Help! Help by changing one airfoil for another

[cdfigueredo]

Hi folks, I've been evaluating my next project and I'm thinking of building a Piper PA-18 Super Cub.

The trick is that basically I want a plane that is quite aerobatic but also stable on landings, for this I want to make some modifications such as increasing the flaps and ailerons to 1/3 of the wing chord, configure a mix to use the flaps as ailerons to get a more agile performance, and finally change the wing profile from a flat bottom for a semi symmetrical profile to get better performance in inverted flight.

Now, what worries me is that although I have an idea of how to make the modification, I am not 100% sure.
Of course I want to keep the same chord and wingspan, but my doubt is what would be the incidence of the new airfoil. My first bet would be to keep the chord line or angle of attack the same, but I don't know how correct this is. All this is assuming that I will keep the elevator and engine with the original incidence of the plane.

Here is the plan https://aerofred.com/details.php?image_id=98162
I will resize it to 1500mm wingspan

Any ideas?

 

[Merv]

I made my own version of the Cub, just took 3D drawings and cut away anything that didn’t look like a Cub.
I put a full symmetrical wing on it and have it setup with full length flaperons. Mind doesn’t need the flaps, I seldom use them. I made the first version with a longer wing, it made landing difficult, way too much float. I shortened the wing, now it flys great.

As far as incident, I’d start with 1-2 degrees of positive

 

[cdfigueredo]

I made my own version of the Cub, just took 3D drawings and cut away anything that didn’t look like a Cub.
I put a full symmetrical wing on it and have it setup with full length flaperons. Mind doesn’t need the flaps, I seldom use them. I made the first version with a longer wing, it made landing difficult, way too much float. I shortened the wing, now it flys great.

As far as incident, I’d start with 1-2 degrees of positive

ohh, i see. Would u like to share me the drawings u used?

 

[Merv]

ohh, i see. Would u like to share me the drawings u used?

I don’t think I kept them. They were nothing special, the plans you have will work just as well.

 

[Merv]

I found the plans.

 

[Tench745]

Do you want the easy way, or the "right" way?
The easy way is, make your semi-symmetrical wing and match angle of incedence of the chord line with whatever the old wing was. Correct any issues with elevator trim or if you're picky, go back and adjust the wing saddle.

The "right" way looks something more like figuring out the stall angle of new wing and what you want the plane's pitch-attitude at touchdown to be. Mount the wing so these angles work well together. Figure out the pitching-moment of the airfoil at cruise speeds, and adjust the H-stab incidence to neutralize that.

 

[danskis]

What Tench said but its hard to adjust the horizontal stabilizer once its glued on. As Tench said Its easier to attach the wing with rubber bands and then shim the back (or front) of the wing to get the right decalogue (then glue it on when you get it right).

I'll bet you won't need to do that though with a semi-symmetrical airfoil.

 

[cdfigueredo]

Do you want the easy way, or the "right" way?
The easy way is, make your semi-symmetrical wing and match angle of incedence of the chord line with whatever the old wing was. Correct any issues with elevator trim or if you're picky, go back and adjust the wing saddle.

The "right" way looks something more like figuring out the stall angle of new wing and what you want the plane's pitch-attitude at touchdown to be. Mount the wing so these angles work well together. Figure out the pitching-moment of the airfoil at cruise speeds, and adjust the H-stab incidence to neutralize that.

Matching the incedence angle of the string line would be the viable solution for me, and then correcting with elevator trim. Playing with the wing incidence is not possible because in this model the wing is inserted on both sides of the fuselage using reinforcing rods, which means that the wing can only be inserted with a specific incidence and cannot be modified.
Just like this:
View attachment 236250

 

[Merv]

...in this model the wing is inserted on both sides of the fuselage...

That model most likely has the correct incident build in. I would not change it, just attach the wing with the new airfoil.

 

[cdfigueredo]

That model most likely has the correct incident build in. I would not change it, just attach the wing with the new airfoil.

that's the main question here. i can go with the easy way as Tench745 said, matching the angle of incedence of the chord line.