Struct FinAero

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pub struct FinAero { /* private fields */ }

Expand description

One fin’s normal force through the speed regimes: its geometry and outline, and the two ends of its transonic join, computed once.

Subsonic, M ≤ 0.8: Diederich’s slope with Prandtl–Glauert (FinGeometry::single_fin_slope) at the quarter mean aerodynamic chord.
Supersonic, from M_s = max(1.2, 1/cos Γ_L, 1/cos Γ_T, √(1 + 1/A²), √(1 + (c_t/2s)²)): linear theory (FinOutline::supersonic). Its strips need supersonic leading and trailing edges, whose Mach numbers square to the edge, M cos Γ_L and M cos Γ_T, are past 1 (NACA TN 2114’s case). Its half-load tip cone holds while the mirror fin’s cone stays off this fin’s tip, β ≥ c_t/(2s) with c_t the tip chord, and while βA ≥ 1, with A = 2s²/A_fin the aspect ratio of the fin and its mirror image (for a rectangle the two agree, and the slope peaks there at 2A). So a swept, stubby or inverse-tapered fin starts later than Mach 1.2.
Transonic, between: slope and CP each linear in M between their values at the two ends. No method in the sources gives this region in closed form (MIL-HDBK-762 reads it from transonic-similarity charts, pp. 5-104–5-105); the join keeps both continuous, with the slope’s peak at M_s, where linear theory takes over.

Implementations§

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impl FinAero

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pub fn geometry(&self) -> &FinGeometry

The fin’s subsonic geometry.

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pub fn outline(&self) -> &FinOutline

Its outline.

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pub fn reference_area_m2(&self) -> f64

The reference area of the slopes, m².

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pub fn supersonic_mach(&self) -> f64

Where supersonic linear theory starts, M_s. It can pass Mach 5 for a stubby or a very swept fin (a strake 0.5 m long and 0.02 m tall starts at Mach 12.5); the fin’s slope and CP then stay on the join toward that value up to the normal force’s limit, and linear theory is never used.

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pub fn new( planform: &FinPlanform, reference_area_m2: f64, ) -> Result<Self, AeroError>

A planform’s normal force on reference_area_m2.

§Errors

As FinGeometry::from_planform and FinOutline::from_planform, and AeroError::Domain for a non-positive reference area.

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pub fn loading(&self, mach: f64) -> Result<FinLoading, AeroError>

The fin’s slope and CP at mach.

§Errors

AeroError::Mach outside [0, 5) (crate::model::NORMAL_FORCE_MACH_LIMIT).

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impl FinAero

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pub fn roll( &self, mach: f64, body_radius_m: f64, reference_diameter_m: f64, ) -> Result<FinRoll, AeroError>

One fin’s roll forcing and damping at mach on a body of radius body_radius_m, on the reference area and the reference diameter reference_diameter_m, by strip theory (Barrowman 1967 §3.13–3.14 and appendix A; Niskanen 2009 §3.3):

Subsonic, to Mach 0.8: the fin’s lift at its mean aerodynamic chord, C_lδ = (C_Nα)₁ (r_t + y_MAC)/d (Barrowman eq. 3-35, Niskanen eq. 3.66), and each strip at the local incidence −pξ/V with the fin’s own slope per unit area, a = (C_Nα)₁ A_ref/A_fin: C_lp = −2a ∫ξ² dA/(A_ref d²) (Barrowman eq. 3-40–3-48, Niskanen eq. 3.67–3.70). Barrowman’s text writes the airfoil’s C_Nα0 for a; his computed curve for the Basic Finner, −34.2 at Mach 0 (Fig. 5-7), is this, −33.5, not the airfoil’s −69 (the roll decision, ADR-031).
Supersonic, from M_s (FinAero::supersonic_mach): the load 4α/β of FinOutline::supersonic, halved in the tip’s Mach cone, C_lδ = (4/β)(∫ξ dA − ½∫_cone ξ dA)/(A_ref d) and C_lp = −(8/β)(∫ξ² dA − ½∫_cone ξ² dA)/(A_ref d²) (Barrowman appendix A, first order).
Transonic, between: each linear in M, as the fin’s slope is.