Helicopters

VI. Helicopters History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1483, DaVinci Developed “Helix” Kind of aerial screw Shows basic understanding that the atmosphere can support weight but no provisions for torque on fuselage History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1800s, Forlanini (Italy) Used steam engine Counter-rotating “butterfly” wings Could ascend (without pilot) to 40 feet for about 20 minutes History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1907, Cornu (France) First piloted helicopter Flew for few seconds Used internal combustion engine No controls but well balanced History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1909, Igor Sikorsky (Russia) Small counter-rotating coaxial rotors First use of airfoil shaped rotors History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1920s, Petroczy & Von Karmon (Austria) Counter-rotating, coaxial, airfoil rotors 3 40HP engines No controls, just made to lift straight up History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1923, de Bothezat (U.S.) 4 rotors Complicated power transmission system Low power Several flights of 1 minute @ 6 feet History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1923, de la Cierva (Spain) Developed Autogyro Solved some control problems by allowing rotors to Flap History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1936, Focke-Wulfe (Germany) FW-61 established endurance & speed records Mostly flown by Hannah Reich Flown inside stadium for most of records History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters History 1939, Sikorsky (U.S.) Developed VS-300 Broke all FW-61 records Used 3-bladed main rotor, vertical 2-bladed tail rotor & 2 horizontal 2-bladed outrigger rotors for stability and control History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Configurations Autogyros Developed by de la Cierva Uses free-spinning main rotor with airplane-like engine/prop for forward motion No power to main rotor, spins from air action = can’t hover or ascend vertically History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Configurations Dual Rotor 2 counter rotating main rotors No tail rotor needed May be separate or coaxial Used extensively through history, today few (Boeing, Kaman) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Configurations Single Rotor Most used design 1 main rotor for lift and control Tail rotor for anti-torque FAA calls it “Auxiliary Rotor” More precisely known as “Anti-torque Rotor” History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Configurations Single Rotor History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Hughes Helicopter H-17 Skycrane 1952 Function: transport Crew: 2 Engines: 1 * G.E. J35 Rotor Span: 130ft Length: Height: 30ft Disc Area: Empty Weight: Max.Weight: 46000lb Speed: Ceiling: Range: 65km Load: 25000lbs Hot Cycle Blades

Helicopters Configurations Tilt Rotor Bell V-22 Engines and main rotors (“PropRotors”) mounted on wingtips Rotate so rotor is horizontal (on top) to takeoff and land like helicopter Rotate so rotor is vertical to act like prop for high speed forward flight History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors General All must change blade angle or Pitch for control actions Called “Feathering” Is rotation around the span axis of the blade History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors General Some also: Flap or Teeter History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors General Some also: Lead/Lag (Hunt or Drag) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors Semi-Rigid Rotor 2-bladed Blades Feather and entire rotor Teeters No Hunting action allowed Very popular in early Bell designs (and others) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Semi-Rigid Bell 206 Helicopters Types of Rotors History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors Fully Articulated Rotor 3 or more blades Blades can Feather, individually Flap, and Hunt History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Hunting limited by mechanical Dampers

Helicopters Types of Rotors Fully Articulated Is most complicated but smoothest in flight Problem: Ground Resonance potential History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors Fully Articulated Hughes 500 (McDonnell-Douglas, Boeing) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors Fully Articulated Sikorsky S58 History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors Fully Articulated AStar 350 History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Types of Rotors Rigid 2 or more blades Blades Feather but all other forces absorbed by bending of the blades Strongest and most maneuverable but needs composites to withstand fatigue History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Static Forces Gravity pulls down and blades can bend relatively low Called Droop All need some kind of Droop (Static) Stop to prevent too low and possible Tail Boom strike Especially for Fully Articulated at low RPM History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Turning Forces Centrifugal Force tries to hold the blades straight out but lift tries to bend up Result is Coning Upward bending into Cone shape More lift = more Coning History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Torque From Newton’s 3 rd Law Main rotor turns in one direction = fuselage tries to turn opposite (Torque) Is directly proportional to power applied to M/R History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Torque Compensated for by Tail Rotor thrust History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems What happens if Tail Rotor fails during flight?

