Flying and Handling Qualities

• This module discusses Flying and Handling Qualities.

Context

• Performance in speed, range, and endurance are what airplanes are sold on.
• Flying and Handling Quality standards are used to evaluate airplane design.
• Evaluations determine if an airplane is safe, effective, and easy to fly in its mission area.

Three Subjects

• These standards cover Flying Qualities (FQ), Handling Qualities (HQ), and Pilot In the Loop Oscillation (PIO).

Flying Qualities (FQ)

• Flying Qualities are the stability and control characteristics influencing flight safety.
• Flying Qualities also contribute to the pilot's impression of the ease of flying in steady flight and maneuvers.

Handling Qualities (HQ)

• Handling Qualities are qualities of an airplane which dictate the ease and precision with which a pilot can perform flight tasks.
• These characteristics are required to support the aircraft's function.

Pilot in the Loop Oscillation (PIO)

• PIO is an unintentional oscillation that is sustained or uncontrollable.
• PIO often results from a pilot's efforts to control the aircraft.

Flying Qualities vs Handling Qualities

• Flying Qualities are task-related.
• Handling Qualities are response-related.

Aircraft Stability

• Aircraft Stability is the plane's ability to maintain or return to its original flight path after a disturbance.

Static Stability

• Static Stability refers to the initial response of an aircraft after a disturbance.

Positive Static Stability

• Aircraft tends to come back to the original attitude.

Negative Static Stability

• Airframe tends to deviate from original attitude.

Neutral Static Stability

• The aircraft remains at its new altitude.

Aircraft design

• Positive Static Stability is a desired design.

Types of Positive Static Stability

• Longitudinal Stability
• Lateral Stability
• Directional Stability

Longitudinal Static Stability

• Longitudinal Static Stability refers to the initial response of an aircraft to a disturbance in pitch.
• To understand longitudinal stability, one must examine the wing airfoil.

Center of Gravity and Pressure and forces

• Relevant factors included these locations, and the impact of weight forcing it down, while lift force goes up

CP ahead of CG

• Represents a negative longitudinal static stability. The aircraft tends to deviate from its original attitude.

CP behind CG

• Positive longitudinal static stability occurs.
• The is a tendency to return to the original attitude, and the aircraft's nose goes down.
• To prevent nose-down motion, the horizontal stabilizer gives nose-up force.
• Positive longitudinal stability allows the aircraft to keep level flight.

Lateral Static Stability

• Lateral Static Stability is present when the aircraft tends to roll with the wind after a ROLL disturbance.
• Vertical Stabilizer and wing structure helps provide stability

Lift

• Lift Increases help bring the aircraft back to its original attitude.

Directional Static Stability

• Directional Static Stability means the nose will YAW in the same direction as the wind.
• The tail will YAW in the direct opposite to the wind.
• Increase in drag helps in directional static stability.

Vertical stabiliser

• Vertical Stabilzers and other design features such as aircraft and wing structures help positive Static Stability

Dynamic Stability

• Dynamic Stability includes the aircraft's response over a certain time period.

Positive Dynamic Stability

• Deviation due to Disturbance will diminish over time, returning to Original flight path

Negative Dynamic Stability

• Aircraft deviates from Original Position with increasing deviation over time

Neutral Dynamic Stability

• Aircraft Maintains Same Oscillation After Certain Time Period

Longitudinal Dynamic Stability

• Longitudinal Dynamic Stability involves disturbance in PITCH where oscillations are quickly Damped

Lateral/Directional Dynamic Stability

• ROLL and YAW are interconnected

Spiral instability

• Bank Angle Increases as airframe rolls left and yaws left

Dutch Roll

• Dutch Roll refers to the combination of ROLL and YAW whereby Aircraft Tries to Come Back to Original Attitude

Positive Dynamic Stability

• Positive Dynamic Stability can be improved by ensuring the aircraft has Positive Static Stability with the C.P. behind the C.G.
• Wing Design (Swept Back, Dihedral / Anhedral are added)
• Tail Section Design
• Positive Inputs made by the Pilot, or AP, to Dampen Oscillations: Elevators , Rudder, Ailerons
• Dynamic Stability is a major pilot and engineer concern to avoid Pilot Command or Weather Perturbation Issues during the flight.
• These include Flight Airspeed and Altitude variation, Angle of Attack and Vertical velocity variation, and Lateral Velocity variation.

Kinds Of Dynamic Stability

• Longitudinal and Lateral-Directional Dynamic Stability

Longitudinal Dynamic Stability

• Phugoid mode oscillation of flight airspeed and altitude (-long & slow)
• Short period oscillation of angle of attack and vertical velocity (-short & fast)

Lateral-Directional Dynamic Stability

• Spiral, rolling, and Dutch Roll modes

Aircraft Stability and Control

• Hardware concretization presented on board through AFCS (Automatic Flight Control System) and AP (Autopilot)

Aircraft Control Scheme

• System composed of connections between Pilot/Autopilot, AFCS, Engines, Aerodynamic Module, Atmospheric Module, Sensors, Cockpit, and Equations of Motion

Aircraft Dynamic Stability

• A good study of requires determining the Aircraft Reaction (or response) through the time to any variation coming from the Pilot or External Disturbance.
• Modeling & Simulation of aircraft systems, using Aircraft Equations of Motion, can realize this

Aircraft Parameters

• Forces can be defined as F (Thrust), δe (Elevator), δa (Ailerons), δr (Rudder),
• Wind can be defined as Wx, Wy, Wz
• Moments of L, M, N
• Atmospheric conditions
• Aircraft Equations of Motion
• Kinematic Equations
• Output State variables U Axial Velocity, V Side Velocity, W Vertical Velocity, P Roll Rate, Q Pitch Rate, R Yaw Rate, x Axial Position, y Lateral Position, z Vertical Position, 𝜓 Yaw Angle, θ Pitch Angle, ϕ inclinaison

Aircraft Equations of Motion

• Aircraft have 6 degrees of freedom (3 translational, 3 rotational)
• 3 displacements: Horizontal motion (U axial velocity, Side motion (V lateral velocity), and vertical motion ( W vertical velocity 
• Aircraft Equations of motion, axis systems
  • Axis Systems: Yaw, Pitch, Roll angles with associated formula as applied for use with Earth and Body axis systems  

Cinematic Equations

• Describes movement and angle.

Equations of Motion

• Newton's 2nd Law is applied in the inertial frame in scalar form. Fx = d(mU)/dt. Fy = d(mV)/dt. Fz = d(mW)/dt