wing thikness
 

i just came home from flying my own design funflyer with an 18 % airfoil and could not se the difrence from flying it with a 12 % airfoil ! my quistion is does it relly make that much diffrense?
at low speed were it relly shoud shine the reynolds numbers is low ... am i totally wrong?? some guys even fly a flat wing and the plane does not seme to mind.

RE: wing thikness
 

you are seeing things as they really are .
Here is the short course:
On these small slow planes -- the thick wing is easier to build and get best strength.
It also is LESS efficient- but less critical to angles of attack.
So -if you could build it at say 5%- yet mantain rigidity -it would fly just fine .
We have tested this to a fare thee well.
radical angle of attack changes with no funny tipping /snapping etc., is easy
The secret (no secret ) is make it as light and strong as possible lots of control throw -lots of reserve power .
and make it at least as long from prop to tail as wing tip to wing tip -
All rules about "why do things fly "and CG nature does apply BUT the very nature of being small and light gives you a huge window of design to play in .

RE: wing thikness
 

thank you fore your quik reply.. i only build foam wings so it would be just as easy to build a 12% ving as i would not have to make it hollow.

RE: wing thikness
 

by making it hollow- how many oz's would you save vs the many hours of trying to make the center hollow? also extra internal bracing activity? forget it and plunge ahead. dick

RE: wing thikness
 

foam weighs one pound per cubic foot.
You are lucky to scoop out an ounce - if you leave in torsional resistance.
It is the least effective weight reduction method.
The strength drops faster than the weight!
Thick stuff - yes - double cut the wing -one outer cut -one inner cut.
here is the tricky part
make the inner cut with a little bit of draft -such that you can re-insert the center and it will slide in tightly
Now - slice off a few 1/2" wide ribs -from the cente cut - wet them with a mix of ProBond and water and slide em into place
This is effective weight reduction as the strength is still good .
but under a 12% airfoil - fer get it

RE: wing thikness
 

making a hollow foam wing is not mutch trouble .. i make them in to pieces and glue them together with white glue , and it will save me 1/2 the weigth off the foam. i just made a 10% wing 1100 mm x 350mm weigth 290 grams (with brown paper skin) the hollow 18% was 380 grams..

RE: wing thikness
 

I'm not going to beat the airfoil thickness into the ground because I believe Dick's analysis is pretty much on the mark. I will however, add this: Generally speaking you see real thick airfoils on 3D and fun fly type aircraft which are flown slowly and close in. A thick wing is draggy and will help keep the plane from accelerating too much on down lines.