Stability Stability Characteristic of an airplane that causes

Stability

Controllability and Maneuverability • Controllability is capability of airplane to respond to control inputs • Maneuverability is characteristic of plane that permits you to maneuver it easily and allows it to withstand stress • • • Size Weight Flight controls Structural Strength Thrust © 2015 Coast Flight Training. All Rights Reserved.

Three Axes of Flight • Longitudinal • Lateral • Vertical • All referenced around

Longitudinal Axis • Movement with the ailerons • Also known as roll • Aileron works by decreasing angle of attack on one side, while increasing the angle of attack on the other © 2015 Coast Flight Training. All Rights Reserved.

Lateral Axis • Movement with the elevator / stabilator • Also known as pitch • Elevator works by decreasing or increasing the angle of attack at the horizontal stabilizer © 2015 Coast Flight Training. All Rights Reserved.

Vertical Axis • Movement with the rudder • Also known as yaw • Rudder works by decreasing or increasing the angle of attack at the vertical stabilizer © 2015 Coast Flight Training. All Rights Reserved.

Longitudinal Stability • Refers to pitching of the aircraft – confusing • Airplane returns

Longitudinal Stability - Balance • Balance between: • Center of Pressure • Tail-down force • Center of Gravity • Boldmethod demonstration • Airplanes have CG limits to keep longitudinally stable © 2015 Coast Flight Training. All Rights Reserved.

Longitudinal Stability – CG location • CG too far forward? • Nose heavy • Stable • Eventually stabilator can’t lift nose • CG too far aft? (more dangerous) • Tail heavy • Unstable • Stabilator ineffective for stall or spin recover © 2015 Coast Flight Training. All Rights Reserved.

Preventing Aft CG • Load heaviest passengers in front • Follow loading recommendations per the POH • Never overload baggage • Pause for the “speed limit talk” © 2015 Coast Flight Training. All Rights Reserved.

Power and Pitch • Related fundamentally • Reduction in power results in a nose down tendency • Increasing power increases downwash on the elevator, causing nose to rise © 2015 Coast Flight Training. All Rights Reserved.

Lateral Stability • Refers to the roll - confusing • Airplane return to level

Lateral Stability • Design characteristics: • • Weight distribution (minimally) Dihedral Sweepback Keel Effect

Weight Distribution • Imagine the airplane is a giant teeter-totter • If too much weight on one side, then airplane wants to roll in direction of the weight • Pronounced with heavy flight-instructor and light student or vise versa © 2015 Coast Flight Training. All Rights Reserved.

Dihedral • Dihedral is the airplane’s soft V shape • If the aircraft turns, the lower wing creates more lift due to an increased angle of attack • Mainly only in sideslip conditions (crosswind) • The more lift will roll the airplane back to level © 2015 Coast Flight Training. All Rights Reserved.

Sweepback • Wing tips are not directly across from the wing root • Moves Center of Lift aft of the CG • In a situation where the airplane is turning, the upwind wing creates more drag, yawing it back to the right © 2015 Coast Flight Training. All Rights Reserved.

Keel Effect • Aircraft fuselage and wheels acts as a giant keel or centerboard

Directional Stability • Stability controlled by the rudders (yaw) • Mainly controlled by the

Static Stability • Stability after an initial movement • Does the airplane get away from initial movement? Stay at initial movement? Or go back to it’s equilibrium? • Think of a ball on a bowl or plate: © 2015 Coast Flight Training. All Rights Reserved.

Dynamic Stability • Stability over time • Think of the oscillations of the aircraft • Is the airplane going back to equilibrium or going away from? • Helpful to draw graphs: © 2015 Coast Flight Training. All Rights Reserved.

Stalls • Stability changes the aircraft’s stall characteristics • Important to do stalls in every new airplane to understand it’s stability and stall characteristics • Affected by: • • • Weight Location of CG Wing surface modifications Ice or frost accumulation Turbulence © 2015 Coast Flight Training. All Rights Reserved.

