Old 7th Jan 2008, 03:31
  #10 (permalink)  
Join Date: Feb 2004
Location: Australia
Posts: 1,300
"So what obvious ( to you lot) blooper have I made?"

None. If the 737-300 is anything like the NG series, stabiliser trim is a complex beast indeed.

The A/P trims at a different rate to manual electric trim.

Trimming speeds vary, dependent on flap position.

There are different trim limits depending on trim mode (auto/manual) and flap position.

There is interaction between control column movement (and manual electric trim) and autostab trim operation.

There are position feedback circuits to different autopilot computers. e.g. The A/P knows how fast the trim drive motor is running. The A/P also has links to the elevator tab servo valve and the mach trim actuator.
There are messes of electrical relays (these will have to be linked to the electrical busses in proper simulations).

There is a trim sensor monitor in the A/P which, during dual autoland, "compares the Neutral Shift expected value from stabilizer position and Mach Trim feedback with the actual Neutral Shift Sensor input. If the difference is more than 0.5 degrees, the autopilot will disengage."
Etc, etc...

Then there is the matter of "Speed Trim" (controlled by the A/P computer, but only when the A/P is DISengaged). This uses CAS, Mach, Intertial Vertical Speed, Roll Angle and AOA, Radio Altimeter, N1 speeds, flap position....)

It's painfully obvious that no one has a 100% understanding of these systems (you realise this when sim programmers ask embarrassing questions )

Regards (and good luck with the programming).


Last edited by NSEU; 7th Jan 2008 at 03:52.
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