User manual

8 AUTOPILOT
The SP series of executables introduced a much improved 3-Axis autopilot (AP) for realistic
avionics users. There are however some opportunities remaining to improve upon that system.
This version of the BMS executable introduces a significant overhaul to the realistic mode
autopilot.
8.1
CHANGES FROM SP3
The SP3 autopilot had a tendency to “porpoise” (significant rate and magnitude oscillations of
nose position up and down) in ALT HLD mode. This tendency has been fixed by adding some
damping to the autopilot altitude holding functions. The AP should now meet or exceed the real
jet’s performance of holding altitude +/- 100 feet either side of the selected reference. In doing so,
pitch changes when the jet is close to the selected reference altitude are very much smaller so
you should end up with a rather more “straight and level” experience when selecting this mode.
Roll mode selections are now independent of the pitch mode selection. What this means is that
you can select pitch ATT HLD (attitude hold) and any of the three roll modes. Fixed pitch climbing
turn to waypoint heading?? No problem! Previously the SP3 autopilot would only allow pitch
ATT HLD if the roll modes switch was in ATT HLD also.
Pitch ATT HLD mode completely revised. The new function is able to hold selected pitch much
more effectively while also implementing stick steering as described below. The pitch reference is
now driven from the same reference value used to place the FPM on the HUD pitch ladder. What
this means is that when you engage pitch ATT HLD mode, you should get (near enough) the
pitch displayed in the HUD as the reference value for the AP to hold.
Stick steering implemented. When you have either pitch ATT HLD or roll ATT HLD selected, you
can change the pitch or roll reference angles respectively at any time by merely applying
pressure to the control stick (i.e. joystick). When pressure is released again, the AP will attempt to
hold the new pitch and roll at the time the pressure was released. Stick steering will work for
either axis if it selected, regardless of the selected AP state of the other axis; i.e. if you have pitch
ATT HLD and roll in STRG SEL, you will be able to manually change pitch by direct stick inputs
but not roll (unless you also depress AP Override of course!).
Self-centering pitch mode AP control switch implementation completed. In the real jet, the right-
most AP control switch is a spring loaded self-centering switch. It is held in ALT HLD or ATT HLD
positions by a magnetic capture mechanism. Capturing the switch in either one of these two
positions is what engages the AP. The AP will operate within limits of plus or minus 60 degrees
from straight and level in both pitch and roll axes. If you exceed these limits with the AP
operating, the AP function is suspended but the AP pitch switch is not released from its current
position. In order to re-engage the AP in this case, you must center the pitch mode switch
manually and then reselect the required AP pitch mode to turn on the AP. Also, if certain other
conditions arise during AP operation, the AP will self-disconnect, releasing magnetic hold and
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