Nacelle Flap Straightening Device for Aircraft Reverse Thrust
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Solution Overview
Problem
Aircraft turbojet engines with high bypass ratios face challenges in implementing thrust reversal systems that do not increase mass, bulk, and drag, while existing solutions for reverse thrust, such as hatches and grids, are inefficient and those using variable pitch fans are complex.
Innovation Solution
A nacelle air outlet with a straightening device featuring pivotable flaps on the trailing edge, which change angle to straighten the reverse air flow during reverse thrust, reducing recirculation and enhancing flow rate without compromising thrust performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If hatches and grids are integrated in the secondary flow path to enable reverse thrust, then reverse thrust capability is improved, but mass, bulk and drag increase significantly
Solution Approach 1:
The patent applies the dynamics principle by making the flaps movable rather than fixed. The flaps can pivot between a first position (aligned with the trailing edge) during thrust phase and a second position (deployed at an angle) during reverse thrust phase. This dynamic adjustment allows the same structure to serve dual purposes: maintaining aerodynamic efficiency during normal operation and enabling reverse thrust when needed, without permanently increasing drag or requiring separate fixed reverse thrust mechanisms.
Solution Approach 2:
The flaps serve multiple functions: during thrust phase, they remain aligned to maintain aerodynamic profile; during reverse thrust phase, they deploy to straighten the reverse air flow. This multi-functionality eliminates the need for separate dedicated reverse thrust mechanisms like hatches or grids, thereby reducing overall mass while maintaining both thrust and reverse thrust capabilities.
2Adaptability or versatility
If hatches and grids are integrated in the secondary flow path to enable reverse thrust, then reverse thrust capability is improved, but drag increases significantly
Solution Approach 1:
The flaps dynamically adjust their position based on operational phase. During thrust phase, they are aligned with the trailing edge to maintain smooth airflow and minimal drag. During reverse thrust phase, they deploy to their second position to straighten the reverse air flow. This dynamic behavior ensures drag is minimized during normal operation while still enabling effective reverse thrust when required.
3Productivity
If the air outlet profile tapers downstream to guide secondary air flow, then thrust phase performance is improved, but reverse thrust performance deteriorates due to recirculation zones
Solution Approach 1:
The flaps provide dynamic adaptability to the tapered air outlet profile. During thrust phase, they remain aligned with the taper to guide secondary air flow efficiently. During reverse thrust phase, they deploy at angles to straighten the reverse air flow and eliminate recirculation zones that would otherwise form in the tapered section. This allows the tapered profile to maintain its thrust performance while becoming adaptable to reverse thrust requirements.
Solution Approach 2:
The flaps change the flow parameters (direction and velocity distribution) of the air passing through the tapered outlet. During reverse thrust, deploying the flaps modifies the flow angle and reduces turbulence, effectively changing the operational characteristics of the tapered profile to suit reverse flow conditions while maintaining its geometric advantage for thrust phase operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution increases reverse thrust performance, reduces recirculation, and maintains thrust phase efficiency by modifying the twisted motion of the reverse air flow, allowing for effective braking and improved operability in adverse conditions.
Implementation Method 1
each flap being pivotable between a closed position, wherein each flap extends along the pivoting axis in an aerodynamic extension of the trailing edge to facilitate a thrust phase, and at least one deployed position, wherein each flap extends in a deployed plane forming an angle of deployment with respect to the closed position around the pivoting axis, so as to straighten the reverse air flow admitted into the air outlet
Data Source
AI summary
Disclosed is an air outlet of a nacelle for an aircraft turbojet engine, the nacelle forming a solid of revolution about a longitudinal axis, the air outlet having a straightening device having a plurality of flaps mounted circumferentially and protruding, each flap being mounted pivoting around a pivot axis, forming, with respect to the longitudinal axis, an angle of convergence in a radial plane, between a closed position, in which each flap extends along the pivot axis in the aerodynamic prolongation of the trailing edge in order to support a thrust phase and a deployed position, in which each flap extends in a deployed plane forming an angle of deployment with respect to the closed position about the pivot axis, so as to support a reverse thrust phase.