Helicopters Forces on the Rotors Torque Compensated for by Tail Rotor thrust or counter-rotating M/Rs History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Torque Problem: Tail Rotor causes “Translating Tendency” or “Drift” Is movement of entire helicopter in direction of T/R thrust (to right in U.S.) Compensated by slight tilt of M/R mast to left History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Gyroscopic Precession Any rotating body (M/R) acts like a Gyroscope and exhibits 2 characteristics: Rigidity Precession Rigidity resists the change from it’s position in relation to space, not the Earth Precession is the fact that the effect of any upsetting force applied to the body is felt 90 o later in direction of rotation Affects the design and rigging of the M/R History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Gyroscopic Precession For flight = need to tilt “Rotor Disk” in direction of desired flight Changes lift & thrust vectors toward that direction = movement of helicopter To accomplish = need to make pitch change 90 o earlier History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems De sired direction of flight

Helicopters Forces on the Rotors Gyroscopic Precession For flight = need to tilt “Rotor Disk” in direction of desired flight Changes lift & thrust vectors toward that direction = movement of helicopter To accomplish = need to make pitch change 90 o earlier History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Ground Effect Increased lift within ½ rotor diameter of ground “Cushion of Air” Comes from change in angle of attack near ground because relative wind changes History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Ground Effect Out of Ground Effect (OGE) Rotor wash is free to accelerate straight down = given angle of attack and lift and large tip vortex History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Rotation Angle of Attack Downwash Relative Wind

Helicopters Forces on the Rotors Ground Effect In Ground Effect (IGE) Rotor wash is forced to move outward as well as down = reduced down vector = increased angle of attack + smaller tip vortex History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Downwash Rotation Angle of Attack Relative Wind

Helicopters Forces on the Rotors Flight Forces Same as airplane: Lift up Weight (Gravity) down Thrust forward and up Drag back and down History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Flight Forces In hover: Lift and Thrust both act up Weight and Drag act down History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Forces on the Rotors Flight Forces Forward Flight: Thrust vector tilted in desired direction = overall loss of upward lift = need more power applied Similar to airplane in turn History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Dissymmetry of Lift At a hover with no wind the rotor blades are all traveling at the same speed in relation to the air around them History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Dissymmetry of Lift Any relative air motion (wind or flight) = blade going into wind ( Advancing Blade ) travels faster than Retreating Blade Think in terms of Airspeed History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems 100 mph

Helicopters Flight Conditions Dissymmetry of Lift Faster airfoil = more lift on Advancing side (and less lift on Retreating side) Lift not equal = Dissymmetry of Lift Without compensation = roll to left (and gets more severe with speed increase) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Dissymmetry of Lift Compensated for by allowing the blades to Flap or the rotor to Teeter Advancing blade Flaps (Teeters) up = decrease in angle of attack due to upward vector of Relative Wind History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Dissymmetry of Lift Compensated for by allowing the blades to Flap or the rotor to Teeter Retreating blade Flaps (Teeters) down = increase in angle of attack due to Relative Wind change History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Coriolis Effect Caused by Flapping or Teetering up Blade flaps up = Center of Mass moves closer to axis of rotation = RPM increases History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Coriolis Effect The inertia of the rotor stays constant so as the Axis of Rotation is reduced the Speed of Rotation must increase Is same as skater in spin with arms out then speeds up when arms are moved in to sides History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Coriolis Effect Creates force to accelerate the blade (Hunting action) Fully Articulated head allows limited Hunting action Uses hydraulic or composite dampers to minimize movement History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Coriolis Effect Semi-Rigid usually uses “UnderSlung Rotor Head” Teetering Axis is above Feathering Axis (“Delta Hinge” arrangement) = as teeters it also swings to high side History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Coriolis Effect Semi-Rigid usually uses “UnderSlung Rotor Head” Center of Mass of the Rotor then stays basically in line with driveshaft/mast History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Translational Lift Increased lift during the translation to forward flight from a hover Occurs between 16 and 24 knots airspeed Feel vibration and definite increase in lift (that point is called “Effective Translational Lift”) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Translational Lift At hover and below 15 knots , the ground is forcing the rotor downwash outward and creating some turbulence around rotor blades History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Translational Lift At hover and below 15 knots , the ground is forcing the rotor downwash outward and creating some turbulence around rotor blades History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Above 15 kts , the blades “bite” into undisturbed air = more efficient = less power needed

