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Help-- Pitch trim values

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yankee-flyer

Well Known Member
I'm way too old for all this computerized avionics stuff!! I think-- but am far from positive-- that I figured out the takeoff pitch trim settings. The "values" I recorded were:
Upper (Pitch trim full up)--- 0
lower (Pitch trim full down)---- 490
Takeoff (Green line 1/3 the way down in the lower half of the bar per Marty)
325.

Did anyone else record the values and do these look close? Wanna have it right for the first lift-off!!

Wayne 120241 N143WM almost
 
Trim calibration

Wayne,
I got the same numbers for full up and down trim. Did not record the takeoff number, but each builder will be a little different depending on weight and balance and personal preference. For the first takeoff, too much down trim is better than too much up trim.
Joe
 
THANKS, Joe

I feel much better hearing that someone else has the same numbers! I'm also a bit amazed that I figured out the process correctly.

Wayne
 
I tried to configure my trim settings last night and I had the following numbers. Did anyone else see numbers near this? Do I have the wrong travel distance somehow on my servo? My D-180 firmware is at 5.4 if that makes a difference.

-Ron

Pitch trim full up--- 0
Pitch trim full down----163
 
Ron:

I don't have access to mine right now to check the numbers on the Dynon. However, have you checked the trim tab as per the PAP? It has you do measurements relative to the trailing edge of the stabilator at both full pitch up and full pitch down settings. This is the way to check your servo travel distance to make sure you are getting full travel. Also, how long is it taking to go the full distance? If significantly less than the recommended time, that would also be a clue as to whether you are achieving full travel.
 
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Speed pot too slow?

Do I have the wrong travel distance somehow on my servo?
Click to expand...
The linkage might need to be adjusted. Like Ron said, check the travel per the PAP. After holding the DOWN button in until the trim tab stops, check the trim tab to see if it is binding. You could disconnect the linkage to the servo and see if the numbers change a significant amount.
The Dynon sends 5vdc to the trim pot which sends a voltage back to the Dynon that varies between 0 and 5 volts, depending on servo position. The Dynon displays this voltage as trim position with a number that is between 0 and 500 (corresponding to 0 to 5 volts). I would expect the number on the Dynon to be closer to 500 with full down trim. At least that is the way it was with the old version of Dynon software. I have not rechecked it after upgrading to 5.4 but doubt that it changed.
Another reason for the low number with full down trim could be that the trim speed pot on the control board is adjusted too slow. At a very slow speed, the trim motor might not have enough power to overcome minor mechanical binding. Have a helper listen to the motor to see if it is still making noise after the trim tab moves to full nose down. If it is still making noise, then something is binding, either the trim tab or linkage or internal servo gears. I remember one builder saying that his servo was defective and he exchanged it.
Joe
 
Well, I just got back from the hanger tonight and the trim numbers matched this time. The only thing I did last night, that I did not do tonight was play with the trim timing. I powered on the D-180 and proceeded to configure the trim range... maybe running it up and down so many times to get the timing right caused a low voltage problem with my battery.

Thanks,
-Ron
 
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Glad to hear that

Ron. Follow Marty's suggestions on setting the takeoff trim position-- that worked very well for me for a no-flap takeoof but I need more up (Ie, line further down--confusing?) for Van's recommended half-flap takeoff.

Given the way the -12 gets off the ground (I've been flyng an AA-1 Yankee for 12 years) I really don't see any reason for half-flap takeoff with the resultant need for quite a bit of trim change when you retract the flaps.

Wayne 143WM
 
Good point. I do not use flaps for T/O with a 5500 foot runway. That way I do not have to remember to retract them. The trim setting that i have recommended is with ZERO flaps.
 
Trim Settings

I think there is too many variables to do it by voltage. In my opinion if there is someone that has a 12 that he flies & has the takeoff trim setting nailed down, if this person would set his trim for take off position & then go to the back of the airplane & hold the elevator against the upper & lower stops & give us both of those measurements as is done when checking the linkage adjustment we would have a pretty good starting point for our initial takeoff adjustment. I need to get that from somebody or maybe I can get them at sun & fun. Just my opinion. If anyone has these measurements I would appreciate them.
RV12 ready for the inspector.
Thanks, Stan Bahrns
 
That's exactly what I used to set the initial trim position. I still have not changed it but I feel that it sometimes requires a slight forward push to maintain the 75 knots speed goal for climb out. So I usually set it to a bit more nose down and use the take-off trim marker as a (do not trim further nose up than this) position.
 
That's a first cut

Trim indicator position will change with your CG. If you, like me, fly solo a lot. set the trim indicator so you can maintain the 75 kt climb with whatever fuel you usually carry on first takeoff. Just remember that if you got a passenger (especially a stout one) you'll need more nose-up trim than the bug to rotate and if you're very light, you'll need more nose-down. Almost everyone's trom bug should be set differently.

Wayne 120241/143WM
 
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