291]

Helicopters and keels

A pilot once told me that helicopters actually are incapable of flight - it's just that they are so ugly, the earth repels them.Having no official schooling in aero or hydrodynamics, but being very curious about those topics, I'd like to extend the discussion into the area of what an ideal fin keel shape would be. I know there are other considerations involved in sailboat design: the need to rest the weight of the boat on the keel, the limitation of draft to a practical number, etc. But the contrast in shapes of cruiser/racer keels since the early 60s shows that lots of development and changing of theories occurred. Also, the overall shape of the foil is of interest to me. I've read that some keels were made with a deliberate concavity in the run from the widest point to the trailing edge, and that it caused the boat to point unusually high through increased lift. Other sources say that's a bad design and will hurt performance. Since some of you guys seem to know your stuff and snow is falling here, I'm happy to hear what you have to say.