Rotor Blade Design Overview

The upper and lower surfaces of the blade are identical.

The upper surface has a higher camber (curvature) than the lower surface, which is flatter.

Symmetrical blades have better aerodynamic pitching characteristics.

Asymmetrical blades produce more lift.

Sweeping the trailing edge of an asymmetrical blade upwards by 3 degrees improves its pitching characteristics.

The most common rotor blade design is symmetrical.

Previous instability issues with asymmetrical blades have been resolved, leading to increased use by manufacturers.

The leading edge and trailing edge of the blade run parallel, with a constant chord distance from root to tip.

The leading and trailing edge converge towards the tip, resulting in a decreasing chord length.

The most favored planform due to its cost-effectiveness.

Tapered planforms provide even lift production without needing corrections.

Uniform planforms have unequal lift production, with the tip generating significantly more lift than the root.

A negative twist is introduced into uniform planforms to compensate for unequal lift production.

The amount of negative twist is determined by the speed difference between the root and tip.

Despite the differences in angle of attack, equal lift production is achieved due to the compensation for varying speeds.

A uniform planform produces greater lift if the blade area is equal.

Tapered planforms inherently account for speed variations, resulting in even lift production.

Stainless steel capping on the leading edge protects against erosion caused by dust particles.

The bottom of the blade is painted flat black to reduce glare.

Composite rotor blades require static discharge capabilities.

Bonding strips built into the blade conduct static electricity from the tip to the root, then to the airframe.

Rotor blades can be made from metal, composite, or wood.

Tap testing is the primary inspection method for rotor blades.

Bonded construction is favored for rotor blades due to its increased strength and lack of weakening from mechanical fasteners.

Single-pocket blade construction involves only one large skin, making it simpler to manufacture.

Multi-pocket blade construction allows for easier repair but is more complex and costly to build.

Spanwise balance weights are located at the blade tip, in the center of the width.

Chordwise balance weights are positioned on the leading edge, generally between 30% and 50% of the blade's length.

Tracking balance weights are positioned at the blade tip, one forward on the leading edge and one aft on the trailing edge.

Only chordwise balance weights are movable, and this is done only during repair.

Trim balance weights, located at the blade tip, adjust the blade's tracking.

Adding weight forward causes the blade to track lower, while adding weight aft causes it to track higher.

Trim tabs located on the trailing edge, at about 75% of the blade's length, serve as an alternative to trim balance weights.

Trim tabs utilize airflow velocity to achieve track adjustments.

Bending the trim tab upwards causes the blade to fly higher.

A process that ensures proper hydraulic pressure is removed before rigging.

The collective is the first system to be rigged, often connected to the throttle.

The auto-throttle must be rigged independently before connecting to the collective.

A ground run, a hovering flight test, a full flight test, and an auto-rotational check are conducted following rigging.

The portion of the blade closest to the aircraft's main body.

The furthest end of the blade from the aircraft's main body.

The thickest part of the blade, where it first encounters airflow.

The thinnest part of the blade, where airflow exits.

Servo tabs control the angle of attack of the blade, eliminating the need for hydraulic power.

The benefits of servo tabs include infinite life, hub simplification, removal of hydraulic systems, reduced vibration, quieter operation, and built-in electric servos.

Additional benefits include ground and flight tracking, faster auto-rotation response, and lower vibration.

The KMAX collective, a specialized collective system, helps maintain a level attitude while the aircraft is pitching.