- 133
5.2.1.5.1 Dual-Control CVS Maneuver
The control law is given by equation (5.32) and equation (5.33) for IAS-based and Mach-
based control, respectively – the same as for Region 7. The desired speed is given by
equations (5.36) and (5.37) for IAS-based and Mach-based control, respectively. The
desired altitude rate is as commanded.
Once in a dual-control CVS, if the aircraft becomes slow, that means it is losing speed. It
is expected that this can happen only in a climbing maneuver in which the aircraft does
not have enough thrust or power to maintain airspeed and vertical speed concurrently. If
left in the CVS climb, the speed will only continue to fall. In this case, the aircraft must
break out of the CVS maneuver and into a Mach or CAS climb.
Once in a dual-control CVS, if the aircraft becomes fast, that means it is gaining speed. It
is expected that this can happen only in a descent maneuver in which the aircraft does not
have enough drag to maintain airspeed and vertical speed concurrently. In this case, there
is an alternative to breaking out of the CVS maneuver: deploy speed brakes. If the speed
error moves back within ½ the SP
error
(i.e., five knots), speed brakes can be turned off. It
is possible for the aircraft to get in a cycle of turning speed brakes on and off – an
unrealistic scenario – but this should yield acceptable performance.
With speed brakes on, if the aircraft continues to gain speed (i.e., if the speed error
exceeds 1 ½ times the SP
error
- i.e., 15 knots), it shall break out of the CVS descent and
into a Mach or CAS descent.
5.2.1.5.2 Idle-Thrust CVS Maneuver
In this maneuver, the aircraft is not lowenergy and is descending. The altitude error is
necessarily negative (an entry condition) and the commanded vertical speed is negative.
The speed is not controlled; the maneuver is entirely independent of speed behavior. The
throttle is set to idle and the system uses altitude rate feedback to maintain the
commanded vertical speed. The control law is given by equation (5.29).
This maneuver also needs a break-out condition. It is necessary for the success of this
maneuver that the aircraft’s energy rate is negative. This is the purpose of setting idle
thrust. As an example, if the commanded descent rate is so high that the aircraft must
accelerate to extreme speeds in order to capture the commanded descent rate, the
aircraft’s energy may actually be increasing, even though the throttle is at idle. Therefore,
if the energy increment, as given by equation (5.40), is positive, the aircraft can first
deploy speed brakes. If the energy increment is still positive, the aircraft shall break out
of the CVS descent and into a Mach or CAS descent.
5.2.1.5.3 Max-Thrust CVS Maneuver