REFLECTOR: Aerodynamic trim

[Pat Shea]

Hi Dave,

Just so you know, this is a common problem which is
not the sparrow strainer's fault. The builder sets the
position of the trim by *guessing* the position that
the fiberglass trim spring should be mounted to the
elevator torque tube. Only after you fly do you know
how good or bad your guess was. The manual just says
to give yourself more up than down trim. Almost
everyone overdoes this and ends up w/ too much up and
not enough down trim. This is unfortunate since it's a
LOT easier to add in a spacer for more up trim later.

Sooo, you can remove your canard, drill out the rivets
that connect your trim spring bracket to the elevator
torque tube, and then re-drill and re-rivet with the
elevator trailing edge set up a little higher (more
down trim). I would consider overdoing this since it's
real easy to add a spacer between the trim motor
attach bracket and the trim spring if you go too far
and need more up trim.

As another option, someone mentioned installing a
spacer between the trim spring and the V shaped
mounting bracket on the elevator torque tube to get
more down trim. This seems like it would work too -
maybe even a wedge shaped spacer.

Although removing or adjusting the sparrow strainer
would also change your trim setting, this is a design
change that I would not make solely to adjust your
trim. The sparrow strainer is not designed to be a
trim device - as you've seen it actually works against
your trim at high speeds

Pat



--- Dave Philipsen <velocity at davebiz.com> wrote:

> Just a question for anyone that is currently flying
> with the "sparrow 
> strainer".  I have one of these on my canard and,
> since I'm a new owner, 
> I'm just getting used to some of the quirks.  I was
> flying home 
> cross-country this evening and noticed that as I
> started my descent from 
> 5500 feet to my home airport, I could only get about
> a 300-400 fpm 
> descent with the trim max'd out all the way down. 
> As the airspeed 
> started to build up in the descent, the "sparrow"
> evidently became more 
> effective and I actually lost all of the available
> pitch down trim that 
> I had started with.  So, I had to hold the stick
> forward with a fair 
> amount of pressure to maintain a 500-600 fpm
> descent.   As I slowed down 
> entering the pattern, the pitch down became
> effective once again. 
> 
> Should I experiment with trying to effectively
> disable maybe 50% of that 
> "sparrow" airfoil and see what happens?  Has anyone
> else had the same 
> experience?
> 
> -- 
> Dave Philipsen
> STDFG
> N171SP
> 
> soon-to-be N83DP


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