8.4 flight stability and dynamics Flashcards
stability in an aircraft affects two areas what are they
menoeuvrability and controllability
aircraft principal axes of flight pass through what point
CG centre of gravity
motion about the vertical axis is what and controlled by what
Yaw and the rudder
a positive yawing motion moves the nose of the aicraft which way
to the right
lateral axis is a line drawn from what points
wingtip to wingtip. directed to the right
motion about the lateral axis is called what
pitch
a positive pitching motion does what to the nose of the aircraft
raises nose and lowers the tail. primarily controlled by the elevators
what is the motion about longitudinal axis called
roll.
longitudinal axis has a line which does what
directed forward parallel to the fuselage reference point
angular displacement about the longitudinal axis is called a what
bank
a positive rolling motion lifts which wing
left wing and lowers the right wing.
what are the primary and secondary controls on a bank
primary = ailerons
secondary effect = rudder
what is the axis of stability for yaw
directional
what is the axis of stability for pitch
longitudinal
what is the axis of stability for roll
lateral
what does static stability mean
aircrafts initial tendency to return back to a position of equilibrium
what are the three kinds of static stability
positive static stability
neutral static stability
negative static stability
positive static stability is
tendency to return to original state of equilibrium.
neutral static stability is
tends to stay in its new attitude when its disturbed. eg. if turbulence pitches nose up 5 degrees it will stay at 5 degrees nose up
negative static stability is
continues moving away from its original attitude when its disturbed. e.g if turbulence pitches nose up it continues pitching up. very undesirable situation.
what is dynamic stability
aircraft response over time when disturbed from pitch, yaw, bank.
the three types of dynamic stability are
positive dynamic stability
neutral dynamic stability
negative dynamic stability
positive dynamic stability is where aircraft has
oscillations that dampen out over time and because it is positive, it returns toward its equilibrium state
neutral dynamic stability is where aircraft has
oscillations that never dampen out.
negative dynamic stability is where the aircraft has
oscillations that get worse over time
static longitudinal stability, or instability in an aircraft depends on what three factors
-location of wing in respect to CG
-location of horizontal tail surfaces in respect to CG
-area or size of tail surfaces
if the distance between the cg and aerodynamic centre is great..
then the longitudinal stability is high. if distance is small stability is low.
the directional or “weathercock” stability depends on what
the fin aka vertical stab and the sweepback of the wing
some aircraft increase the surface area behind the cg to improve what type of stability
directional by methods such as a dorsal fin, keel surface.
what are the four main factors that make aircraft laterally stable
dihedral
sweep-back
keel effect
weight distribution
what reduces sideslip
dihedral angle
what is sideslip angle
it is the angle between the aircraft centreline and the sideslip direction
high wing aircraft have a lesser or greater keel effect than low wing aircraft
greater
the keel effect is
in a sideslip, the fuselage provides a broad area upon which the relative wind strikes, forcing the fuselage to become parallel to the wind.
if one axis or stability is stronger than the other what could happen
spiral dive or dutch roll
spiral dive is when there is a greater effect on
the directional stability than on the lateral stability
dutch roll exists when there is a greater effect on the
lateral stability than on the directional stability . lateral-directional oscillation
dutch roll can be partially overcome by
reducing sweep angle and improving directional stability
directional stability can be improved by
increasing size of vertical stab but this has weight and drag drawbacks
aircraft which have neutral or negative stability is aka
relaxed stability
relaxed stability allows aircraft to be designed for purely
aerodynamic efficiency opposed to handling or ‘‘flyability”
stability increases as speed increases true or false
true
