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Like I said, I'm confused. I only become dangerous when I don't think
I'm confused.
<P>Bob Richards wrote:
<BLOCKQUOTE TYPE=CITE>George, It would be real interesting to stick
(no pun intended) a "stick" in a wind tunnel and see how the flow actually
changes with yaw. Same with a Cap21. I think the effect of the
vertical fin as you described is reduced by the fact that the rudder is
deflected. In other word, the deflected rudder creates camber in the overall
vertical surface, and also causes high pressure on the side of the fin
where the rudder is deflected. If the fuselage could be yawed without
deflecting the rudder, then it might act as you describe. Bob R.
<P><B><I>George Kennie <geobet@gis.net></I></B> wrote:
<BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid">I'm
having some problems with this one. Nothing serious, mind you,
<BR>but just a little confusion.
<BR>If we take this stab/fuse joint pressure build up to be causative,
<BR>then it should logically follow that in order to achieve
<BR>equilibrium, the rudder area above and below the stab should be
<BR>equal.
<BR>Then if we take the Stick, everything (area) is above the stab,
<BR>which lends credence to the hypothesis, but if we go back to the
<BR>Cap, the area is now closer to equal, but probably weighted slightly
<BR>in one direction or the other, but closer to the equality that we
<BR>are seeking, and yet the reaction is just as violent except in the
<BR>opposing direction.
<BR>Therefore, we must assume that the point of equilibrium is at some
<BR>point between the two locations.
<BR>With our thoeretical airplane with it's adjustable stab, we end up
<BR>determining that indeed the point of equilibrium appears to be at a
<BR>much lower point (relative to the rudder area) than we would have
<BR>originally anticipated. So we, at this point find ourselves doing
<BR>some serious head scratchin'.
<BR>On the other hand, if we take the two airframes together and analize
<BR>the force arrangements we find that they are basically inverted
<BR>mirror images of one another,i.e., Stick, ........wing on top, stab
<BR>on bottom. Cap, wing on bottom, stab on top. And yet the rudder area
<BR>intersect points are definitely not mirror images.For that to be the
<BR>case, the Cap would have to be a T-Tail. Something doesn't jibe!
<BR>Here we have the Cap with close to a balanced area scenario and yet
<BR>we have the dreaded pitch to the belly. If we now turn the Cap
<BR>upside down and cut off the canopy and glue it to the belly
<BR>pretending that the belly is now the top and fly the airplane it now
<BR>pitches to the canopy( new top, but still really to the belly). The
<BR>problem with this scenario is that, in this inverted position the
<BR>Cap's fin and rudder become equivalent to the biggest sub-fin,
<BR>ventral, strake, whatever you want to call it and yet it doesn't
<BR>correct the pitching problem.
<BR>I have strong feelings that the dynamics are located in a different
<BR>area and would contend that a poorly designed force arrangement
<BR>cannot be corrected with a band-aid approach.
<BR>This is not intended to raise anybody's hackles, just my two cents.
<BR>G.
<BR>
<BR>
<BR>
<BR>
<P>Since were still guessing at cause of pull to top in knife edge,
<BR>Here is my Suspect -
<BR>Stab is on bottom of fuse- true with this design?
<BR>When rudder is applied, air pressure builds at intersection of fuse
<BR>& Fin,
<BR>with the top of the stab. Pressure on top of stab creates a nose up
<BR>condition. There is no equivalent pressure on bottom, cause there
<BR>is little or no fuse and fin.
<P>If that is the cause, adding a strake to bottom might improve it.
<P>Later, Ron Lockhart
<BR>
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