Newport 27 Rudder??

[Paul B]

Originally Posted by jbassion

Listen Guys,
I'm an Architect, I use Auto Cad all day. I lofted lines from Herrishof's notebook for a previous boat I built, but I have no idea how to transulate the numbers I downloaded (NACA0012) into a plottable (is that a word?) set of coordinates. If someone can direct me to a help section I can get the curve into my cad program and plot out a full size template.

Look Here: http://www.pdas.com/profiles.htm#0012


This is the offset table for the foil (half thickness). The numbers in the x column are the percentages of the chord length aft of the leading edge. The numbers in the y column are the percentages of the chord length in thickness, from the center line. So at 30 % aft of the leading edge the foil is 6% thick out from the CL on each side, for total 12% (hence the 0012 designation). For a 10" chord length (leading edge to trailing edge) your max thickness is at 3" from the leading edge and it is 0.6" from the Center Line on each side (1.2" thick).

So lay out your x axis, put in the leading edge radius as an arc, then add the points at 0.5, 0.75, 1.25, 2.5, 5, 10, 15%.. aft of the leading edge at the proper thickness. Connect the dots.

Do this for the top of the rudder, the bottom (assuming some taper is involved) and at least the midpoint and probably the chord halfway between the mid and bottom.

A lot of people ask how thick the trailing edge of a foil should be. Well, it is actually right on the chart at 0.126% at 100% chord for the half thickness.

[jbassion]

Thanks!
Now I can understand what to do. I owe you, If you ever need a template let me know and I'll draw it for you on the computer.
Jerry

[Paul B]

Originally Posted by jbassion

Thanks!
Now I can understand what to do. I owe you, If you ever need a template let me know and I'll draw it for you on the computer.
Jerry

I have an Excel spreadsheet that I use for scaling NACA foil sections for Keels and Rudders. You might want to write one up if you want to quickly scale the thickness percentage to meet your needs, based on whatever shaft you decide to use.

I can make templates in ACad as well, but usually I like to work in SolidWorks.

[jbassion]

O.K I'v been one-upped. I could tell you that I lofted all my lines in 3d studio but I wouldn't do that, because I still appreaciate your help.

Since you offered could you email the spread sheet as an attachment?

jbassion@bellsouth.net

Thanks
Jerry

[Paul B]

Originally Posted by jbassion

O.K I'v been one-upped. I could tell you that I lofted all my lines in 3d studio but I wouldn't do that, because I still appreaciate your help.

Since you offered could you email the spread sheet as an attachment?

jbassion@bellsouth.net

Thanks
Jerry

I don't recall offering anything, but I've e-mailed it to you anyway.

Let's see if I can attach it here.

[Tim B]

Well, it can seem to be a problem if you haven't done it before, but drawing aerofoils/hydrofoils is really fairly simple. I personally use Rhino 3 which makes the job very quick because you can just read in the points. In autocad I suspect you'll have to type them in by hand.

If you open the aerofoil file (say, NACA0012.dat) you will be faced with something like...

NACA-0012 smoothed airfoil
1.0000 0.0100
0.9800 0.0500
etc.

what we have is a header (NACA....) and then 'X and Y' co-ordinates of points (one remembers the axis convention at this point). Before you go any further, I suggest that you print out this file if you're using autocad. If you are using Rhino, remove the header and save it as a text file (N0012.txt for example) then just open it using the open command. There may be a similar trick in autocad, I don't know, otherwise, it's typing it in by hand.

Now, the next bit is dependant on how you intend to build the rudder. The easiest way is to use a foam core with obechi veneer over it. it is easiest to cut the foam with a hot wire (nicrome in an aluminium or wooden frame) and then add leading edge, trailing edge etc. epoxy on the veneer (DON'T USE POLYESTER!!!! it will melt the foam) and then epoxy some woven glass fibre (of carbon if you wish) over the veneer.

In the case of the foam-cored rudder (I will ignore the built-up version) it should be obvious that we only need one template each time the geometry changes (ie. where we go from straight to tapering). Each template should be marked with percentage chord marks every 5% or 10% and numbered. The maximum length you can cut easily is just over 3 feet. The templates (taken from a 1:1 scale print-out) should have offsets drawn in to accomodate the veneer and glass fibre. This is easily acheived using Autocad and Rhino, or can be done with a little geometry (see my website for a program to do this for you (open source but written in BBC Basic)). The core should allow for the incorporation of a false leading edge (behind the main le), and internal trailing edge to mould onto a solid rear edge.

In search of stiffness.... I would personally put a spar top and bottom with a vertical web, use spruce and plane all sections to fit before epoxying it in (rest the foil in the origenal foam blocks (with some non-stick paper) to get it straight and true) dependant on thickness the web may not be necessary. The spars will give you a first port of call to attach the rudder stock to (if you are clever, the spars can be the stock (with a little fairing). In either case a few ribs should go between the stock, the spars, and the edges of the foil (all epoxied to the foam core). These are developed in the same way as the templates, but interrupt the web where they cross the spar. Plywood is fine for this purpose (1/8" max) if you are worried about the point-loading on the skins, recess the rib and a little of the foam and lay-up some carbon in the recess.

The tip of the foil can be hand-carved from foam or wood and finished like the rest of the foil. there should also be a root rib incorporated into the foil, under the veneer.

