Hello!

I've started working on design and fabrication of a tandem wing aircraft as a part of my project in college. I am usiing a 2.5 cc engine to power my aircraft, i've all material like balsa wood, servo motors, etc. Its weight would be arround 1700 gms But i am facing a few problems for the same. Like i dont know what airfoil to use, placement of of wings( distance b/w the two wings), chords of airfoils.

I am taking this aircraft as http://soartech-aero.com/ivens_files/image040.jpg as a referance to my design.

i will be using NACA 4-digit, but really dont know how to choose the right one.
Please help me out with this, I'll be really thankful.

Suggestions

For a .15 (2.5cc), 1700 grams or 3.75 pounds is a tad heavy. Shoot for AUW of 2.5#.

Airfoil: if your a bit "green" in constructing a wing, I would suggest the Clark Y airfoil rather than a semi-symmetrical NACA. A flat bottom wing is easier to construct. But if you insist on NACA, use the 2412.

Wings: go with about 300-350 sq in total area. Aspect ratio of about 6 to 1 (span to chord). Horizontal separation gap of 2x wing chord. Vertical separation of about 1x chord. Dihedral angle of 3 degrees on each 1/2 wing panel.

Have fun.

Thank you for your reply sir!

If i want to distribute lift on the wings as for front wing gives 60% of lift while the rear one gives 40%. will it effect the moments about CG ie if front wing is ahead of cg so pitch up moment is given to the aircraft hence affecting its stability, how can i neutralize this problem?

Here is a graphic Center of Gravity Calculator that takes into account two lifting surfaces. If you want a 60/40 split, suggest your wing areas should be in the same ratio.

http://www.geistware.com/rcmodeling/cg_super_calc.htm