budyerly(at)msn.com
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 Posted: Mon Jan 26, 2009 11:32 am Post subject: Elevator Trim Tab slot. Note from the Company!!! |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Dan, Bruno and others,
The standing rule in aviation is all flight controls should be made to be absolutely free from binding or potential binding. The trim T bar for which the slot is made has a rather long moment arm, and any drag in this area will bind/restrict/degrade stabilator control. Chapter 19 step 9 indicates the rigging de-rigging aid of two pieces of ply with a 3/4 inch gap doesn't seem elegant, but it is functional, easy to remove for access in the event of damage or a new antenna idea. Dan and Steve have just gilded the lily on what the book says. By adding another access hole in the side of the aircraft you can still get access. If I recall, Steve's allows removal of the trim T bar if necessary.
From the building side, keep in mind the 40 hour projects to dress up a virtually hidden slot could be spent on finishing the aircraft sooner.
From the flying standpoint, one should not mess with the gap with any means which would restrict trim tab control movement. I once flew a Europa with slightly binding bushings and I couldn't figure out why it didn't trim quite right and in the flare, when I eased back pressure the plane would not correct back and needed slight forward pressure. Too much if I recall was added. Thank God for tough landing gear. It was drag in the system. Drag on the trim T bar from rubber gap sealing strips would be even more interesting. Your pitch dampening will be affected at a minimum as the stab will be slightly fixed from drag, and the tiny amount of slop in the T bar system will change the tab induced correction.
As Roger Bull from Europa once said:
"Under no circumstances should any attempt be made to close or otherwise restrict the trim tab slot. Possible snags include icing, physical fouling, and changes to the aerodynamics.
This latter is important since all the test flying to optimize handling was carried out with the slot open. The airflow in this area was subject to considerable experimentation, as it was shown to be necessary to fit the flettner strip to achieve satisfactory elevator control, and any change to this setup has not been shown to be safe."
So be conservative. Make nice even slots and fill the foam edges, sand smooth and fill, fill, fill until nice.
Just my thoughts,
Bud
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