Authoritative Standard • USAF Manual
USAF AFFDL-TR-69-42, Chapter 9: Lug Analysis
Air Force Flight Dynamics Laboratory Stress Analysis Manual (1969), by G. E. Maddux • Method Reference
1. Overview and Historical Significance
Published in 1969 by the Air Force Flight Dynamics Laboratory (AFFDL) at Wright-Patterson Air Force Base, AFFDL-TR-69-42 (Stress Analysis Manual) represents one of the most widely referenced and experimentally validated stress analysis handbooks in aerospace history.
Authored by Gene E. Maddux, Chapter 9 ("Lug Analysis") synthesized decades of military aircraft testing, empirical research from Lockheed Aircraft Corp. (Melcon & Hoblit), and plasticity mechanics into a unified, semi-analytical procedure.
2. Structure of Chapter 9 & LugCalc™ Implementation Mapping
Every module of the LugCalc™ calculation engine directly maps to a specific subsection of Chapter 9:
| Chapter 9 Section | Subject & Governing Equations | LugCalc Implementation | Documentation Topic |
|---|---|---|---|
| Section 9.1 | Introduction, scope, and nomenclature. | Global units, coordinate definitions, and nominal geometry. | Lug Sizing Theory |
| Section 9.2 | Lug geometry, radial segments $h_0 \dots h_4$, and harmonic mean $h_{avg}$ (Eq. 9-1). | Geometric solver, edge breakout checks, and derived section properties. | Effective Edge Lengths |
| Section 9.2.1 | Bearing and shear-out strength (Eq. 9-3), Fig. 9-2 ($D/t \le 5$) and Fig. 9-3 ($D/t > 5$). | Axial bearing allowable engine with optional aluminum grain orientation cutoffs. | Bearing Efficiency ($K_{bru}$) |
| Section 9.2.2 | Net-section tension allowable (Eq. 9-4), Fig. 9-4b/c/d parameterized by $F_{ty}/F_{tu}$ and $F_{tu}/(E\varepsilon_u)$. | Tri-linear spline surface interpolation across multi-curve plastic tension charts. | Net Tension ($K_{nu}$) |
| Section 9.2.3 | Transverse strength allowables (Eq. 9-8a/b), Fig. 9-8 curves ($K_{tru}, K_{try}$). | Transverse capacity evaluation based on $h_{avg}/D$ and yield vs. ultimate governance. | Transverse Efficiency ($K_{tru}$) |
| Section 9.2.4 | Bushing bearing strength (Eq. 9-9: $P_{u,B} = 1.304 F_{cy,bush} D_p t$). | Bushing allowable module with independent bushing materials. | Bushing Analysis |
| Section 9.3 | Oblique load interaction (Eq. 9-20: $(R_a)^{1.6} + (R_{tr})^{1.6} = 1$). | Analytical root-finding for combined resultant angles ($0^\circ \le \theta \le 90^\circ$). | Margin of Safety |
| Section 9.4 | Double-shear clevis joint, pin shear (Eq. 9-12), plastic bending (Eq. 9-15), and weak-pin design (Eq. 9-16). | Full joint assembly solver, pin plastic hinge coefficient $k_b = 1.56$, and gap modeling. | Joint & Pin Analysis |
3. Original Document Document Preview & PDF Access
Consult the original Air Force Flight Dynamics Laboratory technical report scan below: