AMT Aerodynamics, Aircra1 Assembly and Rigging Chapter 2 Pressure Vector •  Speed -­‐ the rate of moAon 100 Knots !  If you are going 100 knots, where are you going? !
•  You don’t know •  Vector -­‐ quanAty which has both direcAon and magnitude •  Velocity -­‐ the rate and direcAon of moAon !
Southwest at 100 knots Vector 45°
Vector “A” shown here has a length, or magnitude, of 10 units, and its direcAon is 45° clockwise from north.
Sum of Two Vectors -­‐ Resultant The resultant, vector R, is the hypotenuse of a right triangle with vectors A and B as the two sides. The length of R is the square root of the sum of the squares of the lengths of A and B.
Newton’s First Law of MoAon •  Objects at rest tend to remain at rest; objects in moAon tend to remain in moAon at the same speed and in the same direcAon. !
Objects don’t like to change Newton’s Second Law of MoAon •  When a force acts upon a body, the momentum of that body is changed. The rate of change of momentum is proporAonal to the applied force. The harder you push, the faster you go !  AcceleraAon and DeceleraAon !
Newton’s Third Law of MoAon •  For every acAon there is an equal and opposite reacAon. The law behind thrust propulsion !  Push enough air backwards and the aircra1 moves forward !
Bernoulli’s Principle Bernoulli’s Principle •  ConverAng energy forms !
PotenAal to KineAc •  Height to speed !
KineAc to PotenAal •  Speed to height !
The amount of energy must always stay the same •  Bernoulli’s insight was to apply these principles to fluids Airfoil Airfoil Li1 •  Li1 produced when the aircra1 moves through the air •  Flight surfaces use special shape to create li1 The shape is called an airfoil !  Pressure differences between the top and bo_om of the airfoil creates li1 !
Airfoil Aerodynamic li1 is produced by a relaAvely low pressure above the airfoil surface pulling air down to the surface, while a relaAvely high pressure below the surface forces the air away. The mass of the air deflected downward is balanced by an equal upward force on the airfoil. Airfoil Li1 •  Bernoulli's Principle !
The total energy in the air flowing over an airfoil remains constant •  ConservaAon of Energy Any increase in its velocity will cause a corresponding decrease in its pressure !  Airflow moves faster over the top of a wing !
•  Lower pressure !
Airflow moves slower over the bo_om of a wing •  Higher pressure !
Difference between high and low pressure is li1 Airfoil Li1 •  Newton’s third law -­‐ For every force there is an equal and opposite reacAng force •  The air hibng the bo_om of the wing and leaving the trailing edge push up on the wing !
That is li1 Airfoil Aerodynamic li1 is produced by a relaAvely low pressure above the airfoil surface pulling air down to the surface, while a relaAvely high pressure below the surface forces the air away. The mass of the air deflected downward is balanced by an equal upward force on the airfoil. Airfoils Wing Geometry Angle of Incidence Angle of A_ack (AOA) Wing Angles •  Angle of Incidence – the angle made by the aircra1’s longitudinal axis and the wings cord. !
This is fixed during flight •  A mechanic may change this while rigging the aircra1 •  Angle of A_ack (AOA) – the angle between the cord line of the wing and the direcAon of the relaAve wind Center of Pressure Center of Pressure •  Center of Pressure -­‐ the point on the chord line of an airfoil at which all of the aerodynamic forces are concentrated •  Typically located somewhere around 30% to 40% of the chord line back from the leading edge (subsonic) •  Center of pressure, for a asymmetrical airfoil, moves forward as the angle of a_ack increases, and backward as it decreases Center of Pressure •  Center of pressure, for a symmetrical airfoil, does not move, but remains in essenAally the same locaAon as the angle of a_ack changes Center of Pressure Aerodynamic Li1 •  As air density goes down, li1 goes down Higher air temperature, lower density !  Higher alAtude, lower density !
•  Higher airspeed, higher li1 !
Li1 goes up by the square of the airspeed •  Double airspeed -­‐> 4 Ames the li1 •  Li1 increases as angle of a_ack increases !
0° to 20° Aerodynamic Li1 •  CriAcal angle of a_ack – The angle when the air ceases to flow smoothly over the top of the wing, and the wing stalls !
