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greeneg

Query concering correct position for elevator trim when AP active...

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Hi allI'm using a X-36 Saitek joystick with the elevator trim assigned to one of the rotaries.Say, if I decided to takeoff and climb manually, trimming the elevators to suit a constant climb, then i decide to allow the Autopilot to climb the rest at the current attitude.During this time of switching Autopilot on and on a postive rate of climb, I haven't centred the rotary, leaving the elevator trim in the positive position - as when flying manually. I noticed during the climb the trimmer wheel is constantly moving about, from what looks like it's having to match trim to suit my rotary position ie. positive. In this position, the trimmer can't seem to settle down to a correct VSI eg. 2000ft/min, and e.g. after about 5-10 mins later the VSI needle has a negative reading when it should be in the climb (speed is fine during this, only VSI is the error).I then decided to move the trimmer rotary (while the Autopilot is enabled) to a central position and monitored it closely. The VSI now settles down to a constant rate of climb with no malfunctions occuring.**QUESTION**I'm wondering, when one is in the climb, with Autopilot enabled, does one have to centralise the trimmer wheel/ is it meant to be centralised when Autopilot is controlling the rate of climb to the desired altitude?Many thanksWill :-wave

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Hi Will. If I am not mistaken ( and I am certain that someone will tell me if I am) you do not have any manual contol over trim with the autopilot engaged.Best Regards,

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HiIn a way you are wrong. Autopilot in my FS tries to change the trimmer to suit what position it was last left in. If one then decides to MOVE the trimmer rotary on the joystick to say central position, it MOVES the trimmer in the cockpit (ie therefore having partial manual control) and then FS balances the a/c around this new trim.In short, it seems one does have partial manual control when AP is active; AP only balances out around a chosen setting, but depending on the position the rotary was last left in, it can sometimes cause errors to occur (as stated in original posting), thats why i'm asking if one leaves it in the central position, would this solve these errors occuring?CheersWill

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The only way I can answer your question Will is telling the way I do it with the same stick.Set trim for take-off, climb and engage A/P. Once at a reasonable height, with A/P on I set the trim rotary back to centre. I have noticed a slight dip in v/s as i do this until the A/P catches up which is why I don't centre until at a reasonable height, say 3,000ft.Having said that, I don't fly the default planes, that may make a difference.HTH

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Hi VulcanYou've answered my question perfectly! I've also noticed the dip in the VSI as the AP catches up. I find this quite annoying, especially as one wouldn't expect this to happen in the real world.I'll adjust the trim to it's central position "Smoothly", that may minimize the VSI dip, but then again it may take even longer for the AP to settle down...Just trial and error I guess.Thanks for the helpWill

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Once I am sufficiently achieved enough AGL, I tend to slowly move the trim wheel on the stick (a CH) back to its center detent. I do this so at least in theory the trim/pitch axis will not run out of range by hitting its limits since the AP controls by trim on the models I've used.I seldom trim for climb in the sim (not the safest) because I engage the AP while still pulling back on the stick. I do not have force feedback. My trim control has a center detent and is actually in series with the stick pitch axis, not a seperate analog control, and that can make a difference.

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I use the Saitek X45, which is something like the X-36 isn't it? But I don't use the rotory dial for trim. The X-45 has two hat switches on the joystick, and I use the upper left one for elevator trim and the lower one for view changing. This method provides an excellent "feel" in the stick itself for trimming. I trim constantly when ever the need is there. While in climb, cruise, or descent.Since I'm usually trimmed for any condition, if I set the auto-pilot to on, it doesn't have to fight an out of trim condition, and I don't see any trim wheels on the screen making wild movements; just a few slow ones. In answer to your question ---- NO, I wouldn't attempt to center a trim wheel visually or to a detent. It's all by feel, and trim forces out before turning the auto-pilot on. The only time I really care about the position of a trim indicator is the takeoff position. I notice, that once in level cruise with the MSFS auto-pilots that the trim indicator ends up in the neutral range.L.Adamson

