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Ron Jones
Joined: 25 Apr 2008
Posts: 19
Location: UK
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 Posted: Sat Oct 02, 2021 8:18 am Post subject: Flap binding issue - how to shorten the flap actuating cros |
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Hi Bud / Jeff,
It seems you are talking about a small amount of tube- shortening ( 1 or 2 mil perhaps?) Is it worth considering shortening the flap? The glass flange at the tip of the flap could stand being reduced that amount without undue weakening (I think!) and there is enough "spring" in the hinges to allow that - or spacers added to the hinge bolts?
(I should add that its 25 years since I was at that stage on my Mono so it's all a bit hazy now!)
Regards to you both,
Ron Jones,
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 285
Location: Florida USA
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| Posted: Sat Oct 02, 2021 2:37 pm Post subject: Re: Flap binding issue - how to shorten the flap actuating |
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Jeff and Ron and folks:
Sorry to add fuel to this
I agree, the easy way would be to just whack things.
I'm a bit more concerned that I don't know how much the flap tube is pushing the flap outboard.
Perhaps the flap outboard closeout is not perfectly square after finishing.
Is the flap tube linear actuator drive biasing the flap outboard because it is installed at an angle instead of dead parallel to the center line?
Is there too much paint and filler added to the flap tip?
Was the wing flap closeout filled and painted too much?
Were the flap arms installed differently during the final assembly?
Is it something simple like some glue or filler preventing the flap pin from fully seating in the flap tube bearing when retracted which is causing rig and retraction binding?
So if Jeff is measuring carefully, as I'm sure he is, and he has de-rigged the wing, checked the flap extension and retraction motion, assured the outboard clearance is not binding and there is anywhere between 1/8 and 3/16 inch of clearance in the up position. Then when the wing is rigged the and flap binds with the pin fully seated something in the drive isn't right. Fixing the drive seems to be the correct course of action.
If the wing is installed, and the flap is pushed outboard to say 1/16 inch from the outboard wing closeout when down, during retraction it will definitely bind. If the bind is reduced by only sanding the outboard flap closeout until clear in the up position, how much force is on the hinges to keep it there.
What we all want on retraction is a just a nice contact with the wings retracted pushing the whole flap very slightly outboard. When we extend the flaps we want the pin straight portion slightly exposed and when we pull the wing flap outboard until the flap hits the wing closeout near the aileron and the flap movement will still not disengage the flap pin, it is safe. In fact we want about 10mm / 3/8 inch max exposed of the pin. SB 16 is fairly clear. Bottom line, the flap pins should not disengage when full down when pulled hard outboard and common sense says when up do not put excessive force on the flap outboard and of course not bind.
If this is what we have in flap extension and retraction the flaps will last and operate flawlessly.
I prefer to fix the rig so nothing is forced over a lifetime. There will be less pressure on the glass and bearings. Wing fairings fit right and don't drag and life is good. Not good enough, but good... for a lifetime.
Quick fixes tend to cause lasting consequences. If you do it right, you can sleep at night and the plane lasts a lifetime.
Of course as my friend Ira says: "Better is the enemy of good, and good is the enemy of good enough". I'm a centrist, good is good.
Bud Yerly
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