Author: Harry L. Whitehead

Author: Harry L. Whitehead
III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: General To insure an airplane has good handling qualities in all flight regimes, we need it to be STABLE, MANEUVERABLE, and CONTROLLABLE STABILITY is the characteristic of an airplane in flight that causes it to return to a condition of equilibrium, or steady flight, after it is disturbed. 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: General To insure an airplane has good handling qualities in all flight regimes, we need it to be STABLE, MANEUVERABLE, and CONTROLLABLE MANEUVERABLILITY is the characteristic that permits the pilot to easily move the airplane about its axes and to withstand the stress from these moves 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: General To insure an airplane has good handling qualities in all flight regimes, we need it to be STABLE, MANEUVERABLE, and CONTROLLABLE CONTROLLABILITY is the capability to respond to the pilot’s control inputs 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: General Unfortunately, these characteristics are at odds with each other Increase in one leads to a decrease in another = all airplane designs are compromises If make it too stable = it’s hard to control 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: General Types 2 TYPES OF STABILITY STATIC The ability of an object to return to its equilibrium state after being disturbed DYNAMIC The way the object moves after being disturbed 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: General Types 3 CONDITIONS OF STABILITY: POSITIVE The disruption of an object gets less over time NEGATIVE The disruption gets greater over time NUETRAL The disruption neither increases or decreases over time 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Positive Stability: Stability: General Types The tendency to return to the original equilibrium Example: Ball in a trough Generally desirable in an airplane but does decrease maneuverability 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Negative Stability: Stability: General Types The tendency to move away from the equilibrium Example: Ball on a hill Undesirable in an airplane 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Nuetral Stability: Stability: General Types The tendency for the correcting forces to neither increase or decrease over time Example: Ball on a flat surface Somewhat OK in an airplane 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes Since we have 3 main axes of an aircraft, we also have 3 main types of Stability: LONGITUDINAL LATERAL DIRECTIONAL 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY Is the ability of an aircraft to remain stable ABOUT (OR AROUND) THE LATERAL AXIS Is PITCH STABILITY Or keeping the Longitudinal Axis stable 9/17/2018 Author: Harry L. Whitehead

Since the CENTER OF PRESSURE (or CENTER OF LIFT) moves with Angle of Attack changes III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY We need to be sure the Center of Gravity doesn’t get behind the Center of Pressure or severe flight problems will occur (such as can’t lower the nose) 9/17/2018 Author: Harry L. Whitehead

