where does the model roll?

[John Ferrell]

To make things even worse, it seems to me that it would only be logical to
put the wings, stab, cg and center of lateral area on the engine thrust
line. The problem with that is every attempt I have seen with even pieces of
that criteria tends to be unstable in some condition!

Building a pattern airplane is different from any other kind of airplane.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



----- Original Message -----
From: "george kennie" <geobet at gis.net>
To: <discussion at nsrca.org>
Sent: Friday, January 10, 2003 4:25 PM
Subject: Re: where does the model roll?


> Boy, this stuff can really get you started doing a lot of head scratchin'.
I
> think Oddino has the right slant on this one.It seems to me that it all
comes
> down to the location of the vertical C.G.  Any displacement of the wing
> centerline from the location of the vertical C.G. should logically cause
the
> wing center line to travel concentrically around the point of vertical
C.G.
> placement. This would mean that the wing, while rolling, would execute a
very
> small barrel roll around the C.G. point. If it were possible to get the
location
> of the vertical C.G dead-on on the centerline of the wing, and also
dead-on on
> the pitch axis C.G., then you would be the lucky owner of a perfectly
axially
> rolling aircraft. However, as John points out in the case of the Hideout
with
> the tank in the canopy, the problem becomes more complex due to the fact
that as
> the tank empties the vertical C.G. is under constant change which means
that the
> rolling axis will be under constant differential adjustment.
> This is a great brain-teaser and has really made me consider a set of
parameters
> that I had never really thought about before.It seems to me that when you
> consider the layout of our contemporary models with the head of the engine
> hanging down below the datum line,the pipe on the bottom of the bird,
fixed gear
> with wheel pants sticking down 12 or more inches below center that the
tank in
> the canopy would probably be great at the beginning of the flight. Sounds
to me
> like good reason to maybe get the wing centerline somewhat below the datum
line
> so as to attempt to align the wing center line with the vertical C.G. as
much as
> possible.
> Maybe the next big fad we'll see is guys putting two 8 oz. tanks fore &
aft of
> the wing tube,............hmmmmm...........
> Georgie
>
> John Ferrell wrote:
>
> > IMHO:
> > The airplane that rolls around the thrust line presents better for our
> > purposes.
> > The location of the neutral point, cg and center of lateral area appear
to
> > play a part as well.
> > You have a measure of control with the shape and positions of the
ailerons.
> > You can usually influence the roll axis with aileron differential.
> >
> > I obviously don't really understand the subject because I cannot
quantify
> > it!
> >
> > One reason the Snaky airplanes like the Prophecy were such a success is
that
> > it about impossible to get the neutral point and the CG too far from the
> > thrust line or the wing center line.
> >
> > I never saw a flyer that was happy with a Hydeout that had a big tank
> > stuffed in the canopy area.
> > It is another condition to consider with the wide bodies that are so
popular
> > now.
> >
> > John Ferrell
> > 6241 Phillippi Rd
> > Julian NC 27283
> > Phone: (336)685-9606
> > Dixie Competition Products
> > NSRCA 479 AMA 4190  W8CCW
> > "My Competition is Not My Enemy"
> >
> > ----- Original Message -----
> > From: "Koenig, Tom" <Tom.Koenig at actewagl.com.au>
> > To: "'Discussion'" <discussion at nsrca.org>
> > Sent: Wednesday, January 08, 2003 6:31 PM
> > Subject: where does the model roll?
> >
> > > Hi Guys,
> > >
> > > I've just been asked this question.........it never occurred to me to
> > really
> > > think about this, now I'm open to opinions, facts and anyone that has
the
> > > cold hard knowledge.
> > >
> > > I have always assumed that a model rolls around the datum line ie: the
> > > crankshaft center line (not taking down and side thrust into
> > consideration)
> > >
> > > Now a mate of mine swears black and blue that in actual fact the model
> > rolls
> > > around the wing center line ie: it is the wing that rolls and all else
> > > scribes an arc around this.
> > >
> > > Can anyone can set us straight......please?
> > >
> > > Thanks
> > >
> > > Tom
> > >
> >
> > =====================================
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> > #
>
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