Good luck,

Tim B.

ps. whoops, didn't read the last bit to be posted. lol, hope this helps anyway.

[jbassion]

You all have been great. By combining the last 3 replys I have all the info I need to get started with some degree of confidance.

I like your idea of an internal web for strength, but I don't see how to get a hard attachment to the wood to the SS rudder post. That's why I was planing to weld a center plate or "fingers" off the shaft. I guess the web could be made from 1/8" plate and welded to the post. I think I'm at a point that I can start. Thanks again guys.
Jerry

[Tim B]

sorry, didn't make myself quite clear enough, the ribs (running fore/aft) provide the connection point for the stock. There are a hundred ways of connecting stock, spar and ribs, though you may consider welding on your 'fingers' and then binding them to the ribs with cotton, or (if they are flat plates) bolting them to the ribs. remember, that in the method described the joint will be encapsulated in epoxy.

Of course, if you wanted to do it with even less weight, you could build yourself a jig, then build up the whole rudder using ribs. (as in the picture above) with some clever design you could even use the spar as the rudder stock. obviously you would have to fair it into a tube, but that is not a hard moulding to do.

Good Luck,

Tim B.

[tspeer]

Originally Posted by Tim B

...Now, the next bit is dependant on how you intend to build the rudder. The easiest way is to use a foam core with obechi veneer over it. it is easiest to cut the foam with a hot wire (nicrome in an aluminium or wooden frame) and then add leading edge, trailing edge etc. epoxy on the veneer (DON'T USE POLYESTER!!!! it will melt the foam) and then epoxy some woven glass fibre (of carbon if you wish) over the veneer.
...

But don't hotwire a polyurethane foam! Only hotwire polystyrene foam. Polyurethane will give off poisonous gas when heated by the wire. Instead, use a square metal tube with sandpaper glued on one side as a full-span sanding block, and set up the templates so bare metal of the tube rides on them. Other than that, the process is similar to hotwiring.

You can use polyester resin with polyurethane foam.

[Tim B]

Some example pictures

[asathor]

I modified my rudder to the "humpback" scallooped front edge and can recommend it highly. With its substantially reduced friction and better stall angles you gain substantial size flexibility and performance to boot.

The only disadvantage is that it is unconventional. Humpback Whales do not have computers and spectacles so why would their experience count? Well a bunch of professors came to their defence as seen in:

Physics & Fluids May, 04 by Fish, Howle, Miclosovic and Murray.

[SuperPiper]

I remember this discussion from a different thread.

You will need to give more detail. Do you have a photo of what you did? What size is your boat? What are the proportions of the undulations? As the leading edge zigs and zags in and out, do you maintain a foil shape in section with a varied cord length?

You imply that the modification is better so I assume that it is definitely not worse.

I want to be the first guy on the block to try it!

[asathor]

Note that these guys took out a patent which would make a difference for commercial use. Some of the authors are professors at the Naval Academy.

I decided that since the whale's fin-bumps are not that regularly shaped that a manual implementation would be entirely sufficient and I decided empirically to carry my bumps back to the cord - my bumps foil is a little sharper than the original (Freedom 21) rudder. se attachment whick appear to be a fairly blunt NACA shape - I also extended the trailing edge which was very blunt by about an inch. see attachment.

I got more than I expected so I am leaving it like that - it certainly seems that I am at or above the predicted improvement .

The research paper can be bought here ($20): http://scitation.aip.org/getabs/serv...cvips&gifs=yes

Scientific American had a good article with summary information (sorry its locked) :
Bumpy Flying; August 2004; by Steven Ashley; 2 page(s)

Here a thread from the flyboys with a picture of a whale: http://www.ozipilotsonline.com.au/fo...ings-13931.htm

Here is another sumary that someone posted:

Bumpy Wings - From the "There's nothing new under the sun" department...

My latest copy of "Scientific American" has an article on page 9
describing a new wing design which appears to increase lift by 8 percent
and reduces drag by as much as 32 percent. (No, that's not an error-
thirty-two percent!!) Furthermore, the wing withstands stall at angles
40 percent steeper than conventional wings.

The author- Frank E Fish (I'm not joking... this isn't April first) got
the idea when he noticed that the leading edges of the flukes on
humpback whales have a series of lumps spaced at even intervals.
This was so contrary to conventional wisdom- and practice in both
aviation and nature- that he decided to research it. He designed plastic
replicas of the humpback's fins- one with the lumps and one without. The
one without looked like a conventional aircraft wing- similar to the
Discus glider- and performed as expected. The one with the lumps gave
the performance increases stated above.

The reason for the improvement is pairs of counterrotating vortexes
generated either side of the lumps (which he calls "tubercules"). The
vortices keep the airflow attached to the upper surface rather than
allowing it to separate. Apparently this improves the whales'
manoeuverability- which helps when they hunt schools of herring and
sardines.

Fish says the discovery could also have application to props and rotors
as well as wings. Naturally, the Navy is also very interested and funded
some of the research. You can expect to see lumps on the diving planes
of submarines anytime soon.

[asathor]

Wooden boat thread with pix

http://media5.hypernet.com/ubb/ultim...c;f=2;t=003758

[SuperPiper]

So the darker material has been added to the rudder? Or, are the darker regions where you have sanded away material from the foil shape?