Rotor Blade Designs Overview

Rotor Blade Designs

• Two main rotor blade designs exist: symmetrical and asymmetrical.
• Symmetrical blades have better aerodynamic pitch characteristics.
• Asymmetrical blades produce more lift for the same surface area.
• Asymmetrical blades have higher camber on one side.
• Engineers achieve similar pitching characteristics in asymmetrical blades by sweeping the edges upward (3 degrees). This improves aerodynamic stability.
• Symmetrical blades are the most common design due to their greater aerodynamic stability.
• Two main planform types exist: parallel (uniform) and tapered.
• Uniform planforms have leading and trailing edges parallel to each other.
• Uniform planforms generally create greater lift due to their chord line.
• Tapered planforms have a converging leading and trailing edge, with a decreasing chord length towards the root.
• Manufacturers prefer uniform planforms due to cost-effectiveness, needing only one machine stamping for ribs, and maintaining a consistent chord length.
• Tapered planforms require different rib numbers for each rib due to varying chord length.
• Tapered planforms provide more equal lift across the blade's length due to their ability to account for varying speed.
• Parallel blades have negative twist to achieve appropriate angle of attack (AOA) at the root and tip, compensating for varying blade rotational speeds.

Rotor Blade Skin Configurations

• Single-pocket skin configurations are faster to build due to a larger single skin section and less concern about rib placement.
• Multi-pocket skin configurations are easier to repair due to replaceable individual segments.
• If a single-pocket skin is damaged, the entire section is replaced.
• Bonded construction is preferred for strength, eliminating the need for drilling holes.

Rotor Blade Mass Balance Weights

• Chordwise mass balance weights are located within 30-50% of the leading edge.
• Spanwise balance weights are centrally located at the blade tip.
• Tracking balance weights are positioned towards the leading and trailing edges.
• Adding weight toward the leading edge results in a lowered flight path.
• Adding weight toward the trailing edge results in a higher flight path.
• Trim tabs are used to adjust flight attitude; this is generally easier to implement than repositioning permanent weights.

Helicopter Flight Controls

• Collective and cyclic controls, and anti-torque pedals are rigged in order; collective first, followed by cyclic, ending with anti-torque pedals.
• Before connecting collective and throttle, ensure individual rigging for accurate operation.

Servo Tabs

• Servo tabs are airfoil shaped panels (75% span) affixed to the trailing edge of rotor blades to allow for increased aerodynamic efficiency.
• Servo tabs simplify the hub, eliminating the need for hydraulics, allowing for quieter operation.
• Servo tabs increase autorotation reaction time.

Droop Compensator and Correlator

• The droop compensator is a mechanism for governing the governor's output.
• A correlator establishes a mechanical link between the collective and throttle, adjusting the linkage between the two.
• The correlator mechanism prevents lag or delay during power adjustments.

Helicopter Vibration Absorbers

• Two main vibration absorber types exist: bifilar and hub vibration absorbers.
• Bifilar absorbers have four arm disks to dampen vibrations.

Rotor Blade Systems

• Force trim systems return cyclic controls to their original positions.
• Gradient springs position the cyclic.
• Elevator function adjusts the attitude direction.
• Inverted airfoil configuration provides downward lift.
• Fixed-elevator helicopters use inverted airfoils for downward lift control.

This quiz covers the fundamental aspects of rotor blade designs, focusing on the differences between symmetrical and asymmetrical blades. It explores their aerodynamic characteristics, planform types, and manufacturing preferences. Test your knowledge on these essential engineering concepts related to rotor dynamics.