It was only yesterday, while observing the effect of the stabilizer trim function that I came to realize that the entire horizontal stabliizer moves up and down(quite astonished me, it did)!! Until then, I had assumed that the purpose of the stab trim was to operate the trim tabs on the elevators to trim out control forces. Can someone explain why this former method is used in association with the more conventional trim tab method, please? And then, how DO you move the trim tabs on the elevators?On a somewhat related issue, I

as for the rudder it is a joystick problem. jerky movement of the stabilizer is fue to some MSFS limitation if i remeber correctly.. i'm quite sure it has been explained a long time ago.. a serach could possibly help on this. Can't answer the technical part about the stabilizer and trim movements al manuals are buried somewhere in the living room... my precioussssss Bulfer :) Bye, Luca

Frank,As to your first question this is the norm with large jets. You'll get more astonished by a 777...The elevator comprises the whole horizontal "stabiliser" (called a "stabilator") which by the way is of the size of a 737-200 main wing.The NG contains an electronic trim limiter per button click. The reason for this is that many joysticks in combination with some inherent weakness of FS9 (not previous versions mind you...) result in impossibly large trim changes per click and make the aircraft difficult to fly manually the way it should be. The (visual) jerkiness is a result of dis-synchronisation between (a) FS wanting to do its own wrong little thing and (:( our stuff (thru FSUIPC) making it right (note that this should only be really observable while setting t/o trim). In the latter case just try click-at-a-time for a (non)-visual effect.Best,Vangelis===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================

>And then, how DO you move the trim tabs on the elevators?Frank,The 737NG has no trim tabs on the elevator, they are not needed since the stabiliser is moved instead.In fact this is not only the case with the 737 but also with most other large airliners.Regards,Markus

Ah, thanks, Markus. I didn't see any trim tabs, but thought they had to be there.Thank you for clearing this up for me.BR,Frank

Thanks, Luca. Hope you find your Bulfer soon! :-)BR,Frank

That's very interesting, Vangelis. It's hard to imagine a stabilizer as big as you mention! Wow!I understand what you're saying about PMDG attempts to allow proper trim inputs. To get the effect I mention, you have to keep your finger on the buttons continuously. In any case, I doubt I'll be using it very much, except to set T/O trim.Many thanks,Frank

>Ah, thanks, Markus. I didn't see any trim tabs, but thought they had to be there.Look a bit closer at the tail in the NG outside view, guys... and you WILL see them ;-)Yes, the 737NG does have an elevator trim tab system. This has been mentioned previously on the forum... Just can't seem to find my posting on it... so....The elevator trim tab system is a complex one (system) which looks at flap position, the availability of hydraulics and electrics, elevator input, etc.The tabs may operate in balance mode (move opposite in direction to elevator) or anti-balance mode (in the same direction as the elevator). For the latter mode, the flaps must be in the out of up position and hydraulics (sys A & :( and electrics must be available.For every degree of elevator movement, there is a corresponding angular movement of the tabs. In balance and anti-balance modes, the degree of movement is different however.Hope this clarifies things.Cheers.Ian.

Thanks, Ian.In that case, can I ask my question again - how do you operate the trim tabs?BR,Frank

>Thanks, Ian.>In that case, can I ask my question again - how do you operate>the trim tabs?>BR,>FrankYou don't... They don't operate directly in response to any one thing you do. The flight control system automagically uses them for a little extra "oomph" to either work against a deflection force (in balance mode) or enhance a deflection force (in anti-balance mode). Their purpose is to make the airplane fly smoothly, much like the way spoilers are used to help impart roll in flight in conjunction with aileron on some airplanes.

Or manually using this:http://www.b737.org.uk/trim_wheel.jpghttp://www.b737.org.uk/flightcontrols.htmYou guys know I have to throw in something from the 737 site. :)

>Or manually using this:I don't see the connection, Jered... Why would operating the manual stabilizer trim affect the Elevator Trim Tabs?AFAIK, Elevator Trim Tabs only respond to elevator input.Cheers.Ian.

Hi Tim,Thanks very much. That clears it up for me!BR,FrankPS Like your neologism, "automagically" :-)

Hi Ian,Looks like the same confusion I had!BR,Frank

Apparently not, Jered!Thanks,Frank