About 20° Aerodynamic Li1 Stall Wing Plalorm and Progression of Stalls Slots Ahead of Aileron Figure 1-­‐24. A fixed slot in the leading edge of the wing ahead of the aileron forces high-­‐energy air down over the aileron and prevents this porAon of the wing from stalling before the inboard porAon of the wing stalls. Stall Strips Figure 1-­‐25. A stall strip forces the root of the wing to stall before the Ap area stalls. This allows the pilot to have lateral control during the stall. DisconAnuous Leading Edge Boundary Layer Development of boundary layer on a smooth flat surface. Boundary Layer •  Goal is to keep air layer smooth •  Slots and slats force high-­‐energy air from below the wing into the upper-­‐surface boundary layer at high angles of a_ack to help control air at high angles of a_ack •  Wing fences -­‐ verAcal vanes that extend chord wise across the upper surface of an wing to prevent airflow from bleeding along the span •  No one has been able to get an pracAcal acAve boundary layer to system to work !
Boeing is working on one for tail surfaces Vortex Generators •  Pairs of small low-­‐aspect-­‐raAo airfoils •  Installed on the upper surface of a wing, on both sides of the verAcal fin just ahead of the rudder, and on the underside of the verAcal stabilizer •  Pulls high-­‐energy air down to the surface, which energizes the boundary layer and prevents airflow separaAon unAl the surface reaches a higher angle of a_ack. Vortex Generators Vortex generators pull high-­‐energy air down to the surface to energize the boundary layer and reduce drag. Vortex Generators Vortex Generators •
•
•
•
Four Forces in Balance Thrust Li1 Downward force (Weight/Gravity) Drag Four Forces in Balance Four Forces in Balance •  Thrust – Push from propeller or jet engine Part of the power from the helicopter main blades !  A falling aircra1 creates thrust !
Four Forces in Balance •  Li1 – Most of it comes from the wings !
Some can come from the fuselage and addiAon surfaces •  Down Force – Weight of plane and load !
The lighter the load the more efficient the aircra1 Four Forces in Balance •  Drag -­‐ sum of the forces that hold it back against the forward force of thrust Induced drag – drag produced by an airfoil when it is producing li1 !  Parasite drag – Drag caused by fricAon between the air and the surface over which it is flowing !
Aerodynamic Li1 and Induced Drag •  Five factors affect aerodynamic li1 and induced drag: Shape of the airfoil secAon !  Area of the airfoil !  Air density !  Speed of the air relaAve to the airfoil surface !  Angle between the airfoil and the relaAve wind (the angle of a_ack) !
•  Induced Drag Drag Increases with increased angle of a_ack !  For a given li1, angle of a_ack decreases with increased speed !
•  Induced drag decreases with increased speed •  Parasite Drag increases as speed increases •  Behind the power curve – total drag is greater than the thrust provided by the engine !
Pilot must convert alAtude to thrust Drag Wing-­‐Tip VorAces Wing-­‐Tip VorAces Winglets extend upward from the wing Aps of many modern airplanes to reduce drag and increase the L/D raAo by minimizing wing-­‐Ap vorAces. Aircra1 Axes Stability •  StaAc Stability -­‐ The characterisAc of an aircra1 that causes it to return to straight and level flight a1er it has been disturbed from that condiAon •  Dynamic stability is the measurement of how changes to stability reacts StaAc Stability Dynamic Stability Longitudinal Controls •  Longitudinal controls control the aircra1 along the longitudinal axis and about the lateral or pitch axis Horizontal stabilizer and elevator !  Stabilator -­‐ flight control that acts as both a stabilizer and an elevator. The enAre horizontal tail surface pivots and is moved as a unit !
•  Uses anA-­‐servo tab !
Ruddervators – V-­‐ tail. Control surfaces move together to act like an elevator; move differenAally (opposite each other) to act like a rudder Horizontal Stabilizer and Elevator Stabilator Ruddervators Ruddervators Lateral Controls •  Lateral controls control the aircra1 along the lateral axis and about the longitudinal, or roll axis. Aileron !  Spoilers !  Adverse yaw -­‐ induced drag pulls the nose the opposite direcAon !
•  Minimized by the use of differenAal aileron travel -­‐ aileron moving upward travels a greater distance than the aileron moving downward •  Corrected with Rudder Aileron Aerodynamic Balance Spoilers Turn The horizontal component of li1 pulls the nose of a banked airplane around in a turn. When the bank is started, the down aileron produces enough induced drag to temporarily start the nose moving in the wrong direcAon. Dihedral •  Dihedral – The posiAve angle formed between the lateral axis of the airplane and a line that passes through the center of the wing or horizontal stabilizer !
Increases lateral stability of an airplane •  About the longitudinal axis Dihedral Dihedral produces lateral stability. When the right wing drops in flight, its angle of a_ack increases, and the angle of a_ack of the le1 wing decreases. Increasing the angle of a_ack increases the li1, and the wings return to level flight. DirecAonal Stability •  Stability about the verAcal axis is called direcAonal stability, and it causes the nose of the airplane to turn into the relaAve wind when it has been disturbed from this condiAon !
