Strange Trim behaviour

[ark4diusz]

Recently I've been encountering that when landing the 737-300 the elevator trim decides to go full nose up and i'm unable to stop it from doing so with the trim button.  The only way i'm able to stop it is to disconnect the autopilot trim servo by the thrust levers. 

I must add that before take off I perform a control surface check and the trim also works fine.. 

Anyone else encountered this?

[Litjan]

Oh, that is a new one! Does it happen before you touch down (during flight) or afterwards?

There are three electrical trim inputs working the elevator - the pilots trim switches on the yoke, the autopilot trim and the speed trim (we do not model Mach trim).

To further troubleshoot what is happening to you would need either a better explanation (state of flight-director/autopilot, engaged modes) or even better some screenshots or (the best) a short movie.

I am sure we can find out what is going on.

Cheers, Jan

 

[737allday]

Hi Jan,

I am encountering the same problem as stated by ark4diusz. After takeoff with flaps f.ex. selected to 5 the aircraft pitch trims the nose all the way up, thereafter fully down. It is kinda time critical to me because I wanted to use your product as preparation, so I am looking forward to your answer. Let me know how I can provide you with the most important information to solve this issue pls.

 

state of flight-director/autopilot, engaged modes: Takeoff/fully manual/ nothing engaged, rawdata takeoff, ready for takeoff state selected, even tried different hardware such as stick and yokes with trim buttons selected or unselected. No change..

 

Happy landings,

Jan

[Litjan]

This is most likely the speed trim function at work. It is a function of the real aircraft as well and it will try to "trim" the airplane for a certain speed to add speed stability (you can google its function).

To stop it you can select flaps up (it only works while flaps are down) and it only works while thrust setting is high.

The speed the trim system aims for is determined by the position of the speed cursor, so make sure you set it to the appropriate speed you want to fly (like if you accelerate for clean up).