Hello all. I'm a senior in college graduating with a physics degree and since I have a passion for radio control, I was trying to find a topic to research for my seminar project. This is an all semester project which I give a half hour seminar at the end of the semester. I was wondering if there are any topics that need to be researched with aerodynamics. I was initially going to do wing tip vortex reduction but I think that I should do something a little more complex.
I was just wondering if there's any outlying questions with aerodynamics that I might be able to solve, such as wing tip vortex reduction. I also plan on designing and building my own airplane to learn CAD and apply my research to my airplane (this part is just for fun).
So, if you guys have any questions or any experimental things that I could try, that would be great!!

Thanks!

-Jesse Goebel
UW-River Falls Physics Dept. River Falls, WI 54022

Jesse, Send me your E-mail address, in a PM if you prefer, and I'll send you some design articles. Dan.

Just looking through a bunch of the threads in the Aerodynamics part I've found some terms I have an idea what they are but not 100% sure. Ground effect, Chord, Airfoil camber, wing washout are all terms that I think i could try tweaking to get better performance, but what questions are there related to these terms that need to be answered or could use a solution? Also, my friend was telling me about the buildup of air pockets on the wing of air that's not moving because of the friction from the wing. We were thinking of a way of decreasing that.

I sent you two E-mails with about 4 to 5meg attachments. Dan.

Dan that was pretty much a book on how to build an RC airplane. Thank you very much for sending that I'll probably read through that before I build mine.
I'm just wondering if there's any questions such as...how to reduce ground effect or wing tip vortices etc...Are there any other outlying questions like that?

There's nothing really new under the sun. All these items you mention above have been studied for years. Tip vortex reduction is why many aircraft use those tip fins on the wings. It's also why sailplanes use the Schumann planform in a lot of cases. For the ultimate use of the ground effect google for ekranoplane. The rest of the stuff is all things we modellers use or not as needed depending on the flight mission of the model. As for the "air pockets" look up "separation bubbles" and "laminar flow" as it applies to airfoils. Then go look for information on turbulators, invigorators and other options for forcing the earlier breakdown of the laminar flow and why this is often preferrable to extending laminar flow even though there's a drag penalty. All this and more is out there either in books or on the web. I'm not trying to shoot down your enthusiasm but it's wise to study the field of existing aerodynamics and then see if there's a hole in there someplace. Since most study has been aimed at full sized aircraft that operate at far, far higher reynolds numbers than our models there's actually a LOT of holes as pertains to our size of airplane building. Most are not really important as any drag penalties are actually an advantage as in the flat foam 3D models that use the "bad" charactaristics to advantage and in a typical sport model just adding a bigger engine will mask a host of drag issues. Also it's not like any of our models flies in a steady state for long. If they did they'd soon go out of sight. So in real use our models are constantly shifting radically through a very wide range of lift coefficients so even trying to select an airfoil that is optimized for any one small range of use is a useless passtime in many cases. Having said this there are a few specialty areas in modelling where all my downplaying of this is not valid. These are such things as racers, sailplanes and heavy load lifting designs as used in the SAE contest.

So best of luck with picking your topic. I also suggest that you'll likely get better marks if you really narrow down on a topic and then dig deep rather than a broader field with less in depth analysis. At least all my prof's liked the more focused and deeper study.

Wow thank you very much for that info. My lab partner had been talking about something to do with laminar flow and reducing drag and air pockets that build up on the tops of the wings.
Actually I was reading that you want the turbulence on the tops of the wings... Right?

So I was just reading about ground effect and how it works. So if it works from wing tip vortex reduction and creating a cushion of air, is this why biplanes were developed? What if you had a second wing that was strictly for creating a false ground effect? I believe it could be made lighter and still create the ground effect.

