Fixed Trim Tab vs Servoed Trim Tab

[alaskabearhawk]

He did change the cable at the tab to exit the bottom instead of the top of the horizontal stab

[patrickh99]

I bought Dan Riffee's project, and he had one of the earlier plan sets, with two elevator trim tabs. The work he did was excellent so I was hesitant to undo anything, however, when I rigged the controls with some temporary connections, I was surprised at the amount of servo action from the trim tabs. And it was not linear, changing from positive to negative servo action as the elevator is moved. As a result, I have removed the right-hand trim tab and am in the process of copying a Citabria's trim mechanism, which uses two control cables. I expect it to work very similar to Pat's.IMG_1771.JPG

[rv8bldr]

Anyone know what kind of cable Pat used on his trim? I've been surfing around the Aircraft Spruce web site and can't find anything that resembles it. It kind of looks like Bowden cable with good quality threaded forks on the ends ....

Thanks

[rv8bldr]

Never mind, looks like I found it (or at least something VERY similar);

https://www.aircraftspruce.ca/catalog/appages/a920.php

[Mark Moyle]

Pat used Morris control cables... Mcmaster-Carr is much cheaper than ACS. I don't have the part numbers on this iPad...


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[rv8bldr]

Pat used Morris control cables... Mcmaster-Carr is much cheaper than ACS. I don't have the part numbers on this iPad...


Sent from my iPad using Tapatalk

Thanks, Mark.

Unfortunately, I'll probably have to get them from ACS. McMaster-Carr refuses to ship anything to Canada. Not sure why, maybe the cold ? :-)

-29C here at home this morning, -40C with the wind chill.


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[nichzimmerman]

I just got two 5 ft A-920 cables in the mail from ACS. If you fix one end from moving, the other end has 1/8" of play. That's fine for a throttle or carb heat, but I believe it's too loose for a trim tab and will invite flutter. I will be returning them.

[Battson]

Those cables will be just fine, I think. Easy for me to say, I know...

My trim tabs have plenty of free play, over 3/8s at the trailing edge of the tab from memory. Maybe a lot more. This causes no problems whatsoever, they are not inclined to flutter.

You could add friction to damp the system if you are really concerned.

[alaskabearhawk]

My latest YouTube video on a modified elevator trim system similar to Pat Fagan's: https://youtu.be/zJiWSkgq8kI

[Chris In Milwaukee]

Wow! You really step it up, Paul. Well executed, as always.

[whee]

Very nice AKBH! Certainly built to last. Thanks for making and sharing the video.

[rodsmith]

Great job Paul!. I think this is a worthwhile mod but I don't have enough ambition to take it on. I did modify the original tabs to the smaller ones. My trim wheel is mounted on the floor next to the flap handle, seems more natural to me not to reach down for the flaps and then up for the trim wheel. Looks like you are making great progress.

[Bdflies]

That's some mighty fine work and well documented!

Bill

[Cameron Ramsey]

Has anyone thought about using the old style, longer trim tab but just installing it on the right elevator instead of both elevators? That way you would only need one cable. One thing that may need to be considered is the stress that it may impose where the two elevators bolt together. May have to run this idea by Bob.

[jaredyates]

We have talked in the past about even using one small trim tab, but I'm not sure if anyone ever got around to asking Bob about the twisting stresses. The number of cables is the same (1) with one or two tabs, but a single tab would save a pushrod and a couple of other pieces.

[Cameron Ramsey]

Has anyone installed a jack screw like the Pipers have that will adjust the stabilizer and just do away with the trip tabs?