REFLECTOR: Sparrow Strainer

[steve korney]

Thanks Pat....

That's a great explanation.....

Best... Steve



----Original Message Follows----
From: Pat Shea <xl340hp at yahoo.com>
Reply-To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: Sparrow Strainer
Date: Sat, 4 Feb 2006 12:26:24 -0800 (PST)

Hmmm,

There seems to be some confusion on this issue. The
fact that Steve completely altered the design and
function of of his "sparrow strainer" and turned it
into an "aerodynamic trim tab" isn't helping, but I'm
glad it's working for him.

For everyone else using it in it's original design
configuration...

Probably the easiest way to analyze the function of
the "sparrow strainer" is to take it and the trim
spring out of the picture. In that scenario, at high
cruise speed the pilot would need to press forward
(hard) on the stick to maintain level flight. Now add
on the sparrow strainer which will be pulling down on
the trailing edge of the elevator with its inverted
airfoil and negative incidence relative to the
elevator, and the pilot has to push forward even
harder. Yes, it's actually working against you at high
cruise speeds. The pitch trim spring simply replaces
this force required by the pilot. Therefore, the pitch
trim spring has to work harder at high cruise speeds
with the sparrow strainer installed.

Here comes the purpose...

Since the pitch trim spring is working harder, it is
further "pre-loaded." This gives the stick a heavier
(or stiffer, or whatever...) feel in pitch at high
cruise speeds. This higher pre-loading of the pitch
trim spring also makes the elevator (and therefore the
plane) less susceptible to pitch deviations from
turbulence, etc.

What's all this mean? If you are prefer heavier stick
forces at cruise and a little more stability, use the
sparrow strainer. If you prefer lighter stick forces
at cruise and are willing to forgo a little stability,
take it off or even turn it into an aerodynamic
trim...

Pat

--- Ron Brown <romott at adelphia.net> wrote:

 > More trim "info" from something I saved from Mike
 > Pollack a while back:
 >
 > "The sparrow strainer has negative lift by design.
 > As the airspeed
 > increases, the sparrow strainer tries to pull the
 > aft side of the elevator
 > down causing the nose of the airplane to rise which
 > slows the airspeed. It
 > works in relation with the fixed trim system to give
 > a wider trim range
 > airspeed without retrimming manually.  It also seems
 > to keep the canard more
 > stable in level flight. I have flown with and
 > without one and prefer the
 > sparrow strainer."
 >
 > And to add fair and balanced coverage, here is what
 > Steve Korney had to say:
 >
 > "My sparrow strainer works as a trim tab...The
 > faster I go, the more it
 > pushes the elevator up, keeping the nose down...My
 > sparrow strainer has a
 > positive incidents of about 15 degrees...That is,
 > the cord line angles up
 > from the trailing edge to the leading edge...Are we
 > all confused...???"
 >
 > Yep,
 > Ronnie
 >
 >
 > ----- Original Message -----
 > From: "Pat Shea" <xl340hp at yahoo.com>
 > To: "Velocity Aircraft Owners and Builders list"
 > <reflector at tvbf.org>
 > Sent: Wednesday, February 01, 2006 2:51 PM
 > Subject: Re: REFLECTOR: Elevator Trim Spring
 >
 >
 > > Steve,
 > >
 > > Actually, if the sparrow strainer is installed as
 > the
 > > factory prescribes, it makes the trim situation
 > WORSE
 > > at cruise. It has a negative angle of attack
 > relative
 > > to the elevator and is an upside down airfoil.
 > Both of
 > > this work to pull the trailing edge of the
 > elevator
 > > down at high cruise. Since the Trialing edge of
 > the
 > > elevator is above the in-trail position at high
 > > cruise, the sparrow strainer is working against
 > you
 > > the faster you go. Of course all this would be
 > very
 > > undesirable without a pitch trim system - the good
 > > news is we have one.
 > >
 > > The purpose of the sparrow strainer it to pre-load
 > the
 > > pitch trim spring more (by making it work harder)
 > at
 > > higher speeds. This helps stabilize the plane by
 > > increasing the pilot force required to move the
 > > elevator at these speeds. This increased
 > pre-loading
 > > also increases the amount of external force
 > > (turbulence) requires to induce a pitch change.
 > >
 > > I know you changed you sparrow to be an
 > aerodynamic
 > > trim, but that is a completely different
 > arrangement.
 > >
 > > Pat
 > >
 > > --- steve korney <s_korney at hotmail.com> wrote:
 > >
 > >>
 > >> Guys.....
 > >>
 > >> The sparrow strainer takes care of the trim in
 > >> cruise and top speed...  If
 > >> it's set right...
 > >>
 > >>
 > >> Best... Steve





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