Overview
ISO 1151-1:1988 - "Flight dynamics - Concepts, quantities and symbols - Part 1: Aircraft motion relative to the air" is an international standard that establishes basic definitions, symbols and conventions for describing an aircraft’s motion with respect to the atmosphere. It assumes the atmosphere is at rest or in translational motion at constant velocity relative to Earth and treats the aircraft as rigid (many definitions are applicable to flexible airframes). The document provides a consistent vocabulary and notation set for flight dynamics, aerodynamics and stability work.
Key topics
- Axis systems: clear definitions for earth-fixed, normal earth-fixed, aircraft-carried, body, air-path and intermediate axis systems used in flight-dynamics analysis.
- Orientation and angles: standardized terms and symbols for angle of attack, angle of sideslip, bank, azimuth/inclination (air-path) and related rotation sequences.
- Velocities and rates: definitions for aircraft velocity, airspeed, Mach number, components of translational velocity (u, v, w) and angular velocity components (p, q, r) plus normalized angular rates.
- Inertia and reference quantities: moments and products of inertia, radii of gyration, reference area and reference length, normalized mass and nondimensional time units used for scaling and normalization.
- Forces, moments and coefficients: conventions for resultant forces and moments (aerodynamic and propulsive), load factors, thrust and resultant propulsive moments, plus non-dimensional aerodynamic coefficients and component symbols.
- Control and motivator forces: definitions for control forces and moments and the loads/forces on actuators (motivators).
- Annexes: symbol lists for aerodynamic force components and a classification of main flight-dynamics topics.
Practical applications
- Producing consistent technical reports, flight-test data and simulation inputs/outputs by using standardized symbols and definitions.
- Developing flight-dynamics and flight-simulation models (aerodynamic coefficients, inertial models, normalized rates).
- Supporting aircraft stability and control analysis, control-law design, and system integration by providing common reference frames and angle conventions.
- Harmonizing documentation for regulatory submissions, certification evidence and international collaboration.
Who should use this standard
- Aerospace and flight-dynamics engineers
- Flight-test engineers and data analysts
- Simulation and flight-simulator developers
- Aerodynamicists, control-system designers and researchers
- Certification authorities and standards bodies
Related standards
ISO 1151 is a multi-part series; Part 1 is complemented by Parts 2–7 covering motions relative to Earth, derivatives, stability parameters, measurement quantities, geometry and flight envelopes - useful cross-references when performing comprehensive flight-dynamics work.
Open preview (PDF)Flight dynamics — Concepts, quantities and symbols — Part 1: Aircraft motion relative to the air
