Angle of Incidence Calculations

[SimoneFlight]

Hello,
I'm new to Flight this year and have been reading some of the conversations in the forum. I've noticed angle of incidence is often referred to in terms of degrees. How would you convert angle of incidence from inches to degrees?
Thank you for your help,
Simone

[pumptato-cat]

I often use millimeters/centimeters instead.
I don't convert incidence to angles(it's just easier to think about it in terms of removing/adding a millimeter IMHO) but you could use inverse sine, I think? The hypotenuse would be the wing chord and the "opposite" side would be the difference in height between front and back post.

sin = opposite/hypotenuse = (frontpost-backpost)/wing chord, so arcsin(opposite/hypotenuse)=angle or something along those lines. I might be wrong because I've only done this with stab tilt and rudder offset(which is better to log with degrees).

This gives the wing angle so you'd do the same for the stab and then subtract that from the wing to find incidence.

[bjt4888]

I often use millimeters/centimeters instead.
I don't convert incidence to angles(it's just easier to think about it in terms of removing/adding a millimeter IMHO) but you could use inverse sine, I think? The hypotenuse would be the wing chord and the "opposite" side would be the difference in height between front and back post.

sin = opposite/hypotenuse = (frontpost-backpost)/wing chord, so arcsin(opposite/hypotenuse)=angle or something along those lines. I might be wrong because I've only done this with stab tilt and rudder offset(which is better to log with degrees).

This gives the wing angle so you'd do the same for the stab and then subtract that from the wing to find incidence.

Cat,

Exactly correct. Calculating angle is useful to compare to typical useful decalage range. Very low decalage for designs like FF and J&H would be around 1.5 degrees and very high would be around 3 degrees. Designs like the Super Simple, with flat plate wings take a little more usually.

We always calculate and discuss decalage as an angle.

Brian T

[pumptato-cat]

Got it, thank you! I'm used to hearing people discuss in mm, but degrees will probably be what I log from now on.

Why do flat plate wings take more incidence?

[bjt4888]

Got it, thank you! I'm used to hearing people discuss in mm, but degrees will probably be what I log from now on.

Why do flat plate wings take more incidence?

Cat,

Flat plate wing doesn’t generate as much lift as a curved airfoil. To compensate for this, usually greater decalage angle and more conservative CG and SSM is necessary. We’d need an actual aerospace engineer to give a more technical and precise explanation.

Brian T

[pumptato-cat]

Got it, thanks!!