Trim Calibration Question for Neutral

[jc2da]

I ran the calibration for my Elevator trim and have an issue. The calibration step asks for full nose up 0V, full nose down 5V, and take-off position. However, it doesn't ask for neutral. Thus, i am assuming it takes the average of full up and full down for neutral? 2.5V?

However, in my case, that value does not correlate with a neutral trim position. Neutral trim for me seems to be at around 3.2V.

I would think i am not the only one with this issue. It would be great if we could calibrate the neutral trim position as a user calibrated value, too.

Jae

 

[dynonsupport]

So first, the ends don't need to be 0V and 5V. Both ends need to be within that range. But the point of the calibration is for it to sense, say 2-3V as the full range. So if you're forcing the end points to be 0V and 5V when that's not the real range of the sensor, that could cause the display to look off.

Next, the calibration is linear between the two endpoints.

But finally, I'm not sure I see why you'd care about the true geometric "neutral" position though at al, or even a slightly non-linear scaling of the indicator. Once you have the take-off position set (which may or may not be the true middle of the throw), is there any reason that you care about any other setting besides how far away you are from that position? Also, note that the take-off position may in fact not be in the middle of the throw. In that case, the line is shown a bit relatively higher or lower in the bar than center.

 

[skysailor]

Bearing in mind that elevator trim actually trims the aircraft to an angle of attack, the "neutral" position will vary depending based on that factor. It would only be in the exact same position when the aircraft weight, indicated speed and G loading are identical to the time the original Neutral determination was made.

 

[jc2da]

Unfortunately, it has been too long since i have been an active pilot. thus, i can't remember much about how other trim indicators worked.

however, just intuitively, it seemed useful to know where my neutral trim tab position physically is. there is no way for me to visually see the elevator trim tab position in flight.

Skysialor, this is for an RV-10 that has 2 trim tabs on the trailing edge of the elevator. Neutral position would be when both trim tab's trailing edge is inline with the elevator trailing edge. Right, in flight, level or neutral could vary, but that is why I thought knowing the physical alignment of the trim tab would be useful, since i can't directly see it from the cabin.

i will ask around and see then.

a workaround solution could be to set the full up position at 1.4V, which should center the indicator at my 3.2V neutral position. however, it would mean i would not get the full nose up resolution but at least it would indicate center.

Jae
RV-10

 

[skysailor]

Jae,

I see where you are trying to go with this. Actually, if you install the position sensors and calibrate the full up and down positions, the Skyview will know the entire range. Once this is done you could simply put the trim tabs to the faired position you seek and note the position on the display. By changing the settings on the trim widget you could give yourself an index for that position on the gauge so you would always know when the trim tabs are faired.. I plan to have a green index for the takeoff trim position in the plane I am building.