VerAcal Stabilizer •  Parallel to the verAcal axis but not the longitudinal axis !
Longitudinal offset provides direcAonal stability and correcAon for engine thrust. DirecAonal Stability Figure 1-­‐37. DirecAonal stability. DirecAonal Controls •  Yaw control •  Rudder •  Ruddervators – V-­‐ tail. Control surfaces move differenAally (opposite each other) to act like a rudder Rudder Ruddervators •
•
•
•
•
•
Secondary Control Surfaces Also known as Auxiliary Control Surfaces Tabs Flaps Spoilers Speed Brakes Slat & Slots Secondary Control Surfaces •  Purposes Reduce primary control forces !  Reduce land/takeoff speed or length !  Change aircra1 speed !
•  Must provide a means to indicate to the pilot the posiAon of the trim device Secondary Control Surfaces Secondary Control Surfaces Tab •  Used to move control surface •  Tab forces control surfaces in the opposite direcAon !
e.g. up facing tab forces control surface down Servo Tab •  Acts like power assist •  Tab is used to move flight control •
•
•
•
Spring Tab Spring is used to help link tab movement Acts like power assist Has more effect at high control forces Several different spring configuraAons Balance Tab •  Acts like power assist AnA-­‐Servo Tab •  Acts against the pilots acAons •  Helps add stability to a control AnA-­‐Servo Tab Ground Adjustable Tab Adjustable Surface •
•
•
•
Flap Increase li1 Used at slow speed Increase drag Moves center of pressure a1 on the airfoil !
Causes a nose-­‐down pitching moment Flap Plain Flap Split Flap Slo_ed Flap Fowler Flap •  Only flap type that increases the wing size Fowler Flap Leading Edge Slot Leading Edge Slat Leading Edge Flap Spoiler Spoiler Speed Brake Helicopter Main Components Video
Bell Huey Video
Helicopter •  The main rotor blades are rotaAng wings •  Rotor turns a constant RPM •  The angle of a_ack (AOA) of the blades are changed to change the li1 Change all the blades at once, more li1 is generated !  Change individual blades and direcAonal thrust is generated !
•  Forward/backwards •  Side to side Main Rotor System Swashplate Video 1
Video 2
Main Rotor System •  Classified by how blades move relaAve to the main hub •  3 types: Fully arAculated (having a joint) !  Semi-­‐rigid !  Rigid !
Fully ArAculated Rotor System Semi-­‐Rigid Rotor System Stabilizer Bar Rigid Rotor System Video
Helicopter Cockpit Controls CollecAve CollecAve •  Raise the collecAve Increase li1 !  Raise the swashplate !  Increase the pitch of ALL blades !  Increase engine power !  Pilot must correct for extra torque !
•  Can be locked in place Cyclic Control Cyclic Control Moving the cyclic control changes the pitch of the main rotor blades at a point in their rotaAon. This Alts the rotor disc and creates a horizontal component of li1 that moves the helicopter in the direcAon the disc is Alted. Cyclic Control •  Changes blade pitch to match direcAonal change !
Blades move independently •  Move forward and back Pitch helicopter forward or back !  Forward pitch – less forward li1/more backward li1 !  Backward pitch – more forward li1/less backward li1 !
Cyclic Control •  Move le1 and right Pitch helicopter le1 or right !  Le1 pitch – less le1 li1/more right li1 !  Right pitch – more le1 li1/less right li1 !
•  Horizontal stabilizer helps pitch stability !
Some horizontal stabilizers move •  Gyroscopic precession -­‐ inputs are made 90 degrees before the direcAon change needed •  Cyclic input robs li1 !
More collecAve to maintain level Horizontal Stabilizer A horizontal stabilizer on a helicopter provides a downward aerodynamic force to hold the tail down in forward flight. Gyroscopic Precession The rotor of a helicopter acts as a gyroscope and is affected by gyroscopic precession. If the blade pitch is increased on the le1 side of the rotor, the disc will Alt forward. AnA-­‐Torque System Torque of the engine driving the main rotor tries to rotate the fuselage to the right. This rotaAon is prevented by thrust from the tail rotor. AnA-­‐Torque System •  Main blades turns one way, helicopter body wants to turn the other way US helicopters blades turn counter-­‐clockwise !  Overseas helicopter blades turn clockwise !
•  AnA-­‐torque systems are used to stop the rotaAon •  Tail rotors oppose the torque generated by the main rotors !
More li1 – more torque AnA-­‐Torque System •  Pilot adjusts torque with anA-­‐torque (rudder) pedals •  Tail rotor blades turn at a constant speed !
