Coefficient of Lift Confusion

Interesting....

Could it be due to the amount of induced drag? More details please...

Ok what's confusing is that the 1/2 scaled wing has a higher aspect ratio. AR=S/C, where S is the wing span which is constant in my case and C is the chord of the airfoil where the chord C2(case 2) is half C1(Case 1). which implies that AR2 is bigger than AR1. It is known that higher aspect ratio wings have lower drag, which is completely the opposite of the simulation results i got.

Is the chord line constant/wing tapered?

no it's not tapered

Are you using a constant angle of attack? or changing it to obtain the max cL for each size airfoil?

C is the chord of the airfoil where the chord C2(case 2) is half C1(Case 1).

From Lennon, Andy; Basics of R/C Model Aircraft Design, Practical Techniques for Building Better Models; Air Age Inc; Wilton, CT; 1996

The actual lift, total drag, and pitching moment of a wing depends on seven factors not directly related to its airfoil section. These are:
1. Speed - Lift, drag, and pitching moment are proportional to the square of the speed.
2. Wing Area - All three are proportional to wing area.
3. Wing Chord(s) - Pitching moment and Reynold number are proportional to chord.
4. Angle of Attack (AoA) - In the useful range of lift, from zero to just before stall, lift, profile drag and pitching moment increase as the AoA increases.
5. Aspect Ratio (AR) - All three are affected by aspect ratio.
6. Planform - i.e., straight, tapered, or elliptical. All impact lift, drag, and pitching moment.
7. Reynolds Number (Rn) - This reflects both speed and chord and is a measure of "scale effect."

The Reynolds number, Rn for an airfoil = Chord (in inches) x Velocity (in mph) x 780 (at sea level)

Based on what you have written so far, it doesn't appear to me that both cases are NOT dynamically similar.

What i understand is that when the chord changes, in my case C2 is half C1 i would have a different reynolds, thus resulting to a different speed. So i should recalculate the speed for Case 2???

It is known that higher aspect ratio wings have lower drag, which is completely the opposite of the simulation results i got.

See following link that has graph of Lift Coefficient to Angle of Attack for various Aspect Ratios. Please note for the same Angle of Attack the Wing Lift Coefficient is directly proportional to the Aspect Ratio

http://worldofaerospace.googlepages.com/How-Aspect-Ratio-Wing-Lift-RC-plane.htm

Same airspeed, case 1 and 2? Not altering dihedral angle?

Yes i did run the simulation with the same airspeed and there's no dihedral angle.

I'd guess that the lower Reynolds number is affecting the lift of the shorter chord (higher aspect ratio) section adversely. Some sections are quite sensitive to Reynolds number, and for most sections there is some very low Reynolds number where lift can fall off dramatically. (I'd guess that Reynolds number would need to be below 1x10⁶ to see this effect.)

If the aspect ratio of the shorter span section is already high (let's say 10) then I'd think that Reynolds effect would dominate.

It would be interesting to build models and see if the Ansys analysis is correct. It would also be interesting to model it in Fluent etc. to see if the results are the same.

Actually, this is what am doing. i've been working a lot so far with fluent6.3 and recently i switched to ansys fluent. I am trying to see how accurate is the software (numerical analysis) compared with experimental results.

no Kidding?