Re: Wing Post Socket Mounting in a Rolled Motor Stick

From: Bruce McCrory <hbm55_at_comcast.net>
Date: Fri, 20 Jul 2007 03:05:34 -0000

Well, that was a crummy bit of CG help. Here's how I locate my wing:

Finish the fuse; attach the stab and fin; hang the motor weight you
want, or need to use. Put everything but the wing onto the model.

Balance the mess. Lazy people, like me use a pen, but a loop of
string is the scientific method. When everything rocks - or appears
to, since it is squirelly - equally, that balance point is 90% of the
wing chord.

I don't know why I use 90%. It seems to work fine. But, if I don't
like the looks, I push the rear post 10% ahead of the balance point;
then move everything back during trimming, after I've forgotten where
the point was.

My models generally fly at the high end of decalage. They have
excellent recovery from bumps, and love to stall under launch torque.
80% of chord may be better, but if there is one, my stuff goes to
obstacles like magnets.

Bruce


--- In Indoor_Construction_at_yahoogroups.com, "Bruce McCrory"
<hbm55_at_...> wrote:
>
>
> Super job, and technique! Exactly how I would have done it. . ...;>
>
> Actually, There is a ten-point method for trimming a model by John
> Koptonak in the Downloads section of Small Flying Arts. John told
me
> he was surprised by how popular the guide was. If you aren't
familiar
> with it do check it out. He mentions 30% of chord for CG (typically
> scale) but indoor duration wants to push the CG toward the TE. The
> guide works; I just ignore the CG part.
>
> BTW, sometimes people don't offer help - often, they don't know the
> answer. When that happens to me, I just toss a few insults, earn
the
> majority's hatred, get booted off the list, and keep the solution
to
> myself. Simple. I had a lobotomy recently, so like Jack, smile a
lot.
>
> Bruce (the smart_at_##)
>
>
>
> - In Indoor_Construction_at_yahoogroups.com, "calgoddard"
> <calgoddard_at_> wrote:
> >
> > Thanks all for the advice.
> >
> > I ended up determining the best estimate for the CG by mounting
the
> > prop, putting on a 2.0 gram rubber motor and taping the wing
posts
> > to the side of the motor stick (MS) but without flying, just
> > balancing the plane on a thread.
> >
> > I rolled some wing post sockets, then determined the drill size
> that
> > would make the right size mounting hole. I tested the drill on
> some
> > similar balsa and determined it was sharp enough to cut through
> > without splitting.
> >
> > I then made a drill jig with two inch long diameter brass tubes
to
> > guide the drill. The tubes were held between two 1/16 inch balsa
> > sheets glued to opposite sides of a balsa frame. The tubes were
> > spaced apart the proper chord dimension to match up with the wing
> > posts. The drill fit snugly in each tube without slop but could
be
> > easily twisted.
> >
> > The drill jig had legs to grip opposite sides of the rolled MS
> > without damaging the same. I taped the jig to the MS after
> > alignment to ensure it would not rotate.
> >
> > I then hand twirled the drill bit in each tube, and was able to
> > neatly cut through the MS. I held a piece of scrap balsa against
> the
> > bottom of the MS to ensure a clean lower hole with no break out
or
> > cracking. When the drill jig was removed I had two aligned,
> > diametrically extending holes with no damage to the MS. This was
> > nice since it took me a few hours to make my first rolled MS.
> >
> > It was then easy to glue the sockets in the MS with Duco cut 50%
> > with acetone. The wing posts slid into the sockets just fine. I
> > then put some wash in on the inboard TE of the wing.
> >
> > I will see how my guess on the CG location works tomorrow when I
> fly
> > the plane for the first time.
> >
> > This is pretty basic stuff for you F1D guys, but may help anyone
> > just making their first indoor plane with a rolled MS.
> >
> > I did come in .4 grams below my target weight for the plane, and
> > this was made possible by use of the rolled MS. This allowed me
to
> > use really hard wing posts. I hate it when those things break.
> >
>
Received on Thu Jul 19 2007 - 20:05:37 CEST