Elevator trim tab modification

[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

[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 6455 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 6455 times

The cut out piece is used, along with a C or Z channel to close it out.

[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

[rizzz]

Here’s a picture of a Sonex with such a built in trim tab:

trim_tab.jpg (445.76 KiB) Viewed 6363 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.

[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.

[fastj22]

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.

[dcstrng]

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...

[tonyr]

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

[fastj22]

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.

[rizzz]

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: