I'm thinking of building my self a set of new daggerboards.
I don't understand mutch about Profiles, but I'm thinking of using a asymetrical profile like the NACA 4412.

what are the recommandations? state of the art profiles?
Any expiriences?

When using a asym. profile the downside is the windward board will always need to be raised. The lift generated by this profile will be in one direction. The two will oppose each other if they are both down.
Which is OK if you are dilligent enough to always remember.

JMO

Clayton

I would contact someone with an CNC machine that could cut the cores exactly to specs out of any material you wish and do the layup myself. If you don't have someone locally try Phil's Foils. He made thr rudder for my F25c which INMO is absolutely perfect.

thom

When I built my A-class, I did a bit of research on rudders and daggerboard profiles. One of the things that I came across was an article by Martin Fischer on the DAG rudder profile that he had designed that has a hollow trailing edge. This provides a reduction on drag by allowing the rudder to pull less water along behind it. He had data on how much less drag it produced compared to a NACA 64 series board which is a good design already. The website was for a Mikan A-Class and is now defunct, but most of the A-cat designers are using the DAG profile. If your 44 series profile were to be made symetrical, it would resemble the 64 series design.

As his Dag rudder profile was proprietary, and unavailable, I aquired an Eppler assymetric foil shape set of coordinates that featured a hollow trailing edge, and made a symmetric set of coordinates from them, and then used those coordinates to build the foils. To make them work well, you have to work hard to get the trailing edge very fine, and then they are fragile. It is real hard to get the foil exactly right. The first set I made were too thick in both the leading edge and trailing edge.

The reference I followed for the planform was a text by model aircraft builders that state that an elliptical shape is best. The trailing edge should be straight, andt hen the front should be straight for about half the legnth, then start to taper, and then the end should be rounded off to a 90 degree angle with the trailing edge. Alternately, a taper with a rounded end is almost as good. That is what Marstom boats use if you can find a picture of the foils on one of those A-Cats.

I made my rudders at just under 10% thickness to chord. The daggerboards were made at about 8% of the chord thickness. It took a while to make a decent plug of the correct thickness. After 4 trys, I finally made a square ended daggerboard plug by laminating cedar together wide enough on plate glass glued on a frame, then shaping it with a 3 inch wide wood block that had been routed to the correct shape and using a jig to keep everything straight. Then I overlaid it with one very thin layer of 3 oz fiberglass cloth, and then sanded it fair using the same block to get close to the correct foil shape. I made the mold by laying several layers of fiberglass over this with plywood edging. So my daggerboards wind up being straight with a square bottom. If I were to do it again, I would make them the tapered design.

It is not even close to easy to make a real good foil. The suggestion to get a mold made for you by Phils Foils or some other shop with a computerised shaper is a very good idea. You will then get a perfect foil shape and be able to replicate foils over and over. One other thing to consider when making your own foils is that it is esy to make them too flimsy. I have broken both original rudders and one daggerboard so far. So as the first daggerboards proved too short in light air, I made 2 new ones. The second pair of daggerboards are noticeably better than the first ones, as I took more care to ensure the daggerboard halves were not too fat at the leading and trailing edge.

I hope this helps.

You can cut a fairly accurate core with a device called a Feather Cut foam cutter. It is used in model glider (and powered) wing manufacture. They are inexpensive and easy to use.

Rick

Hi Conrad:

Could you post some coordinates for your rudder sections? I have promised a friend to build some Tornado rudders for him this winter, and it would be fun to try something else than the standard Marstrøm sections.

Have you run your sections trough e.g. XFoil and compared lift/drag/stall datas for your section as compared with e.g. NACA 12 sections ?

I have not tried this, so I can't swear it will work.

Many RC planes use foam core wings. There are suppliers on the internet and in many cities. They can supply foam cores in many stock airfoils. Mostly NACA 00XX and 40XX. For a setup fee they can make published airfoil you want. The foils can be straight, tapered or strange. A example of strange is NACA 0012 transitioning to a oval at the other end. You can make complex shapes by gluing tapered section togather.

The RC model websites have LOTS of articles on how to cut foam or who to buy airfoils from. I am not getting invloved with that. However the hotwire method is pretty primative and uses blocks and lines. A winter use for your rigging?

