where does the model roll?

[george kennie]

Affirmative John,
I built two ships that were midwing birds with wings, stabs, everything on the
datum line in an effort to try and eliminate pitch to the belly and both of them
required more mix to correct than any of my other ships.The only thing that I
liked was that one of them will do about 50 foot diameter K.E. loops and it's
about 11&1/2 pounds.Seems that all my original designs end up surprising me in
some way or other.
Georgie

John Ferrell wrote:

> 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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> >
>
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