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Not Enough Elevator Trim???

N787TR

Active Member
Per the manual, the trim tab should move up and down 25-30 degrees... but with the Ray Allen trim motor I can only get about 40 degrees in total (e.g. 25 degrees up and 15 down). Has anybody else had this problem? Suggestions?

-Todd
 
contact?

Todd,

Make sure the linkage from the servo to the trim tab is not making contact with the cover plate. Most builders have to elongate the stock cutout to get full travel.
 
Todd,

Yes, I ran into this too. And I suspect that everyone does who takes the time to measure the deflection limits (kudos!).

Possible interference of the linkage with the elevator skin is not the problem (also common, but it's a separate issue). With no interference, the travel is still limited to about 40 deg total as you said. It's simply that the maximum travel of the Ray Allen servo, coupled with the lever arm length of the trim tab horn, just doesn't give quite the specified amount of trim tab deflection.

I spoke with Van's about this (a few years ago). They indicated that this is normal, and that the available travel should be sufficient under all flight conditions (which begs the question: why did they specify wider travel limits in the manual?). Anyway, I'm not flying yet, so can't confirm first hand, but that's what I was told by Van's.

-Roee
 
If you are stroking the servo full travel, it is good enough. You will only use a small range of it anyway.....if you have to use all of it, something is wrong with your rigging or W&B!
 
Just as a point of reference, I have never had to use more than 10 degreees of trim tab travel.
 
I concur, mine didnt achieve the spec Van's has listed. This has been discussed before...should be more info in the archives if you really want to dig into it.
 
lots of nose up light and slow on final...

i use lots of nose up trim on final... all of it when very light. very little nose down except when heavy at a high elevation airport during roll out to help hold the tail up.
 
Thanks

Thanks for the replies... I suspected (hoped) that the limited travel wasn't builder error but still provided adequate trim.

-Todd
 
Trim range of motion

Thanks for this post. I?m getting only 23 degrees of up and 22 degrees down on my electric trim servo and thought I had a problem.

But for purpose of nose up landing, I?m wondering if I should shorten the rod to get more nose up deflection. I suppose I could fly then decide.
 
I am sure you will find that you require very little nose down trim and that you will have enough nose up. I would fly it first. If you find you are not happy with it, it is an easy change after.

I typically do not fully trim nose up on final. I prefer a little nose up trim as I slow down on the downwind or base and then just use the stick after that. This way in the event of an overshoot I don't require a lot of pressure on the stick to hold the nose from ballooning as power is applied. Just my personal preference. No issues with the amount of trim doing this.

In cruise the electric trim is extremely sensitive (just requires a tap on the button) if you don't slow the trim speed down, however, in a go-around situation it seems like it takes a while even when at full trim speed.

Al
 
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