Elevator trim tab modification

[floridasonex]

The discussion on the sonextalk group has gotten a little rabid. All I was looking for was someone
who'd made that modification and some real world experience with it. I found that and had a nice
phone conversation with him about it. It works fine with no issues. There are some huge egos
on the yahoo group that go nuts if you question their "expertise". I appreciate the more respectful
discussion on here.
I thought about the dial-a-trim setup when I built .. but didn't like the spring loading of the controls.
I just like to feel their natural pressure and felt a trim tab was more comfortable for me. I have two
motivations for changing. First .. effectiveness. I think the stock tab is a little small .. probably to
avoid adding a lot of weight that far out from the elevator hinge. From guidelines I've heard they
should be around 5% of the total elevator surface. My informal looking at those on various
experimentals seem to reinforce that. Second ... I just don't like the looks of that external
tab hanging on there.
At this point I'm working on constructing the tab out of some leftover control surface skin and
seeing how it comes out. Then I'll make a final decision on going ahead with it.
Thanks for the discussion

RT

[Bryan Cotton]

Let us know how it works out. If you do the Vne dive with a free tab, make sure you get video!

[sonex1363]

Yup its descended to personal offline abuse, I wont mention the perpetrators name, apparently a comment I made about teeth gnashing, mouth frothing and channeling John Thorpe hit a nerve.

I can only imagine who the perp is. With pretty good confidence too. He's an ass.

Yep. I just wanted to chime in that I had the *exact* same experience, sure seems like it was the same individual. I left that poisonous forum and never looked back. It's so much nicer/constructive here (thanks, guys!).

And now back to the regularly scheduled topic. This elevator trim tab conversation has been informative.

[Bryan Cotton]

If it is not too far off topic, I would be curious about the particulars of tuning the spring trim. Mostly what are the spring forces required.

[fastj22]

If it is not too far off topic, I would be curious about the particulars of tuning the spring trim. Mostly what are the spring forces required.

I think this requires some trial and error. And it isn't easily understood, at least for me. I'm not there yet and another builder had the same issues.
My problem was I was running out of forward trim adjustment. It was basically at the end of the screw and I need some more. So I move the aft spring back a bit on the elevator rod and flew again. Now I had plenty of throw but when I changed the CG, I now didn't have enough on the other end.
I'm now thinking I need to increase tension on the forward spring too.
When I get back in the air, I'll keep tweaking and report.

[sonex892]

Its not only the dial a trim that struggles to have enough trim range. The standard agricultural looking trim tab on the elevator also doesn't trim out at the extremes. At full aft C of G I would like a bit more forward trim. With 2 or 3 stages of flap I would like some more aft trim.

A larger trim tab as suggested could be a fix for a sonex. Looking at the photos of John Davis's Sonex it certainly looks more professional.


Steve 892

[floridasonex]

All the BS about flutter and cable breakage applies equally to the standard trim tab... possiblly more so as the "fulcrum" is further away from the hinge line.
Cheers Tony

My thoughts were it was more likely with the standard setup. It's loose fitting .. and the plans say attach the cable by
sticking a "Z" bend thru a hole. In addition to it having more leverage since it's further out. I think the new one is
going to work out fine and look way better.

As for the perpetrator and chief antagonist over there .. it's about bullying and control.

RT

[ededoad]

Speaking of going nuts with flutter on the other web site, it was the deciding factor in my install of a integral tab. It works on most aircraft. If the actuating cable breaks near the horn you will get flutter anyway unless the trim tab is balanced. I made my tab with a little less area than the plan tab.
Ed