Helicopters Flight Conditions Translational Lift Above about 50 knots , drag starts to increase greatly and we need more power to further accelerate History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Transverse Flow Effect At slow airspeeds (less than 20 kts.) = air through rear of rotor is accelerated downward longer than air at front = decrease in angle of attack in rear History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Transverse Flow Effect Effect felt 90 o later = drift to right Pilot must compensate with some left Cyclic to keep going in a straight line History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Transverse Flow Effect As airspeed increases = entire rotor has basically undisturbed airflow = no Transverse Flow Effect is felt History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations Flight with no engine power applied to the main rotors Air is normally drawn down through rotors but if have engine failure = aircraft drops and wind goes up through rotors = keeps them rotating at near normal RPM History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations When engine fails, pilot lowers Collective stick to bottom = sets in minimal angle on all blades and adjusts Cyclic to certain forward airspeed History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations With Relative Wind from underneath and forward: Lift and Drag vectors are changed so Resultant is forward of Axis of Rotation = tries to accelerate rotor and is called Autorotative Force History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations With Relative Wind from underneath and forward: Occurs in middle 25 – 75% of rotor Is called the Autorotative (Autorotation) Region History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations With Relative Wind from underneath and forward: In outer 30% of rotor = blade twist makes the angle of attack low and the speed makes the drag high Resultant is behind the Axis of Rotation History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations With Relative Wind from underneath and forward: Is a Decelerating force (Anti-Autorotative Force) and is called the Driven (or Propeller) Region History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations With Relative Wind from underneath and forward: Inner 25% has an angle of attack higher than the Critical Angle of the airfoil = Stall Region and also creates an Anti-Autorotative Force History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations At some forward airspeed these forces combine to stabilize the RPM (achieve equilibrium) RPM means Inertia = energy available to use when near the ground This Autorotation RPM is critical rigging adjustment History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations At about 50 feet above the ground, the pilot pulls back on the Cyclic to flare the aircraft (pulls the nose up some = reduced airspeed) = momentary increase in airflow and higher RPM (= more inertia) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations At about 10 feet above the ground, the pilot pulls up on the Collective and starts to use that energy in the rotor to cushion the landing History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Autorotations Also leads manufacturers to publish “Height-Velocity Diagram” in Flight Manual Also known as the “Dead Man’s Curve” If fly in shaded area combinations of Height (Altitude) and Velocity = can’t successfully Autorotate History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Retreating Blade Stall As we move forward = Retreating Blade flaps down to compensate for Dissymmetry of Lift by increasing the angle of attack At some high forward airspeed (especially if the rotor RPM is allowed to get low) a portion of the airfoil (rotor disk) will exceed the Critical Angle of Attack and Stall History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Retreating Blade Stall Generally occurs at the 7 – 9 o’clock position (looking down on the rotor = left rear of rotor) = vibrations + nose pitches up gyroscopic precession = loss of lift in rear of rotor History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Retreating Blade Stall Nose pitch up = excessive angle of attack in front (stall) = loss of lift on left and roll to left History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Vortex Ring State (Settling With Power) If descending at 300 fpm or more + less than 10 mph forward airspeed + 20 to 100% power applied = can descend inside rotor downwash History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Vortex Ring State (Settling With Power) Blades produce tip vortices (like any airfoil) + upward flow of air in middle of rotor (from descent) = Vortex across entire rotor = loss of lift and increased descent rate History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Vortex Ring State (Settling With Power) Increasing power to control descent rate = increases problem by increasing the amount of vortex created Must accelerate out of it or descend below it (if there’s enough altitude) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Vortex Ring State (Settling With Power) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Flight Conditions Ground Resonance History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems http://www.chinook-helicopter.com/Fundamentals_of_Flight/Ground_Resonance/Ground_Resonance.html

