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Old Jul 20, 2005, 08:35 PM
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Costa Rica, San Jose, San Pedro
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Another wing design question (or may be two)

I'm having my building cravings one more time and not having anything around I'm thinking in that second set of wings for my Aquila XL fuse.
I've been looking around for a more sleek airfoil but if I go with something like an AG40 would not fit the roots in the fuse, so I think the best I can do is just put some phillips entry in the original (flat bottom) airfoil. And make it something like the Aquila Grande (only more grande ).
I also was thinking it might be fun to try and make a 4 servo wing with flaps and ailerons, for that I was thinking in getting rid of the poly and go with just the dihedral at the root.(Am I getting into deep water here???)
Now my questions are:
1.- Would it be better (or would it make any difference) to tapper the whole wing from root to tip continously, or just make the center pannel straight and tapper the wing tips only, like the original just getting rid of the poly.?

2.- should I keep the same wing surface? or change it for bigger or smaller?

3.- If I decide to put some CF on the spar caps, what it is the best way?
Should I put it on the top of both sparcaps?, on the bottom of the lower and the top of the upper? Or only on top of the upper one?

4.-Should I keep the same airfoil all the way? I noticed the AG goes from phillips entry at the root but it decreases as it gets to the tip and end up with flat bottom at the very tip of the wing. Any reason for that?

Any suggestions would be appreciated.
Thanks,
Fernando
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Old Jul 20, 2005, 10:12 PM
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By design reason:

"Design Philosophy"

by Don Stackhouse

"There have been some rather heated discussions lately on the R/C Soaring Exchange about the relative merits of computer analysis versus old cut-and-try methods in the aerodynamic design of wings. Similar threads have argued over the shape of the "ideal" planform, the "best" airfoil, the "optimum" aspect ratio, and the validity of modified airfoils or of blending from one root airfoil into a different tip airfoil. All this controversy reminds me of one of my favorite stories:

"The Four Blind Men and the Elephant (an old Hindu parable)

"One day four blind men encountered an elephant for the first time. They approached it cautiously, but with great curiosity. The first one grabbed hold of the trunk and declared "Aha! An elephant is just like a snake!" The second found an ear and replied "No, an elephant is exactly like a tent." The third bumped into a leg and decided the elephant was just like a tree, and the fourth caught the tail and maintained that the elephant was just like a rope. They all went home arguing, each steadfastly insisting that he was right and the other three were wrong.

"The flight of a model sailplane is a complex phenomenon, each portion of the model seeing its own unique set of conditions at any given time, yet still having an influence on all of the other parts of the model at the same time. In addition, we expect our models to perform well at a wide variety of operating points within the overall flight envelope. To help us achieve this aim we have available a large database of experimental data and theoretical analysis tools, plus the insight garnered from all of our own experiences and the experiences of others, and the results of actual tests of the model. The results depend on how well we use all of this information together to reach the final design.

"If we get hung-up on one parameter, or one design technique, or one phase of the design process, we automatically give ourselves a case of "tunnel vision". There is no single airfoil, aspect ratio, planform, tail size or type, etc., that is optimum at all flight conditions for even a single model, much less a variety of models.

"While it is true that the section at the mid-span of a wing of two wildly different tip and root airfoils may have or may not have any of the characteristics of its parents, it is also just as risky to believe that the airfoil that is optimum for the conditions at the root will be equally appropriate at the tip. Ideally you should study the sections at a variety of points along the wing, as well as local chord, twist, flow characteristics, et cetera.

"The effects of what is happening at the tail, along the fuselage, along the span of the wing, all influence each other in different ways at different flight conditions, with corresponding effects on the overall control, stability and performance of the model.

"None of our design tools is perfect. None of our data is completely reliable at all conditions, and some of it isn't very reliable at any condition. In my experience the best approach is to use all of the available tools and data to the fullest extent possible, then look for the consensus forming between the different approaches. This way the strong points of the different approaches can compensate for their individual shortcomings. The first '93 Monarch hlg went through 150 hours of computer work, PLUS six fuselages, seven tails and eight wings before we froze the design.

