I was just wondering if there were any good online resources that explain a little bit about the different airfoils, and the advantages/disadvantages to some of them. I've looked around some, and havn't been able to find much. Any help would be great. Thanks!

The information you want is usually not posted per se.
You have to have a specific use in mind...
glider, pylon racer, pattern.. then find sites with those interests.

It would be mostly for aerobatic/pattern planes.

i am pretty sure on aerobatic airplanes with symetrical airfoils that the top is arched a little more other wise no lift would be created and the plane would not fly.

i read that in a book called Basic Aerobatics.

An airfoil doesn't need camber (the arch you mentioned) in order to generate lift, it just needs an angle of attack.

For aerobatic airplanes, you want to look at symmetrical airfoils because in aerobatics you will want an airfoil with right-side-up performance equal to (or at least similar to) upside-down performance.

What exactly are you trying to learn about airfoils?

Ken - www.litkoaero.com
R/C Aircraft Laser Cutting and Design

Here are two great sources of info that can actually be applied to models:

First, I recommend Andy Lennon's Book, "The Basics of RC Model Aircraft Design" (ISBN: 0-011295-40-2) which is available through Air Age Publishing (Model Airplane News) You can depend on his math.

Second, the Selig database will probably interest you, at http://www.aae.uiuc.edu/m-selig/ads/aircraft.html

Searching through glider-oriented web sites and articles is a great source of information, too.

The research you do can make a serious difference in how your planes fly. I think it's worth it.

Cool, thanks. I'll have to look into that book. As for what I'm looking to do with all of this, I'm trying to design my own aerobatic plane. Yea, I know if I baught one it would probably fly better, but that's not the point now, is it? ;-)

Perhalps I should open a new thread but how exactly does the symetrical foil creat lift if the air is soposed to move faster over the top of the wing to creat a vacum (lift)? Its not realy a symetrical foil hun?

.
NO, you should search here for this beaten-to-death subject!

Say it with me now... "CIR-CU-LA-TION"

My aerodynamics professor would be proud!

Ken - www.litkoaero.com
R/C Aircraft Laser Cutting and Design

He may need a little more detail.

To picture what Ken's saying about needing only angle of attack, not camber, go for a drive with a flat object like your hand or a book out the window.

The aerodynamic pressure on the side exposed to the oncoming airflow will push that side toward the other... so if you slope the flat thing with its leading edge up, the airflow will hit the lower surface and the thing will be pushed upward. That's lift gained the cheap and dirty way, but it's lift.

You could also generate lift using a more curved upper side, but that makes for a lot of drag that works against you when you want to go fast. For that reason, go-fast airplanes use symmetrical airfoils and generate lift by angling them instead.

Sorry! I was being facetious.

If your not afraid to read some mathematics, take a look at "Low-Speed Aerodynamics" by Katz & Plotkin (Cambridge).

Some web resources...

Here's one decent explanation:
http://zardoz1.topcities.com/aviation/490476.htm

This next one is nice because it gives a bunch of explanations:
http://www.aerospaceweb.org/question...cs/q0005.shtml

Unfortunately, neither of the above cover symmetrical airfoils, but the previous post does!


Ken - www.litkoaero.com
R/C Aircraft Laser Cutting and Design

Hi Lance,
Maybe some plain talk would help?
First symmetrical airfoils and lift>
Angle of attack is the angle any object on an aircraft is set at
relative to the line of flight Such angles are labeled incidence.
When a symmetrical foil is set at a zero angle of attack lift is
created in two directions, upwards and downwards. If the foil
is precise (upper and lower curves exactly identical) both of the
lifts will be equal, cancel each other.
Now if you set such a foil at a positive angle of attack both sides
still create lift however the lift on the upper side is of greater
magnitude, thus there is a lift differential in favor of the upper side
The amount of the differential is the positive lift created.
Experience has shown how surprising it is to see desired lift
created by seemingly small angles of attack such as from one to
two degrees.
In the past the NACA developed some mathmatical generated
airfoils which have proven excellent. Good lift and low drag.
This is the 65000 series. In that the 65015 is fine for pattern,
the 65012 is even more stable.
Good luck! Need more E-Mail me, OK?

