Stability Lecture - Lateral
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Transcript of Stability Lecture - Lateral
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8/13/2019 Stability Lecture - Lateral
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AIRCRAFT STABILITY AND CONTROL
STATIC LATERAL STABILITY AND CONTROL
BY
Y.K.SINHA
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SIDE SLIP AND YAW ANGLE
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LATERAL STABILITY
Stability about the aircrafts longitudinal axis,
which extends from the nose of the aircraft to its
tail, is called lateral stability. This helps to stabilizethe lateral or rolling effect when one wing gets
lower than the wing on the opposite side of the
aircraft.
It is the ability of the aircraft to recover from a rollwithout pilots intervention.
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For a aircraft to be laterally stable
Clshould be positive
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There are four main design factors that
make an aircraft laterally stable:
Dihedral
Wing placement on lateral stability
Vertical tail placement on lateral stability
Keel effect and weight distribution Sweepback
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ESTIMATION OF DIHEDRAL EFFECT
If a disturbance causes one wing
to drop relative to the other, thelift vector rotates and there is a
component of the weight acting
inward which causes the
airplane to move sideways in this
direction. When wings havedihedral, the wing toward the
free-stream velocity, hence the
lower wing, will experience a
greater angle of attack than the
raised wing and hence greaterlift. There results a net force and
moment tending to reduce the
bank angle.
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Positive sideslip (nose left) creates an upward
velocity on right wing and downward velocityon left wing
Equivalent of downwash
Increases angle of attack over right wing,decreases angle of attack over left wing
Results in a rolling moment to the left
The stabilizing effect of this configuration is
known as the dihedral effect.
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EFFECT OF WING PLACEMENT ON LATERAL STABILITY
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EFFECT OF VERTICAL TAIL PLACEMENT ON LATERAL STABILITY
INTERFERENCE OF WING ON VERTICAL PALNE
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During flight, the side area of the
airplane's fuselage and vertical finreact to the airflow in much the
same manner as the keel of a ship.
That is, it exerts a steadying
influence on the airplane laterally
about the longitudinal axis. Such
laterally stable airplanes areconstructed so that the greater
portion of the keel area is above
and behind the center of gravity.
Thus, when the airplane slips to
one side, the combination of the
airplane's weight and the pressureof the airflow against the upper
portion of the keel area (both acting
about the CG) tends to roll the
airplane back to wings-level flight.
EFFECT OF VERTICAL TAIL PLACEMENT ON LATERAL STABILITY OR
KEEL EFFECT
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Sweepback
The secondary effect of sweepback is to improve
lateral stability. When a side-slip
occurs, the lower wing presents a larger span as
seen from the direction of the approaching air,
and as with dihedral, the effect is to roll the
aircraft back towards the horizontal.
In general, as the sweepback angle is increased
the dihedral angle will be reduced.
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Airbus380
HARRIER
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EFFECT OF FLAP DEFLECTION ON LATERAL STABILITY
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EFFECT OF POWER ON LATERAL STABILITY
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LATERAL CONTROL
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SPANWISE LIFT DISTRIBUTION
DUE TO AILERON DEFLECTIONS
LOAD DISTRIBUTION DUE
TO ROLLING VELOCITY
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At a given helix angle, the distance
to complete a roll remains constant
regardless of forward speed.
The helix angle is the ratio of tip
velocity in roll, pb/2, to the aircrafts
forward velocity, V.
E ti ti f L t l C t l P
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Estimation of Lateral Control Power
Strip IntegrationAssumptionThe airplane to be a single degree of
freedom in roll about X AxisThe wing is considered to be a rigid structure with therolling moment arising due to aileron deflection (a)anddamping moment due to angular velocity (p)
The two parameters rolling moment due to aand damping
moment due to p can be evaluated by strip integration
method
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Note: For a given aileron deflection pb/2V is constant
For a tapered wing
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Aileron Reversal
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End