WING AIRFOILS (how they affect flight)?

[brasscorpion]

I know there is probably a whole library on the subject...but for our purposes (mine specifically) I would like to know your opinions or "facts" on how an Airfoil affects flight characteristics.

For example. Lets take a plane...let's choose a ww2 warbird. P-40, P-51 or anything else.

With everything else being left the same let's change only the wing. Now lets use three categories of wing profiles.

Uncambered:

Cambered:

Flat Plate:

Doing a comparison between these three categories, on the same plane, what would be the Differing flight characteristics of each? :confused:

For example higher speeds needed to keep a flate plate wing in the air over an uncambered wing. Higher stall speeds on a cambered vs uncambered. I also realize that the airfoils on a wing can be changed dramaticaly...from symetrical to semi-symetrical, Clark Y to Modified Clark Y. Not quite sure how these would fit in here. :confused:

Oh yeah and the SQUARE in. and wing loading will also be left equal for each generation.

Is a flate plate wing a good wing for an aileron trainer???

Brass

[Ollie]

If you want to under stand differing flight characertictics of airfoils, throw out the categories Undercambered, Cambered and flat plate.

Better categories are: Mean Camber Line and, Thickness. All zero mean camberline airfoils belong to the class are same upright as inverted performance. The skinny thickness, zero mean camber line is the flat plate. As the mean camber line increases the maximum lift increases as the attack angle increases up to the stall. As the mean camber line increases as the maximum angle attack increase at the stall. If the thickness is zero the drag is minimum when the camber is zero and the angle of attack at zero. Etc, etc, etc. I would have to write a book and I am out of energy.

[biber]

Well, then you have to determine some other parameters too, e.g. relative thickness, amount of camber, leading edge radius, actual Reynolds number, aspect ratio of the wing, and so on...

That issue is so complex that really simple answers are hard to give.

biber

[Sparky Paul]

...

Is a flat plate wing a good wing for an aileron trainer???

Brass
.
Yes. If the plane is a foamie.

[slipstick]

If "Brass" meant what he wrote he was talking about UNcambered not UNDERcambered.

Flat plate is just a special case of zero camber (or symmetrical if you like the old-fashioned names). It's usually high drag and has rotten stall characteristics, more so than a smoother zero camber airfoil.

Foils with camber cover everything else. There are thousands of them and they sure as heck don't all behave the same.

Steve

[raptor22]

Flat plate is just a special case of zero camber (or symmetrical if you like the old-fashioned names). It's usually high drag and has rotten stall characteristics, more so than a smoother zero camber airfoil.

Not entirely true.

If you have a very small plane, like a foamie, the flat plate is good. At smaller reynolds numbers (small slow plane), a flat plate is actually superior to thicker, more traditional, airfoils.

--Alex

[brasscorpion]

Thanks guys.

Okay so if a Flate Plate wing is basically an Uncambered airfoil then we only have 2 types of airfoils to discuss. Those that "lift" and those that don't.

I understand how they work...the air travels over the wing at different rates. Faster under the bottom...slower over the top. This causes X pressure and then up and away.

I know the type of wings used on Park flyer and slow flyers have airfoils that allow the plane to fly really slow so they basically never stall as long as the prop is turning.

But 3D planes also fly around really slowly but have a flat plate wing.

Now I know that 3D planes FLY ON THE PROP, which basically is just a prop spinning carrying a motor and some gear behind it. But can these planes fly like normal planes. Also I heard that some people will debate that a wing with an airfoil will outperform one that is a flat plate.

But here is the catch...the electric combat guys are building flate plate wings, so there has to be some benefit. I am just trying to figure out what that is other than ease of construction.

Do these planes fly "BETTER" with flat plates. So as someone said these types of Flat Pl;ate wings stall really bad. That is what I am trying to find out...FLIGHT CHARACTERISTICS

What if I put a Dihedral on a flat plate???

Brass

PS I think I meant UNCAMBERED. Don't know what undercamber is. Also I am used to the older terminology like "symetrical" and such...

[biber]

[QUOTE=brasscorpion]Thanks guys.

"Okay so if a Flate Plate wing is basically an Uncambered airfoil then we only have 2 types of airfoils to discuss. Those that "lift" and those that don't."

They all do lift! Only the angle of attac has to be bigger on symetrical (uncambered) airfoils, since they don't lift at zero angle of attac and cambered ones do even then.

"I understand how they work..."

I'm not sure.

"the air travels over the wing at different rates. "

Yes that's right to some extend.

" Faster under the bottom...slower over the top."

No, it's really more the other way around.

This causes X pressure and then up and away.
But 3D planes also fly around really slowly but have a flat plate wing.

Angle of attac is the key. If AoA applied on a "symetrical" airfoil the situation itself isn't symetrical anymore and topflow isn't a reflected image of the bottomflow. So while there ARE different things happening on top and bottom, why shouldn't be there lift?

Try to imagine the wing deflecting the airflow around itself (on top and bottom aswell)!
If the oncoming air is deflected downwards, the wing has to do this by using some downforce on the air since air has a mass and thus inertia.
Surely you have heard the thing of actio = reactio.
The reactio to that is the upforce of the deflected air on the wing, that's lift.

And that's why there's (and has to be) downwind behind wings when lifting.

"Now I know that 3D planes FLY ON THE PROP, which basically is just a prop spinning carrying a motor and some gear behind it. But can these planes fly like normal planes."

Yes of course they can. Not very efficient though but this is easily compensated by some more power.

" Also I heard that some people will debate that a wing with an airfoil will outperform one that is a flat plate."

The advantage of a more complicated wingsection is not too big in some special cases, so that it doesn't pay of then.

"But here is the catch...the electric combat guys are building flate plate wings, so there has to be some benefit. I am just trying to figure out what that is other than ease of construction."

Maybe no other benefit. But isn't to simplify construction a good reason?

Do these planes fly "BETTER" with flat plates. So as someone said these types of Flat Pl;ate wings stall really bad. That is what I am trying to find out...FLIGHT CHARACTERISTICS

At very low RE-numbers they are not that bad, but for bigger REs there are many better options.

"What if I put a Dihedral on a flat plate???"

Basicaly the all same as on any other wing.

biber

[BMatthews]

The foamies and similar will work with flat plates because they ARE so light. Also they use the terrible stall charactaristics to actually brake suddenly in the performance of their spectacular maneuvers. For the job they do in that arena they work great. For a 40 size trainer a zero camber flat plate would be a disaster.

All else being equal camber in an airfoil helps the airfoil to achieve a higher lift coefficient before the stall occurs. So a model with a NACA 0010 (10% symetrical) will stall at a lower airspeed than the same model with a NACA 3410 ( 3% camber at the 40% point and still 10% thick).

Again, all else being equal a thicker wing will stall at a higher lift coefficient than a thinner wing. So a model with a NACA 3408 (figured out the numbering yet?) will stall earlier than the same model with a NACA 3415.

The Clark Y and similar is not a unique airfoil just because it has a flat bottom. It's still a symetrical envelope around an arched center line.

Finally, for my part at least, airfoils for models work best over a proven size and camber range. Cambers that work best for us tend to be from 0% to 6% with a few special cases showing up in the heavy lift design area thanks to some serious windtunnel work by Selig, Eppler and a few others. Thickness for models ranges from 0% for indoor duration and some single surface parkflyers to 18% for some fun fly types that are trying to do their very best to resist stalling in the quest for super tight and quick multiple loops. With the current trend to 3D we are now starting to see the thickness come back down to where the wing will just hold the radio gear.