Offset Turboprop Engine Mounting for Lift and Drag Reduction
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Solution Overview
Problem
The existing designs of gas turbine engines and propellers in turboprop systems face challenges in packaging and aerodynamic efficiency, particularly in reducing the heat signature and optimizing the angle of the engine and propeller axes for improved lift and reduced drag.
Innovation Solution
A turboprop propulsion system with a gas turbine engine and propeller axis forming an offset angle, integrated into a nacelle within the airframe, featuring a gearbox to accommodate this offset and an infrared suppressor to direct exhaust gases for reduced heat signature, along with an exhaust duct providing a direct line of sight from the engine to the nacelle outlet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the gas turbine engine is mounted at an offset angle relative to the propeller axis, then lift during ground operations is enhanced and drag is reduced, but the packaging complexity and device complexity increase
Solution Approach 1:
The gas turbine engine is mounted at an asymmetric offset angle (10-15 degrees) relative to the propeller axis, creating an asymmetric configuration that generates beneficial aerodynamic forces. This asymmetric mounting allows the exhaust gases to be directed at an angle that provides additional lift during ground operations while reducing drag, accepting increased packaging complexity as a trade-off for improved aerodynamic performance.
Solution Approach 2:
The engine mounting introduces a dimensional change by angling the engine axis offset from the propeller axis in the vertical dimension. This angular offset creates a three-dimensional configuration where exhaust gases are directed not only rearward but also at an upward angle, generating lift component forces that were not available in conventional aligned configurations.
2Loss of energy
If the exhaust duct is shaped to provide a direct line of sight from the exhaust discharge outlet to the nacelle outlet, then pressure losses are minimized, but the aerodynamic heating of surrounding structures increases
Solution Approach 1:
An infrared suppressor is introduced as an intermediary component between the exhaust duct and the surrounding airframe structures. This suppressor intercepts the hot exhaust gases and provides thermal protection to adjacent structures, allowing the exhaust duct to maintain its direct line-of-sight configuration for minimal pressure losses while preventing harmful aerodynamic heating of the nacelle and airframe.
Solution Approach 2:
The infrared suppressor converts the harmful thermal energy of the exhaust gases into a beneficial protective function. By positioning the suppressor in the exhaust flow path, it absorbs and redirects thermal energy away from sensitive structures, transforming what would be a harmful heating effect into a controlled thermal management solution.
3Object-affected harmful factors
If the infrared suppressor is positioned to have a direct line of sight from the exhaust discharge outlet, then the infrared signature is effectively suppressed, but the device complexity increases
Solution Approach 1:
The infrared suppressor is designed to perform multiple functions within a single component: it provides thermal protection to surrounding structures from aerodynamic heating, suppresses the infrared signature of the exhaust gases, and maintains acceptable pressure losses in the exhaust flow. This multi-functionality reduces the need for separate components and justifies the added device complexity by delivering multiple benefits from a single integrated solution.
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
This configuration enhances lift during ground operations, reduces drag, minimizes pressure losses, and effectively suppresses the infrared signature by directing exhaust gases efficiently, resulting in improved aerodynamic performance and reduced weight.
Implementation Method 1
an infrared suppressor coupled to the gas turbine engine and configured to conduct exhaust gases at least part way from the exhaust discharge outlet of the gas turbine engine to the exhaust-outlet aperture of the nacelle
Data Source
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AI summary
An airplane (10) including an airframe (12) and a turboprop propulsion system (14) is disclosed. The turboprop propulsion system (14) includes a propeller (20) mounted for rotation about a propeller axis (30) and a gas turbine engine (22) coupled to the propeller (20) to drive rotation of the propeller (30). The gas turbine engine (22) rotates about an axis (32) which is offset from the propeller axis (30).