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From the Puckerbrush...

Editor's Column

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Sealing Control Surface Gaps (Part I)

You've finished up the plane. It's covered in glorious color, the radio gear is installed and working properly, the plane is laterally and longitudinally balanced. You're ready to fly!

Well, maybe not. Are the hinge lines sealed?

``Huh?'', you say? I know, you've all seen lots of planes fly OK without any fuss over hinge lines. But there are real advantages to sealing those hinges. How about less drag, quicker rolls, better turns, more precise control, eliminating flutter? All this with little work, expense, or extra weight!

Why is this true? A typical aileron, shown below in its trim position, undeflected, acts as part of the wing. The wing depends on smooth airflow around it to generate higher air pressure on the bottom, lower pressure on top. It is this pressure differential that gives rise to airfoil lift. When our aileron is deflected, we get a higher (in the case shown) pressure differential, causing extra lift. On the other wing, raising the aileron would cause less (or no) pressure differential decreasing or even eliminating lift on that wing. And thus, the plane rolls.

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With the aileron gaps unsealed (below), we get the same type of result, but at a great cost in efficiency. Firstly, air bleeds through the hinge gap, from high to low pressure, decreasing the pressure differential and reducing the control surface effectiveness. Secondly, the air bleeding through the gap causes some disruption in the smooth airflow over that part of the wing. These two effects will decrease lift and increase drag, and in extreme cases, will induce and enhance control surface flutter, which can destroy an aircraft.

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Your plane will fly more precisely and efficiently with hinge gaps sealed, and the difference will likely be noticeable! We'll explore ways to do this... next month!


next up previous
Next: Calendar of Events Up: Front Page Previous: At the Last Meeting...

Craig Kulesa
Wed Jun 30 22:29:14 MST 1999