I was thinking....have they accounted for race planes always being in a loop? do they have special airfoils? just curious

[link=http://www.mh-aerotools.de/airfoils/pylondev.htm]http://www.mh-aerotools.de/airfoils/pylondev.htm[/link]

Well, yes and no. Ideally for minimum drag you want the flow to stay laminar from LE to TE. On the big stuff with mega high Reynolds numbers this can just about work. Note the airfoil used on the old P51 with the really far back maximum thickness point. Those were the so called "laminar flow" airfoils that were shaped that way to promote a longer than typical for the time laminar flow for much of the airfoil. The drag reduction in cruise was very noticable on that plane. Modern sailplanes use such airfoils as well to reduce the energy needed to fly at any given airspeed so they sink slower.

The downside is that laminar airflow is more prone to separating when the going gets tough. One way of reducing or delaying this separation is to purposely turbulate the airflow that is very close to the wing's surface. This turbulent boundry layer is much more "sticky" than a laminar boundry layer so it tends to hold the air flowing a bit further away more to the airfoil shape. This can delay the formation of separation bubbles, reduce their size and speed the re-attachment as the angle of attack is reduced. Some books or articles will say that a turbulent boundry layer delays the stall. In a way it does since the leadup to the stall is the formation of the separation bubbles. The stall occurs when the separation bubble no longer re-attaches before the trailing edge. This is the difference between an airfoil having a "hard" or "soft" stall. The hard stall is when the flow separates and just lets go rather than form a bubble with a downstream re-attachment. Airfoils that have a "soft" stall or show signs of a higher drag mode before the stall do so because of a large separation bubble over a range of angles of attack before the actual bubble flows off the trailing edge for a "proper" stall.

Now an airfoil that uses turbulent boundry layers to reduce or delay the separation bubble formation is more draggy than one that has a big portion of the airflow as laminar. But the issue is that when the laminar flow breaks down the drag is really high while with the turbulent flow the drag is initially a little higher but the drag hit when it does produce the much smaller separation bubbles is far less. So you trade a little optimum performance of the laminar flow for the wider sweet range and more consistent performace of the turbulent boundry flow.

This is the Reader's Digest version. There's more to it all than this if you really want to get into it.... MUCH more. Suction and blowing boundry layer augmentation, various options for generating turbulent boundry layers and on and on.

And before you suggest "Great! We'll do a laminar airfoil that can be used on models!" there's more bad news. Due to the Reynolds numbers our size stuff operates at it is VERY hard to maintain laminar flow. Also if we can for a while then when it rips free of the airfoil surface it tends to form much larger and more harmful separation bubbles than on the full sized stuff. And then there's the fact that for such critical airflow patterns the airfoil shape not only needs to be mirror finished but it needs to be very accurately formed to a level that is just within the ability or techniques used by modelers. The only method that comes close is cored double skin composite moldings pressure formed in CNC milled metal molds. Such wings have been done for some of the very fancy and high priced contest sailplanes used at the world champ level. However they are just far too expensive for mainstream use.

I'd suggest you just drop this avenue unless you're actually trying to go down that Ekranoplane path. Keep in mind that planes only experience ground effect for a very, very short part of their flight. It's one of those things that just is rather than something to be optimized. On any given flight the plane is through and past the ground effect mode in way less than 1% of the flight duration unless you're flying a crop duster. Crop dusters do fly in ground effect conditions for much of the flight but they are already optimized pretty well for it by either using a biplane configuration such as the Grumman Ag-Cat or the old Piper Pawnee. Even there I'd be highly surprised if the designers actually optimized these planes to fly well in the ground effect other than as a side benifit.

Biplanes were developed as they were for an equal blend of structural and aerodynamic reasons. From the structural point of view it allowed the upper and lower spars to be joined with wire diagonals and struts to form a bridge like truss arrangement that handled the flight loads with the rock bottom of materials. Less materials meant less weight that the low power engines of the day had to lift into the air. Also the increased wing area served to reduce the landing speeds and shorten the takeoff and landing distances on the rough grass airfields of the day. It was a very pragmatic choice that was determined by the low power output of the engines they had to work with.

