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Is this airfoil good (for a 1930 biplane made out of foamboard)?

MarioGdV

Active member
#1
Hi, I'm currently designing my own RC Plane for the first time, and I'm looking for a efficient (and not too heavy) airfoil, and I know that there are some pages that shows you thousands of airfoils with data, but I can't understand them. I made this one that looks like a normal one to me .


Sin título.png

What do you think? The plane is going to be 1m long (42"), and the power system is similar to the FT Power Pack C, so maybe it's too big considering that it's a biplane and not a monoplane.
 

Hai-Lee

Old and Bold RC PILOT
#3
The airfoil as drawn will definitely fly though it may not give the lift you initially expect.

I base this on the simple fact that it is similar to most of the FB fold up wings, in particular the TT and even the simple cub.

To improve lift without making the wing larger in cord or span and as it is a biplane design I would suggest that if the lift does not meet expectations then you could either fit the wings with a slight positive incidence angle, shorten the underneath flat portion of the wing so that the TE droops down a little further, or increase the wing cord by lengthening the rear panel of the wing upper surface and introduce a TE droop. All of the things mentioned that you could consider actually provide an actual increase in wing incidence angle.

Early Biplanes had a slight positive incidence angle on the wings almost universally!

As stated earlier the wing will fly but possibly such that it will not land slowly and may even appear tail heavy regardless of where you balance the craft. With positive incidence, (the right amount), it will balance sweetly, float on landing , and maneuver sweetly at all speeds, (above stall that is).

Just my thoughts!

Have fun!
 

Hai-Lee

Old and Bold RC PILOT
#7
Thanks! I will. Are 3º enough? (That's also the degrees I used for the dihedral angle, is it good?)
Here is the rub!

Until the AUW is known then the best you can do is go for a slight to moderate amount of incidence. (It can be a pain getting the most out of a design - the designers dilemma).

I normally look at incidence setup in shim thickness for my initial designs as I shim my way to optimal performance. These shims are just a thickness measurement and for similar designs I would raise the LE, (or drop the TE), by between 1 and 2 mm as a starting point. This could be increased to as much as 3mm if the build is somewhat heavy!

As for angle 3 degrees, it MAY be a little severe, about half of that would be a good starting point. If this is just the prototype or development build you could fix the wing incidence and actually shim the tail for negative incidence until you work out the best angle of incidence difference. Once determined you could then fix the tail to the Fuselage centre line and adjust the designs wing mounts for the calculated/required wing incidence angle.

Have fun!