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Question 1: The main formula is equation 18 on page 15 of the document. It assumes a value for epsilon of 0.25, which is to say the center of gravity is at the center point of the root chord. Epsilon is defined as the distance from the 1/4 chord (referenced from the forward end) to the center of gravity. As the fin sweeps back, the CG moves back and epsilon increases. As the fin sweeps forward, the CG decreases to 0 at 1/4 chord, and negative from there. Given that this is the distance from the 1/4 chord, is an absolute value correct for a forward swept fin? A negative value causes the velocity to enter imaginary space so that is a non-starter. Thoughts?

Question 2: FinsSim handles non-square fin profiles (airfoils, tapered leading and trailing edges, etc) by adjusting fin thickness to create a square profile fin of equivalent volume. I do a similar but different process. FinSim calculates based on the relative areas at the fin root profile, whereas I use the volume divided by the area of the fin side profile. FreeCAD provides the shape volume, so it's an easier calculation that works for all fin profiles. Thoughts?

Question 3: Elliptical fins. Formula 18 calculates an average chord

*(root chord + tip chord)/2.*For an ellipse, the tip chord is 0 so would be approximated as a square fin with a chord of half of the root chord. Is this sufficient for handling elliptical fins, or non-trapezoidal shapes in general?

Question 4: I'm reasonably certain this method isn't up to it, but what about fins of tapered thickness root to tip? Given that thickness is one of the most important variables, is an approximation possible?

I'm also looking at other methods for calculating flutter, such as NACA TN 685, but let's start with this.