Overview
ISO 1151-2:1985/Add 1:1987 is an addendum to the ISO 1151-2 series prepared by ISO/TC 20 (Aircraft and space vehicles) and published on 1987-08-15. It extends Part 2 of the Flight dynamics standard by defining quantities related to the energy of the aircraft with respect to the Earth, clarifying symbols and relationships used in flight dynamics analysis. The addendum sets the zero level of potential energy at geopotential altitude H = 0 and identifies measurable quantities that support consistent energy accounting.
Key Topics
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Total flight-path energy (EtK)
- Defines the aircraft's energy relative to the Earth. The addendum provides the symbol and conceptual expression for total flight-path energy used in flight dynamics.
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Total flight-path altitude (HtK)
- A derived quantity obtained by integrating the total flight-path climb speed over time. The geopotential altitude zero level is used as the reference.
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Total flight-path climb speed (v_tK or b_tK)
- Defined as the scalar product of the flight-path speed-load-factor vector and the flight-path velocity. This quantity is noted as directly accessible by flight measurements.
- The addendum relates climb speed and the rate of change of total flight-path altitude. The relationship given uses the standard acceleration of free fall g_n and the altitude-dependent g(h).
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Total flight-path climb angle (γtK)
- Defined by the sine of the climb angle equal to the ratio of total flight-path climb speed to the flight-path speed (VK). The angle is only defined when the climb-speed magnitude does not exceed VK.
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Symbols and parameters included in definitions:
- m (aircraft mass), VK (flight-path speed), h (geometric altitude), H (geopotential altitude), g(h) (free-fall acceleration at altitude h per ISO 2533), g_n (standard free-fall acceleration).
Applications
This addendum is practical and directly applicable to:
- Flight testing and instrumentation: provides standard definitions that make climb speed and energy measurements comparable across tests.
- Performance analysis and flight mechanics: enables consistent computation of energy-related performance metrics and energy height concepts.
- Simulation and modeling: supplies clear variable definitions and relationships required by flight dynamics models and avionics algorithms.
- Regulatory and standards compliance: ensures uniform terminology and symbols in reports and technical documentation.
Benefits include clearer measurement definitions, consistent energy referencing to geopotential altitude, and improved interoperability of test and simulation data.
Related Standards
- ISO 1151-2 - base part on motions of the aircraft and atmosphere relative to the Earth.
- ISO 2533 - Standard atmosphere used to define g(h) and the standard acceleration of free fall g_n.
- Other parts of the ISO 1151 series and documents from ISO/TC 20 for broader flight dynamics context.
For engineers and test teams, ISO 1151-2:1985/Add 1:1987 provides concise, standardized definitions of energy-related flight-path quantities essential for accurate measurement, analysis and modeling in aerospace applications.
