wing tip shape

[John Pavlick]

Lance,
 Sorry for the confusion. I should have mentioned that I don't normally use
CA hinges. Especially in foam wings, unless the caps in the control surface
area are as thick as the hinge depth. I prefer pin hinges, and I pin them in
place too (dowels or toothpicks). The problem with binding is aggravated by
the fact that the CA hinge pivot point is exactly between the two parts,
because that's where it is allowed to flex (the hinge is not supported by
the surfaces). With a pin hinge, you can move the pivot point to reduce the
interference. The way I was taught to understand this was to think of the
geometry involved. The pivot point should be at the CENTER of the radius,
not on the edge. If you sink the hinge into the control surface you can
realize this with very little gap at all. The control surface now rolls on
the radius instead of binding because the pivot point is always the same
distance from the edge. To put this another way, imagine if a wheel had the
axle located on the edge of the rim instead of in the center. How far would
it turn? Unfortunately, in order to do this on a thick surface you would
need to sink the hinge pretty deep (1/2 the thickness of the surface). The
area near the hinge (in the movable surface) needs to be relieved to
accomodate the hinge on the opposite surface too, because it is in the arc.
If you consider the fact that on pattern planes we don't need to move the
surfaces to extreme angles (like 3D planes do) you can make some tradeoffs
and still get acceptable results. Hope this helps.

John Pavlick
http://www.idseng.com




> -----Original Message-----
> From: discussion-request at nsrca.org
> [mailto:discussion-request at nsrca.org]On Behalf Of Lance Van Nostrand
> Sent: Thursday, November 25, 2004 12:47 AM
> To: discussion at nsrca.org
> Subject: Re: wing tip shape
>
>
> Please someone explain this rounded control surface thing to me.
> If we use
> a CA hinge and but the aileron to the wing, then the only way the surface
> can move is if it has a beveled point.  A rounded interface will
> bind unless
> the aileron has a gap to begin with.  However, if all we are saying is to
> round the part of the bevel that blends into the aileron, then I get it.
>
> Confused again....
> --Lance
>

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