Helicopters Controls Axes of Flight Same as airplane: Longitudinal Axis = Roll, Lateral Axis = Pitch, Vertical Axis = Yaw History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Flight Controls 3 basic controls: Cyclic, Collective, Pedals History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Flight Controls 3 basic controls: Cyclic, Collective, Pedals Cyclic: Controls Pitch and Roll Tilts rotor disk in desired direction of movement Is primary airspeed and flight path control (pitch & roll) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Cyclic: Uses Swashplate to do job Is device with rotating component and stationary component Connected by double-row ball bearing Lower (stationary) part connected to Cyclic stick via push-pull tubes and/or hydraulics Upper (rotating) part connected to main blades and rotates with them History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Cyclic: Uses Swashplate to do job Pilot pushes Cyclic stick in direction of desired movement Swashplate is tilted to change M/R blade pitch a different amount depending on where it is in rotation The pitch changes cyclically as it rotates Direction of tilt is designed to take Gyroscopic Precession into account May or may not tilt same as rotor disk action History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Cyclic: Example system: Huey (Bell UH-1) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Fore & Aft tubes Lateral tubes

Helicopters Controls Axes of Flight Collective: Changes the pitch of all blades the same amount at the same time (collectively) Controls the overall lift generated by the rotors History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Collective: Uses the Swashplate to do the job by raising or lowering it to change the pitch on all blades History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Collective: Collective stick also has engine throttle(s) Motorcycle style rotating throttle except must rotate away from you to increase Turbines usually governed so open throttle wide open and let governor keep RPM steady History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Collective: Example system: Hughes (Schweizer) 269 History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Pedals: Control Yaw by controlling the thrust of the Tail Rotor (on single-rotor helicopters) and driven by main transmission so will still work if engine quits Dual rotors = differential cyclic control by pedals Coaxial rotors = rudder in rotor downwash Push left pedal to yaw to the left, right pedal to yaw to the right Left pedal increases T/R thrust Needed especially during slow and high power conditions (I.e. takeoff and landing) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Tail Rotor Types: Semi-rigid Most common until recently Usually 2-bladed Has same Dissymmetry of Lift problems as M/R so will teeter usually (some let blades flap) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Tail Rotor Types: Semi-rigid Most common until recently Usually 2-bladed Has same Dissymmetry of Lift problems as M/R so will teeter usually (some let blades flap) Most use Offset Hinges so pitch is physically changed as rotor teeters = minimal actual teetering action History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Tail Rotor Types: Fenestron French design Enclosed multi-bladed variable-pitch fan Safer and quieter History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Axes of Flight Tail Rotor Types: NOTAR Developed by Hughes Helicopters (then McDonnell-Douglas now Boeing) Uses fan inside tail boom with exhaust out side of boom through variable vent connected to pedals Also uses Coanda Effect from rotor downwash Air flowing over the curved surface “sticks” to that surface and creates lift sideways History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Miscellaneous Stabilizer surfaces Fixed Horizontal Creates download on tail to keep fuselage more level during high speed flight Synchronized Elevator Connected to Cyclic Changes pitch to change tail down load for various flight speeds Fixed Vertical For directional stability History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Miscellaneous Hydraulics For larger or heavier M/R systems Mostly use Irreversible type systems to overcome flight loads and dampen vibrations in sticks History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Miscellaneous Example system: Bell 206 History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Stabilizer Controls Are inherently unstable As rotor lift/thrust vector tilts away from vertical = creates vector to pull away from center = negative stability History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Compensations Bell Stabilizer Bar Bar below M/R @ 90 o to blade span Acts like gyroscope and uses Rigidity in Space characteristic to try and keep rotor and aircraft in one attitude Worked too well so needs hydraulic damper to limit it’s effectiveness and allow reasonable maneuverability

