CH.3B Stability Flashcards
STABILITY
Characteristic that causes plane to return to condition of equilibrium
POSITIVE STATIC STABILITY
The tendency to return to position from which it was displaced
POSITIVE DYNAMIC STABILITY
coupled with positive static stability - does not happen at once, instead over a period of time and several oscillations
MANEUVERABILITY
Permits you to maneuver it easily and allows manueves
CONTROLLABILITY
response to control inputs, especially with regard to attitude and flight path
THREE AXES OF FLIGHT
Longitudinal (roll)
Lateral (pitch)
Vertical (yaw)
CENTER OF PRESSURE
Point on the wing chord where lift is considered to be concentrated AKA CENTER OF LIFT
What determines the longitudinal stability of an airplane?
The location of center of gravity in relation to the center of pressure (lift)
CG
Center of Gravity - The forward and aft limits coincide with the CG
Effects of forward CG
May seem stable but will be nose heavy
longer take off distance
higher stalling speeds
Effects of aft CG
Tail heavy and very unstable in pitch regardless of speed
Stabilator (elevator) may be ineffective for stall or spin recovery
THIS IS MORE dangerous that forward CG
Keep heavier passengers and baggage more far forward
TAIL-DOWN FORCE
The position of the horizontal stabilizer to offset the nose-heavy tendency. It creates a negative angle of attack, negative lift on the tail (downward force), to counteract the hose heaviness.
THRUSTLINE
Where the propeller is mounted and where thrust acts
LATERAL STABILITY
Runs along the longitudinal axis (from nose to tail)
The tendency to resist roll:
Weight distribution
Dihedral
Sweepback (also help vertical axis/directional stability)
Keel effect (also help vertical axis/directional stability)
DIHEDRAL
(Structural design)
The upward angle of the wing with respect to the horizon
SWEEPBACK
(wing sweep) The characteristic of the wing that creates the angle backward from the wing root
Designed to maintain the center of lift aft of the CG and reduce wave drag at or above speed of sound
(light training airplanes - designed to improve lateral stability)
KEEL EFFECT
The steadying influence exerted by the side area of the fuselage and vertical stabilizer
DIRECTIONAL STABILITY
Stability about the vertical axis. The vertical fin contributes to the directional stability
DUTCH ROLL
Combination of rolling/yawing oscillations caused by control input or wind gusts. (weak directional stability and strong lateral stability)
THREE BASIC TYPES OF STALLS
Power-off stall
Power-on stall
Accelerated stall
POWER-OFF STALL
AC configuration for normal landing approach stall
POWER-ON STALL
These are encountered during takeoff, climb-out and go-arounds when pilot fails to maintain proper control due to premature flap retraction or excessive nose-high trim
ACCELERATED STALL
Stalls at a higher speed
CROSSED-CONTROL STALL
This happens when a pilot tries to compensate for overshooting a runways during a turn from base to final while on landing approach.
STALL RECOGNITION
Mushy controls
Less control effect with decreased speed
(reduced control effectiveness is primarily due to reduced airflow)
Loss of RPMs
Buffeting, uncontrollable pitching or vibrations
Kinesthetic sense (your ability to recognize changes in direction or speed) provides warning of decreased speed or sinking feeling
SECONDARY STALL
Normally caused by poor stall recovery technique
ex. attempting flight prior to attaining sufficient flying speed
What are the steps for proper STALL RECOVERY?
- Decrease angle of attack
- Smoothly apply max allowed power to minimize latitude loss and increase speed
- Adjust power as required, maintain coordinated flight while adjusting power to normal level
SPIN
An aggravated stall which results in a helical (corkscrew) path
What is the stability around the AC longitudinal axis?
This refers to as the lateral stability. Wing dihedrals, sweepback, keel effect, and weight distribution are design features that affect an airplane’s lateral stability
Where does the directional stability come from?
The vertical axis - maintained by the vertical tail
When will a stall occur?
A stall will always occur when the critical angle of attack, or CLmax, is exceeded. This can occur at any airspeed an din an configuration or attitude
In relation to the center of gravity, in which direction would the center of pressure normally move as angle of attack is increased on a cambered wing?
forward
SPIN RECOVERY procedure
- Throttle to idle (eliminates thrust and minimizes loss of altitude)
- Neutralize the ailerons
- Determine direction of rotation (shown on turn coordinator)
- Apply full opposite rudder (opposite of direction of spin)
- Briskly apply elevator (stabilator) forward to aprox. neutral position.
- As rotation stops, neutralize rudders (if not spin could go in opposite direction
- Gradually apply aft elevator to return to level flight (too quickly can result in secondary stall, and possibly another spin.
- adhere to AC airspeed and load limits during recovery and dive
What factors can affect the longitudinal stability of an airplane at hight power settings and low airspeed?
An increase in thrust increases the pitching moment and nose heaviness due to the placement of the thrust line of the AC. This helps counteract the longitudinally destabilizing effect f increased downwash that results from an increase in power and extension of hight lift devices.
Why are high wing AC normally designed with less dihedral than low wing AC
Upwash passing around the fuselage just ahead of the wing tends to roll a high wing AC toward the upright position, contributing to lateral stability. In a low wing airplane, the downwash around the fuselage tends to be laterally destabilizing since it tends to increase the roll. The amount of dihedral is adjusted to compensate for the effects of fuselage upwash and downwash resulting in a greater requirements for dihedral in low wing airplane than in a high wing configuration
Does the propwash resulting from high power settings increase or decrease the contribution of wing dihedral to the lateral stability of an airplane
Decrease
An aircraft with strong directional stability and weak lateral stability is often prone to what type of undesirable side effect
Spiral instability
What should an AC do in terms of airspeed to land in gusty winds and help guard against a stall?
Increase airspeed above normal