Airplanes are designed so the Center of Pressure or Lift is behind of the Center of Gravity = a downward pitching moment on the nose of the aircraft at all times III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability This, coupled with the downward TAIL LOAD created by the HORIZONTAL STABILIZER, create a balanced set of conditions to keep the Longitudinal Axis stable Stability: About the Aircraft Axes LONGITUDINAL STABILITY 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY If the aircraft gets disturbed so the nose goes up, the Horizontal Stabilizer’s Angle of Attack is decreased and creates less Down Load to compensate Hor. Stabs. are usually symmetrical airfoils 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY If the aircraft gets disturbed so the nose goes down, the Horizontal Stabilizer’s Angle of Attack is increased and creates more Down Load to compensate This is Positive Longitudinal Stability 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics The Horizontal Stabilizer will be installed at some particular Angle of Incidence so it can do its job correctly This may be negative, positive, or zero Aircraft Stability Stability: About the Aircraft Axes LONGITUDINAL STABILITY 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LATERAL STABILITY Is the ability of an aircraft to remain stable ABOUT (OR AROUND) THE LONGITUDINAL AXIS Is ROLL STABILITY Or keeping the Lateral Axis stable 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes Provided mostly by wing DIHEDRAL This is the upward angle between the wing and the Lateral Axis LATERAL STABILITY 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls As an airplane is upset so a wing drops, it starts to SIDESLIP toward the low wing Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LATERAL STABILITY Provided mostly by wing DIHEDRAL 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics This slipping motion plus the downward movement of the wing add downward vectors to the Angle of Attack production and lead to an increase in  on the lower wing = more lift on that wing Aircraft Stability Stability: About the Aircraft Axes LATERAL STABILITY Provided mostly by wing DIHEDRAL 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LATERAL STABILITY Provided mostly by wing DIHEDRAL On the wing moving up, the upward vector reduces the  = less lift 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LATERAL STABILITY Provided mostly by wing DIHEDRAL These two changes to lift create a rolling force in the direction to restore the wings to level = Positive Lateral Stability 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes LATERAL STABILITY A HIGH-WING Airplane will not need as much Dihedral as a LOW-WING Airplane since the Center of Gravity is below the Center of Lift it tends to right itself naturally (it’s inherently more Laterally Stable) Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY Is the ability of an aircraft to remain stable ABOUT (OR AROUND) THE VERTICAL AXIS Is YAW STABILITY Or keeping the Vertical Axis stable 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability To be Directionally Stable, an aircraft must have more surface area behind the CG than in front so it acts like a Weather Vane Stability: About the Aircraft Axes DIRECTIONAL STABILITY Provided by the VERTICAL STABILIZER and Fuselage 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability When the aircraft yaws (= SIDESLIP), the Vert. Stab. creates lift in the restoring direction and the sides of the fuselage offer a surface for the wind to push against Stability: About the Aircraft Axes DIRECTIONAL STABILITY Provided by the VERTICAL STABILIZER and Fuselage 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY Is also improved by SWEEPBACK of the wings 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY Is also improved by SWEEPBACK of the wings When yawing (SIDESLIP), the wing which is moving forward has a larger effective wing area = more drag to push it back 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY But sweepback can cause a small problem: Dutch Roll If the aircraft’s wing drops it will tend to yaw into the low wing and the dihedral and sweepback will combine to return the wings to level quickly 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY But sweepback can cause a small problem: Dutch Roll As the low wing moves up the Lateral Stability will return the aircraft to straight flight = the low wing will be moving faster than the high wing = more lift 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY But sweepback can cause a small problem: Dutch Roll = that wing will now rise and the process will repeat in the opposite direction 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY But sweepback can cause a small problem: Dutch Roll The resulting low level oscillation (“Dutch Roll”) doesn’t affect aircraft flight safety but is uncomfortable for passengers 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Aircraft Stability Stability: About the Aircraft Axes DIRECTIONAL STABILITY But sweepback can cause a small problem: Dutch Roll Aircraft susceptible to this usually have YAW DAMPERS connected to the rudder controls to automatically apply corrective rudder action 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Large aircraft, like small, control the aircraft about the same 3 axes: Lateral, Longitudinal, and Vertical Major differences: More control surfaces Hydraulic actuated Power-boosted Hydraulic cylinder in parallel with control rods Pilot moves surface and valve to actuate hydraulic cylinder to help 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Large aircraft, like small, control the aircraft about the same 3 axes: Lateral, Longitudinal, and Vertical Major differences: More control surfaces Hydraulic actuated Power-boosted Boosting is typically about 14:1 ratio Disadvantage: in transonic speed range shock waves form on controls and cause buffeting which is fed back into cockpit 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Large aircraft, like small, control the aircraft about the same 3 axes: Lateral, Longitudinal, and Vertical Major differences: More control surfaces Hydraulic actuated Irreversibles Used to keep buffet from reaching cockpit Hyd. Cylinders in series with control rods Also need “feedback” system to give pilot the feel of the controls 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Uses Irreversible system with 2 separate hydraulic systems, Standby system, and manual backup of Primary Controls (servo tabs) Example: Boeing 727 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Primary Controls: Roll Ailerons and Spoilers 4 ailerons and 14 spoilers Large Aircraft Controls Example: Boeing 727 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Primary Controls: Roll Inboard ailerons and 10 flight spoilers do high speed flight with outboard ailerons locked in neutral position 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Primary Controls: Roll When trailing edge flaps are deployed, outboard ailerons unlocked = all ailerons and flight spoilers work 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Primary Controls: Pitch Elevators for normal pitch action Movable Horizontal Stab. for trim action 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Primary Controls: Yaw 2 independent rudders with anti-balance (anti-servo) tabs 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Primary Controls: Yaw Also receives input from the Yaw Dampers to counteract Dutch Roll 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Auxiliary Lift Devices: Trailing Edge Flaps Triple-slotted Fowler Flaps Take-off = only back, Landing = back and down 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Auxiliary Lift Devices: Leading Edge Flaps Krueger-type Increase area and camber 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Auxiliary Lift Devices: Leading Edge Slats Increase camber Inboard flaps stall first = retain aileron control 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Secondary Controls (Tabs): Ailerons have Balance Tabs which also act as Trim Tabs 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Secondary Controls (Tabs): Elevators have Servo Tabs which also act as Trim Tabs 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Secondary Controls (Tabs): Rudders have Anti-balance (anti-servo) Tabs which also act as Trim Tabs 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Boeing 727 Secondary Controls (Tabs): These Tabs also serve as manual backups in case of total hydraulic failure 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Lockheed L-1011 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics Large Aircraft Controls Example: Airbus A320 9/17/2018 Author: Harry L. Whitehead

III. Basic Aerodynamics The Atmosphere Physics The Airfoil Lift & Drag Stability Large Aircraft Flight Controls Basic Aerodynamics 9/17/2018 Author: Harry L. Whitehead

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