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I did a quick test. I have an X45, which is the same except for USB connections (I think only some X36 have USB). I have elev trim connected to an anlogue rotary axis via FSUIPC 2.975 calibrated so that the center detent gives output of 0. I tested using the default MS 737 and AFSD ver 1.37 (this program obtains real time data from the FSUIPC interface). Per AFSD the range of trim is -20 to +20 using the rotary on the ground.I took off and trimmed to obtain a V/S of 3000 fpm @ 250 KIAS. AFSD reported a trim of +2.74. I then set AP on, Alt mode with dialed in V/S of 2500. Trim reported by AFSD would then vary some as needed to maintain 2500 fpm (Initially +2.19). It was averaging around +3. While AP was on, I moved the trim rotary to the center detent and immediately AFSD reported trim decreased, but the AP started compensating by increasing trim again. I then moved the trim rotary to down (negative) trim and obvserved the same behaviour. The AP overshot the ordered 2500 fpm and went into damped oscillation, after about 3 or 4 excursions it settled out at 2500 fpm. AFSD reported trim as +3.13. I then turned off AP. Trim remained as set by the AP. I then moved the trim rotary to the center detent, after which AFSD reported trim 0. So that appears to be it. The AP works regardless of where you have the trim set manually, as long as you don't move it. If you move it manually it will change as ordered initailly, but the AP will adjust as necessary to compensate. Turning the AP off retains the last trim value until a manual adjustment is made, at which time trim is driven to the manual value.scott s..

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Hi all. Well sounds to me that using the trim wheel on your stick doesnt make the triming realistic to a point. If there was a way to allow the auto pilot to control the wheel movement on your stick, it would make it truely realistic. As in real aircraft trim doesnt move much at all...Its very sensitive. We only trim in clicks in real jets. Unless leveling or climbing/descending or big airspeed changes you dont use a lot of trim at all. In the jet if you trim the aircraft well for the speed or climb, and turn on auto pilot, you wont notice any changes. Even a little bump on the yoke if you are off a little bit.

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Hi RichI agree as well, I was sure that the trimmer and Autopilot shouldn't be working together like this, if I had anything like this occur when i'm flying people around south UK in my Piper, i'm sure they wouldn't appreciate it, maybe even feel abit sick!I'm not too sure if this matter effects ALL joysticks but it's sure sounding like it is.Who knows..... MS might have improved the AP. :DCheers guys.Will

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>Hi Rich>>I agree as well, I was sure that the trimmer and Autopilot>shouldn't be working together like this, if I had anything>like this occur when i'm flying people around south UK in my>Piper, i'm sure they wouldn't appreciate it, maybe even feel>abit sick!>>I'm not too sure if this matter effects ALL joysticks but it's>sure sounding like it is.>I won't go back through all these replies, to get exact impressions of what auto-pilots can or can't do, but I'll give some specifics for auto-pilot connections on GA aircraft.For instance, a great place to connect the auto-pilot servo & arm to an airplanes elevator would be a bell-crank location which controls the push/pull tube to the elevator (if using tubes instead of cables). The auto-pilot in this case, is totally seperated from the trim system. If the airplane is out of trim, then the auto-pilot servo motor has to "fight" it. Seeing how this can be sensed because of added current draw, sensors can be used to either operate annunciator lights which direct the pilot to trim in the proper direction, or additional equipment to litterly control the aircrafts trim systems automatically. If the airplane is already setup for electric pitch trim, then the installation is simplified. Notice that the electric trim in a Piper PA-28 is a servo system which also turns the trim wheel. If the auto-pilot auto-trims, then the wheel will move.As to how FS2002 simulates it, it doesn't matter. The aircraft needs to be trimmed before applying auto-pilot. I can't imagine anyone flying a real aircraft with severe out of trim ---- flipping the auto-pilot switch. In my own case, I've developed the real pilot "feel" which transfers to my joystick. By lightly unloading the stick pressure in my hand, I can see/feel the response to my trimming. The only reference to a moving trim wheel is on the screen. Certainly not the stick. This is another reason I prefer the hat-switch buttons over my rotory trim knobs. That way, all visual trim indication is from the screen & not a detent on a rotary.L.Adamson

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