REFLECTOR: Sparrow Strainer (pitch trim)

[steve korney]

Hi Larry...

Your absolutely right... My sparrow strainer is in fact a trim tab...It's 
also mechanically adjustable from the outside...I adjusted it to give me 
just enough aerodynamic force to aid in the force of the spring at full down 
trim and top speed...

Best...Steve...

----Original Message Follows----
From: "Laurence Coen" <lwcoen at hotmail.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 (pitch trim)
Date: Sat, 4 Feb 2006 12:20:32 -0600

The FAA requires that all general purpose aircraft exhibit both roll and 
pitch stability to be certified.  What Steve is describing is neutral pitch 
stability.  He has achieved this by mounting the sparrow strainer upside 
down.  The reason for the sparrow strainer is to increase pitch stability, 
not make it go away.  Without the sparrow strainer, increasing speed 
increases the aerodynamic loading on the elevator.  Since it is held in 
place by a spring, it is pushed out of the way thus reducing its effective 
trim.  with increasing speed the sparrow strainer increases the down force 
on the elevator helping to maintain the set trim.  The weaker the trim 
spring, the more important this becomes.  Steve seems to be quite happy with 
neutral pitch stability.  Your mileage may vary.

Larry Coen
N136LC SE/RG Franklin

----- Original Message ----- From: "Ron Brown" <romott at adelphia.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Saturday, February 04, 2006 7:54 AM
Subject: REFLECTOR: Sparrow Strainer


>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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>
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