All of this points to the fact that you and your buddy need to read up on aviation more generally to get a better feel for what is important and what is just there as a side effect of no importance. Nothing we've written here is new in any way at all. Other than the reference to the laminar flow airfoils all this was well known and in use by the mid 30's or earlier. And the laminar flow stuff showed up in the later 30's in time to be used on the Mustang which was designed in late 1939 or early in 1940.

Oh, for your racing plane it all comes down to choosing an airfoil that has a low drag range at the very low lift coefficients when on the strightaways and yet can provide reasonably low drag at the moderate lift coefficients in the higher G turns. Again this is known and designers can calculate the requirements and pick from a variety of airfoil families that provide an extended low drag "bucket" as seen on a lift drag coefficiet graph. Sailplane designers of both full and model sizes do the same thing when they select an airfoil for the latest new design. Or if the rules allow using flaps and ailerons that can be deflected to a small droop angle to add camber under high G conditions will alter the airfoil's camber enough to minimize the drag in a high G situation while providing a very low drag low camber shape for the straights.

I hope I don't sound like I'm ripping apart all your ideas. I can see the enthusiasm from here in the way you're writing and I'd hate to be seen as throwing water on the flames. It's just that there isn't anything new here that hasn't already been analyzed and optimized on and on by so many others before you in many ways. Some general reading of historical aerodynamic studys will show you what I mean on this. As for optimizing some aspect of models it's pretty hard. Our models are just not flown in a way that compares to full size stuff other than perhaps jet fighters which come closer to how we fly our models when doing combat maneuvers. The rest of the time the full sized stuff is all obsessed with flying in a straight line at the highest speed and minimum fuel cost for long times. This in no way at all fits in with how we fly models other than the Atlantic crossing by an autopiloted model that set the record a couple of years back.

Wow thanks for all the info. Really all I need is to come up with some experiment to test the different effects and measurements from say wing style A and wing style B. I was talking to my friend who did his seminar last semester and he was just saying you can do things that have been done before, and basically copy someone else' experiment just so we can show that we know how to analyze data collected etc. I think I've decided to jump into wing tip vortex reduction. It's only a 1 credit class so my prof said keep it simple, and I think that wing tip vortex reduction would be a good topic. I also have to include two or more journal articles on this topic from a scientific magazine or other source. I know there's some out there that I've found and I'll use to reference in my final paper too. Any other comments would be appreciated!

Thank you very much for what you've all said so far.

-Jesse

Hey.

I am not trying to discourage you here but aerodynamics is of all topics NOT the one to be completely covered in a semester and then used to make some major improvements on an airplane. For ground effect, there is not really any solution to it I'm afraid. What solves ground effect problems are high or low wings, and the position of the stabilizer. I have a 1000 page book whose 15 pages cover the effects of the ground effect on the neutral point of an aircraft and the elevator defleciton required. Nuetral point is the point on an airplane about which the pitch stability does not change- like the aerodynamic center of an airfoil.

Don't worry if you don't understand as I suck at explaining- I'll send you scans from the book so you can elarn some equations which can aid you at possibly defining a formula for the optimum position of the stabilizer on an airplane depening on ground effect? Yeah, give me your email and I'll send you a couple of useful scans.

Lafayette.

I'm going to just design a wing tip that should help reduce the vortex and drag. I'm not out to find the fundamental theory of aerodynamics or anything...Just a simple seminar on something I covered . Thanks for all your help guys!

So you'll have a normal wing, and one with your tip on it. Why not include a Hoerner tip in the mix.

we'll see, I'll have to look into it

So you're going to narrow the focus down to one aspect. That's a wise choice. It's far more mark worthy to focus on one topic and do a good job of analyzing it than to spread yourself too thin and not cover the topic to the depth that is expected.

An instructor I had for effective presentation once spent 20 minutes talking about eggs. Not all of them. Just the ones we buy and cook for breakfast. I learned a lot about both eggs and the importance of focusing a topic.

For starters on your paper google for schumann, hoerner, maule stol and winglets along with the term "wing tip" to get some starting points. They all have their uses, strong points and weak points that make them perfect for some applications while being an anchor for others.