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I'm trying to design a tandem wing model aircraft with both wings with the same wingspan. The front wing will have 2 and the rear will have 1 deg of incidence angle, also the front wing will have higher aspect ratio. I'm using Clark-Y airfoil for both wings and active yaw stability will be achieved by differential thrust.

I calculated the neutral point with this website as it gave nice flying results for my older designs.

Usually tandem or canard airplanes have their front wing mounted with a higher incidence but because the front wing has the same span as the rear wing, all of the rear wing will be subject to downwash from the front wing, so I'm concerned if the rear wings angle of attack will change considerably to affect its lift.

How will the rear wing incidence affect the neutral point?

Should I keep the rear wing at 1 deg incidence or should I increase it?

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Here is a picture of its approximate form

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  • $\begingroup$ As a rule of thumb, each degree of AoA of the front wing gives a half degree downwash on the rear wing. Which airfoil are you using? How do you control the airplane? Don't you need a vertical stabiliser? $\endgroup$
    – sophit
    Commented Sep 15, 2023 at 6:06
  • $\begingroup$ Thanks, added the info $\endgroup$
    – Kozakov
    Commented Sep 15, 2023 at 6:15

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I am less concerned about your wings than your lack of lateral stability. You can achieve lateral control by means of differential thrust, but not lateral stability. Please add a fin or winglets at the rear wing.

You are right about downwash affecting the rear wing: Due to downwash it will have a lower lift curve slope which in turn will cause your neutral point to move slightly forward. How much it does depends on the wing's aspect ratio.

Should I keep the rear wing at 1 deg incidence or should I increase it?

I think 1 degree less of incidence will give you moderate longitudinal stability. I would not increase the rear wing's incidence but rather keep some margin to decrease it if flight test shows insufficiently low longitudinal stability

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