"If you try to build an elephant with only a tree, or only a rope, a snake, or a tent, your result will almost certainly fall short of your expectations. Likewise, the model that was designed with only theoretical methods, or only past experience, will probably not be the best design possible. Only by using all of the available tools as cooperative members of a team effort can you achieve a design that is more than just the "sum of its parts"."

Start with two design "tools" PC Soar and Profili2:
http://my.athenet.net/~atkron95/pcsoar.htm
http://www.profili2.com/eng/default.htm
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Old Jul 20, 2005, 11:02 PM
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Ideas

Fernando

I am not any kind of designer. I usually do things in a "that looks about right" manner. Don't really know a lot about all the various airfoils. So... just know, that, the following ideas are coming from a TOTAL amatuer, and are just prejudices of mine which you can kick around.

1. Would have no polyhedral and very little dihedral about 2 - 2.5 degrees.
2. Would use a double taper (taper LE and TE) of about 140" span. Starting with a root chord of about 10" to tip of 4".
3. Would use E205 airfoil (mostly flat with high entry) which is fairly easy to build. Would give wings flaps and outboard ailerons to within 2" of tip.
4. Do a D-box construction.
5. Make spar using total carbon fiber top cap and same for bottom cap, with ply forward and rearward shears in root area.
6. Would wrap joiner area with kevlar thread. Pretty much the way the "Houston Hawk" wing is built. As I'm sure you know there's a build thread on the Hawk.

These are just my 1 1/2 cents worth of ideas.

erich
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Old Jul 21, 2005, 12:26 AM
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erich,
Your ideas are OK except for the first. With out ailerons and low dihedral, the plane will have very, very bad turning ability. Without ailerons and low dihedral, the bank might not recover even with the pilot trying with rudder and elevator. The Houston Hawk uses about six times the polyhedral angle compared to the dihedral 2 - 2.5 degrees.
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Old Jul 21, 2005, 12:49 AM
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Looking more closely

Ollie

I know. See end of #3 in #3. Now what do you think?

erich
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Last edited by erich; Jul 21, 2005 at 12:51 AM. Reason: Looking more closely
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Old Jul 21, 2005, 05:15 AM
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erich,
I think you read better than I do. Thanks.
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Old Jul 21, 2005, 09:17 AM
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I wouldn't build a low dihedral wing without ailerons, actually the only reason I would get rid of the poly is to add ailerons.
I saw on previous threads that a poly ship doesn't like ailerons (normally).
Now Erich, when you say to use total cabon for the caps, do you mean the whole cap made of carbon?.
Thanks,
Fernando
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Old Jul 21, 2005, 12:10 PM
Gliders, Helis, and 3D
Eric Zanutto's Avatar
San Diego, Ca
Joined Jul 2005
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as far as the carbon fiber goes....you want to use uni-tape for the spar. this basically looks like what its called, tape. the sole purpose of uni-tape along the spar is to limit up and down flexing of the wing. think of the uni-tape acting as a support cable in a suspension bridge.

so this plane doesn't have ailerons now and you want to make a new wing with ailerons? if this is the case ( im not sure what your plane looks like) then I would go with a slight dihedral and either full span ailerons or half flap half aileron. if you decide to go with a wing design that tapers you will difinetly loose wing area if the same span is kept, but will most likely gain performance. in performance you will notice better penetration and speed, especially if you plan on tapering thickness too. however, this new wing design will not climb as readily as before but I think you will have a better performing aircraft thats more fun to fly. If I were you i'd add the ailerons, thin the airfoil, and keep a strait wing with tapered tips. just easier to make.

if you are not ading ailerons then poly hedral it the way to go. last year I designed a glider with v-tail and no ailerons. the wing only has up bent wing tips. this mixxed with the v-tail made a very manuverable airplane but it yas tons of uncanny yaw. but i wsan't trying to make a very stably ac.
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Old Jul 21, 2005, 12:17 PM
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San Diego, Ca
Joined Jul 2005
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p.s.

you probably saw the post from my dad on his sensor 117. this originally had a poly hedral with no ailerons but I convinced him to put ailerons on it, we'll see how it goes.
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Old Jul 21, 2005, 04:32 PM
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Fernando

They're called carbon fiber laminates I got them from "Aerospace Composites"
Here's a link to the page: I got the Cl-6 .060" by 1/2" by 36" this was for a Houston
Hawk wing. It takes the place of the spruce spar caps (top and bottom). Used epoxy on the shear web to spar cap joint. Worked fine.