Once you have the foam core in the right size, turning it into a daggerboard or rudder is matter of vacuum bagging glass, kevlar, carbon, etc over it. You could lay it up by hand if you really wanted to.

In terms of cost. I spent a week cutting out 38 in long NACA 0008 cores for a daggerboard. I later found I could buy two 37 in long sections for $12 plus shipping. I can assure you, that is the bargin of a lifetime.

Also, in terms of Marstrom Rudders. Once you pay for the setup for a foam core, it becomes almost a stock item. I would interested in splitting the setup fee for a foam core. Or if someone has cores made let me know where

I have some excellent modern foam core lifting hydrofoil NACA shapes 36 inches long that were cut by a model airplane foam-cutter in California. He shipped them to me covered with light model airplane fiberglass cloth/epoxy. The trailing edges are thin and hollow as described.
These hydrofoil shapes were not tapered: IMHO this aspect could be a nuisance- best done by expert wing cutters.

How are you going to get from a foam core to a finished daggerboard that won't break? By the time you glass it w/ many layers of carbon or whatever the shape won't be the same as the intended foil.
A wood core milled on a cnc machine would need minimal glassing. you can make foil templates to check your curves, and shape a wood blade by hand too.
the blade should be nearly the same shpe as the opening of the trunk under water or excessive water will shoot in the trunck causing lots o'drag.
on the other hand, anything will work, and a sheet of aluminum w/rounded corners will act as a daggerboard. no kidding they exist and do work.
hope this helps.

To get the accurate shape that you can replicate at will, you have to make a mold. Once you have a plug that is the foil shape and thickness you want, you laminate it on a very flat surface large enough so there is extra room on all sides so that you can vacuum bag. I used 1/4 inch thick plate glass glued with the 3M boat glue on to a very flat and true frame made out of 3/4 X 2 inch hardwood.

Next, take a piece of plywood and cut the foil planform shape out of it, leaving about 1/4 inch extra space all around the foil so the plywood will lay flat on top of the layup. If it is too close to the foil shape, the plywood cannot get down to the glass, and you will have to start over. Make sure that the foil plug is waxed good, and has mold release on it, and then lay up 6 to 10 layers of fiberglass cloth on top of the rudder plug, and then put the plywood over the whole affair and vac bag it. You will get a very nice mold that you will be able to duplicate foils from over and over. I did not fill in the back of my rudder mold with anything, but if you use foam, then you can vac bag to some other surface other than the mold. My mold wound up warping a bit, so I had to clamp it down to a flat surface anyway, but I had left about 2 inches around the mold as a vac bagging flange. I would recommend 4 inches actually. If you e-mail Phil at Phils foils, he will make you a mold out of whatever material you specify that is accurate to the coordinates that you chose the whole way down the legnth of the foil for very little money. I think that is what I would do now.

I used foam core for my rudders. Once you have the mold, you will be able to use foam that is shaped close to the correct foil shape to use as a core. It will bend to fit. Some people recommend cedar core for the top half of the foil core... I found it heavy and akward to fit in place. I just used more layers of uni carbon to stiffen it.

I found out that if you try to lay up lots of layers of uni carbon on top of a perfect shaped foam blank, you get a thick foil. That is when I decided to make my blanks with cedar, and one 3 oz layer of glass. Then the mold was a lot closer to correct. Plus you need to use an extra layer of uni near the top of the foil so that it braces the area where the foil goes through the hulls, or just under the rudder bracket, so that would leave a hump under the top layer of the layup. I guess you can use another full layer of uni the whole legnth, but that is not needed for stregnth, and it iwll add extra thickness if you are laminating on top of a blank that is already at proper thickness...

The last few foils I made, I laid up the carbon first, and then glued in the foam once the carbon was cured. Plus I used more layers, I think 3 layers of 9 oz uni carbon, 1 of 5.7 oz kevlar on the inside, and 1 of carbon cloth covering the whole deal. Plus I added another layer of uni that extended down to about 6 inches below the hull or the rudder housing. For my daggerboards, I used 4 full layers of uni.

