The dynamic properties of the system, "acs - airplane" mode of stabilization altitude
The
dynamic
properties
of the system,
"ACS
-
the plane"
is largely dependent
on
the
control law
implemented
in the
ACS.
For
definiteness,
assume
that the
aerobatic
circuit
controls
the
pitch
angle
and
trajectory
-
forms
specified
signal.
We
assume that the
aerobatic
circuit
instantly
fulfills
predetermined
pitch
angle,
ie
always
have
the equality
.
Adopting
this
assumption
due
to the fact
that
the time
control
when
managing
pitch,
usually
on the
order
of magnitude smaller
than
in
the management of
the
flight altitude.
For
the analysis of
the
dynamic properties and
the
calculation
of
gear
ratios
to
determine
the
transfer function
.
To
derive the
use
of the following
relationships:
;
;
;
.
Block diagram corresponding to equation is shown in Fig.
Block diagram corresponds to the following transfer function
.
The
analysis
of
the transfer function
leads
to the following
conclusions:
-
dynamic
properties of the
loop
stabilization
altitude
above
assumptions
are
described
in
the
link
of
the
second order;
-
damping
ratio
is
defined as the
loop
stabilization
properties
of its own
aircraft
and the
gear
ratio
;
-
natural
frequency of the
circuit
is
determined by
the
speed
of
flight,
the
derivative
of
lift
angle
of attack
and
coefficient
;
- in the absence of external disturbances current height is given, that is, static error is absent. For the calculation of transfer coefficients and you can use the default factors.
The influence of external disturbances on the control loop height
Altitude deviation from its set value may be caused by altimeter or SGC, action, disturbing moment, dumping cargo or vertical wind. Consider the work of ACS, the management, in contact with the aircraft in a steady upward flow. After the cessation of small movements caused by an increase in the angle of attack, the aircraft gets wind speed and begins to deviate from the desired height. Of the altimeter go signal proportional to the height deviation from set point. This leads to a rejection of the elevator, the emergence of diving moment, the negative growth of the angle of attack and pitch angle. But when you change the pitch angle signal is proportional to the angle of pitch, opposite in sign to signal, proportional to the mismatch. As a result, the elevator deflection is reduced. When the signals cancel each other out, the elevator will return to the starting position. Thus, we have
,
whence
.
But
the flight
at
a constant altitude
is
only possible
when
the longitudinal
axis
of
the
aircraft will be
tilted
down
at
an angle
.
Consequently,
the
static
error
in
maintaining
altitude
determined
by the expression
.
Note that the static height-keeping error in the volatile atmosphere in the presence of a signal in the pitch control law will be the case with any type of feedback, not just hard. This is explained by the fact that the signal change in altitude is always compensated signal changes of height, and set the position of the elevator does not depend on a steady wind. Under the action of disturbing moment ACS with JOS does not maintain a specified pitch. Therefore, if any of the control law aircraft will depart from a given height. With speed and PID feedbacks aircraft to keep its current height and the action constant disturbing moment. In addition, a disturbing moment ASTATISM can ensure that the control law of the integral of height-keeping errors.