STAB TRIM

[sirraj]

I found my original PS1 CDs and installed the program on both a Windows XP PC and a Windows 7 PC. On the Windows 7 PC I am running a virtual copy of XP using Microsoft's Virtual PC. I was unable to use the 747IPC Auto-Installer because I can't find my PS1 manual. (Searched everywhere, I just can't remember where I put it).

Anyway, PS1 runs pretty well on both PCs except for one problem. When I get ready for take off, the stabilizer trim is way off, and I can't adjust it. Neither the keyboard nor the mouse will adjust the stab trim. Has anyone else seen this problem? Is there something I'm doing wrong?

Thank you,

Sirraj

[Hardy Heinlin]

Hi Sirraj,

is any autopilot on? PS1's A/P uses the stab trim to control the pitch (as it cannot move the joystick). It may try to pitch up to initial TOGA attitude.


Cheers,

|-|ardy

[John Davis PC]

we had a similar thing in my sim 3 times during World flight, by the time we taxied out the stab trim was way out and just wouldnt budge, we had to start again, as far as I recal we never checked if any autopilot was on, if its happens again I will check, we assumed as we changed a couple of bits of software just before the event something was causing it, but we never got to the bottom of the problem.
I havent had the problem since worldflight so its probably one of my crew engaging the autopilot as they are scared to fly the thing even on take off

[Jeroen Hoppenbrouwers]

I once engaged the A/P during takeoff roll around 40 knots on the Lufthansa full flight sim and watched the show.

Around V1 the nose slowly came up, but the A/P did not dare to pitch up to actual rotation attitude and the result was a smooth takeoff, using a bit more runway than absolutely needed.

Hey, who said that aircraft cannot take off using A/P?   :mrgreen:

[sirraj]

You are correct, the autopilot was on. That solved my problem ... thank you all very much.

Sirraj

[Qavion]

I once engaged the A/P during takeoff roll around 40 knots on the Lufthansa full flight sim and watched the show.

What A/P mode was the LH sim in, Hoppie?
(I recall) On our 744's, as soon as you push a CMD switch with TOGA mode armed, the A/P reverts to the basic HDG HLD, V/S.

Rgds/
Q>

[Hardy Heinlin]

As far as I recall (from Mel?), FLCH should work. When you approach your selected speed (V2 is usually close to Vr), FLCH pulls the nose up to maintain the airspeed.

|-|

[Qavion]

Can't recall if it was Mel.

Engaging FLCH initially commands nose down at low speeds on the ground (so I'm wondering if the Stab will start running in the wrong direction)

We may need input from someone with sim time ; )

[Jeroen Hoppenbrouwers]

I don't remember, but most likely I just pushed CMD which means blank-TOGA-TOGA. I don't recall having to thumb V/S up. I also did not watch the elevator position.  

[Qavion]

TO | TO is not a valid A/P mode on the ground, Hoppie ; )

Something is fishy, here )

[Jeroen Hoppenbrouwers]

Well, it was 02:30 at night and the coffee corner was occupied by an aircrew.

[John Golin]

I can see this being a bullet point feature on the PSX Box

* Accurately modelled autopilot behaviour at takeoff

[Hardy Heinlin]

Engaging FLCH initially commands nose down at low speeds on the ground (so I'm wondering if the Stab will start running in the wrong direction)

Sure, nose down at low airspeeds, but when approaching the target airspeed, FLCH starts pulling the nose up. And when the airspeed trend is large and positive (which it is on a takeoff roll), the nose up command occurs earlier. For any automated steering, trend values are more important than current values, in order to avoid oscillations and overshootings.


Cheers,

|-|ardy

[Qavion]

Of course, agreed, but I'm sure there wouldn't be much upwards command at/under stall speed : P

[Jeroen Hoppenbrouwers]

Still... what is the FD pitch command line doing at standstill?

[Qavion]

Nose down (with FLCH). I vaguely remember 10 degrees, but I'll recheck.

[Jeroen Hoppenbrouwers]

It indicates nose up with __|TOGA|TOGA. Of course the APFD mode may/will switch out of this when you select CMD during the takeoff roll, but until somebody does this again, we'll never know for sure what happens.