Rotor Blades - Test Prep PDF

# Rotor Blades ## Symmetrical & Asymmetrical - **Symmetrical:** Upper and lower surface are identical. - **Asymmetrical:** Upper surface has higher camber and lower surface is flatter. - **Better Aerodynamic Pitching Characteristic:** Symmetrical. - **More Lift:** Asymmetrical. - **How Engineers...

# Rotor Blades ## Symmetrical & Asymmetrical - **Symmetrical:** Upper and lower surface are identical. - **Asymmetrical:** Upper surface has higher camber and lower surface is flatter. - **Better Aerodynamic Pitching Characteristic:** Symmetrical. - **More Lift:** Asymmetrical. - **How Engineers Achieve Same Aerodynamic Pitching Characteristics with Asymmetrical Blade:** By sweeping trailing edge 3 degrees upward. ## Common Design - **Common Design:** Symmetrical - **Reason:** Asymmetrical blades were previously unstable, but that issue has been resolved with the 3 degree up-pitch. Manufacturers are now using the asymmetrical design more. ## Planforms - **Two Types of Planforms:** Parallel/uniform and tapered. - **Parallel/Uniform:** Leading edge and trailing edge run parallel and the chord distance stays the same from root to tip. - **Tapered:** Leading and trailing edge converge towards the tip and the chord length decreases. - **Manufacturer's Preference:** Uniform. - **Reason for Preference:** Uniform planform is more cost-effective because the same rib can be reused at all points along the blade. - **Even Lift Production Without Correction:** Tapered. - **Reason:** Tapered planform accounts for the variation of speed at different points along the blade. It creates more lift near the root where it spins slower and has a longer chord length. It creates less lift at the tip where it spins faster and has a shorter chord length. - **Unequal Lift Production in Uniform Planforms:** Tip produces considerably more lift than the root. - **Compensation for Unequal Lift Production in Uniform Planforms:** Engineers put a negative twist in the blade. - **Example:** 5 degrees AOA at the root (200 mph) and 2.5 degrees AOA at the tip (400 mph). This results in equal lift production because the angle difference accounts for the variance in speed. - **Greater Lift Produced If Blade Area is Equal:** Uniform blade. - **Unequal Lift Production in Tapered Planforms:** No. It accounts for the variation of speed. Near the root, the long chord length produces more lift. ## Leading Edge - **Common Feature on all Rotor Blades:** Stainless steel capping at the leading edge to protect against erosion. - **Reason for Erosion:** Dust particles in the air. - **Paint:** Bottom of blade painted flat black to prevent glare. ## Composite Rotor Blades - **Static Discharge:** Require static discharge capabilities. - **Feature:** Built-in bonding strips that run from the tip to the root to conduct static electricity to the airframe. ## Materials - **Rotor Blade Materials:** Metal, composite, or wood. - **Inspection Method:** Primarily tap testing. - **Bonded Construction:** Preferred because it is stronger and doesn't weaken the material by drilling holes for mechanical fasteners. ## Blade Construction - **Types:** Single-pocket and multi-pocket. - **Easier to Manufacture:** Single-pocket. - **Reason:** Only one large skin needs to be laid out. - **Multi-pocket Advantages:** Easier to repair. - **Multi-pocket Disadvantages:** More costly and complex to initially build. ## Balance Weights - **Types:** Spanwise, chordwise, and tracking. - **Spanwise:** Located at the tip of the blade in the center. - **Chordwise:** Located on the leading edge of the blade, usually between 30-50%. - **Tracking:** Two weights are located on the blade tip: one forward in the leading edge and one aft in the trailing edge. - **Movable Weight:** Only chordwise weights are movable, and that is only during repair. ## Trim Balance Weights - **Location:** Two weights, one in the leading edge and one forward of the trailing edge at the tip of the blade. - **Effect of Added Weight:** - **Forward:** Causes the blade to track lower. - **Aft:** Causes the blade to track higher. - **Alternative to Trim Balance Weights:** Trim tabs. - **Location of Trim Tabs:** Trailing edge at approximately 75% of the blade. - **Purpose:** They rely on the velocity of the airflow to achieve the required track adjustments. - **Bending Trim Tab Up:** Causes the blade to fly higher. ## Rigging - **Pre-Rigging:** Ensure hydraulic pressure is removed before starting rigging. - **First System to Rig:** Collective. - **Collective Connection:** Often tied to the throttle. - **Auto-Throttle Check Before Connecting to Collective:** Auto-throttle must be rigged independently. - **Sequence of Rigging and Testing:** - Rig the auto-throttle. - Rig the collective. - Ground run. - Hovering flight test. - Full flight test. - Auto-rotational check (done at minimum gross weight to ensure that the helicopter will fall rapidly enough to maintain minimum rotor RPM). ## Rotor Blade Parts - **Root:** Closest to the mass of the aircraft. - **Tip:** Furthest from the mass of the aircraft. - **Leading Edge:** Thickest part of the blade, first to strike the air. - **Trailing Edge:** Thinnest part of the blade, last to see airflow. ## Servo Tabs - **Purpose:** Control blade angle of attack, avoiding the need for hydraulic power. - **Benefits:** - Infinite life - Simplification of the hub - Removal of hydraulic systems from the aircraft pitch change - Decreased vibration - Quieter operation - Built-in electric servos. - **Added Benefits:** - Track both on the ground and in flight. - Increased reaction time for auto-rotation (because the servo tab would automatically reduce the AOA preventing rotor speed degradation). - Less vibration produced. ## KMAX Collective - **Function:** When the collective is tightened to a movable elevator, it helps to keep the aircraft at a more leveled or comfortable attitude when the aircraft has pitch changes.