Date: 18 Apr 98 00:49:30 From: firstname.lastname@example.org Organization: Netcom Online Communications Services (408-241-9760 login: guest) References: 1 2 3 Followups: 1
View raw article or MIME structure
In article <airliners.1998.584@ohare.Chicago.COM> Julian Scarfe <email@example.com> writes: >Could you clarify the systems for pitch control on the A320 and family for >me. My understanding so far is: > >Direct law: direct relation between elevator deflection and stick position, >with maximum stick defelection corresponding to maximum elev deflection Correct, except there's filtering for center of gravity position (i.e., elevator travel is limited by the CG position). There are, otherwise, no flight envelope protections. >Alternate law: stick deflection controls lift, with maximum stick defelection >corresponding to maximum permissible loading Sort of. In pitch, it performs similarly to Normal Law (below). The main differences are in how pitch and low/high speed stability protections are performed. Alternate law can also exist in a mode without high- or low- speed stability protections (just load factor protections). >Normal law: stick deflection controls lift, with maximum stick defelection >corresponding to maximum permissible AOA (or is the AOA protected in a >different way?) Look at it a different way. When you move the stick, you're commanding a load factor. The flight control system reacts to provide that factor. So suppose you pull back. You're increasing load, increasing pitch. You let go. Stick centers. You're now commanding 1G in the last known attitude. Airplane holds the pitch angle and maintains 1G. Normal law also includes load protections, pitch protections, high AOA protections, and high speed protections. It also includes a load alleviation function, which reduces wing loading in turbulence by automatically modulating selected spoiler panels. >Is that anything like correct? How does the pilot select Alt or Direct law? The pilot reaches up and turns off the various flight control computers, with successive degrees of degradation. There is no "on/off" switch for the various laws. -- Robert Dorsett Moderator, sci.aeronautics.simulation firstname.lastname@example.org email@example.com "Bother," said Pooh when his engine quit on take-off.