Trimming Help

Tue Mar 30 09:18:09 AKST 2004

Hi Bob,
They are measured relative to each other, but there are two other things to consider. The lesser of these is the thrustline, which will strogly affect the UPline. It can be adjusted, though. The biggie is the relative height of the stab above the wing. Picture an extreme example: you add 5 degrees of positive incidence to both the wing and stab; now the plane flies along tail-high, with its nose down like a huntin' dawg. It is now a different design ... some planes have the wing and stab almost in line, and others have the stab up in air that is less affected by the wing. Depending on stab size, CG, and tail length, different stab-over-wing heights work, and others are not quite right. That means they take lots of electronics to fix the knife edges, or have no sweet-spot where the verticals are straight. 
You do realize that this opens up a large can of worms!
Hope this helps
    Dean P.

-----Original Message-----
From: Bob Kane [mailto:getterflash at yahoo.com]
Sent: Tuesday, March 30, 2004 8:55 AM
To: discussion at nsrca.org
Subject: RE: Trimming Help

I have to ask . . . . .   what is the difference between adding positice incidence to the wing versus negative to the stab? Are they not relative? 

Dean Pappas <d.pappas at kodeos.com> wrote: 

Hi again Paul,
Many planes trim nicely with a small amount of positive incidence in the wing, compared to the stab.
The typical amount is about 1/4 to 1/3 degree, or a little over 1/16" over the wing chord. If you have full degree of incidence in the wing, you may have a belly-pitch in knife edge, unless terribly nose-heavy. Now we need to ask those of you out there with well trimmed Tai-Ji to tell us where your CG is. There's no sense in re-inventing the wheel. Put the CG there, and adjust/shim the incidence 'till the elevator trim goes away, and let's see where we are.

Before doing that, are you sure that the ailerons aren't both trailed up or down, even a little?

Don't let us forget you, until this problem is licked,
Dean

-----Original Message-----
From: David Lockhart [mailto:DaveL322 at comcast.net]
Sent: Monday, March 29, 2004 11:06 AM
To: discussion at nsrca.org
Subject: Re: Trimming Help

Paul,

Most of the trim advice being given is based (rightly so) on some
assumptions -
- the plane is straight and true,
- ail hinges are sealed,
- servos are tracking evenly throughout the range of throw (as measured by a
throw meter - Budd Laser, CRC, Ivans Gadget, etc),
- all references to ail throw and ail differential refer to actual measured
throw at the aileron (as opposed to an ATV/endpoint/differential setting in
the radio).

Another thing I would suggest - if possible, have another experienced
pattern pilot fly the plane and see if they find the same problem - and it
gives you an opportunity to very critcically watch the plane and evaluate
without needing to concentrate on the actual flying.

As Dean P said, negative ail differential is rarely needed, but not out of
the question. Most of my planes end up with no differential, or a very
slight amount of positive differential - but I did have one that required
negative differential.

Good luck,

Dave Lockhart
DaveL322 at comcast.net

----- Original Message -----
From: "Paul Lawrence" 
To: 
Sent: Monday, March 29, 2004 8:19 AM
Subject: RE: Trimming Help

> The plane is a Tai Ji 60. I may have found an
> incidence
> problem too. I don't really know where the reference
> line is for this model and I am also still learning
> how to check incidence, but if I block up the plane
> and get the wings at 0 degrees and then check the
> stab, it is showing -1 degree of incidence. That seems
> excessive.
>
> I'm flying Intermediate and the yaw really shows up on
> the humpty bump and full roll up on stall turn. When I
> perform the humpty bump, I pull to vertical, 1/2 roll
> right and the plane heads off to the left(belly in).
> On the full roll up, the plane heads off to the right
> after rolling right.
>
> So far, I have received a lot of good advice and have
> several things to try. Thanks.
>
>
>
> >
> > -----Original Message-----
> > From: Paul Lawrence [mailto:pwl45 at yahoo.com]
> > Sent: Sun 3/28/2004 10:33 PM
> > To: discussion at nsrca.org
> > Cc:
> > Subject: Trimming Help
> >
> >
> > After getting soundly beat in Ocala last weekend, I
> > realized that I have been getting proverse yaw as my
> > plane rolls.
> > It wasn't evident until I saw other well-trimmed
> > planes flying.
> > The plane yaws in the direction of roll input and I
> > have been experimenting with a multitude of aileron
> > differential settings and can't seem to remove the
> > yaw.
> > With zero differential, the plane still yaws in the
> > direction of roll.
> > The trimming chart says to reduce differential in
> > this condition, but I have reduced it to zero.
> > Should I program in negative differential(doesn't
> > sound good) or should I program a litle bit of
> > opposite rudder correction to offset the proverse
> > yaw?
> >
> > Also, does CG and Incidence affect adverse or
> > proverse yaw while rolling?
> > The plane was a little nose heavy and I have also
> > been adding tail weight to try and clean up the
> > rolls, but still can't get that yaw out of the
> > rolls.
> >
> >
> >
>
> =====================================
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>

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Bob Kane
getterflash at yahoo.com 

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