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Trim sensitivity

tomkk

tomkk

Well Known Member
My stabilator trim is very sensitive in cruise. A brief tap of the switch can put it from a nose up trim to nose down trim and it's difficult to get in between those.

The trim motor takes 25 seconds from full up to full down, so the basic setting is within spec.

I can adjust the pot on the Control Module to adjust the motor speed but it's trial and error and I'd have to remove the cover skin for each trial. I was hoping someone else might have had a similar problem and already gone through this.

So, if anyone has adjusted the trim motor speed, about how much change in the pot produces a noticeable change in trim sensitivity?
 
All I can suggest is to adjust the pot so that the motor runs as slow as possible without stalling.
 
It is kind of touchy. If I adjust trim in cruise flight I do it with just the briefest of taps of the switch. I haven't adjusted the speed because it's fine for use in the pattern, plus there is no trim speed adjustment that I know of in the D180 setup. I'd have to do something external to the system.

Never thought I'd say this but I kind of miss manual trim.
 
You could use a switch and a trim speed adjustment pot to have a "high" and "low" setting (or less confusingly, takeoff/landing and cruise). Bypass the adjustment pot for the takeoff/landing setting, and put it in series for higher speeds. At least, I've seen this done for the Ray Allen and similar servos; not sure exactly how the -12 stab trim is set up.
 
tomkk said:
My stabilator trim is very sensitive in cruise. A brief tap of the switch can put it from a nose up trim to nose down trim and it's difficult to get in between those.

The trim motor takes 25 seconds from full up to full down, so the basic setting is within spec.

I can adjust the pot on the Control Module to adjust the motor speed but it's trial and error and I'd have to remove the cover skin for each trial. I was hoping someone else might have had a similar problem and already gone through this.

So, if anyone has adjusted the trim motor speed, about how much change in the pot produces a noticeable change in trim sensitivity?
Click to expand...

Tom,
The procedure in the KAI specifies that the adjustment be done with a battery charger connected to the battery so that the buss voltage is close to what it will be in flight. Higher the voltage, the faster the trim will travel.
So if it gets adjusted without a charger connected, it will be faster in flight.

The PAP specifies that trim speed from one end of travel to the other be 25 - 30 seconds with the buss voltage at approx. 13.6 volts from a connected battery charger.

Adjustment can be done without removing the fwd top skin. You can gain access by removing the EFIS screen. Shorten the kit supplied adjusting tool by cutting it in half at the mid point to make it in to two tools.
The adjusting pot is 25 turns so it takes a bit of turning to cause a change.
Clockwise to make it slower.... counter clock wise to make it faster.
 
MMiller said:
Dale,
yes the trim is adjustable on the D180 version. The pot is in the back and on the bottom of the Vans control board.
Click to expand...
Ha!! Missed that, I was looking at the PDF and had it blown up to see the top half. Thanks for pointing it out.
 
Trim speed

9A I fly sometimes is like that. Instead of adding yet another box just flick the switch at cruise speed. Might take a couple of flicks to get as much trim as you want. At pattern speeds trim switch can be held for a full second and that works out about right.

Don Broussard

Rv9 Rebuild in Progress.
 
rmartingt said:
You could use a switch and a trim speed adjustment pot to have a "high" and "low" setting (or less confusingly, takeoff/landing and cruise). Bypass the adjustment pot for the takeoff/landing setting, and put it in series for higher speeds. At least, I've seen this done for the Ray Allen and similar servos; not sure exactly how the -12 stab trim is set up.
Click to expand...

cajunwings said:
9A I fly sometimes is like that. Instead of adding yet another box just flick the switch at cruise speed. Might take a couple of flicks to get as much trim as you want. At pattern speeds trim switch can be held for a full second and that works out about right.

Don Broussard

Rv9 Rebuild in Progress.
Click to expand...

This thread is in the RV-12 forum.

The RV-12 has a design specific trim system with a speed control, that doesn't easily adapt to what many builders do on the other models.
 
rvbuilder2002 said:
Tom,
The procedure in the KAI specifies that the adjustment be done with a battery charger connected to the battery so that the buss voltage is close to what it will be in flight. Higher the voltage, the faster the trim will travel.
So if it gets adjusted without a charger connected, it will be faster in flight.

The PAP specifies that trim speed from one end of travel to the other be 25 - 30 seconds with the buss voltage at approx. 13.6 volts from a connected battery charger.

Adjustment can be done without removing the fwd top skin. You can gain access by removing the EFIS screen. Shorten the kit supplied adjusting tool by cutting it in half at the mid point to make it in to two tools.
The adjusting pot is 25 turns so it takes a bit of turning to cause a change.
Clockwise to make it slower.... counter clock wise to make it faster.
Click to expand...

Thanks, Scott. It was actually easier than I expected. As you suggested, I removed the EFIS screen and actually just removed 3 of the 4 screws holding the Control Module and rotated it slightly for access to the pot. My, but that's a VERY small pot adjusting screw, isn't it? :)

You're right, it does take quite a few turns to get any appreciable change.

Turns out mine was actually about 22 seconds and I slowed it to 27. That seems to be a great improvement in cruise and still good in the pattern but I've only had one flight on the new setting.
 
I have mine set to about 60 seconds.
It is much less sensitive in cruise.
It takes a long time to set for takeoff, but that gives me something to do while the Rotax warms up.
 
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