Airfoil selection question

[rtfm]

Hi,
While playing with DesignFoil (v6) I came across something which has me puzzled:

I was examining the properties of the following wing, using different airfoils and AoA:
Span = 29ft
Root chord = 4ft
Tip chord = 2ft
Area = 87sq ft
(AR = 9.67)

My nominated flight condition was: 3000ft, 130kts, and aircraft weight of 1040lbs

NACA747a315
AoA required: 1.28 deg
Total drag (Friction + Induced) = 30.79lbs
Lift = 1040lbs
Pitch moment = -95.7 ft/lbs
Moment coeff = 0.007
LD = 33.8

However, when I used (for the same wing dimensions) a NACA0012 airfoil, I came up with the following:
AoA required: 2.5 deg
Total drag (Friction + Induced) = 41.65lbs
Lift = 1039lbs
Pitch moment = -1.98 ft/lbs
Moment coeff = 0.000
LD = 16.09

Now, to my untrained eye, it seems that the NACA0012 is a better airfoil in a number of ways - for one, it has (at 130kts) not a lot of extra drag, but almost no pitching moment. And reducing the pitching moment is good, because it means you need very little h-stab down-lift (and hence, drag).

I'm not sure if I've done the math right on the above airfoils, but on the face of it, I can't see a compelling reason NOT to use the NACA0012 for the main wing.

I am ready to be educated - so educate away!

Regards,
Duncan

 

[PTAirco]

 

[rtfm]

 

[Dana]

 

[rtfm]

 

[orion]

 

[plncraze]

 

[rtfm]

 

[Jman]

 

[orion]

 

[rtfm]

 

[Midniteoyl]

 

[orion]

 

[djschwartz]

 

[Mac790]