Helicopters Controls Compensations Offset Flapping Hinge On fully-articulated rotor heads and on some tail rotors Hinge moved a distance from rotor’s rotation axis = acts like lever to provide restoring force History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Compensations Stabilization Augmentation System (SAS) Like simple autopilot One- or two-axis Only to aid stability, not true autopilot History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Large number of moving and rotating parts = susceptible to vibrations Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people Must minimize vibes History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Types Low Frequency Feel as “beat” in structure and may be able to almost count the beats Comes from Main Rotor History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Types Low Frequency History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Vertical vibe Up & down motion Caused by blades being Out-of-Track

Helicopters Controls Vibrations Types Low Frequency History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Lateral vibe Side-to-side motion Comes from blades being out of balance or spaced unequally

Helicopters Controls Vibrations Types High Frequency Felt as “buzz” in structure Comes from cooling fan, engine and/or accessories, gearboxes, or (most commonly) Tail Rotor May only notice if some part of body goes to sleep Feet = Tail Rotor (through pedals) Butt = others History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Measurement of vibes Feel Adjust until feels OK (at minimum level) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Measurement of vibes Electronic Use accelerometers to measure rate and strength accurately Use Strobe light or “Clock” to locate Use above as coordinates on chart to determine exactly where and how much weight to add or remove Can use to troubleshoot (narrow down vibe rate and look at those components operating at that rate) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of balance condition May require Static or Dynamic procedures (or both depending on helicopter) Some require Static balancing after assembly Put on balance stand and adjust until no movement when released T/R done like propeller (knife-edge stand) M/R done on special stand with Bullseye level History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Vibrations Correction of vibes (M/R & T/R) If out of balance condition M/R also may require Blade Sweep to be adjusted (for chordwise balance) = stretch string between blades and adjust until blades are exactly 180 o apart (adjust by “sweeping” blades forward or aft as necessary) Helicopters Controls History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of balance condition Dynamic balancing done during operations on ground and in air Uses Electronic gear to measure rate and strength and charts to show adjustments Some M/Rs don’t need dynamic after static but all T/Rs do History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Example: Chadwick-Helmuth Vibrex ® system

Helicopters Controls Vibrations Measurement of vibes Example chart: T/R balance History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Measurement of vibes Example chart: M/R balance History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Track = path Blade tips follow during rotation In-Track = all tips follow same path (or Cone the same amount) and = minimal vertical vibes All M/Rs need to be checked and adjusted and some T/Rs History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Ground check Use marking stick or Flag Marking Stick uses crayon or grease pencil on end of long stick and carefully raise to bottom of blades to make mark on lowest one (adjust until marks all blades) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Ground check Flag is strip of canvas suspended between F shaped pole + put crayon mark on blade tips (different color on each blade) then move Flag so just touches each blade to get a colored mark Use colors to determine which blade needs adjustment History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Flag Tracking History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Flag Tracking

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Ground check All are adjusted by changing the length of the Pitch Links (controls Angle of Incidence of blades) Link between Swashplate and M/R blade Increase angle = more lift = blade flies higher Each manufacturer usually has standard adjustments (I.e. 1/6 turn = ½” blade movement) Limitation: can’t check in flight History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Ground & Flight Use spotlight or strobe Spotlight uses colored reflectors attached to blade Light shows colored streaks and can see “altitude” difference between them History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Ground & Flight Strobe is keyed by pickup on swashplate Flashes once for each blade Has reflectors on each blade with different angled “Target” line Flashes ‘stop’ targets at one location and can easily see difference and which blade to adjust History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Vibrations Correction of vibes (M/R & T/R) If out of Track condition Ground & Flight For ground and hover adjustment = use Pitch Links For in-flight adjustment = most blades have trailing edge fixed trim tabs to allow limited bending History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating See all types: Horizontal and Vertically mounted Opposed engines & some Radials History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating Verticals and Radials usually are Dry-sump with M/R Transmission (GearBox) mounted on top and using same oil supply History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating Verticals and Radials usually are Dry-sump with M/R Transmission (GearBox) mounted on top and using same oil supply History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Bell 47

