HQ35/12 Airfoil

[Fred]

Well, the symetric profiles generate no lift at 0 degrees and generate lift at incidence, but this thin type of profile stall rapidely, well, before starting to generate "lots" of lift.

That's why, on the "fun fly" type of plane, you do a really thick profile (stall later and can go to greater incidence) with a big LE (if that stall, that will stall "gently").  but those profiles are neutral, fly the same inverted and normal.

[Happy Days]

Right...................... (I think :?: )
So now we come to the core of the matter, Fred.

A symmetric wing produces no lift at 0 degree of incidence, the same as a "flat" wing produces no lift at 0 degree of incidence. They both only produce lift by deflecting air downward. Neither wing produces any induced lift

A non-symmetric wing produces lift by both deflecting air downwards, via the underside of the wing, AND produces lift from the camber on the top of the wing. (What I call 'induced lift')

Assuming what I've just written to be true, Question; Why does any one bother producing a symmetricaly cambered wing when, according to the above, it flys no better than a plank of wood?
Why aren't all wings semi-symmetric or flat bottomed? They produce far more lift. (Induced and reactive lift)

I know there must be a reason for symmetric wings, but I just don't know what it is.  :!:

So come on Fred, you aerodynamic guru,..........hit me with the answer!

[Fred]

That's an easy one !  
As ymetric wing is far more efficient than a plank !
Less drag, and will stall later at far greater incidence !

Why aren't all wings semi-symmetric or flat bottomed? They produce far more lift. (Induced and reactive lift)

Because they don't produce more lift !    A cambered profile like the Go535 will produce far more lift than a ClarkY or maybe any flat bottomed profile.

All that without taking account of the speed of the plane of course ! A flat bottomed or semi-symetric profile (well, not all of them.) will be much more efficient at a speed range, before the air layer stop sticking to the profile.
And all that without even talking about the Reynolds number !    

[Happy Days]

Hmmmmmmmmmmmm :?:

Firstly Fred I have to say I'm very impressed with you being awake at such an early hour of the day.............very good :clap:

Now I'm starting to get confussed, which is very easy at my age!

Could you tell me please where I might be able to find a diagram of a Go535 and a Clark Y profile?

You see, I'm thinking if simply having a later stall and offering less drag is the only advantage of a symmetric wing over a plank, why not have a semi symmetric wing with slots in the LE. Surley they reduce  the stall yet offer less form drag than a symmetric wing.

[Happy Days]

I've found a Clark Y airfoil diagram, still can't find a Go535 though. :x

[Alan_Perse]

OK we need to make somthing clear first, this may be a long post     . The camber of a wing is the maxium distance between the camber line and the chord line ( the red and blue lines on the diagram on the prevoius page). It is not the curvature of the top and bottom surfaces of the wing, although the curvature of the top and bottom surfaces of the wing effect the shape of the camber line.
And here's a spanner in the works   , wings that have camber can creat lift at small negative angles of incidence. The reason a symetrical wing creats no thift at 0 degrees incidence is because it has no camber. The top and bottom surfaces of the wing have the same shape, thus the camber line is in the same position as the chord line. As a result there is no distance between them thus no camber.
If your wondering why i know so much its because I have two or three books on aerodynamics to look at   . But I'm not an expert, its the books that are talking     . One of them is called "Model Aircraft Aerodynamics" by Marin Simons, its very good book.

[IceWind]

Alan that seems a good reading!
Thanks for sharing.
I still prefer to read real books than be reading from the web...

[Alan_Perse]

I still prefer to read real books than be reading from the web...

I agree

[Happy Days]

Yes,..........I think I agree with Alan in that probably the best thing for me is to go back to basics.  :roll:  
At the moment as soon as I hear one answer, my brain, (what there is of it) pops up another question.
The problem with understanding lift is that there seems to be no black and white answers. The 'goal posts' are not fixed

Think I'll click on Amazon Books and order a copy of that "Model aircraft Aerodynamics"

As I remember it,..................... "Pi multiplied by R squared over 4', ................ take away the number you first thought of!! "  

 Hmmmm, this could take a bit of time :?:

[IceWind]

Well, compelled by the curiosity i went to Amazon... and yes i bought the book.
There is much info out there i still need to learn.
I dont wanna be around RTF's and ARTF's forever!!!

[Alan_Perse]

Oh No don't tell me I've started something       .

[IceWind]

Ahah!

You probably are getting some commission by making ppl buy that book aren't you?

From my side I've been trying to gather some more info regarding RC airplanes, when you mentioned that book and i went to amazon and saw the comments it seemed a good choice. Also the price for a used one was cheap.

[IceWind]

Just to warn my book has arrived.
Pretty soon you may start asking questions!

[Alan_Perse]

Whats a Book?        :wink:

[Peter]

I was reading an article today on the physics of sailing which mentioned a Nasa aerodynamics e-book site at http://www.grc.nasa.gov/WWW/K-12/airplane/short.html.  Some quite interesting stuff here, including quite a bit on theories of lift (see earlier posts here).  Check out the simulations of airflow and pressure over aerofoils and plates.