Hard linked to main rotor •  Tail rotor blades change pitch to change torque •  VerAcal fins help reduce tail rotor load during forward flight •  Robs power from power plant •  Stay clear – very dangerous Tail Rotor Fenestron NOTAR AnA-­‐Torque System •  Tail rotor dri1 or translaAng tendency Combined effect of tail rotor thrust and main rotor li1 -­‐ causing helicopter to dri1. !  The tail rotor and mast is Alted to correct for this !  Pilot must add cyclic input to correct !
TranslaAng Tendency Hover •  Flying with no movement •  Requires the most power •  Easier to hover in “ground effect” Heights less than 1/2 main rotor diameter !  Effected by ground surface material !
•  Density alAtude and temperature will effect how well a helicopter can hover Ground Effect Forward Flight •  Move cyclic forward •  Part of main rotor li1 pushes helicopter forward •  TranslaAonal or transiAonal li1 An increase of air volume through the blade caused by forward movement !  Causes increase li1 !  Happens at about 15 knots !
Forward Flight •  Transverse flow effect Air passing through the rear porAon of the rotor disc has a higher down wash velocity than air passing through the forward porAon !  Rear porAon of disc losses li1 !  Gyroscopic precession means is causes li1 imbalance between the le1 and right sides of the rotor disk !
•  VibraAon felt around 12 to 15 knots Dissymmetry of Li1 Dissymmetry of Li1 •  Happens in forward flight •  Forward moving blade has higher relaAve airspeed !
More li1 •  Backward moving blade has lower relaAve airspeed !
Less li1 •  Helicopter will try to roll towards backward moving blade Dissymmetry of Li1 •  Limits forward speed of helicopters •  Blade flapping helps solve problem Forward moving blade – moves up !  Backward moving blade – moves down !  Coriolis force – blade coning !
•  Semi-­‐rigid rotors Alt to solve the problem Vortex Rings Airflow through a helicopter rotor during power se_ling. •
•
•
•
AutorotaAon Land when there is a power failure Sprag clutch disengages power plant Lower collecAve to store energy in blades Raise collecAve to flare !
Convert energy in spinning blades into li1 to slow down descent •  Video Dead Man's Curve/Coffin Corner Helicopter Turbine Engine Helicopter Clutch •  Enable engine starAng •  Types: Centrifugal !  Belt Drive !
•  Turbine engines don’t need clutch !
Video Freewheeling Unit •  AutomaAcally disengages the engine from the main rotor when engine rpm is less than needed to maintain the main rotor rpm !
Allows the main rotor and tail rotor to conAnue turning at normal in-­‐flight speeds •  Most common type is a one-­‐way sprag clutch •  Video Blade Adjustment •  Both main and tail rotors are adjusted •  Blade tracking – adjust links to bring the Aps of all blades into the same Ap path throughout their enAre cycle of rotaAon Blades should cone the same amount if tracked correctly !  Doesn’t adjust their path of flight !  Flag and Pole !  Electronic !
•  Balance and vibraAon !
Electronic Flag and pole StaAon Numbers and LocaAon IdenAficaAon •  Fuselage StaAons – numbered in inches from a reference or zero point know as the reference datum. (length wise) •  Bu_ock Line (bu_ line) – width measurement le1 or right of, and parallel to, the verAcal center line. (width wise) •  Water Line – the measurement of height in inches perpendicular from a horizontal plane located at fixed number of inches below the bo_om of the aircra1 fuselage (height wise) Water Line and Fuselage StaAon Bu_ock Line Rebalance of Control Surface The trialing edge is checked
Rebalance of Control Surface •  A control surface must be rebalanced a1er any maintenance that will effect the weight or balance of the surface !
This includes painAng •  Each manufacturer and aircra1 will have it’s own procedures !
Follow the manufacturer’s service manual Rigging InformaAon •  Type CerAficate Data Sheets (TCDS) will contain informaAon on how far a control surface should move (deflecAon). O1en in angle of moAon !  Doesn’t include procedures (how to) !
•  Manufacturer’s Service and Maintenance Manual will contain both data and procedures !
Gold Standard •  Airworthiness DirecAve (AD) may contain informaAon •  Service Le_er and BulleAns include recommendaAons Rigging Work Setup •  Conduct inside a hanger so there is not wind disturbing the aircra1 !
If outside, face aircra1 nose into wind •  Insure the aircra1 is level •  If aircra1 is jacked up, insure all criAcal stress panels and plates are installed !