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating Horizontals usually use some form of Belt Drive Multiple V-belts or one wide “timing” belt History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating None have propeller for cooling air blast and “fly wheel” for starting All use some form of Cooling Fan driven by engine to blow air across cylinders All are generally hard to start (no fly wheel to help process keep going) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating Instruments Since M/R is essentially a Variable-pitch Propeller = all use both Tachometer (RPM) and Manifold Pressure gauges for power measurement Engines must be operated at relatively constant RPM (to allow enough Lift & Thrust) and usually very near the manufacturer’s Overspeed limit History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating Usually uses Correlated Throttle and Collective Pull up on collective = more blade pitch = more lift/thrust generated = more drag Need more engine power to keep RPM constant Correlation increases throttle automatically as Collective is pulled up (may not do entire job, though) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Reciprocating Usually uses Correlated Throttle and Collective Pull up on collective = more blade pitch = more lift/thrust generated = more drag Need more engine power to keep RPM constant Correlation increases throttle automatically as Collective is pulled up (may not do entire job, though) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Bell 47

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are ideal powerplants as operate most efficiently at constant RPM and have very high power to weight ratio History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are TurboShaft engines All output power is converted to rotating shaft power (Torque) Torque sent to Transmission to drive Main & Tail Rotors and other necessary components History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are TurboShaft engines Two basic types: Direct Shaft & Free Turbine Direct Shaft has PTO shaft connected to all Compressor and Turbine section stages Are very hard to start as must turn all engine + Main and Tail rotors History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are TurboShaft engines Two basic types: Direct Shaft & Free Turbine Free Turbine has some Turbine stages which only supply PTO power Easier to start as rotors not mechanically connected to main part of engine History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are TurboShaft engines Measure power output with Tachometers, Torquemeters, and Turbine Temperature gauges Tachs measure RPM in % (due to high actual RPM) Free Turbine versions need to measure both main engine (N 1 ) and Power Turbine (N 2 ) and usually have separate gauges History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are TurboShaft engines Torquemeters measure power being absorbed by M/Rs Similar to MAP gauge on recips Measures in % or in Pounds of Torque History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Powerplants Turbines Are TurboShaft engines Turbine Temps very important as are directly proportional to how hard the engine’s working and critical during the start cycle May be TIT, ITT, TOT, or EGT system (manufacturer’s choice) CAN NOT exceed max. limit or will damage Turbine section components History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Transmissions For speed and/or directional change of rotating shaft(s) May be Rack & Pinion or Planetary Gear systems Uses engine oil or has own supply History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Transmissions For speed and/or directional change of rotating shaft(s) May be Rack & Pinion or Planetary Gear systems History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems Schweizer (Hughes) 269 Transmission: Rack (Ring Gear) and Pinion

Bell 47 Transmission: Planetary system

Helicopters Controls Power Systems & Other Components Transmissions Engine drives M/R Transmission which in turn drives the T/R, Hydraulic pumps, Electrical Generator, Cooling Fans (if appropriate for the aircraft), and Rotor Tach sending unit connected to (usually) Dual Tach (Rotor and Engine RPM on same gauge) History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Clutch USED TO RELIEVE THE ENGINE LOAD DURING STARTING May be Manual, Electrical, or Centrifugal Manual and Electrical pull Idler Pulley against Belt(s) to tighten them and connect engine with Transmission History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Clutch Centrifugal uses hinged Shoes pushed against a Drum by Centrifugal Force Shoes on arms attached to engine crankshaft Drum attached to Transmission History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters Controls Power Systems & Other Components Freewheeling Unit FOR AUTOROTATION PURPOSES Disconnects M/R from engine if engine turns slower than M/R Usually either Roller or Sprag style History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions Controls Stabilizer Controls Vibrations Power Systems

Helicopters

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Helicopters