Adjusting airfoil parameters - HELP!

[zbrubaker]

I'm building a model airliner, and I'm having some design issues with the wing. I plan on using a good-old Ckark-Y airfoil. The root chord is 11.5" long and the tip chord is 2.5" long. I'm using Compufoil to generate my foam cutting templates. I'm not sure how adjusting the thickness, camber, etc will effect the performance of the airfoil. I obviously don't want a really fat airfoil at the root.

Here's a little airframe info if it would help:
span: 42"
AUW: 17-19oz.

It's a multi-sweep wing (almost identical to a DC-10)

[Sparky Paul]

Your plane is too small to be concerned about the details of airfoil design. The Clark-Y unaltered will do just fine.

[Sail 'n Soar]

But watch that taper ratio (<.22). Outer portions of the wing will be working much harder - operating at a higher local CL/angle of attack than the inner are, tending toward tip stalls.

[zbrubaker]

It's a swept, multi-tapered (two) wing. I plan on building 3 degrees of washout into the outter wing panel.

I'm not looking for any major aerodynamic gains by changing the airfoil parameters, I just don't want the wing to look ridiculous with a extremely thick root airfoil section.

All I'm looking for is to find out if there would be any negative effects of cutting the thickness of the root airfoil down to 3-4%

[BMatthews]

Originally posted by zbrubaker
It's a swept, multi-tapered (two) wing. I plan on building 3 degrees of washout into the outter wing panel.

I'm not looking for any major aerodynamic gains by changing the airfoil parameters, I just don't want the wing to look ridiculous with a extremely thick root airfoil section.

All I'm looking for is to find out if there would be any negative effects of cutting the thickness of the root airfoil down to 3-4%

There could be if you thin it too much. The stall and lift charactaristics will change. But for the bad or the better is up for grabs.

If you want a thinner wing then check out the thin AG series of flat bottom hand launch glider airfoils by Mark Drela. The AG 03 is only 6% thick and is made for good lift at low wing loadings and Reynolds numbers.

[MikeSt]

Originally posted by Sparky Paul
Your plane is too small to be concerned about the details of airfoil design. The Clark-Y unaltered will do just fine.

(Here's a little airframe info if it would help:
span: 42"
AUW: 17-19oz.)




Interesting. At what size do the airfoil effects become noticeable ?

[Sparky Paul]

" Interesting. At what size do the airfoil effects become noticeable ?"
.
With the extreme difference between root and tip..
11 to 2, a flat plate with a rounded front and tapered rear would be sufficient.
Expecting to control aerodynamic effects with such a small wing isn't feasible as the Re is in the region of insect flight at the tip, and model airplanes at the root.
And a model aiplane won't behave well (aerodynamically) with the small Re this one has overall.
.
As for cutting the root thickness to 3-4%, it would make more sense to build an undercambered section all the way out. The root would then look real (who looks at the bottom anyway) and the plane would be a decent but slow flyer, if the weight could be halved.
Otherwise, it's going to have a high wingloading, which means it must fly fast to fly at all.

[zbrubaker]

Hi Sparkey,

Thanks for the input. After looking into it, I'm going to use an Eppler 379 (under-cambered with some reflex at the T.E.). I want this model to be in the parkflyer category, so slow is what I'm looking for.

Most people seem to think that aerodynamics don't matter at this small scale, but they do. If you don't believe me, look into the the work that Mat Keenon has done with micro sized aircraft.

My wing loading will be pretty light...somewhere between 8.5 to 9.5 oz/sq. ft. I'm attaching a pic of the wing planform.

[Sail 'n Soar]

It is going to be tough making any specific airfoil accurately with the cord sizes of most of your wing. This is especially true of the very small cords of the outer panels. I'd suggest using a single surface foil consisting of curved balsa sheet with underside exposed rib. Rib top surface defined by your favorite French Curve, with the high point at about the 30% point. Leading and trailing edges would consist of simply putting a radius on the sheet wood. Of course, this will not provide much torsional stiffness. You can increase the torsional stiffness by covering the lower surface with MonoKote, etc. That will reduce the alpha = 0 CL by about half, but for an 8% foil that should give a CL(0) ~ .4.