HELIPROPLEC MIDTERM - Reviewer

Propeller

Device that converts rotational motion into thrust by creating a pressure difference in the surrounding fluid

Efficiency (propeller)

Ratio of thrust horsepower (or propeller power) to engine brake horsepower

Number of Blades

More blades improve thrust distribution but reduce efficiency, requiring a design trade-off

Diameter

Larger diameter yields more power and thrust but is limited by structural and installation constraints

Blade Outline

Blade planform area; smaller area improves efficiency but excessive reduction weakens the blade

Angle of Attack

Angle between the incoming airflow and the blade's chord line

Camber

Curvature of the blade's airfoil that increases lift at the cost of higher drag

Lift and Drag Distributions

Use of specific airfoils and prescribed angles of attack across the blade to maximize L/D

Velocity of Flow

Airspeed through the propeller that dictates pitch distribution; ideal pitch/diameter ratio is 1:1

Geometric pitch

Distance a propeller would move forward in one revolution under ideal (no-slip) conditions

Effective pitch

Real distance traveled per revolution, accounting for slip

Slip

Difference between geometric pitch and effective pitch, expressed in inches or as a percentage

Blade Element Theory

Model dividing the blade into segments that each have unique velocity, angle, and lift/drag

Velocity Formula

V = 2π r × rpm, where V is blade-segment speed, r is radius, and rpm is revolutions per minute

Helix Angle

Angle between the relative airflow vector and the propeller's plane of rotation

Geometric Pitch

Theoretical distance advanced per revolution; G.P. = 2π r × tan ε

Effective Pitch

Actual distance advanced per revolution; E.P. = 2π r × tan ε

Slip Formulas

Slip(in) = G.P. - E.P.; Slip(%) = (G.P. - E.P.)×100% / G.P.

Propeller Diameter Formula

D = (303 × N⁴ × BHP / Vmax) × 12, where N is rpm, BHP is brake horsepower, Vmax is ft/sec

Helicopter

Aircraft lifted and propelled by one or more horizontal rotors instead of fixed wings

Rotorcraft

Category of aircraft whose lift is generated by rotating blades rather than fixed-wing surfaces

Primary Advantage

Ability to perform vertical takeoff/landing and efficient hover without runways

Chinese Bamboo-Copter

400 BC toy demonstrating rotational lift principles

Da Vinci's Aerial Screw

1480s conceptual design for vertical flight by Leonardo da Vinci

VS-300

Igor Sikorsky's 1939 prototype, first viable U.S. helicopter

Sikorsky R-4

First mass-produced helicopter, introduced in 1942

Kaman K-225

First turbine-powered (turbo-shaft) helicopter, introduced in 1951

Helicopter Uses

Transportation, construction, firefighting, search and rescue, and remote-area operations

Main Rotor

System of horizontally mounted blades generating lift

Tail Rotor

System of vertically or near-vertically mounted blades counteracting main-rotor torque

Tilt-Rotor Variant

Design with nacelles that rotate rotors from vertical lift to horizontal thrust

Hover Flight

Flight condition with zero forward speed and lift equal to aircraft weight

Forward Flight

Cyclic input tilts rotor disc forward/back to pitch nose down/up and change airspeed

Collective Pitch Control

Changes pitch angle of all main-rotor blades equally to climb or descend

Throttle Control

Twist-grip on collective that regulates engine rpm, assisted by governor and correlator

Governor

Device sensing rotor/engine rpm and auto-adjusting fuel/air to maintain target rpm

Correlator

Mechanical linkage that adjusts throttle as collective is moved to keep rpm constant

Cyclic Pitch Control

Tilts rotor disk by varying blade pitch during rotation to direct horizontal movement

Antitorque Pedals

Foot pedals controlling tail-rotor blade pitch to counter main-rotor torque and yaw

Single Main Rotor

One main rotor plus a separate tail rotor to counteract torque

Tandem Rotor

Two counter-rotating main rotors (fore and aft) eliminating the need for a tail rotor

Coaxial Rotor

Two rotors on concentric shafts rotating oppositely to cancel torque and control yaw

Intermeshing Rotor (Synchropter)

Two inclined masts with intermeshing, counter-rotating rotors; no tail rotor

Tilt-Rotor

Wingtip nacelle rotors that pivot between vertical lift and horizontal thrust modes

Compound Helicopter

Hybrid with main rotor for lift, propellers for high-speed thrust, and small wings

Airframe

Structural framework supporting all helicopter components

Fuselage

Central body housing cabin, engine, transmission, avionics, and controls

Main Rotor System

Mast, hub, blades, and swashplate assembly generating lift

Anti-Torque System

Tail rotor or alternative system countering main-rotor torque

Powerplant

Engine type—reciprocating (piston) or turbine (turbo-shaft)

Transmission System

Gears, shafts, clutch, freewheeling unit transferring and reducing engine rpm

Landing Gear

Skids (fixed) or wheels (fixed/retractable) supporting the helicopter on ground

Semirigid Rotor

System with two blades on a teetering hinge absorbing lead/lag via bending

Rigid Rotor

System with fixed blade roots, no flapping/lead-lag hinges; highly responsive, more vibration

Fully Articulated Rotor

Each blade can flap, lead/lag, and feather independently

Fenestron

Ducted-fan tail rotor housed within the tail boom for anti-torque

NOTAR

No-tail-rotor system using internal fan airflow (Coandă effect) and direct jet thruster

Rotor Anatomy

Hub and mast connect blades; swashplate adjusts blade pitch (feathering)

Feathering

Rotation of the blade about its pitch axis to change lift

Flapping

Up-and-down motion of a blade about its flapping hinge

Multicopter

Aircraft with more than two fixed-pitch rotors; motion controlled by varying rotor speeds

Synchropter

Intermeshing-rotor multicopter providing high stability without tail rotor

Tandem Rotor (multirotor)

Fore-and-aft rotors sharing load; no tail rotor

Coaxial Rotor (multirotor)

Opposing rotors on one mast; increased drag, requires rigid blades

Tricopter

Three-rotor multicopter with yaw control by tilting one rotor

Quadcopter

Four rotors in counter-rotating pairs eliminating torque control issues

Volocopter

Electric 18-rotor air taxi with redundancy allowing operation despite motor failures

Tilt-Rotor Technology

VTOL system morphing rotors between lift (hover) and thrust (cruise)

Tilt-Rotor Advantages

Seamless VTOL-to-cruise transition, STOL heavy-cargo, combined helicopter/airplane envelope

Tilt-Rotor Controls

Yaw by opposite nacelle tilt; roll by differential thrust; pitch by cyclic or nacelle tilt

Bell V-280 Valor

Third-generation tilt-rotor; 280 kts cruise, 11 passengers, 250 nm radius; first flight 12/18/2017

Dissymmetry of Lift

Unequal lift on advancing vs retreating blades in forward flight, mitigated by coaxial designs

Coaxial Rotor Advantages

No tail-rotor power loss, compact footprint, reduced noise, safer ground ops

Coaxial Rotor Disadvantages

Mechanical complexity, dual swashplates, higher fault and self-collision risk

Sikorsky S-97 Raider

Rigid coaxial main rotors plus pusher propeller; fly-by-wire and dynamic anti-vibration