Blade Bending Feedback for VTOL Rotor Stability

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Solution Overview

Problem

Stiff hingeless rotors in high-speed VTOL aircraft are unstable, requiring large horizontal stabilizers that incur weight and drag penalties, and conventional control systems face noise issues with angular acceleration feedback.

Innovation Solution

A system that processes blade bending measurements from sensors and inertial measurement unit data to generate commands that stabilize the aircraft, improving signal-to-noise ratio and reducing the need for large stabilizers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a large horizontal stabilizer is used to counteract rotor instability, then aircraft stability is improved, but weight and drag increase

Engineering Contradiction:

Improveaircraft stabilityVSAvoidstabilizer weight

Core Design Contradiction:

Stability of the object's compositionVSWeight of moving object

Solution Approach 1:

The system uses blade bending moment sensors to detect rotor blade vibrations and feeds this information back to the flight control system. The control system processes this feedback signal and applies compensating control moments to stabilize the aircraft, replacing the need for large passive stabilizers with an active feedback control mechanism.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces the mechanical stabilizer system with an electronic sensing and control system. Instead of using a large physical horizontal stabilizer to provide aerodynamic restoring forces, the system uses sensors to detect blade bending moments and electronic controls to generate stabilizing commands, substituting mechanical aerodynamic stability with electronic control stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If angular acceleration feedback is used to improve stability, then aircraft stability is enhanced, but noise content in the signal increases

Engineering Contradiction:

Improveaircraft stabilityVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent uses blade bending moment as an intermediary measurement that correlates with aircraft pitch acceleration but can be measured with better signal-to-noise ratio than direct fuselage accelerometers. The bending moment signal serves as a mediator that provides acceleration information without the high noise content of direct differentiation of angular rate signals.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the measurement parameter from direct angular acceleration (obtained by differentiating angular rate) to blade bending moment. This parameter change provides a more reliable signal for control feedback, as bending moment sensors can provide cleaner signals than differentiated rate signals, improving the signal-to-noise ratio while maintaining the ability to enhance stability.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3097013B1Rotor moment feedback for stability augmentation

Publication Date: 2019.05.15 SIKORSKY AIRCRAFT CORP

Figure 1A
Figure 1B~1C
Figure 2

AI summary

Embodiments are directed to obtaining at least one measurement of blade bending associated with at least one blade of at least one rotor of an aircraft, processing, by a device comprising a processor, the at least one measurement to obtain moment data, obtaining data from an inertial measurement unit (IMU), and processing, by the device, the moment data and the data from the IMU to generate a command configured to stabilize the aircraft.