Hal [email protected]

http://cromagnon.stanford.edu/~sturd.../liftsuck.html

http://www.aa.washington.edu/faculty/eberhardt/lift.htm

http://www.turnertoys.com/G1/aeroScience/default.htm

are three good sites to read respect to lift of wings. To do it properly you must do, as Ken said, the math. But the bottom line is,

That it is not really impact on the bottom of the airfoil or flat plate.

That anything at angle of attack undergoes what is called "circulation" and in the process there is a lower pressure generated on the top and a higher pressure on the bottom.

That pressure differential produces the "lift" that the wing feels.

The process of generating lift makes downwash behind the wing, the magnitude of which is representative of the lift being generated.

Some folks think that the downwash flow reaction is what generates lift. It is not. It is a result, not a cause of lift.

It is not a simple easily described subject based on the fact that there are a whole lot of text books written on the subject. There is also a lot of misinformation about it resulting from bad science presented as fact for years.

When a airfoil generates lift from just angle of attack or incidence is that as effectient as a foil that generates it with conventional flat bottom airfoil. Also does this ( symetricla) airfoil creat drag, with the incidents set at only a few degres. Is this way of generating lift better/ worse than conventional. Besides being able to fly upside down?

Good questions --
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When a airfoil generates lift from just angle of attack or incidence is that as effectient as a foil that generates it with conventional flat bottom airfoil.
---------

It depends (kinda wisheywashy answer isn't it). For instance the big gliders that are used in competition are about the peak of efficiency for lift at low drag (and those speeds, flight conditions and a lot of other stuff that is considered). In this case thay use airfoils that have some undercamber and are fairly thin.

This would seem to make the airfoil with some camber (and it could be flat bottom) the most efficient.

An airplane designer starts out with a set of requirements. With those in hand and a lot of work a airfoils falls out as being the best. Gliders need some undercamber, aerobatic machines need to be symmetrical, heavy lifters need low drag at high angle of attack which will be something else. In most cases the airfoil is a compromise due to the need to take off at low speeds and then do something in the air. What is efficient for one is not for the other.

----------
Also does this ( symetricla) airfoil creat drag, with the incidents set at only a few degres.
---------

A symmetrical airfoil at even the smallest angle will create lift and drag. Anything moving through the air usually creates drag, sometimes lift. The drag due to creating lift will be the highest for the airfoil that is set at the largest angle relative to the wind, regardless of airfoil since it is just a vector quality of the amount of lift being created and the angle of the wing.

The cambered wing can be set at a lower angle to achieve the same lift as the symmetrical wing and so the drag due to lift will be lower. There are other inputs to drag that should be considered also. A search of this forum will give some good discussions.

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Is this way of generating lift better/ worse than conventional. Besides being able to fly upside down?
-------------

It depends, again, on what you want the airlane to be able to do. A symmetrical airfoil on a glider that is set at a few degrees incidence will not be as good as a purpose designed airfoil that has some undercamber.

That undercambered airfoil will not work too well on a aerobatic machine.

Most airplanes used in some sort of competition for a number of years tend to evolve toward an ideal planform/airfoil combinition for that particular competition. Look over the airplanes in competition, the internet is a good source of examples) and see what airfoil is being used and build up a mental data base. You will get a "feel" for what is the best for a given set of requirements.

Basically what it comes down to is the shape of the wing. The shape of the wing depends on the performance requirements of the aircraft. This is where you start getting into high or low aspect ratio, taper, twist, sweep and myriad other things.

Just like Ben said, the airfoil that you need to use drops out of the overall design. And again, airfoils currently in use on other similar craft are a good starting point for creating a new design. You need to look at a similar craft, find out what drove all the design decisions there, and come up with your own informed conclusions.

Ken - www.litkoaero.com
R/C Aircraft Laser Cutting and Design

P.S. Ben... you got my head cranking from that previous thread we had together. I need to re-evaluate my own design decisions w.r.t stability!

Ken, imagine my surprise when it was pointed out to me several years ago.

I was working on the F-4 and F-15 where down tail load was needed often to the point that MD put the inverted slat on the horizontal of the F-4. You tend to develop a mind set of down tail. I would pick up a model, see the big motor on the nose, and not thinking much about it conclude the tail had to balance it (well it does weight wise but not aero wise which is what I was thinking). I was flying rudder only contest ships with big negative tail settings and forward CG and it seemed totally impossible to have an up load.

I have to admit it was like hitting a brick wall, I had to ask my self why had I missed that, it seems so simple.

Oh well, life continues to be interesting.