Home page: http://www.acp-composites.com/ACP-CAT.HTM

Specific page: http://www.acp-composites.com/acp-ucfl.htm
on this page click on "pricing info" to see table from which I purchased
mine.


erich
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Old Jul 23, 2005, 03:48 PM
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Eric Z:
Thanks, that is the idea (ailerons + flaps, slight dihedral), I'll see what can I do about the airfoil, may be I can start at the root for a couple of ribs with the original (otherwise the roots on the fuse will be off the wing's root) and then start thinning it with a different one. If I do so, I think tapering the whole wing would be easier than just the tips as I probably need to cut ribs one at a time anyway.
Quote:
I convinced him to put ailerons on it, we'll see how it goes.
Let me know...
Quote:
( im not sure what your plane looks like)
The plane is a floater (I've posted few pics, the Aquila XL) and I'd like to have a set of wings for windy days, so acording to what you've said this would work (in theory at least).

erich:
Darn! I've already place the order a week ago or so and ordered only few CL1's
I didn't think about using CF spars caps only.
I might need to place another order.
So, if I'm correct the CL6 would be like 1/16 of an inch or 1.5 mm thick (is that enough for spar cap on it own, of course with the shear webs)?
Fernando
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Old Jul 23, 2005, 06:15 PM
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Fernando

You can get different thicknessess. I used this thickness because it's what was called for on the Houston Hawk. Am not absolutely sure, but I believe every Houston Hawk built, used the same CF as I did. And have heard nothing but good results during launchings. Actually what the, plans for the Hawk, call for is .06"(CL6) for top spar cap and .03" (CL3) for bottom cap. And this is what I used. This is just my unscientific test, but I tried to break a small length of the CF and also same length of spruce it seemed to take at least twice the force to break CF over the spruce. When you get one of these sized pieces of CF you will see it's just as rigid as the same size spruce. But a lot stronger. It was also very easy to work with.

Here's a link to Janco Models which sells the Hawk. On the web site are names of distributers and a bill of materials. Check it out, especially the link to "houston hawk project" and then "bill of materials".

http://www.jancomodels.com/hawk.html

Here's a photo of my Hawk wing with CF top spar clearly visible, the yellow is kevlar thread, which the instructions recommended in the root area.

erich
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Old Aug 12, 2005, 02:41 PM
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ok, here goes another one,
If I get rid of the poly and make it dihedral only, I guess it's better to taper the wing from the root to the tip continously, at least for the looks, I'm not sure if this will afect the performance (does it????).
If I do taper completely, do I want to keep the same area???
I guess changing the airfoil to a faster one, getting rid of the poly and adding ailerons and flaps will make the plane faster and better in windy conditions but not as good in thermal flying. So do I want to keep the same wing area or should I keep the original root and tip chords and consider losing some surface area?
Fernando.
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Old Aug 12, 2005, 02:55 PM
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Another thought...

In this case, that the project is an Aquila Grande and share the same fuse as the original Aquila, I guess losing some wing area is not a big deal, isn't it?
Considering that the Aquila had a fair amount less wing area than the grande.
What about the tail feathers?.
Fernando
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Old Aug 12, 2005, 10:45 PM
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Wilsonville, OR, USA
Joined Mar 2000
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Hi Fernando.

I don't like the look of straight tapered wings, but that's me.

For the wing root to match a different airfoil it might be possible to create a fairing. And your idea of having the root rib as the original airfoil might work quite well.

For construction tips look at Mark Drela's Bubble Dancer at http://www.charlesriverrc.org/articles.htm. He shows CF techniques on the spar. Very informative.

For planform analysis look at Liftroll and the Liftroll Cookbook http://www.geocities.com/jebbushell/COOKBOOK.htm . It talks about spanwise lift distribution caused by the planform and why that is good or bad. I used this when I was designing my DLG wing. Ollie needs to add this tool to his list.

Different airfoils are chosen at the end of each panel where the Reynolds number is different. Mark Drela plans often show the Reynolds number right on the plan. Then the airfoil is chosen based on the Reynolds number.
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