Aircraft Elevator Authority Limits for Horizontal Tail Load Relief
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Solution Overview
Problem
Existing aircraft systems face challenges in optimizing horizontal tail loads during pitch maneuvering, leading to sub-optimal elevator authority and maneuvering capability due to excessive load limitations at high dynamic pressures.
Innovation Solution
A method and system for controlling the elevator by identifying the current stabilizer angle of incidence and adjusting the elevator position limit based on threshold values and aircraft parameters, such as Mach number and airspeed, to reduce tail loads while maintaining sufficient pitch control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If elevator authority is excessively limited as a function of airspeed to reduce tail loads, then tail loads are reduced, but maneuvering capability deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of elevator position limits based on real-time flight conditions including stabilizer angle of incidence, airspeed, and Mach number. The system transitions from static speed-based limits to dynamic condition-based limits, allowing the elevator authority to adapt continuously to changing flight states rather than being excessively limited across all high-speed conditions.
Solution Approach 2:
The system changes the parameter used for limiting elevator authority from solely airspeed-based to a multi-parameter approach incorporating stabilizer angle of incidence, Mach number, and dynamic pressure. This allows differentiation between flight conditions with the same airspeed but different tail load characteristics, enabling reduced limits only when actually needed while preserving maneuvering capability in other conditions.
2Strength
If elevator authority is limited to prevent excessive maneuvering capability at high dynamic pressure, then structural loads are reduced, but pitch control responsiveness deteriorates
Solution Approach 1:
The system incorporates feedback from multiple sensors including stabilizer angle of incidence sensors, airspeed sensors, and Mach number calculations. This feedback loop allows the flight control computer to continuously monitor actual flight conditions and adjust elevator position limits accordingly, ensuring limits are applied only when structurally necessary while maintaining responsiveness when safe.
Solution Approach 2:
The patent applies different elevator position limits based on local flight conditions rather than uniform limits across all high-speed flight. By analyzing stabilizer angle of incidence and dynamic pressure locally, the system applies restrictive limits only in specific condition zones where tail loads would exceed structural capacity, while allowing full authority in other zones where structural capacity is sufficient.
3Stability of the object's composition
If uniform pitch response is prioritized over maneuvering capability, then pitch response linearity is improved, but elevator authority is excessively restricted
Solution Approach 1:
The system dynamically adjusts elevator position limits based on real-time stabilizer angle of incidence and flight conditions rather than applying static uniform limits. This allows the pitch response to remain linear and predictable through controlled limit application while preserving adequate elevator authority for necessary maneuvers, avoiding the excessive restriction that would result from uniform limiting across all conditions.
Data Source
AI summary
A method of controlling an elevator of an aircraft includes selecting a factor for increasing or decreasing a predetermined horizontal tail load alleviation (HTLA) authority limit for an elevator based on at least one aircraft parameter. The HTLA authority limit decreases with an increase in Mach number and/or airspeed. The method also includes computing an elevator position limit as a product of the HTLA authority limit and the factor, and moving the elevator to a commanded elevator position that is no greater than the elevator position limit.