Stalls - Weight • Heavier aircraft means a higher angle of attack to maintain the same amount of lift • Heavy = increase stall speed • Airplane AOA is much closer to the Critical AOA © 2015 Coast Flight Training. All Rights Reserved.

Stalls - CG • More forward CG creates more downward force to balance the

The Lift Equation 1 2ρ Lift = CL 2 v 2 S © 2015

Stalls – Surface of Wing • The Lift Equation • Any increase in wing surface area results in an increase of lift • What changes the surface of the wing? • High Lift Devices (Slats) • Flaps © 2015 Coast Flight Training. All Rights Reserved.

Stalls – Surface of Wing • Ice or Frost accumulation interrupts smooth airflow • Smooth airflow over the upper surface of wing is needed to create lift • If the flow is disrupted, there is a huge reduction in lift • Up to 60% reduction in lift • Also increases weight and drag • Always clear ice or frost from the surfaces on the airplane © 2015 Coast Flight Training. All Rights Reserved.

Stalls – Turbulence • Unpredictable nature of turbulence can cause the aircraft to stall at a higher airspeed • Vertical gusts change the direction of the relative wind abruptly increases the angle of attack • During takeoff and landing in gusty conditions, increase speed to compensate © 2015 Coast Flight Training. All Rights Reserved.

Stalls – Turbulence • If encountering turbulence, reduce the airplane to it’s maneuvering speed • Always calculate exact maneuvering speed before going flying • The POH has only maximum and minimum © 2015 Coast Flight Training. All Rights Reserved.

Why practice Stalls? • We practice stalls to practice stall RECOVERY • The set-up for the stall is not required for FAA certification, only the recovery itself • At Coast, we practice the set-up to aid in familiarization of WHEN the stall will occur • Also, we need to ensure that the individual is procedures oriented, which is the goal of the Stage 1 check © 2015 Coast Flight Training. All Rights Reserved.

Types of Stalls – What We Do at Coast • Power-off • Simulates a stall during the approach to landing • Power-on • Simulates a stall upon takeoff or departure • Accelerated • Simulates a stall at a higher airspeed • We won’t practice these, but we will demonstrate them for you © 2015 Coast Flight Training. All Rights Reserved.

Types of Stalls – Other • Cross-controlled Stall • Incoordination changes the relative wind, creating lift on one wing, but not on the other • Secondary Stalls • Poor stall recovery technique • Happens when positive control of the aircraft is not gained • Aggravated Stall • A stall that is held in a stall, recovery is not practiced or not completed correctly © 2015 Coast Flight Training. All Rights Reserved.

Stall Recognition • Stall Warning Horn about 10 knots prior to the stall • Mushy Controls (ineffective control movements) • Loss of RPM may be evident • Reduction in sound • Buffeting • Pitching • Other Vibrations • Sinking Feeling © 2015 Coast Flight Training. All Rights Reserved.

Spins • An aggravated stall that results in the airplane descending in a helical or corkscrew path • All light airplanes must demonstrate stall recovery – but performance beyond these limits is unknown • Never intentionally spin an aircraft without an instructor on board • Only to be completed in utility category © 2015 Coast Flight Training. All Rights Reserved.

Spins • In order for a pin to happen, a stall must have occurred • If uncoordinated, the wing that is more completely stalled will fall before the other, causing a rotation in the direction of the stalled wing • The wing that is still creating lift, or partially stalled will continue the rotation © 2015 Coast Flight Training. All Rights Reserved.

Spins - Phases • Incipient • Rotation starts • Fully Developed • Rotation continues

Spins -Types • Erect Spin • The “normal” spin • Inverted Spin • Aircraft is upside down • Flat Spin • Yaw only • Killed goose • Almost completely unrecoverable © 2015 Coast Flight Training. All Rights Reserved.

Aerodynamics of Maneuvering Flight