This may include closing the hatches and doors Primary Flight Control Surfaces Cessna Aileron Control Cables 3° max deflection for Fairlead
Cable Guides Pulleys are used to change cable direction
Cable Rigging •  Control surfaces are o1en moved by cables, push-­‐pull rods or torque tubes (twisAng) •  Cable material !
Carbon steel •  Older style •  Corrodes !
!
!
Coated in zinc or An Lubricate with Par Al Ketone CRES •  May be coated in nylon !
Comes pre-­‐streched Control Cable Control Cable Cable Rigging •  Cable DesignaAon Number of strands !  Number of wires per strand !  e.g. 7 X 19 – 7 strands, each strand has 19 wires !
•  7 X 19 is the only acceptable type for primary controls Most flexible !  Minimum size is 1/8” diameter for primary controls !
•  7 X 7 used for things like engine controls and flaps Cable Rigging •  Cable TerminaAons !
Woven splice •  75% of cable strength •  Not used any more !
Nicopress •  100% of cable strength •  Use “go”/ “no go” gauge for tesAng !
Swage type •  AN & MS type terminaAons •  100% of cable strength •  Use “go”/ “no go” gauge for tesAng •  Test the cable by proof-­‐loading it to 60 percent of its rated breaking strength Nicopress Thimble
Nicopress Nicopress Swag Type TerminaAons Swag Type Gauge Cable Splices Cable Splices •  Used to fix broken cable •  Used in free lengths of cable which do not pass over pulleys or through fair-­‐leads •  Locate splices so that no porAon of the splice comes closer than 2” to any fair-­‐lead or pulley •  Locate connecAons at points where jamming cannot occur Cable InspecAon/Replacement •  Look for corrosion with carbon steel cables •  Passing a cloth over an area to snag on broken wires !
Don’t use your hand •  Look for hairline crack May need magnifying glass !  Remove and bend cable to show cracks !
•  Look for cracks in nylon jacket •  Look for outer wires wear of 40 to 50 percent •  Most breakage occurs at ends, pulleys and through fairleads Cable InspecAon Cable InspecAon Tensiometer Cable Tension Turnbuckle Cable Tension •  A1er maintenance or a repair, check and adjust the tension of the cables •  Use a Tensiometer •  Rigging charts are calibrated with temperature •  As the temperature lowers, the aircra1 shrinks faster than the cables Cable loosen with colder temperatures !  Large aircra1 use tension regulators to retain the correct tension as temperature changes !
•  Excessive tension causes the control to feel sAff or “heavy” Turnbuckle Turnbuckle •  No more than three threads can be exposed •  On iniAal installaAon, the turnbuckle terminals should not be screwed inside the turnbuckle barrel more than four threads •  Witness holes are used to insure terminal is screwed in far enough !
Look for thread in hole •  A piece of wire should not pass through hole •  Safety wire or “clip” turnbuckle !
Safety wire requires a minimum of 4 turns around the terminal end shanks Turnbuckle Safety Wire Turnbuckle Safety Wire Clip Type Turnbuckle MS Clip-­‐type locking device for turnbuckles.
Pulley Wear Check bearing wear also
Push Pull Rod Rod A_achment End Cessna Type Wing Adjustment The angle of incidence of some canAlever airplanes is adjusted by rotaAng eccentric bushings in the rear wing spar fibng.
Wing Measurement Measurement taken on the front spare
The dihedral angle is checked with a dihedral board and a spirit level.
Rigging Wing •  Dihedral -­‐ The posiAve angle formed between the lateral axis of an airplane and a line that passes through the center of the wing or horizontal stabilizer •  Wash IN -­‐ A twist in an airplane wing that INcreases its angle of incidence near the Ap !
Increase wash in – wing li1 is INcreased and drag is INcreased •  Wash out -­‐ A twist in an airplane wing that decreases its angle of incidence near the Ap !
Increase wash out – wing li1 is decreased and drag is decrease Rigging Wing •  Wing heavy -­‐ An out-­‐of-­‐trim flight condiAon in which an airplane flies hands off, with one wing low The low wing is the heavy wing !  Correct by: !
•  Increase the angle of incidence (add wash in) to the low wing, or •  Decrease the angle of incidence (add wash out) to the high wing, or •  Both Rigging Wing •  The manufacturer will give you instrucAon on how to create a dihedral board; and fixtures to measure incidence and twist !
The boards and fixtures are then measured with a level •  Also called a bubble level or spirit level !
Dihedral board is usually placed on the front spar Propeller Protractor Propeller Protractor •  Used to measure the deflect of control surfaces such as the ailerons, elevators, and flaps •  Protractor is “zero” with the control surface in the neutral posiAon •  Measurements are made in degrees