Stability Flashcards
22.26.2 Explain static stability and dynamic stability.
Static stability of an aircraft describes the tendency of and aircraft to retain its original position when subjected to unbalanced forces or moments acting on the aircraft.
Dynamic stability describes the form of motion an aircraft in static stability undergoes when it tries to return to its original position.
22.26.4 Differentiate between stability and controllability.
Stability is the inherent ability of the aircraft to return to its original attitude after being disturbed without any action been taken by the pilot.
Controllability refers to the ease with which a pilot can manoeuver the aircraft and change its attitude by using the control surfaces.
- 26.6 Define longitudinal stability and explain:
(a) the action of the tailplane in maintaining longitudinal stability.
The restoring a moment and the effectiveness of the tailplane in maintaining longitudinal stability are in large part determined by its design. Features that affect the restoring moment include, the distance between the tailplane CP to the aircraft CofG, tailplane area and shape, and the effect of the downwash from the wing.
- 26.6 Define longitudinal stability and explain:
(b) wing pitching moments.
The pitching moment on the wing of an airplane is part of the total moment that must be balanced using the lift on the horizontal stabilizer.
- 26.6 Define longitudinal stability and explain:
(c) the effect of CG position.
The further rearward the CG, the more unstable the aircraft due to a longer arm.
22.26.8 Define directional stability and explain the factors affecting it.
Directional stability is in the yawing plane about the normal axis. It may be considered as the inherent ability of an aircraft to ‘weathercock’ so that the nose remains pointed into the oncoming airflow. Factors which affect it are; the greater the fin area and keel surface behind the CofG and the greater the arm moment, the greater the directional stability.
22.26.10 Define lateral stability and explain the factors affecting it (dihedral, shielding, wing position, keel surface/fin area, sweepback).
Lateral stability is the inherent ability of an aircraft to recover from a disturbance in the lateral plane without any control input by the pilot. Dihedral, shielding, high wing position, tall fin with high T-tail and a low CofG, and sweepback all help increase lateral stability.
22.26.12 Explain the requirement to match lateral and directional stability.
If the aircraft has strong directional but weak lateral stability a spiral instability will occur and in the opposite case a dutch roll will occur.
22.26.14 Explain the conditions of spiral instability, dutch roll, and snaking.
If the aircraft has strong directional but weak lateral stability a spiral instability will occur and in the opposite case a dutch roll will occur. Snaking is when a yawing motion in a dutch roll is much more pronounced than the oscillation in roll.
- 26.16 With respect to stability and control on the ground, explain:
(a) the importance of CG position.
For the aircraft to be stable on the ground, the position of the CG must be within the perimeter of the 3 wheels.
- 26.16 With respect to stability and control on the ground, explain:
(b) the differences between nosewheel and tailwheel configurations.
Tricycle planes are more stable for ground as the CG is in front of the main wheels compared the tail draggers.
- 26.16 With respect to stability and control on the ground, explain:
(c) handling of controls in strong crosswinds.
“climb into wind” “dive out of wind” aileron into wind.
22.26.18 For a single-engine propeller aircraft, explain the factors affecting swing on take-off.
Slipstream effect (propeller imparts a ‘corkscrew’)
Torque reaction (cause plane to rotate opposite to propeller)
Gyroscopic effect (tail rises causes swing to left)
Asymmetric blade effect (when the axis of rotation of the propeller becomes tilted back with respect to the direction of travel, the down-going blades in the propeller disc develop more thrust than the up going blades. As a result the line of thrust is shifted toward the down-going blade side of the disc and a yawing moment is produced.)
22.26.20 Describe cross-wind take-off and landing techniques.
Rudder in opposite direction, aileron into wind, land on windward wheel first.
22.26.22 Explain ground effect, and relate it to take-off and landing.
As the aircraft climbs out of ground effect on takeoff, lift will decrease and induced drag will increase. A slight sagging in takeoff performance will be noticeable but this does not normally present a problem unless the aircraft is being operated at very high weight from a short strip.
On final approach to land, the aircraft will enter ground effect at about one wing span height. Ground effect generally tends to cause the aircraft to ‘float’ briefly before touchdown. To prevent this floating in ground effect from becoming excessive, avoid having excess speed at the beginning of the flare and ensure power is properly reduced.
