Function roll_forcing_interference 

pub fn roll_forcing_interference(
    span_m: f64,
    body_radius_m: f64,
) -> Result<f64, AeroError>

The body’s interference with the roll forcing of canted fins (Barrowman 1967 eq. 3-95 and 3-105, from slender-body theory, his reference 23), with τ = (s + r_t)/r_t:

k_T(B) = (1/π²)[ (π²/4)(τ + 1)²/τ² + π(τ² + 1)²/(τ²(τ − 1)²) asin((τ² − 1)/(τ² + 1))
         − 2π(τ + 1)/(τ(τ − 1)) + (τ² + 1)²/(τ²(τ − 1)²) asin²((τ² − 1)/(τ² + 1))
         − 4(τ + 1)/(τ(τ − 1)) asin((τ² − 1)/(τ² + 1)) + 8/(τ − 1)² ln((τ² + 1)/2τ) ]

It is 1 with no body (r_t = 0), 0.940 at τ = 2 and 0.935 for the Arcas Robin’s fins (τ = 2.87). Below τ = 1.001, a fin shorter than a thousandth of the body’s radius, the terms cancel to rounding, and past τ = 10⁶ they overflow; it is held at its value at each.

Errors

AeroError::Domain for a non-positive span or a negative body radius.