Elevator trim tab modification
Posted: Fri Jan 24, 2014 11:18 pm
by floridasonex
I posted on the yahoo group .. but that site is pretty much unusable since they
changed the format so I’ll try here.
I’m wanting to modify the elevator trim tab so instead of being external on the trailing edge, it’s
part of the elevator trailing edge, like the way it’s done on may other airplanes. RV and the new Panther being a good example. I’ve seen a pic too of it done on a Sonex. I’ve thought about flutter, but don’t think there would very much change in weight .. very slight. Ideas? Anyone who I can talk to who’s done this? Concerns?
RT
Re: Elevator trim tab modification
Posted: Sat Jan 25, 2014 12:36 am
by Bryan Cotton
I think if it works on Cessnas, and it works on RV’s that it should work on a Sonex. Here is a 182 trim tab from the top:
image.jpg (83.37 KiB) Viewed 6317 times
From the bottom you see there is a horn and rod. The RV4 tail I built, IIRC, used a push-pull cable to move it. Cessnas use a linear actuator. Long trim cables are moved by the trim wheel and then move a little wheel on the actuator. You don’t want Cessna parts, they are too heavy.
image.jpg (77.37 KiB) Viewed 6317 times
The cut out piece is used, along with a C or Z channel to close it out.
Re: Elevator trim tab modification
Posted: Sat Jan 25, 2014 7:04 am
by floridasonex
That’s what I’m thinking of. I’ll most likely stay with the same cable actuator setup .. except maybe go to a .090 music wire for less play in the tab.
RT
Re: Elevator trim tab modification
Posted: Mon Jan 27, 2014 11:28 pm
by rizzz
Here’s a picture of a Sonex with such a built in trim tab:
trim_tab.jpg (445.76 KiB) Viewed 6225 times
This discussion is going a bit nuts on the yahoo groups, flutter concerns etc., but what I wanted to ask was, why would you want to do this mod.
If it is purely for aesthetical reasons, why not just go with the standard Sonex dial-a-trim with spring trim system, you’ll eliminate the trim tab all together.
Re: Elevator trim tab modification
Posted: Tue Jan 28, 2014 12:02 am
by Bryan Cotton
It is nuts over there. I think I am done with that conversation. I do like the simplicity of spring systems. The Pawnee had one and it worked great.
Re: Elevator trim tab modification
Posted: Tue Jan 28, 2014 10:59 am
by fastj22
Bryan Cotton wrote:It is nuts over there. I think I am done with that conversation. I do like the simplicity of spring systems. The Pawnee had one and it worked great.
Having a Waiex, I have no option other than the springs. I will say that the Waiex is so well balanced that its easy to fly it without adjusting the trim. Stick pressures are just not great.
The spring system does require some fine tuning of the spring tension. Still working on that.
Re: Elevator trim tab modification
Posted: Tue Jan 28, 2014 1:12 pm
by dcstrng
Bryan Cotton wrote:I do like the simplicity of spring systems.
Steve W. used a similar system in his birds – generally also light stick forces. I’m sure there are TW’s out there with tabs, but I don’t recall seeing one… The Sonex screw/spring arangement is (to my eyes) just of sophisticated version of what Wittman did on his (both Buttercup and Tailwind). Wittman used a sort of friction arangement, and Sonex uses the threaded screw, but they end up doing the same thing… wurks fer me…
Re: Elevator trim tab modification
Posted: Tue Jan 28, 2014 5:32 pm
by tonyr
fastj22 wrote:
Bryan Cotton wrote:It is nuts over there. I think I am done with that conversation. I do like the simplicity of spring systems. The Pawnee had one and it worked great.
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 have flown a Sonex with the standard trim, nothing wrong with it, good authority, ease of use.. apart from looking like dogs b_lls on a hot day.
My reasoning for considering a recessed tab is purely aesthetic, but the time taken to implement decided me against it. I have taken long enough to get this point! (Once I’m done with paint ‘n’ polish, ready to inspect)
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.
My main concern with the dial trim is that it can run out of authority in some situations, i.e. full flap approach. That could be an adjustment issue.
I have fitted a dial trim anyway to my aircraft.
Cheers Tony
Re: Elevator trim tab modification
Posted: Tue Jan 28, 2014 8:44 pm
by fastj22
tonyr wrote:
fastj22 wrote:
Bryan Cotton wrote:It is nuts over there. I think I am done with that conversation. I do like the simplicity of spring systems. The Pawnee had one and it worked great.
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 have flown a Sonex with the standard trim, nothing wrong with it, good authority, ease of use.. apart from looking like dogs b_lls on a hot day.
My reasoning for considering a recessed tab is purely aesthetic, but the time taken to implement decided me against it. I have taken long enough to get this point! (Once I’m done with paint ‘n’ polish, ready to inspect)
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.
My main concern with the dial trim is that it can run out of authority in some situations, i.e. full flap approach. That could be an adjustment issue.
I have fitted a dial trim anyway to my aircraft.Cheers Tony
I can only imagine who the perp is. With pretty good confidence too. He’s an ass.
As for the authority of the dial a trim, for me, it seems the biggest problem is finding a sweet spot where you can have various loads, and still have plenty of adjustment of the trim. Example, if I tune the springs to handle the W/B of myself an fuel, when I carry a passenger with some luggage, I run out of nose down adjustment. If I adjust the springs to handle that, then I run out of adjustment when solo on the nose up.
Re: Elevator trim tab modification
Posted: Tue Jan 28, 2014 10:17 pm
by rizzz
fastj22 wrote:Example, if I tune the springs to handle the W/B of myself an fuel, when I carry a passenger with some luggage, I run out of nose down adjustment. If I adjust the springs to handle that, then I run out of adjustment when solo on the nose up.
Sounds like you urgently need to convert your Waiex to a “Viking Sport” :mrgreen:
Re: Elevator trim tab modification
Posted: Wed Jan 29, 2014 9:15 am
by 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
Re: Elevator trim tab modification
Posted: Wed Jan 29, 2014 9:35 am
by Bryan Cotton
Let us know how it works out. If you do the Vne dive with a free tab, make sure you get video!
Re: Elevator trim tab modification
Posted: Wed Jan 29, 2014 4:00 pm
by sonex1363
fastj22 wrote:
tonyr wrote: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.
Re: Elevator trim tab modification
Posted: Wed Jan 29, 2014 6:41 pm
by 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.
Re: Elevator trim tab modification
Posted: Wed Jan 29, 2014 8:31 pm
by fastj22
Bryan Cotton wrote: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.
Re: Elevator trim tab modification
Posted: Thu Jan 30, 2014 5:08 am
by 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
Re: Elevator trim tab modification
Posted: Mon Feb 10, 2014 9:46 pm
by floridasonex
tonyr wrote: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
Re: Elevator trim tab modification
Posted: Wed Mar 26, 2014 11:29 am
by 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