This Eppler 184 shape has been made symetrical. I did not check out the drag charachteristics. It may be junk for all I know, but seems to work okay. These coordinates are for the rudder thickness... 9.14% thick. I used 8.32 on the daggerboards. The rudders have only stalled on me once in real light air when I had the daggerboards too far forward.

Table
x y
0 1 0
1 0.99683 0.000115494
2 0.98765 0.000573575
3 0.97313 0.001439918
4 0.95362 0.002625577
5 0.92911 0.004159835
6 0.89973 0.006194461
7 0.86584 0.008779829
8 0.82782 0.01189228
9 0.78612 0.015479569
10 0.74122 0.01948562
11 0.69362 0.023805694
12 0.64387 0.02831204
13 0.59253 0.032792143
14 0.5402 0.036928659
15 0.48747 0.040461195
16 0.43492 0.043184139
17 0.38317 0.044960773
18 0.3328 0.04571328
19 0.28437 0.045484214
20 0.23841 0.044402896
21 0.19544 0.042516787
22 0.1559 0.039869581
23 0.1202 0.036447137
24 0.08869 0.032327963
25 0.06166 0.027555898
26 0.03935 0.022198573
27 0.02188 0.016351074
28 0.00938 0.01020189
29 0.00189 0.003696
30 0.0001 0.0005005

When I was deciding, I made a few copies of the different foil shapes one on top of the other for comparison. If you do that, make it fairly long so that you can compare better. I made mine 10 inches long, but would make them longer next time.... like 20 inches. It is easier to get a better idea of shapes if they are larger.

One thing to consider is that thick foils ventilate sooner than thin ones. There was an artical in Tank Talk on a 505 website that recommended a 12 % thick foil.... Other stuff recommends a thinner foil, like 10%. I figure that with the elongated tail on the Eppler, the front part of the foil is very close to a NACA 64010 with the elongation added. Check it out for yourself.

Thank you, Conrad!

Hi Conrad,
The NACA 63 series foils have the hollow/concave surfaces approaching the trailing edge. When you look at the Cd vs Cl curve, drag coefficient vs lift coefficient, you also see that there is a significant drag coefficient reduction in this curve, called the drag bucket, at low angles of attack relative to other foil shapes.
It doesn't cost any more to make a mold that produces parts of lower drag characteristics than it does to make a mold that produces parts of higher drag characteristics. Have you ever seen a production daggerboard or rudder foil shape with the hollow surfaces approaching the trailing edge on any production boat, Hobie, Prindle, NACRA, etc, except the Marstrom Tornado?
Bill
PS If you are really interested in NACA foil sections, get the book, THEORY OF WING SECTIONS" by Abbott and Von Doernhoff.

There were a couple of questions I know the answer to.

Foam Core Dagger boards being too thick - The foam core is cut to accommodate the skin.i.e. the foam core is made thinner than the final shape. For many shapes the trailing edge ends up solid and has to be tapered by hand or use a modified Blount trailing edge or what is called an interrupted foil. The interrupted foil is where the design foil is a little longer than you want. You interrupt the foil to have a 2-3mm thick, Blount, sharp edge, trailing edge. Verbally, test people tell me this will have minimal impact except at high angles of attack and less impact than a chewed up fragile edge

Foam Core Not Strong Enough - On the board I cut by hand I am using 6 lb/ft3 Styrofoam with ~1mm carbon-Kevlar-carbon skin. I would not want to jump up and down on it but it will hold my weight. The RC method for handling the strength issue is to cut the core longitudinally every x inches or so. Replace the foam lost from cutting (1-3 mm) with carbon. This gives you longitudinal ribs and makes the structure strong enough to jump up and down on. I have been told the quick way to make the ribs is to make 48"x6"x1/8" carbon up in advance then cut out what you need on a table saw.

In terms of materials I found 45x45 degree carbon - 90x90 kevlar - 45x45 carbon - 1.0 oz 90x90 glass to work and required minimal finish work. The board I made with uni carbon may be stronger but it was a lot more difficult to finish. I will never use Uni carbon held with monofilament again.

I agree that cedar core would be stronger. I have built both. My one summer of use has shown the carbon foam to be strong enough and it terms of time and money I would cry a lot less if I had to replace a carbon foam board.