Parking Tail Rotor for Compound Aircraft Drag Reduction
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Solution Overview
Problem
Existing compound aircraft designs suffer from significant parasitic drag and energy consumption due to continuously rotating tail rotors at high forward speeds, which reduces aircraft efficiency and power availability.
Innovation Solution
The implementation of a parking tail rotor system with two single-bladed rotors that rotate in the same direction, oriented horizontally and balanced by counterweights, which passively stop and orient in the aft direction at high speeds to minimize drag, and restart to balance main rotor torque as needed, using either a common drive shaft or individual electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the tail rotor continues to rotate at high forward speeds to balance main rotor torque, then control authority is maintained, but parasitic drag and energy consumption increase significantly
Solution Approach 1:
The tail rotor system transitions dynamically between two states: rotating to balance main rotor torque at low speeds, and stopping to reduce drag at high speeds. The system adapts its operational state based on aircraft speed and control requirements, allowing the tail rotor blades to be powered down and stop at high forward speeds when the rudder provides adequate control authority
Solution Approach 2:
The system changes the operational parameter of tail rotor rotation from continuous to conditional based on aircraft speed. At high forward speeds when the rudder has adequate authority, the tail rotor parameter changes from rotating to stopped, eliminating parasitic drag while maintaining control capability through the rudder
2Reliability
If the tail rotor continues to rotate at high forward speeds, then torque balance is maintained, but power consumption increases reducing available power for other uses
Solution Approach 1:
The invention extracts the torque balancing function from the tail rotor at high speeds and transfers it to the rudder. When the aircraft reaches high forward speeds, the rudder provides adequate control authority to balance the remaining main rotor torque, allowing the tail rotor to be powered down and stop, thereby eliminating unnecessary power consumption
3Device complexity
If a single tail rotor with two blades is used, then the structure is simpler, but the disc area is smaller resulting in higher disc loading
Solution Approach 1:
The tail rotor is segmented into two separate single-bladed rotors disposed at opposing ends of the horizontal stabilizer. This segmentation increases the effective disc area compared to a single two-bladed rotor, reducing disc loading while maintaining structural simplicity and achieving the same force output
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 design significantly reduces parasitic drag and energy consumption by eliminating the need for continuous tail rotor operation at high speeds, while maintaining control authority and stability through variable or fixed-pitch blades and flapping hinges, enhancing aircraft efficiency and power management.
Implementation Method 1
Each of the two blades has a counterweight integral with the spar of the blade, with the blade disposed on one side of the tail rotor axis of rotation and the counterweight disposed on the opposite side of the tail rotor axis of rotation. The purpose of the counterweights is to balance the weight of each rotor blade to reduce vibration normal to the axis of rotation.
Implementation Method 2
At high forward speeds, the tail rotor blades stop and passively park in the downwind direction to reduce parasitic drag. With increased speed, the force of the relative wind on the tail rotor blades passively rotates the blades until both blades are in a parked position with the two rotor blades extended in the aft direction parallel to the longitudinal axis of the fuselage
Data Source
AI summary
A parking tail rotor for a rotary wing aircraft stops rotating at a high forward aircraft speed when aircraft control surfaces have adequate control authority to balance main rotor torque without the rotating tail rotor. When stopped, the blades of the parking tail rotor move due to the force of the relative wind to a parked position in which the span of the blades extend in the aft direction, reducing air resistance to the forward motion of the aircraft.